Historical Concrete Design

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Historical approaches to the designof concrete buildings and structures

A cement and concrete industry publication

Technical Report No. 70


Acknowledgements

The work of preparing this Technical Report was partly funded by John Doyle Construction

Limited using the proceeds from winning the CONSTRUCT Award for Innovation and Best

Practice 2008. The award was given for the use of Twin-Wall Hybrid RC Cores at More London 7.

The Concrete Society acknowledges the contributions of the people who provided

information and guidance during the preparation of this document, including members of

The Society's Standing Committees. Particular thanks are due to the following:

Simon Hartshome (Highways Agency)

Dawn Humm (Hurst Peirce and Malcolm)

Patjansen (Gifford)

Tony Jones (Arup)

Deborah Lazarus (Arup)

Stuart Matthews (BRE)

Edwin Trout (The Concrete Society)

Published by The Concrete Society

CCIP-049

Published July 2009

ISBN 978-1-904482-57-4

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Historical approaches to the design ofconcrete buildings and structures

Contents

List of tables

1. Introduction

1.1 Development of Codes and Standards

1.2 Appraisal and repair

1.3 Scope and format

2. Development of concrete and concrete structures

2.1 Concrete

2.2 Concrete structures

3. Development of design codes

4. Development of materials standards

4.1 Units

4.2 Concrete constituents

4.2.1 Calcium chloride as an accelerator

4.2.2 High alumina cement (HAC)

4.3 Mix proportions and strength

4.3.1 Buildings and other structures

4.3.2 Highway and railway structures

4.4 Design exposure conditions

4.4.1 Buildings and other structures

4.4.2 Bridges

IV

1

1

2

2

4

4

4

6

9

9

9

9

9

10

11

19

24

25

27


4.5 Reinforcement and prestressing

4.5.1 Detailing symbols

4.5.2 Imperial bar sizes

4.5.3 Yield stresses

4.5.4 Fabric

4.5.5 Early reinforcement systems

4.5.6 Early prestressing systems

5. Design

5.1 Loading

5.2 Reinforcement design strengths

5.3 Bending and axial load

5.3.1 Buildings

5.3.2 Bridges

5.4 Shear and punching in reinforced concrete

5.4.1 Buildings

5.4.2 Bridges

5.5 Shear in prestressed concrete

5.5.1 Buildings

5.5.2 Bridges

5.6 Fire resistance

5.7 Bond and anchorage

5.7.1 Buildings

5.7.2 Bridges

5.8 Serviceability

5.8.1 Buildings

5.8.2 Bridges

5.9 Robustness

5.10 Analysis

5.10.1 Frame analysis

5.10.2 Slabs

28

29

29

30

30

30

31

32

32

33

34

34

37

39

39

43

48

48

50

52

56

56

58

60

60

63

65

67

67

68


6. Guidance relating to specific types of structures

6.1 Precast systems

6.1.1 Concrete frames

6.1.2 Precast floor and roof units

6.1.3 Large panel systems

6.1.4 On-site construction

6.1.5 Non-traditional houses

6.1.6 Standard bridge beams

6.1.7 Bearings for precast units

6.2 Foundations

6.3 Water-retaining structures

6.4 Houses: in-situ construction

6.5 Other structures

7. General information on concrete deterioration

7.1 Alkali-silica reaction (ASR)

7.2 Sulfate attack

7.3 Mundic

7.4 Clinker concrete

8. Other sources of information

References

Further reading

Appendix A. Proprietary floors

Appendix B. Non-traditional houses: precast and constructed in-situ

70

70

70

71

11

73

73

73

74

74

75

80

80

81

81

81

82

82

83

85

89

90

92


List of tables

Table 1 Some key steps in the development of Codes and Standards

Table 2 Publication dates for main Codes

Table 3 Publication dates for highway bridge design Standards

Table 4 Approximate conversion table.

Table 5 Designations of some concrete mixes

Table 6 Detailing symbols

Table 7 Specified yield stresses

Table 8 Loading Codes for buildings

Table 9 Highway loading Standards

Table 10 Design stresses for reinforcement


Introduction 1

1. Introduction

There are many instances in which an engineer is asked to appraise an existing building,

or other structure, perhaps due to a planned change of use or as part of a refurbishment

process. A common example might be an office block built in the 1960s, although with

the move towards conservation, it is likely that many earlier buildings and structures will

be refurbished or upgraded rather than being demolished and replaced. As a first stage in

this process, it is useful to have as much information as possible about the structure, such

as what Code or Standard it was designed to, what the concrete and steel strengths were

likely to have been at the time of construction, what design approaches were adopted, what

proprietary precast concrete units were available, etc. The aim of this Technical Report is

to provide an outline of this information and to list some of the relevant publications and

other sources of readily available information, up to about 1990. (Although this Report is

primarily intended to cover UK practice, many British Codes and Standards were, and are,

used abroad and hence the guidance should be equally applicable overseas.)

1.1 Development of Codesand Standards

To engineers familiar with modern design Codes, some of the approaches adopted by earlier

Codes will appear strange. This Technical Report summarises the key changes that have

occurred in successive Codes in the UK up to about 1990, for example in the design for

shear and the provision of shear reinforcement. Some of the key points are given in Table 1.

Date Key points in design guidanceTable 1Some key steps in the development of Codes

and Standards.

The emphasis in this report is on the information contained in the structural Codes and

Standards, which are concerned with the strength of the concrete for design purposes and

generally do not consider the concrete constituents. It is only recently that there has been

crossover between the materials Standards and the structural Standards with, for example,

the required cover being related to the type of cement being used. However, the use of

some materials, such as high alumina cement (HAC), is covered by the structural Standards

and these are mentioned where appropriate.


1.2 Appraisal and repair This document is not intended to cover the process of the appraisal of a structure nor

materials testing as these are well covered elsewhere. General guidance on appraisal may

be found in the Institution of Structural Engineers Appraisal of existing structures®, which

deals with all types of construction materials, not just concrete. It covers aspects such as

the reasons for an appraisal, the approval process itself, testing and monitoring. Also

included is some guidance on the use of modified materials partial safety factors when

assessing the structural capacity.

All aspects of the assessment of concrete bridges are covered in the Concrete Bridge

Development Group's Guidance on the assessment of concrete bridges®. The Highways

Agency's Design Manual for Roads and Bridges® contains a number of Standards for the

assessment of concrete bridges. Network Rail has its own Standards for the assessment

of railway bridges'4'.

Guidance on the reuse of concrete buildings is given in BSRIA Guidance Note GN 8/99,

Refurbishment of concrete buildings-structural and services options® and has been reviewed

by Gold'6'. The reuse of components, such as piles, is covered by CIRIA Report X332, Building

with reclaimed components and materials -A design handbook for reuse and recycling®.

General aspects of the deterioration of concrete structures are not dealt with in detail in

this document as they are well covered elsewhere. However, some forms of deterioration

are specifically related to structures of a certain age, such as reinforcement corrosion due

to the inclusion of calcium chloride in the concrete. These are considered in this document,

particularly when guidance concerning their use has been incorporated into later Codes.

Defects may be visible on the surface of the concrete; Concrete Society Technical Report 54,

Diagnosis of deterioration in concrete structures®, describes their appearance and significance.

Technical Report 22, Non-structural cracks in concrete®, describes the various types (plastic

settlement, plastic shrinkage, early thermal contraction, etc.) that may occur and explains

the principles that govern their formation.

This document does not cover the repair of concrete structures. Reference should be made

to the European Standard EN 1504'10' for general guidance and to publications such as

Concrete Society Technical Report 69, Guide to the repair of concrete structures with

reference to BS EN 7504'11' and those from the Concrete Repair Association.

1.3 Scope and format This Report is intended to give a general overview of the requirements contained in the

relevant British Standards and Highways Agency/Department of Transport documents

available at the time, supported by other appropriate publications. The emphasis of this

Report is on the design of reinforced and prestressed concrete buildings, bridges and other

structures, concrete was widely used for housing in the 1950s and 1960s. There were a

variety of precast concrete systems, some of which were less successful than others'12',

which are mentioned briefly. In addition, there were a number of proprietary precast

concrete frame systems used for industrial and commercial buildings, some details of

which are included.


Introduction 1

The reader should generally refer to the original cited document for further information.

However, this may be difficult in some cases, particularly when considering some of the

older Standards. For this reason alternative references have been given in some cases, such

as some of the Handbooks to the British Standards'1"8' and to the various editions of

Reinforced concrete designers' handbook^, which reproduce much of the material in the

Standards. Additionally, further sources of information are given in Chapter 8.

Rather than summarise the information given in each Code or Standard in turn, this

Report is divided into topics. Thus, for example, Section 4.3 shows how specified concrete

mix proportions and strength have changed over the years and Section 5.4 looks at how

the guidance relating to the design for shear and punching, and the provision of shear

reinforcement, has developed.


2. Development of concrete and concretestructures

The aim of this chapter is to give a very brief overview of the development of concrete

and of its use in structures.

2.1 Concrete Joseph Aspdin's patent of 1824 for Portland cement (so called due to its resemblance when

hardened to Portland stone) is often considered as a landmark in the history of cement

production, although in reality the material was closer to a hydraulic lime than a modern

cement. Further developments by William Aspdin, and Isaac Johnson in the 1850s, led to

the production of cements very similar to those of today.

Up to about the mid-1950s, concrete was made only with Portland cement. At that time,

fly ash (or pulverised fly ash, pfa) was introduced on a small scale and the first Standard,

BS 3892, Pfaforuse in concrete, was published in 1965. However, fly ash was not commercially

marketed until the mid-1970s. Ground granulated blastfurnace slag (ggbs) became com-

mercially available in the Midlands and north of England in the mid-1960s, extending to the

south of England in the 1980s. (Concrete Society Technical Report 40'20' gives information

on the introduction and development of fly ash and ggbs.) Silica fume (or microsilica)

became commercially available in the 1970s.

2.2 Concrete structures The development of concrete and its use in structures has been reviewed in various

publications, such as those by Hurst'21', Newby'22', Somerville'23' and Sutherland'24'.

Stanley'25' gives a brief overview of the history of concrete.

Unreinforced concrete was used for the construction of some houses in the first half of

the 19th century, but the concept of reinforced concrete did not appear until William

Wilkinson's patent in 1854. Concrete was widely used for the construction of industrial

buildings and, in particular, cotton and woollen mills, during the second half of the 19th

century, chiefly because of its fire resistance. By the 1890s concrete was being used

extensively for bridges and other civil engineering applications. The first multi-storey

reinforced concrete building in Britain was Weavers Mill in Swansea, which was completed

in 1898 using the Hennebique reinforcement system. Prestressed concrete was developed

between the First and Second World Wars, following the lead of Freyssinet.The first ready-

mixed concrete plants started to operate in the early 1930s.


Development of concrete and concrete structures 2

Chrimes'26' traces the use of concrete for bridges in the British Isles from its 19th century

origins to the outbreak of the Second World War. The publication contains many photographs

and working drawings of early bridges and has over 200 references. The earliest known UK

example of a mass concrete bridge was on the District Line, near Cromwell Road, London,

built in about 1865.The use of reinforced concrete for bridges began in the first decade of

the 20th century, mainly using the Hennebique system. Other systems followed, including

Monier, Kahn, Considere and Coignet. The first reinforced concrete rail bridge was built in

Dundee in 1903. By the 1930s there were about 2000 reinforced concrete bridges in the UK.

Smith'27' has reviewed the development of concrete bridges in the UK since 1940, starting

with the application of prestressed concrete in bridges during the Second World War. The

publication concentrates on bridges built during the first and second decades after the war,

concluding with a brief overview of later developments. By the 1950s concrete bridges had

been built using the Freyssinet and Magnel systems. In the UK a stock of emergency pre-

stressed concrete beams had been held during the Second World War and used afterwards

in permanent bridgeworks. The first major prestressed concrete road bridge was the

replacement for Northam Bridge, Southampton, in 1954.


t

3. Development of design codes

The first National Design Code for concrete structures was published in 1934, although

regulations for reinforced concrete had been introduced in London in 1915. Prior to the

development of Codes, designs were either proprietary or were in accordance with textbooks,

such as Reinforced concrete simply explained by Oscar Faber'28'. There were also various

guidance documents issued by The Institution of Structural Engineers (then known as The

Concrete Institute) and others.

Over the years, new Codes have been introduced. The publication dates for the main design

Codes for buildings and other structures up until 1990 are given Table 2; those for bridges are

given in Table 3. Invariably there was some overlap at each transition between an old and

a new Code. In addition, Codes are subject to revision before they are eventually replaced.

Often the Amendments are relatively trivial, for example correcting typographical errors,

but sometimes they have major implications for design. The more important changes are

identified in the following sections.

Table 2Publication dates for main Codes.

Date Design Code


Development of design codes

Some Codes listed in Table 2 were accompanied by Handbooks when they were originally

published, as follows:

• 1934 Code of Practice, Scott and Clanville(13>

• CP114,Scottefa/.(14>

• CP 115, Walley and Bate'15'

• CP 110, Bate eta/.f16'

• BS 5337, Anchoreta/.<17>

• BS 8110, Rowe eta/.f18'

Note that Scott and Glanville'13' and Scott eta/.'14' reproduce the whole of the Code of

Practice to which they refer. The other Handbooks have to be read in parallel with the

relevant Standard.

The British Standards Institution (BSI) maintains an archive of withdrawn Codes and

Standards; copies of withdrawn British Standards may be obtained through the BSI

Knowledge Centre (contact [email protected]).

In parallel with the national Codes and Standards, aspects of design may have been

covered by local by-laws. This is particularly so in London, as detailed in subsequent

sections of this Report.

The design of concrete highway bridges has always been covered by their own Standards

and Specifications, although many of these have made reference to the Codes for the

design of buildings. Initially these were issued by the Ministry of Transport (which became

the Department of Transport and then the Highways Agency), see Table 3. In 1978 the

first Standard was issued by BSI (BS 5400), but this was not implemented until 1983 by

the Highways Agency in BD 17/83 (which contained a large number of amendments and

additions, most of which were incorporated into the subsequent version of BS 5400). Thus

in the interim there were two sets of guidance available.

Table 3, and the subsequent discussions in this Technical Report, considers only the main

bridge design Standards and not the guidance issued for other 'special' structures, such as

those given in Section 2 of the Design Manual for Roads and Bridges.


Table 3Publication dates for highway bridge design

Standards.

The Highways Agency maintains an archive of superseded bridge standards. Enquiries

should be addressed to [email protected] (note the underscore).

There are relatively few 'historic' concrete railway bridges. It would appear that they were

generally designed to in-house guidance documents, rather than using the highways

Standards. Initially the guidance documents were prepared by the different Regions but later

common guidance was prepared, such as British Railways Board Technical Note 18, Design

of reinforced or prestressed concrete, which was issued in 1968. Railway archive material

has been transferred to the National Archives in Kew (www.nationalarchives.gov.uk).


Development of materials standards 4

4. Development of materials standards

This chapter reviews the way in which the concrete and steel strengths in successive

Codes and Standards have developed over the years.

4.1 Units

Table 4Approximate conversion table.

It should be noted that earlier Codes and Standards (up to the late 1960s) were written in

imperial units (pounds-force, feet and inches). In the following sections the original units

have been used throughout to avoid confusion. The following approximate values may be

used to convert from imperial units to metric units:

For ease of reference, approximate metric values are given in brackets in the text after the

imperial values.

4.2 Concrete constituents This report is chiefly concerned with the structural design of reinforced and prestressedconcrete. Structural Codes have generally assumed that the concrete constituents beingused would be sound and will not cause any long-term durability problems. However,there are two materials, namely calcium chloride and high alumina cement, that havecaused problems and have been subsequently banned; their early use is summarisedbelow and in the relevant parts of Section 4.3.

4.2.1 Calcium chloride as anaccelerator

Calcium chloride was used as an accelerating admixture in concrete up until the mid-1970s.Changing attitudes to its use in British Codes have been reported by Pullar-Strecker'29'. Atthe time that early codes were drafted, it was not appreciated that the use of calciumchloride would lead to corrosion of embedded reinforcement. As experience developed,so the guidance changed, and the use of calcium chloride was effectively banned in 1977.

4.2.2 High alumina cement(HAC)

High alumina cement (HAC), also known as calcium aiuminate cement (CAC), differs fromPortland cement, being composed of calcium aluminates rather than calcium silicates. Itsrapid strength development made HAC popular from 1950 to 1970. However, mineralogical'conversion' sometimes caused reductions in concrete strength and increased vulnerabilityto chemical attack. As experience developed, so the guidance changed.


HAC concrete was effectively banned for use in new structural concrete in the UK following

a few well-publicised collapses in the 1970s. Time and experience have shown that the

primary causes of these collapses were poor construction details or chemical attack, rather

than problems with the concrete itself. Most HAC concrete in the UK went into precast

beams. It is estimated that up to 50,000 buildings with similar beams remain successfully

in service today in the UK. The beams can be found in public and industrial buildings such as

schools, flats and business units. The prerequisite for maintaining their structural integrity

is the provision of a stable, dry environment.

If the presence of HAC is suspected, confirmation requires chemical or laboratory testing

of samples. (HAC concrete tends to be darker than concretes using Portland cement, which

can be an aid to identification.) If the presence of HAC is confirmed, professional advice

on its condition may be required. However, it is important to remember that the majority

of these buildings are performing perfectly adequately. The Building Research Establishment

(BRE) has produced various relevant publications, see for example Special Digest 3<30' and

Dunstereta/'31'32).

4.3 Mix proportions andstrength

Letters or Roman numerals were used in some earlier Codes and Specifications to identify

standard concrete mixes, see Table 5; details are given in subsequent Sections under the

relevant Code or Specification. It should be noted that in some documents the standard

mixes were listed in ascending order of strength (for example Mix C was stronger than Mix A)

while in others it was the other way round (Mix III was weaker than Mix I), which could

cause confusion. In other early documents the mixes were referred to by their proportions,

either by volume of cement and aggregates or by weight of cement and volume of aggregates.

Some of the latter worked on the basis of 112 lbs (1 cwt or hundredweight) which was the

standard weight of a bag of cement at the time. More detailed guidance on the design of

concrete mixes, such as the appropriate water/cement ratio and suitable aggregate gradings,

was given in standard publications such as Design of concrete m/xes'33' (commonly known as

Road Note 4) which was first published in 1950 and Concrete mix design^ first published

in 1964.

As shown in the following sections, there was steady increase in the strength of the standard

concrete mixes given in successive Codes and Specifications, reflecting improved cement

properties and better quality control. Somerville*23' noted that 28-day cement strengths

increased from about 32 N/mm2 in the late 1940s to about 47 N/mm2 in the early 1990s.

Earlier cements gained strength more slowly than modem cements, and continued to gain

strength beyond the specified 28 days. This was reflected in some Codes, which allowed

an enhanced strength to be used when the structure was to be loaded at a significantly

later date; again this is detailed, where appropriate, in the following sections.

10



From about 1970, concrete was specified simply in terms of its strength, initially in psi

(e.g. Class 4500) and later in N/mm2 (e.g. Class 30). Note that in all the Codes and

Specifications considered, 'strength' referred to the cube strength at 28 days rather than

the modern dual method of using both cylinder and cube strengths, e.g. 40/50.

The earlier design Codes included guidance on the production of concrete and on aspects of

construction. Gradually the material aspects were transferred into Codes such as BS 1926,

Ready-mixed concrete, and BS 5328, Methods for specifying concrete including ready-mixed

concrete (which later became BS 5328, Concrete). In 1982,Teychenne<35) noted that there

were a number of confusing differences between the design Codes and the concrete Codes.

In the following sections, only the guidance in the design Codes has been considered.

The strength of the concrete in historic structures is likely to be very variable. The only

sure way of determining it is to take cores that are then tested in accordance with Part 120

of BS 1881, Testing concrete, or Parts 1 and 3 of BS EN 12504, Testing concrete in structure.

However, if design information is available, guidance on the likely minimum concrete

strength may be obtained from the Codes of Practice current at the time.

4.3.1 Buildings and other

structures

Reinforced Concrete Designers' Handbook, 1932'19'

The First Edition of 'Reynolds' gave a series of concrete Mixes A to F specified on the basis

of cementfine aggregate:coarse aggregate ratios by volume with corresponding 'standard'

working stresses for the hardened concrete; cube strengths were not given. On the assumption

that the working (or permissible) stress was one-third of the cube strength as in subsequent

Codes, the strengths for the Mixes were as follows:

Mix A

MixB

MixC

MixD

MixE

MixF

1:3:6

1:21/2:5

1:2:4

V.VA3V3

V.VA3

1:1:2

1200

1500

2100

2250

2400

2625

psi

psi

psi

psi

psi

psi

(8 N/mm2)

(10 N/mm2)

(14 N/mm2)

(16 N/mm2)

(17 N/mm2)

(18 N/mm2)

11Licensed copy: mouchelic, Mouchel International Consultants, 27/10/2009, Uncontrolled Copy, ®The Concrete Society

It is not clear from the Handbook whether the London County Council By-laws used the

same designation letters.

London County Council By-laws, 1938

The by-laws gave four mixes specified on the basis of cementfine aggregate:coarse

aggregate ratios by volume, equivalent to Mixes C to F in the First Edition of 'Reynolds'

detailed above, but with slightly different cube strengths as follows:

• 1:2:4 1800 psi (12 N/mm2)

• 1:12/3:31/3 1950 psi (13 N/mm2)

• V.V/z:3 2025 psi (14 N/mm2)

• 1:1:2 2250 psi (16 N/mm2)

Code of Practice for reinforced concrete, 1934

The Code specified three grades of concrete, designated 'Ordinary Grade', 'High Grade'

and 'Special Grade', with corresponding levels of control. The Explanatory statement in

the code noted that:

"... industry has at this time reached a stage in development when advantage

should be given to the engineer who is prepared to spend time and money in

producing consistently controlled concrete. In other words the day has passed

when one stress only should be permitted for a mix regardless of the care

exercised."

For Ordinary Grade concrete, four nominal mixes were specified on the basis of cementfine

aggregate:coarse aggregate ratios by volume, with corresponding 28-day cube strengths,

as follows:

Mix 1

Mix II

Mix III

Mix IV

1:1:2

1:1.2:2.4

1:1.5:3

1:2:4

2925

2775

2550

2250

psi

psi

psi

psi

(20 N/mm2;

(19 N/mm2)

(18 N/mm2)

(16 N/mm2)

Though the same mix proportions were given for High Grade concrete, additional control

was required, leading to strengths that were about 30% higher, as follows:

Mix

Mix

Mix

Mix

I

II

III

IV

1:1:2

1:1.2:2.4

1:1.5:3

1:2:4

3750

3600

3300

2850

psi

psi

psi

psi

(26 N/mm2)

(25 N/mm2)

(23 N/mm2)

(20 N/mm2)



Further control, including control of the water/cement ratio, was required for Special Grade

concrete, which could lead to strengths not more that 25% greater than the corresponding

High Grade concrete mix.

