Economic Long Span Concrete Floor Slabs 142u32
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A survey of 40 office buildings with long-span concrete floors P.W. Matthew BE, MSc, MIE(Aust) and D.F.H. Bennett BSc, MSc, CEng, MICE
FOREWORD This publication was commissioned by the Reinforced Concrete Council. The Group was set up in 1988 to promote better knowledge and understanding of reinforced concrete design and building technology. Its are Co-Steel Sheerness plc and Allied Steel & Wire, representing the major suppliers of reinforcing steel in the UK; and the British Cement Association, representing the major manufacturers of Portland cement in the UK. The authors of this publication are Peter Matthew, partner with consulting engineers Powell, Tolner & Associates and David Bennett, Senior Engineer in the Marketing Division of the British Cement Association.
ACKNOWLEDGEMENTS The authors wish to thank the following organizations for their considerable help in providing the building data for the survey: Anthony Hunt/YRM Partnership Beers Bison Limited Bunyan Meyer & Partners Composite Structures Limited DGI International plc Ferguson & McIlveen Frank Hodgson & Associates James-Carrington and Partners Jan Bobrowski and Partners Ove Arup & Partners Powell, Tolner & Associates Skidmore, Owings & Merrill Waterman Partnership Thanks are also due to Brian Dyer of Tower Associates for drafting the floor plans.
97.311
Published by the British Cement Association on behalf of the industry sponsors of the Reinforced Concrete Council.
ISBN 0 72101386 4
British Cement Association Telford Avenue, Crowthorne Berks RG45 6YS
First published 1990 Reprinted 1994, 1995
Price Group F
Tel (01344) 762676 Fax (01344) 761214
@ British Cement Association 1990 All advice or information from the British Cement Association is intended for those who will evaluate the significance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence] for any loss resulting from such advice or information is accepted. Readers should note that all BCA publications are subject to revision from time to time and should therefore ensure that they are in possession of the latest version.
CONTENTS INTRODUCTION
2
NOTES ON SURVEY
2
DESIGN FEATURES OF SPECIAL INTEREST
3
CHOICE OF FLOOR SLAB DESIGN
4
Solid flat slabs Ribbed slabs Waffle slabs One-way spanning solid slabs and beams Precast slabs Composite precast slabs
CONCLUSION
6
SURVEY DATA
7
Section 1:
Solid flat slabs Reinforced - Buildings 1 to 7 Prestressed - Buildings 8 to 12
Section 2:
Ribbed slabs Reinforced - Buildings 13 to 15 Prestressed - Buildings 16 to 22
Section 3:
Section 4:
Section 5:
15-19
20-22 23-29
Waffle slabs Reinforced -Buildings 23 to 25
30-32
Prestressed - Buildings 26 to 28
33-35
One-way spanning solid slabs and beams Buildings 29 to 33
36-40
Precast slabs Buildings 34 to 36
Section 6:
8-14
41-43
Composite precast slabs Buildings 37 to 40
44-47
INTRODUCTION Traditional concrete designs for office building have been associated with either beam and slab or flat slab floors, typically with 6 to 7.5 m spans. Occasionally, longer-span floors have been designed using ribbed or waffle construction. In recent times, changes in the requirements of end-s and in developers’ specifications have led to more open-plan offices and larger floors. This has increased spans from 6 to 9 m, even to 15 m and more. To the competitiveness of concrete long-span floors, a survey has been conducted of concrete-framed office buildings, the majority constructed in recent years. Forty buildings of in situ, precast and composite construction with long spans have been surveyed. In each category, examples were found of floors designed in reinforced and prestressed concrete to carry similar office floor loadings. For in situ structures, solid flat slabs and ribbed slab designs were common, with spans varying from 6 to 15 m. A number of precast structures with long spans, some over 20 m, are reported, with composite in situ slabs acting with precast ribs or other precast .
(Figure 1) indicates a braced structure where the horizontal forces are transmitted to shear walls by the floors acting as diaphragms. In the case of an unbraced structure [Figure 2), stability is provided from within the frame by the interaction of columns and floors and referred to as ‘frame action’. All tables should be read in conjunction with the corresponding floor plans and section details.
a
Shear walls
NOTES ON SURVEY The survey data are presented in the second part of this publication, beginning on page 7. The information has been arranged according to structural floor types as follows: Section 1 - Solid flat slabs Section 2 - Ribbed slabs Section 3 - Waffle slabs Section 4 - One-way spanning solid slabs and beams Section 5 - Precast slabs Section 6 - Composite precast slabs The structural information and quantities of material for each building surveyed are presented in tabular form and are accompanied by a typical floor plan and floor section. For each building studied, quantities of concrete, reinforcement and prestressing steel are expressed in units/m2 of floor area. All quantities related to vertical components, i.e. columns, walls, etc., have been excluded, thus the effect of storey height and number of storeys is eliminated. The span/depth ratios given in the tables are based on the maximum spans. Notes on the design Code of Practice, concrete grade and method of achieving frame stability have been added to provide useful information on the design of the structure. The column headed ‘Design loads’ gives the floor loadings used in the structural design, i.e. imposed load, finishes, partition and service loads: it does not include the self-weight of the floor. The method of achieving frame stability for each building is indicated in the column headed ‘Stability’ by ‘shear walls’ or ‘frame action’. The term ‘shear walls’ 2
Figure
I:
Lateral stability provided by shear walls.
Figure 2: Lateral stability provided by frame action.
DESIGN FEATURES
Overall to suit column size c
OF SPECIAL INTEREST
J--r 650
r
Notes on a few of the buildings surveyed are given below to highlight certain construction and design features that provide particular economic advantages for a given floor tY Pe. Building 5 310 mm reinforced solid flat slab, span 9.5 x 7-3 m. Lightweight aggregate concrete with a compressive strength of 30 N/mm2 was used in order to reduce the self-weight of the floor and the cost of the foundations. As the span/depth ratio exceeded the guiding limits in the Code (llO), compliance with maximum deflection in the serviceability limit state was proved by calculation. The floor slab was designed as a beam ing a one-way spanning flat slab, all within the 310 mm depth of construction. The beam, 2.5 m wide, spans longitudinally from the interior column to the lift core. The one-way spanning slab is simply ed at the perimeter and continuous over the beam.
-A-
Plan
Building 7
255 mm reinforced solid flat slab, span 9.2 x 6-0 m. The deflection of the 255 mm flat slab was checked by finite element analysis, taking full of edge stiffening from the perimeter columns and beams in addition to the internal columns and frame. A lateral stability check was carried out on a three-dimensional computer model of the structure. The inherent stiffness of the perimeter beams and columns plus the internal frame eliminated the need for shear walls.
Section
Figure 3: Detail of steel shearhead.
Building 10 300 mm post-tensioned solid flat slab, span 9.4 x 9.0 m. Steel cross-bracing, in combination with the floor slab acting as a diaphragm, provided the lateral stability. Drop s were eliminated by forming shearheads within the slab depth (Figure 3). All external columns were connected to steel beams, composite with the slab, to cater for punching shear. Building 13 450 mm reinforced ribbed slab, span 9.0 m. The wide-rib profile, spaced at 1.5 m centres, provides adequate flexibility to accommodate small and large service openings in the floor. The rib profile made it possible to use table forms with integral grp rib moulds to ensure a fast building programme (Figure 4). Building 14
425 mm reinforced ribbed slab, span 9.0 m. The irregular floor plan of the building and the client’s requirement for minimum column sizes resulted in it being inappropriate to provide stability by frame action. Shear walls, with no returns and a minimum of cross walls, were specified to facilitate rapid construction of walls.
Figure 4: Grp rib moulds fixed to table forms. 3
Building 26 500 mm prestressed/reinforcement waffle slab, span 12.0 X 12-O m. The solid beam strips were post-tensioned, with the waffle section reinforced. This allowed the waffle section to be reinforced independently of the beams, thus speeding up construction, whilst maintaining an economical floor depth. Building 31 335 mm one-way spanning prestressed solid slab, span 12.6 m. The frame was designed as a stacked portal, with 160 mm precast perimeter walls ing a 335 mm post-tensioned solid slab. An important benefit in post-tensioning the slab was that the end moments transferred to the precast walls, due to dead load, were negligible. This in turn led to manageable transfer moments in the wall under ultimate load conditions. The structural solution proved both economic and fast to build, with a maximum net to gross floor area. Building 36 200 mm precast floor slab, span 7.7 m. The precast columns were designed as vertical cantilevers fixed at the base to provide frame stability. The precast floor beams were simply ed and designed as pin t connections to the columns. Building 37 560 mm double-T floor units with in situ topping, span 14.5 m. Stability was achieved by a combination of shear walls at the ends of the building and frame action developed from the precast perimeter H frames. The H sections are formed by adjacent perimeter columns and the perimeter edge beam (Figure 5a). The precast column ts are positioned at mid-storey height, i.e. the point of contra-flexure, so a full moment connection to the double-T floor beam was possible (Figure 5b). The precast frame was erected in just under ten weeks.
2400
-II/
(a) Elevation
Figure 5: Detail of precast H frame. 4
4800
CHOICE OF FLOOR SLAB DESIGN In assessing the structural cost of a multi-storey building, it is evident that the bulk of the cost is often for the floor slab construction. Therefore, the overall economy of a structure may depend on the efficiency and economy of the floor slab’ system. While quantities of materials reflect the efficiency of the design and structural layout, the actual cost of the structure may also depend on such factors as s p e e d o f construction, local market conditions, competitive tendering, availability of labour and equipment and cost of construction finance. Consequently a structural design that has proved to be competitive in one region may not always be competitive in another. For a building to meet the needs of major financial occupiers in today’s market, the choice of floor design is often determined by one or more of the following considerations: l
The need for long spans to provide floor space uninterrupted by cores and columns.
