Quick selection selection guide guide for insitu floors:
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Flat Plate :
A flat plate is a one- or two-way system usually supported directly on columns or load bearing bearing walls walls Fig.2. Fig.2. The principal feature of the flat plate floor is a uniform or near-uniform thickness . The floor allows great flexibility for locating horizontal services above a suspended ceiling. An economical span for a reinforced flat plate is of the order order of 6 to 8 m and for prestressed flat plates is in the range of 8 to 12 m. The The span span 'L' 'L' of a rein reinfo forc rced ed conc concre rete te flat flat--pla plate is app approxi roxima mate tely ly D x 28 for for simp simply ly supported, D x 30 for an end span of a continuous system, to D x 32 for internal continuous s ans. The economical s an of a flat late can be extended b prestressing to approximately D x 30, D x 37 and D x 40 respectively, where D is the the dept depth h of slab slab..
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Flat Plate :
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Fig: 2
Flat Plate :
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Flat Plate : Adv ant ages: Simple formwork and suitable for direct fix or sprayed ceiling.
No beams—simplifying under-floor services.
Minimum structural depth and reduced floor-to floor height.
Disadvantages: Limited lateral load capacity as part of a moment frame.
May need shear heads or shear reinforcement at the columns or larger
columns for shear. May not be suitable for supporting brittle (masonry) partitions.
May not be suitable for heavy loads.
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Flat Slab :
A flat slab is a one-way or two-way system with thickenings in the slab at the columns and load bearing walls called 'drop panels' as per Fig.1. Drop panels act as T-beams over the supports. ey ncrease e s ear capac y an e s ness o e oor sys em un er vertical loads, thus increasing the economical span range. Less popular in recent years because of the limit on economical spans of about 9.5 m for reinforced slabs and about 12 m for prestressed slabs. The plan dimensions of the drop panels are a minimum of 1/3 of the span in the direction under consideration. The overall depth of the drop panel is typically taken as 1.75 to 2 times the depth of . The economical span 'L' of a reinforced concrete flat slab is approximately D x 32 for an end span and D x 36 for an interior span. Prestressing the slab increases the economical span to D x 40 and D x 45 respectively, where D is the depth of the slab excluding the drop panel.
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Flat Slab :
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Fig:1
Flat Slab :
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Flat Slab :
Adv ant ages : Simple formwork.
No beams—simplifying under-floor services outside the drops.
Minimum structural depth.
Usually does not require shear reinforcement at the c olumns.
Disadvantages:
Generally not suitable for supporting brittle (masonry) partitions.
Drop panels may interfere with larger mechanical ducting.
Vertical penetrations need to avoid area around c olumns.
For reinforced flat slabs, deflection at the middle strip may be critical.
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Beam and Slab :
This system consists of beams framing into columns and supporting slabs spanning between the beams Figure 3.
It is a very traditional system. The relatively deep beams provide a stiff floor capable of long spans, and able to resist lateral loads.
The complications of beam formwork, co-ordination of services, and overall depth of floor have led to a decrease in the popularity of this type of floor.
The traditional reinforced concrete beam-and-slab floor has an economical span 'L' of D x 15 for a single span and D x 20 for a multi-span, where D is the depth of the slab plus beam. Prestressing is not normally used with this system.
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Beam and Slab :
Advantages:
Traditional effective solution
Long spans.
Disadvantages: Penetrations through beams for large
ducts difficult to handle. Depth of floor.
Greater floor-to-floor height.
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Ribbed (Waffl e) Slab:
Ribbed floors consisting of equally spaced ribs are usually supported directly by columns Figure 4. They are either one-way spanning systems known as ribbed slab or a two-way ribbed s stem known as a waffle slab. This form of construction is not very common because of the formwork costs and the low fire rating. Ribbed slabs are suitable for medium to heavy loads, can span reasonable distances, are very stiff and particularly suitable where the soffit is exposed. Slab depths typically vary from 75 to 125 mm and rib widths from 125 to 200 mm. Rib spacing of 600 to 1500 mm can be used. spans of up to 15 m if reinforced, longer if post-tensioned.
For ribs at 1200-mm centres (to suit standard forms) the economical reinforced concrete floor span 'L' is approximately D x 15 for a single span and D x 22 for a multi-span, where D is the overall floor depth.
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Ribbed (Waffl e) Slab:
Fig: 4
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Ribbed (Waffl e) Slab:
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Ribbed (Waffl e) Slab:
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Band Beam and Slab:
This system consi sts of a s eries of parall el , wide, shall ow beams (known as band beams or thickened slab bands) with the floor slab spanning transversely between the bands Figure 5. The floor slab is designed as a continuous slab, with the shallow band beams carrying all loads from the slab. Band beams are commonly used for longer span structures often with the bands post-tensioned and the slabs reinforced. The band beam has a relatively wide, shallow cross section which reduces the overall depth of floor while permitting longer spans similar to the traditional concrete beam. The conc rete s ec tion sim pl ifi es both the for mwork and s erv ices whic h can pass under the beams. For single span reinforced concrete floors the economical span 'L' of the band beam is D x 20 to D x 22 depending on the width and spacing of the band beam, where D is the depth of the slab plus band beam. Prestressing the band beam gives economical band-beam spans in the range of D x 24 to D x 28. In multi pl e spans using rei nforc ed conc rete, the econom ical sl ab of the band beam 'L' i s approximately D x 22 for 1200-mm-wide band beams and D x 26 for a 2400-mm-wide beams at 8400-mm centres. Prestressing increases the economical span 'L' to D x 24 to D x 28 for similar beam widths. D is the depth of slab plus band beam in each case. Page
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Band Beam and Slab:
Figure 5 Page
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Band Beam and Slab:
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Band Beam and Slab:
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Band Beam and Slab:
Ad vantages:
Relatively simple formwork. .
