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NEW APPLICATIONS OF HOLLOW-CORE COMPONENTSIN HOUSING, ADMINISTRATIVE, AND PUBLIC BUILDINGS
by
FARNAZ A. BEROUKHIM
Bachelor of Art in ArchitectureSouthern California Institute of Architecture
Santa Monica, California1982
SUBMITTED TO THE DEPARTMENT OF ARCHITECTUREIN PARTIAL FULFILMENT OF THE REQUIREMENTS OF THE DEGREE
MASTER OF SCIENCE IN ARCHITECTURE STUDIES AT THEMASSACHUSETTS INSTITUTE OF TECHNOLOGY
JUNE, 1985
O Farnaz A. Beroukhim 1985
The Author hereby grants to M.I.T.permission to reproduce and to distribute publicly copies
of this thesis document in whole or in part.
Signature of the author ~v U, ~
Farnaz A. BeroukhimDepartment of Architecture
Certified by wy"rV - k_ -/: C Waclaw P. ZalewskiProfessor of Structures
Thesis Supervisor
Accepted byJulian Beinart
ChairmanDepartmental Committee for'Graduate Students
ROW-1
MA SSA CHUSETI S IN5INTEOF TECHNOLOGY
JUN 0 3 1985L!BP.AIS
UV
New Applications of Hollow-Core Componentsin Housing, Administrative, and Public Buildings
by
Farnaz A. Beroukhim
Submitted to the Department of Architecture May 8, 1985in partial fulfilment of the requirements for the Degree ofMaster of Science in Architecture Studies.
ABSTRACT
Standard prestressed hollow-core slabs have many advantagesas construction members while being relatively very low in cost.The principal advantages include the ease of mass production,a small cross-sectional area, light weight, and flat surfaces.In addition, the slabs have the advantages of concrete,precasting and prestressing.
The only specifications which make hollow-core componentsunsuitable for wall members are their lack of weight and mass,their inability to be used as long members because of thelimited distance between the floor-to-floor height, and, in somecases, insufficient insulating qualities.
This thesis recommends a practical and economical systemfor the structural use of hollow-core components which have beenmodified with two other additional structural members - acontinuous precast "L" beam and a precast support panel. Thissystem will allow a high degree of standardization and anadditional saving in the total cost of the equipment andformworks. Most of all, the wall members have the advantages ofprecast prestressed hollow-core slabs and their low cost.
The new system's applications are mainly directed towardshousing, administrative and public buildings.
A design example is also introduced and analyzed in termsof possible variations in area of the individual units and thetotal cost of the building. The latter case shows that thetotal cost of structure per square-foot for the recommendedsystem is considerably lower than the other construction types.
Thesis Supervisor: Waclaw P. ZalewskiTitle: Professor of Structures
ACKNOWLEDGEMENT
I am grateful for the insightful advice and criticism of myadvisor, Professor Waclaw P. Zalweski of Massachusetts Instituteof Technology.
I appreciate the valuable comments and suggestions of my dearhusband, Professor Menashi D. Cohen of Northeastern University.I also very much appreciate his full support, patience andunderstanding.
I wish to thank people at Lonestar/San-Vel for providinginformation throughout the thesis.
I am also thankful to Professor Leon Groisser of M.I.T. and Mrs.Janet Polansky of Jewish Vocational Service for providingfinancial support.
In addition, I thank the Women's Scholarship Organization fortheir scholarship award in 1985.
Most of all, I am grateful to my parents, brother, and sistersfor their support and encouragement.
I also wish good luck to my dear friend, Kai-ie Lie, 1984graduate of Architecture Department, at M.I.T..
iii
TABLE OF CONTENTS
ABSTRACT. ....................
ACKNOWLEDGEMENTS..............TABLE OF CONTENTS.............LIST OF FIGURES AND TABLES....
1.0 INTRODUCTION AND OVERVIEW............................
2.0 CONCRETE.000000000000000000000
2.1 Concrete Block*.............2.2 Cast-In-Place Concrete...2.3 Precast Concrete.........
2.3.1 Connections......2.3.2 Finishes.........
2.4 Reinforced Precast Types.2.4.1 Reinforced.......2.4.2 Prestressing the
Prestres2.5.12.5.2
2.5.32.5.42.5.5
Cost forMaterial2.6.12.6.22.6.32.6.4Concludi
Co ncre te Pre-nIs Z 1 = 0 0 0 0 0 0 S t 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Post-Tensioning the Steel..............Prestressing types-Circular and Linear.Partial Prestress Reinforcements .......sed Standard Types.....................Double Tee...........Single Tee.............Solid Flat Components.................Hollow-Core Components.................Other Components .......................
Common Types of Structural Constructio
Prestressed Standard Types ............Cast-In-Place Concrete................Brick Veneer/Wood Stud Backup..........Concrete Block Wall....................rg Discussion ................... 0......
3.0 PRESENT APPLICATIONS OF STANDARD PRECAST PRESTRESSEDHOLLOW-CORE COMPONENTS ..................................
3.1 Hollow-Core Slab.................................3.1.1 Typical Connections....... .. ..........3.1.2 Coordination with Electrical, Mechanical,
Plumbing, Services and other Sub-Systems.3.2 Hollow-Core Wall.......... .. .. .. ......... .3.3 Corewall Insulated Wall Panel....................
4.0 NEW APPLICATIONSCORE COMPONENTS.4.1 System 1
4.1.14.1.2
4.1.3
OF STANDARD PRECAST PRESTRESSED HOLLOW-00.00..000.00..00000.000..000000.000000.
- Required Structural Components .......Hollow-Core Slab 0........................
Hollow-Core Wall Panel..................Precast "L" Beam ....... 0000.0000000..00
.iv
.vi
a..... 1
0.4
.10
.11
.12
.15
.16
.16
.16
2.5
2.6
2.7
PAGE
i
d
PAGE
4.1.4 Precast Support Panel.....................524.1.5 Sequence of Erection......................053
4.2 System 2 - Required Structural Components.........554.3 Advantages and Disadvantages......................56
5.0 EFFECTS OF THE NEW SYSTEMS ON HOUSING, ADMINISTRATIVE ANDPUBLIC BUILDINGS...........................58
5.1 Housing .............. ............. 0 00.. . .59
5.2 Administrative and Public Buildings...............605.3 Design Example ................................. .. 61
5.3.1 Variations in Unit Dimensions.............625.3.2 Cost Estimate .......... ..... ....... .. 64
5.4 Variations of Planning ............................ 66
6.0 CONCLUDING DISCUSSION. .............................. ...... 68
REFERENCES..................... 0000... 70
LIST OF FIGURES AND TABLES
Table 2-1
Table 2-2
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Table
Table
Table
Tab 1 e
Table
Table
Table
Tab 1 e
Figure
Figure
Figure
Figure
Figure
Figure
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-3
2-4
2-5
2-6
2-7
2-8
2-9
2-10
3-1
3-2
3-3
3-4
3-5
3-6
The strength of concrete decreases as the w/cratio increases..............
Approximate relative strengthaffected by type of ce
Deformed reinforcing b
Manufacturing processconponents............
Channels for post-tens
Double Tee............
Single Tee............
Solid flat slab.......
Hollow-core slab ......
Precast double "T" bea
Precast single Tees...
Precast planks........
Flat precast concrete.
Cast-in-place flat pla
Cast-in-place concrete
Brick veneer/wood stud
Concrete block wall...
Dy-core...............
Dynaspan..... .........
Flexicore.............
Spancrete ...... .......
Span-deck ..........
Spiroll, corefloor....
ne nt.of concrete as
PAGE
.. 6
.. . . . .. . . . . 7
..12
concre
ns....
tefor precast............
ioning tendo
...........
wall . . . .
...........
.. o..........
wall.......
backup .....
vi
.13
..18
. . 22
..23
....... 24
....... 24
....... 26
....... 926
....... &27
....... 27
....... 28
....... 28
....... 029
....... 30
*......34
....... 34
....... 35
...... 35
..... 36
......
.. .. &
.. .. 0
PAGE
Figure 3-7
Figure 3-8
Figure 3-9
Figure 3-10
Figure 3-11
Figure 3-12
Figure 3-13
Figure 3-14
Figure 3-15
Figure 3-16
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
3-17
3-18
3-19
4-la
4-lb
4-2
4-3
4-4
Typical connection details of hollow-core slabto structural wall-Exterior joints..............37
Typical connection details of hollow-core slabto structural wall - Interior joints............37
Typical connection details of hollow-core slabtobeal..................s.......low-core..la...3
Typical connection details of hollow-core slab toshear wall ............................... ....... 38
Typical connection details of hollow-core slabs toeach ot e . . . . . . . . . . . . . . . . . . . 3
Underfloor electrical ducts can be embedded withina concrete topping..............................39
Large openings in floors and roofs are made duringmanufacture of
Kitchen/bathroom modules can be pre-assembled onprecast prestressed slab ready for installation insystem buildings.............................
