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Istructe Manual for the Design of Concrete Building Structures
IStructE Manual for the Design of Reinforced Concrete Building Structures (Birtish Code)
IStructE suggested textbook list.pdf
Published by The Institution of Structural Engineers
building sfructures
StructE/ICE Reinforced concrete building structures 2nd edition
5D J. Lee, BScTech, DIG, FEng, FlStructE, FICE, FIHT, Chairman until 1994
S. J. Alexander, MA, CEng, MiStructE, MICE
P. Beckmann, MSc(Eng), CEng, FiStructE, MICE, HonRIBA, MIngF
P. G. Cobb, CEng, MICE
*B. H. Fisher BSc, CEng, FlStructE, FICE
R. S. Narayanan, BE, MSc, DIC, CEng, FlStructE, Chairman since 1994
R. F. D. Povey, CEng, FlStructE
H. C. Symonds, MA, CEng, FlStructE, MICE
E Walley, CB, MSc, PhD, FEng, FlStructE, FICE
D. J. Wilson, BSc(Eng), CEng, MlStructE
K. R. Wilson, MA, CEng, MICE
P. F. Winfleld, CEng, FlStructE
R. J. W. Mime, BSc, Secretary to the ad hoc Committee
#deceased April 2001
*deceased November 1989
The second edition was edited by R. S. Narayanan, FREng, BE, MSc, DIC, CEng, FISiructE, August 2001.
First edition published 1985. Reprinted with minor corrections: December 1985, June 1986 and
Telephone: +44(0)20 7235 4535
+44(0)20 7235 4294
mailistructe.org.uk
ISBN 0901297 21 6
2002: The Institution of Structural Engineers, The Institution of Civil Engineers.
Cover illustration: Use of the Rorcon column connector at Prospect Park, Heathrow, UK
(courtesy of O'Rourke Civil Engineering/CONSTRUCT)
The Institution of Structural Engineers and the members who served on the Task Group that produced this
report have endeavoured to ensure the accuracy of its contents. However, the guidance and reconimendations given should always be reviewed by those using the report in the light of the facts of their particular
case and any specialist advice. No liability for negligence or otherwise in relation to this report and its
contents is accepted by the Institution, the members of the Task Group, its servants or agents.
by any means without prior permission of the Institution of Structural Engineers, who may be contacted at
11 Upper Belgrave Street, London, SW1X 8BH.
StructE/ICE Reinforced concrete buflding structures 2nd edition
1.1 Aims oftheManual
1.3 Contents of the Manual
2.7 Serviceability limit states
2.8 Material design stresses
2.6Loading
3.4 Structural form and framing
3.5 Fire resistance and durability
3.6 Stifflhess
3.6.1 Slabs
3.6.2 Beams
3.7.2 Loading
3.7.3 Width of beams and ribs
3.7.4 Sizes and reinforcement of columns
3.7.5 Walls
3.7.6 Shear in flat slabs at columns
3.7.7 Adequacy of chosen sections to accommodate the reinforcement, bending moments
3.9 Reinforcement estimates
4.1.1 Checking of all information
4.1.2 Preparation of a list of design data
4.1.3 Amendment of drawings as a basis for final calculations
IstructE/ICE Reinforced concrete building structures 2nd edition
4.1.4 Final design calculations
4.2 Slabs
4.2.2 Fire resistance and durability
4.2.2.1 Fire resistance
4.2.2.2 Durability
4.2.3 Bending moments and shear forces
4.2.3.2 One-way spanning slabs of approximately equal span
4.2.3.3 Two-way spanning slabs on linear supports
4,2.3.4 Flat slabs
4.2.4 Span/effective depth ratios
4.2.4.1 Slabs on linear supports
4.2.4.2 Flat slabs without drops
4.2.5 Section design solid slabs
4.2.5.1 Bending
4.2.5.2 Shear
4.2.5.3 Openings
4.2.6 Section design ribbed and coffered slabs
4.2.6.1 Bending
4.2.6.2 Span/effective depth ratios
4.2.6.3 Shear
4.2.6.4 Beam strips in ribbed and coffered slabs
4.2.7 Notes on the use of precast floors
4.3 Structural frames
4.3.1 Division into sub-frames
4.3.3 Redistribution of moments
4.3.4 Design shear forces
4.4.2 Fire resistance and durability
4.4.2.1 Fire resistance
4.4.2.2 Durability
4.4.3 Bending moments and shear forces
4.4.4 Span/effective depth ratios
4.4.5 Section design
4.4.5.1 Bending
4.4.5.2 Minimum and maximum amounts of reinforcement
4.4.5.3 Shear
4.5.2 Slenderness, fire resistance and durability
4.5.2.1 Slendemess
4.5.2.2 Fire resistance
4.5.2.3 Durability
IStructE/ICE Reinforced concrete duilding structures 2nd edition
4.5.3 Axial loads and moments
4.5.4 Section design
4.5.5 Biaxial bending
4.5.6 Reinforcement
4.6.2 Slenderness, fire resistance and durability
4.6.2.1 Slenderness
4.6.2.2 Fire resistance
4.6.2.3 Durability
4.6.3 Axial loads and moments
4.6.3.1 In-plane bending
4.6.3.2 Bending at right-angles to the walls
4.6.4 Section design
4.6.4.1 Walls resisting in-plane moments and axial loads
4.6.4.2 Walls resisting in-plane moments, axial loads and transverse moments
4.6.4.3 Intersecting walls
4.6.5 Reinforcement
4.6.6 Openings in shear and core walls
4.7 Staircases
4.7.2 Fire resistance, durability and concrete grades
4.7.3 Bending moments and shear forces
4.7.4 Effective spans
4.7.4.1 Stairs spanning between beams or walls
4.7.4.2 Stairs spanning between landing slabs
4.7.4.3 Stairs with open wells
4.7.5 Span/effective depth ratios
4.7.6 Section design
4.8 Design of non-suspended ground floor slabs
4.9 Guidance for the design of basement walls
4.9.2 Bending moments and shear forces
4.9.3 Section design
4.9.4 Foundation
4.9.5 Reinforcement
4.10.2 Durability and cover
4.10.3 Types of foundation
4.10.4 Plan area of foundations
4.10.5 Design of spread footings
4.10.5.1 Axially loaded unreinforced pad footings
4.10.5.2 Axially loaded reinforced pad footings
4.10.5.3 Eccentrically loaded footings
4.10.6 Design of other footings
4.10.6.1 Strip footings
4.10.6.2 Combined footings and balanced footings
4.10.7 Reinforcement
4.10.8 Design ofrafts
4.10.9 Design of pile caps
4.10.10 Reinforcement in pile caps
4.11 Robustness
4.11.2 Tie forces and arrangements
4.12 Detailing
4.12.2 Bond and anchorage
4.12.3 Laps and splices
4.12.4 Hooks, bends and bearings
4.12.5 Curtailment of reinforcement
4.12.6 Corbels and nibs
Appendix A Reinforcement qunntities
Appendix B Design dnta
Appendix C Exposure conditions
Appendix D Column design chnrts
Table 2 Minimum member sizes and cover for initial design of continuous members
Table 3 Span/effective depth ratios for initial design of slabs
Table 4 Span/effective depth ratios for initial design of beams
Table 5 Ultimate loads for stocky columns
Table 6 Ultimate bending moments and shear forces
Table 7 Fire resistance requirements for slabs
Table 8 Durability requirements for slabs