0 A maximum floor-to-floor height which allows adequate space for services and ducts, balanced against planning pressure to limit overall building height. 0 An adaptable floor structure which can accommodate future tenant alterations with maximum speed and minimum disruption. The wide range of floor construction in both reinforced and prestressed concrete, highlighted in this survey, demonstrates that concrete floors can be designed economically to meet these requirements. The types of floors and the reasons for choosing them are given opposite.
I/
I I I I
2400 4,
(b) Section
Solid flat slabs (with or without drops) The principal feature of the dropless floor is its flush soffit which requires only simple formwork and is easy to construct (Figure 6a). The overall depth of this floor is a minimum and it allows great flexibility for locating horizontal services. However, the economical span range of a reinforced floor is limited by shear in the vicinity of the column s and the need to control long-term deflection. The provision of drop s at the column s (Figure 6b) avoids the need for shear reinforcement and increases the stiffness of the slab and the economical span range. Alternatively, a structural steel shearhead can be incorporated to maintain a flush soffit to allow for easy construction and efficient use of large forming systems (Figure 6c).
Ribbed slabs Providing ribs to the soffit of the floor slab can reduce the quantity of concrete and reinforcement, and thus the weight of the floor. The deeper, stiffer floor permits longer
spans to be used. Formwork complexity can be minimized by the use of standard modular, re-usable formwork. When flying form s are used, the ribs should be positioned away from the column lines. Ribbed slab floors are very adaptable for accommodating a range of service openings (Figure 7).
Waffle slabs Waffle slab floors are commonly used when buildings are subjected to heavy imposed loading. They are very efficient in the use of materials and provide very economical long spans, but the additional complexity of formwork can often slow the construction. Where speed of construction is critical, a ribbed slab or a shallow beam solution is often preferred.
One-way spanning solid slabs and beams A wide, shallow beam profile is often preferred in order to reduce the overall depth of the floor, whilst permitting longer spans. The one-way spanning solid slab between the beams facilitates the use of table forms for fast construction (Figure 8).
1-2-1::: 1r-1
I--
“~~-~~-l'-'
'-::-~J--,:-;:-:
:-,r-
Figure 7: Ribbed slab for flexibility to accommodate openings.
(b)
Figure 6: Solid flat slab: (a) without drop s; (b) with drop s; (c) with shearhead.
Figure 8: Band beam and slab construction using tableforms. 5
Precast slabs
Composite precast slabs
Precast slabs offer the advantage of off-site manufacture, with a reduction in site labour and site formwork. When the slabs are prestressed there are additional benefits of longer spans and higher load capacity. A popular type of precast floor is the hollow core slab (Figure 9). The relatively lightweight units form a flush soffit when placed. A shear key between units ensures load sharing and the construction is commonly capable of developing diaphragm action without the need for a structural topping. The precast units are easy to remove and can accommodate a wide range of floor openings.
Composite precast slabs combine precast floor elements with in situ concrete in an economical way, eliminating traditional formwork for floor construction, and providing long-span floors. Thin precast concrete floor plates can be combined with an in situ topping to form composite one-way spanning floors up to 6 m long, or, in combination with precast beams, to form a composite ribbed slab (Figure lOa). For extremely long spans, double-T precast beams and a composite in situ topping is preferred (Figure 10b).
CONCLUSION The buildings surveyed in this publication demonstrate that reinforced and prestressed concrete floors with spans ranging from 6 to 20 m, are technically feasible and economically competitive. This is a direct consequence of improved design and analysis techniques, higher strength materials, better construction methods and finally, more construction-led design.
Figure 9: Precast hollow core planks:flexibility for alterations.
Figure IO: Composite floors: (a) precast ribbed floor; (b) double-T beam floor. 6
SURVEY DATA Section 1:
Solid flat slabs Reinforced - Buildings 1 to 7 Prestressed - Buildings 8 to 12
Section 2: Ribbed slabs Reinforced -Buildings 13 to 15 Prestressed -Buildings 16 to 22
Section 3: Waffle slabs Reinforced -Buildings 23 to 25 Prestressed - Buildings 26 to 28
Section 4:
One-way spanning solid slabs and beams Buildings 29 to 33
Section 5: Precast slabs Buildings 34 to 36
Section 6:
Composite precast slabs Buildings 37 to 40
7
SECTION 1 SOLID FLAT SLABS
m
2
I
7.2x7.2
mm I
ratio I
300
24
1
m3 1
I
0.30
Jr
kg I
30.0
3600
Ji
1 I
6-O
Solid flat slab -reinforced
’ r ~~~~ ’ Frame
action
3600
1"
GradeC40 Code BS 8110
7200
'i
3600
n
1"
3600
I
I-
300 slab
-
7 J
-
n
7
_I
-
8
n
Solid flat slab -reinforced
No. of floors 10
Materials per m2 Design of floor area load Depth Span/depth Conc;ete Rebar kN/,,$ Slab
Span m
mm
ratio
7.5x6.1 3 0 0
Stability
Notes
Shear walls
Grade C35 Code BS 8110
kg
25
0.30
45.0
6-O
I
I
I
I
8
I
I
I
300 slab I
-
I
I
I
I
I
I
I
Typical floor plan
A
9
Solid flat slab -reinforced
3000
3000
5 i(J 7500
A i
n
8 2
400 slab
400 slab
E
mi
n 1
I
_L
1 /
i
Typical floor plan
10
Solid flat slab -reinforced
No. of floors 7
Materials per m* Design of floor area load Depth Span/depth Conc;ete Rebar kN/,-,-,* mm ratio kg Slab
-
Span m 65x45
250
26
0.25
29.0
5 0
Stability
Notes
Shear walls
Grade C35 Code BS 8110
I
17 ccc 45 Typical floor plan
1`
Solid flat slab -reinforced
No. of floors 4
Materials per m* Design of floor area load
Slab Span m
Stability
Depth Span/depth Conc;ete Rebar kNirn2 mm ratio kg
9-5x 7.3 310
30.6
0.31
Typical floor plan
41.5
5.0
Shear walls
Notes (See page 3)
C30 lightweight Code 110
Solid flat slab -reinforced
Materials per m2 Design of floor area load Depth Span/depth Co;;ete Rebar kN/r-$ mm ratio kg Slab
No. o f Span floors m 13
5800
8 0x7.2
275
3 irr 7200
275 slab
Typical floor plan
29
0.28
5800
40.7
5-o
Stability
Notes
Shear walls
Grade C35 Code BS 81 10
Solid flat slab -reinforced
Stability I
I
9.2x6.0
7 I
I I
255 II
I
0.26
36
I
I
I
I
I
I
Notes (See page 3)
I
I
II
24.0 II
5.2
-
h
6200
4
5 ((I 6000
255 slab
Typical floor plan
14
Solid flat slab - prestressed
2
(”
Span m
P
x
x
Design load Depth Span/depth Con$ete Rebar Strand kN/r-$ ratio mm kg kg
8.0x8-0 275
29.1
10-2
0,275
,.~- . .
I
Gl
Materials per m2 of floor area
Slab
No. of floors
4
8
10..0
Stability
Notes
Shear walls
Grade C40 Code BS 8110
.‘j----
X i..t
:*
x
x
I”
m
x
x
x x x
0
X
0
Eico
x
Atrium
X
X
m
m
m
m
PI
m
m
P1
J
First-floor plan
Column head detail
I
I
15
Solid flat slab - prestressed
Stability
a
7.2x 7.2 240
30.0
0.240
2.4
4.7
Notes
Shear walls
6.5
* See Concrete Society TechnIcal Reports No 17 and No 25
3 ((I 7200
4800
0 0
cu
P-
n
n
Typical floor plan
c
:i,
950
I / Column head detail
c
475
”
’ 240 $ 50 i 250
Solid flat slab - prestressed
Materials per m’ of floor area
Slab
No. of floors
9
Span m
Depth Span/depth Conx$ete mm ratlo
9 4x9-o 300
31 3
0 300
Design l o a d Rebar Strand kN/mz kg kg
14-l
78
50
Stability
Steel bracing to columns
Notes (See page 3) Grade C40 Code BS 8110 CS TR 17 & 25* Steel c o l u m n s with shearheads
* See Concrete Society TechnIcal Reports No 17 and No 25
45000
P
m
B
a
I
m
I
Typical floor plan
Cross-bracing
17
Solid flat slab - prestressed
No of floors
7
Materials per m* of floor area
Slab Span m
11 5 x 7 5 325
35 4
O-325
11
1
See Concrete Society TechnIcal Reports No 17 and No 25
Typical floor plan
8
Design
load Depth Span/depth Concrete Rebar Strand kN/mz mm ratio m3 kg kg
65
50
Stability
Notes
Frame action
Grade C40 Code BS8110 CSTR 17&25*
Solid flat slab - prestressed
Slab Stability
r
7200
c
3600
*
Typical floor plan
Typical column head detail
7200
2400 *II
7200
+
3600
*
7200
Notes
J
SECTION 2 RIBBED SLABS
Ribbed slab -reinforced
Materials per m* Rib Beam No. Des of floor area ,__ign of wad floors Span Depth Span/depth Span B x D Span/depth Concrc ?te R e b a r kN/m* 10
m
mm
ratio
m
mm
ratio
m3
kg
9.0
450
20.0
8.0
1200 x 450
13.3
0.23
39.5
7.5
Notes
Stability
(See page 3)
Frame action
Grade C35 Code BS 8110
7 ((1 9000
1
I
Typical floor plan
Typidal rib section
20
Typical beam section
Ribbed slab - reinforced
No. of floors 11
Materials per m2 of floor area f$$” Stability
Beam
Rib
Notes (See page 3)
Span Depth Span/depth Span B x D Span/depth ConcJete Rebar kN/m* mm ratio kg m ratio mm m 9.0
425
9000
21 .l
9.0
1800 x425
6750
21.1
4 @ 7500
5.0
38.5
0.27
i
6750
1
Shear walls
Grade C35 Code BS 8110
9000
5 (u, 9000 Typical floor plan 1500 _~~ __~ 125 L
-t
‘T 1425 I I
l-l
7Ii
425
: 1800
250
Typical rib section
Typical beam section
Ribbed slab - reinforced
floors Span Depth Span/depthSpan m
5
mm
9.0 3 0 0
Materials per m2 of floor area Dri,n Stability
Beam
Rib
No.
ratio
30.0
m
B x D Span/depth
mm
1800 7-2 x 4 0 0
ratio 18.0
0.32
6 ((I‘ 7200
29.0
5.0
Shear walls
I
9000
1800 Typical rib section
22
Notes
Conc;ete Rc??r kN/mz
Typical beam section
Grade C35 Code BS 8110
i
7200
i
Ribbed slab - prestressed
No. of
Rib
Materials per m* of floor area
Beam
Design load
Stability
Notes
Frame action
Grade C35 Code BS 8110
floors Span Depth Spacing Span/depth Span B x D Span/depth Type Concrete Rebar Strand kN/& m mm mm ratio m mm ratio kg kg 3
9.0
3 2 5
1200
27-7
1800
18-5
6.0 x 3 2 5
Pt’
0 194
12 6 3.65
6.0
‘Prestressed
Typical floor plan
100 325
Typical rib section
ki!