Prefabricated wet-wall plumbing systems incorporatepre-assembled piping.... ..................... 42
Methods of attaching suspended ceilings, cranerails, and other sub-systems.......... .43
Sections through vertical joints................44
Typical corner detail...... ..................... 45
Typical top connection......................... .45
Three degrees of diversity for prefabricates....48
The new degree of diversity for prefabricates...48
Hollow-core slab....................... ......... 49
Hollow-core slab with post-tensioning conduits..49
Hollow-core wall panel - Section................50
Figure 4-5 Wall panels have equal heights at eachlevel of erection..................... . .51
vii
the units ................. e.. .. 40
Figure 4-6
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
4-7
4-8
4-9
4-10
4-11
4-12
4-13
5-1
5-2
5-3
Figure 5-4
Figure 5-5
Figure 5-6
The height of every other wall panel vary inone story increments .................................
PAGE
.. 51
Precast "L" beam................................
Precast support element .........................
Floor to bearing wall connection-Detail A......
Typical section................................
Typical connection of floor slabs to load-bearinwall panel ...................................
Section through load-bearing wall panels........
Optional exterior finish-Detail B ..............
Design example - Plan. .................... ......
Design example - Section ........................
Considering the width between two structuralwalls........................... .... *. .. 000000
Considering the width between three structuralwalls ........ . . . . . . . . . . . . . . . . .
Considering the width between four structural
Variations of planning.............. ...........
viii
52
53
54
55
g56
56
57
61
61
62
62
63
66
1.0 Introduction and Overview
-1-
1.0 INTRODUCTION AND OVERVIEW
The primary goal of the construction industry today is to
incorporate the advantages of prefabrication, while achieving
the architectural requirements of a space in a practical and
economical way.
Cost is one of the most important factors affecting a
decision on the choice of materials and the nature of
construction. Precast concrete products are usually used only
when rapid construction is more important than cost.
On the other hand, when analyzing the costs, types, and
manufacturing means of precasting, we notice that precasting,
while being an expensive way of construction, can also be the
least expensive way as well. For example, the reinforced
precast panels are now produced for about $18 to $20 per S.F.,
while standard hollow-core slabs are produced for about $3.50
per S.F.
Therefore, it is not the precasting which is expensive,
but the method of precasting which makes the difference.
The main advantages of standard hollow-core slabs, in
comparison with all other types of flooring and roofing
systems, are their very low cost, small thickness, light
weight, and flat surfaces. They also have all the advantages
of prestressing, precasting and concrete.
While these specifications make concrete an ideal material
for slab, other characteristics make it less practical and
economical for wall members: its lack of weight, mass, and in
some cases insufficient insulating qualities, in addition to
-2-
its not being suitable for use as long members.
The goal of this thesis is to introduce a system in which
standard hollow-core components and/or their modifications can
be used practically and economically as structural floor and
wall panels while maintaining the advantages of hollow-core
slabs and satisfying the architectural requirements of a space.
The principal advantages of using homogeneous floor and
wall members will be:
a. The manufacturing time is minimized through mass
production of a simple cross-sectional shape.
b. A standard method and technique can be used for
ma nufacturi ng.
c. A significant saving in cost of equipment and
formworks will be achieved.
d. Machines and equipment will mainly be used for
manufacturing.
Therefore, all of these will result in a significant
saving in the total cost of the components.
-3-
2.0 CONCRETE
-4-
2.0 CONCRETE
Concrete has many characteristics that make it one of the
most widely used construction materials. Concrete products
account for more than $250 billion dollars per year. Tha main
characteristics of this material are its availability, low
price, formability, and the relative ease with which its
properties can be modified. The main properties include
strength, durability, economy, and fire resistancy; concrete is
also a good sound insulator.
Concrete is a mixture of aggregates, water and portland
cement. The active ingredients are water and cement which
combine chemically to form a paste that binds the aggregates
together. This process is called hydration.
AGGREGATES
The major function of aggregates is to make concrete more
economical. In a mass, as hydration and evaporation take
place, the aggregates keep the concrete from shrinking and
cracking. Therefore, the number and sizes of the aggregates
can be adjusted for the strength and workability of the mix.
Fine aggregate can be either sand or rock screenings, and
the particles range from very fine sand to 1/4 inch in size.
Course aggregate is either gravel or crushed stone 1/4
inch to 1-1/2 inch in diameter.
Light-weight aggregates of various types may also be used
to control the weight, thermal insulating, and nailing
characteristics of concrete. Also, depending on the type of
-5-
light-weight aggregate, the shrinkage, strength and insulating
properties of the mix will vary.
WATER
For mixing concrete, it's best to use water that is fit to
drink. If at a specific job site potable water is not
available, tests on samples must show that the compressive
strength of the mix at 7 and 28 days is at least equal to 90%
of the concrete made with potable water.
The common testing age for compressive strength of
concrete, both normal and high-strength, is 7 and 28 days.
The more water added, above a certain amount, to a given
amount of cement, the weaker the concrete will ultimately be.
This relationship of water and cement is known as the water
cement ratio or W/C. Table 2-1 shows that the strength of
concrete decreases as the W/C ration increases.
Approx.W/C Gallon& 28-day
(weight) per beg atWe;th
.45 5.0 5,000
.49 5.5 4,500
.53 6.0 4,000
.57 6.5 3,500
.62 7.0 3.000
Table 2-1 The strength of concrete decreases as the W/C ratio
increase.
PORTLAND CEMENT
The manufacturing of portland cement requires raw
materials which are mainly lime, silica, alumina, and iron.
There are five types of portland cement based on ASTM
standards. Each is intended for a specific purpose although
they all achieve about the same strength after curing for three
months.
-6-
ASTM TYPE I (Normal)
This is the most common type of general purpose cement,
and is used when a specific type is not required. It is
generally not used in large masses because of the generated
heat from hydration. Its uses include most residential
constructions, bridges, railway structures, tanks, water pipes,
pavements, sidewalks, and masonary units.
ASTM TYPE II (Moderate Heat or Modified)
Type II cement is used where low heat generation during
hydration or resistance to moderate sulfate attack is
important. It has been used in warm climates and structures of
mass, such as piers, abutments, and retaining walls.
ASTM TYPE III (High Early Strength)
Type III cement is used when an early strength gain is
important and heat generation is not a critical factor. For
example, it can be used when forms have to be removed for reuse
and/or the member will be put under full load within a few
days.
Table 2-2 shows the approximate relative strength of
concrete as affected by the type of cement and days of curing.
Compressive Strength (PercentType of of Strength of Type I or Normal
Portland Cement Portland Cement Concrete)ASTM CSA I day 7 days 28 days 3 mos.
I Normal 100 100 100 100II 75 85 90 100
III High-Early-Strenkth 190 120 110 100IV 55 55 75 100V Sulfate-Resisting 65 75 85 100
Table 2-2 Approximate relative strength of concrete as
affected by type of cement.
-7-
ASTM TYPE IV (Low Heat)
Type IV cement is used where the rate and amount of heat
generated must be minimized. The strength development for type
IV is slower than for type I. Type IV is primarily used in
large mass placements such as dams.
ASTM TYPE V (Sulfate-Resisting)
Type V is primarily used where the soil or ground water
contains high sulfate concentrations and the structure would be
exposed to severe sulfate attack. Type V gains strength much
more slowly than type I.
Approximate amounts of heat generation during the first 7
days of curing, using type I cement as the base, are as
follows:
Type I 100%
Type II 80-85%
Type III 150%
Type IV 40-60%
Type V 60-75%
ADMIXTURES
Admixtures can be classified into two groups: (1)
chemical admixtures, and (2) mineral admixtures.
Chemical admixtures are:
1. Air-entraining
This admixture stabilizes bubbles formed by air
incorporated in the concrete during the mixing process.
The bubbles create tiny voids which allow the concrete
to withstand the freeze-and-thaw cycle.
-8-
2. Retarders
These admixtures are frequently used in high-strength
concretes to control the rate of hydration. They can
be used on hot days to prolong the setting time from 30
to 60 percent. In addition, retarders often provide an
increase in compressive strength.
3. Water Reducer
This admixture allows as much as 15 percent reduction
of water in a mix. Therefore, it helps to minimize
problems relating to an excess of water (which causes
cracking in the concrete). The admixture also
increases the concrete's strength and its bond to
steel.
4. Accelerators
These admixtures are not normally used in high-strength
concrete. They are counterproductive and lead to
long-term strength reduction. Accelerators can be used
to get an early set in freezing weather.
Mineral Admixtures are:
1. Fly Ash
A replacement of 10 to 30 percent by weight of cement
with fly ash will increase the compressive strength.
2. Silica Fume
Using silica fume as partial replacement of or an
addition to cement will increase the compressive
strength.
-9-
Admixture Combination
The combination of superplasticizers with water reducers
or retarders has become common in order to achieve optimum
performance at the lowest cost. In certain circumstances,
combinations of water-reducers or retarders plus an accelerator
have been proven to be useful.