Interestingly, the Code noted that concrete that failed to reach its specified strength at

28 days should not be condemned if subsequent tests at 56 days gave a strength of at

least 10% more than the 28-day strength. This reflected the relatively slow rate of gain of

concrete strength at the time and the continuing gain in strength after 28 days.

The Code permitted the use of Portland cement, Portland-blastfurnace cement and high

alumina cement, but did not differentiate between the various cements in the above

mixes and strengths. The Handbook'13' advised that the use of high alumina cement should

be limited to Mix IV, i.e. 1:2:4.


Here mixes were given both on the basis of cementfine aggregate:coarse aggregate ratios

by volume and on the basis of weight of cement (lb):fine aggregate (cu. ft):coarse

aggregate (cu. ft). Six mixes were given for structural applications, with corresponding 28-

day cube strengths as follows:

Mix

Mix

Mix

Mix

Mix

Mix

1

II

III

IA

IIA

IIIA

1:1:2

1:1Vz:3

1:2:4

1:1:2

1:1V2:3

1:2:4

112:iy4:2y2

112:1 VSSVA

W2-2Vr5

-]1Z:VA:ZVz

112:17/s:33/4

112:2y2:5

2925

2550

2250

3750

3300

2850

psi

psi

psi

psi

psi

psi

(20 N/mm2)

(18 N/mm2)

(16 N/mm2)

(26 N/mm2)

(23 N/mm2)

(20 N/mm2)

Note that, in terms of strength, the LCC Mixes I, II and III correspond with the 1934 Code

of practice for reinforced concrete Mixes I, II and IV, which could cause confusion.

There were an additional four mixes, using all-in aggregate, with corresponding 28-day

cube strengths as follows:

Mix IV

MixV

Mix VI

Mix VII

1:6

1:8

1:10

1:12

112:7y2

112:10

112:12y2

112:15

1480 psi (10 N/mm2)

1110 psi (8 N/mm2)

740 psi (5 N/mm2)

370 psi (3 N/mm2)

The above information was also given in Reinforced concrete simply explained^ and in

Practical examples of reinforced concrete design^.

13


Code of practice for the design and construction of reinforced concrete structures for

the storage of liquids, 1938

The Code specified minimum concrete grades in terms of weight of cement (lb):fine

aggregate (cu. ft):coarse aggregate (cu. ft) as follows:

• 112:2:4 for general use

• 112:214:5 for slabs greater than 24 inches (610 mm) thick

CP114, Structural use of normal reinforced concrete in buildings, 1948

The Code was the first to assume that design was entrusted to:

"Structural or civil engineers experienced in reinforced concrete and that the

execution is carried out under the direction of a qualified engineer."

As a consequence of this, the different levels of quality control considered in the 1934

Code were no longer included in CP 114:1948, as:

"It is felt that proper supervision must be assumed and provided for all

reinforced concrete, and is an essential part of the cost of the work. No work

ought to be done without it as it is impossible to calculate the disastrous

effect which may result... from a failure to produce a specified mixture."

Specification was still on the basis of cementfine aggregatexoarse aggregate ratios by

volume, with the introduction of a clause dealing with the control of the water/cement

ratio. The number of standard mixes was reduced from four to three. The minimum 28-

day cube strengths, using Portland cement or Portland-blastfurnace cement, were slightly

higher than those for the High Grade mixes, as follows:

• 1:1:2 4500 psi (31 N/mm2)

• 1:11/2:3 3750 psi (26 N/mm2)

• 1:2:4 3000 psi (21 N/mm2)

For a 1:2:4 mix using high alumina cement, a strength of 5000 psi (35 N/mm2) was

specified at two days.

Calcium chloride was permitted, with the following guidance in the section dealing with

Work in cold weather.

"Calcium chloride may be used to accelerate the rate of hardening - usually

V/z% by weight of cement will prove sufficient and there are dangers associated

with excess."



CP 114.100, Suspended concrete floors and roofs, 1950

The sub-Code used the same standard mixes as in CP 114:1948, defined by volume, with

the same 28-day strengths. However, it suggests that the cement content, and ideally the

aggregate contents, should be determined by weight. While CP 114:1948 gave general

guidance on the control of the water content in the mix, CP 114.100 specified maximum

water/cement ratios of 0.43, 0.51 and 0.58 for the three standard mixes when using

uncrushed gravel aggregates; the sub-Code suggested that a slight increase would be

necessary for other aggregates. When "compacting by vibration" the maximum values

should be reduced by 20%.

Surprisingly, high alumina cement comes before Portland cement and Portland-blastfurnace

cement in the Code's list of suitable cements in the Code. However, it does warn that:

"High alumina cement may be unsuitable for use with certain aggregates ....

The user can only be guided by previous experience in determining whether it

is suitable for use with such aggregates."

The sub-Code gives the same guidance as CP 114:1948 on the use of calcium chloride.

CP 114, Structural use of reinforced concrete in buildings, 1957

The nominal mixes and their associated strengths were the same as in the 1949 version.

The Code allowed the permissible stresses in compression to be increased by the following

percentages for members loaded significantly later than 28 days:

• 2 months

• 3 months

• 6 months

• 12 months

10%

16%

20%

24%

The guidance on calcium chloride was modified to:

"Calcium chloride may be used to accelerate the rate of hardening of Portland

cement concrete but not more than 2% by weight of cement should be used."

On the use of high alumina cement, the 1957 version warns that:

"High alumina concretes are sometimes unsatisfactory in warm, moist

conditions. The cement should be only used in accordance with the

manufacturer's recommendations".


CP 115, The structural use of prestressed concrete in buildings, 1959

The Code contained no nominal mixes but specified minimum 28-day cube strengths of

6000 psi (41 N/mm2) for pre-tensioned concrete and 4500 psi (31 N/mm2) for post-

tensioned concrete. It required the use of Portland cement or Portland-blastfurnace cement,

indicating that other cements might be desirable in certain circumstances but they should

only be used with the engineer's approval. Again it warned against the use of high alumina

cement.

This appears to be the first Code to consider the risk of corrosion resulting from the use of

calcium chloride, saying:

"Calcium chloride should not be used when steam curing is employed. Until

more is known about corrosion, the use of calcium chloride cannot be

recommended. There may be dangers associated with excess."

CP 2007, Design and construction of reinforced and prestressed concrete structures

for the storage of water and other aqueous liquids, 1960

Guidance inCP 2007 is generally in line with CP 114 and CP 115, but the Code recommends

two nominal mixes, specified on the basis of weight of cement (lb):fine aggregate (cu. ft):

coarse aggregate (cu. ft) but referred to in the Code on the basis of cementfine aggregate:

coarse aggregate ratios by volume, with a corresponding 28-day strength, as follows:

• 112:2:4 1:1.6:3.2 3600 psi (25 N/mm2)

• 112:2y2:5 1:2:4 3600 psi (25 N/mm2)

Note that both mixes were required to have the same 28-day strength; the 1:2:4 mix was

suggested for use in thicker sections.

London Building (Construction) By-laws, 1964

The 1964 by-laws appear to use the same concrete mixes as in the 1938 by-laws, (see

page 13) but they are referred to as Grades I to III and lAto IIIA rather than 'Mixes'.

CP 116, The structural use of precast concrete, 1965

The Code specified five Grades of concrete, with specified 28-day cube strengths as follows:

Grade A

Grade

Grade

Grade

Grade

B

C

D

LLJ

3000

3750

4500

6000

7500

psi

psi

psi

psi

psi

(21

(26

(31

(41

N/mm2)

N/mm2)

N/mm2)

N/mm2)

(52 N/mm2)



The guidance on the use of calcium chloride was more definite than that in CP 115:1959,

saying:

"Calcium chloride is not recommended either as an admixture or internally

mixed with cement in any form of prestressed work. The total amount of

calcium chloride in conventionally reinforced concrete should not exceed 2%

(1.5% anhydrous CaCl2) and should be dissolved in some of the mixing water.

When calcium chloride is used in concrete, not less that 25 mm of cover

should be given to all steel unless permanent protection is provided."

Guidance on the use of high alumina cement, similar to that in Appendix Bof CP 114:1959,

was included in the main body of the Code. It stated that high alumina cement concrete

should not be used in wet or humid conditions at temperatures above about 27°C without

prior consultation with the manufacturer.

CP 114, Structural use of reinforced concrete in buildings - Metric version, 1969

Three Nominal Mixes were given (as in the 1957 version), with 28-day cube strengths

using Portland cement or Portland-blastfurnace cement of 30, 25.5 and 21 N/mm2. In

addition a Table of Standard Mixes by weight was included for the three concrete strengths,

30, 25.5 and 21 N/mm2. The Code contained the same percentage increases in permissible

stress for members loaded at later than 28 days as in CP 114:1957.

The strength of the 1:2:4 high alumina cement mix was specified as 40 N/mm2 at two

days. The Code warns against the use of high alumina cement in warm moist conditions

and contains Appendix B which gives guidance on approaches for reducing the harmful

effects of conversion.

Reinforced Concrete Designer's Handbook(19)

The Ninth Edition of the Handbook gave the same information asCP 114:1969 (for 19 mm

aggregate only) but defined the mixes in terms of the letters A, B and C; Standard Mix A

was equivalent to the 21 N/mm2 mix in CP 114, Mix B was equivalent to 25.5 N/mm2 and

Mix C was equivalent to 30 N/mm2. The Handbook also included Designed Mixes D and E,

with 28-day cube strengths of 40 and 50 N/mm2 respectively.

CP 110, The structural use of concrete, 1972

Described as 'The Unified Code', CP 110 brought together the separate Codes relating to

reinforced, prestressed and precast concrete. Design in CP 110 (and all subsequent Codes)

was based on specified concrete strength grades, from 20 N/mm2 up to 50 N/mm2.

Minimum concrete grades were specified for different types of element, as follows:

20 N/mm2

30 N/mm2

40 N/mm2

reinforced concrete

post-tensioned prestressed concrete

pre-tensioned prestressed concrete


The Code again gave a table of design strengths at different ages, but in the form of actual

strengths for a given concrete grade, rather than the percentage increases given in earlier

Codes. (The percentage increases were similar but the concrete strengths were rounded.)

The Code permitted a range of cement types, which did not include high alumina cement.

The Code specified the amount of anhydrous calcium chloride, i.e. the material containing

no water, stating that:

"In concrete containing embedded metal calcium chloride must not be added

in such proportion that the total from the admixture and the total from the

aggregates exceeds 1.5% by weight of cement. Calcium chloride should never

be used in prestressed concrete."

An amendment in May 1977 effectively outlawed the use of calcium chloride as an

accelerating admixture because:

"Experience shows that corrosion of prestressing tendons, reinforcement and

embedded metal usually results from the combination of factors including

excess addition of calcium chloride ... departure from specified mix proportions,

poor compaction, inadequate cover and poor detail design."

BS 8110, Structural use of concrete, 1985

Minimum strengths were not clearly stated in BS 8110, but by implication they may be

assumed to be as follows:

20 N/mm2

25 N/mm2

30 N/mm2

reinforced concrete

precast concrete

prestressed concrete (slightly lower than in CP 110)

Section 6, Concrete: materials, specification and construction, banned the use of calcium

chloride, stating that:

"Calcium chloride and chloride-based admixtures should never be added in

reinforced concrete, prestressed concrete and concrete containing embedded

metal."

It also placed a limit on the total chloride content in the mix from other sources.

Section 6 also gave guidance on avoiding alkali-silica reaction.



BS 8007, Code of practice for design of concrete structures for retaining aqueous

liquids, 1987

While it generally refers to BS 8110, Structural use of concrete, BS 8007 specified a 35 N/mm2

concrete with a minimum cement content of 325 kg/m3 (compared with 300 kg/m3 in

BS 8110) and a maximum water/cement ratio of 0.50 (compared with 0.55 in BS 8110),

which was classed as grade C35A.

The Code specified maximum cement contents for reinforced concrete of 400 kg/m3 of

ordinary Portland cement or cements containing ggbs or 450 kg/m3 for cements containing

fly ash. For prestressed concrete the quantities could be increased to 500 kg/m3 and

550 kg/m3 respectively.

4.3.2 Highway and railway

structures

The guidance for highway and railway structures has always been somewhat different

from that for buildings.

Ministry of Transport, 1945

Four nominal mixes were specified on the basis of cementfine aggregate:coarse aggregate

ratios by volume and also weight of cement (lb):fine aggregate (cu. ft):coarse aggregate

(cu. ft), with corresponding 28-day cube strengths as follows:

1:2:4

1:12/3:3V3

1:1i/2:3

1:1:2

112

112

112

112

21/2

2Vi

:17/s:

:VA

:5

2:41/6

21/2

2250

2580

2700

3600

psi

psi

psi

psi

(16 N/mm2)

(18 N/mm2)

(19 N/mm2)

(25 N/mm2)

Note that these are the same ratios as given in CP 114:1948 but the 28-day strengths are

somewhat lower. The details are also given in the Third Edition of Reinforced concrete

designers' handbook^.

Ministry of War Transport Memorandum 557, Bridge design and construction, 1945

(reprinted 1949)

Three nominal mixes were given on the basis of weight of cement (lb):fine aggregate (cu. ft):

coarse aggregate (cu. ft), with corresponding 28-day cube strengths as follows:

MixA

MixB

MixC

150:2:4

120:2:4

90:2:4

3600 psi (25 N/mm2)

3300 psi (23 N/mm2)

2850 psi (20 N/mm2)

These mixes were the same as Mixes II, III and IV for High Grade concrete in the 1934

Code of Practice for reinforced concrete, which was current at the time.


Ministry of Transport, Specification for Road and Bridge Works (First Edition), 1951

A range of concrete Classes were given, specified on the basis of the maximum aggregate/

cement ratio, with the maximum water/cement ratio and the 28-day cube strength given

for the stronger mixes. For Classes A to C the maximum aggregate size was % inch (19 mm).

For Classes D and E the maximum aggregate size was 114 inches (38 mm), indicated by 1

after the letter, or 214 inches (64 mm), indicated by 2 after the letter. The values were as

follows:

5500 psi (38 N/mm2)

5000 psi (35 N/mm2)

4500 psi (31 N/mm2)

3200 psi (22 N/mm2)

Class AClass B

Class C

Class D1

Class D2

Class E1

Class E2

4.2:14.5:1

6:1

7:1

8.5:1

9:1

10:1

0.43

0.5

0.55

0.65

not specified

not specified

not specified

Recommended proportions of finexoarse material (in cu. ft) per 112 Ib of cement were

given for Classes D2, E1 and E2 for both angular and irregular aggregate.

For prestressed concrete, the Specification required a maximum water/cement ratio of

0.4 and a 28-day strength of 5500 psi (38 N/mm2). For piles, Class B was required.

Ministry of Transport, Specification for Road and Bridge Works (Second Edition), 1957

The same designations of concrete Classes were given, but the proportions and properties

were different; the 28-day strengths were significantly lower. The Classes were now specified

on the basis of weight of cement (lb):fine aggregate (cu. ft):coarse aggregate (cu. ft), for

both irregular and angular aggregates, with corresponding 28-day cube strengths. As

before, for Classes A to C the maximum aggregate size was % inch (19 mm). For Classes

D and E the maximum aggregate size was 114 inches (38 mm), indicated by 1 after the

letter, or 214 inches (64 mm), indicated by 2 after the letter.

For angular aggregate the values were as follows:

Class A

Class B

Class C

Class D1

Class D2

Class E1

Class E2

112:2:3

112:21/4:3

112:2V2:3V2

V\2AVA:6

112:414:7

112:51/4:7V2

0.5

0.55

0.6

0.65

0.65

not specified

not specified

3600 psi (25 N/mm2)

3300 psi (23 N/mm2)

2850 psi (20 N/mm2)

2400 psi (17 N/mm2)

2400 psi (17 N/mm2)

For irregular aggregate, the proportions were slightly different but the 28-day strengths

were the same.



The Specification mentions calcium chloride but gives no guidance on its use, simply

saying that it should be of a good industrial grade and from an approved source. The use

of high alumina cement was permitted, apparently without any restrictions.

Ministry of Transport Memorandum 785, Permissible working stresses in concrete

and reinforcing bars for highway bridges and structures, 1961

Three nominal mixes were specified on the basis of weight of cement (lb):fine aggregate

(cu. ft):coarse aggregate (cu. ft) as in Memorandum 557 but with increased 28-day cube

strengths, as follows:

• Mix A

• MixB

• MixC

150:2:4

120:2:4

90:2:4

4200 psi (29 N/mm2)

3750 psi (26 N/mm2)

3000 psi (21 N/mm2)

This would appear to be the only document that specified a standard amount of aggregate

and varied the amount of cement to give the various mixes; the general approach was to

specify varying amounts of aggregates to be used with a standard weight or volume of

cement.

Ministry of Transport, Specification for Road and Bridge Works (Third Edition), 1963

A range of concrete Classes with specified 28-day cube strengths were given. For Classes

A to E, the total volume of aggregate (cu. ft) per 112 Ib of cement was given; it was

suggested that the proportion of coarse:fine aggregate would normally be 2:1 but could

be varied between 11/2:1 and 3:1. Details were as follows:

Class A

Class B

Class C

Class D

Class E

Class X

Class Y

Class Z

112:472

112:55/8

112:71/2

112:972

112:10V4

Not specified

Not specified

Not specified

4200 psi

3750 psi

3000 psi

2400 psi

strength

7500 psi

6000 psi

4200 psi

(29 N/mm2)

(26 N/mm2)

(21 N/mm2)

(17 N/mm2)

not specified

(52 N/mm2)

(41 N/mm2)

(29 N/mm2)

In addition the maximum aggregate size was given. For example, D.IV2 indicated a 2400 psi

(17 N/mm2) concrete with a 11/2 inch (38 mm) maximum aggregate size.

Strangely, maximum water/cement ratios, which were given in the Second Edition, were

not given for Classes A to E in the Third Edition, the amount of water being simply limited to:

"that required to produce a dense concrete with sufficient workability to enable

it to be placed and compacted."

For Classes X to Z, which were 'special' concretes, the water/cement ratio was limited to 0.5.


The guidance on calcium chloride and the use of high alumina cement was the same as

in the Second Edition. There was a general statement that:

"Admixtures shall not be used without the specific approval, in writing, of the

Engineer".

British Rail Midland Region, Drawing Office Handbook, circa 1960

Four nominal mixes were specified on the basis of cementfine aggregate:coarse aggregate

ratios by volume, with corresponding 28-day cube strengths, as follows:

Mix A

MixB

MixC

MixD

MixA1

1:11/z:3

1:2:4

1:3:6

1:4:8

not specified

4000 psi (28 N/mm2)

3000 psi (21 N/mm2)

1500 psi (10 N/mm2)

no specified strength

7000 psi (48 N/mm2) (for prestressed concrete)

British Rail Southern Region, Specification for Norwood High Street Bridge, 1968

This Specification gave various standard mixes as follows: S (standard mix), Y (contractor

designed mix), A-E (as CP 116), LWT (lightweight concrete) and RH (rapid hardening).

Note: It is not clear whether this was a standard Southern Region specification or whether it

was specific to this contract.

Ministry of Transport Memorandum 577/2, Reinforced concrete for highway

structures: materials, workmanship, design requirements and permissible stresses,

1968

The Memorandum listed four Classes of concrete, specified by their 28-day cube strengths,

as follows:

Class 7500

Class 6000

Class 4500

Class 3000

7500 psi (52 N/mm2)

6000 psi (41 N/mm2)

4500 psi (31 N/mm2)

3000 psi (21 N/mm2)

Minimum cement contents were given for the various maximum aggregate sizes and a

maximum cement content given for all mixes.

Technical Memorandum BE 10, Reinforced concrete for highway structures, 1968

BE 10 stated that concrete should be in accordance with Clause 1601 of the DOE Specification

and noted that Classes higher than 30 would not generally be required for reinforced

concrete. Tables in the Memorandum cover three Classes of concrete, namely 22.5 N/mm2,

30 N/mm2 and 37.5 N/mm2.



Technical Memorandum BE 20, Prestressed concrete for highway structures, 1969

Two classes were specified for prestressed concrete, Class 7500 (52 N/mm2) and Class 6000

(41 N/mm2). There was also an 'exceptional' class, Class 9000 (60 N/mm2), though the

Memorandum suggests that this should be avoided because of the difficulty of maintaining

the strength and because of the shrinkage associated with high cement contents.

BE 1/73: Reinforced concrete for highway structures and BE 2/73: Prestressed

concrete for highway structures, 1973

As in BE 10, BE 1/73 stated that concrete should be in accordance with Clause 1601 of the

DOE Specification and noted that classes higher than 30 would not generally be required

for reinforced concrete. Tables in the Memorandum again covered three Classes of

concrete, namely 22.5 N/mm2, 30 N/mm2 and 37.5 N/mm2. BE 2/73 noted that concrete

should generally be Class 52.5 or Class 45. Higher strengths could only be used when

economically justifiable and account was taken of the possible difficulty in maintaining

the strength.

BS 5400, Steel, concrete and composite bridges, Part 4: Code of practice for design

of concrete bridges, 1978

(Note that BS 5400 Part 4:1978 was not implemented by the Highways Agency until the

publication of BD 17/83.)

In BS 5400:1978, and subsequent versions, design was based on specified concrete strength

grades, from 20 N/mm2 up to 60 N/mm2. By implication in various tables, minimum

concrete grades were specified for different types of element: 20 N/mm2 for reinforced

concrete, 30 N/mm2 for post-tensioned prestressed concrete and 40 N/mm2 for pre-

tensioned prestressed concrete.

The Code gave the same increase in design strengths at different ages as in CP 110.

The requirements for materials and workmanship were covered in BS 5400 Part 7,

Specification for materials and workmanship, concrete, reinforcement and prestressing

tendons. The use of calcium chloride was totally banned by the clause stating that:

"Calcium chloride or admixtures containing calcium chloride shall not be used

in structural concrete containing reinforcement, prestressing or other embedded

metal."