23
Ribbed slab - prestressed
I
No.
I
-I of floors
Materials per m* of floor area
Beam
Rib
Stability
Notes
Span Depth Spacing Span/depth Span B x D Span/depth Type Con;;ete Rebar Strand kN/t-$ m
22
9.0
mm
mm
250
750
ratio
36.0
m
mm
ratio
2200 7.5 x 2 5 0
30.0
kg
Pt’
0.186
kg
7 . 0 3 5.79
*Prestressed
10 @ 7500
i
Typical floor plan
2200
750 125
,
A -
-r
s
.250
250
I-
\
175 Typical rib section
24
Design load
Column head detail
5.0
Shear walls
Grade C40 Code 110
Ribbed slab - prestressed
Materials per m2 Beam Rib NO. Design of floor area of load floors Span Depth Spacing Span/depth Span B x D Span/depth Type Con;;ete Rebar Strand kN/m* mm
mm
ratio
9.8 400
725
24.5
m
8
m
ratio
mm
1 9 4 1200 x 800
24.2
Pt”
0.354
kg
kg
16.9
9.76
6.0
Stability
Shear walls
Notes
Grade C40 Code 110 ‘Prestressed
I.
I.
I. 13000
9350
9350
I.
10000
I
Typical floor plan
c
725
75
725
P
725
Typical rib section
25
Ribbed slab - prestressed
Materials per m2 Rib Beam No. Design of floor area o f load floors Span Depth Spacing Span/depth Span B x D Span/depth Type Concrete Rebar Strand kN/r-$ m 5
L
mm
10.85 450
mm 850
ratio
m
mm
ratio
24.1
12.5
1500 x450
28.0
‘Prestressed
Typical floor plan
Typical section
L
Pt*
m3
kg
kg
0.280
8.3
6-63
5.0
Stability
Notes
Shear
Grade C40
walls
Code 110
Ribbed slab - prestressed
Materials per m* Beam Rib Design No. of floor area load o f floor s Span Depth Spacing Span/depth Span B x D Span/depth Type Conc;ete Rebar Strand kN/m* m 5
mm
135 475
mm
ratio
1500
28 4
m
mm
ratio
9 . 0 1500 x475
Pt*
18.9
0,285
kg
kg
15.0
4.93
Notes
Stability
Shear walls Grade C40 and frame Code BS 8110 action
60
l Prestressed
I II II II I II II I II II I II II
I
u /’
/
/
II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II I I II
II II II II II II II II II II II I I II II II
I I I I
L~LJLJL~LJLJLJLJLJLJLJLJLJL.~L.n n w
I
riririr~r~rlrlr~r~r~r~r~r~r~r~,
ririr
II II II II II I II II I/ I II II II II II II 11 II II II I’ II I II I II II II II II II II II II II II L~L~L~L~L~L~L~L~L~L~~~~~~~~~~~~~~~~~,~~
I I
I II II II II II II I /I II II II II I I II
I
r-i r
II
II
I I I I II II II
iririr~r-lr~r~r~r1rlrlrlr~r~r~r~rlrl
II II II II II I I I II II II II II I I I II II II II II I I I L J -JLJLJ LJLJLJL-ILJLJ I I I
n
II II II
I I I
II
II II
n
r -1 -1rir-i r Iririririrl
I
I
II II
I I I
II II II
II II II
II II II
II II II
II II II
II II II
II II II
II II II
I I I
I
LJL~ILJLJLJLJLJLJLJ
n
n riririririr
I
I
II II II II II II II II I II II II II II I I LA _ _J L A L A LJLJLJLJLALJ LJLJLJLJLJLJLJLJL.~J II
II
I
8
10
ll~-lrlrl -
I”
Typical floor plan
1500 125
‘r
1500
Typical beam section
1, J:
1
425
Typical rib section
27
Ribbed slab - prestressed
Materials per m2 Rib Beam Design No. of floor area of load floors Span Depth Spacing Span/depth Span B x D Span/depth Type Concrete Rebar Strand kN/m2 m
5
mm
14.4 650
mm
m
ratio
22.2
2400
mm
ratio
1200 7.2 x 6 5 0
R.C.*
0,268 1 4 . 7
Notes
Shear walls
Grade C40 Code BS 8110
kg
kg
11 .0
Stability
4.33
7.0
“Reinforced
B0
8 @ 7200 1
f
: I I
II
II II II
II
I I
II
I II I II I II
II II II II II
:I II
jl 11
II
n
ll iI iI II
II II II II
II II II I
ll
II
II
II
n II
E
n Ii
I7 II
11 II
r7 II
fl II
I4 L L
M -IL I I - I I AIL u lb ““““““/
Typical floor plan
2400
28
II II
;
J u u u H H H H H - u .-IL Al- u -IL ii- il -IL II_
Typical section
II
500
Ribbed slab - prestressed
Materials per m’ Rib Beam Design No. of floor area load of floors Span Depth Spacing Span/depth Span B x D Span/depth Type Concrete Rebar Strand kN/m’ m mm mm ratio m mm ratio kg kg 4
16.3 525
31 .0
850
6.3
275 X1000
R.C.*
6.3
0.225
9.8
5.66
Stability
Shear walls
6.0
Notes
Grade C40 Code 110 ‘Reinforced
7 @ 6300
_
i
t
Typical floor plan
100
I
850
8
5
0 %
850
i
Typical section
29
SECTION 3 WAFFLE SLABS No. of floors 5
Column spacing m
Waffle slab - reinforced
Materials per m* Design of floor area Depth Span/depth load Stability mm ratio Con-v$ete R e b a r S t r a n d kN/m2 21.2
6.6 X 7.43 350
5835
0.245
kg
kg
24.0
-
7425
I
Frame Grade C35 Code BS 8110 action
6-O
3 @ 4950
---*
Typical floor plan
Ribs at 900 crs
! 125
4;7 I
1600 Section at column head
30
Notes
Waffle slab - reinforced
No. of floors 3
Column spacing m
Materials per m2 Design of floor area Depth Span/depth load mm ratio Con;;ete R e b a r S t r a n d kN/m2
7.5x10 5 5 2 5
, 7500
typical
20.0
0.450
kg
kg
67.0
-
6-O
Stability
Notes
Frame Grade C35 action Code BS 8110
,
Typical floor plan
Typical section
31
Waffle slab - reinforced
No. of floors
Column spacing m
3
10.18 x10.18
Depth Span/depth mm ratio 550
_
Materials per m* of floor area
Design load Stability
18-5
0.396
37.0
-
k
Typical section
9.0
Shear Grade C35 Code BS 8110 walls
3 @ 10180
Typical floor plan
32
Notes
Conc;ete R e b a r S t r a n d kN/m2 kg kg
125 14
Waffle slab - prestressed
No. of floors 1
Materials per m2 of floor area
Design Notes Depth Span/depth load Stability (See page 4) mm ratio Compete Rebar Strand kN/m2 kg kg Shear Grade C40 15.9 2.52 6.0 0.349 24.0 12.0x12.0 500 Code BS 6110 walls Column spacing m
6000
4 @ ’ 12000
q
CIOOOOOOO
rlnnnnnnrin
Typical floor plan
Typical section
125
33
Waffle slab - prestressed
No. of floors 2
Column spacing m
Materials per m* Design of floor area Depth Span/depth load Stability mm ratio Cor?$ete R e b a r S t r a n d kN/m*
12.7x12.7 500
25.4
*
0.341
12700
Typical floor plan
Typical section
kg
kg
12.2
5.60
6.0
Shear walls
Notes
Grade C35 Code BS 8110
Waffle slab - prestressed
Stability
Notes
~c~~~
Grade C40 Code BS 8110 CS TR No. 17*
*See Concrete Society Technical Report No 17
5 @ 15000
1
1 ,;:j; ji
‘: :’ ‘: ‘_-: ::~:: ::p::-::-:,
;.:I.
‘-7.. :.::.
: :: 1
:.
:
li
:’
ij
:
. -. .: ..-.. ~.i[:lI: :.::..:..:.::.:: ‘:~::..l‘i‘: ::..LL
: :~::z..
.I! j :::.: .::
a :, : .;_;;
1_~1;.1;.1;:1:.:1~1!_. ~.. :.~:.~::~’
i
.,: :I..
.iilii:
:.!:~:.~I:.::.::.::.:!.:L.::! !L : :-:“:.::‘I:.‘,~ . . . . . .~..~_.
,..,:
.,
: : ::r::
__,:
Lo:!
::~::
!!
.-..-.
:,
,,
:: :
::=:: ,!