CURING
Proper curing is essential in achieving high-strength
concrete. The compressive strength and durability of concrete
will be fully developed only if it is properly cured for an
adequate period prior to being placed in service. It is best
to keep the concrete moist and warm, above 80 percent relative
humidity and 70 F for about 3 days. If the humidity drops
below 80 percent, the surface of the concrete shrinks,
resulting in a soft, dusty skin which is less resistant.
CONCRETE IN CONSTRUCTION
Concrete can be used in construction either plain or with
reinforcements. In general, concrete without reinforcements
are precast in the form of blocks; with reinforcements, it can
be precast or cast-in-place in any desired form.
2.1 CONCRETE BLOCK
Concrete masonry building units, solid or hollow, are
widely used. They are made from both light-weight and
normal-weight concrete in a great variety of sizes and shapes.
The properties of concrete blocks are made to comply with
certain requirements, such as compressive strength, rate of
-10-
absorption, moisture content, weight, and thermal expansion.
Applications of concrete masonry building units include
exterior and interior load-bearing walls, fire walls, party
walls, curtain walls, panel walls, and partitions.
2.2 CAST-IN-PLACE CONCRETE
Concrete has great compressive strength but lacks tensile
strength, whereas steel has great tensile strength. Reinforced
cast-in-place concrete is a combination of concrete and steel
that uses to best advantage the compressive strength of the
concrete and the tensile strength of the steel. In this method
the reinforcements are placed in position, then the desired
form is located before pouring the concrete mix.
Reinforced concrete is very widely used in the
architectural field for foundations, structural framing,
floors, roofs, walls, etc. Reinforcements can generally be
grouped into two major categories:
1. Steel Wires, Strands and Bars
Steel wires can be welded to form wire mesh or grouped
in parallel to form cable. Strands are wires twisted
together. Bars are made either plain or deformed.
Fig. 2-1 shows deformed reinforcing bars. Deformed
bars create a better bond between concrete and steel.
Steel bars of high strength have also been successfully
applied to prestressing concrete. Steel bars are
designated by the number of eights of an inch in their
-11-
diameter and are available in sizes from number 2 (1/4
inch diameter) to number 18 (2-1/4 inch diameter).
Figure 2-1 Deformed reinforcing bars.
2. Fibers
Fibers which are typically used for the reinforcement
of concrete include steel, glass, and synthetic. The
advantage of fibers, as opposed to continuous strands
or bars, is that they can be included during mixing,
therefore eliminating the labor associated with the
fabrication and placement of reinforcements.
2.3 PRECAST CONCRETE
Precast concrete products are construction items usually
manufactured in a factory, off site or on site, and delivered
for installation into the structure. The precast members can
serve structural, architectural, or a combination of both
structural and architectural purposes. In the two latter
cases, the members are normally called ARCHITECTURAL PRECAST
CONCRETE components.
The standard precast components include pipes, catch
basins, and a variety of structural elements such as beam,
column, wall, floor and roof units.
Fig. 2-2 shows a chart describing the manufacturingprocess for precast concrete components.
-12-
Figure 2-2 Manufacturing process for precast concrete
components.
ADVANTAGES OF PRECASTING
a. The use of the most appropriate methods and equipment
in the factory result in consistently high quality
products and in an increase in productivity.
b. Close supervision, control of materials, and a
specialized work force in a centralized plant produce a
high quality product in a shorter period of time.
c. High quality products reduce the maintenance costs.
d. The need for trained and specialized labor on site is
minimized since the work is restricted to erecting and
jointing.
e. Structural members can be mass produced in a plant
while excavation and foundation works are taking place
at the site. Therefore, precasting considerably
reduces the time of construction.
f. Economy in the amount of equipment and formworks
needed.
-13-
g. Finishing work on concrete surfaces can be done in
various varieties and with better quality while being
easier and more efficient.
h. In most cases the need for scaffolding, shuttering and
other temporary supports will be minimized.
i. The production proceeds independent of weather
conditions.
All the above advantages result in a significant saving in
time and cost. Moreover, it is evident that the larger the
project, the more economical and suitable it is for
prefabrication. The number of identical units increases;
therefore, the cost of erection formworks, and designs
decreases.
CONSIDERATIONS AND LIMITATIONS OF PRECASTING
a. The structure should be composed of a small number of
different types of components.
b. The manufacturing should require little time.
c. The units should be so designed that variants of basic
types can be produced in the same mold.
d. The engineeral design, weight, size and shape of units
should allow an economical and practical handling,
transportation, and erection.
e. The components should be compatible in weight in order
to use the full potential of the cranes.
f. The connections should be simple and quick to
construct, in order to obtain speedy and continuous
erection.
-14-
g. The system should be able to limit the use of
scaffolding and other temporary supports.
h. The height of the structure should be within the
reaching limit of the available cranes.
i. The location of the precasting yard or factory should
be close to the construction site.
DISADVANTAGES OF PRECASTING
a. Often the units must be made larger or more heavily
reinforced than the cast-in-place equivalent because of
the free-ended condition.
b. Adequate provision must be made for the stresses which
precast units may face in demolding, handling,
transportation, and erection.
c. Camponents may be damaged or broken during handling and
erection.
d. The joints between members can pose the greatest
problem.
e. Precasting tends to be less suitable for small projects
or buildings with irregular features.
f. The size and weight of precast members must be
restricted.
g. Lack of monolithic continuity.
2.3.1 CONNECTIONS
The connections between precast members should be capable
of withstanding tension, compression, bending, shearing, or a
combination of any of the four without failure, excessive
deformation, or rotation.
-15-
Tension Connections can be made by one of the following:
a. Welding the projecting reinforcing bars.
b. Projecting of a reinforcing bar from one member into a
cast-in-place concrete section or a grout sleeve in an
adjacent member.
c. Bolting.
d. Post-tensioning.
Shear Connections between precast members can be made by
casting concrete against previously hardened concrete and tied
with steel projecting across the interface.
Compression Connections between precast members can be
made by filling the joint with concrete or grout.
2.3.2 FINISHES
Surface finishes can be formed mechanically, chemically,
by the pattern or texture of the mold, or by coating and
painting.
2.4 REINFORCED PRECAST TYPES
Reinforced precast components belong to three categories:
reinforced, pre-tensioned, and post-tensioned.
2.4.1 REINFORCED
There are two ways of reinforcing precast reinforced
concrete products:
1. Fiber reinforced. Typical fibers are steel, glass, and
synthetic. In this method any type of fiber is mixed
-16-
with concrete before being placed in the forms.
2. Normally reinforced. In this method the steel is
positioned in the form and the concrete is placed
around it. When the concrete has cured, the materials
(concrete and steel) will be bonded together and will
act as one. At least a major part of the
reinforcements in this type of unit is placed in the
same way as it might be in cast-in-place concrete
members.
2.4.2 PRESTRESSING THE CONCRETE-PRE-TENSIONED STEEL
In this method a certain tensile force is applied to the
high-grade continuous steels in the direction of spanning with
hydraulic jacks, before high-strength concrete is placed in the
form. When the concrete has cured and has reached a specified
strength, the tensile force is removed from the steel and
therefore the stress is transferred to the concrete through the
bond between them, and this causes the concrete to be
compressed. As a result, the prestressed concrete is able to
resist some tension; therefore, more load, longer span, or a
thinner cross-section can be achieved.
2.4.3 POST-TENSIONING THE STEEL
This method involves placing and curing a precast member
which is normally reinforced or prestressed and which also has
a number of ducts or conduits through which post-tensioning
-17-
strands or bars will be passed (Fig. 2-3). After the concrete
has reached a specified strength, the post-tensioning tendons
are inserted into the channels and anchored at one end and
stressed from the opposite end by a portable hydraulic jack.
After the member has gained the specified stress, the tendons
are anchored by a automatic gripping device. Thus, the steel
remains in tension and the concrete in compression.
Noncontinuous Channels for post-bearn tensioning tendons
Continuous beam
Figure 2-3 Channels for post-tensioning tendons.
Pre-tensioned or post-tensioned concrete has extended the
usefulness of reinforced concrete by making it more adaptable
to various needs. The main advantage of pre-tensioning or
post-tensioning is the elimination or reduction of the tensile
stresses in the concrete member by pre-compression. These
components, then, are by far more practical and economical than
normal reinforced concrete when they are used for bridges, long
spans, extending longer cantilevers, and controling
objectionable deflections while the cracks are eliminated.
Pre-tensioning has also suitable applications when
combined with precasting or semi-precasting such as composite
or lift-slab constructions.
-18-
ADVANTAGES OF PRE-TENSIONING
In prestressed concrete the employment of higher strength
materials and the applied stress load result in a smaller
cross-section for an applied load and the elimination of
cracks.
