Building Technology - Floors

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Building Technology Floor Types and Finishes

FLOORS

- The functional requirements of floors are:

1. Strength and Stability- Depends on the characteristics of materials used for thestructure of the floor.

2. Considerations- A floor must be strong enough to safely support dead loads, finishes,partitions and services.

3. Resistance to the Elements- Should be able to resist weather especially moisture andtemperature.

4. Durability- Floors should be durable and have a low maintenance requirement for theirexpected design life.

5. Fire Safety- Floor structures should be able to resist fire for an adequate amount oftime (0.5 to 4 hours) to provide sufficient escape of occupants.

6. Resistance to Passage of Heat- In certain instances, floor structures should be able toresist heat transfer between two vertically stacked spaces.

7. Acoustic Integrity- Floors should act as a sufficient barrier to the passage of sound.Floor thicknesses and eventual sound absorbent material finishes can take this into

account.

GROUND SUPPORTED CONCRETE FLOORS

- The functional requirements of ground supported concrete floors are:

Withstand loads, e.g. People and Furniture Prevent moisture penetration by using a damp-proof membrane (D.P.M.) Reduce heat loss into the ground below Be durable and reduce maintenance costs Provide acceptable surface finish

- Ground supported concrete floors are composed of various layers as follows:

1. Hardcore Layer2. Damp Proof Membrane (D.P.M)3.

Concrete Base

4. Cement Screed

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1. Hardcore Layer- Used to fill hollows raise finished level of a slab.

- On wet sites, it provides a firm working surface.

- The best hardcore has hard, durable and chemically inert particles, e.g. Brick, Gravel or Quarrywaste.

Fig. 1: Hardcore Fig. 2: Hardcore on Site

2. Damp Proof Membrane (D. P. M.)- Must be impermeable to water and moisture and tough to remain undamaged when laying

screed and finish.

- D.P.M. can be located below screed or below concrete base.

- Materials usually used as D.P.M. include Nylon, Mastic Asphalt or Bitumen Sheets.

Fig. 3: Damp Proof Membrane on Site

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3. Concrete Base- Composed of concrete mix of cement, sand and aggregate to ratio 1:3:6

- Minimum thickness of 100 mm.

Fig. 4: Concrete Base

4. Cement Screed- Provides level surface to which a floor finish can be applied.

- Composed of cement, sand and water, thoroughly mixed and spread over the concrete base.

- It is then compacted and leveled to a smooth finish.

- Thickness depends on the surface on which the screed is laid.

- The mix shrinks as it dries and the thinner the screed, the more rapidly it dries and the more it

will shrink and crack.

Fig. 5: Cement Screed Fig. 6: Cement Screed Trowelling

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Fig. 7: Ground Supported Concrete Floor Section

SUSPENDED CONCRETE FLOOR SLABS

- There are occasions where due to the ground conditions that a suspended floor is needed

rather than a ground bearing slab.These instances include:

When soil has a low bearing capacity On sloping sites On soils containing aggressive chemicals and On soils with high water levels.

- A steel reinforced concrete slab is used. It may have thicknesses ranging between 100-500

mm.

- A concrete slab may be supported on foundations or directly on the subsoil that makes the

ground floor.

- Other properties of suspended concrete floor slabs:

These are robust and very quick and easy to lay Do not require highly skilled labor for their installation

- They consist of a series of inverted T-shaped reinforced concrete beams, spaced at regular

intervals, with concrete blocks placed in between them to create the main floor surface.

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Fig. 8: Suspended Concrete Floor

Fig. 9: Suspended Concrete FloorSection

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SUSPENDED TIMBER GROUND FLOOR

- This is a floor suspended above ground level. The floor is suspended to prevent the timber

floor from coming into contact with water or moisture. They are common in domestic dwellings

which incorporate timber floors.

- For decking of timber floors, the following materials are commonly used:

Floor grade chipboard Softwood T&G boards Plywood sheets

- The different types of supports for suspended timber floors are the following:

Building into external load-bearing wall Sleeper walls Joist hangers



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- Consists of a series of joists arranged parallel to each other supported on their ends with

sleeper walls and along their length by honeycomb sleeper walls. The sleeper walls are placed

to support the joists which are designed to carry any dead loads (the self-weight of the floor)

and any live loads.

Fig. 12:Joist Supported on Wall Hangers

Fig. 13:Joists Meeting on Internal Load Bearing Wall

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REINFORCED CONCRETE UPPER FLOORS

- They have a better resistance to fire as compared to timber upper floors.