,I
‘: :, : ::-::-::.:, ,I
.,
,,
. . ..i.:
Atrium
Typical floor plan
Typical section
225
35
SECTION 4 ONE-WAY SPANNING SOLID SLABS & BEAMS
One-way spanning solid slab and beam
Materials per m2 Slab Beam No. Design of floor area of . load floors Span Depth Span/depth Type Span B x D Span/depth Type Concrete Rebar Strand kN/+’ m 4
mm
ratio
7.43 200
37.2
m Pt*
9.0 1 5 0 0
‘Prestressed
Typical floor plan
Typical beam section
36
mm
x 500
ratio 18.0
m3 Pt*
0.261
kg
Stability
Notes
kg
1 4 . 0 4.11
4.0
Shear
Grade C35
walls
Code BS 8110
One-way spanning solid slab and beam Slab Beam No. o f floors Span Depth Span/depth Type Span BxD Span/depth Type m
6
mm
10.30 2 5 0
ratio
41.2
m
Pt*
mm
1500 6.0 x 4 5 0
ratlo
13.3
R.C.+
Materials per m2 of floor area
Design load
Stability
Notes
Conc;ete Rebar Strand kN/m* kg kg
0.298
13.9
3.93
t
6.8
Shear walls
Grade C30 Code 110
‘Prestressed +ReInforced
250 slab
Typical floor plan
Typical beam section
37
One-way spanning solid slab and beam Materials per m2 Beam Slab Design No. of floor area load of floors Span Depth Span/depth Type Span BxD Span/depth Type Concrete Rebar Strand kN/m2 ratio m3 kg kg mm m mm m ratio 7
12.6 3 3 5
37.6
Pt*
Precast perimeter wall
‘Prestressed
335 slab
Typical floor plan
38
0 335
11.8 8.25
6.8
Stability
Shear walls
Notes (See page 4)
C40 lightweight Code BS 8110
One-way spanning solid slab and beam
Beam Slab No. of floors Span Depth Span/dept Tyee Spnn BxD Span/depth Type m 10
mm
6 75 220
m
ratio
30 7
R.C.* 10
mm
600x 0 6oo
Materials pe r m2 of floor area
Design load
Stability
Notes
Shear walls
C40 lightweight Code 110
Conc;et e %??r StFgn d kN/m2
ratio
16.7
R.C.*
0.26
42-O
-
5 0
*ReInforced
E0
Typical floor plan
Main beam section
39
One-way spanning solid slab and beam
No. of floors
Slab
Materials per m2 of floor area
Beam
Design load Span Depth Span/depth Type Span B x D Span/depth Type Con-$ete Rebar Strand kN/& m mm m mm ratio ratio kg kg
5
6.0
175
34.3
R.C.*
9.0
1500 x425
21.2
R.C.*
0.25
52.0
-
‘Reinforced
Typical floor plan
425 :
Typical section
40
5.0
Stability
Notes
Shear walls
Grade C40 Code BS 8110
SECTION 5 PRECAST SLABS
Precast slab
Materials per m2 of floor area Beam Slab Design No. In situ Precast load Stability of floors Span Section Span/depth Span B x D Span/depth Conc;ete Rebar Strand Conc;ete Rebar kN/r-$ m
12
7.0
mm
203
ratio
34.5
m
mm
ratio
300 6.0 x 6 0 0
10.0
kg
0.145
4.8
kg
kg
40
Notes
0,011
0.4
7.0
Shear walls
C50, BS 8110 7% in situ Hollow core planks No topping
6 @ 6000
1
.
Typical floor plan
Precast
“yqFy=
:z
300 Centre beam section
41
Precast slab
m
4
mm
7.2
I
200
I
36.0
Design load B xD Span/depth Concrete Rebar Strand Conc$ete Rebar kN/m2
m
mm
7.2
600 x600
ratio
I
I
m3
ratio
12.0
1
Typical floor plan
Typical section
kg
o-193
I
7200
5400
1
1
kg
Stability
Notes
Shear
Grade C50 Code BS 8110 Hollow core
kg
3.0
7.9
I
7200
7200
42
Materials per m’ of floor area In situ Precast
Beam
Slab No. of floors Span Section Span/depth Span
-
I
-
I
7200
planks No topping
I
7200
5400
1
7.0
1
7200
1
Precast slab
Materials per m2 of floor area Slab Beam No. - Design In situ Precast load of floors Span Sectlon Span/depth Span B x D Span/depth Concrete Rebar Strand Con$ete Rebar kN/m* m
3
77
mm
200
ratio
38.5
m
mm
m3
ratio
7 . 4 3 ,$;o 1 2 . 4
0.157
kg
10.5
kg
Stability
Notes (See page 4)
kg
2.55
- -
6.5
Frame action
Grade C50 Code BS 6110 Hollow core
planks No topplng
Typical floor plan
Typical section
43
SECTION 6 COMPOSITE PRECAST SLABS Rib No. of . floors Span Depth Span/depth Span mm m m ratio
9
14.5
560
25.9
4.8
Composite precast slab
Materials per m2 of floor area In situ Precast
Beam
Design load Depth Span/depth Concrete Rebar Strand Concrete Rebar kN/m2 mm ratio m3 kg kg m3 kg 500x 1000 (Perimeter)
Stability
Grade C60 Code 110 any$$ar Double Tees, wrth In situ topping walls Precast H frame Frame
4.8
0.150
5.75
0.080
6.3
14500
.
2.2
5.0
I
4800 typical
I
47600 Typical floor plan
1200
, In s i t u t o p p i n g
i
-/
Typical section
44
Precast double-T beams
Notes (See page 4)
Composite precast slab
f10 2 Span
m
4
16.7
22.0
4.9
600x 900 (Perimeter)
1.54
Frame action
5.0
9 @ 4877
?
~f?~+kPl-rr~P~~~n’n-n
i
‘II II II ‘I I II ‘II II ‘II II Ii ‘II Il l II II ‘I I II I ‘II II II ‘II II II ‘II II II - + tit c- b !,
z co
0,075
0,133 5 - 4 8 7 . 7 9
5.4
2438 ‘i *
111 1) 1
I
In situ
Notes
load Stability Depth Span/depth Con;;ete Rebar Strand Conc;ete Rebar kN/m’ mm ratio kg kg kg
Depth Span/depth Span mm ratio m
785
Materials per m” o Precast
Beam
Rib
No.
II II I I
II
II
II
II
II
II
II
II
II
2438
8
II
I I I I II
II
II
II
I I II II
I I I I I I I I II
II
II
II
II
II
II
I I I I III I I II III Ill II lib II III II III II III II II IIP II II III I I II III
I I I I I I
I I
I I I I I I I I II II II II I I I I II I I II II I I II II II I I II I I I I II I I II II II II II II I II III L km c hL c Lu,u--u-uLu~ u-u~u-u,u-u-uLu, u u4 Ad 4 u Am11 4 4 44 -IF
Typical floor plan
1200
/’
In situ topping
1 j-=-f
Precast double-T beams Typical section
J
n~n’n~n~n-n’n~~n~~n~nLr~~n111141ild 1’1111Vfb II
I
75 (average)
Grade C60 Code 110 Double Tees, with in situ topping Precast H frame
;710
I
Composite precast slab
Rib No. of floors Span Depth Span/depth Span m
6
mm
/ 12.0 1
m
ratio
610
/
Design
. load
Stability
Notes
Depth Span/depth Concrete Rebar Strand Concrete Rebar kN/m* ratio mm m3 kg kg m3 kg
750x j 9.0 1 ,in”;FU, 1
19.7
Materials per m2 of floor area Precast In situ
Beam
14.8
1 0.134 (13,751 - 1 0.111 110 721
5.7
Frame action
In situ C35 Precast C45 Code BS 8110 55% In situ
I
r ir’ir’ir i r ’ i r ’ i r I I
II II II
ir’ir
II
II
II
II
II
II II
II
II
II
I
ir ir’ir’ir irwirlir ir
II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II Ii II II II II II II II II II II II II
II
II
II
II
II
II
II
II
II
II’
Typical floor plan
55 precast soffit plank Precast rib Typical rib section
46
Typical in situ beam section
Composite precast slab
3
Materials per m2 of floor area Precast In situ
Beam
No. o f floors Span
Design load
Depth Span/depth Concrete Aebar Strand Concrete Rebar kN/m’
m
mm
ratio
m3
kg
kg
m3
kg
21.2
750 Precast
28.3
0,123
4.9
7.6
0.060
2-28
5.0
Stability
Shear walls
Notes
Grade C62 Codes 115, 116 40% In situ
72000
1
c
,
8 cv i;
_ ~n-=-rt-~n-“-~-un~~~~nn~~~“~h~~n~n~n~~~~~nnnunu~~~=-n~~n~~~~ ,, ,, II Ii II I II II II II I I I II 1 II II II II il II II II II I I’ II II II ‘I II II II II II II ‘I II II II II I, II II II II II ,, ,, ‘1,
II
11
II
II
‘II
II
II ‘I ~:I~_:~ ”
11, AlI !I, ‘I, JIl
II II II I! II
II II
II llr :! Id II lli:
I’
II ‘I Nt ~ ‘I ” I’ I’ I
II II II
~~11R# II- 11~;
II II II
II II
II v ,I Ii
;~
II t
II II! II IIL IlL
I
II IIL II II II IIL II II II II II II II 1: 1: I’ II I’ I! I’ II II II II II II II II II II II II II II II II II !I II II II II II II II II II II II II II II II II vYv-Y~~Y~4_yu~~~L-L_-v~y~.~_yu_u_y-y-y _ y--y-y4~-y~y-&icy~~ 4 y u y~y-y~y--y~yy-yy
Typical floor plan
Beams @
Precast soffit planks
Precast beam Typical section
1500 crs.