BE 1/73: Reinforced concrete for highway structures (including Amendment No. 1),

1979

The strength classes were the same as in the 1973 versions of the document, namely

22.5 N/mm2, 30 N/mm2 and 37.5 N/mm2.


BD 17/83: Design of concrete bridges; use of BS 5400: Part 4:1978,1983

This adopted the concrete strength Grades in BS 5400 (20 N/mm2 up to 60 N/mm2).

However, a restriction was placed on the use of enhanced strengths at ages greater than

28 days, with a footnote to the table stating that:

"Increased strengths at these ages should be used only if it has been

demonstrated to the satisfaction of the Engineer that the materials to be used

are capable of producing these higher strengths."



The revised version of the Code contained the same restrictions on the use of enhanced

concrete strengths.

4.4 Design exposureconditions

Early codes paid little attention to the exposure conditions and hence to the durability of

concrete.

Mix proportions were specified on the basis of the quantities of cement and aggregate

required, such as 1:2:4 (cementfine aggregate:coarse aggregate) by volume. While it was

appreciated in the 1920s that the strength of concrete was influenced by the water/cement

ratio, there was little guidance on ratios actually required. For example, Everyday uses of

Portland cement^, published in 1921, stated that:

"The quantity of water should be just sufficient to bring water to the surface

after thorough ramming ....The concrete should be sufficiently wet... to

ensure it passing between the reinforcing bars and thoroughly surrounding

every portion of the steel."

Similarly, there was little guidance on the required cover to the reinforcement. The long-

term effects of some materials, such as calcium chloride accelerator or high alumina

cement (see Section 4.2.2), were not initially appreciated. Similarly, alkali-silica reaction

(see Section 7.1) only manifested itself fairly recently. Code requirements have been slowly

refined as experience of the materials' use in service developed.



4.4.1 Buildings and other

structuresCode of Practice for reinforced concrete, 1934

The Handbook to the Code'13) did discuss problems associated with sulfates and acidic

water (suggesting the use of high alumina cement or Portland-blastfurnace cement). The

authors also discussed problems associated with milk and other liquids. However, there

was no relevant guidance in the Code, which did not mention exposure, simply saying

that the cover to all reinforcement should be at least Vz inch (13 mm) or the diameter of

the bar, whichever was the greater. For main bars in beams and columns the minimum

cover was increased to 1 inch (25 mm) or the diameter of the bar, whichever was the

greater.



The specified minimum cover was generally 1 inch (25 mm) or the bar diameter, when

using the 112:2:4 concrete. This was increased to VA inches (32 mm) or the bar diameter

when the weaker 112:21 :̂5 concrete was used. Where the surface was exposed to water

of a corrosive nature, the minimum cover was increased to 2 inches (51 mm).

CP 114, Structural use of normal reinforced concrete in buildings, 1948

The Code specified covers for only two environments, namely 'internal' and 'external,

buried or aggressive'. Minimum covers were the same as in the 1934 Code except that

the cover to the main reinforcement in columns was increased to VA inches (38 mm).

For all external work and for work against earth faces (and for internal work in aggressive

conditions) all covers were to be increased by Vz inch (13 mm). There would appear to be

no link between the required concrete properties and the exposure.

CP 114, The structural use of reinforced concrete in buildings, 1957

The Code specified covers for the same two environments asCP 114:1948, with neither

the Code nor the Handbook'14' making any link between the required concrete grade and

durability.


The Code made no mention of requirement to control the water/cement ratio, only

saying that:

"It is most important to maintain the water/cement ratio constant."

The two exposure conditions and the cover requirements were as in CP 114:1957.

CP 2007, Design and construction of reinforced and prestressed concrete structures


The guidance inCP 2007 was generally in line with CP 114 and CP 115, but the Code did

give guidance on 'injurious soils' saying that:

"The use of sulfate-resisting cement... may not afford a complete safeguard;

an isolating coat of bituminous or other suitable composition may be required."



The covers given in the by-laws would appear to be largely related to fire resistance.

However, a minimum cover of V/z inches (38 mm) was required where reinforced

concrete was "exposed to the weather or is in contact with a source of damp".


This would appear to be the first Code to specifically consider durability in detail. The two

exposure conditions in CP 114 and CP 115, 'internal' and 'external' were subdivided as follows:

• Internal Non-corrosive

Corrosive, e.g. roof units subject to corrosion

Severely corrosive, e.g. roof units subject to corrosive fumes

• External Sheltered in non-industrial areas

Sheltered in industrial areas or work against non-sulfate bearing earth faces

Exposed in non-industrial areas

Exposed in industrial areas or subject to mild sulfate attack

Exposed to sea water or weak chemical attack

Subject to salt used for de-icing.

The minimum cover appropriate to each grade of concrete was specified for the various

exposure conditions. Minimum cement contents were given for reinforced concrete and

for prestressed concrete, but no values were given for water content.

CP 110, Code of practice for the structural use of concrete, 1972

The Code specified five exposure conditions, namely 'mild', 'moderate', 'severe', 'very severe'

and 'subject to de-icing salts'. Concrete grades and covers were specified for the various

exposure conditions and, for the first time, the Code gave maximum water/cement ratios.


Again five exposure conditions were specified, now termed 'mild', 'moderate', 'severe',

'very severe' and 'extreme'. Maximum water/cement ratios, minimum cement contents

and minimum concrete grades were given for all five exposure conditions. The cover to

the reinforcement was related to the exposure condition and the quality of the concrete,

rather than just the grade as in CP 110.

BS 5328, Concrete, Parti: Guide to specifying concrete, which was developed from BS 8110

Section 6, Concrete: materials, specification and construction, was introduced in 1991. From

that date, BS 8110 referred to BS 5328 (and later to its replacement BS 8500) for guidance

on cover and concrete quality requirements for the different exposure conditions.



4.4.2 Bridges As with buildings, early design Standards for bridges paid little attention to durability. The

guidance has become more detailed over the years.


(reprinted 1949)

The Memorandum does not specifically mention exposure conditions. For retaining walls,

a minimum cover of VA inches (38 mm) was specified. For beams 1 inch (25 mm) was

specified, increasing to VA inches (38 mm) if the structure was 'exposed to sea action'.



1968

The Memorandum identified six different conditions of exposure, ranging from 'Not exposed

to atmosphere' to 'Exposed to sea water'. Minimum covers were specified for three Classes

of concrete, namely 3000 psi (21 N/mm2), 4500 psi (31 N/mm2) and 6000 psi (37.5 N/mm2).

For concrete in contact with the ground, minimum cement contents and maximum

water/cement ratios were given for various cement types and sulfate concentrations.

Technical Memorandum BE 10: Reinforced concrete for highway structures, 1968

BE 10 identified the same six exposure conditions as in Memorandum 577/2. Minimum

covers were specified for three Classes of concrete, namely 22.5 N/mm2, 30 N/mm2 and

37.5 N/mm2. For concrete in contact with the ground, minimum cement contents and

maximum water/cement ratios were again given for various cement types and sulfate

concentrations.

Technical Memorandum BE 20: Prestressed concrete for highway structures, 1969

BE 20 gave no guidance on aspects such as exposure and cover.

Technical Memorandum BE 1/73: Reinforced concrete highway structures and BE

2/73: Prestressed concrete highway structures, 1973

BE 1/73 identified the same six exposure conditions as BE 10, with the same minimum

covers for the same three Classes of concrete. The requirements for concrete in contact

with the ground were also unaltered. For determining the minimum cover, BE 2/73 referred

to BE 1/73, which was somewhat illogical as the concrete strengths in BE 2/73 were

normally required to be 52.5 N/mm2 or 45 N/mm2, which were higher than those covered

by BE 1/73. An additional requirement was that the cover to any duct should be at least

50 mm.





The Code defined three exposure conditions, namely 'moderate', 'severe' and 'very severe',

with associated nominal covers, minimum concrete grades and design crack widths. The

three exposure conditions were each illustrated by two or more examples.


Technical Memorandum BE 1/73: Reinforced concrete highway structures (including

Amendment No. 1), 1979

The Amendment reduced the exposure conditions from six to four, as follows:

• Concrete exposed to abrasive action of sea water or water with pH < 4.5

• Concrete exposed to de-icing salts or sea water spray

• Concrete exposed to driving rain or alternate wetting and drying or freezing while wet

• All other surfaces

Minimum covers were given for the three grades of concrete, namely 22.5 N/mm2,

30 N/mm2 and 37.5 N/mm2.


The Standard amended the three exposure conditions in BS 5400, dividing 'very severe'

into 'very severe' and 'extreme'. The nominal covers for all exposure conditions were

increased, generally by 5mm though in some cases by 10 mm.



The Code adopted the four exposure conditions in BD 17/83, namely 'moderate', 'severe',

'very severe' and 'extreme', along with the associated nominal covers and associated

minimum concrete grades.

BD 24/84, Design of concrete bridges, Use of BS 5400: Part 4:1984,1984

This document implemented the use of BS 5400: Part 4 with minor typographical

amendments, none of which dealt with the exposure conditions.

28

4.5 Reinforcement andprestressing

Just as the Codes and Standards for design have developed over the years, so the types of

reinforcement have changed and their properties have improved. In addition the methods of

identifying the different materials on reinforcement drawings have changed. The information

is summarised in the sections below and in Appendix A of Standard method ofdetailing

structural concrete®**.

Many different types of prestressing system have been available over the years, particularly

prior to the introduction of British Standards. Appendix III of Historic concrete -background

to appraisal1-391 reviews the various early types of proprietary reinforcement, from the 19th

century to about the First World War.

Knowledge of these various developments is clearly essential when assessing existing

structures. Because of the variability of reinforcement, it is advisable to determine the

properties of the reinforcement by testing samples removed from the structures, particularly

when considering structures built prior to about 1960.



4.5.1 Detailing symbols

Table 6Detailing symbols.

The symbols used on reinforcement drawings to indicate the type of reinforcement have

been specified in various Standards over the years, as shown in Table 6.

4.5.2 Imperial bar sizes Before metrication, the generally available size range for both round and square (or

chamfered square) bars was VA inch (6 mm) to VA inches (38 mm) in the following sizes:

Imperial bar sizes

A Vis inch (5 mm) square area bar was also available for a time as were round area bars in

sizes up to 21/4 inches (57 mm).

It should be noted that in American practice the bar designation number refers to the

number of eighths of an inch in the nominal diameter, so a number 6 bar has a nominal

diameter of 3A inch (19 mm). It would appear that the system was occasionally used for

projects in the UK.

Prior to 1964 most square and chamfered square bars were of square area so that nominal

1 inch bars had an area of 1 sq. inch (645 mm2). During the late 1960s a transition to round

areas occurred with nominal 1 inch bars having an area of 0.785 sq. inches (510 mm2).

The nominal size range for twin twisted bars was from VA inch (6 mm) to VA inches (32 mm)

in the increments shown above. In addition smaller twin twisted bars were produced from

12,10, 8, 6 and 5 gauge wires (Standard Wire Gauge or SWG sizes) having diameters of

2.64, 3.4, 4.06, 4.88 and 5.38 mm respectively.

The nominal size of a twin twisted bar referred to the size of one bar in the pair and a

nominal 1 inch bar provided a steel area of 1.571 sq. inches (1010 mm2).


4.5.3 Yield stresses

Table 7Specified yield stresses.

The specified yield stresses in the Standards for reinforcement have varied over the years.

Some values are given in Table 7.

It should be noted that BD 21, The assessment of highway bridges and structures^ states that:

"Pre-1961 reinforcement may be assumed to have a characteristic strength

not greater than 230 N/mm2. For reinforcement after this date, the strength

shall be taken as specified in the appropriate design codes for the period for

high yield and mild steel bars."

4 . 5 . 4 Fabric In the past wire fabric was produced from twisted square sections and twin twistedmaterial as well as plain round drawn wire and ribbed bar. The wire was often measuredin SWG (Standard Wire Gauge) sizes whereas the fabric itself was usually described interms of its mesh type and weight per square yard. It is not practical to summarise therange or describe the expanded metal fabric, which was also used. Identification of thematerial used will require reference to contemporary literature, such as the relevant issuesof Specification^.

4.5.5 Early reinforcement

systems

In the early days of reinforced concrete (from the 1890s to 1920s), a number of proprietaryreinforcement systems were used, see Bussell'42'. Many of these were developed in France,Germany and the USA and imported into the UK. Details can be found in Appendix III ofHistoric concrete - background to appraisal^, which also covers various patented floorsystems.

30



The importance of the bond between the reinforcement and the concrete was identified

at an early stage. Most of the systems are recognisable as variations on modern bars, with

a wide variety of surface characteristics. For example, the Hennebique System used plain

round (mild steel) bars with flattened 'fish tail' ends for anchorage.

A very unusual product was the Kahn bar, which consisted of a square section with two

projecting strips on diagonally opposite corners. These were slit along short lengths and

bent up to form shear reinforcement. In the USA and UK the system was adopted by the

Trussed Concrete Steel Company, which became abbreviated toTruscon.

4.5.6 Early prestressing

systems

The commercial use of prestressing in the UK began just before the Second World War.

During and just after the war it was used to overcome material shortages. The early designs

were mainly by refugee European engineers and the systems manufactured were not British.

After about 1950 various British systems were developed.

Walley'43! reviewed the early history of prestressed concrete. He discussed the materials

used and the systems for pre- and post-tensioning in use, particularly in the early days,

along with various applications.

Detailed information on systems available between 1940 and 1985 may be found in CIRIA

Report 106, Post tensioning systems for concrete in the UK: 1940-1985^4\ A number of

the systems described ceased to be used after about the 1960s. Thus, when assessing an

existing structure, identification of the type of anchorage used may give an indication of

the age of the structure.

Structural precast concrete by Glover'45' gives details of the strands, anchorages and other

components of various post-tensioning systems, as follows:

• BBRV

• CCL

• Dywidag

• Freyssinet

• Gifford-Burrow

• Gifford-Udall

• Macalloy

• Magnel-Blaton

• PSC

• PZ

• SDL

31


5. Design

A paper by Bussell'46) looked at the development of the understanding of reinforced concrete

behaviour, textbooks, codes and standards up to the publication of CP 114 in 1948.

Subsequent developments were reviewed briefly.

The Reinforced Concrete Designers' Handbook^ by Charles Reynolds has been one of the

standard guidance documents since it was first published in 1932. It has been constantly

revised and updated as Codes and Standards have developed. (Later editions were

additionally authored by JC Steedman.) Reynolds was also the author of Practical examples

of reinforced concrete design^. First published in 1938, designs were in accordance with

the 1934 Code and the 1938 London County Council By-laws. In 1952, Reynolds produced

Examples of the design of reinforced concrete buildings^ in line with CP 114:1948. The

Second edition, published in 1959, was updated in accordance with the 1957 version of

CP 114. In 1962, he published Basic reinforced concrete design, a textbook for students and

engineers^. Guidance on the use of CP 110 was given by Allen in Reinforced concrete

design to CP 110 simply explained^.

The following sections are not intended to be a summary of the relevant Codes but rather to

simply pick out their salient points and identify areas in which there have been significant

changes with successive Codes. Specific guidance on the design of water-retaining structures

is outlined in Section 6.3.

5.1 L o a d i n g Table 8 lists the dates of the introduction of the main loading Codes for buildings. In

addition there were local loading requirements, such as the London County Council (LCC)

Regulations for Ferroconcrete. Office loadings appear to have been largely unchanged

over the years. In the 1934 Code, office loading was given as 80 lbs/ft2, which is equal to

about 3.8 kN/m2, compared with the 4 kN/m2 that is often used these days. Mitchell's

Building Construction (1930) makes reference to the LCC Regulations for Ferroconcrete,

which required 100 lbs/ft2, or 4.8 kN/m2. Details of the design loadings for offices and

other buildings are given in the relevant Editions of Reynolds'19'.

32

Table 8Loading Codes for buildings.


Table 9Highway loading Standards.

Design 5

Dawe'50) has reviewed the development of rules for traffic loading from their introduction

in the early 1920s up to the present day. Table 9 lists some of the key stages in this

development but there were many interim guidance notes produced by the Ministry of

Transport (laterthe Department of Transport), as detailed in Dawe's book.

Date Standard

Summaries of the loadings required for railway bridges are given in the relevant editions

of Reynolds!19).

5.2 Reinforcement designstrengths

Table 10Design stresses for reinforcement.

The reinforcement stresses to be used in design, as specified in the Code current at the

time, have changed over the years as shown in Table 10.

Standard Reinforcement

33


5.3 Bending and axial load In the early Codes, design was on the basis of elastic behaviour underworking loads, with

limiting 'permissible' stresses in the concrete and steel. The 1957 version of CP 114

introduced an alternative approach, namely load-factor design. Limit state design was

adopted by CP 110 in 1972, and has been used in all subsequent Codes.

5.3.1 Buildings Reinforced Concrete Designers' Handbook (First Edition), 1932(19)

Working stresses were given for six Mixes A to F, as shown below.

• Mix A

• MixB

• MixC

• MixD

• MixE

• MixF

1:3:6

VIVz-.S

1:2:4

I.VA3V3

V.VA3

1:1:2

400 psi (2.8 N/mm2)

500 psi (3.5 N/mm2)

700 psi (4.8 N/mm2)

750 psi (5.2 N/mm2)

800 psi (5.5 N/mm2)

875 psi (6.0 N/mm2)


The by-laws used Mixes C to F as above, but with slightly reduced stresses, as follows:

1:2:4 600 psi (4.1 N/mm2)

650 psi (4.5 N/mm2)

675 psi (4.7 N/mm2)

750 psi (5.2 N/mm2)

V.VA3

1:1:2

Code of Practice for reinforced concrete, 1934Design was on the basis of elastic behaviour under working loads limited by 'permissible

stresses' in the concrete and steel. In bending, the permissible stress in the concrete was

one-third of the 28-day cube strength, namely for Ordinary Grade concrete:

Mix

Mix

Mix

Mix

I

II

III

IV

1:1:2

1:1.2:

1:1.5:

1:2:4

2.4

3

975

925

850

750

psi

psi

psi

psi

(6.7

(6.4

(5.9

(5.2

N/mm2)

N/mm2)

N/mm2)

N/mm2)

and for High Grade concrete:

Mix I

Mix II

Mix III

Mix IV

1:1:2

1:1.2:2.4

1:1.5:3

1:2:4

1250 psi (8.6 N/mm2)

1200 psi (8.3 N/mm2)

1100 psi (7.6 N/mm2)

950 psi (6.6 N/mm2)

Design equations were given for axially loaded short columns and for long columns.The

Handbook'13' gave tables for the permissible loads on square and octagonal columns for a

range of concrete mixes and amounts of reinforcement.


Design 5


The permissible stresses for the six mixes, specified on the basis of weight of cement (Ib):

fine aggregate (cu. ft):coarse aggregate (cu. ft), were as follows:

Mix I

Mix II

Mix III

MixIA

Mix HA

Mix MIA

112:11/4:2l/2112:17/s:33/4

112:214:5

112:11/4:2V2

112:17/s:33/4

112:2y2:5

975 psi (6.7 N/mm2)

850 psi (5.9 N/mm2)

750 psi (5.2 N/mm2)

1250 psi (8.5 N/mm2)

1100 psi (7.6 N/mm2)

950 psi (6.6 N/mm2)

This information was also given in Reinforced concrete simply explained^2®.


As in the 1934 Code, design was on the basis of elastic behaviour underworking loads

limited by 'permissible stresses' in the concrete and steel. These permissible stresses in

the concrete were again one-third of the corresponding 28-day cube strength, i.e.:

1:1:2 1500 psi (10.4 N/mm2)

V.V/r.3 1250 psi (8.6 N/mm2)

1:2:4 1000 psi (6.9 N/mm2)


In the 1957 version of CP 114, design could be either by the established permissible stress

approach or by the load-factor approach. The latter was carried out at the ultimate load,

taken as being twice the working load on the member. In the calculation of the ultimate

moment capacity for beams and slabs, the compressive stress in the concrete was limited

to two-thirds of the cube strength and the compressive stress block was limited to half the

effective depth. The reinforcement was assumed to be acting at its yield (or proof) stress.

For the design of columns, the permissible stress approach could be used for both short

and long columns. The Handbook'14' gave tabulated values for the permissible load on

short square columns with helical reinforcement for a range of column dimensions and

concrete grades. Guidance was also given for the design of short columns using the load-

factor approach. This again limited the concrete stress to two-thirds of the cube strength

but here the cube strength was to be taken as only 76% of the actual cube strength (i.e.

the stress was limited to 50% of the actual cube strength). The Handbook gave a design

chart for eccentrically loaded short columns using the loaded-factor method.

At the time, cements were such that concrete gained strength more slowly. The Code

recognised that there would be a significant gain in strength after the statutory 28 days

(see Section 4.3.1) and indicated that, where the member being designed would not

receive its full design load until a later age, the design stresses could be increased by an

appropriate amount. Some consultants regularly allowed for about a 20% increase in

concrete strength, particularly when designing columns as this would lead to a significant

reduction in the amount of reinforcement required.



Design of prestressed beams was on the basis of permissible stresses at working loads

followed by calculation of the ultimate strength.


The permissible stresses in bending for the six mixes were slightly changed from those in

the 1938 By-laws, as follows:

Grade I

Grade II

Grade III

Grade IA

Grade IIA

Grade IIIA

970 psi (6.7 N/mm2)

850 psi (5.9 N/mm2)

750 psi (5.2 N/mm2)

1500 psi (10.4 N/mrrv

1250 psi (8.6 N/mm2)

1000 psi (6.9 N/mm2)


The Code was published in three parts. The main body of the guidance was given in Parti,

Design, materials and workmanship. Design charts for beams and columns were given in

Part 2, Design charts for singly reinforced beams, doubly reinforced beams and rectangular

columns, and Part 3, Design charts for circular columns and prestressed beams, all based on

the assumptions in Part 1. CP 110 introduced the concept of limit state design, with partial

safety factors applied both to the loads (or 'actions' in Eurocode parlance) and to the

material properties. This approach has been used by all subsequent codes.

Three characteristic strengths were specified for high yield reinforcement, namely 410 N/mm2,

425 N/mm2 and 460 N/mm2, depending on the bar diameter and the method of manu-

facture. A partial safety factor of 1.15 was applied to the characteristic steel strength.

The resistance to bending could be determined using the rectangular-parabolic concrete

stress block. Alternatively, an equivalent rectangular stress block could be used equal to

0.4/cu over the full depth of the compression zone.