Table 9 Ultimate bending moment and shear force in one-way spanning slabs
Table 10 Bending moment coefficients for two-way spanning rectangular slabs
Table 11 Ultimate bending moment and shear force in flat slabs
Table 12 Span/effective depth ratios for solid slabs
Table 13 Modification.factors for M/lxF for slabs
Table 14 Lever arm and neutral axis depth factors for slabs
Table 15 Ultimate shear stress for v flat slabs
Table 16 Span/effective depth ratios for ribbed and coffered slabs
Table 17 Fire resistance and cover for beams
Table 18 Durability requirements for beams
Table 19 Design ultimate bending moments and shear forces for beams
Table 20 Span/effective depth ratios for beams
Table 21 Modification factors for M/ba for beams
Table 22 Modification factors for compression reinforcement for beams
Istruct F/ICE Reinforced concrete building structures 2nd edition
Table 23 K'factors for beams
Table 24 - Lever arm and neutral axis depth factors for beams
Table 25 Minimum areas of tension reinforcement for beams
Table 26 Clear distance between bars in mm according to percentage distribution
Table 27 Ultimate shear stresses v (N/mm2) for beams
Table 28 Minimum provision of links in beams
Table 29 Effective height factors for columns
Table 30 Fire resistance requirements for colunms
Table 31 Durability requirements for columns
Table 32 Enhancement coefficients for biaxial bending
Table 33 Effective height factors for walls
Table 34 Fire resistance requirements for walls
Table 35 Durability requirements for walls above ground
Table 36 Span/effective depth ratios for stairs
Table 37 Modification factors for M/bcf for stairs
Table 38 Depth/projection ratios for unreinforced footings
Table 39 Reinforcement percentages, depth/projection ratios and ground pressures for reinforced footings
Table 40 Ultimate anchorage bond lengths and lap lengths as multiples of bar size
Table 41 Minimum radii, bend and hook sizes and effective anchorage lengths
Table Al Solid slabs and stairs
Table A2 Ribbed and coffered slabs
Table A3 Beams
Table A4 Columns
Table AS Walls
ftructE/ICE Reinforced concreto duilding structures 2nd edition
In 1982 the Institution of Structural Engineers formed a Committee to prepare a Manual for the design of
reinforced concrete building structures which would be compatible with British Standard BS 8110. Happily
the Institution of Civil Engineers has joined in this task and this document is the result. It has been written
by and for practising designers and thus reflects the logical sequence of operations which a designer follows.
The Manual covers the majority of reinforced concrete buildings, but with the deliberate exclusion of
some items. For example, prestressed and lightweight concretes are not covered and the range of structures
is limited to those not dependent on the bending of columns for resistance against horizontal forces. The first
limitation does not imply a bias against the use of prestressed or lightweight concrete in buildings while the
second limitation recognizes that buildings are usually designed to be braced by strongpoints such as shear
walls, infill panels and the like.
Users will note that the recommendations given in this Manual fall within the wider range of options in
BS 8110.
The Committee has aimed at clarity and logical presentation of reinforced concrete design practice in
writing the Manual. It is hoped that the concise format will be welcomed.
The Manual offers practical guidance on how to design safe, robust and durable structures. The initial
design section is a novel feature of the Manual, and the guidance given will make a positive contribution to
design practice. If these initial design procedures are followed, the final calculations can be carried out
expeditiously. The information has been laid out for hand calculation but the procedures are suited for
electronic computations as well.
The preparation of the Manual has proceeded concurrently with, but independently of, BS 8110. Helpful
comment has been received from members of the BS 8110 Committee, including the Chairman, Dr D. D.
Matthews, DrA. W. Beeby and Mr H. B. Gould. Indeed there has been a valuable two-way exchange which
has had an impact on BS 8110.
During the preparation many people have commented, and I would be grateful if any further comment
could be forwarded to the Institution.
Lastly I would like to express my thanks to the members of the Committee and their organizations and
also to our Secretary, Mr. R. J. W. Mime, for the enthusiasm and harmonious relations which have
characterised our work.
Since the publication of the Manual in 1985, a number of changes affecting the design of reinforced concrete
structures have occurred. The most significant of these include:
Amendments to BS 8110, which was republished in 1997 and further amended in 2001;
The publication of BS 8002 for the design of earth retaining structures; and
The publication of BS 8666, which superseded BS 4466.
This amendment to the Manual reflects the effect of all of the above. The most notable changes to BS 8110
include amendments to partial factors for loads when earth and water loads are present, the reduction of Ym
for reinforcement from 1.15 to 1.05 and changes to punching shear formulae. The reduction of the partial
factor for reinforcement also affects the modification factor for spanldepth ratio and the values of spacing
Bending dimensions for the reinforcement shown in the Manual comply with the new BS 8666.
As a result of feedback from practising engineers, some spanldepth values for initial design have also
All the amendments are signified by a line in the margin.
ThisManual provides guidance on the design of reinforced concrete building structures. Structures design
in accordance with this Manual will normally comply with BS 8110'.
The range of structures and structural elements covered by the Manual is limited to building structures, using
normal weight concrete and which do not rely on bending in columns for their resistance to horizontal forces.
This will be found to cover the vast majority of all reinforced concrete building structures. For detailing rules
the Standard method of detailing structural concrete2 should be used.
For structures or elements outside this scope BS 8110' should be used.
general principles that govern the design of the layout of the structure
fmal design of members.