- They are of different types:

1. Self-centering T-Beams and Infill Blocks2. Hollow Beams Floor Units3. Reinforced Concrete and Clay Block Floors4. Monolithic Reinforced Concrete Floors

1. Precast T-Beam & Infill Block- Used for comparatively small spans and load capacities.

- A concrete topping is added for a greater bearing capacity by spreading the loads over beams

and infill blocks.

Fig. 14: Pre-cast T-Beam Fig. 15: Concrete In-fill Block

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Fig. 16: Pre-cast T-Beam and In-fill Block

2. Hollow Beam Floor Units- Here, reinforced beams are pre-cast around inflatable formers to produce hollow cross-sectional units.

- The sides of the concrete beams are indented to provide a key for concrete topping. To

transfer and distribute point loads, a layer of constructional concrete is included.

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Fig. 17: Hollow R.C. Floor Beam

3. R. C. and Clay Block Floor- Resistance to fire of a reinforced concrete floor depends on to the cover of reinforcement. The

thicker the cover to reinforcement, the higher the fire resistance and vice versa.

- If instead of concrete; pieces of burnt clay are cast between the reinforcing bars; the floor

obtains a better resistance to fire. This principle is applied in this floor system.

Fig. 18: Hollow Clay Block Floor

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4. Monolithic R. C. Floor- This is the traditional way of constructing reinforced concrete floors. Temporary formworks or

centering is required.

- Steel reinforcement is raised 20mm above the formwork by the use of concrete spacers thatare tied using binding wires.

- Concrete is then poured, compacted and leveled.

Fig. 19: Monolithic R.C. Floor Section

Fig. 20: Monolithic R.C. Floor Plan View

REINFORCEMENT

STEEL

STEEL

REINFORCEMENT

BARS

STEEL REINFORCEMENT

BARS

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TIMBER UPPER FLOORS

- Timber floors are basically made of joist as the primary structural members. The style of

construction of upper floors has not altered significantly over a long period of time, as it is a

series of joists supporting a floor covering with a finish on the underside Traditionally the joists

were rectangular sections of solid timber spaced at regular intervals, these being built into the

external wall, this either being solid or the inner leaf of a cavity wall. Later timber joists were

supported on joist hangers. The traditional timber joist has fairly recently been replaced with

prefabricated timber joists, some of which also include sections of galvanized steel. These joists

utilize the principle of structural economy by reducing the amount of material within the joist

to a minimum.

Fig. 21:Joists nailed to hangers Fig. 22:Joists built into wall

Strutting Systems

- Upper floor joists are required to span greater distances than ground floor joists and therefore

the depth of the joists will be greater making them more susceptible to lateral or sideways

movement or buckling. This problem can be resolved by providing a means of restraint called

strutting. There are three main types of strutting namely: Solid timber strutting; herring bone

timber strutting and galvanized steel strutting.

Fig. 23: Strutting

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- There are three main types of strutting that can be used:

1. Solid Timber Strutting- The struts are cut from short ends of joists and can be fixed flush with the top and bottom of

the joists or reduced in size to approximately two thirds of the joist depth. This form of strutting

tends to become loose when the timber shrinks making it less efficient.

Fig. 24: Solid Timber Strutting

2. Herringbone strutting- This type of strutting is very effective since it tightens when the joist shrinks. It is kept below

the level of the floor and to assist nailing and prevent the ends of the struts splitting.

Fig. 25: Herringbone Strutting

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3. Galvanized strutting- This is an alternative to timber herringbone strutting. This metal strut is shaped and designed

so as not to buckle and is fixed in a similar way to timber herringbone strutting.

Fig. 26: Galvanized Strutting

SUPPORT SYSTEM FOR TIMBER UPPER FLOORS

- There are two support methods: The Wood joist system and the Wood plank and beam

system. In the wood joist system, one should use relatively short spans for subflooring,

underlayment, and for the applied ceiling. As for the wood plank and beam, concentrated loadsand floor openings may require an additional framing.

- These two flooring systems have their member installed in two different ways. As shown

below:

Fig. 27: Wood Joist System Fig. 28: Plank and Beam System

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Spaced Beam

- The built-up wood beam and spaced wood beam too, are better than the single solid beam

since they possess a greater dimensional stability.

- When steel beams are used to support the wood planks and joists,a member known as theSCAB is introduced. A scab serves the following purposes:

Ties the joists together Maintains horizontal continuity of the floor structure Supports the sub-floorWood beams mainly use joist hangers. They may use a scab too as shown below:

Fig. 29: Spaced Beam

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- The beams and joists are subsequently connected to the columns in the following ways:

Fig. 30: Connections of Beams and Joists to Columns

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FLOOR FINISHES

1. Cement Screed- It is low-cost.

- Usually used where considerations of ease of cleaning are not of high importance, e.g. garages

and stores.