The Code was published in three parts, as follows:

• Pa rt 1: Code of practice for design and construction

• Part 2: Code of practice for special circumstances

B Part 3: Design charts for singly reinforced beams, doubly reinforced beams and

rectangular columns.

Design charts for circular columns were published by Batchelor and Beeby of the BCA in

Unlike CP 110, only a single characteristic strength was specified for high yield reinforcement,

namely 460 N/mm2. A partial safety factor of 1.15 was applied to the characteristic steel

strength.


Design 5

While the rectangular-parabolic stress curve for concrete was the same as that given in

CP110, the simplified rectangular stress block was modified to 0.45/cu applied over a depth

of 0.9x, where x was the effective depth.

5.3.2 Bridges The design approaches for bridges mirrored those for buildings, moving from permissible

stress design to limit state design, though the latter was adopted more slowly.


(reprinted 1949)

The permissible stresses in bending were given for three concrete Mixes, specified on the

basis of weight of cement (lb):fine aggregate (cu. ft):coarse aggregate (cu. ft), as follows:

Mix A

MixB

MixC

150:2:4

120:2:4

90:2:4

1200 psi (8.3 N/mm2)

1100 psi (7.6 N/mm2)

950 psi (6.6 N/mm2)

Permissible stresses in direct loading were 80% of those in bending.



The permissible stresses in bending were again given for three concrete Mixes, specified

on the basis of weight of cement (lb):fine aggregate (cu. ft):coarse aggregate (cu. ft), as in

Memorandum 557, but increase slightly follows:

Mix A 150:2:4

MixB 120:2:4

MixC 90:2:4

1400 psi (9.7 N/mm2)

1250 psi (8.6 N/mm2)

1000 psi (6.9 N/mm2)

Permissible stresses in direct loading were 76% of those in bending.



1968

The elastic design approach was based on that in CP 114. The permissible stresses in

bending were one-third of the 28-day concrete strength and in direct compression, the

stresses were approximately one-quarter of the 28-day strength. Stresses were given for

three Classes of concrete, as follows:

Class 6000 Bending 2000 psi (13.8 N/mm2)



Direct 1500 psi (10.4 N/mm2)



37


BE 10: Reinforced concrete for highway structures, 1968

As in Memorandum 577/2, the elastic design approach was based on that in CP 114. The

permissible stresses in bending were again one-third of the 28-day concrete strength and

in direct compression the stresses were one-quarter of the 28-day strength. Stresses were

now given for three Classes of concrete, as follows:

ClassClass

Class

37.530

22.5

Bending 12.

Bending 10

Bending 7.5

5 N/mm2

N/mm2

N/mm2

Direct 9.5

Direct 7.6

Direct 5.7

N/mm2

N/mm2

N/mm2

BE 1/73: Reinforced concrete for highway structures, 1973

The elastic design approach was based on that in CP 114 and CP 116, with the same

permissible stresses as in BE 10. In addition to the elastic design approach, the ultimate

moment of resistance of reinforced concrete parapet walls and bridge supports was

determined using a rectangular-parabolic stress-strain curve for the concrete with a

maximum compressive stress of 0.44uw. Alternatively a rectangular stress block 0.4uw

over the full depth of the neutral axis could be used. The tensile stress in the reinforcement

was "derived from the appropriate stress-strain curves supplied by the manufacturer".





The Code was closely based on CP 110:1972, with the same specified characteristic strengths

for the reinforcement (410 N/mm2, 425 N/mm2 and 460 N/mm2) and the same approach

for the design of members in bending. The equivalent rectangular stress block was taken

as 0.4/cu over the full depth of the compression zone. BS 5400 referenced the design charts

in Parts 2 and 3 of CP 110.


1979

The design approach was unchanged from the 1973 version.


Although the Standard contained a significant number of amendments, these were largely

matters of clarification and did not affect the approach to design for flexure. One minor

change was that only two specified characteristic strengths were given the reinforcement,

namely 425 N/mm2 and 460 N/mm2.



Most of the editorial changes identified in BD 17/83 were incorporated in the 1984

edition of BS 5400: Part 4.




amendments.



Again there were no significant differences in the design approach, with the equivalent

rectangular stress block equal to 0.4/cu over the full depth of the compression zone.

However, reference was now made to the design charts in Part 3 of BS 8110:1985.

5.4 Shear and punching in

reinforced concreteThe approaches to designing for shear and for punching have changed significantly over

the years, as outlined in the following sections.

5.4.1 Buildings Reinforced Concrete Designers' Handbook (First Edition), 1932

Permissible shear stresses were given for the six Mixes A to F, as follows:

Mix A

MixB

MixC

MixD

MixE

MixF

1:3:6

1:2y2:5

1:2:4

1:1%:3V3

1:iy2;3

1:1:2

40 psi (0.28 N/mm2)

50 psi (0.35 N/mm2)

60 psi (0.41 N/mm2)

63 psi (0.43 N/mm2)

65 psi (0.45 N/mm2)

70 psi (0.48 N/mm2)


The applied shear stress on the cross-section, s, was determined on the basis of a uniform

distribution as follows:

s = S/ba

where

S =

b =

a =

applied shear force

breadth of the section

lever arm.

Permissible shear stresses were given for Ordinary Grade concrete (see Section 4.3.1), as

follows:

• Mix I 1:1:2 98 psi (0.68 N/mm2)

a Mix II 1:1.2:2.4 93 psi (0.64 N/mm2)

• Mix III 1:1.5:3 85 psi (0.59 N/mm2)

B Mix IV 1:2:4 75 psi (0.52 N/mm2)


And for High Grade concrete as follows:

• Mix

• Mix

• Mix

• Mix

1

II

III

IV

1:1:

1:1.

1:1.

1:2

2

2:2.4

5:3

:4

125 psi (0.86 N/mm2)

120 psi (0.83 N/mm2)

110 psi (0.76 N/mm2)

95 psi (0.66 N/mm2)

The permissible shear stress for Special Grade concrete was one-thirtieth of the 28-day

cube strength (the same proportion as for the other Grades) but not more than 150 psi

(1.04 N/mm2).

Where the applied shear stress exceeded the permissible stress, shear reinforcement was

required to carry all the shear force. However, the Code required that the shear stress

should not exceed four times the permissible value. The spacing of the stirrups should not

exceed the lever arm. There was no requirement to provide a minimum amount of shear

reinforcement in members.

For the punching shear resistance of slabs, the Code identified two critical sections, namely

at a distance of one effective depth from the column head and at the perimeter of the

drop if used. The shear stresses should not exceed the permissible values given above; no

guidance was given on the provision of shear reinforcement.


The permissible shear stresses for the six mixes, specified on the basis of weight of

cement (lb):fine aggregate (cu. ft):coarse aggregate (cu. ft), were as follows:

Mix

Mix

Mix

Mix

Mix

Mix

III

III

IA

HA

IIIA

11Z:11/4:21/2

112:17/s:33/4

112:21/2:5

-]-\2:VA:2V2

112:17/s:33/4

112:2y2:5

98 psi (0.68 N/mm2)

85 psi (0.59 N/mm2)

75 psi (0.52 N/mm2)

125 psi (0.86 N/mm2)

110 psi (0.76 N/mm2)

95 psi (0.66 N/mm2)

CP114, Structural use of normal reinforced concrete in buildings, 1948

The approach was the same as in the 1934 Code except that the permissible stresses in

shear were increased slightly, with the following values for the three concrete grades:

1:1:2

1:iy2:3

1:2:4

130 psi (0.90 N/mm2)

115 psi (0.79 N/mm2)

100 psi (0.69 N/mm2)

Again, if the permissible stress was exceeded, all the shear had to be carried on shear

reinforcement. The spacing of the stirrups should not exceed the lever arm. There was no

requirement for minimum shear reinforcement.


The approach for the punching shear resistance of slabs was modified somewhat from

that in the 1934 Code. The critical perimeters were now at a distance of half the slab

depth from the face of the column or, if column heads or drops were used, at a distance

of half the total depth from the column head or drop. The shear stresses on the critical

perimeters should not exceed the permissible values. Again there was no guidance on the

provision of shear reinforcement.

CP 114.102, Floors and roofs of flat slab construction, 1950

The design for shear and for punching shear were the same as in CP 114:1948.


The general guidance was the same as in CP 114:1948, although the symbols used were

different. As before, where the applied shear exceeded the capacity of the concrete, all

the shear force had to be carried on shear reinforcement. There was no requirement for

minimum shear reinforcement.


The permissible shear stresses for the six mixes were slightly changed from those in the

1938 by-laws, as follows:

Grade I

Grade II

Grade III

Grade IA

Grade IIA

Grade IIIA

97 psi (0.67 N/mm2)

85 psi (0.59 N/mm2)

75 psi (0.52 N/mm2)

130 psi (0.90 N/mm2)

115 psi (0.79 N/mm2)

100 psi (0.69 N/mm2)

CP 114, Structural use of reinforced concrete in buildings - metric version, 1969

Permissible stresses in shear were given for the specified nominal mixes as follows:

1:1:2

1:2:4

0.9 N/mm2

0.8 N/mm2

0.7 N/mm2

The design approach was the same as in the previous versions of CP 114 except that there was

now a requirement for nominal shear reinforcement when the applied shear did not exceed

the shear capacity. The required cross-sectional area of the nominal shear reinforcement

was 0.15% of the horizontal area of the concrete at the section under consideration (or

0.12% if high yield steel was used). Nominal shear reinforcement was not required for

slabs, footings, bases, pile caps and members of minor importance. However, the Code

did warn that:

"A conservative approach should be used when calculating the resistance to

shear of members without shear reinforcement, as recent research has indicated

that, in some circumstances, the margin of safety may be lower than desirable."


CP110, The structural use of concrete, 1972

The approach to designing for shear was radically different from that in previous Codes.

For beams, the shear stress on the cross-section, v, was determined from:

v=V/bd

where

V = shear force due to ultimate loads

b = breadth of the section

d = effective depth.

The allowable shear stress on the concrete section was a function of the concrete grade

(specified values of 20 N/mm2, 25 N/mm2, 30 N/mm2 and 40 N/mm2 or more) and the

amount of tension reinforcement in the cross-section.

If the applied shear stress exceeded the allowable shear stress, shear reinforcement,

designed on the basis of a simple 45° truss, was provided to carry the balance, i.e.:

Total shear capacity = capacity of the concrete plus the capacity of the links.

A minimum area of links was required for beams, equal to 0.12% of the horizontal area

when using high-yield steel and 0.2% with mild steel. (The requirement for high-yield steel

was the same as in CP 114:1969. However, that for mild steel was a significant increase.)

Minimum links were not requiredfor members of minor importance or where the maximum

applied shear stress was less than half the allowable value.

Values were given for the maximum shear stress that could be applied to the cross-section,

which were a function only of the concrete grade, ranging from 3.35 N/mm2 for grade 20

concrete to 4.75 N/mm2 for 40 or more (i.e. about 0.75V/cu where/cu was the characteristic

concrete cube strength). For lower reinforcement percentages these maximum values

were significantly greater than the four times allowed byCP 114.

The Code introduced an allowance for increased shear capacity for beams loaded close to

the support. Where the distance from the support, av, was less than 2c/ (where d equalled

the effective depth) the shear capacity of the concrete could be multiplied by a factor of

2c//av, provided it did not exceed the maximum concrete capacity.

For solid slabs, the maximum shear stress due to ultimate loads was not to exceed half the

appropriate value for a beam. Guidance was given on designing for punching shear, which

was calculated on a critical perimeter at a distance of 1.5 times the overall slab thickness, h,

from the face of the loaded area, resulting in a square/rectangular perimeter with rounded

corners. The shear stress on the perimeter was checked using the same approach as for

beams but with addition of a factor that was related to the depth of the slab; higher shear

stresses were permitted for shallower slabs, with a multiplier ranging from 1.0 for slabs

250 mm or more thick to 1.2 for 150 mm or less. (In 1976, the multipliers were amended to

1.0 for slabs 300 mm or more thick and 1.3 for 150 mm or less.)


If the shear stress on the perimeter at 1.5/) exceeded the allowable value, shear reinforcement

was provided on the perimeter and a similar amount on a perimeter at a distance 0.75/?

inside it. Stresses were determined on perimeters progressively 0.75/) out from the critical

perimeter until the shear stress could be carried by the concrete alone.

The maximum shear stress was limited to half the maximum for beams.


The basic approach to the design of the shear capacity of beams was similar to that in CP 110:

1972. One significant difference was that the depth factor applied to slabs, which increased

the shear capacity of shallower slabs, was extended to beams as well. The design concrete

shear stress, vc, was expressed both in tabular form and also as the following equation:

vc=0.79[100AJbvd)033 ifJZ5)03S {400/d)025/y

where

As = area of tensile reinforcement

bv = section breadth

d = effective depth

/cu = characteristic cube strength of concrete, which should not be taken as greater

than 40

y = partial safety factor taken as 1.25.

Rather than specifying a minimum area of shear links as in CP 110:1972, the requirement

was that they should provide a shear capacity of 0.4 N/mm2, although the resulting area

was similar.

The maximum shear stress was limited to 0.8V/cu but not more than 5 N/mm2, which

was a slight increase on the values in CP 110:1972.

The approach to punching shear was also similar, but the perimeter was now taken as

rectangular (rather than rectangular with rounded corners) at1.5offrom the loaded area.

The maximum design shear stress was limited, as for beams, to 0.8V/cu but not more than

5 N/mm2. The amount of reinforcement required was to be distributed evenly around the

zone on at least two perimeters; note that this differed from the guidance in CP 110. (An

amendment in March 1993 identified two separate situations, namely v< 1.6vc and 1.6v

<v< 2vc, effectively imposing an upper limit of 2vc.)

5.4.2 Bridges The development of the design approaches for shear and punching in bridges mirrored

those for buildings.



(reprinted 1949)

The permissible shear stresses in bending were given for three concrete mixes, specified on

the basis of weight of cement (lb):fine aggregate (cu. ft):coarse aggregate (cu. ft), as follows:

MixA 150:2:4

MixB 120:2:4

MixC 90:2:4

120 psi (0.83 N/mm2)

110 psi (0.76 N/mm2)

95 psi (0.66 N/mm2)

Maximum shear stresses were 2Vz times the permissible values, i.e. 300 psi (2.1 N/mm2),

275 psi (1.9 N/mm2) and 238 psi (1.6 N/mm2) respectively. Where the shear stress exceeded

the permissible value, shear reinforcement was required to carry all the shear force. The

permissible stress in the steel was 18,000 psi (125 N/mm2). Minimum shear reinforcement

was required in beams to carry two-thirds of the permissible stress, i.e. 80 psi (0.6 N/mm2),

73 psi (0.5 N/mm2) or 63 psi (0.4 N/mm2), depending on the mix. There was no requirement

for minimum shear reinforcement in slabs.



The permissible shear stresses were again given for three concrete mixes, specified on the

basis of weight of cement (lb):fine aggregate (cu. ft):coarse aggregate (cu. ft), as in

Memorandum 557, but increased slightly as follows:

MixA 150:2:4

MixB 120:2:4

MixC 90:2:4

125 psi (0.86 N/mm2)

115 psi (0.79 N/mm2)

100 psi (0.69 N/mm2)



1968

The approach to the design for shear was the same as in CP114. Permissible shear stresses

were given for two Classes of concrete, as follows:

Class 4500

Class 3000

130 psi (0.90 N/mm2)

100 psi (0.69 N/mm2)

It was noted that when Class 6000 concrete was used, the permissible shear stress for

Class 4500 concrete should be used.

As in CP 114, when the applied shear force exceeded the permissible value, all the shear force

had to be carried on shear reinforcement. The maximum shear stress should not exceed four

times the permissible value. The permissible stresses in shear reinforcement were as follows:

• Mild steel 20,000 psi (140 N/mm2) for bar sizes up to VA inches (38 mm)

18,000 psi (125 N/mm2) for bars sizes over VA inches

B High yield steel 25,000 psi (175 N/mm2)


Design 5

There is no mention of stirrup spacing. However, as Memorandum 577/2 refers back to

CP 114, presumably the spacing should not exceed the lever arm.

Where the applied shear stress did not exceed the permissible value, there was a require-

ment for minimum links to carry two-thirds of the permissible stress. Minimum links were

not required in slabs.

There was no guidance on designing for punching shear.


Basically the approach to designing for shear was the same as in Memorandum 577/2

(i.e. permissible stress approach) but there were some adjustments to bring it more into

line with CP 110 (limit state design). Shear stresses were determined assuming a uniform

stress throughout the lever arm depth. Permissible shear stresses for reinforced concrete,

except for solid slabs without shear reinforcement, were given for two Classes of concrete,

as follows:

• Class 30 0.87 N/mm2

• Class 22.5 0.72 N/mm2

It was noted that when Class 37.5 concrete was used, the permissible shear stress for

Class 30 concrete should be used.

As in 577/2, when the applied shear force exceeded the permissible value, all the shear

force had to be carried on shear reinforcement. The maximum shear stress should not

exceed four times the permissible value. The permissible stresses in shear reinforcement

were as follows:

• Mild steel 140 N/mm2 for bar sizes up to 40 mm

125 N/mm2 for bars sizes over 40 mm

• High-yield steel 175 N/mm2

The stirrup spacing should, presumably, not exceed the lever arm.

Again, where the applied shear stress did not exceed the permissible value, minimum links

were required to carry two-thirds of the permissible stress and there was no guidance on

designing for punching shear.


The basic approach to designing for shear in beams was the same as in BE 10, but there

were some additional clauses, which brought the document more into line with CP 110.

An increased shear capacity was permitted for beams loaded close to the support. Where

the distance from the support, a, was less than 2d (where d equalled the effective depth),

the shear capacity of the concrete could be multiplied by a factor of Zd/a, provided it did .

not exceed the maximum concrete capacity. The increased shear capacity could not exceed

twice the basic permissible stress.


For solid slabs without shear reinforcement, the permissible shear stresses were related to

the Class of concrete (22.5 N/mm2, 30 N/mm2 and 37.5 N/mm2) and the percentage of

flexural tensile steel (<0.25 to >3.0). (BE 1/73 notes that the values given were based on

those on CP 110, but multiplied by Vi-5 to remove the partial safety factor and multiplied

by 2 so that they are directly applicable to unfactored working stress design.)

For shallow slabs, the permissible shear stress was modified by a multiplier which ranged

from 1.0 for slabs 250 mm or more thick and 1.2 for 150 mm or less. Again, the increased

shear capacity could not exceed twice the basic permissible stress.

For punching shear, the critical section was taken at a distance of 1.5/7 from the face of

the column, where h was the overall slab depth, on a rectangular perimeter with rounded

corners.





The approach was basically the same as in CP 110:1972. A minimum area of links was

required for beams, equal to 0.12% of the horizontal area when using high yield steel and

0.2% with mild steel. Minimum links were not required for members of minor importance

or where the maximum applied shear stress was less than half the allowable value.

The approach for punching shear was the same as in CP 110:1972, with the 1976 amendment

to the multipliers taking account of increased shear capacity for shallower slabs (multiplier

| s o f 1.0 for slabs >300 mm thick ranging up to 1.3 for 150 mm or less). The necessary

amount of shear reinforcement was provided on the perimeter under consideration and

an equal amount on a perimeter 0.75/7 inside it, where h was the overall slab depth.


1979

The design approach for shear was the same as in the 1973 version.


There were a number of editorial changes but the basic approach to the design for shear

in beams was the same as in BD 5400:1978. One significant change introduced by the

Standard was that the table of values for the multiplier | s was extended so that the shear

of members deeper than 500 mm was now reduced, with those for shallower members

being unchanged (i.e. multiplier of 0.71 for slabs >2000 mm thick ranging up to 1.3 for

150 mm or less). The multiplier was now applied to beams as well as slabs.


BD 17/83 introduced a check on the area of longitudinal reinforcement in the tensile

zone,As, such that:

V vs " (d-dc/Z)

where

A^= cross-sectional area of two legs of a link

d = effective depth

dc = depth of concrete in compression.

The Standard introduced significant modifications to the design approach for punching

shear. The critical perimeter was now located at 1.5c/, where cfwas the effective depth of

the slab, rather than at 1.5/J. While the guidance in BS 5400 was limited to loads applied

near the middle of a slab, the Standard introduced modified perimeters for loads near the

edge of a slab or the corner of a cantilever slab. Guidance was also given on the shear

capacity of voided slabs, which was not covered in BS 5400.



The approach to the design of the shear capacity of beams was similar to that in previous

versions of BS 5400 Part 4, with the incorporation of the majority of the amendments

listed in BD 17/83. The design concrete shear stress, vc, was again expressed in tabular

form but was also given by the following equation:

where

k=

bv=

/ c u=

y =

(/cu/25)°3

area of tensile reinforcement

section breadth

characteristic cube strength of concrete, which should not be taken as greater

than 40

partial safety factor taken as 1.25.

Neither the table nor the equation for vc took any account of the depth of the member. As

before, this was covered by the multiplier £s. As in BD 17/83, the values of |s, which was

given as equal to (500/d)°2S, increased the shear capacity of shallow members and reduced

the capacity of deep members. The tabulated values of £s were the same as in BD 17/83

but slightly rounded (e.g. 0.84 became 0.85).

The maximum shear stress was limited to 0.75V/cu but not more than 4.75 N/mm2, i.e.

the same values as previously although the table was removed.


Minimum links to carry a shear stress of 0.4 N/mm2 were required for all beams, unlike

BS 5400: Part 4:1984 where they were not required for members of minor importance or

where the maximum applied shear stress was less than half the allowable value.

The check on the area of longitudinal reinforcement in the tensile zone,/\s, was modified to:

As>V/{Z(0.87fy)}

where

/ = characteristic strength of the reinforcement

V = shear force due to ultimate loads at the section under consideration.

As in BD 17/83, the critical punching shear perimeter was taken at a distance of 1.5c/from

the loaded area and perimeters were given for loads near the edge of a slab or the corner

of a cantilever as well as near the middle of a slab.



amendments.



The approach to the design of the shear capacity of beams was the same as in BS 5400:

1984, except that/\s was now defined as additional longitudinal reinforcement in the

tensile zone in excess of that required to carry bending.

5.5 Shear in prestressed

concrete

As with reinforced concrete, the requirements for shear in prestressed concrete have

developed over the years.