Economic long-span concrete floors P.W. Matthew and D.F.H. Bennett BRITISH CEMENT ASSOCIATION PUBLICATION 9 7.3 11
CI/SfB I
(13)
I
q4
I
(Y6)
UDC 624.073.012.4.003.1
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A survey of 40 office buildings with long-span concrete floors P.W. Matthew BE, MSc, MIE(Aust) and D.F.H. Bennett BSc, MSc, CEng, MICE
FOREWORD This publication was commissioned by the Reinforced Concrete Council. The Group was set up in 1988 to promote better knowledge and understanding of reinforced concrete design and building technology. Its are Co-Steel Sheerness plc and Allied Steel & Wire, representing the major suppliers of reinforcing steel in the UK; and the British Cement Association, representing the major manufacturers of Portland cement in the UK. The authors of this publication are Peter Matthew, partner with consulting engineers Powell, Tolner & Associates and David Bennett, Senior Engineer in the Marketing Division of the British Cement Association.
ACKNOWLEDGEMENTS The authors wish to thank the following organizations for their considerable help in providing the building data for the survey: Anthony Hunt/YRM Partnership Beers Bison Limited Bunyan Meyer & Partners Composite Structures Limited DGI International plc Ferguson & McIlveen Frank Hodgson & Associates James-Carrington and Partners Jan Bobrowski and Partners Ove Arup & Partners Powell, Tolner & Associates Skidmore, Owings & Merrill Waterman Partnership Thanks are also due to Brian Dyer of Tower Associates for drafting the floor plans.
97.311
Published by the British Cement Association on behalf of the industry sponsors of the Reinforced Concrete Council.
ISBN 0 72101386 4
British Cement Association Telford Avenue, Crowthorne Berks RG45 6YS
First published 1990 Reprinted 1994, 1995
Price Group F
Tel (01344) 762676 Fax (01344) 761214
@ British Cement Association 1990 All advice or information from the British Cement Association is intended for those who will evaluate the significance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence] for any loss resulting from such advice or information is accepted. Readers should note that all BCA publications are subject to revision from time to time and should therefore ensure that they are in possession of the latest version.
CONTENTS INTRODUCTION
2
NOTES ON SURVEY
2
DESIGN FEATURES OF SPECIAL INTEREST
3
CHOICE OF FLOOR SLAB DESIGN
4
Solid flat slabs Ribbed slabs Waffle slabs One-way spanning solid slabs and beams Precast slabs Composite precast slabs
CONCLUSION
6
SURVEY DATA
7
Section 1:
Solid flat slabs Reinforced - Buildings 1 to 7 Prestressed - Buildings 8 to 12
Section 2:
Ribbed slabs Reinforced - Buildings 13 to 15 Prestressed - Buildings 16 to 22
Section 3:
Section 4:
Section 5:
15-19
20-22 23-29
Waffle slabs Reinforced -Buildings 23 to 25
30-32
Prestressed - Buildings 26 to 28
33-35
One-way spanning solid slabs and beams Buildings 29 to 33
36-40
Precast slabs Buildings 34 to 36
Section 6:
8-14
41-43
Composite precast slabs Buildings 37 to 40
44-47
INTRODUCTION Traditional concrete designs for office building have been associated with either beam and slab or flat slab floors, typically with 6 to 7.5 m spans. Occasionally, longer-span floors have been designed using ribbed or waffle construction. In recent times, changes in the requirements of end-s and in developers’ specifications have led to more open-plan offices and larger floors. This has increased spans from 6 to 9 m, even to 15 m and more. To the competitiveness of concrete long-span floors, a survey has been conducted of concrete-framed office buildings, the majority constructed in recent years. Forty buildings of in situ, precast and composite construction with long spans have been surveyed. In each category, examples were found of floors designed in reinforced and prestressed concrete to carry similar office floor loadings. For in situ structures, solid flat slabs and ribbed slab designs were common, with spans varying from 6 to 15 m. A number of precast structures with long spans, some over 20 m, are reported, with composite in situ slabs acting with precast ribs or other precast .
(Figure 1) indicates a braced structure where the horizontal forces are transmitted to shear walls by the floors acting as diaphragms. In the case of an unbraced structure [Figure 2), stability is provided from within the frame by the interaction of columns and floors and referred to as ‘frame action’. All tables should be read in conjunction with the corresponding floor plans and section details.
a
Shear walls
NOTES ON SURVEY The survey data are presented in the second part of this publication, beginning on page 7. The information has been arranged according to structural floor types as follows: Section 1 - Solid flat slabs Section 2 - Ribbed slabs Section 3 - Waffle slabs Section 4 - One-way spanning solid slabs and beams Section 5 - Precast slabs Section 6 - Composite precast slabs The structural information and quantities of material for each building surveyed are presented in tabular form and are accompanied by a typical floor plan and floor section. For each building studied, quantities of concrete, reinforcement and prestressing steel are expressed in units/m2 of floor area. All quantities related to vertical components, i.e. columns, walls, etc., have been excluded, thus the effect of storey height and number of storeys is eliminated. The span/depth ratios given in the tables are based on the maximum spans. Notes on the design Code of Practice, concrete grade and method of achieving frame stability have been added to provide useful information on the design of the structure. The column headed ‘Design loads’ gives the floor loadings used in the structural design, i.e. imposed load, finishes, partition and service loads: it does not include the self-weight of the floor. The method of achieving frame stability for each building is indicated in the column headed ‘Stability’ by ‘shear walls’ or ‘frame action’. The term ‘shear walls’ 2
Figure
I:
Lateral stability provided by shear walls.
Figure 2: Lateral stability provided by frame action.
DESIGN FEATURES
Overall to suit column size c
OF SPECIAL INTEREST
J--r 650
r
Notes on a few of the buildings surveyed are given below to highlight certain construction and design features that provide particular economic advantages for a given floor tY Pe. Building 5 310 mm reinforced solid flat slab, span 9.5 x 7-3 m. Lightweight aggregate concrete with a compressive strength of 30 N/mm2 was used in order to reduce the self-weight of the floor and the cost of the foundations. As the span/depth ratio exceeded the guiding limits in the Code (llO), compliance with maximum deflection in the serviceability limit state was proved by calculation. The floor slab was designed as a beam ing a one-way spanning flat slab, all within the 310 mm depth of construction. The beam, 2.5 m wide, spans longitudinally from the interior column to the lift core. The one-way spanning slab is simply ed at the perimeter and continuous over the beam.
-A-
Plan
Building 7
255 mm reinforced solid flat slab, span 9.2 x 6-0 m. The deflection of the 255 mm flat slab was checked by finite element analysis, taking full of edge stiffening from the perimeter columns and beams in addition to the internal columns and frame. A lateral stability check was carried out on a three-dimensional computer model of the structure. The inherent stiffness of the perimeter beams and columns plus the internal frame eliminated the need for shear walls.
Section
Figure 3: Detail of steel shearhead.
Building 10 300 mm post-tensioned solid flat slab, span 9.4 x 9.0 m. Steel cross-bracing, in combination with the floor slab acting as a diaphragm, provided the lateral stability. Drop s were eliminated by forming shearheads within the slab depth (Figure 3). All external columns were connected to steel beams, composite with the slab, to cater for punching shear. Building 13 450 mm reinforced ribbed slab, span 9.0 m. The wide-rib profile, spaced at 1.5 m centres, provides adequate flexibility to accommodate small and large service openings in the floor. The rib profile made it possible to use table forms with integral grp rib moulds to ensure a fast building programme (Figure 4). Building 14
425 mm reinforced ribbed slab, span 9.0 m. The irregular floor plan of the building and the client’s requirement for minimum column sizes resulted in it being inappropriate to provide stability by frame action. Shear walls, with no returns and a minimum of cross walls, were specified to facilitate rapid construction of walls.
Figure 4: Grp rib moulds fixed to table forms. 3
Building 26 500 mm prestressed/reinforcement waffle slab, span 12.0 X 12-O m. The solid beam strips were post-tensioned, with the waffle section reinforced. This allowed the waffle section to be reinforced independently of the beams, thus speeding up construction, whilst maintaining an economical floor depth. Building 31 335 mm one-way spanning prestressed solid slab, span 12.6 m. The frame was designed as a stacked portal, with 160 mm precast perimeter walls ing a 335 mm post-tensioned solid slab. An important benefit in post-tensioning the slab was that the end moments transferred to the precast walls, due to dead load, were negligible. This in turn led to manageable transfer moments in the wall under ultimate load conditions. The structural solution proved both economic and fast to build, with a maximum net to gross floor area. Building 36 200 mm precast floor slab, span 7.7 m. The precast columns were designed as vertical cantilevers fixed at the base to provide frame stability. The precast floor beams were simply ed and designed as pin t connections to the columns. Building 37 560 mm double-T floor units with in situ topping, span 14.5 m. Stability was achieved by a combination of shear walls at the ends of the building and frame action developed from the precast perimeter H frames. The H sections are formed by adjacent perimeter columns and the perimeter edge beam (Figure 5a). The precast column ts are positioned at mid-storey height, i.e. the point of contra-flexure, so a full moment connection to the double-T floor beam was possible (Figure 5b). The precast frame was erected in just under ten weeks.
2400
-II/
(a) Elevation
Figure 5: Detail of precast H frame. 4
4800
CHOICE OF FLOOR SLAB DESIGN In assessing the structural cost of a multi-storey building, it is evident that the bulk of the cost is often for the floor slab construction. Therefore, the overall economy of a structure may depend on the efficiency and economy of the floor slab’ system. While quantities of materials reflect the efficiency of the design and structural layout, the actual cost of the structure may also depend on such factors as s p e e d o f construction, local market conditions, competitive tendering, availability of labour and equipment and cost of construction finance. Consequently a structural design that has proved to be competitive in one region may not always be competitive in another. For a building to meet the needs of major financial occupiers in today’s market, the choice of floor design is often determined by one or more of the following considerations: l
The need for long spans to provide floor space uninterrupted by cores and columns.