This section outlines the general principles that apply to both initial and final design and states the design
parameters that govern all design stages.
One engineer should be responsible for the overall design, including stability, and should ensure the
compatibility of the design and details of parts and components even where some or all of the design and
details of those parts and components are not made by the same engineer.
The structure should be so arranged that it can transmit dead, wind and imposed loads in a direct manner
to the foundations. The general arrangement should ensure a robust and stable structure that will not collapse
progressively under the effects of misuse or accidental damage to any one element.
Lateral stability in two orthogonal directions should be provided by a system of strongpoints within the
structure so as to produce a 'braced' structure, i.e. one in which the columns will not be subject to sway
moments. Strongpoints can generally be provided by the core walls enclosing the stairs, lifts and service
ducts. Additional stiffness can be provided by shear walls formed from a gable end or from some other
external or internal subdividing wall. The core and shear walls should preferably be distributed throughout
the structure and so arranged that their combined shear centre is located approximately on the line of the
resultant in plan of the applied overturning forces. Where this is not possible, the resulting twisting moments
must be considered when calculating the load carried by each strongpoint. These walls should generally be
of reinforced concrete not less than 180mm thick to facilitate concreting, but they may be of 21 5mm
brickwork or 200mm solid blockwork properly tied and pinned to the framing for low- to medium-rise
Strongpoints should be effective throughout the full height of the building. If it is essential for
strongpoints to be discontinuous at one level, provision must be made to transfer the forces to other vertical
It must be ensured that floors can act as horizontal diaphragms, particularly if precast units are used.
Where a structure is divided by expansion joints each part should be structurally independent and
designed to be stable and robust without relying on the stability of adjacent sections.
All members of the structure should be effectively tied together in the longitudinal, transverse and vertical
A well-designed and well-detailed cast-in-situ structure will normally satis' the detailed tying
requirements set out in subsection 4.11.
Elements whose failure would cause collapse of more than a limited part of the structure adjacent to
them should be avoided. Where this is not possible, alternative load paths should be identified or the element
in question strengthened.
Movement joints should be provided to minimise the effects of movement caused by, for example,
shrinkage, temperature variations, creep and settlement.
The effectiveness of movement joints depends on their location. Movement joints should divide the
structure into a number of individual sections, and should pass through the whole structure above ground
level in one plane. The structure should be framed on both sides of the joint.
Some examples of positioning movement joints in plan are given in Fig. 1.
Fig. 1 Location of movement joints
Movementjoints may also be required where there is a significant change in the type of foundation or
For reinforced concrete frame structures, movement joints at least 25mm wide should normally be
provided at approximately 50m centres both longitudinally and transversely. In the top storey and for open
buildings and exposed slabs additional joints should normally be provided to give approximately 25m spacing.
Attention should be drawn to the necessity of ensuring that joints are incoiporated in the fmishes and in
the cladding at the movement joint locations.
In order for a structural member to be able to cany its load during and after a fire its size may need to be
greater than that which is dictated by purely structural considerations. Similarly, the cover to reinforcement
necessaiy to ensure durability may dictate the lower limit of the cross-sectional dimensions.
This Manual adopts the limit-state principle and the partial factor format of BS 81 tO'. The loads to be used
in calculations are therefore:
Characteristic dead load, Gk: the weight of the structure complete with fmishes, fixtures and fixed
partitions (BS 648)
Characteristic imposed load, Qi (BS 6399, Part 1)
Characteristic wind load, Wk (CP 3, Chapter V; BS 6399, Part 2)
Nominal earth load, E (BS 80026)
At the ultimate limit state the horizontal forces to be resisted at any level should be the greater of:
(i) 1.5% of the characteristic dead load above that level, or
(ii) The wind load derived from BS 6399 Part 2 multiplied by the appropriate partial safety factor.
The horizontal forces should be distributed between the strongpoints according to their stiffliess.
The design loads are obtained by multiplying the characteristic loads by the appropriate partial safety
factor yf from Table 1.
The 'adverse' and 'beneficial' factors should be used so as to produce the most onerous condition.
Table 1 Partial safety factors for load
dead, Gk
earth* and
imposed, Ok
wind Wk
water, E
1 dead and imposed
(and earth and
2. dead and wind
3. dead, wind and
imposed (and
earth and wafer
* The earth pressure is that obtained from BS 80026 including an appropriate mobilisation factor. The more onerous of the two
factored conditions should be taken.
* The value of 1.2 may be used where the maximum credible level of the water can be clearly defined, If this is not feasible.
a factor off .4 should be used.
Unplanned excavation in accordance with BS 8002 Cl .3.2.2.2 not included in the calculation.
6Unplanned excavation in accordance with BS 8002 Cl 3.2.2.2 included in the calculation.
Provided that the span/effective depth ratios and bar spacing rules are observed it will not be necessary to
check for serviceability liniit states.
Design stresses are given in the appropriate sections of the Manual. The partial safety factors for strength of
materials, 7m, are the same as those given in BS 8110'.
lStructE/ICE Reinforced concrete butding structures 2nd edition
In the initial stages of the design of building structures it is necessary, often at short notice, to produce
alternative schemes that can be assessed for architectural and functional suitability and which can be
compared for cost. They will usually be based on vague and limited information on matters affecting the
structure such as imposed loads and nature of finishes, let alone firm dimensions, but it is nevertheless
expected that viable schemes be produced on which reliable cost estimates can be based.
It follows that initial design methods should be simple, quick, conservative and reliable. Lengthy
analytical methods should be avoided.
This section offers some advice on the general principles to be applied when preparing a scheme for a
structure, followed by methods for sizing members of superstructures. Foundation design is best deferred to
later stages when site investigation results can be evaluated.
The aim should be to establish a structural scheme that is suitable for its purpose, sensibly economical,
and not unduly sensitive to the various changes that are likely to be imposed as the overall design develops.
Sizing of structural members should be based on the longest spans (slabs and beams) and largest areas
of roof and/or floors carried (beams, columns, walls and foundations). The same sizes should be assumed
for similar but less onerous cases this saves design and costing time at this stage and is of actual benefit in
producing visual and constructional repetition and hence, ultimately, cost benefits.
Simple structural schemes are quick to design and easy to build. They may be complicated later by other
members of the design team trying to achieve their optimum conditions, but a simple scheme provides a
good 'benchmark' at the initial stage.