The smaller cross-section for members allows:
a. Saving in foundations, columns, and floor-to-floor
height.
b. Considerable reduction in the use of materials and thus
the reduction of weight, or dead load. This reduction
in the weight of the units mainly results in a saving
in time and in the costs of handling, transportation
and erection.
From the aesthetic point of view, the density of the
material causes a better surface finish for components. Also,
the smaller cross-section for members gives the structure a
lighter appearance.
DISADVANTAGES OF PRE-TENSIONING
The disadvantages of pre-tensioning include:
a. By its own nature the prestressed units have less
weight and mass. In situations where weight and mass
are required instead of strength, plain or reinforced
concrete could serve at a lower cost.
b. Prestressed units require more care in design,
construction and erection because of the higher
strength materials and smaller cross-section members.
-19-
PRE-TENSIONING OR POST-TENSIONING
The pre-tensioning technique is usually employed in a
plant where mass production of a particular shape, reqardless
of its longation, is required. In this system, the long
members can be produced without difficulty and without the
necessity of precise measurements of the elongation of the
tendons during stressing; the members can then be sawcut to the
desired length. In this method, a high initial investment cost
is required for purchasing the plant and required equipments.
On the other hand, the post-tensioning technique is
usually employed for long members. Post-tensioning is more
expensive than pre-tensioning. This is due to the large amount
of labor required in placing, stressing and grouting the
tendons and cost of the conduits and anchorage devices.
Sometimes, with age, post-tensioning members tend to maintain
their properties better than do pre-tensioning. Furthermore,
the post-tensioning method can be applied to smooth curves.
2.4.4 PRESTRESSING TYPES - CIRCULAR AND LINEAR
Circular prestressing is a term applied to prestressed
circular structures, such as round tanks and pipes, in
which the prestressing wires are wound around in circles. In
contrast to circular prestressing, linear prestressing is used
to include all other types of prestressing, when the cables are
either straight or curved, but not wound in circles around a
circular structure.
-20-
2.4.5 PARTIAL PRESTRESS REINFORCEMENTS
In contrast to the criterion of no tensile stress in the
member, which may be called "full prestressing," the method of
design allowing some tension is often termed "partial
prestressing." Mainly, there is no basic difference between
the two because while a structure may be designed for no
tension under working loads, it will be subjected to tension
under overloads.
Partial prestressing may be obtained by any of the
following methods:
1. Using the same amount of steel, but tensioning it to a
lower level, will give effects similar to those of
method 2 but no end anchorage is saved. Hence the
method is seldom used.
2. Using less prestressed steel and adding some mild steel
for reinforcing will give the desired ultimate strength
and will result in greater resilience at the expense of
earlier cracking.
-21-
2.5 PRESTRESSED STANDARD TYPES
Since prestressed components are being economically
manufactured and used, many standard types have been developed
to provide a greater saving in cost.
2.5.1 DOUBLE TEE
Double tees are used extensively for both roof and floor
constructions. In some applications they may also be used as
wall panels. Double tees are made in a variety of widths and
depths. A typical section of double tee slab is shown in Fig.
2-4. Double tee slabs are structurally efficient, especially
in the case of long spans. Large openings can be provided
within the width of flange between stems.
2" 8'0"5 3/4" 2
20" (varies)
4'1-0"L3 314
Figure 2-4 Double Tee.
2.5.2 SINGLE TEE
Single tees are used for heavy loading requirements and/or
long spans, ranging up to 120 feet or more. These units are
popular for exposed ceilings and where mechanical services are
-22-
channeled between stems for easy access. A typical section of
single tee slab is shown in Fig. 2-5. The section is one of
high structural efficiency and has been used extensively in
many areas of the country.
2-18-0 1 112"
36-' (varies)
Figure 2-5 Single Tee
2.5.3 SOLID FLAT COMPONENTS
Solid flat components include solid flat wall panels and
slabs in a variety of widths and thicknesses. Wall panels are
mainly used for partial, full-story, or multi-story heights for
either curtain wall or load-bearing use.
Solid flat slabs do not have an extensive use in this
country. Instead, hollow slabs and solid post-tensioned slabs
have been used to a very significant degree. A typical section
of solid flat slab is shown in Fig. 2-6. The principal
advantages of prestressed solid slabs are the low cost, better
quality, and more availability. The principal disadvantages of
prestressed solid slabs are the limitation in number of
standardized elements.
-23-
Width varies 2N
1 1/2" 8" (varies)
Figure 2-6 Solid flat slab.
2.5.4 HOLLOW-CORE COMPONENTS
The primary physical difference between this type of
element and solid flat components is the voids. Hollow-core
slabs are lighter and structurally more economical and
efficient. They can carry more load and/or span a longer
distance while having a small cross-section. A typical section
is shown in Fig. 2-7. Due to their low cost, these members
have a major application in housing, administrative, and public
buildings where flat ceilings and long spans are required.
While these specifications make it an ideal material for
slab, the lack of weight, mass, and the limited distance
between the floor-to-floor height (which prevents it from being
used as a long member) make it less practical and economical
for wall members.
4'-0"2"
1 12O ..O.... 8" (varies)
Figure 2-7 Hollow-core slab.
-24-
2.5.5 OTHER COMPONENTS
The other standard types of prestressed components are
beams, girders, columns, and piles.
The standard beams include rectangular beams, L-shaped
beams, and inverted tee beams.
2.6 COST OF COMMON TYPES OF STRUCTURAL CONSTRUCTION MATERIALS
To make a better comparison between the cost of structural
construction materials, the costs of prestressed standard types
and of other common types (such as cast-in-place concrete,
brick veneer with wood stud backup, and concrete block wall are
included.
The following prices are the cost estimates based on Means
Systems Costs, 1985 edition.
2.6.1 PRESTRESSED STANDARD TYPES
The following prices are based upon a 10,000 to 20,000
S.F. project and include the transportation cost for 50 to 100
miles. Concrete is normal-weight and f'c = 5 ksi and for
reinforcement Fy = 250 or 300 ksi, Tables 2-3 to 2-6.
-25-
Table 2-3 Precast double "T" beams.
Table 2-4 Precast single Tees.
-26-
3.5-230 Precast Double ""' Beems - No ToppingSPAN OBLE. "T" SIZE TOTAL LOAD COST(FT.) D (IN.) W (FT.) (P.S.F PER S.F
1500 30 18x8 92 5.421600 18x8 102 5.92700 18x8 112 5.92
1800 18x8 137 5.971900 188 162 5.972000 40 20x8 87 4.372100 20x8 97 4.652200 20x8 107 4.652300 20x8 132 4.782400 20x8 157 5.18
2500 50 24x8 103 4.382600 24x8 113 4.662700 24x8 123 4 762800 24x8 148 4782900 24x8 173 5.19
3000 60 24x8 82 4.78
3100 32x10 104 5.323150 32x10 114 5.143200 32x10 139 5.243250 32x10 164 5.583300 70 32x10 94 5.223350 32x10 104 5.243400 32x10 114 5.583450 32x10 139 5.883500 32x10 164 6.53
3.5-220 Precast Single Tees No ToppingSPAN SINGLE "T" SIZE TOTAL LOAD COST(FT.) D (IN.) W (FT.) (P S.F.) , PER S.F.
1950 60 36:8 104 6.252000 36x8 114 6.252100 368 124 6.252200 36x8 149 6.402300 36x8 174 7.05
2400 70 36x8 104 6.502450 36x8 114 6.502500 36x8 124 6.552550 36x8 149 7152600 36x8 174 7.20
'1 2650 80 48x10 111 7.752700 48x10 121 7.852800 48x10 131 0.202850 48x10 156 8.303000 48x10 181 8.30
3100 90 48x10 111 8.553150 48x10 121 8.753200 48x10 131 8.853300 48x10 156 8.903350 48x10 181 9.003400 :00' 48x10 il 8.903450 48x10 121 8.953500 48x10 131 9.103525 4810 156 9.153550 48x10 101 9.25
3.5-210 Precast Plank With No ToppingSPAN TOTAL TOTAL COSTFT DEPTH (IN.) LOAD (P.S.F.) PER S.F.
0720 .0 4 90 3.302750 6 125 3.29'770 6 150 3.29J800 5 6 90 3.29-820 6 125 3.290850 6 150 3.290875 20 6 90 3.290900 6 125 3.290920 6 150 3.290950 25 6 90 3.290970 8 130 3.40000 8 155 3.40:200 20995 3.40:300 8 130 3.40400 10 170 3.58
.500 40 10 110 3.58:600 12 145 3.94_700 45 12 110 3.94
Table 2-5 Precast plank.
Table 2-6 Flat precast concrete wall.
The costs of "T" beam and "L" beam are as
12" x 20" precast "T" Beam, 20' span is $2.82 per L.F.
12" x 20" precast "L" Beam, 20' span is $1.76 per L.F.
-27-
4.1-1401 Fat Pr mt ConcretePANEL RIGID COST
THICKNESS (IN.) SIZE (FT.) FINISHES INSULATION (IN.) TYPE PER S.F.