5.5.1 Buildings CP 115, The structural use of prestressed concrete in buildings, 1959

The Code gave guidance on design for shear in uncracked sections. The principal tensile

stress due to prestress, bending and shear at working loads was compared with limiting

values of 125 psi (0.86 N/mm2), 150 psi (1.04 N/mm2) and 175 psi (1.21 N/mm2) for

specified works cube strengths of 4500 psi (31 N/mm2), 6000 psi (41 N/mm2) and 7500 psi

(52 N/mm2) respectively. When these stresses were exceeded, shear reinforcement was

required, with the proportion of the stress to be carried by the reinforcement depending

on the level of stress; when the shear stress exceeded 1.5 times the limiting value, all the

shear was carried by the reinforcement. A check was also required at ultimate load.

48


Design 5


The code required design for shear at the ultimate limit state only, giving guidance for beams

both for sections uncracked and cracked in flexure. The background giving the derivation

of the equations in the Code was given in some detail in the Handbook to the Code'14'.

For uncracked sections the approach was similar to that in CP 115:1959, with a limit

being placed on the principal tensile stress at the centroidal axis,/ , equal to 0.24V/cu,

where/cu was the characteristic concrete cube strength. The shear capacity of the

uncracked section, Vco, was given by:

where

/q>= compressive stress at the centroid due to prestress.

An allowance could be made for the effects of any inclined or vertical prestress at the

section under consideration.

CP 110:1972 introduced an equation for the ultimate shear resistance of a section cracked

in flexure, Vcr, as follows:

V =

where

d =

Mn =

1 -0 .55-^ -/ppu

V

effective depth to the centroid of the tendons

moment necessary to produce zero stress in the concrete at the level of the

centroid of the tendons

effective prestress in the tendons after all losses

characteristic strength of the tendons/P.

/ pu

V, M = shear force, bending moment at the section considered

vc = shear capacity .

Minimum shear reinforcement equivalent to a shear stress of 0.4 N/mm2 was required

for all beams, unless lightly loaded or deemed to be of minor importance. Designed shear

reinforcement followed the same approach as for reinforced beams with the exception

that a closer spacing of links was required when the applied shear force exceeded 1.8 times

the capacity of the cracked concrete cross-section. The maximum shear stress was again

0.75V/cu but the table of values was from grade 30 to 60 and over.


The approach in the Code to the shear resistance of uncracked sections was the same as

in CP 110:1972.

The equation for sections cracked in flexure was also the same as in CP 110:1972 but the

term Mo was now defined as the moment to cause zero stress in the concrete at the

extreme tension fibre rather than at the level of the centroid of the tendons.


5.5.2 Bridges The equations used for the design for shear in prestressed concrete bridges were generally

similar to those for buildings.

BE 20: Prestressed concrete for highway structures, 1969

The Memorandum gave no guidance on design for shear, so presumably design was in

accordance with CP 115:1959.

BE 2/73: Prestressed concrete highway structures, 1973

The shear capacity of the uncracked section, Qcw, was based on limiting the tensile stress

at the centroid, as in CP 115 and CP 110. However, the equation was a modified version of

that in CP 110, as follows:

Qcw = 0.67k/V(f t2

where

/ = compressive stress at the centroid due to prestress

/ t = principal tensile stress = 0.294Vuw

d = overall depth of the section

uw= cube strength.

The shear capacity of sections cracked in flexure, Qcm, was calculated from:

Qcm = 0 .045W> w +{Q/M)Mc

where

M = moment at section due to ultimate load

Q = shear force at section due to ultimate load

Mc= cracking moment at the section considered= (o.45V«w+/ep)//y

where

fe = stress due to prestress only at the extreme tensile fibre, at a distance y from the

centroid and / is the second moment of area.

There was a requirement that the spacing of the stirrups along a member should not exceed

the effective depth. When the applied shear exceeded 1.8 times the shear capacity of the

section (the lesser of Qcw and Qcm), the maximum spacing was reduced to half the effective

depth.





For uncracked sections the approach was modified from that in BE 2/73 and was the same

as in CP 110:1972, with a limit being placed on the principal tensile stress at the centroidal

axis,/t, equal to 0.24V/cu, where /cu was the characteristic concrete cube strength.


The shear capacity of uncracked sections, Vco, was given by:

where

/ = compressive stress at the centroid due to prestress.

However, the guidance on sections cracked in flexure was significantly different from that

in CP110. For Class 1 structures (no tensile stresses permitted) and Class 2 structures

(tensile stresses permitted but no visible cracking) the ultimate shear resistance, Vcr, was

calculated from:

Va = 0.037W/cu + {Mt/M)V

where

M = moment at section due to ultimate load

Vt = shear force at section due to ultimate load

Mt = cracking moment at the section considered

= (0.37V/cu + 0.8/pt)//y

where

/ 1 = stress due to prestress only at the tensile fibre distancey from the centroid

which has a second moment of inertia /.

For Class 3 structures (tensile stresses permitted but crack widths limited) Vcr was

calculated from:

Vcr=[\-0.55(fpJp]vcbd + M0

where

Mo= moment necessary to cause zero stress in the concrete at depth d

/ P e = effective prestress in the tendon after all losses have occurred

/ = characteristic strength of the tendon.

An expression was given for determining the effective prestress when there was both

stressed and unstressed reinforcement at the section being considered.

For sections uncracked in flexure, 0.8 times the vertical component of any inclined pre-

stressing force could be added to Vco. No such allowance was made for sections cracked

in flexure.

BD17/83: Design of concrete bridges; use of BS 5400: Part 4:1978,1983

The approach was the same as in BS 5400:1978 but the equations and definitions were

modified slightly to clarify that stresses due to prestress were after losses had taken place

and appropriate safety factors, as follows:


BD 17/83 introduced a clause dealing with the calculation of shear in the transmission

zone of pre-tensioned members, which was taken as the greater of the shear capacity of

the reinforced section (ignoring the area of the tendons) and the capacity of the cracked

or uncracked prestressed section, assuming a linear increase in the stress in the tendons.

The expressions for Vcr were unaltered but Mt was now given by:

with the requirement that the appropriate partial safety factor should be applied t o / t .

With inclined tendons, the shear capacity of uncracked sections could again be modified

but the factor of 0.8 applied to the vertical component was replaced by the appropriate

partial safety factor. Again, no allowance was made for sections cracked in flexure.



It would appear that all the modifications given in BD 17/83 were included in the 1984

version of BS 5400: Part 4.



amendments.



There were no significant changes from the 1984 version of BS 5400 Part 4.

5.6 Fire resistance Early concrete was considered to be fireproof and early proprietary designs, prior to the

introduction of national Codes, were marketed as such. More precise design guidance for

fire resistance has gradually developed with the introduction of successive Codes.

London County Council Reinforced Concrete Regulations: 1915

Columns were required to have a cover of VA inches (38 mm) or the bardiameter if this

was greater.


There was no mention of fire resistance in the design sections of the Code, although

Appendix 1, General building clauses, states that:

52


"For all buildings which are required to be of a specified degree of fire resistance,

the grade of fire resistance of the elements of structure and the incombustible

and non-inflammable properties of materials shall be stipulated in accordance

with British standard specification of fire resistance, incombustibility and non-

inflammability of building materials and structures No. 476."

BS 476, Fire tests on building materials and structures, was first issued in 1932; it was

revised in 1953 and subsequently split into a number of Parts.


The Code stated that:

"Consideration should be given to the fire resistance of reinforced concrete

members to see that they provide the grade of fire resistance for the particular

occupancy and size of a building or compartment as laid down in the Code of

Functional Requirements, Chapter IV, Precaution against fire."

It considered the performance of two types of aggregate in fire, namely Class 1 (limestone,

brick and artificial aggregates such as foamed slag) and Class 2 (all natural aggregates

other than limestone). A table gave the thickness of walls and floors required for various

fire periods, as follows:

• Walls:

• Thickness ranging from 3 inches (75 mm) for a Vz hour period to 9 inches (230 mm)

for 6 hours with Class 2 aggregates.

• Thickness ranging from 3 inches (75 mm) for a Vfe hour period to 8 inches (200 mm)

for 6 hours with Class 1 aggregates.

• Solid slabs:

• Thickness ranging from 3Vz inches (90 mm) for a Vz hour period to 7 inches (180 mm)

for 6 hours (aggregate Class not specified).

• Hollow tile floors:

• Thickness of concrete slab ranging from 2V2 inches (65 mm) for a Vz hour period to

6 inches (150 mm) for 6 hours with Class 2 aggregates.

The only mention of the required cover to the reinforcement was for hollow tile floors,

where V2 inch (13 mm) was specified for Vz hours, % inch (19 mm) for 1 or 2 hours, and

1 inch (25 mm) for 4 hours. (Minimum covers for durability were specified elsewhere.)


The guidance for columns was less explicit, based on the adequacy of specified column

sizes, as follows:

• Small columns (10 to 12 inches across, 250 to 305 mm across):

• Class 2 aggregate 'satisfactory' for resistance of 1 hour.

• Class 1 aggregate 'desirable' for resistance of 2 hours.

• Larger columns:

• Any aggregate may be used to obtain resistance of 2 hours.

• Class 1 aggregate (or a mesh placed centrally in the cover) can be used to obtain a

resistance of 4 hours.


The main body of the Code states that:

"Statutory requirements for fire resistance of buildings, expressed in terms of

periods of fire resistance of various elements of structure, when tested in

accordance with BS 476, Fire tests on building materials and structures, as laid

down in the London building by-laws and in the building by-laws of those

local authorities who have adopted one of the models issued by the Ministry

of Housing and Local Government or the Department of Health for Scotland."

An appendix gives tables of fire resistance for various types of elements (similar to those for

Class 2 aggregates in CP 114:1948), with the addition of the specification of the minimum

cover to the reinforcement for all members. The tables may be summarised as follows:

• Walls:

• Minimum cover 1 inch (25 mm).

• Minimum thickness ranging from 3 inches (75 mm) for a Vz hour period to 9 inches

(230 mm) for 6 hours.

a Floors:

• Minimum thickness ranging from 2Vz inches (65 mm) or 3Vi inches (90 mm),

depending of the form of construction, fora Vz hour period to 5 inches or 6 inches

for 4 hours.

• Minimum cover Vz inch (13 mm) for periods less than 2 hours and 1 inch (25 mm)

for 4 hours.

• Columns:

• Minimum thickness ranging from 6 inches (150 mm) for a Vz hour period to 18 inches

(460 mm) for 6 hours (with the provision for the thicknesses for 4 hours and 2 hours

to be reduced if mesh is placed in the cover).

• Beams:

• Minimum cover ranging from Vz inch (13 mm) for a Vz hour period to 2Vi inches

(65 mm) for 4 hours.

It was noted that the values were conservative when limestone was used for the coarse

aggregate, and reduced values for the minimum column were suggested.


Design 5

London Building (Constructional) By-laws, 1964

Schedule VI of the By-laws gives minimum thicknesses for walls, stairs, columns and beams

for periods ranging from 1 hour to 4 hours, with provision for reduced thicknesses when

elements are covered with plaster. Also given are minimum covers to the reinforcement,

which, confusingly, are stated as being to the main reinforcement in some tables and

simply 'cover to reinforcement' elsewhere.


The Code suggested that the fire resistance of precast elements should be determined in

accordance with Part 1 of BS 476, Fire tests on building materials and structures. In the

absence of results from actual fire test, the notional fire resistance could be obtained from

tables of covers and minimum dimensions, which were very similar to those in CP 114:1957

The Code also gave information on the additional protection provided by different types

of plaster.


The guidance in CP 110 was significantly more detailed than that in CP 114, although many of

the dimensions were similar. Additional information on the behaviour of concrete elements

in fire was given in the Handbook'16'. Covers were defined as average values rather than

minimum values, considering only the tension reinforcement. The contents of the various

tables can be summarised as follows:

• Beams:

• For siliceous aggregates, average cover from 15 mm fora Vz hour period to 65 mm

for 4 hours, with minimum thickness of 80 mm and 280 mm respectively.

• For lightweight aggregates, average cover from 15 mm for a Vz hour period to 50 mm

for 4 hours, with minimum thicknesses of 80 mm and 250 mm respectively.

• Floors (both reinforced and prestressed):

• A range of average covers and overall dimensions depending on the form of

construction (e.g. solid slab, cored slab, hollow box, ribbed floor with hollow infill

blocks, inverted channels).

• Columns (without additional protection):

• For siliceous aggregates, minimum thickness ranging from 150 mm for Vz hour

period to 450 mm for 4 hours with all faces exposed, and 75 mm to 180 mm with

only one face exposed.

• For limestone aggregate or lightweight aggregate, minimum thickness ranging from

150 mm for Vz hour period to 300 mm for 4 hours with all faces exposed.

• Walls (with at least 1% of vertical reinforcement, exposed on one side only):

• For siliceous aggregates, minimum thickness ranging from 75 mm for Vz hour

period to 180 mm for 4 hours.

Additional information was given regarding the effects of protective layers, such as plaster.

55



The basic approach to the design for fire resistance in BS 8110:1985 differed from that in

CP 110:1972 in various respects. Nominal covers were specified to all reinforcement

including links rather than the average cover to the tensile reinforcement. The differing

behaviour of various types of natural aggregates was combined into 'dense' concrete,

although lightweight concrete was still included. Nominal covers for various elements

(for dense concrete) were given in Part 1, Code of practice for design and construction, as

follows:

• Beams:

• Simply supported: 20 mm for a 0.5 hour period to 70 mm for 4 hours.

• Continuous: 20 mm for a 0.5 hour period to 50 mm for 4 hours.

• Floors:



• Ribs:



• Columns:


Part 1 also gave minimum dimensions for members for fire resistances from 0.5 to 4 hours.

Section 4 of Part 2, Code of practice for special circumstances, gave significantly more

details on designing for fire resistance and included curves of the variation of concrete and

steel strengths with temperature. It should be noted that in Part 2, 'cover' was defined as

being to the main reinforcement rather than to all reinforcement as in Parti.

5.7 Bond and anchorage As with other aspects of design, the checks for the bond between the reinforcement and

the concrete have moved from permissible stresses underworking loads in the early Codes

to ultimate limit state design in more modern Codes.

5.7.1 Buildings Code of Practice for reinforced concrete, 1934

Permissible bond stresses were given for Ordinary Grade concrete (see Section 4.3.1), as

follows:

123 psi (0.85 N/mm2)

118 psi (0.81 N/mm2)

110 psi (0.76 N/mm2)

100 psi (0.69 N/mm2)

Mix IMix II

Mix III

Mix IV

1:1:21:1.2:2.4

1:1.5:3

1:2:4


and for High Grade concrete as follows:

Mix

Mix

Mix

Mix

1II

III

IV

11

1

1

:1:2:1.2:

:1.5:

:2:4

2.4

3

150 psi (1.04 N/mm2)

145 psi (1.00 N/mm2)

135 psi (0.93 N/mm2)

120 psi (0.83 N/mm2)

The permissible bond stress for Special Grade concrete was one-thirtieth of the 28-day

cube strength plus 25 psi (the same proportion as for the other Grades) but not more

than 150 psi (1.04 N/mm2).

The local bond stress, sh, was determined from:

sb = S/ao

where

5 = total shear across the section

a = lever arm

o = sum of the perimeters of the tensile reinforcement.

sb was limited to twice the permissible bond stress.

The required anchorage lengths (using smooth reinforcing bars) were determined considering

the actual tension in the bar and assuming a uniform bond stress along the anchorage

not exceeding the permissible value.


The permissible bond stress for the six mixes, specified on the basis of weight of cement (Ib):

fine aggregate (cu. ft):coarse aggregate (cu. ft), was as follows:

123 psi (0.83 N/mm2)

110 psi (0.76 N/mm2)

100 psi (0.69 N/mm2)

150 psi (1.04 N/mm2)

135 psi (0.93 N/mm2)

120 psi (0.83 N/mm2)

This information is also given in Reinforced concrete simply explained^.


The same approach was adopted as in the 1934 Code, except that the permissible average

bond stresses (i.e. anchorage bond stresses) and local bond stresses were stated for each

of the nominal mixes as follows:

• Mix• Mix

• Mix

• Mix

• Mix

• Mix

III

III

IA

IIA

IIIA

112:1V4:21/2112:17s:33/4

112:272:5

112:1V4:21/2

112:178:33/4

112:272:5

1:1:2

1:172:3

1:2:4

Average 150 psi (1.04 N/mm2)



Local 220 psi (1.52 N/mm2)





The Code used the same approach and the same permissible stresses as in CP 114:1948.


The By-laws gave permissible bond stresses (for both average and local bond), as follows:

Average bond

Grade I 116 psi (0.80 N/mm2)

Grade II 102 psi (0.70 N/mm2)

Grade III 90 psi (0.62 N/mm2)

Grade IA 150 psi (1.04 N/mm2)

Grade IIA 135 psi (0.93 N/mm2)

Grade IIIA 120 psi (0.83 N/mm2)

Local bond

175 psi (1.21 N/mm2)

153 psi (1.06 N/mm2)

135 psi (0.93 N/mm2)

220 psi (1.52 N/mm2)

200 psi (1.38 N/mm2)

180 psi (1.24 N/mm2)


The Code used a similar approach to that in CP 114:1957 (although the notation was changed)

but the local and anchorage bond stresses were now at the ultimate limit state. Values

were now given for both plain and deformed bars for concrete grades 20, 25, 30 and >40.

Two types of deformed bar were identified in an appendix to the Code, namely Type 1,

twisted bar, and Type 2, ribbed bar, with bond stresses being increased by 30% forType 2.


Anchorage bond stress, fbu, was determined from:

with tabulated values of the coefficient /? that depended on the type of bar and the

direction of loading. There would appear to be no limit applied to/cu in the equation, but

the table of anchorage bond lengths as multiples of bar size only gave values for concrete

strengths 25, 30, 35 and 40.

There was no longer a specific check for local bond stresses.

5.7.2 Bridges The treatment of bond in the design of bridges was similar to that for buildings.


(reprinted 1949)

The permissible bond stresses in bending were given for three concrete mixes, specified on

the basis of weight of cement (lb):fine aggregate (cu. ft):coarse aggregate (cu. ft), as follows:

• MixA 150:2:4 145 psi (1.00 N/mm2)

• Mix B 120:2:4 135 psi (0.93 N/mm2)

• MixC 90:2:4 120 psi (0.83 N/mm2)

Unlike later highway guidance, the Memorandum did not distinguish between average

and local bond stresses.




The permissible bond stresses were again given for three concrete mixes, specified on the

basis of weight of cement (lb):fine aggregate (cu. ft):coarse aggregate (cu. ft), with the

same values for average bond as in Memorandum 557, but with the addition of local bond

stresses, as follows:

Mix A

MixB

MixC

150:2

120:2

90:2:-

:4

:4

A

Average bond

145 psi (1.00 N/mm2)

135 psi (0.93 N/mm2)

120 psi (0.83 N/mm2)

Local bond

210 psi (1.45

200 psi (1.38

180 psi (1.24

N/mm2)

N/mm2)

N/mm2)

These values could be increased by 25% when cold-twisted or deformed bars were used.



1968

The Memorandum gave average and local permissible bond stresses for plain bars under

HA loading for two classes of concrete as follows:

Class 4500

Class 3000

Average bond

150 psi (1.04 N/mm2)

120 psi (0.83 N/mm2)

Local bond

220 psi (1.52 N/mm2)

180 psi (1.24 N/mm2)

For deformed bars, the permissible stresses were increased by 40%. When Class 6000

concrete was used, bond stresses were limited to those for Class 4500. A 25% overstress

was permitted under HB loading.

BE 10, Reinforced concrete for highway structures, 1968

The permissible bond stresses for plain bars under HA loading were similar to those in

577/2 but rationalised slightly as follows:

Class 30

Class 22.5

Average bond1.00 N/mm2

0.85 N/mm2

Local bond1.47 N/mm2

1.27 N/mm2

For deformed bars, the permissible stresses were again increased by 40%. When Class 37.5

concrete was used, bond stresses were limited to those for Class 30. A 25% overstress was

permitted under HB loading.


The average and local permissible bond stresses were the same as in BE 10, but various

overstresses were permitted under different loading combinations.




(Note that BS 5400 Part 4:1978 was not implemented by the HighwaysAgency until the

publication of BD17/83.)

Ultimate local and anchorage bond stresses were given for both plain and deformed bars for

concrete grades 20, 25, 30 and >40. The stresses were the same as those in CP 110:1972,

with values given for different types of deformed bars, namely Type 1 (twisted) and Type 2

(ribbed).


1979

The bond stresses were the same as in BE 10 and in BE 1/73:1973, except that the 40%

increase for deformed bars was modified to 25% forType 1 deformed bars and by 40%

for Type 2 deformed bars.


The ultimate local and anchorage bond stresses were unaltered from those in BS 5400:1978.



The ultimate local and anchorage bond stresses were the same as in BS 5400:1978.



amendments.

5 . 8 S e r v i c e a b i l i t y Because spans were relatively limited, early codes were mainly concerned with strength

rather than serviceability. Guidance on span/depth ratios was introduced in 1957 and

methods for calculating crack widths in 1972.

5.8.1 Buildings 1934: Code of Practice for reinforced concrete

The Code gave no guidance on serviceability, presumably because spans were relatively

short and hence deflections and cracking were not likely to be a problem.


The Code noted that:

"Reinforced concrete subject to bending action in a building should possess

adequate stiffness to prevent such deflection or deformation as might impair

the strength or efficiency of the structure, or produce cracks in finishes or in

superimposed partitions, etc."

However it gave no guidance as to how this was to be achieved.



The Code gave the same general guidance but introduced maximum span/depth ratios

for beams and slabs, based on the overall depth. For beams the ratios were:

Simply supported

Continuous

Cantilever

20

25

10

The Handbook'14' pointed out that the values were based on experience with stress of

18,000 psi (125 N/mm2) in the reinforcement. Higher stresses were permitted by the

Code and hence the Handbook suggested that the ratios should be reduced, although it

did not give any further guidance.

There would appear to be no specific mention of the control of cracking in the Code.

However, there was a requirement for a minimum amount of reinforcement in solid

slabs, namely 0.15% of the gross cross-sectional area of the concrete in both directions.

In addition, the spacing of the main reinforcement was not to exceed three times the

effective depth of the slab and spacing of the distribution reinforcement was not to

exceed five times the effective depth.

London Building (Constructional) By-laws, 1964

The by-laws used the same span/depth ratios (based on overall member depth) as CP 114:

1957.