Loads should be carried to the foundation by the shortest and most direct routes. In constructional terms,
simplicity implies (among other matters) repetition; avoidance of congested, awkward or structurally
sensitive details and straightforward temporary works with minimal requirements for unorthodox
sequencing to achieve the intended behaviour of the completed structure.
Standardised construction items will usually be cheaper and more readily available than purpose-made
Loads should be based on BS 648, BS 6399: Part l and Part 2, and BS 80026.
Imposed loading should initially be taken as the highest statutory figures where options exist. The
imposed load reduction allowed in the loading code should not be taken advantage of in the imtial design
stage except when assessing the load on the foundations.
Dead loading on plan should be generous and not less than the following in the initial stages:
floor finish (screed)
ceiling and service load
demountable lightweight partitions
l.8kNIm2
1 .OkN/m2
24kN/m3
The design ultimate load should be obtained as follows:
Density of reinforced concrete should be taken as
dead load + imposed load
1.4 x characteristic dead load + 1.6 x characteristic imposed load
1.0 x characteristic dead load + 1.4 x characteristic wind load, or
1.4 x characteristic dead load + 1.4 x characteristic wind load
dead load + imposed load + wind load
1.2 x all characteristic loads
Fornormal construction in the UK, a characteristic concrete strength of 30N/mm2 should be assumed for the
initial design. In areas with poor aggregates this may have to be reduced. In the final design a higher grade
concrete may have to be specified to meet durability requirements.
In the UK a characteristic strength of 460N1mm2 should be used for high-tensile reinforcement and
250N/mm2 for mild steel. European and American steel may, for some time to come, have different yield
strengths, and corresponding values should be used.
3.4 Sfructural form and framing
provide stability against lateral forces and ensure braced construction by arranging suitable shear
walls deployed symmetrically wherever possible
adopt a simple arrangement of slabs, beams and columns so that loads are carried to the foundations
by the shortest and most direct routes
allow for movement joints (see subsection 2.4)
choose an arrangement that will limit the span of the slabs to 5tim and beam spans to 8lOm on a
regular grid; for flat slabs restrict column spacings to 8m
adopt a minimum column size of 300 x 300mm or equivalent area
ensure robustness of the structure, particularly if precast construction is envisaged.
The arrangement should take account of possible large openings for services and problems with foundations,
e.g. columns immediately adjacent to site boundaries may require balanced or other special foundations.
The size of structural members may be governed by the requirement of fire resistance and may also be
affected by the cover necessary to ensure durability. Table 2 shows the minimum practical member sizes for
different periods of fire resistance and the cover to the main reinforcement required for continuous members
in mild and moderate environments. For severe exposures, covers should be increased. For simply supported
members, sizes and covers should be increased (see section 4).
3.6 Stiffness
To ensure adequate stiffliess, the depths of slabs and the waist of stairs should not be less than those derived
The ratios for two-way slabs have been calculated for a square panel. For a 2 x 1 panel, the ratio for a
one-way panel should be used and the ratios interpolated for intermediate proportions. The depth should be
based on the shorter span.
Flat slab design should be based on the longer span dimension. For exterior panels, 85% of the ratios
quoted in Table 3 should be used.
StructEPCE Re+torced concrete butd+g structures 2nd edfficn
Table 2 Minimum member sizes and cover for inital design
of continuous members
Columns fully
Slabs with plain soffit
Slabs with ribbed
open soffit and no
thickness of structural topping plus any non-combustible screed
Ribbed slabs should be proportioned so that:
the rib spacing does not exceed 900mm
the rib width is not less than 125mm
the rib depth does not exceed four times its width.
The minimum structural topping thickness should preferably be 75mm, but never less than 50mm or onetenth of the clear distance between ribs, whichever is the greater.
For ribbed slabs, 85% of the ratios quoted in Table 3 should be used.
Two-way spanning
One-way spanning
Beams should be of sufficient depth to avoid the necessity for excessive compression reinforcement and to
ensure that an economical amount of tension and shear reinforcement is provided. This will also facilitate
the placing of concrete. For initial sizing the effective depth should therefore be determined from Table 4. If
other considerations demand shallower construction, reference should be made to subsection 4.4.
For spans greater than 1 Om the eftective depth ratios should be multiplied by I O/)span in metres).
When the depths of slabs and beams have been obtained it is necessary to check the following:
width of beams and ribs
column sizes and reinforcement
shear in flat slabs at columns
practicality of reinforcement arrangements in beams, slabs and at beam-column junctions.
Ultimate loads, i.e. characteristic loads multiplied by the appropriate partial safety factors, should be used
throughout. At this stage it may be assumed that all spans are fully loaded, unless the members concerned
are sensitive to unbalanced loading.
For purposes of assessing the self-weight of beams, the width of the downstand can be taken as half the
depth but usually not less than 300mm.
The width should be determined by limiting the shear stress in beams to 2.ON/mm2 and in ribs to O.6N/mm2
for concrete of characteristic strength ? 30N/mm2:
widthofbeam(inmm) =
widthofrib(inmm) =
o.6d
where V is the maximum shear force (in kN) on the beam or rib, considered as simply supported and
d is the effective depth in mm.
ForJ < 30N/mm2 the width should be increased in proportion.
IStructE/ICE Reintorced concrete building structures 2nd edition
Stocky colunms should be used, i.e. columns for which the ratio of the effective height to the least lateral
dimension does not exceed 15, where the effective height equals 0.85 times the clear storey height.
The colunms should be designed as axially loaded, but to compensate for the effect of eccentricities, the
ultimate load from the floor immediately above the column being considered should be multiplied by the
For columns loaded by beams and/or slabs of similar stifihess on both sides of the column in two
directions at right-angles to each other, e.g. some internal columns
For colunms loaded in two directions at right-angles to each other by unbalanced beams and/or
slabs, e.g. corner columns
In all other cases, e.g. faade columns
It is recommended that the columns are made the same size through at least the two topmost storeys, as the
above factors may lead to inadequate sizes if applied to top storey columns for which the moments tend to
be large in relation to the axial loads.
The ultimate loads that can be carried by columns of different sizes and different reinforcement
percentages p may be obtained from Table 5 forf = 30N/mm2 andf = 460N/mm2.
300x 350
*provided that the smallest dimension is not less than 200mm, any shape giving on equivalent area may be used.