3200 6 5:18 smooth gray 2 ow rise 8.413250 6:18 7.203300 0x20 7193350 12x20 6.59
3400 8 5x18 smooth gray 2 low rise 9.123450 6:18 8.693500 0x20 7.973550 12x20 7.31
4000 6 4x8 white face none low rise 15.054050 8x8 11.42
4100 10x10 10.04
4150 _ _0xI 9.3
4200 6 4x8 white face 2 low rise 16.15
4250 8x8 12.57
4300 10x10 11.19
4350 20x10 9.23
4400 7 4x8 white face none low rise 1540
4450 8xe 11.82
4500 10x10 10.614550 20x10 9.69
4600 7 4x8 white face 2 low rise 16.504650 8x8 12.97
4700 10x10 11,71
4750 20x10 1084
4800 8 4x8 white face none low rise 15 74
4850 0x8 12.11
4900 10x10 10.90
4950 20x10 10.04
5000 8 4W8 wnite face 2 iow rise 16.89
5050 8W8 13.26
5100 10x10 12.05
5150 20x10 1119
follows:
2.6.2 CAST-IN-PLACE CONCRETE
The concete is normal weight and f'c =
re i nforceme nts
4 ksi and for
F'y = 60 ksi. Forms are for use, the finish
steel trowel, and curing is based on spraying on the membrane.
Tables 2-7 and 2-8.
aw-1so C.. Ft Ph"t_BAY SIZE MINIMUM SLAB TOTAL COST
(FT.) COLUMN SIZE (IN.) THICKNESS (IN.) LOAD (P.S.F.) PER S.F.
2000 15 x 15 12 5-1/2 109 5.562200 14 5-1/2 144 5.572400 20 5-1/2 194 5.702600 1 22 5-1/2 244 5.76
3000 15 x 20 14 7 127 5.913400 16 7-1/2 169 6.17
3600 22 8-1/2 231 6.523800 24 8-1/2 281 6.544200 20 x 20 16 7 127 5.914400 20 7-1/2 175 6.174600 24 8-1/2 231 6.515000 24 8-1/2 281 6.555600 20 x 25 18 8-1/2 146 6.49
6000 20 9 188 6.626400 26 9-1/2 244 6.996600 30 10 300 7.177000 25 x 25 20 9 152 6.61
7400 24 9-1/2 194 6.907600 30 10 250 7.17
8000 1 1 _
2-7 cast-in-place flat plate.COST PER S.F.
4.1-110 t In Place Concret MAT. INST. TOTAL2100 Conc wall reintorced. 8' high. 6" thick. plain fmish, 3000 P SI 2.26 6.75 9.012200 4000 P S.I. 2.31 6.75 9.06
2300 5000 PSI. 2.37 6.75 9.122400 Rub concrete I side. 3.000 P.SA 2.30 8 10.302500 4000 P.S.I. 2.35 8 10.352600 5000 P Si 2.41 8 10.412700 Aged wood liner. 3000 P SI 3.38 7 05 10.432800 4000 P SI 3.43 7.05 10.482900 5000 P S.I 3.49 7,05 10.543000 Sand blast light I side. 3000 P.S.I 2.35 7 35 9.703100 4000 P SI 2.40 7.35 9.753300 5000 P S.I 2.46 735 9.813400 Sand blast heavy I side. 3000 P SI 2.59 8.55 11.14
3500 4000 P S.I 2.64 8.55 11.193600 5000 P S I 2.70 8.55 11.253700 3/4" bevel rustication strip. 3000 P S.I 2.34 8.30 10.64
3800 4000 P St 2.39 8.30 10.693900 5000 P S.I. 2.45 8.30 10.754000 8" thick. piain tinisn. 3000 P SI 2.64 6.95 9.594100 4000 P S.1 2.72 6.95 9.674200 5000 P S.1 2.79 6.95 9.74
4300 Rub concrete i sine. 3000 P.SI. 2.68 8.20 10.884400 4000 P SA 2.76 8.20 10.9614500 5000 P S1 283 8.20 11.0314550 8" thick, aged wood liner. 3000 PS.I 3 76 7.25 11.014600 4000 P.S.I 3.84 7.25 11.094700 5000 P.S.I 391 7.25 11.164750 Sand blast hiht I side. 3000 P.S I 2 73 7 55 10.284800 4000 PS 1 281 755 10.364900 5000 P.SI 2,88 7 55 10435000 Sand blast heavy I side. 3000 P S 1 2.97 8 75 11.725100 4000 P.S.1 3.05 8 75 11.805200 5000 P.S 1 3 12 7075 11.875300 3/4" bevel rustication strip. 3000 P.S1 272 850 11.22
5400 4000 PS1 2.80 8.50 11.3V5500 5000 P'S 1 2.87 850 11.37
cast-in-place concrete wall.
-28-
Table
Table 2-8
2.6.3 BRICK VENEER/WOOD STUD BACKUP
Exterior brick veneer/stud backup walls are defined in the
following terms: type of brick and studs, stud spacing and
bond. All systems include a brick shelf, ties to the backup,
and all necessary dampproofing and insulation. Table 2-9.
Table 2-9 Brick veneer/wood stud backup.
2.6.4 CONCRETE BLOCK WALL
The following prices include horizontal joints
reinforcing, alternate courses, control joints, and insulation
in cases of hollow units. Table 2-10.
-29-
4.1-22 Brick Veneer/Wood Stud BackupSTUD STUD COST
FACE BRICK BACKUP SPACING (IN.) BOND PER S.F.100 Stanaard 2x4-wood 16 running 10.95
1120 common 11.901140 Flemish 13.461160 English 14.82
1400 2x6-wood 16 running 11.141420 common 12.091440 Flemish 13.651460 English 15.01
1500 24 running 10.881520 common 11.831540 Flemish 13.441560 English 14.80
4.1-211 Concrete Block Wall - Regular WeightSIZE STRENGTH COST
TYPE (I N.) (P.S.I.) CORE FILL PER S.F
1200 Hollow 4x8x16 2.000 none 3.55
1250 4500 none 3.921300 6x8x16 2.000 perlite 4.70
1310 styrofoam 4.59
1340 none 3.90
1350 4,500 perhte 5.11
1360 styrotoam 6.43
1390 none 4.31
1400 8x8x16 2.000 perite 5.411410 styrotoam 51440 none 4.311450 4.500 perlite 6.111460 styrotoam 5.701490 none 5.01
1500 12x8x16 2.000 perite 7.49
1510 styrotoam 6.621540 none 5.78
1550 4,500 peride 8.14
1560 styrotoam 7.27
1590 none 6.432500 Solid 4x8x16 2.000 none 3.812550 4.500 none 415
2600 6x8x16 2.000 none 4.32
2650 4,500 none 4.772700 8x8x16 2.000 none 4.87
2750 4,500 none 5.45
2800 12x8x16 2.000 none 6.68
2350 4.500 none 7.53
Table 2-10 Concrete block wall.
2.7 CONCLUDING DISCUSSION
In comparing the common types of structural materials, we
conclude that hollow-core slabs have the highest economical
advantages. While having the advantage of prestressing,
precasting and concrete, these slabs are light in weight and
have smooth surfaces. In addition, hollow-core slabs can be
manufactured in a standard fashion and used as long members.
From the point of view of cost, hollow-core slabs are the
least expensive type of flooring and roofing material. This is
because of their ease of manufacture, handling, erection and
efficiency in use of construction materials. In addition, the
-30-
manufacturing requires the least amount of labor and time in
comparison to other types of structural construction materials.
While these specifications make hollow-core components an
ideal material for slabs, the fact that they cannot be used as
long members make them less practical for wall members.
Therefore, this thesis presents ways in which these
deficiencies can be minimized and it's use for wall
panels be made more practical.
-31-
3.0 PRESENT APPLICATIONS OF STANDARD PRECAST
PRESTRESSED HOLLOW-CORE COMPONENTS
-32-
3.0 PRESENT APPLICATIONS OF STANDARD PRECAST PRESTRESSED
HOLLOW-CORE COMPONENTS
Hollow-core is a standard type of precast prestressed
concrete components. Hollow-core components have an economical
and speedy manufacturing procedure based on the use of machines
and equipment rather than labor. The members are produced in
long beds and sawcut to the desired length after they have
gained a sufficient strength. Normally for hollow-core
members, 3 men are required to produce 4 lines of 500' x 5',
while for other precast types 7 to 10 men are required to
produce 5 panels of 6' x 30'.
In addition, hollow-core components have small depth to
length and/or weight ratio when they are positioned under
tension. This mainly results from the use of high-strength
materials, the voids, and the applied stress.
3.1 HOLLOW-CORE SLAB
In comparison to all other types of flooring and roofing
systems (including prestressed standard types), the main
advantages of standard hollow-core slabs are the low cost, flat
surfaces, small thickness, and light weight. They also have
all the advantages of prestressing, precasting and concrete.