The Code indicated that deflections should be limited to span/250 to avoid damage to

partitions, etc. Span/depth ratios, now based on the effective depth rather than the overall

depth, for beam spans less than 10 m were limited to:

Simply supported

Continuous

Cantilever

20

26

7

An additional table gave span/depth ratios for simply supported and continuous beams

for spans between 10 m and 20 m. Further clauses and tables gave modification factors

to account for the amount of tension and compression reinforcement present.

CP 110:1972 would appear to be the first Code to mention cracking in reinforced and

prestressed concrete, saying that:

"Cracking of concrete should not adversely affect the appearance or durability

of the structure."


It suggested the following as 'reasonable' limits:

• Reinforced concrete

• 0.3 mm or 0.004 times the cover to the main reinforcement for structures in 'very

severe' environments.

• Prestressed concrete

• Class 1 - No tensile stresses

• Class 2 -Tensile stresses but no visible cracking

• Class 3 - 0.1 mm in 'very severe' environments and 0.2 mm elsewhere.

Minimum areas of main reinforcement were specified for beams and slabs, 0.15% £>tdwhen

using high-yield reinforcement and 0.25% btd when using mild steel reinforcement where

btwasthe breadth of the section and dthe effective depth. Minimum areas of secondary

reinforcement were 0.12% btd and 0.15% btd respectively.

The Code suggested that the detailing rules would generally be control flexural cracks but

that advantage might be gained by calculating crack widths in accordance with the

following expression, given in Appendix A:

3 a c r £ m

1 + 2h-x

where

min

h =

X =

distance between point considered and the surface of the nearest longitudinal bar

average strain at the level at which cracking is considered

minimum cover

overall depth of the member

depth of the neutral axis.


The guidance was somewhat more detailed than in CP 110:1972. The total deflection was

still limited to span/250 but the deflection occurring after the construction of finishes and

partitions was limited to span/500 or 20 mm, whichever was the lesser. The span/effective

depth ratios for beams up to 10 m span were the same as in CP 110:1972. Modification

factors were again given for the effects of tension and compression reinforcement.

A specific limiting crack width for reinforced concrete was not given in Parti, Code of

practice for design and construction, which simply said that:

"Cracking should be kept within reasonable bounds by attention to detail. It

will normally be controlled by adherence to the detailing rules."


The guidance on the requirements for minimum reinforcement percentages were more

detailed than in CP 110, covering both sections mainly in tension and sections in flexure. For

the latter, percentages were given for both flanged beams and for rectangular solid sections.

Guidance on the calculation of crack width, if required, was given in Part 2, Code of practice

for special circumstances, using the same expression as in CP 110:1972.

5.82 Bridges Limiting crack widths for bridges were introduced in 1968, somewhat earlier than for

buildings, presumably reflecting the fact that bridges are more exposed to the environment.


(reprinted 1949)

The Memorandum gave no guidance on serviceability matters, such as limiting crack widths.


Crack widths (excluding under HB loading and 112 kN HA loading) were limited to 0.25 mm,

with the crack width being taken as:

3.3c£a where the reinforcement perpendicular to the crack was deformed bars

3.8c£a where the reinforcement perpendicular to the crack was smooth bars

where

c = distance from the point being considered to the nearest bar running perpendicular

to the crack or the distance to the neutral axis, whichever is the lesser

£a = apparent tensile strain in the concrete at the point under consideration.


The approach for determining the crack width was the same as in BE 10, but a crack width

of 0.30 mm was now given for HB loading, the two 112 kN wheel loads or accidental

loading.





Unlike the general guidance given in the earlier BE documents, the design crack widths

were given for three exposure conditions, as follows:

Moderate

Severe

Very severe

0.25 mm

0.20 mm

0.10 mm


The design surface crack width for beams was:

where

acr = distance from the point considered to the nearest longitudinal bar

e, = average strain at the level where cracking is being considered, ignoring tension

stiffening.

For the flanges in beam and slab construction and top flanges in rectangular voided slab or

box-beam construction the surface crack width was determined from the same expression

as in CP 110:1972, namely:

1 + 2h-x

where

£m = average strain at the level at which cracking is considered allowing for the effect

of tension stiffening, which was given by a separate equation

cmjn = minimum cover

h = overall depth of the member

x = depth of the neutral axis.


1979

The permissible crack widths were amended slightly from those in the 1973 version.


The design crackwidths were the same as in BS 5400:1978, with the addition of 0.10 mm

for the 'extreme' condition.

The crack width for solid rectangular sections was now calculated in accordance with the

BS 5400:1978 expression for flanges, modified slightly to:

1 + 2h-x I

wherecnom = recluired nominal cover to the tensile reinforcement, or the actual cover if greater.

The equation for determining em differed from that in BS 5400:1978.


For other sections, such as flanges in beam and slab construction, the crack width was

calculated from the expression:

where

£, = average strain at the level where cracking is being considered, ignoring tension

stiffening.



The amendments given in BD 17/83 were generally incorporated in BS 5400:1984.

Design crack width for 'very severe' exposure was relaxed slightly, so the widths for the

four exposure conditions were as follows:

ExtremeVery severe

Severe

Moderate

0.10 mm0.15 mm

0.25 mm

0.25 mm

The expressions for the surface crack widths were the same as in BD 17/83 except that

the notation was changed slightly and the application of 3acr£m being clarified as being

"for flanges in overall tension".



amendments. It emphasised that:

"The clauses of BS 5400: Part 4 that are expressed in the form of recommenda-

tions using the word 'should' are to be considered as mandatory."



The requirements were the same as in the 1984 version.

5.9 Robustness The progressive collapse of the Ronan Point multi-storey flats in 1968 following a gas

explosion led to the publication of Ministry of Housing and Local Government Circulars

62/68 and 71/68, requiring the appraisal of all blocks over six storeys in height built of

large precast concrete panels, and to the introduction of minimum requirements for

robustness in buildings of five or more storeys, given in an Amendment to the Building

Regulations in 1970 and an Addendum to the Code for precast concrete.


Addendum No. 1 to CP 116:1965 and CP 116: Part 2:1969, Large-panel structures

and structural connections in precast concrete, 1970

This addendum to CP 116, The structural use of precast concrete, was the first to specifically

consider accidental loads and to include a requirement to avoid disproportionate collapse.

Serious damage should not involve more than three storeys or more than 70 m2 or 15%,

whichever was the lesser, of any affected storey, following removal of any one element of

the structure. Alternatively the structure should be able to resist a load of 34 kN/m2 (5 psi)

applied simultaneously with the appropriate combination of dead, applied and wind loads.

(Clearly 5 psi was selected by the drafting committee as being the critical pressure, which

was then converted to 34 kN/m2; it might have been more logical to 'round' the metric

pressure to 35 kN/m2.)

Specific robustness requirements included:

• horizontal connections between load-bearing walls and floors or roof equal to 25 kN/m

length of joint at the top of the wall and 12.5 kN/m at the bottom

• a peripheral tie at each floor and roof level capable of resisting a force of 40 kN,

without exceeding the permissible stress in the steel

• internal ties at each floor and roof level capable of carrying 25 kN/m in the direction

of the span and 12.5 kN/m transverse.

The Addendum also gave guidance on the effects of misalignment and lack of plumb,

suggesting an allowance of (12Vn)mm, where n was the number of storeys, or an eccentricity

of 20 mm across a joint.

CP 110, Code of practice for the structural use of concrete, 1972

The Code spelled out the requirements in more detail, now in limit state terms rather

than on the basis of permissible stresses. For all buildings of five or more storeys, the

following were required:

• A peripheral tie to be provided at each floor and roof level to carry a force of Ft.

• Internal ties to be provided at each floor level per metre to carry {Ft{gk + qk)/7.5}{l/5}

but not less than Ft.

• External columns and walls to be tied horizontally into the structure at each floor level

and comer columns to be tied in two directions at right angles, with a tie capable of

carrying the lesser of 2Ft and (/0/2.5)Ft, but not less than 3% of the total ultimate

vertical load at the floor level considered.

where

Ft = the lesser of (20 + 4ns) or 60, kN

ns = number of storeys

(gk + qk) = sum of average characteristic dead and imposed floor loads in kN/m2

/ = span of the tie in the direction considered, but not exceeding five times the

clear storey height

/0 = floor to ceiling height in metres.


Design 5

Amendments to CP 110 in 1976 extended the requirement for internal ties and external

ties to "each floor and roof level". The requirements for stability were strengthened by the

statement that:

"The engineer responsible for the overall stability of the structure should

ensure the compatibility of the design and details of parts and components.

There should be no doubt of this responsibility for overall stability when all or

some of the design and details are not made by the engineer."


The Code contained the same provisions as in CP 110:1972, although there had been

editorial changes. BS 8110:1985 introduced the concept of 'key elements' defined as

elements whose failure:

"would cause the collapse of more than a limited portion close to the element

in question".

Guidance on the design of such elements, which were required to carry an accidental

load of 34 kN/m2 in any direction, was contained in Part 2 of BS 8110. In addition there

was the requirement:

"that any vertical load-bearing element other than a key element can be

removed without causing the collapse of more than a limited portion close to

the element in question".

A later Amendment to BS 8110 extended the requirements to all buildings rather than to

those of five or more storeys.

5.10 Analysis The Handbooks to CP 110 and BS 8110'16;18' give background information on the method

of simplified frame analysis adopted by the Codes.

5.10.1 Frame analysis 1934: Code of Practice for reinforced concrete

The Code considered two loading cases:

• alternate spans loaded and all other spans unloaded

• adjacent spans loaded and all other spans unloaded.


The Code suggested that the maximum span moments could be increased by not more

than 15% provided that the support moment was reduced by the same amount.

The loading patterns were basically unaltered with the publication of successive Codes.


With the introduction of limit state design, the wording was amended although the

approach was unaltered. The two loading cases became:

• alternate spans loaded with total ultimate load (1.4Ck +1.6Qk) and all other spans

loaded with minimum dead load (1.0CJ

• any two adjacent spans loaded with total ultimate load (1.4Gk + 1.6Qk) and all other

spans loaded with minimum dead load (1.0Ck)

where

Gk = characteristic dead load

Qk= characteristic live load.

Obviously, the introduction of partial safety factors slightly altered the balance between

the assumed loading on loaded and unloaded spans.

5.10.2 Slabs Code of Practice for reinforced concrete, 1934

The Code gave guidance on the moments on slabs, either simply supported or fixed/

continuous on four sides. The Handbook'13' expanded the guidance in the Code considerably

for various types of loading. The Code also gave guidance on the design of flat slabs of

uniform thickness, with or without drops, with approximately equal panels. It introduced

the concept of a middle strip and a column strip and gave coefficients for the positive and

negative design moments. Guidance was given on the provision of reinforcement for both

two-way reinforcement (bars running parallel to the grid lines) and four-way reinforcement

(bars parallel to the grid lines but also on the diagonal between columns).

CP 114, The structural use of normal reinforced concrete in buildings, 1948

The Code gave the same coefficients for slabs simply supported on four sides but extended

the guidance for restrained slabs. Elastic behaviour was assumed.

CP 114.102, Floors and roofs of flat slab construction, 1950

The sub-Code extended the approach given in CP 114:1948 and gave specific guidance

on the design of flat slabs, including the division of panels into middle strips and columns

strips, the associated bending moments and the detailing of reinforcement.


The Code gave similar bending moment coefficients for slabs simply supported on four sides

(although expressed slightly differently), based on elastic analysis. As an alternative approach,

load-factor design could be used, with the moments determined from Johansen's yield-line

theory or other acceptable methods. The Code included guidance on the design of flat slabs.



The 1969 version of CP 114 gave the same guidance for the design of slabs as the earlier

version. However, an Amendment in March 1976 deleted the clauses covering flat slabs,

stating that they should be designed in accordance with CP 110 (which had been

published in 1972).


The moment coefficients were the same as inCP 114:1957. The Code indicated that:

"Moments and shear forces resulting from both distributed and concentrated

loads may be determined by elastic analysis such as that by Pigeaud or Wester-

gaard. Alternatively, Johansen's yield-line of Hillerborg's strip method may be

used provided the ratio between support and span moments are similar to

those obtained by the use of elastic theory; values between 1.0 and 1.5 are

recommended."

In the 1960/70s, flat slabs were frequently designed by yield line methods and as a con-

sequence the reinforcement layout may not have been in accordance with the classical

layout of bars, i.e. column and middle strips. With yield line the reinforcement tended to

be concentrated in patches over the columns. To maintain the overall compatibility with

wP/8 the span reinforcement tended to be larger than current elastic layouts which had a

secondary benefit of improving deflection control.


The guidance was the same as in CP 110:1972, with the addition of a table of shear force

coefficients for rectangular panels supported on four sides.


6. Guidance relating to specific types ofstructures

While the design Codes and Standards are applicable to the majority of structures and

structural elements, additional guidance is required for some applications, as outlined in

this Chapter.

6.1 Precast systems The first British Standard Code of Practice covering the structural use of precast concrete

in general, CP116, was published in 1965. (Prior to that time guidance on standard precast

beams for bridges had been prepared by the Cement and Concrete Association, see later.)

The Code covered the design of both reinforced and prestressed units and included aspects

such as connections and workmanship.

6.1.1 Concrete frames There have been various attempts to develop 'standard' precast concrete frames for

industrial and commercial use. Various systems in the UK, Europe, Scandinavia and the

USA have been described by Diamant(52'.The Comprehensive Industrialised Building Systems

Annual 1970 compiled by Deeson*53' gives brief details of concrete, steel and timber systems

for the construction of all types of structures, from tower block, industrial buildings and

schools to houses and bus shelters. (For further information on system-built houses see

Section 6.1.5, Non-traditional houses, below.)

The Public Building Frame, developed by the Ministry of Public Building and Works in 1966,

consisted of basic precast column, beam, slab and wall units, with a range of standardised

cross-sections, as outlined in a report by Creasy'54'. The system was based on a one-foot

(305 mm) module vertically, with column spacing based on a module of two or three feet

(610 or 915 mm). The standard columns were single storey with a dowel connection. Various

precast units were used to form the floor, all with a two-inch (50 mm)-thick structural

screed. Creasy's report contains indicative design curves linking floor loading and spans.

The National Building Frame was used for the construction of low-, medium- and high-

rise buildings such as schools and factories. Some typical details of the system are given

by Elliott<55>.

The Intergrid system was developed in conjunction with the Ministry of Education as part

of the programme to aid the school building programme. It is understood that components

were manufactured by at least 18 companies and were used in over 200 buildings. Intergrid

was a horizontal two-way prestressed grid using standard precast components. The first


Guidance relating to specific types of structures

generally available system was the Mark II, which was first produced in 1954, later super-

seded by Marks III, IV and V over the next 23 years. In the Mark II, the floor and roof beam

components consisted of precast lattice units 40 inches (1015 mm) long and 16 inches

(405 mm) deep. These units were assembled into beams and prestressed together, with

tendons running externally that were covered with mortar after stressing. Secondary beams

of the same depth were placed transversely between the primary beams and stressed

together to form the complete grid. Details are given in the BRE report The structural

condition ofIntergridbuildings of prestressed concrete^. The Mark III, introduced in 1959,

used monolithic units (or segmental units with internal steel ducts) for the main beams

to form the grid. In the Mark IV, introduced in 1964, the secondary beams were bolted to

the main beams, to reduce the amount of prestressing on site. The system was further

modified in 1966 (Mark IV L) and 1968 (Mark IV*) and a metric version with a 1800 mm

module was introduced in 1972. It is not clear when production of the system ceased.

The CLASP (Consortium of Local Authorities Special Programme) system was first developed

in the late 1950s by local authorities who needed to build school buildings as quickly and

cheaply as possible. Initially intended for use in areas subject to mining subsidence, the

system was based on a light steel frame with concrete floors and precast concrete cladding

panels'57'.

Attempts were made in the mid-1970s to develop a standard system for the construction

of hospitals, known as the Harness system'58'59). While a full-scale demonstration building

was constructed, the system was not widely used.

Beam-column connections

Various approaches have been adopted for the connections between precast concrete

beams and columns. Elliott'55' suggests that the number of different solutions in the 1960s

and 1970s was as great as the number of precast frame manufacturers, about 20 at the

time. Some (such as Trent around 1975) used a system of bolted cleats, while FC Precast

used billeted connections up to the mid-1970s. Dow Mac used billets from 1980 onwards.

6.1.2 Precast floor and roof

unitsMany different types of precast flooring units have been produced; Appendix A lists some

of the systems that were produced in the 1960s. Structural precast concrete by Glover'44'

and the BCSA publication, Prefabricated floors for use in steel framed buildings^ give details

of a range of precast concrete floor systems, giving the relevant dimensions, the weights

of the structural units, the load capacity per unit width and limiting spans for the loading

Standard (CP 3 Chapter V) current at the time, etc.

Wood-wool slabs

In the past, wood-wool was used extensively as permanent formwork. For example, in the

Neolith and Marlith systems wood-wool panels covered the tops of the precast trough units,

supporting the in-situ concrete. In the Spanform system, the concrete of the in-situ topping

also flowed into the voids between the wood-wool 'beam' units to form a ribbed slab.


In 1975 the Wood Wool Manufacturers Association investigated the compaction of concrete

in wood-wool formers'61'62'. The reports concluded that, with care, good compaction of

reinforced concrete ribs could be achieved. However, CIRIA Report C558 Permanent

formworkin construction^ noted that, in practice:

"Problems occurred due to the high energy absorption of the material reducing

the effectiveness of vibration, resulting in poor compaction, exacerbated in

the case of low workability concrete."

Poor compaction would tend to lead to poor durability. This was particularly so with

systems such as Spanform where it was necessary to achieve good compaction around

the reinforcing bars at the bottom of the ribs.

Reinforced autoclaved aerated concreteReinforced autoclaved aerated concrete planks (mainly under the trade names Siporex and

Durox) were used for roof slabs for a number of years. After some time in service, there was

a tendency for such planks to develop cracks on the soffit and to exhibit excessive and

progressive deflections. The large deflections could lead to ponding on the roof and damage

to the waterproof membrane, leading to water penetration. The problems in 20-year-old

units have been reviewed by BRE, see for example IP 10/96'64' and BR 445'65'. Laboratory

tests carried out on defective planks showed that they still had adequate load capacity.

When originally constructed, the reinforcement was protected by a latex-cement coating

but this had broken down, leading to localised corrosion of the reinforcement. The BRE

reports concluded that the residual service life of the units would be heavily dependent

on their moisture content.

Design guidance for autoclaved aerated concrete was given in CP 110:1972. Similarly,

guidance was given in Part 2 of BS 8110 when it was first published in 1985, but the

complete section was subsequently deleted, presumably following the in-service problems

outlined above.

Precast shellsStructural precast concrete by Glover'44' gives details of Omega precast hyperbolic paraboloid

shell units, funicular shell units, long-span roof systems and north light shell roof systems.

6.1.3 Large panel systems Large panel systems were widely adopted in the early 1960s as a solution to the shortage

of housing. Various systems were developed in Continental Europe and the major British

contractors bought licences to manufacture them in the UK. Laings bought the Jespersen

system and developed it into the 12M. Taylor Woodrow bought the Larsen Neilsen system

and renamed it Taylor Woodrow Anglian. The collapse of the Ronan Point 22-storey tower

block in 1968 following a gas explosion led to a reappraisal of the systems by BRE and the

publication of a range of reports, some relating to specific systems such as the Taylor Woodrow

Anglian system (BRE Report 63<66') and some dealing with more generic issues. The work

led to the introduction of robustness requirements in Codes, see Section 5.9 above.



6.1.4 On-site construction There are several on-site construction systems that may be classed as 'precast' as the units

are cast in one position and then lifted into their final location. Probably the best known

was the Liftslab method, in which the floor slabs were cast on top of each other at ground

level and then jacked upon precast columns to their final location. The slabs were held in

position by wedges engaging into welded steel shear collars cast into the slab. After

installation the joints were grouted to give a moment connection. One drawback with

the system was that poor tolerances in setting the wedges supporting the slab at each

column could result in all the reaction being taken by one wedge, significantly increasing

the effective shear force.

A variation on the Liftslab system was the Jackblock system developed by Costain. Here the

top storey was constructed at ground level and then jacked up so that the top-but-one

storey could be constructed below it. The sequence was repeated until the building reached

its intended height.

6.1.5 Non-traditional houses The term 'non-traditional housing' may be used to describe all the various methods of

house building that have moved away from the traditional 'bricks and mortar'. As far as

concrete is concerned, many different systems have been developed over the years, using

combinations of precast and in-situ concrete. In some cases, many thousands of units

have been built. In other cases only a few prototypes were constructed. Some have been

successful (some examples have actually been statutorily 'listed' as being of architectural

or historic importance) while others have suffered from basic design faults.

BRE has carried out extensive investigations into the various housing systems and has

published Non-traditional houses: Identifying non-traditional houses in the UK 7978-75'12'.

This covers metal-framed and timber-framed houses as well as concrete. Some 450 housing

types are covered in detail, with brief information on a further 230. For each main type

there is an isometric drawing that provides a clear explanation of the construction details,

which will significantly help to diagnose problems and issues. Appendix B lists some of

the more common house types.

The publication comes with a CD ROM to help identify houses by type, local authority,

construction class, identifying characteristics or by any combination of these. It also

includes six Government reports on non-traditional housing.

6.1.6 Standard bridge beams Various standard precast prestressed concrete beams have been developed over the years.

Information on section properties, typical spans, etc. was published by the Cement and

Concrete Association'67^59'. The development of precast beams since the Second World War

has also been reviewed by Taylor'70', with aspects of the detailing of beams in the 1970s

being considered by Green'71'. Standard Tee beams for railway bridges were developed

initially for the Eastern Region and subsequently became a British Railways standard.


6.1.7 Bearings for precast

unitsThe guidance on bearings for precast concrete units has gradually developed with successive

Codes.

CP116, The structural use of precast concrete, 1965

CP116, the first Code for precast concrete, indicated that precast units should have a bearing

of at least 4 inches (102 mm) on masonry or brickwork supports and at least 3 inches

(76 mm) on steel or concrete. It suggested that these values might be reduced in special

circumstances but that consideration should be given to relevant factors such as tolerances

and the provision of continuity rods.


The Code gave the same guidance as in CP 116 (with the imperial dimensions changed to

metric equivalents, i.e. 100 mm and 75 mm respectively), with the additional requirement

that, when reduced bearings were used, the minimum anchorage length in the precast

unit should still be provided and precautions taken to avoid collapse due to accidental

displacement during erection.