The values of the cross-sectional areas in Table 5 are obtained by dividing the total ultimate load,
factored as above, by a 'stress' that is expressed as:
0.35f + ji0.67fy 0.35f)
wheref is the characteristic concrete strength in N/mm2
is the characteristic strength of reinforcement in N/mm2, and
is the percentage of reinforcement.
Walls canying vertical loads should be designed as columns. Shear walls should be designed as vertical
cantilevers, and the reinforcement arrangement should be checked as for a beam. Where the walls have
returns at the compression end, they should be treated as flanged beams.
1250w (area supported by column)
0.6N/mm2
(colunm perimeter+9h) d
where w is the total ultimate load per unit area in kNIm2,
is the thickness of the slab at the colunm in mm, and areas are in m2.
1250w(areasupportedbycolumn)
(column perimeter) d
0.8 ,/ f or5N/mm2 whichever is the lesser.
3.7.7 Adequacy of chosen sections to accommodate the reinforcement,
In the initial stage the reinforcement needs to be checked only at midspan and at the supports of critical
Bending moments and shear forces in continuous structures can be obtained from Table 6 when:
the imposed load does not exceed the dead load
there are at least three spans and
the spans do not differ in length by more than 15% of the longest span.
F = total design ultimate
load on span
Central point loads
design ultimate point load
0.100 FL
0.080 FL
0.150 WL
0.175 WL
0.65 F
where L is the spars
Alternatively, bending moments and shear forces may be obtained by moment distribution.
If the longer span l,, does not exceed 1.5 times the shorter span 1, the average moment per metre width may
be taken as:
w kNmper metre
lStructE/ICE Reinforced concrete building structures 2nd edition
where w is the ultimate load in kN/m2, and l, and 1,, are in metres.
If 1>1.5 l, the slab should be treated as acting one-way.
Determine the moments per unit width in the colunm strips in each direction as 1.5 times those for one-way
Assess the bending moments at midspan on a width equal to the rib spacing, assuming simple supports
If the longer span does not exceed 1.5 times the shorter span, estimate the average rib moment in both
directions as:
lyix kNm
If 1> 1.5 1 the slab should be treated as acting one-way.
Assess the average bending moment at midspan on a width equal to the rib spacing using Table 6. For the
column strips increase this by 15%.
0.95f xO.8d
where M is the design ultimate bending moment under ultimate load at the critical section and d is the
effective depth.*
If, for a rectangular section, M> 0.1 5fbd2, compression reinforcement is required:
M0.15fbd2
0.95f(dd')
Where A'5 is the area of the compression steel, d' is the depth to its centroid, b is the width of the section
and d its effective depth.*
If, for flanged sections, M> 0.4fb fh f (d 0.5h the section should be redesigned.
b and h fare the width and the thickness of the flange. h should not be taken as more than 0.5d.
When the areas of the main reinforcement in the members have been calculated, check that the bars can be
* Consistent units need to be used in the formula
arranged with the required cover in a practicable manner avoiding congested areas.
In beams, this area should generally be provided by not less than 2 nor more than 8 bars. In slabs, the
bar spacing should not be less than 150mm nor more than 300mm; the bars should not be less than size 10
nor normally more than size 20.
At this stage general arrangement drawings, including sections through the entire structure, should be
prepared and sent to other members of the design team for comments, together with a brief statement of the
principal design assumptions, e.g. imposed loadings, weights of fmishes, fire ratings and durability.
The scheme may have to be amended in the light of comments received. The amended design should
form the basis for the architect's drawings and may also be used for preparing reinforcement estimates for
In order for the cost of the structure to be estimated it is necessary for the quantities of the materials,
including those of the reinforcement, to be available. Fairly accurate quantities of the concrete and brickwork
can be calculated from the layout drawings. If working drawings and schedules for the reinforcement are not
available it is necessary to provide an estimate of the anticipated quantities.
The quantities are normally described in accordance with the requirements of the Standard method of
measurement (SMIM)7. In the case of reinforcement quantities the basic requirements are, briefly:
for bar reinforcement to be described separately by: steel type (e.g. mild or high yield steel), size
and weight and divided up according to:
(a) element of structure, e.g. foundations, slabs, walls, columns, etc. and
(b) bar 'shape', e.g. straight, bent or hooked; curved; links, stirrups and spacers.
for fabric (mesh) reinforcement to be described separately by: steel type, fabric type and area,
divided up according to 1(a) and 1(b) above.
There are different methods for estimating the quantities of reinforcement; three methods of varying
accuracy are given below.
The simplest method is based on the type of structure and the volume of the reinforced concrete elements.
Typical values are, for example:
warehouses and similarly loaded and proportioned structures: 1 tonne of reinforcement per 10m3.
residential, schools: 1 tonne per 15.0m3.
However, while this method is a useful check on the total estimated quantity it is the least accurate, and it
requires considerable experience to break the tonnage down to SMM
Another method is to use factors that convert the steel areas obtained from the initial design calculations to
weights, e.g. kg/rn2 or kg/rn as appropriate to the element. Tables Al to A5 in Appendix A give factors for
the various elements of the structure that should be used for this purpose.
If the weights are divided into practical bar sizes and shapes this method can give a reasonably accurate
assessment. The factors, however, do assume a degree of standardization both of structural form and
This method is likely to be the most flexible and relatively precise in practice, as it is based on
reinforcement requirements indicated by the initial design calculations.
For this method sketches are made for the 'typical' cases of elements and then weighted. This method has
the advantages that:
the sketches are representative of the actual structure
the sketches include the intended form of detailing and distribution of main and secondary
an allowance of additional steel for variations and holes may be made by inspection.
This method can also be used to calibrate or check the factors described in method 2 as it takes account of
individual detailing methods.
When preparing the final reinforcement estimate, the following items should be considered:
Laps and starter bars
A reasonable allowance for normal laps in both main and distribution bars, and for starter bars has
been made in Tables Al to AS. It should however be checked if special lapping arrangements are
The drawings should be looked at and sufficient allowance made for the reinforcement required for
such 'non-structural' features
A contingency of between 10-15% should be added to cater for some changes and for possible
IStructE/ICE Reinforced concrete building sfructures 2nd edition
4.1 Infroduction
Section 3 describes how the initial design of a reinforced concrete structure can be developed to the stage
where preliminary plans and reinforcement estimates maybe prepared. The cost of the structure can now be
Before starting the final design it is necessary to obtain approval of the preliminary drawings from the
other members of the design team. The drawings may require flirther amendment, and it may be necessary
to repeat this process until approval is given by all parties. When all the comments have been received it is
then important to marshal all the information received into a logical format ready for use in the final design.