Typical voids in the slab may be of circular, oval, or,
sometimes, rectangular cross-section. The various
cross-sections are shown in Fig. 3-1 to 3-6. As a rule, the
voids run in the direction of the span. The ribs between the
ducts are sufficiently stiffed by the top and bottom plates to
make cross ribs superfluous.
-33-
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3.1.1 TYPICAL CONNECTIONS
During the lifetime of prestressed concrete hollow-core
slabs, many types of connections have been developed. The most
common type includes its connection to walls, beams,
nonstructural elements and to each other. See Fig. 3-7 to 3-11.
T _ d a
tgt tg
Premt wall panel
2 Rrbws between gapsfrom wail into topping
illow-core floor slab
Figure 3-7 Typical connection details of hollow-core slabstructural wall-Exterior joints.
to
d
Figure 3-8 Typical connection details of hollow-core slab tostructural wall-Interior joints.
-37-
Figure 3-9 Typical connection details of hollow-core slab tobeam.
Precast wall panel
Rebars fromwalls into topping
Welded wire fabric
iTop ping
Figure 3-10 Typical connection details of hollow-core slab toshear wall.
Hollow-coreGrouted key
Welded wire fabric
kO~ ~ .oooOO 0OOFigure 3-11
Hollow-core slabs--- -/
Typical connection details of hollow-core slabs toeach other.
-38-
r
3.1.2 COORDINATION WITH ELECTRICAL, MECHANICAL, PLUMBING,
SERVICES AND OTHER SUB-SYSTEMS
Prestressed hollow-core slabs are used in a wide variety
of building types. Therefore, it is important to have
economical and practical ways to integrate them with
electrical, mechanical, plumbing, services and other
sub-systems.
ELECTRICAL
Since a cast-in-place topping is usually placed on
prestressed floor members, conduit runs and floor outlets can
be readily buried within the topping (Fig. 3-12). The other
options are to run them along the beams or at the intersection
wall and floor. In the latter option the conduit runs and
outlets are positioned on the wall.
Figure 3-12 Under floor electrical ducts can be embedded
within a concrete topping.
-39-
MECHANICAL
There are two common ways of incorporating the duct work
within a hollow-core slab system:
1. Using the voids inside the slab. Additional openings
can be drilled in the field to allow the continuity of
the system.
2. Using a suspended ceiling. Large openings through the
floor and roof members are provided by block-outs in
the forms during the manufacture, Fig. 3-13:
Figure 3-13 Large openings in floors and roofs are made during
manufacture of the units.
PLUMBING SERVICE
To reduce the on-site time and labor, prefabricated
bathroom units or combinations of bathroom and kitchen modules
have been developed (Fig. 3-14). Such units can include
bathroom fixtures, kitchen cabinets and sinks, as well as wall,
ceiling and floor surfaces. To eliminate a double floor, the
module can be plant built on the structural members, with the
-40-
option of incorporating the prefabricated wet-wall plumbing
systems (Fig. 3-15). It is more practical and economical in
precast multi-story construction to locate the service units in
a stack fashion with one type of service directly over the one
below.
Figure 3-14 Kitchen/bathroom modules can be pre-assembled on
precast prestressed slab ready for installation
in systems buildings.
-41-
Figure 3-15 Prefabricated wet-wall plumbing systems
incorporate pre-assembled piping.
Some core modules not only feature bath and kitchen
components, but also HVAC components all packaged in one unit.
These modules can also be easily accommodated in prestressed
structural systems by placing them directly on the prestressed
members with shimming and grouting as required.
OTHER SUB-SYSTEMS
Suspended ceilings, crane rails, and other sub-systems can
be easily accommodated with standard manufactured hardware
items and embedded plates as shown in Fig. 3-16.
-42-
#
0 0
Figure 3-16 Methods of attaching suspended ceilings, crane
rails, and other sub-systems.
3.2 HOLLOW-CORE WALL
Even though precast prestressed hollow-core slabs are
widely used in the construction industry, they do not have many
applications as structural wall panels. This is mainly because
of the diversity in requirements of a floor and wall member.
The main disadvantages of hollow-core components as a wall
member include their lack of weight, mass and, in some cases,
their insufficient insulating qualities. They are also not
able to be used as long members in structure.
Hollow-core wall panels have been used in some structures
in 8' to 9' long members. The typical section includes
Dy-core, Dynaspan and Span-Deck, Fig. 3-1, 3-2 and 3-5
respectively.
3.3 COREWALL INSULATED WALL PANEL
Many attempts were made to standardize the manufacturing
of a practical and economical load bearing and non-load bearing
wall panels. As a result of these attempts, corewall insulated
-43-
wall panels were introduced in 1981 (Fig. 3-17).
G.E. SILPRUF SEALANT FOR 4 HOUR RATING,TREMCO DYMERIC SEALANT FOR 3 HOUR RATING
EXTERIOR POLYETHYLENE FOAMED ROD BACK-UP
8" COREWALL PRESTRESSEDCONCRETE PANEL WITH2" POLYSTYRENE INSULATION,1 LBiCU FT DENSITY
INTERIOR TREMCO CERA BLANKET.1/" MINIMUM DEPTH
TREMCO MONO SEALANT
Figure 3-17 Section through vertical joints.
The advantages of corewall panels are the fact that the
members can be mass produced in a standard fashion and can be
used in long members, while achieving high insulating
qualities.
The main disadvantages of the corewall insulated panels
include the following:
a. The height of the building is limited. The maximum
practical lengths for 8" and 10" thick corewall panels
are 26' and 32' respectively. Therefore, the building
can be only about two to three stories height.
b. Most of the roof and intermediate floor loads are
transferred to the "I" shape steel columns through the
steel "I" beams, instead of the structural wall panels.
Fig. 3-18 and 3-19. In addition, the steel members
have to be fireproofed.
-44-
8" Corewall panelInsulation
6" slotted insert
- Strap anchor/ welded to beam
- Erection "10"clip (tenporary)
Rib -' * 1 Min.
Alternate location-D Rof connection
STANDARD RIB
Figure 3-18 Typical corner Figure 3-19 Typical top
detail. connection.
C. The production of a panel is done in three steps and
all the connections have to be inserted into the wall
panel .
d. Limited flexibility exists in the location of openings
since the panels come in 8' wide modules and special
panels should be designed individually for each
opening which varies in dimension.
Corewall panels are not suggested for load bearing or a
shear wall. They are best used for curtain wall applications
or to carry light roof loads under certain conditions.
-45-
4.0 NEW APPLICATIONS OF STANDARD PRECAST
PRESTRESSED HOLLOW-CORE COMPONENTS
-46-
4.0 NEW APPLICATIONS OF STANDARD PRECAST PRESTRESSED HOLLOW-
CORE COMPONENTS
In general, structural prefabricated floor and wall
panels can be classified in three degrees of diversity (Fig. 4-la):
1. The floor and wall panels differ from each other in
basic shape, cross-section, and in their production
demands, and they require separate formwork and
different technology.
2. The floor and wall panels each have variations in
length or width, but their variations can be cast by
the same method and using the same formwork.
3. The floor and wall panels each have variations in the
internal details, but their variations do not affect
the basic sizes or production methods (incorporating
window openings, surface treatment, etc.).
This thesis presents another degree of diversity, for
structural prefabricated panel units (Fig. 4-lb) which is:
-The floor and wall panels do vary in length or width
(4' or 8' modulars) but they can be cast by the same
method and using the same formwork.
The first degree of diversity essentially affects the
capital expenditure while the second and third degree dictate
the organization of production, storing and erection. In
addition, the third degree affects the capital expenditure as
well.
-47-
The new degree of diversity will minimize the capital
expenditure, but it will require some degree of organization in
storinq and erection.
Figure 4-la Three degrees of diversity for prefabricates.
Figure 4-lb The new degree of diversity for prefabricates.
In the earlier chapters the advantages of standard precast
prestressed concrete hollow-core slabs were analyzed. This
chapter introduces two systems in which this component and its
-48-
modification can be used practically and economically as
structural floor and wall panels while maintaining those
advantages.
4.1 SYSTEM 1 - REQUIRED STRUCTURAL COMPONENTS
The essential components of this system include the
following:
4.1.1 HOLLOW-CORE SLAB
Two types of hollow-core slabs are required.
1. Standard prestressed hollow-core slab, Fig. 4-2.
voids
prestressed bar
.0.0. .0.0 .0.0.00.0L8'-0''
Figure 4-2 Hollow-core slab.
2. Partially prestressed hollow-core slab with
post-tensioning conduits, Fig. 4-3.
Post-tensioning conduit Prestressed bars
0o nd uit s.
The manufacture of this component can be done using the
same method and equipment as the standard prestressed
hollow-core slab in Fig. 4-2. The only differences in the
-49-
members are the replacement of four prestressing strands and
two voids with two post-tensioning conduits. The applied force
-which may be partial- to the prestressing strands should be
capable of handling the weight of the unit, and hence the
cracks are eliminated during the handling and erection of the
component.