Minimum structural depth and reduced floor-tofloor height
Long spans.
Good cost/time solution
Allows the use of flying forms.
s a van ages:
Long-term deflection may be controlling factor and post-tensioning may be
required.
May need service penetrations through beams which are difficult to handle.
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Slab and Joist :
This system consists of a slab spanning between beams (which span between columns) and usually an intermediate joist in one direction.
For the widely spaced rib or joist floor the economical span 'L' is D x 18 for a single span and D x 22 for a multi-span. Prestressing the joists permits the span to be increased to D x 24 and D x 28 respectively, where D is the depth of floor including the slab and joist.
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Slab and Joist :
Ad vantages:
Thin slab panels possible
Suits industrial structures
Long spans
Vertical penetrations between beams easily accommodated.
Disadvantages:
More formwork o s s an
eams n ru e on serv ces
Depth of floor
Greater floor-to-floor height
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Precast And Composite Floor Systems:-
These systems consist of precast floor elements spanning one way onto either in-situ or precast beams or precast beam shells or other suitable supports. e precas
oor e emen s are usua y s mp y suppor e .
Offers the advantages of off-site manufacture under factory conditions and fast erection on site. When combined with prestressing, additional benefits of long span and high load-capacity can be obtained. A quick selection of possible floors can be made from the chart-2.
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Precast And Composite Floor Systems:-
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Hollowcore:-
Hollow core floor planks are precast, prestressed units produced on long-line casting beds using slide forming (Fig).
Durin manufacture, cores are formed throu hout the unit, reducin its self-wei ht.
Planks are usually 1200-mm-wide, though some manufacturers can produce 2400mm-wide units.
These wider units may require increased crane capacity but offer greater speed of placement, less joints, grouting and sealing.
Thicknesses vary from 150–400 mm in 50-mm increments.
The thickness is determined by span, loading, fire rating and cover to reinforcement to satisfy exposure conditions.
The economical typical span for a precast hollow core unit is approximately D x 30 to D x 35 where D is the depth of the precast unit plus topping.
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Hollowcore:-
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Hollowcore:-
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Soffit Slabs:-
The system, known by several names depending on the manufacturer (eg Transfloor,
Humeslab) incorpora tes prec as t conc rete slabs, usual ly 55-m mthic k, with em bedded reinforcement and trusses (Fig).
To complete the floor, an insitu concrete topping acts compositely with the precast panels.
For long spans, soffit slabs require temporary props for support until the composite section is
able to carry the construction loads. The bottom reinforcement embedded in the precast panel may consist of a layer of mesh, the
bottom chords of the trusses and additional reinforcing bars as required by the designer. The trusses provide strength and stiffness for handling and transport, allow panels to support
construction loads with a minimum of temporary propping, contribute to the top and bottom reinforcement, and act as bar chairs to support the top reinforcement. Since the product is cast in a steel mould using wet-mix process, considerable flexibility of
plan shape is possible, while openings for stairs and major services may be cast-in. Small penetrations for electric wiring and plumbing can be cut on site. Page
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The system imposes few restrictions on designers because there are no standard panel sizes.
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Soffit Slabs:-
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Soffit Slabs:-
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Composite Floors – Beam and Infill :-
The system, known as Ultrafloor and similar, comprises precast, prestressed concrete inverted T-beams, spaced apart with an infill material spanning between the flanges of the beams (Figure).
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After the in-situ concrete has hardened, its compressive strength acts compositely with the tensile strength of the precast beams to efficiently carry the design loading on the floor.
In longer spans, where the load of the fresh concrete would be critical, a row of temporary props can be placed under the centre of the beams during concreting. These remain in place for approximately three days until the prestressed beams are able to act compositely with the .
In addition to offering the well-established advantages of precast flooring, it has a number of further benefits, including ready accommodation of site tolerances and service penetrations (with adjustment of beam positions) and enhanced acoustic performance with appropriate detailing.
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Composite Floors – Beam and Infill :-
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Composite Floors – Beam and Infill :-
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Single and Doub le T-Beams :-
Single and double T-beams cover the span range beyond slab-type members such as hollow core planks (Figure).
They are a very efficient structural shape. The typical range for double-tees is 12 to 24 m an s ng e- ees rom o m. roug e use o a us a e mou s, e ep , an o a lesser extent width, can be varied to suit the application.
Beams are usually topped with a levelling or structural screed concrete on-site.
The units are cast on a long-line pretensioning bed with straight (preferred arrangement).
Long units are carri ed on arti culated vehic les and si te ac ces s m us t take account of thi s. Erection is normally by mobile crane and access for these vehicles will also have to be taken .
The economical span 'L' between supporting beams is approximatel y D x 15 to D x 20 (dependi ng on the l evel of prestress) whe re D is the over al l depth of the T-beam i nc ludi ng topping.
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Single and Doub le T-Beams :-
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Single and Doub le T-Beams :-
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