The guidance in BS 8110 was considerably expanded from that in earlier codes, with the

required bearing area being determined from the applied load and the capacity of the

concrete, e.g. 0.4/cu for concrete on concrete. Allowances were made for construction

inaccuracies and the effects of spalling at the edges of both the support and the supported

member.

6.2 Foundations The history of the development of foundations and substructures has been reviewed by

Chrimes(72'.The early 19th century saw the first use of (lime) concrete as a foundation

material in Britain. Portland cement was used in concrete from around 1865, although

the material had been in use in mortars and renders from some years earlier. Hurst'21)

notes that while it was used for the footings of 'large and important buildings' from this

time, it was another 20 years or so before it was used more generally, and later still for

'domestic buildings'. For this latter category, strip footings were originally built of corbelled

brickwork. In the late 19th century a requirement was introduced to place a layer of

unreinforced lime concrete below the brickwork, and later mass concrete was used for the

entire footing. At this same time, mass concrete composed of Portland Cement started to

be used also for retaining walls, for example in the approach ramps for the Connaught

railway tunnel beneath the Royal Docks, completed in 1878.

The London Metropolitan Buildings Act of 1844 gives prescriptive wall thicknesses relating

to height and building use, with footing depths indicated. The London Building Act of 1894

provides similar prescription and also specifies the width of footing in relation to the wall

thickness. From these it is possible to infer bearing pressures that might approach 250 kN/m2

for the heavier loading classes. These values are probably higher than would be used today

for modern construction on London Clay, but slower rates of building and use of less brittle

mortars meant settlements would not have been such an issue at that time.



Chrimes notes that a 'plain concrete slab' was typically used towards the end of the 19th

century. This might be 150 mm where the wall footings were separate, but otherwise would

be at least 225 mm, with 300 mm being more usual. For heavy loads the raft would be

thicker, and in some cases iron rails were used as reinforcement, with steel beams as a

subsequent replacement.

Reinforced precast concrete piles were developed at the end of the 19th century and the

beginning of the 20th century; Chrimes illustrates various types, such as the Hennebique,

Considere and Coignet piles and the Mouchel hollow pile. He also reviews early forms of

in-situ piles. Prestressed precast piles were developed by Freyssinet in the 1930s. Bored

piles came into use after about 1930 and were only more generally used from the 1950s

onwards. Under-reams at the pile base to increase load-carrying capacity of single piles

followed soon afterwards. Embedded retaining walls were also developed in the 1950s

with the first diaphragm wall in the UK being installed in London in 1961.

The Third Edition of Reinforced Concrete Designers' Handbook^ published in 1946 gives

some coverage of precast piles with approaches for determining their load capacity. There

is little coverage of cast-in-situ piles with the author stating that "there are many different

patented systems". It is suggested that Mix III Ordinary Grade or Mix III High Grade in

accordance with the 1934 Code of Practice, i.e. 2550 psi (18 N/mm2) or 3300 psi (23 N/mm2),

would be suitable for precast piles.

The First Edition (1951) of the Specification for road and bridge works required a 28-day

strength of 5000 psi (35 N/mm2), which was significantly higher that the strengths

suggested by the Reinforced Concrete Designers' Handbook.

The Sixth Edition of the Reinforced Concrete Designers' Handbook (1961) gives slightly

different concrete strengths, 2450 psi (17 N/mm2) and 3600 psi (25 N/mm2), for precast

piles and indicates a cover of V/z inches (38 mm) for the main bars and 1 inch (25 mm)

for binders in accordance with CP 114. The same information is given in the Seventh

Edition (1971).

The Piling and diaphragm walling handbook^ provides an overview of the various techniques

used in the early 1970s but little in the way of design guidance. (This handbook was

published by Cementation Piling and Foundations, but is presumably representative of

industry practice.)

6.3 Water-retainingstructures

Early water-retaining structures have been described in a paper by Gould'74' and the

development of the various types of dam, with some consideration of the materials used,

by Bruggemann eta/(75).

75


Gould and Cleland(76) reviewed the development of reinforced concrete water towers.

They noted that reinforced concrete became common after about 1900 and discussed

various aspects of water tower development, including multi-legged designs, solid-sided

towers, shafts with fins and single stem towers. The paper included over 120 references,

many of them contemporary articles describing the design and construction of specific

water towers.

The Third Edition of Reinforced Concrete Designers' Handbook^ published in 1946 gave

some guidance on the design of water-retaining structures. It suggested that Mix III Ordinary

Grade or Mix III High Grade in accordance with the 1934 Code of Practice, i.e. 2550 psi

(18 N/mm2)or3300 psi (23 N/mm2), would be suitable. For circular tanks the tensile stress

in the concrete should be limited to 175 psi (1.2 N/mm2). For elements of rectangular

tanks in bending, the compressive stress should be limited to 880 psi (6.1 N/mm2) and

the tensile stress to 250 psi (1.7 N/mm2).



Published by the Institution of Civil Engineers, this was the first Code for the design of water-

retaining structures. The Introduction notes that the 1934 DSIR Code of practice for

reinforced concrete specifically excluded water-retaining structures and hence the

Institution had prepared the present document on the basis of industry best practice.

General guidance was given on the provision of joints and the selection of materials.

Design was in accordance with the DSIR Code but with certain limitations applied. As

indicated in Section 4.3.1 above, the ICE Code specified minimum concrete grades in

terms of weight of cement (lb):fine aggregate (cu. ft):coarse aggregate (cu. ft) as follows:

• 112:2:4 for general use

• 112:21/2:5 for slabs greater than 24 inches (610 mm) thick

To resist cracking, stresses were limited to 175 psi (1.2 N/mm2) in direct tension and 250 psi

(1.7 N/mm2) in bending and shear. The minimum cover was 1 inch (25 mm) or the bar

diameter for the stronger concrete and VA inches (32 mm) or the bar diameter for the

weaker concrete. Where the surface was exposed to water of a corrosive nature, the

minimum cover was increased to 2 inches (51 mm).

CP 2007: Design and construction of reinforced and prestressed concrete structures


The design approach in CP 2007 was based on that in CP 114 and CP 115, with some

modifications. The introduction to the Code noted the importance of reducing the

permeability of the concrete and controlling cracking. It said that:

"Cracking may result from excessive tensile stress in the concrete due to

applied loading, to temperature change, to drying shrinkage or to settlement

... acting either singly or in combination."


Guidance relating to specific types of structures 6

Other sections of the Code recommended the use of Portland cements with lower rates

of strength development giving lower rates of heat of hydration.

As indicated in Section 4.3.1, the Code recommended two nominal concrete mixes,

1:1.6:3.2 and 1:2:4, both with a 28-day strength of 3600 psi (25 N/mm2).To restrict

cracking, tensile stresses were limited as follows:

Mix 1:1.6:3.2

Mix 1:2:4

Direct tension

190 psi (1.31 N/mm2)

175 psi (1.21 N/mm2)

Bending

270 psi (1.86 N/mm2)

245 psi (1.69 N/mm2)

The Code noted that these stresses would also limit the tensile stresses in the reinforcement;

with an assumed modular ratio of 15, a tension of 190 psi (1.3 N/mm2) in the concrete

would limit the steel stress to 2850 psi (20 N/mm2).

The Code gave guidance on the provision of movement joints and gave details of various

types of watertight joint. General guidance was given on construction, for example limiting

the size of lifts for thick walls.

The Code suggested that no separate allowance was required for stresses due to shrinkage

or temperature change in the concrete provided that the stresses were limited, care was

taken in construction and adequate movement joints were provided. However, Concrete

Society Technical Report 22 (Third Edition), Non-structural cracks in concrete® notes that:

"Walls designed to CP 2007 were extremely likely to suffer unacceptable

cracks despite warnings given in the Forward of the Code."

BS 5337: Code of practice for the structural use of concrete for retaining aqueous

liquids, 1976

The revised Code was published in 1976 and the accompanying Handbook'17' was published

in 1979. Two different design approaches were given, either in line with CP 110 (i.e. limit

state design) or in line with CP 114 and CP 115 (i.e. permissible stress design as used in

CP 2007). When designing in accordance with CP 110, the Code specified that the bond

stresses for horizontal bars in sections in direct tension should not be greater than 0.7 times

the values given in CP 110. The Handbook explains the reason for this restriction,,saying:

"Horizontal bars which are in direct tension suffer from water-gain effects and

a lack of transverse shear; hence the values are reduced."


|dlp|G||€@pes of structures

The Code defined two exposure conditions for concrete exposed to water, as follows:

• Class A Exposed to moisture or subject to alternate wetting and drying

• Class B Exposed to continuous or almost continuous contact with liquid

with crack widths in reinforced concrete of 0.1 mm and 0.2 mm respectively. The

following expression was given for determining the surface crack width due to flexure:

4 -5I 3 f~

1 + 2 5 ' cr min

h-x

where

acr = distance between point considered and the surface of the nearest longitudinal bar

sm = average strain at the level at which cracking is consideredcmin = minimum coverh = overall depth of the member

x = depth of the neutral axis.

Alternatively, crack widths could be assumed to be satisfactory if the steel stresses were

limited as follows:

Class A

Class B

Plain bars85 N/mm2

115 N/mm2

Deformed bars100 N/mm2

130 N/mm2

When using the CP114/CP 115 approach, the concrete stresses were limited, as in CP 2007,

but they were related to two Grades of concrete and not to the exposure Class, as follows:

Grade 30

Grade 25

Direct tension1.44 N/mm2

1.31 N/mm2

Bending2.02 N/mm2

1.84 N/mm2

While the earlier code had identified the problem of early thermal stresses, it only gave

guidance on modifying the concrete and the construction process. BS 5337 introduced

the concept of a critical reinforcement ratio, pcrit, given by:

Peril = fa/fy

where

fa = direct tensile strength of the immature concrete taken as 1.15 N/mm2 for Grade 25

concrete and 1.3 N/mm2 for Grade 30 concrete

/ = characteristic strength of reinforcement but not exceeding 425 N/mm2.

When the amount of reinforcement exceeded the critical ratio, the likely maximum

spacing of cracks, smax, was given by:



where

(fa/fb) = ratio of the tensile strength of the concrete to the bond strength, taken as 1.0

for plain bars, Vs for deformed Type 1 bars and 2A for Type 2 bars

0 = diameter of the reinforcing bar

p = actual ratio of steel provided.

It was suggested that, under normal climatic conditions, the maximum crack width, wmax,

could be related to smax as follows:

where

a

r.= coefficient of thermal expansion of concrete

= fall in temperature between peak and ambient.

It was suggested that 7", should be taken as >30°C for concreting during the summer and

as >20°C for concreting during the winter, with both values increased for cement contents

above 340 kg/m3 and wall thicknesses above 400 mm. The Code also indicated that there

would be a further temperature fall, T2, due to seasonal variations, but gave no indication

what values should betaken. However, the Handbook suggests 20°C for casting in summer

and 10°C for winter.

An Amendment in June 1982 gave further information on the parameters on which the

values for 71 had been based. It suggested that lower values could be used with lower

ambient conditions, but should never be less than 20°C for walls and 15°C for slabs.

BS 8007: Code of practice for design of concrete structures for retaining aqueous

liquids, 1987

The design approach adopted by the Code was fully in accordance with BS 8110 and the

option for permissible stress design was finally dropped. The exposure conditions were the

same as in BS 8110, with a nominal cover of at least 40 mm and crack widths for 'very

severe' exposure conditions limited to 0.2 mm.

The approach to dealing with early thermal effects was the same as in BS 5337, but some-

what modified as follows:

• When determining pcrit, only one value for/ct was given, namely 1.6 N/mm2 for Grade

C35A concrete.

• For deformed bars, only Type 2 was considered with (fct/fb) given as 0.67.

• More detailed guidance was given for determining I, with values given for different

section thicknesses, formwork materials and cement contents. For further information

reference was made to CIRIA Report 91(77l Again, no guidance was given for the

seasonal drop in temperature, Tr

• The expression for calculating crack widths in flexure was modified to bring it into line

with BS 8110, namely:

1+2h-x

79


f l l l l

6.4 Houses: in-situconstruction

Between the 1930s and the late 1950s there were a large number of different systems for

constructing houses in situ. As with the precast systems covered earlier, the BRE has carried

out extensive investigations into the various systems, and has published information in

Non-traditional houses: Identifying non-traditional houses in the UK 7978-75'12'. See also

Section 6.1.5. Appendix B lists some of the more common types.

Some of the systems (e.g. those of George Wimpey and the Scottish Special Housing

Association) were constructed using no-fines concrete. This consists of a single-size coarse

aggregate coated in a cement slurry with no fine aggregate addition. Because it does not

contain any fine aggregate the fresh concrete cannot segregate and consequently it can be

dropped from a height. Formwork pressures are lower than for normal concrete so shutters

can be lighter and pour height lifts greater. BRE Report BR 191 entitled The renovation of

no-fines housing1?® records that around 450 000 housing units were constructed between

about 1945 and the early 1980s. No-fines concrete was used for the main load-bearing

structure in about 85% of the units. In the remainder it was simply used for infill panels.

The report concludes that the structural performance of most no-fines buildings was

satisfactory, although there were problems with condensation and water ingress in some

cases. In addition the open texture of the concrete causes problems if buildings are upgraded,

for example with the fixing of replacement windows.

6.5 Other structures Concrete is widely used in many types of structures other than those specifically covered

earlier in this report. Developments of its use in some types of structures have been

reviewed by various authors, as follows:

• Sharp'79' considered marine structures, from coastal protection schemes to oil and gas

production platforms.

• Information on the development of shell roof structures is given by Morice and

Tottenham'80' and by Anchor'81'. See Section 6.1.2 above for information on precast

concrete shells.

• Muir Wood'82' surveyed the use of cast-in-situ, precast and sprayed tunnel linings from

about 1880 to the present.

• The development of concrete roads from the 1860s to the present has been reviewed

by West'83'.

• Weiler'84' has reviewed the use of concrete in military applications from the early 19th

century to the Second World War.


General information on concrete deterioration 7

7. General information on concretedeterioration

Properties of concrete by Neville'85', which was first published in 1963, is one of the

definitive works of reference on concrete, giving information on a wide range of materials.

Lea's chemistry of cement and concrete^, which was first published in 1935, deals with

the chemical and physical properties of cements and concretes, including durability.

The Concrete Society website (www.concrete.org.uk) includes the information system

ConcreteatYourFingertips, which contains over 900 'nuggets' of information on a wide

range of concrete-related topics, some of which have been reproduced in this publication.

7.1 Alkali-silica reaction(ASR)

ASR is the most common form of alkali-aggregate reaction. It occurs when the alkaline

pore fluid and siliceous minerals in some aggregates react to form a calcium alkali silicate

gel. This gel absorbs water, producing a volume expansion which can disrupt the concrete.

The main external evidence for damage to concrete due to ASR is cracking. In unrestrained

concrete the cracks have a characteristic random distribution often referred to as 'map

cracking' where there is a network of fine cracks bounded by a few larger cracks. However,

the only reliable evidence for diagnosing ASR as the cause of damage is by microscopic

examination of the interior of concrete to identify positively the presence of the gel, of

aggregate particles which have reacted and the presence of internal cracking, characteristic

of that induced by ASR.

Guidance notes aimed at minimising the risk of alkali-silica reaction were first published by

the Cement and Concrete Association in1983'87' and Concrete Society Technical Report 30,

Alkali-silica reaction-minimising the risk of damage to concrete^ was published in 1987.

The introduction of specifications to limit alkali content and reactive aggregates in concrete

has meant that no confirmed incidence of ASR has been noted in the UK in structures

built since the mid-1980s.

A report by the Institution of Structural Engineers'89) considers the structural effects of ASR.

7.2 Sulfate attack Sulfates react with concrete, resulting in an expansive formation of ettringite or gypsum

in hardened concrete causing cracking and exfoliation. If there is a continuous supply of

sulfate, through movement of groundwater, the cracks will allow contact with more concrete

surface and the reaction can lead to a softening and further disintegration of the concrete.

A rare form of sulfate attack is through the formation of thaumasite as a result of the

reaction between calcium silicates in cement, calcium carbonate in limestone aggregates

and sulfates usually from an external source.


This reaction causes the concrete to soften and progressively disintegrate from the contact

surface. For this reaction to occur, the following conditions must apply:

• temperature below 15°C

• consistently high relative humidity

• supplies of calcium, sulfate and carbonate

• initial presence of reactive alumina (0.4-1.0%).

7.3 M u n d i c The equity value of many mainly pre-1950 houses in Devon and Cornwall has been

adversely affected by uncertainties in the nature of the concrete building material used in

their original construction. Mundic is a Cornish word used to describe a mineral of iron

containing sulfur, known as pyrite or iron pyrites. This mineral occurs frequently in the

lodes or veins of tin and copper mined for centuries throughout Cornwall and Devon. Vast

quantities of mine waste were extracted and dumped on the surface. During the early part

of the 20th century builders used this cheap and readily available source of aggregate for

the production of concrete blocks and concrete for construction. In the presence of moisture,

the pyrites chemically alters and expands causing concrete to deteriorate. In the 1950s,

Standards for aggregates used in concrete minimised this contamination. Whilst it is still

possible that some properties built after 1950 may be affected, the problem is more likely

to affect concrete properties built between 1900 and 1950.

7.4 Clinker concrete Clinker, the fused or sintered ashes remaining from the combustion of coal, was used as a

form of artificial aggregate in concrete for various applications such as jack arches and filler

joist slabs prior to about the 1930s. However, the use of clinker for reinforced concrete

applications was specifically prohibited by the structural Codes, such as the 1934 Code of

Practice for reinforced concrete. However, the Code did suggest that prohibited materials

could be used if tests showed that the requirements for strength and durability could be

achieved.

The Handbook to the 1934 Code'13' suggested that:

"Clinker, breeze or coke breeze concretes are unsuitable for use in contact

with any reinforcement or steel work. They are as a rule somewhat permeable

and ... together with the sulphur compounds contained usually result in

corrosion of any steel in contact with them."


Other sources of information 8

8. Other sources of information

Appendix 1 of Historic concrete - background to appraisal^ provides a comprehensive list

of sources of further information on historic concrete. Some of the key sources are listed

below.

Technical information on the original construction of the structure being investigated

may be available in articles in contemporary magazines and periodicals, such as:

• Civil Engineering and Public Works Review (1906-1989)

• CONCRETE (1966 onwards)

• Concrete and Constructional Engineering (1906-1966)

• Proceedings of the Institution of Civil Engineers (1837 onwards)

• Reinforced Concrete Review (1945-1961)

• Structural Concrete (1962-1966)

• The Builder (1843-1966)

• Transactions of the Concrete Institute (now The Institution of Structural Engineers)

(1909-1922)

• The Structural Engineer (1923 onwards)

It may be necessary to carry out a library search to obtain additional background information

relating to the structure or to the materials/systems used in its construction. The Concrete

Society's library contains more than 130,000 books, journal and magazine articles, standards,

conference proceedings, details of trade names, etc. dealing with all aspects of concrete

and its use in construction. Contact [email protected].

The libraries of the Institution of Civil Engineers ([email protected]), the Institution of

Structural Engineers ([email protected]) and the Royal Institute of British Architects

([email protected]) are obviously less specialised and hold publications on the complete

spectrum of construction materials. The ICE Library also administers an international e-

mail discussion group Civil Engineering Heritage Exchange (CEHX); contact mike.

[email protected].

The Consultants Tracker, developed by The Institution of Structural Engineers, is intended to

help trace a firm of civil and structural engineering consultants that has merged, been taken

over, closed down or changed its name. Co to www.istructe.org/library/consultanttracker.asp.

The Concrete Year Book$°\ published annually from 1924 onwards, gives guidance on

contemporary Standards, materials and design approaches. It also contains a useful list of

trade names and brands. Similarly Specification^, published by Architectural Press annually

since 1898, gives information on proprietary systems and materials, with specification

clauses and product information arranged by type of work and supported by indexes and

articles. It was a standard work of reference well into the 1960s and 1970s.


As indicated earlier, The Highways Agency maintains an archive of superseded bridge

standards. Enquiries should be addressed to [email protected]

(note the underscore).

Copies of withdrawn British Standards may be obtained through the BSl Knowledge Centre,

which holds a comprehensive collection of Standards going back to the 1900s. Each

amended version of a Standard is available, enabling developments to be traced. Copies

of Standards can be purchased either as PDFs or as hard copies. Enquiries should be

addressed to [email protected].

The National Archives in Kew (www.nationalarchives.gov.uk) hold some material relating

to the development of the railways in the UK.


References

References

1 INSTITUTION OF STRUCTURAL ENGINEERS. Appraisal of existing structures (Third Edition),

Institution of Structural Engineers, London, 2009.

2 CONCRETE BRIDGE DEVELOPMENT GROUP. Guidance on the assessment of concrete bridges,

Technical Guide No. 9, The Concrete Society (on behalf of the Concrete Bridge Development

Group), Camberley, 2007.

3 HIGHWAYS AGENCY. Design manual for roads and bridges, Highways Agency, London. Available at

http:/www.standardsforhighways.co.uk/dmrb/index.htm

4 NETWORK RAIL, NR/GN/CIV/025. Underbridgeassessment, Network Rail, 2006.

5 GOLD, CA and MARTI N, AT. Refurbishment of concrete buildings -structural and services options,

GN 8/99, Building Services Research and Information Association, Bracknell, 1999.

6 GOLD, C. Recycling concrete buildings for the 21st century, CONCRETE, Vol. 33, No. 7, July/August

1999, pp. 46-47.

7 CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION ASSOCIATION. Building with

reclaimed components and materials-A design handbook for reuse and recycling (Author Addis, B),

Report X332, CIRIA, London, 2006.

8 THE CONCRETE SOCIETY. Diagnosis of deterioration in concrete structures: Identification of defects,

evaluation and development of remedial action, Technical Report 54, The Concrete Society,

Camberley, 2000.

9 THE CONCRETE SOCIETY. Non-structural cracks in concrete, Technical Report 22 (Third Edition),

The Concrete Society, Camberley, 1992. (NOTE: This Report is currently being revised and updated.)

10 BRITISH STANDARDS INSTITUTION, BS EN 1504. Products and systems for the repair and protection

of concrete structures-Definitions, requirements, quality controland evaluation of conformity, Part 1:

Definitions, Part 2: Surface protection systems for concrete, Part 3: Structural and non-structural

repair, Part 4: Structural bonding, Part 5: Concrete injection, Part 6: Anchoring of reinforcing bars,

Part 7: Reinforcement corrosion protection, Part 8: Quality control and evaluation of conformity,

Part 9: General principles for the use of products and systems, Part 10: Site application of products

andsystems, and quality control of the works, BSI, London, various dates.