This may be carried out in the following sequence:
checking of all infonnation
preparation of a list of design data
amendment of drawings as a basis for final calculations.
To ensure that the initial design assumptions are still valid, the comments and any other information received from
the client and the members of the design team, and the results of the ground investigation, should be checked.
Ensure that no amendments have been made to the sizes and to the disposition of the shear walls. Check that
any openings in these can be accommodated in the final design.
Check that the loading assumptions are still correct This applies to dead and imposed loading such as floor
finishes, ceilings, services, partitions and extemal wall thicknesses, materials and finishes thereto.
Make a final check on the design wind loading and consider whether or not loadings such as earthquake,
accidental, constructional or other temporary loadings should be taken into account.
Fire resistance, durabifity and sound insulation
Establish with other members of the design team the fife resistance required for each part of the structure,
the durability classifications that apply to each part and the mass of floors and walls (including finishes)
required for sound insulation.
Examine the information from the ground investigation and decide on the type of foundation to be used in
the final design. Consider especially any existing or future structure adjacent to the perimeter of the structure
that may influence not only the location of the foundations but also any possible effect on the superstructure
and on adjacent buildings.
Structt/ICE Reintorced concrete buflding structures 2nd edition
Decide on the concrete mixes and grade of reinforcement to be used in the final design for each or all parts
of the structure, taking into account the fire-resistance and durability requirements, the availability of the
constituents of concrete mixes and any other specific requirements such as water-excluding concrete
construction for basements.
The information obtained from the previous check in subsection 4.1.1 and that resulting from any
discussions with the client, design team members, building control authorities and material suppliers should
be entered into a design information data list. A suitable format for such a list is included in Appendix B.
This list should be sent to the design team leader for approval before the final design is commenced.
The preliminaiy drawings should be brought up to date incorporating any amendments arising out of the
fmal check of the information previously accumulated and fmally approved.
In addition the following details should be added to all the preliminaiy drawings as an aid to the fmal
Establish grid lines in two directions, mutually at right-angles for orthogonal building layouts. Identify these
Give all walls, columns, beams and slabs unique reference numbers or a combination of letters and numbers
related if possible to the grid, so that they can be readily identified on the drawings and in the calculations.
Mark on the preliminary drawings the loads that are to be carried by each slab. It is also desirable to mark
on the plans the width and location of any walls or other special loads to be earned by the slabs or beams.
When all the above checks, design information, data lists and preparation of the preliminary drawings have
been carried out the final design calculations for the structure can be commenced. It is important that these
should be carried out in a logical sequence. The remaining sections of the Manual have been laid out in the
following order, which should be followed in most cases:
retaining walls, basements
robusiness, and
IStructE/ICE Reinforced concrete building strucfures 2nd edition
There will be occasions when this sequence cannot be adhered to, e.g. when the foundation drawings are
required before the rest of the structural drawings are completed. In such instances extra care is required in
assessing the loads and other requirements of the superstructure design.
The first step in preparing the final design is to complete the design of the slabs. This is necessary in order
that the fmal loading is determined for the design of the frame.
The initial design should be checked, using the methods described in this subsection, to obtain the fmal
sizes of the slabs and to calculate the amount and size of reinforcement.
This subsection gives fire resistance and durability requirements, and bending and shear force
coefficients for one-way spanning slabs, two-way spanning slabs on linear supports, flat slabs, and ribbed
and coffered slabs. The treatment of shear around columns for flat slabs and the check for deflection for all
types of slab are given, together with some notes on the use of precast slabs. The coefficients apply to slabs
For those cases where no coefficients are provided the bending moments and shear forces for one-way
spanning slabs may be obtained from a moment distribution analysis. These moments may then be
redistributed up to a maximum of 30%, although normally 15% is considered a reasonable limit. The
following criteria should be observed:
Equilibrium must be maintained
The redistributed design moment at any section should not be less than 70% of the elastic moment.
Check that the section complies with requirements for fire resistance
Check that cover and concrete grade comply with requirements for durability
Make final check on span/depth ratios
Calculate reinforcement
For flat slabs check shear around columns and calculate shear reinforcement if found to be
4.2.2 Fire resistance and durabitity
The member sizes and reinforcement covers required to provide fire resistance are given in Table 7. The
covers in the Table may need to be increased to ensure durability (see clause 4.2.2.2).
Where the cover to the outermost reinforcement exceeds 40mm special precautions against spalling may
be required, e.g. partial replacement by plaster, lightweight aggregate or the use of fabric as supplementary
reinforcement (see BS 8110, Part 2').
If the width of the rib is more than the minimum in Table 7 the cover maybe decreased as below:
Decrease in cover, mm
Increase in width, mm
Plain soffit solid slob
(including hallow pot, joist + block)
Minimum overall depth, mm
Ribbed soffit
(including 1-section + channel section)
Minimum thickness/width, mm/mm
an upper limit to the water/cement ratio
a lower limit to the cement content
a lower limit to the thickness of cover to the reinforcement
good compaction and
Values for (a), (b) and (c) which, in combination, will be adequate to ensure durability are given in Table 8
As (a) and (b) at present cannot be checked by methods that are practical for use during construction,
Table 8 gives, in addition, the characteristic strengths that have to be specified in the UK to ensure that
requirements (a) and (b) are satisfied.
The characteristic strengths quoted in Table 8 will often require cement contents that are higher than
those given in the Table. The potential problems of increased shrinkage arising from high cement and water
contents should be considered in the design.
4.2.3.1 Genera!
Slabs should be designed to withstand the most unfavourable arrangements of design loads.
iSfrucfE/ICE Reinforced concrete building sfrucfures 2nd edition
Cover to all reinforcement
Maximum free water/cement ratio
Minimum cement content. kg/m3
(For definitions see Appendix C)
Charactetstic concrete strength in the UK, N/mm2
1. The cover to oil reinforcement should not be less than the nominal maximum size of the aggregate
2. The cover in mm to the main reinforcement should not be less the bar size
Design for a single load case of maximum design ultimate load on all spans or panels will be sufficient
In a one-way spanning slab the area of each bay exceeds 30m2. In this context, a bay means a strip
across the full width of a stnucture bounded on the other two sides by lines of supports (see Fig. 2)
The variation in the spans does not exceed 15% of the longest span
The ratio of the characteristic imposed load to the characteristic dead load does not exceed 1.25
The characteristic imposed load does not exceed 5kN/m2 , excluding partitions
In the analysis the elastic support moments other than at a cantilever support should be reduced by
20%, with a consequential increase in the span moments. The resulting bending moment envelope
should satisr the following provisions:
(i) Equilibrium must be maintained
(ii) The redistributed moment at any section should not be less than 70% of the elastic moment
Where a cantilever of a length exceeding one-third of the adjacent span occurs, the condition of maximum
load on the cantilever and minimum load on the adjacent span must be checked.