4.1.2 HOLLOW-CORE WALL PANEL
The wall panels can be made in the same form and by a
manufacturing method similar to that used for standard
prestressed hollow-core slabs. However, three modifications
are required in order to be able to use hollow-core slabs
practically and economically as wall panels (Fig. 4-4):
holes for post-tensioning/rods to pass through prestressed bars
ino:oo: :00: :oo.il o08'-0"
Figure 4-4 Hollow-core wall panel-Section.
1. Prestressed tendons should be added at the top of the
slab and some being eliminated at bottom during
manufacturing in order to secure symmetrical forces in
the cross-section of the unit.
2. Some or all voids should be eliminated in order to
achieve a more solid section for compressive forces.
Two of the eliminated voids in the wall panel should be
perpendicular to the post-tensioning conduits in the
floor panel.
-50-
3. Holes should be provided to enable the slab's
post-tensioning rods to pass through. The holes can be
drilled in the factory after manufacturing.
The walls can be put beside each other, vertically, in two
basic patterns:
a. The height of wall panels should be equal at each level
of erection (Fig. 4-5).
b. The height of every other panel should vary in one
story increments. This method adds support and
rigidity when construction continues in height. Fig.
4-6.
CN'
CN 0
Figure 4-5 Wall panels have equal
heights at each
level of erection.
'-4
0
.4-JV)
Figure 4-6 The height of
every other wall
panel vary in one
story increments.
4.1.3 PRECAST "L" BEAM
A vital component of this system is the precast "L" Beam
(Fig. 4-7). The function of these beams are as follows:
1. Provide a temporary bracing for prestressed concrete
wall panels at different stages of erection.
2. Align prestressed concrete wall panels when positioned
in place.
3. Provide a bearing support for prestressed floor slabs.
-51-
4. Allow openings between wall panels.
5. Increase the overall lateral rigidity.
hole is pre-drilledin the factory
Figure 4-7 Precast "L" beam.
Because the precast "L" beams are connected by the
post-tensioning rods to the wall panels, holes should be
provided through the beam. Moreover the holes have to be
aligned with holes in prestressed wall panels and thus with the
placement of post-tensioning conduits.
4.1.4 PRECAST SUPPORT ELEMENTS
The function of support elements is to support the
continuous precast concrete beams both during erection and
permanently. Fig. 4-8 shows a typical precast support element.
These elements are placed perpendicular to the wall panels and
"L" beams.
-52-
4 -Dowel for aligment &U placement of upper panel
00Holes for bolting the concreteduring erection
4 -Width of adjacent wall panel
Width of concrete beam
-4
U
0
-)For connecting the. -support panel below
\-Width of adjacent member
Figure 4-8 Precast support element.
4.1.5 SEQUENCE OF ERECTION
It is assumed that the foundation walls, or the footings
of the foundations, have been casted and have reached
sufficient strength:
1. The prefabricated concrete support elements are placed on
top of the foundation walls and grouted. The elements
are placed perpendicular at both ends of the forthcoming
beams and load-bearing wall panels.
2. The prefabricated concrete beam is hoisted on the
designed ledges of the support panels and bolted.
3. The prestressed concrete wall panels are placed in a
sequential order on top of the foundation walls and then
grouted. The concrete beam acts as a lateral support for
the panels. The lengths of the panels can vary in
one-story increments that are staggered at the top ends
of the panels to add support and rigidity when
-53-
construction continues in height.
4. The temporary supports are connected for the erection
of the slabs to the wall (See Fig. 4-9).
Drypack or epoxy grout
Prestressed hollow-core slabPost-tensioning rod
Post-tensioning conduit
4. - * .For erection only- a I
-Prestressed bar
" IL " I bea m o
Figure 4-9 Floor to bearing wall connection- Detail A.
5. After the partially prestressed concrete floor slabs
have been placed on the temporary supports, the rods
are inserted into the two post-tensioning conduits
within the slab and is tensioned against the beam (Fig.
4-9). The cross-section area of each post-tensioning
rod is equal to the total cross-section area of the two
eliminated prestressing bars. In addition, the
reinforcing steel bars should be inserted between every
keyway and grouted.
6. The standard prestressed concrete floor slabs should be
placed on the "L" beams (Fig . 4-10). Reinforcing steel
bars should be inserted between every keyway and
grouted.
-54-
Prestressed wall panel
Prestressed Hollow-corefloor panel w/ post- Standard prestressedtensioning conduits. hollow-core slab
Precast continuous"L" beam
Figure 4-10 Typical section.
The procedure of erection can continue in the same
fashion.
4.2 SYSTEM 2 - REQUIRED STRUCTURAL COMPONENTS
In this system the floor slabs are standard prestressed
hollow-core. The wall panels are typically manufactured by the
same method as introduced in 4.1.2. The major differences are
the placement of infilled voids and drilled holes. Fig. 4-11
and 4-12. The holes are drilled perpendicular to the center of
infilled voids. The holes are used to boltthe precast beams to
the wall panels and therefore provide a support (the beam) for
the floor slabs. The precast beams are rectangular.
Furthermore, in this method reinforced concrete support panels
are also used to support the beams during erection. The
support beams have two ledges on the sides for supporting a
precast beam on each side.
-55-
Grouted Ve
PrestressWall Pane
Prestress
Grouted J
IV. .----------------- f H igh-S tre]|- "-- - --- " " '''' S teel Bo l
- #3 Rebarnto Keyw
rt. Keyway
ed Conc.I
ed Tendonoint
ength
Grouteday
Figure 4-11 Typical connection of
floor slabs to load-
bearing wall panel.
Figure 4-12 Section through load-
bearing wall panels.
4.3 ADVANTAGES AND DISADVANTAGES
The principal advantages of using homogeneous components
for floor and wall units are that one standard method and
technique can be used for manufacturing and that there is a
significant saving in the cost of equipment and formworks.
The principal advantage of the new systems is that the
wall members can have all the advantages of standard precast
prestressed concrete hollow-core slabs -- including the
advantages of standardization, precasting, prestressing,
-56-
concrete and hollow-core slabs -- while meeting the
requirements of a wall member. In addition, the wall panels
can be used as long members, up to 3 or 4 stories in height,
and the need for bracing and scaffolding is minimized.
A major disadvantage of hollow-core components is the lack
of high insulating qualities for exterior wall members. This
problem can be solved in the new system as shown in Fig. 4-13.
Prestressed Face brickhollow-core slab --
Rigid insulation
1Alb -- Continuous conicrete beam
For post-tensioning rods
Prestressed wall panel....... Prestressed bar
Rebar grouted into keyway
Figure 4-13 Optional exterior finish-Detail B.
In case of openings in system 1 an additional member
should be placed in the cavity between the cross-section of the
floor panels and the continuous beam.
-57-
5.0 EFFECTS OF THE NEW SYSTEMS ON HOUSING,
ADMINISTRATIVE AND PUBLIC BUILDINGS
-58-
5.0 EFFECTS OF THE NEW SYSTEMS ON HOUSING, ADMINISTRATIVE,
AND PUBLIC BUILDINGS
5.1 HOUSING
In no other sector of the building industry has
industrialization became so urgently necessary as in
residential building contruction. The reasons for
industrialization are both economical and social. The
economical reasons include the following present conditions:
a. Small productivity per man-hour and high wages;
b. The man-power shortage;
c. The shortage of housing accommodation. As in many
countries, the output of housing is not keeping pace
with the increase of population.
The social reasons include the following:
a. The need to provide better working conditions;
b. The permanent place of work which is sheltered from the
weather and unaffected by the seasonal variations.
The major concern about using prefabricated components has
always been to avoid rigidity in planning and to provide
variety and flexibility. In cases where some flexibility and
variety in the plan were accomplished, the system failed to be
economical.
The new system's incorporation of large members produces
large volumes and a high degree of flexibility in space for
planning while remaining economical. Since the system is based
-59-
on an open-plan space in a variety of dimensions, the
interiors, except the location of services, can be custom made
in order to satisfy a variety of plans and wishes.
5.2 ADMINISTRATIVE AND PUBLIC BUILDINGS
Multi-story buildings used for industrial purposes present
a very wide range of variety. Because live loads, spans and
story heights vary considerably, different structural solutions
may be applied. It is possible, however, to establish some
basic principles.
Multi-story industrial buildings are characterized by
heavy live loads, large story heights and, in general, a
relatively small number of stories. On the other hand, in
administrative buildings (office buildings) the live loads
seldom exceed 75 lb/SF, the story heights are not more than 12
ft., and there are often a large number of stories. Public
buildings, particularly school and university buildings, have
generally the same live loads and story heights as
administrative buildings, but seldom have a large number of
stories.
Thus, public buildings occupy an intermediate position
between industrial buildings and residential buildings as far
as their structural solution with prefabricated components is
concerned.