11 THE CONCRETE SOCIETY. Guide to the repair of concrete structures with reference to BS EN 1504,

Technical Report 69, The Concrete Society, Camberley, 2009.

12 HARRISON, H, MULLIN, S, REEVES, B and STEVENS, A. Non-traditional houses: Identifying non-

traditional houses in the UK 1918-75, BRE, Garston, Watford, 2004.

13 SCOTT, WL and GLANVILLE, WH. Explanatory handbook on the Code of Practice for reinforced

concrete as recommended by the Reinforced Concrete Structures Committee of the Building

Research Board, Concrete Publications Limited, London, 1934. (Second Edition published 1939.)

14 SCOTT, WL, GLANVILLE, W and THOMAS, FG. Explanatory handbook on the BSCode of Practice for

reinforced concrete, Concrete Publications Limited, London, 1950 (revised 1957, Second Edition 1965).

15 WALLEY, F and BATE, SCC. A guide to the BS Code of Practice for prestressed concrete, CP 115:1959,

Cement and Concrete Association (now Mineral Products Association -Cement), Camberley, 1961.

16 BATE, SCC eta/. Handbook to the Unified Code for structural concrete (CP 110:1972), Cement and

Concrete Association (now Mineral Products Association-Cement), Camberley, 1972.

17 ANCHOR, RD etal. Handbook on BS 5337:1976 (the structural use of concrete for retaining

aqueous liquids), Cement and Concrete Association (now Mineral Products Association - Cement),

Camberley, 1979 (Second Edition 1983).

18 ROWE, RE etal. Handbook to British Standard BS 8110:1985, Structural Use of Concrete, Palladian

Publications Limited, London, 1987.


19 REYNOLDS, CE. Reinforced Concrete Designers' Handbook (First Edition). Concrete Publications

Limited, London, 1932. Subsequent editions (the later ones co-authored with JC Steedman) were

published as follows: Second Edition 1939, Third Edition 1946, Fourth Edition 1948 (revised 1951

and 1954), Fifth Edition 1957, Sixth Edition 1961 (revised 1964), Seventh Edition 1971 (revised

1972), Eighth Edition 1974, Ninth Edition 1981, Tenth Edition 1988

20 THE CONCRETE SOCIETY. The use ofggbsandpfa in concrete, Technical Report 40, The Concrete

Society, Camberley, 1991.

21 HURST, BL. Concrete and the structural use of cements in England before 1890, Historic concrete-

background to appraisal (Sutherland, J, Humm, D and Chrimes, M, Eds), ThomasTelford, London,

2001, pp. 45-65. Also in Proceedings of the Institution of Civil Engineers: Structures and Buildings,

Vol. 116, No. 3 and 4, August/November 1996, pp. 283-294.

22 NEWBY, F. The innovative use of concrete by engineers and architects, Historic concrete -

background to appraisal (Sutherland, J, Humm, D and Chrimes, M, Eds), Thomas Telford, London,



23 SOMERVILLE, G. Cement and concrete as materials; changes in properties and performance,

Historic concrete-background to appraisal (Sutherland, J, Humm, D and Chrimes, M, Eds), Thomas

Telford, London, 2001, pp. 105-116. Also in Proceedingsof the Institution of Civil Engineers: Structures

and Buildings, Vol. 116, No. 3 and 4, August/November 1996, pp. 335-434.

24 SUTHERLAND, RJM. Understanding historic concrete, Proceedings of the Institution of Civil Engineers:

Structures and Buildingsyol 116, No. 3 and 4,1996, pp. 255-263.

25 STANLEY, CC. Highlights in the history of concrete, Cement and Concrete Association (now Mineral

Products Association -Cement), Camberley, 1979.

26 CHRIMES, MM. The development of concrete bridges in the British Isles prior to 1940, Historic

concrete-background to appraisal (Sutherland, J, Humm, D and Chrimes, M, Eds), Thomas Telford,

London, 2001, pp. 211-249. Also in Proceedings of the Institution of Civil Engineers: Structures and

Buildingsyol 116, No. 3 and 4, August/November 1996, pp. 404-431.

27 SMITH, WJR. UK concrete bridges since 1940, Historic concrete - background to appraisal

(Sutherland, J, Humm, D and Chrimes, M, Eds), Thomas Telford, London, 2001, pp. 251-273. Also

in Proceedings of the Institution of'Civil Engineers, Structures and fiu/W/ngs, Vol. 116, No. 3 and 4,

August/November 1996, pp. 432-448.

28 FABER, O. Reinforced concrete simply explained, Oxford University Press, 1922 (Third Edition 1944).

29 PULLAR-STRECKER, P. Corrosion damaged concrete; assessment and repair, Published on behalf of the

Construction Industry Research and Information Association, London, by Butterworths, London, 1987.

30 BUILDING RESEARCH ESTABLISHMENT. HAC concrete in the UK, BRE Press, Garston, Watford, 2002.

31 DUNSTER, A, BIGLAND, D, HOLTON, I and REEVES, B. Durability of ageing high alumina cement

(HAC) concrete: A literature review and summary of BRE research findings, Report 386, Building

Research Establishment, Garston, Watford, 2000.

32 DUNSTER, A, BIGLAND, D, REEVES, B and HOLTON, I. The durability of pre-cast HAC concrete in

buildings, Information Paper IP 8/00, Building Research Establishment, Garston, Watford, 2000.

33 ROAD RESEARCH LABORATORY. Design of concrete mixes, Road Note No. 4, HMSO, London, 1950.

34 MclNTOSHJD. Concrete mix design, Cement and Concrete Association (now Mineral Products

Association - Cement), Camberley, 1964.

35 TEYCHENNE, DC. Codesand standards-time for harmonisation, CONCRETE, Vol. 16, No. 8,

August 1982, pp. 10-12.

36 REYNOLDS, CE. Practical examples of reinforced concrete design, Concrete Pu blications Limited,London, 1938.

37 THE CEMENT MARKETING COMPANY. Everyday uses of Portland cement-a practical handbook on

the economical employmentof Portland cement (Fourth Edition), The Cement Marketing Company

Limited, London, 1921 (First Edition published 1909.)

86


References

38 THE INSTITUTION OF STRUCTURAL ENGINEERS/THE CONCRETE SOCIETY. Standard method of

detailing structural concrete. A manual for best practice (Third Edition), The Institution of Structural

Engineers, London, 2006.

39 SUTHERLAND, J, HUMM, DandCHRIMES, M (Eds). Historic concrete -backgroundto appraisal,

Thomas Telford, London, 2001.

40 HIGHWAYS AGENCY, BD 21. Design manual for roads and bridges, Volume 3: Highway structures:

inspection and maintenance, Section 4: Assessment, Part 3: The assessment of highway bridges and

structures, The Highways Agency, London, 2001.

41 Specification, Architectural Press (now EMAP), published annually since 1898.

42 BUSSELL, MN.The era of the proprietary reinforcing systems, Historic concrete-backgroundto

appraisal (Sutherland, J, Humm, D and Chrimes, M, Eds), Thomas Telford, London, 2001, pp. 68-82.

Also in Proceedings ofthe Institution of Civil Engineers, Buildings and Structures, Vol. 116, No. 3 and 4,


43 WALLEY, F. Prestressing, Historic concrete-background to appraisal (Sutherland, J, Humm, D and

Chrimes, M, Eds), Thomas Telford, London, 2001, pp. 191-210.Also in Proceedings ofthe Institution of

Civil Engineers, Structures and Buildings, Vol. 116, No. 3 and 4, August/November 1996, pp. 390-403.

44 AUDRPM,Alar\dTURUm,EH.Posttensioning systems forconcreteintheUK: 1940-1985, Report 106,

CIRIA, London, 1985.

45 GLOVER, CW. Structural precast concrete, CR Books Limited, London, 1964.

46 BUSSELL, M N. The development of reinforced concrete: design theory and practice, Historic concrete

-background to appraisal (Sutherland, J, Humm, D and Chrimes, M, Eds), Thomas Telford, London,

2001, pp. 83-103. Also in Proceedings ofthe Institution of Civil Engineers: Structures and Buildings,


47 REYNOLDS, CE. Examples ofthe design of reinforced concrete buildings, Concrete Publications

Limited, London, 1952 (revised 1959).

48 REYNOLDS, CE. Basic reinforced concrete design, a textbook for students and engineers, Volume 1:

Elementary, Volume 2: More advanced design, Concrete Publications Limited, London, 1962.

49 ALLEN, AH. Reinforced concrete design to CP 110 simply explained, Cement and Concrete Association

(now Mineral Products Association - Cement), Camberley, 1974.

50 DAWE, P. Traffic loading on highway bridges, Thomas Telford, London, 2003.

51 BATCHELOR, WG and BEEBY, AW. Charts forthe design of circular columns to BS 8110, Report 43.503,

British Cement Association (now Mineral Products Association - Cement), Camberley, 1990.

52 DIAMANT, R. Industrialised Building: 50 international methods, Iliffe Books, London, 1969.

53 DEESON, AFL. The Comprehensive Industrialised Building Systems Annual 1970, Morgan-Grampian

(Publishers) Ltd, West Wickham, Kent, 1970.

54 CREASY, LR. The Public Building Frame, Cement and Concrete Association (now Mineral Products

Association - Cement), 1966.

55 ELLIOTT, KS. Multi-storey precast concrete framed structures, Blackwell Science, Oxford, 1996.

56 BUILDING RESEARCH ESTABLISHMENT. The structural condition of Intergrid buildings of prestressed

concrete, HMSO on behalf of BREandthe Department of the Environment, London, 1978.

57 MINISTRY OF EDUCATION. The Story of CLASP, Building Bulletin 19, Ministry of Education,

London, 1961.

58 BEEBY, AW, READ, JB and LEWIS, HE. The Harness Hospital system, Part 2: Testing of a prototype

structure, Proceedings ofthe Institution of Civil Engineers, Part 1, Design and Construction, Vol. 60,

Issue 3, August 1976, pp. 423-443.

59 LEWIS, HE and TAYLOR, N. The Harness Hospital system, Part 1: Design of a standard structure

and construction of a prototype, Proceedings ofthe Institution of Civil Engineers, Part 1, Design and

Construction, Vol. 60, Issue 3, August 1976, pp. 401-423.

60 BRITISH CONSTRUCTIONAL STEELWORK ASSOCIATION. Prefabricated floors for use in steel

framed buildings, Publication M2, BCSA, London, 1964 (revised 1965 and 1977).


61 GAZE, A and THOM PSON, MS. Investigation into the compaction of reinforced concrete ribs in wood

wool formers - 50 mm slump concrete, Wood Wool Slab Manufacturers Association, London, 1975.

62 LEVITT, M and GAZE, Al. Investigation into the compaction of reinforced concrete ribs in wood wool

formers -120 mm slump concrete. Wood Wool Slab Manufacturers Association, London, 1975.

63 CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION ASSOCIATION. Permanent

formwork in construction (Author Wrigley, RG), Report C558, CIRIA, London, 2001.

64 CURRIE, RJ and MATTHEWS, SL. Reinforced autoclaved aerated concrete planks designed before

1980, Information Paper IP 10/96, Building Research Establishment, Garston, Watford, 1996.

65 MATTHEWS, S, NARAYANAN, N and GOODIER, A. Reinforced autoclaved aerated concrete panels;

review of behaviour and developments in assessment and design, Report BR 445, Building Research

Establishment, Garston, Watford, 2002.

66 BUILDING RESEARCH ESTABLISHMENT. The structural performance of Ronan Point and otherTaylor

WoodrowAnglian Buildings, Report 63, BRE, Garston, Watford, 1985.

67 CEMENT AND CONCRETE ASSOCIATION. Standard beam sections for prestressed bridges, C&CA

(now Mineral Products Association - Cement), Camberley.

1. InvertedT beams for spans 25-55 ft (2nd edition 1963, addendum 1966)

2. Box beams for spans 40-85 ft (1963)

3. Box section beams for spans from 85-120 ft (1964)

4.1 section beams from 40-85 ft (1964)

5.1 section beams for spans from 85-129 ft (published 1964)

68 SOMERVILLE, G and TILLER, RM. Standard bridge beams for spans 7-36 m, Report 46.005, Cement

and Concrete Association (now Mineral Products Association - Cement), Camberley, 1970.

69 MANTON, BH and WILSON, CB. MoT/C&CA standard bridge beams, Report 46.012, Cement and

Concrete Association (now Mineral Products Association - Cement), Camberley, 1971 (Revised 1975).

70 TAYLOR, HPJ. The precast concrete bridge beam - the first 50 years, The Structural Engineer, Vol. 76,

No. 21, November 1998, pp. 407-414.

71 GREEN, JK. Detailing for standard prestressed concrete bridge beams, Report 46.018, Cement andConcrete Association (now Mineral Products Association - Cement), Camberley, 1973.

72 CHRIMES, MM. Concrete foundations and sub-structures: a historic review, Historic concrete -




73 ANON. Piling and diaphragm walling handbook, Cementation Piling and Foundations,

Rickmansworth, circa 1970.

74 GOULD, M. Water-retaining structures in Britain before 1920, Historic concrete -background to

appraisal (Sutherland, J, Humm, D and Chrimes, M, Eds), Thomas Telford, London, 2001, pp. 323-341.

75 BRUGGEMANN, DA, HOLLOCK, KJ and SIMS, GP. Historic concrete in dams, Historic concrete -


2001, pp. 343-357.

76 GOULD, MH and CLELAND, DJ. Development of design form of reinforced concrete watertowers,

Proceedings of the Institution of Civil Engineers, Structures and Buildings, Vol. 146, No. 1, February

2001, pp. 3-16.

77 HARRISON, TA. Early-age thermal crack control in concrete, Report 91, CIRIA, London, 1981.

78 WILLIAMS, AW and WARD, GC. The renovation of no-fines housing, Report BR 191, Building Research

Establishment, Garston, Watford, 1991.

79 SHARP, B. Reinforced and prestressed concrete in maritime structures, Historic concrete-




88


References

80 MORICE, P and TOTTENHAM, H. The early development of reinforced concrete shells, Historic

concrete-background to appraisal (Sutherland, J, Humm, DandChrimes, M, Eds), Thomas Telford,

London, 2001, pp. 165-175. Also in Proceedings of the Institution of Civil Engineers: Structures and

Buildings, Vol. 116, No. 3 and 4, August/November 1996, pp. 373-380.

81 ANCHOR, R. Concrete shell roofs, 1945-65, Historic concrete-background to appraisal

(Sutherland, J, Humm, D and Chrimes, M, Eds), Thomas Telford, London, 2001, pp. 177-189. Also in

Proceedings of the Institution of Civil Engineers: Structures and Buildings,Vo\. 116, No. 3 and 4,


82 MUIRWOOD, A. Concrete in tunnels, Historic concrete -background to appraisal (Sutherland, J,

Humm, D and Chrimes, M, Eds), Thomas Telford, London, 2001, pp. 315-322.

83 WEST, G. Concrete roads, Historic concrete - background to appraisal (Sutherland, J, Humm, D and

Chrimes, M, Eds), Thomas Telford, London, 2001.

84 WEILER, J. Military, Historic concrete -background to appraisal (Sutherland, J, Humm, D and

Chrimes, M, Eds), Thomas Telford, London, 2001.

85 NEVILLE, AM. Properties of concrete (Third Edition), Longman, Essex, 1995.

86 HEWLETT, PC (Ed.). Lea's chemistry of cement and concrete (Fourth Edition), Arnold, London, 1998.

87 HAWKINS, MR (Chairman of Working Party). Minimising the risk of alkali-silica reaction -guidance

notes. A report of a Working Party, Report 97.304, Cement and Concrete Association (now Mineral

Products Association - Cement), Camberley, 1983.

88 THE CONCRETE SOCIETY. Alkali-silica reaction - minimising the riskof damage to concrete.

Guidance notes and model specification clauses, Technical Report 30, The Concrete Society,

Camberley, 1987 (Revised Edition 1995, Third Edition 1999).

89 INSTITUTION OF STRUCTURAL ENGINEERS. Structural effects of alkali-silica reaction, Institution

of Structural Engineers, London, 1992.

90 ANON. The Concrete Year Book, Concrete Publications Limited, London, published annually from

1924 onwards.

Further reading BECKMANN, P and BOWLES, R. Structural aspects of building conservation (Second Edition),

McGraw-Hill Book Company, London, 2004.

BEEBY, AW and HAWES, FL. Action and reaction in concrete design, 1935-1985, Reprint 3/86,

Cement and Concrete Association (now Mineral Products Association -Cement), Camberley, 1986.

BREBBIA, CA and FREWER, RJB. Structural repair and maintenance ofhistorical buildings,Vol. 111,

Computational Mechanics Publications, Southampton, 1993.

CONSTRUCTION INDUSTRY RESEARCH AND INFORMATION ASSOCIATION. Structural

renovation of traditional buildings, Report 111, CIRIA, London, 1994.

HART, WO. Construction of buildings in London, Greater London Council, 1958.

KNOWLES, CC and PITT, PH. The history of Building Regulation in London 7789-7972, Architectural

Press, London, 1972.

LEY, AJ. A history ofBuilding Controlin Englandand'Wales 1840-1'990, RICS Books, London, 2000.

MACDONALD, S (Ed.). Concrete building pathology, Blackwell Science Ltd, Oxford, 2003.

PARKINSON, G, SHAW, G, BECK.JKand KNOWLES, D. Appraisal and repair of masonry, Thomas

Telford, London, 1996.

89


WM

Appendix A. Proprietary floors

A wide range of proprietary precast concrete floor systems have been produced over the

years. The list below is taken from Prefabricated floors for use in steel framed buildings,

published by BCSA'60', which gives the properties and safe load capacities of various

systems available in the 1960s. Those marked with an asterisk (*) are also described in

Structural precast concrete by Glover'45'.

• Allison T-beam floor

• Anglian prestressed floor

• Armocrete precast floor

• Arrow precast floor

• Atlas-Omnia trough slab

• Bison precast or prestressed hollow floor; solid or hollow plank floor*

• Blatchford's channel floor beam; prestressed double tee unit; precast trough floor,

precast hollow floor

• BRC hollow steel mould floor

• Chipcrete lightweight composite floor

• Corite hollow floor*

• Croft precast hollow floor

• Dabro Cheam precast hollow block floor; Shere precast composite system

• Dow-mac single-core hollow beams; twin-core hollow beams

• Ebor Duron trough beam; Duron hollow beam

• Evanstone (single core hollow beam)

• Evercrete channel floor beam; hollow beam

• Filigree beam and block floor; wideslab floor*

• Fram precast X joist floor; composite floor*

• Girling precast floor; prestressed floor*

• Greenwood's Greecon floor; hollow beam floor; Myko floor

• Gypklith precision beams

• HBS self-centering floor

• Helicon precast trough floor: precast hollow floor

• Invictus (single-core beams, triple-core beams or channels)

• Kaiser floor

• Lyncrete precast floor

• Marley floor and roof beams

• Marlith wood-wool floor and roof formers*

• Matthews precast channels; precast hollow beam

• Milbank composite floor*

• Musker

• Neolith wood-wool floor units

a Omnia semi-precast hollow block floor*

• Parcrete precast composite system

a Pierhead prestressed concrete floor; composite floor

• Rapid floor

90


Appendix A

• Shockcrete precast floor

• Siegwart precast trough floor: precast hollow floor*

• Sindall floor

• Smith's fireproof floor

• Spancrete prestressed composite floor

• Spanform wood-wool composite floor

• Stahlton

• Stotam Roth prestressed floor: prestressed plank floor

• Stuarts precast trough floor; precast hollow floor

• Tembo prestressed floor*

• Thermaflor

• Tilecast floor*

• Trent and Hoveringham prestressed floor

• Triad composite floor

• Truscon Type 1 & 2 floor units; mini-tee unit*

• Truspan prestressed hollow floor

• Viking floor

Also included in Prefabricated floors for use in steel framed buildings are three steel-concrete

systems:

• Hoiorib composite floor (similar to modern steel decking)

• Q-floor (similar to modern steel decking)

• QC-floor (using a flat steel plate with an upstand).

Structural precast concrete also gives details of:

• Bradfords precast floors

• Eagle floors and roofs

• Siporex floor and roof slabs

91


Appendix B. Non-traditional houses:precast and constructed in-situ

Details of a large number of system-built houses are given in Non-traditional houses;

identifying non-traditional houses in the UK 7978-75(12>. A list of the more common types is

given below; the criterion for inclusion in Non-traditional houses is that more than 1000

were built.

Precast Airey

Boot Pier and Panel

Camus

Dorran (includes Myton, Newland andTarran)

Gregory

Intergrid

Kenkast

Orlit (Types I and II)

Reema Hollow Panel

Smith

Stent

Underdown (including Winget)

Wates

Woolaway

Bison Wallframe

Bryant Low Rise

Cornish (Types I and II)

Glasgow Foamed Slag

HSSB System

Jestersen 12M

Lecaplan (Types A and B)

Parkinson

Skarne

Spacemaker

Taylor Woodrow Anglian

Unity (Types I and II)

Whitson-Fairhurst

XW

Constructed in-situ Boswell

Duo-Slab

Farrans No-Fines

Mowlem

Schindler

Universal

Diatomite

Easiform (Types I and

Fidler

Parkwell

Unit No-Fines

Wimpey No-Fines

92



There are many instances in which an engineer is asked to

appraise an existing building, or other structure, perhaps due to

led change of use or as part of a refurbishment process,

i example might be an office block built in the 1960s,

although with the move towards conservation, it is likely that

many earlier buildings and structures will be refurbished or

upgraded rather than being demolished and replaced. As a first

stage in this process, it is useful to have as much information

as possible about the structure, such as what Code or Standard

t was designed to, what the concrete and steel strengths were

likely to have been at the time of construction, what design

pproaches were adopted, what proprietary precast concrete

units were available, etc.

The aim of this Technical Report is to provide an outline of this

information and to list some of the relevant publications and other

sources of readily available information, up to about 1990. (Although

this Report is primarily intended to cover UK practice, many British

Codes and Standards were, and are, used abroad and hence the guidance

should be equally applicable overseas.)

CCIP-049

Published July 2009

ISBN 978-1-904482-57-4

© The Concrete Society

Riverside House, 4 Meadows Business Park,

Station Approach, Blackwater, Camberley, Surrey, CUV 9AB

Tel: +44 (0)1276 607140 Fax: +44 (0)1276 607141

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