The effective width of solid slabs assumed to resist the bending moment arising from a concentrated load
may be taken to be:
Width=1 +2.4 (1
is the load width
is the distance to the nearer support from the section under consideration
isthespan
For loads near an unsupported edge see BS 8110'.
lStrucfE/ICE Reinforced concrete building structures 2nd edition
Fig. 2 DefinitIon of panels and bays
Where the conditions in clause 4.2.3.1 are met, the moments and shear forces in continuous one-way
spanning slabs may be calculated using the coefficients given in Table 9. Allowance has been made in these
coefficients for the 20% reduction mentioned above.
Bending moments in two-way slabs may be calculated by yield-line analysis. Alternatively, the following
coefficients may be used to obtain bending moments in the two directions for slabs whose ratio of the long
span to the short span is 1.5 or less and with edge conditions described in Table 10:
where f3 and J3 are the coefficients given in Table 10 and 1 is the shorter span.
The distribution of the reactions of two-way slabs on to their supports can be derived from Fig. 3.
4.2.3.4 Flat slabs
Ifa flat slab has at least three spans in each direction and the ratio of the longest span to the shortest does not
exceed 1.2, the maximum values of the bending moments and shear forces may be obtained from Table 11.
Where the conditions above do not apply, bending moments in flat slabs have to be obtained by frame
analysis (see subsection 4.3). A single load case may be applicable subject to satisfying the conditions in
clause 4.2.3.1. The structure should then be considered as being divided longitudinally and transversely into
frames consisting of columns and strips of slab. The width of slab contributing to the effective stiffness
should be the full width of the panel. The stiffening effects of drops and column heads may be ignored for
the analysis but need to be taken into account when considering the distribution of reinforcehient.
Table 9 Ultimate bending moment and shear force in one-way spanning
End support/slab connection
lnteor
- 0.O4Fl
- 0086Ff
- 0.063F1
where F is the total design ultimate load 11 .4Gk + 1 .6Qkl for each span and I is the effective span
Table 10 Bending moment coefficients for two-way spanning
Types of panel and moments
coefficients f<
Values of l/l
Iy//x
Negative moment at continuous
2. One short edge discontinuous
3. One long edge discontinuous
4. Two adlacent edges discontinuous
1. The reactions shown apply when all edges are continuous (or discontinuous)
2. When one edge is discontinuous, the reactions on all continuous edges should
be increased by 10% and the reaction on the discontinuous edge may be reduced
3. When adjacent edges are discontinuous, the reactions should be adjusted for elastic
shear considering each span separately
Fig. 3 Dishibution of reactions from two-way slabs on to supports
- 0.086Fl
0.063F1
- 0.063Fl
O.46F
0.04Ff
O.022F1
0.075Fl
0.086F/
where F is the total design ultimate load on a panel bounded by four columns and I is the effective spon.
Note: The moments at supports taken from this table may be reduced by 0.015Fh
Allowance has been made for 20% redistribution as a'lowed in BS 8110.
*These moments may have to be reduced to be consistent with the capacity to transfer moments to the columns. The midspan
moments t must then be increased correspondingly.
Flat slab panels should be assumed to be divided into column strips and middle strips (see Fig. 4). In the
assessment of the widths of the column and middle strips, drops should be ignored if their smaller dimension
is less than one-third of the smaller dimension of the panel.
(Longer span)
Fig. 4 DMsion of panel without drops into strips
The design moments obtained from analysis of the frames or from Table 11 should be divided between the
column and middle strips in the proportions given below:
In general, moments will be able to be transferred only between a slab and an edge or corner colunm by a
column strip considerably nanrower than that appropriate for an internal panel. The breadth of this strip, b,
for various typical cases is shown in Fig. 5 be should never be taken as greater than the column strip width
appropriate for an interior panel.
The maximum design moment that can be transferred to a column by this strip is given by:
MmaxO.15fu bed2
where d is the effective depth for the top reinforcement in the column strip. The moments obtained from
Table 11 or a frame analysis should be adjusted at the columns to the above values and the midspan moments
Where the slab is supported by a wall, or an edge beam with a depth greater than 1.5 times the thickness
of the slab, the design moments of the half column strip adjacent to the beam or wall should be one-quarter
of the design moments obtained from the analysis.
The critical consideration for shear in flat slab structures is that of punching shear around the columns. This
should be checked in accordance with clause 4.2.5.2 except that the shear forces should be increased to allow
for the effects of moment transfer as indicated below.
After calculation of the design moment transmitted by the connection, the design effective shear force
Ver at the perimeter of the column should be taken as:
Vff = 1.15 Vt for internal columns with approximately equal spans
where V is the design shear transferred to the column and is calculated on the assumption that the maximum
design load is applied to all panels adjacent to the colunra considered.
For internal columns with unequal spans
Vcf V+
where x is the side of the column perimeter parallel to the axis of bending and M is the design moment
transmitted to the column.
At corner columns and at edge columns bent about an axis parallel to the free edge, the design effective
shear is Verr =1.25 V.
For edge columns bent about an axis perpendicular to the edge, the design effective shear is 1 .4V5, for
approximately equal spans. For edge columns with unequal spans
Veff = V+
l.5M5
Compliance with the ratios below will generally limit total defiections to span!25O.
The span/effective
depth should not exceed the appropriate value in Table 12 multiplied by the modification
factor in Table 13.
Cx+ Cy
S Column strip as defined in figure 4
y is the distance from the face of the slab to the innermost face of the column
Fig. 5 Definition of breadth of effective moment transfer strip, be
lStructE,'ICE Reinforced concrete building structures 2nd edition
Table 13 Modification factor for M/bd2 for slabs
M/bd2
(f= 250) 167
(f = 460) 307
1. For spans in excess of tOrn, the above ratios should be multiplied by 1O/(span in metres).
2. M in the Table is the design ultimate moment at the centre at the span or tor a cantilever at the support.
3. For two-way slabs the ratio reters to the shorter span, and the short span moment should be used forM.
The ratio of the longer span to the corresponding effective depth should not exceed the values for slabs on
linear supports multiplied by 0.90.