On the other hand, it should be noted that public buldings
are often very large projects and that developments in
-60-
prefabricated construction techniques for such buildings are
extremely rapid and economical.
The new system, which can provide relatively large areas
without intermediate columns or walls, allows a fair degree of
versatility in the manner in which the space is utilized. For
example, thus it permits a layout as open-plan offices of
single-zone type (offices on one side of a corridor) or of the
double-zone type (offices on both sides of a central corridor).
5.3 DESIGN EXAMPLE
The following plan and section, Fig. 5-1 and 5-2, are
analyzed in terms of variations in the dimension of the units
and the total cost of the building. The building is based on
4' or 8' x 34' slab modulars and 24' depth of a typical living
unit.
C -
34'-'' lyp. Typ. Typ. -4'-'I170'-0"
Figure 5-1 Design example - Plan.Prestressed hollow-coreslab w/ p.t. conduits
Standard prestressedhollow-core slab Detail A Detail B
$-404--j
Cn
U-)
Figure 5-2 Design example - Section.
-61-
5.3.1 VARIATIONS IN UNIT DIMENSIONS
1. Considering the width between two structural walls or
34' width of the slabs (Fig. 5-3).
24' Depth x 34' Width = 816 S.F. Area
34'-0"
Figure 5-3 Considering the width between two structural
walls.
2. Considering the width between three structuarl walls,
or 2 x 34' width of the slabs (Fig. 5-4a and 5-4b).
a) 24' Depth x 68' Width = 1632 S.F. Area
I .
34'-0' 34'-"68'-0"
Figure 5-4a Considering the width between three structural
walls.
b) 24' Depth x 20' Width and 24' Depth x 48' Widthto
24' Depth x 25' Width and 24' Depth x 43' Width
which is:
480 S.F. Area and 1152 S.F. Areato
600 S.F. Area and 1032 S.F. Area
-62-
Therefore the area of units range from 480 S.F. to 600
S.F. and 1152 S.F. to 1032 S.F.
34'-9".20'-0"1. 5' 9'-Q" 34'-O'
43' to 48'2F'to 25'e
Figure 5-4b Considering the width between three structural
walls.
3. Considering the width between four structural
3 x 34' width of the slabs (Fig. 5-5).
24' Depth x 43' Width and 24' Depth x 39'to
24' Depth x 39' Width and 24' Depth x 43'
which is:
walls, or
Width
Width
1032 S.F. Area and 1416 S.F. Areato
1416 S.F. Area and 1032 S.F. Area
Therefore the area of the units range from 1032 S.F. to
1416 S.F.
, 34'-0"
34'-0" , 16' . 9', 34'-0"
II43' to 59'
43' to 59'
Figure 5-5 Considering the width between four structural
walls.
-63-
Based on 4' or 8' x 34' slab modulars and 24' depth of the
units, then, the following sizes and ranges can be achieved:
480 S.F. to 600 S.F., 816 S.F., 1032 S.F. to 1416 S.F.,
and 1632 S.F.
It should be also mentioned that the location of
partitions between units can vary on each floor; therefore,
different sized units can be achieved at each floor.
5.3.2 COST ESTIMATE
The assumptions for calculating the cost of a typical
building based on system 1 and Fig. 5-1 and 5-2 are as follows:
Building type = Residential
Building height = 5 stories
Cost of hollow core components (from table 2-6) = $3.50 /S.P.
Cost of precast "L" beam = $1.80 /L.F.
Cost of support panels for 2' x 9' @ 3.75 S/S.F. = $67 /each
It should be mentioned that the cost of the components
includes transportation and erection costs.
Total floor area = 56' width x (34' x 5) length x 5 no.
of stories = 47,600 S.F.
Total wall area = 56' width x (9' x 5) height x 6 no.
of walls - (8' width x (9' x 5)
height x 7 no. of omitted walls)=
15,120 S.F. - 2,520 S.F. = 12,600 S.F.
Total floor and wall area = Total area of hollow-core comp-
onents required = 47,600 S.F. + 12,600 S.F. = 60,200 S.F.
(1)
(2)
(3)
-64-
therefore:
Total cost of hollow-core components=60,220 S.F.x $3.5 /S.F.=
$210,700 (4)
Total cost of precast "L" beams = 56' length x 6 no. at
each floor x 5 stories x 1.80 $/L.F.= $ 3,024 T $ 3,000 (5)
Total cost of support panels = 24 no. at each floor x
5 stories x 6 7 $/each = $8,040 * $8,000 (6)
Total cost for post-tensioning the tendons = (72 at each
floor x $11 a piece for reuseable grip devices x 1/2 since
it is reusable) + $595 hydraulic RAM = $991 m $1000 (7)
Therefore, the total cost for structure, not including the
foundation and slab on grade cost, of a 5 stories and 47,600
S.F. is:
(4) + (5) + (6) + (7) = $210,700 + $3,000 + $8,000 + $1,000 =
$222,700 (8)
Consequently the cost of the structure per square foot is:
(8) : (1) = $222,700 : 47,600 S.F. = $4.67 /S.F.
The cost for the usual reinforced precastpanel is $18 per S.F. and
for the cast-in-place concrete floor or wall is about $8 per S.F.
-65-
5.4 VARIATIONS OF PLANNING
Several variations of planning with this system are schem-
atically shown in this section.
Direction of spaning
I I I
II
Direction of spaning
-66-
.
'a a
-1~ aI a
I a
I a
a--i
a S* II I
L
I-
a a
* a
a aa I
---. 5
-67-
6.0 CONCLUDING DISCUSSION
-68-
6.0 CONCLUDING DISCUSSION
The recommended systems makes it possible to incorporate
large members horizontally (floors) as well as vertically
(walls). Therefore, large areas or volumes can be provided
with a high degree of flexibility in space for planning.
In addition, using the same method of manufacturing for
both floor and wall members will minimize the capital
expenditure mainly by saving in the cost of formworks and
equipment. Moreover, by developing an appropriate floor-to-
bearing wall detail connection, wall components can be
manufactured and erected in long members. This will increase
the level of productivity in the plant and the speed of
erection at the site. Further, since the components (floor and
wall) are compatible in weight, the cranes are used to their
full potential.
Above all, the recommended structural systems are is
considerably lower in cost.
-69-
REFERENCES
-70-
REFERENCES
1. ACI Committee 506. "State-of-the-Art Report on FiberReinforced." Concrete International (December,1984), pp. 15-27.
2. Cornell University, Center for Housing and EnvironmentalStudies. The New Building Block. CornellUniversity, 1968.
3. Glover, C.W. Structural Precast Concrete. C.R. BooksLimited, 1965.
4. Hartland, .A. Design of Precast Concrete. Halsted Press,1975.
5. Herubin, C.A. and Marotta, T.W. Basic ConstructionMaterials. Reston Publishing Company 1981.
6. Hornbostel, C. Materials for Architecture. ReinholdPublishing.
7. Klitsikas, M. State-of-the-Art Report on High-StrengthConcrete. Master's Thesis. Department of CivilEngineering, Northeastern University, 1985.
8. Koncz, T. Manual of Precast Concrete Construction Vol. 1,2, and 3. Bauverlag GmbH, 1971.
9. Lewicki, B. Building with Large Prefabricates. ElsevierPublishing Company, 1966.
10. Libby, J.R. Modern Prestressed Concrete. Van NostrandReinhold Company, 1977.
11. Lin, T.Y. Design of Prestressed Concrete Structures.John Wiley and Sons, Inc., 1955.
12. Lin, T.Y. and Kelly, J.W. Prestressed Concrete Buildings.Gordon and Breach, 1962.
13. Lonestar/San-Vel. Corewall Insulated Wall Panel Catalog.Lonestar/san-vel, 1981.
14. Lay, T. "Concrete." Fine Homebuilding, 1943.
15. Means, R.S. Means System Costs. Means PublishingCompany, 1985.
16. Morris, A.E.J. Precast Concrete in Architecture.Whitney, 1978.
-71-
17. PCI. Architectural Precast Concrete. PrestressedConcrete Institute, 1973.
18. PCI. Manual on Design of Connections for PrecastPrestressed Concrete. Prestressed Concrete Institute,1978.
19. PCI. Manual for Quality Control. Prestressed ConcreteInstitute, 1968.
20. PCI. Manual for Structural Design of ArchitecturalPrecast Concrete. Prestressed Concrete Institute,1977.
21. PCI. PCI Design Handbook. Prestressed ConcreteInstitute, 1978.
22. Proceedings of May 1967 Symposium. Design Philosophy andits Applications to Precast Concrete Structures.Cement and Concrete Association, 1968.
23. Simonic, L. The Development of an Alternative BuildingSystem. Master's Thesis, Department of Architecture,MIT, 1984.
24. Smith, R.C. Materials of Construction. McGraw-Hill BookCompany, 1979.
25. Society for Studies on the Use of Precast Concrete.Precast Concrete Connection Details Structural DesignManual. Beton-Vertage GmbH, 1978.
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