0 A maximum floor-to-floor height which allows adequate space for services and ducts, balanced against planning pressure to limit overall building height. 0 An adaptable floor structure which can accommodate future tenant alterations with maximum speed and minimum disruption. The wide range of floor construction in both reinforced and prestressed concrete, highlighted in this survey, demonstrates that concrete floors can be designed economically to meet these requirements. The types of floors and the reasons for choosing them are given opposite.
I/
I I I I
2400 4,
(b) Section
Solid flat slabs (with or without drops) The principal feature of the dropless floor is its flush soffit which requires only simple formwork and is easy to construct (Figure 6a). The overall depth of this floor is a minimum and it allows great flexibility for locating horizontal services. However, the economical span range of a reinforced floor is limited by shear in the vicinity of the column s and the need to control long-term deflection. The provision of drop s at the column s (Figure 6b) avoids the need for shear reinforcement and increases the stiffness of the slab and the economical span range. Alternatively, a structural steel shearhead can be incorporated to maintain a flush soffit to allow for easy construction and efficient use of large forming systems (Figure 6c).
Ribbed slabs Providing ribs to the soffit of the floor slab can reduce the quantity of concrete and reinforcement, and thus the weight of the floor. The deeper, stiffer floor permits longer
spans to be used. Formwork complexity can be minimized by the use of standard modular, re-usable formwork. When flying form s are used, the ribs should be positioned away from the column lines. Ribbed slab floors are very adaptable for accommodating a range of service openings (Figure 7).
Waffle slabs Waffle slab floors are commonly used when buildings are subjected to heavy imposed loading. They are very efficient in the use of materials and provide very economical long spans, but the additional complexity of formwork can often slow the construction. Where speed of construction is critical, a ribbed slab or a shallow beam solution is often preferred.
One-way spanning solid slabs and beams A wide, shallow beam profile is often preferred in order to reduce the overall depth of the floor, whilst permitting longer spans. The one-way spanning solid slab between the beams facilitates the use of table forms for fast construction (Figure 8).
1-2-1::: 1r-1
I--
“~~-~~-l'-'
'-::-~J--,:-;:-:
:-,r-
Figure 7: Ribbed slab for flexibility to accommodate openings.
(b)
Figure 6: Solid flat slab: (a) without drop s; (b) with drop s; (c) with shearhead.
Figure 8: Band beam and slab construction using tableforms. 5
Precast slabs
Composite precast slabs
Precast slabs offer the advantage of off-site manufacture, with a reduction in site labour and site formwork. When the slabs are prestressed there are additional benefits of longer spans and higher load capacity. A popular type of precast floor is the hollow core slab (Figure 9). The relatively lightweight units form a flush soffit when placed. A shear key between units ensures load sharing and the construction is commonly capable of developing diaphragm action without the need for a structural topping. The precast units are easy to remove and can accommodate a wide range of floor openings.
Composite precast slabs combine precast floor elements with in situ concrete in an economical way, eliminating traditional formwork for floor construction, and providing long-span floors. Thin precast concrete floor plates can be combined with an in situ topping to form composite one-way spanning floors up to 6 m long, or, in combination with precast beams, to form a composite ribbed slab (Figure lOa). For extremely long spans, double-T precast beams and a composite in situ topping is preferred (Figure 10b).
CONCLUSION The buildings surveyed in this publication demonstrate that reinforced and prestressed concrete floors with spans ranging from 6 to 20 m, are technically feasible and economically competitive. This is a direct consequence of improved design and analysis techniques, higher strength materials, better construction methods and finally, more construction-led design.
Figure 9: Precast hollow core planks:flexibility for alterations.
Figure IO: Composite floors: (a) precast ribbed floor; (b) double-T beam floor. 6
SURVEY DATA Section 1:
Solid flat slabs Reinforced - Buildings 1 to 7 Prestressed - Buildings 8 to 12
Section 2: Ribbed slabs Reinforced -Buildings 13 to 15 Prestressed -Buildings 16 to 22
Section 3: Waffle slabs Reinforced -Buildings 23 to 25 Prestressed - Buildings 26 to 28
Section 4:
One-way spanning solid slabs and beams Buildings 29 to 33
Section 5: Precast slabs Buildings 34 to 36
Section 6:
Composite precast slabs Buildings 37 to 40
7
SECTION 1 SOLID FLAT SLABS
m
2
I
7.2x7.2
mm I
ratio I
300
24
1
m3 1
I
0.30
Jr
kg I
30.0
3600
Ji
1 I
6-O
Solid flat slab -reinforced
’ r ~~~~ ’ Frame
action
3600
1"
GradeC40 Code BS 8110
7200
'i
3600
n
1"
3600
I
I-
300 slab
-
7 J
-
n
7
_I
-
8
n
Solid flat slab -reinforced
No. of floors 10
Materials per m2 Design of floor area load Depth Span/depth Conc;ete Rebar kN/,,$ Slab
Span m
mm
ratio
7.5x6.1 3 0 0
Stability
Notes
Shear walls
Grade C35 Code BS 8110
kg
25
0.30
45.0
6-O
I
I
I
I
8
I
I
I
300 slab I
-
I
I
I
I
I
I
I
Typical floor plan
A
9
Solid flat slab -reinforced
3000
3000
5 i(J 7500
A i
n
8 2
400 slab
400 slab
E
mi
n 1
I
_L
1 /
i
Typical floor plan
10
Solid flat slab -reinforced
No. of floors 7
Materials per m* Design of floor area load Depth Span/depth Conc;ete Rebar kN/,-,-,* mm ratio kg Slab
-
Span m 65x45
250
26
0.25
29.0
5 0
Stability
Notes
Shear walls
Grade C35 Code BS 8110
I
17 ccc 45 Typical floor plan
1`
Solid flat slab -reinforced
No. of floors 4
Materials per m* Design of floor area load
Slab Span m
Stability
Depth Span/depth Conc;ete Rebar kNirn2 mm ratio kg
9-5x 7.3 310
30.6
0.31
Typical floor plan
41.5
5.0
Shear walls
Notes (See page 3)
C30 lightweight Code 110
Solid flat slab -reinforced
Materials per m2 Design of floor area load Depth Span/depth Co;;ete Rebar kN/r-$ mm ratio kg Slab
No. o f Span floors m 13
5800
8 0x7.2
275
3 irr 7200
275 slab
Typical floor plan
29
0.28
5800
40.7
5-o
Stability
Notes
Shear walls
Grade C35 Code BS 81 10
Solid flat slab -reinforced
Stability I
I
9.2x6.0
7 I
I I
255 II
I
0.26
36
I
I
I
I
I
I
Notes (See page 3)
I
I
II
24.0 II
5.2
-
h
6200
4
5 ((I 6000
255 slab
Typical floor plan
14
Solid flat slab - prestressed
2
(”
Span m
P
x
x
Design load Depth Span/depth Con$ete Rebar Strand kN/r-$ ratio mm kg kg
8.0x8-0 275
29.1
10-2
0,275
,.~- . .
I
Gl
Materials per m2 of floor area
Slab
No. of floors
4
8
10..0
Stability
Notes
Shear walls
Grade C40 Code BS 8110
.‘j----
X i..t
:*
x
x
I”
m
x
x
x x x
0
X
0
Eico
x
Atrium
X
X
m
m
m
m
PI
m
m
P1
J
First-floor plan
Column head detail
I
I
15
Solid flat slab - prestressed
Stability
a
7.2x 7.2 240
30.0
0.240
2.4
4.7
Notes
Shear walls
6.5
* See Concrete Society TechnIcal Reports No 17 and No 25
3 ((I 7200
4800
0 0
cu
P-
n
n
Typical floor plan
c
:i,
950
I / Column head detail
c
475
”
’ 240 $ 50 i 250
Solid flat slab - prestressed
Materials per m’ of floor area
Slab
No. of floors
9
Span m
Depth Span/depth Conx$ete mm ratlo
9 4x9-o 300
31 3
0 300
Design l o a d Rebar Strand kN/mz kg kg
14-l
78
50
Stability
Steel bracing to columns
Notes (See page 3) Grade C40 Code BS 8110 CS TR 17 & 25* Steel c o l u m n s with shearheads
* See Concrete Society TechnIcal Reports No 17 and No 25
45000
P
m
B
a
I
m
I
Typical floor plan
Cross-bracing
17
Solid flat slab - prestressed
No of floors
7
Materials per m* of floor area
Slab Span m
11 5 x 7 5 325
35 4
O-325
11
1
See Concrete Society TechnIcal Reports No 17 and No 25
Typical floor plan
8
Design
load Depth Span/depth Concrete Rebar Strand kN/mz mm ratio m3 kg kg
65
50
Stability
Notes
Frame action
Grade C40 Code BS8110 CSTR 17&25*
Solid flat slab - prestressed
Slab Stability
r
7200
c
3600
*
Typical floor plan
Typical column head detail
7200
2400 *II
7200
+
3600
*
7200
Notes
J
SECTION 2 RIBBED SLABS
Ribbed slab -reinforced
Materials per m* Rib Beam No. Des of floor area ,__ign of wad floors Span Depth Span/depth Span B x D Span/depth Concrc ?te R e b a r kN/m* 10
m
mm
ratio
m
mm
ratio
m3
kg
9.0
450
20.0
8.0
1200 x 450
13.3
0.23
39.5
7.5
Notes
Stability
(See page 3)
Frame action
Grade C35 Code BS 8110
7 ((1 9000
1
I
Typical floor plan
Typidal rib section
20
Typical beam section
Ribbed slab - reinforced
No. of floors 11
Materials per m2 of floor area f$$” Stability
Beam
Rib
Notes (See page 3)
Span Depth Span/depth Span B x D Span/depth ConcJete Rebar kN/m* mm ratio kg m ratio mm m 9.0
425
9000
21 .l
9.0
1800 x425
6750
21.1
4 @ 7500
5.0
38.5
0.27
i
6750
1
Shear walls
Grade C35 Code BS 8110
9000
5 (u, 9000 Typical floor plan 1500 _~~ __~ 125 L
-t
‘T 1425 I I
l-l
7Ii
425
: 1800
250
Typical rib section
Typical beam section
Ribbed slab - reinforced
floors Span Depth Span/depthSpan m
5
mm
9.0 3 0 0
Materials per m2 of floor area Dri,n Stability
Beam
Rib
No.
ratio
30.0
m
B x D Span/depth
mm
1800 7-2 x 4 0 0
ratio 18.0
0.32
6 ((I‘ 7200
29.0
5.0
Shear walls
I
9000
1800 Typical rib section
22
Notes
Conc;ete Rc??r kN/mz
Typical beam section
Grade C35 Code BS 8110
i
7200
i
Ribbed slab - prestressed
No. of
Rib
Materials per m* of floor area
Beam
Design load
Stability
Notes
Frame action
Grade C35 Code BS 8110
floors Span Depth Spacing Span/depth Span B x D Span/depth Type Concrete Rebar Strand kN/& m mm mm ratio m mm ratio kg kg 3
9.0
3 2 5
1200
27-7
1800
18-5
6.0 x 3 2 5
Pt’
0 194
12 6 3.65
6.0
‘Prestressed
Typical floor plan
100 325
Typical rib section
ki!