Fig. 31: Cement Screed Portion

2. Granolithic Paving Screed- Used for factories, stores or garages as it withstands heavy wear.

- Composed of cement, sand and crushed granite particles at a ratio of 1:1:2 which is mixed

with water.

- It is expensive.Non-slip finish can be obtained by sprinkling Carborundum.Colored finish can

be obtained by using pigmented cement.

A minimum of 7 days is provided for curing.

Fig. 32: Granolithic Paving Screed

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3. Fibre Reinforced Screed- This is cement screed reinforced with polymer fibre.The fibre reinforces screed against drying,

shrinking and cracking.

Fig. 33: Fibre Reinforced Screed on Site

4. Anhydrite Floor Finish- Anhydrite is a mineral product obtained from heating gypsum.It is then mixed with water and

sand, where it acts as cement to bind sand grains into a solid mass. It readily combines with

water. It is therefore not suited for damp situations, e.g. kitchens and bathrooms as it readily

absorbs water. It does not shrink or crack as it dries up. It can be pigmented to obtain different

colors.

5. Epoxy Resin Floor Finish- Provides a highly decorative and versatile resin floor finish for showrooms, offices, swimming

pools surrounds as well as in the home.It has an open structured surface which contains

countless pores filled with air. It is resistant to wear.

Fig. 34: Epoxy Resin Floor Finish Fig. 35: Epoxy Resin Finish on Stairs

Fibres

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6. Mastic Asphalt Floor Finish- It has damp-proof properties and hard wearing qualities.

- Mastic asphalt can be quickly installed using a hot charge process, and it cools very rapidly.

- Once installed, mastic asphalt offers a quality, dust free, seamless and user-friendly surface

especially with places with high traffic.

- Mastic asphalt also provides the ideal base for carpet, vinyl or other types of smooth flooring.

7. Flexible Sheet and PVC Tiles- The primary components of PVC are crude oil and rock salt.Additives are added to it to

improve its qualities. These include pigments, fillers, plasticizers, stabilizers and polymers. It

formed into solid sheets of by heat and pressure. It is applied to smooth, leveled sub-floor using

specially formulated vinyl adhesive or tile mastic.

- PVC is used for flooring in high traffic areas due to its durability, low cost installation and

maintenance.

- PVC flooring comes in a wide variety of patterns and textures. Designs are printed onto the

sheets and a clear laminate layer is added onto it to seal the design. It also makes the surface

easy to clean.

Fig. 36: PVC Tiles at Box TV Room

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8. Linoleum- It is manufactured from solidified linseed oils, wood flour (sawdust) and ground cork dust.

Additives such as pine resin, pigments and calcium carbonate (mineral filler) are added to it to

improve its qualities.

- Linoleum is manufactured in form of tiles. It is organic in nature. It is flexible, durable and

aesthetically pleasing. It comes in a wide variety of colors. It is used in high traffic areas such as

hallways and passages in residences and institutions.

Fig. 37:A variety of Linoleum Floor Finish

9. Clay Floor Finish- Has a heat resistance of up to 1250C. Its also acid resistant and hard wearing. It provides a

rustic and warm feeling underfoot.It may be polished using a specialized sealant to prevent

staining and fungal growth.

Fig. 38: Different sizes of Clay Floor Finish

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10.Concrete Floor Finish- Mainly used in airplane hangars, basement parking and storage warehouses.After a thin layer

of concrete is applied; burnishing and polishing processes are employed to give the surface anappealing finish.

Fig. 39: Polished Concrete Floor Finish

11.Stone Floor Finish- It is utilized when an antique floor finish is required.They may either be manually quarried or

machine cut to obtain a desired and consistent size.

- Color motifs may also be employed at the discretion of the designer.

Fig. 40: Colored Natural Stone Floor Finish

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REFERENCES

Barry R.1999, The Construction of Buildings, Volume 1. 7thEdition. Blackwell Science,UK.

Francis D. K. Ching, 2008, Building Construction Illustrated, 4thEdition. John Wiley andSons Inc. Hoboken, New Jersey.

Ivor H. Seeley, 1995, Building Technology, 5thEdition. Palgrave MacMillan, UK. Stroud J. Foster, Raymond Harington, 2000, Mitchells Structure and Fabric, 6thEdition.

Longman, England.

http://www.learning.covcollege.ac.uk http://www.elmbridge.gov.uk http://www.northumbria.ac.uk

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Building Technology - Floors