23
Ribbed slab - prestressed
I
No.
I
-I of floors
Materials per m* of floor area
Beam
Rib
Stability
Notes
Span Depth Spacing Span/depth Span B x D Span/depth Type Con;;ete Rebar Strand kN/t-$ m
22
9.0
mm
mm
250
750
ratio
36.0
m
mm
ratio
2200 7.5 x 2 5 0
30.0
kg
Pt’
0.186
kg
7 . 0 3 5.79
*Prestressed
10 @ 7500
i
Typical floor plan
2200
750 125
,
A -
-r
s
.250
250
I-
\
175 Typical rib section
24
Design load
Column head detail
5.0
Shear walls
Grade C40 Code 110
Ribbed slab - prestressed
Materials per m2 Beam Rib NO. Design of floor area of load floors Span Depth Spacing Span/depth Span B x D Span/depth Type Con;;ete Rebar Strand kN/m* mm
mm
ratio
9.8 400
725
24.5
m
8
m
ratio
mm
1 9 4 1200 x 800
24.2
Pt”
0.354
kg
kg
16.9
9.76
6.0
Stability
Shear walls
Notes
Grade C40 Code 110 ‘Prestressed
I.
I.
I. 13000
9350
9350
I.
10000
I
Typical floor plan
c
725
75
725
P
725
Typical rib section
25
Ribbed slab - prestressed
Materials per m2 Rib Beam No. Design of floor area o f load floors Span Depth Spacing Span/depth Span B x D Span/depth Type Concrete Rebar Strand kN/r-$ m 5
L
mm
10.85 450
mm 850
ratio
m
mm
ratio
24.1
12.5
1500 x450
28.0
‘Prestressed
Typical floor plan
Typical section
L
Pt*
m3
kg
kg
0.280
8.3
6-63
5.0
Stability
Notes
Shear
Grade C40
walls
Code 110
Ribbed slab - prestressed
Materials per m* Beam Rib Design No. of floor area load o f floor s Span Depth Spacing Span/depth Span B x D Span/depth Type Conc;ete Rebar Strand kN/m* m 5
mm
135 475
mm
ratio
1500
28 4
m
mm
ratio
9 . 0 1500 x475
Pt*
18.9
0,285
kg
kg
15.0
4.93
Notes
Stability
Shear walls Grade C40 and frame Code BS 8110 action
60
l Prestressed
I II II II I II II I II II I II II
I
u /’
/
/
II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II I I II
II II II II II II II II II II II I I II II II
I I I I
L~LJLJL~LJLJLJLJLJLJLJLJLJL.~L.n n w
I
riririr~r~rlrlr~r~r~r~r~r~r~r~,
ririr
II II II II II I II II I/ I II II II II II II 11 II II II I’ II I II I II II II II II II II II II II II L~L~L~L~L~L~L~L~L~L~~~~~~~~~~~~~~~~~,~~
I I
I II II II II II II I /I II II II II I I II
I
r-i r
II
II
I I I I II II II
iririr~r-lr~r~r~r1rlrlrlr~r~r~r~rlrl
II II II II II I I I II II II II II I I I II II II II II I I I L J -JLJLJ LJLJLJL-ILJLJ I I I
n
II II II
I I I
II
II II
n
r -1 -1rir-i r Iririririrl
I
I
II II
I I I
II II II
II II II
II II II
II II II
II II II
II II II
II II II
II II II
I I I
I
LJL~ILJLJLJLJLJLJLJ
n
n riririririr
I
I
II II II II II II II II I II II II II II I I LA _ _J L A L A LJLJLJLJLALJ LJLJLJLJLJLJLJLJL.~J II
II
I
8
10
ll~-lrlrl -
I”
Typical floor plan
1500 125
‘r
1500
Typical beam section
1, J:
1
425
Typical rib section
27
Ribbed slab - prestressed
Materials per m2 Rib Beam Design No. of floor area of load floors Span Depth Spacing Span/depth Span B x D Span/depth Type Concrete Rebar Strand kN/m2 m
5
mm
14.4 650
mm
m
ratio
22.2
2400
mm
ratio
1200 7.2 x 6 5 0
R.C.*
0,268 1 4 . 7
Notes
Shear walls
Grade C40 Code BS 8110
kg
kg
11 .0
Stability
4.33
7.0
“Reinforced
B0
8 @ 7200 1
f
: I I
II
II II II
II
I I
II
I II I II I II
II II II II II
:I II
jl 11
II
n
ll iI iI II
II II II II
II II II I
ll
II
II
II
n II
E
n Ii
I7 II
11 II
r7 II
fl II
I4 L L
M -IL I I - I I AIL u lb ““““““/
Typical floor plan
2400
28
II II
;
J u u u H H H H H - u .-IL Al- u -IL ii- il -IL II_
Typical section
II
500
Ribbed slab - prestressed
Materials per m’ Rib Beam Design No. of floor area load of floors Span Depth Spacing Span/depth Span B x D Span/depth Type Concrete Rebar Strand kN/m’ m mm mm ratio m mm ratio kg kg 4
16.3 525
31 .0
850
6.3
275 X1000
R.C.*
6.3
0.225
9.8
5.66
Stability
Shear walls
6.0
Notes
Grade C40 Code 110 ‘Reinforced
7 @ 6300
_
i
t
Typical floor plan
100
I
850
8
5
0 %
850
i
Typical section
29
SECTION 3 WAFFLE SLABS No. of floors 5
Column spacing m
Waffle slab - reinforced
Materials per m* Design of floor area Depth Span/depth load Stability mm ratio Con-v$ete R e b a r S t r a n d kN/m2 21.2
6.6 X 7.43 350
5835
0.245
kg
kg
24.0
-
7425
I
Frame Grade C35 Code BS 8110 action
6-O
3 @ 4950
---*
Typical floor plan
Ribs at 900 crs
! 125
4;7 I
1600 Section at column head
30
Notes
Waffle slab - reinforced
No. of floors 3
Column spacing m
Materials per m2 Design of floor area Depth Span/depth load mm ratio Con;;ete R e b a r S t r a n d kN/m2
7.5x10 5 5 2 5
, 7500
typical
20.0
0.450
kg
kg
67.0
-
6-O
Stability
Notes
Frame Grade C35 action Code BS 8110
,
Typical floor plan
Typical section
31
Waffle slab - reinforced
No. of floors
Column spacing m
3
10.18 x10.18
Depth Span/depth mm ratio 550
_
Materials per m* of floor area
Design load Stability
18-5
0.396
37.0
-
k
Typical section
9.0
Shear Grade C35 Code BS 8110 walls
3 @ 10180
Typical floor plan
32
Notes
Conc;ete R e b a r S t r a n d kN/m2 kg kg
125 14
Waffle slab - prestressed
No. of floors 1
Materials per m2 of floor area
Design Notes Depth Span/depth load Stability (See page 4) mm ratio Compete Rebar Strand kN/m2 kg kg Shear Grade C40 15.9 2.52 6.0 0.349 24.0 12.0x12.0 500 Code BS 6110 walls Column spacing m
6000
4 @ ’ 12000
q
CIOOOOOOO
rlnnnnnnrin
Typical floor plan
Typical section
125
33
Waffle slab - prestressed
No. of floors 2
Column spacing m
Materials per m* Design of floor area Depth Span/depth load Stability mm ratio Cor?$ete R e b a r S t r a n d kN/m*
12.7x12.7 500
25.4
*
0.341
12700
Typical floor plan
Typical section
kg
kg
12.2
5.60
6.0
Shear walls
Notes
Grade C35 Code BS 8110
Waffle slab - prestressed
Stability
Notes
~c~~~
Grade C40 Code BS 8110 CS TR No. 17*
*See Concrete Society Technical Report No 17
5 @ 15000
1
1 ,;:j; ji
‘: :’ ‘: ‘_-: ::~:: ::p::-::-:,
;.:I.
‘-7.. :.::.
: :: 1
:.
:
li
:’
ij
:
. -. .: ..-.. ~.i[:lI: :.::..:..:.::.:: ‘:~::..l‘i‘: ::..LL
: :~::z..
.I! j :::.: .::
a :, : .;_;;
1_~1;.1;.1;:1:.:1~1!_. ~.. :.~:.~::~’
i
.,: :I..
.iilii:
:.!:~:.~I:.::.::.::.:!.:L.::! !L : :-:“:.::‘I:.‘,~ . . . . . .~..~_.
,..,:
.,
: : ::r::
__,:
Lo:!
::~::
!!
.-..-.
:,
,,
:: :
::=:: ,!
,I
‘: :, : ::-::-::.:, ,I
.,
,,
. . ..i.:
Atrium
Typical floor plan
Typical section
225
35
SECTION 4 ONE-WAY SPANNING SOLID SLABS & BEAMS
One-way spanning solid slab and beam
Materials per m2 Slab Beam No. Design of floor area of . load floors Span Depth Span/depth Type Span B x D Span/depth Type Concrete Rebar Strand kN/+’ m 4
mm
ratio
7.43 200
37.2
m Pt*
9.0 1 5 0 0
‘Prestressed
Typical floor plan
Typical beam section
36
mm
x 500
ratio 18.0
m3 Pt*
0.261
kg
Stability
Notes
kg
1 4 . 0 4.11
4.0
Shear
Grade C35
walls
Code BS 8110
One-way spanning solid slab and beam Slab Beam No. o f floors Span Depth Span/depth Type Span BxD Span/depth Type m
6
mm
10.30 2 5 0
ratio
41.2
m
Pt*
mm
1500 6.0 x 4 5 0
ratlo
13.3
R.C.+
Materials per m2 of floor area
Design load
Stability
Notes
Conc;ete Rebar Strand kN/m* kg kg
0.298
13.9
3.93
t
6.8
Shear walls
Grade C30 Code 110
‘Prestressed +ReInforced
250 slab
Typical floor plan
Typical beam section
37
One-way spanning solid slab and beam Materials per m2 Beam Slab Design No. of floor area load of floors Span Depth Span/depth Type Span BxD Span/depth Type Concrete Rebar Strand kN/m2 ratio m3 kg kg mm m mm m ratio 7
12.6 3 3 5
37.6
Pt*
Precast perimeter wall
‘Prestressed
335 slab
Typical floor plan
38
0 335
11.8 8.25
6.8
Stability
Shear walls
Notes (See page 4)
C40 lightweight Code BS 8110
One-way spanning solid slab and beam
Beam Slab No. of floors Span Depth Span/dept Tyee Spnn BxD Span/depth Type m 10
mm
6 75 220
m
ratio
30 7
R.C.* 10
mm
600x 0 6oo
Materials pe r m2 of floor area
Design load
Stability
Notes
Shear walls
C40 lightweight Code 110
Conc;et e %??r StFgn d kN/m2
ratio
16.7
R.C.*
0.26
42-O
-
5 0
*ReInforced
E0
Typical floor plan
Main beam section
39
One-way spanning solid slab and beam
No. of floors
Slab
Materials per m2 of floor area
Beam
Design load Span Depth Span/depth Type Span B x D Span/depth Type Con-$ete Rebar Strand kN/& m mm m mm ratio ratio kg kg
5
6.0
175
34.3
R.C.*
9.0
1500 x425
21.2
R.C.*
0.25
52.0
-
‘Reinforced
Typical floor plan
425 :
Typical section
40
5.0
Stability
Notes
Shear walls
Grade C40 Code BS 8110
SECTION 5 PRECAST SLABS
Precast slab
Materials per m2 of floor area Beam Slab Design No. In situ Precast load Stability of floors Span Section Span/depth Span B x D Span/depth Conc;ete Rebar Strand Conc;ete Rebar kN/r-$ m
12
7.0
mm
203
ratio
34.5
m
mm
ratio
300 6.0 x 6 0 0
10.0
kg
0.145
4.8
kg
kg
40
Notes
0,011
0.4
7.0
Shear walls
C50, BS 8110 7% in situ Hollow core planks No topping
6 @ 6000
1
.
Typical floor plan
Precast
“yqFy=
:z
300 Centre beam section
41
Precast slab
m
4
mm
7.2
I
200
I
36.0
Design load B xD Span/depth Concrete Rebar Strand Conc$ete Rebar kN/m2
m
mm
7.2
600 x600
ratio
I
I
m3
ratio
12.0
1
Typical floor plan
Typical section
kg
o-193
I
7200
5400
1
1
kg
Stability
Notes
Shear
Grade C50 Code BS 8110 Hollow core
kg
3.0
7.9
I
7200
7200
42
Materials per m’ of floor area In situ Precast
Beam
Slab No. of floors Span Section Span/depth Span
-
I
-
I
7200
planks No topping
I
7200
5400
1
7.0
1
7200
1
Precast slab
Materials per m2 of floor area Slab Beam No. - Design In situ Precast load of floors Span Sectlon Span/depth Span B x D Span/depth Concrete Rebar Strand Con$ete Rebar kN/m* m
3
77
mm
200
ratio
38.5
m
mm
m3
ratio
7 . 4 3 ,$;o 1 2 . 4
0.157
kg
10.5
kg
Stability
Notes (See page 4)
kg
2.55
- -
6.5
Frame action
Grade C50 Code BS 6110 Hollow core
planks No topplng
Typical floor plan
Typical section
43
SECTION 6 COMPOSITE PRECAST SLABS Rib No. of . floors Span Depth Span/depth Span mm m m ratio
9
14.5
560
25.9
4.8
Composite precast slab
Materials per m2 of floor area In situ Precast
Beam
Design load Depth Span/depth Concrete Rebar Strand Concrete Rebar kN/m2 mm ratio m3 kg kg m3 kg 500x 1000 (Perimeter)
Stability
Grade C60 Code 110 any$$ar Double Tees, wrth In situ topping walls Precast H frame Frame
4.8
0.150
5.75
0.080
6.3
14500
.
2.2
5.0
I
4800 typical
I
47600 Typical floor plan
1200
, In s i t u t o p p i n g
i
-/
Typical section
44
Precast double-T beams
Notes (See page 4)
Composite precast slab
f10 2 Span
m
4
16.7
22.0
4.9
600x 900 (Perimeter)
1.54
Frame action
5.0
9 @ 4877
?
~f?~+kPl-rr~P~~~n’n-n
i
‘II II II ‘I I II ‘II II ‘II II Ii ‘II Il l II II ‘I I II I ‘II II II ‘II II II ‘II II II - + tit c- b !,
z co
0,075
0,133 5 - 4 8 7 . 7 9
5.4
2438 ‘i *
111 1) 1
I
In situ
Notes
load Stability Depth Span/depth Con;;ete Rebar Strand Conc;ete Rebar kN/m’ mm ratio kg kg kg
Depth Span/depth Span mm ratio m
785
Materials per m” o Precast
Beam
Rib
No.
II II I I
II
II
II
II
II
II
II
II
II
2438
8
II
I I I I II
II
II
II
I I II II
I I I I I I I I II
II
II
II
II
II
II
I I I I III I I II III Ill II lib II III II III II III II II IIP II II III I I II III
I I I I I I
I I
I I I I I I I I II II II II I I I I II I I II II I I II II II I I II I I I I II I I II II II II II II I II III L km c hL c Lu,u--u-uLu~ u-u~u-u,u-u-uLu, u u4 Ad 4 u Am11 4 4 44 -IF
Typical floor plan
1200
/’
In situ topping
1 j-=-f
Precast double-T beams Typical section
J
n~n’n~n~n-n’n~~n~~n~nLr~~n111141ild 1’1111Vfb II
I
75 (average)
Grade C60 Code 110 Double Tees, with in situ topping Precast H frame
;710
I
Composite precast slab
Rib No. of floors Span Depth Span/depth Span m
6
mm
/ 12.0 1
m
ratio
610
/
Design
. load
Stability
Notes
Depth Span/depth Concrete Rebar Strand Concrete Rebar kN/m* ratio mm m3 kg kg m3 kg
750x j 9.0 1 ,in”;FU, 1
19.7
Materials per m2 of floor area Precast In situ
Beam
14.8
1 0.134 (13,751 - 1 0.111 110 721
5.7
Frame action
In situ C35 Precast C45 Code BS 8110 55% In situ
I
r ir’ir’ir i r ’ i r ’ i r I I
II II II
ir’ir
II
II
II
II
II
II II
II
II
II
I
ir ir’ir’ir irwirlir ir
II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II Ii II II II II II II II II II II II II
II
II
II
II
II
II
II
II
II
II’
Typical floor plan
55 precast soffit plank Precast rib Typical rib section
46
Typical in situ beam section
Composite precast slab
3
Materials per m2 of floor area Precast In situ
Beam
No. o f floors Span
Design load
Depth Span/depth Concrete Aebar Strand Concrete Rebar kN/m’
m
mm
ratio
m3
kg
kg
m3
kg
21.2
750 Precast
28.3
0,123
4.9
7.6
0.060
2-28
5.0
Stability
Shear walls
Notes
Grade C62 Codes 115, 116 40% In situ
72000
1
c
,
8 cv i;
_ ~n-=-rt-~n-“-~-un~~~~nn~~~“~h~~n~n~n~~~~~nnnunu~~~=-n~~n~~~~ ,, ,, II Ii II I II II II II I I I II 1 II II II II il II II II II I I’ II II II ‘I II II II II II II ‘I II II II II I, II II II II II ,, ,, ‘1,
II
11
II
II
‘II
II
II ‘I ~:I~_:~ ”
11, AlI !I, ‘I, JIl
II II II I! II
II II
II llr :! Id II lli:
I’
II ‘I Nt ~ ‘I ” I’ I’ I
II II II
~~11R# II- 11~;
II II II
II II
II v ,I Ii
;~
II t
II II! II IIL IlL
I
II IIL II II II IIL II II II II II II II 1: 1: I’ II I’ I! I’ II II II II II II II II II II II II II II II II II !I II II II II II II II II II II II II II II II II vYv-Y~~Y~4_yu~~~L-L_-v~y~.~_yu_u_y-y-y _ y--y-y4~-y~y-&icy~~ 4 y u y~y-y~y--y~yy-yy
Typical floor plan
Beams @
Precast soffit planks
Precast beam Typical section
1500 crs.
Economic long-span concrete floors P.W. Matthew and D.F.H. Bennett BRITISH CEMENT ASSOCIATION PUBLICATION 9 7.3 11
CI/SfB I
(13)
I
q4
I
(Y6)
UDC 624.073.012.4.003.1
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