Check that the applied moment is less than the moment of resistance using the formulas that are
based on the stress diagram in Fig. 6.
bd2 where K' is obtained from below:
For concrete the moment of resistance M =
%moment
ValuesK'
IStructE/ICE Reintorced concrete building structures 2nd edjtion
'Neutral axis
depthx=n.d
N------------ ----
dePth=O.9x_j,_
Lever arm z = aid
O.95fA
Fig. 6 Stress diagram
(O.95f)z
where z is obtained from Table 14.
For two-way spanning slabs, care should be taken to use the value of d appropriate to the direction
K=Mfbd2f 0.05 0.06
0.09 0.100 0.104 0.110 0.119 0.130 0.132 0.140 0.144 0.150 0.156
0.86 0.84 0.82 0.82 0.81 0.80 0.79 0.775
0.32 0.35 0.39 0.40 0.43 0.45 0,47 0.50
01 = (z/d)
n = (x/d)
Limit of Table for various % of moment redistribution
The spacing of main bars should not exceed the lesser of:
3d, 300mm, or
70000/3
wherep is the reinforcement percentage and 0.3 <p < 1.0 and
3 istheratio:
moment after redistnbution
moment before redistribution
Ifp 1 usep= 1 in fonnula above.
Spacing of distribution bars should not exceed the lesser of:
3d or 400mm.
Main bars in slabs should not be less than size 10.
The area of reinforcement in either direction should not be less than the greater of:
one-quarter of the area of main reinforcement, or
0.OOl3bh in the case of high yield steel, or
0.0024bh in the case of mild steel, or
if control of shrinkage and temperature cracking is critical, 0.0025bh high yield steel or 0.OO3bh
where h is the overall depth of the slab in mm.
The reinforcement calculated from the bending moments obtained from clause 4.2.3.3 should be
provided for the frill width in both directions.
At corners where the slab is not continuous, torsion reinforcement equal to three-quarters of the
reinforcement in the shorter span should be provided in the top and bottom of the slab in each
direction for a width in each direction of one-fifth of the shorter span.
Column and middle strips should be reinforced to withstand the design moments obtained from
clause 4.2.3.4. In general two-thirds of the amount of reinforcement required to resist the negative
design moment in the column strip should be placed in a width equal to half that of the column strip
symmetrically positioned about the centreline of the colunm.
The minimum amounts of reinforcement and the maximum bar spacing should be as stated in (b).
In the absence of heavy point loads there is normally no need to calculate shear stresses in slabs on linear supports.
For heavy point loads the punching shear stress should be checked using the method for shear around
columns in flat slabs.
In flat slabs, shear stresses should be checked first at the column perimeter:
v = 1000VeffN/rmfl2
where Veff is the effective shear force in kN (see clause 4.2.3.4)
d is the average effective depth in mm of both layers, and
U is the colunm perimeter in mm.
or 5N/mm2, whichever is the lesser.
v must in this case not exceed 0.8
v 1000VOffN/ffun2
where Uis the shear perimeter in mm as defined in Figs. 7 and 8.
Where a column is close to a free edge, the effective length of a perimeter should be taken as the lesser
of the two illustrated in Fig. 9.
Perimeter (c)
Perimeter (b)
Column perimeter
Fig. 7 Shear perimeters for internal columns
When openings are less than six times the effective depth of the slab from the edge of a column then
that part of the perimeter that is enclosed by radial projections from the centroid of the column to the
openings should be considered ineffective as shown in Fig. 10.
The first perimeter; Perimeter (b) in Fig. 7, is checked. If the shear stress here is less than the permissible
ultimate shear stress v in Table 15, no further checks are required. If v> v , successive perimeters have to
be checked until one is reached where v < v.
If the shear stress exceeds v but is less than 2v, shear reinforcement could be provided where the slab
thickness is at least 250mm. If the shear stress exceeds 2v, column heads or drop panels should be
incorporated or the slab thickness increased to reduce the shear to less than 2v.
Shear reinforcement should consist of vertical links. The total area required is calculated from equations
(a) or (b) below, whichever is appropriate. These equations should not be applied where v > 2v.
Where v<v1.6v
(v v ) ud
Where l.6v<v 2v
5(0.7v v)ud
However, A should not be taken as less than 0.4ud/0.95f.
O.75d
Failure zone 1
'a)a
Reinforcement common to 2
failure zones may be used
Required area of reinforcement
should be provided within failure zone
Fig. 8 Zones for punching shear reinforcement
Fig. 9 Shear perimeter for edge column
Fig. 10 Effect of opening on shear perimeter
Table 15 Ultimate shear stress v for flat slabs
1 ODA5
Notes to Table 15
= 30N/mm2
The tabulated values apply for
= 25N/mm2 the tabulated values should be divided by 1.062
35N/mm2 the tabulated values should be multiplied by 1.053
For = 40N/mm2 the tabulated values should be multiplied by 1.10
The reinforcement should be provided on at least two penmeters between the colunm perimeter and
perimeter (b) (see Figs. 7 and 8). The first perimeter of reinforcement should be located approximately 0.5d
from the face of the column area and should contain not less than 40% of A The second perimeter should
be located at not more than 0.75d from the first. The spacing of the legs of links around any perimeter should
not exceed 1 .5d.
The shear is now checked on perimeter (c). If reinforcement is required then this is provided between
perimeters (a) and (c) in an analogous way to that used for the check on the critical perimeter.
When openings in floors or roofs are required such openings should be trimmed where necessary by special
beams or reinforcement so that the designed strength of the surrounding floor is not unduly impaired by the
opening. Due regard should be paid to the possibility of diagonal cracks developing at the corners of
The area of reinforcement interrupted by such openings should be replaced by an equivalent amount,
half of which should be placed along each edge of the opening.
4.2.6 Section design - ribbed and coffered slabs
The bending moments per metre width obtained for solid slabs from clause 4.2.3 should be multiplied by
the spacing of the ribs to obtain the bending moments per rib.
The rib section should be checked to ensure that the moment of resistance is not exceeded by using the
methods for beams described in subsection 4.4. The area of tension reinforcement should be obtained from
the same subsection. Structural topping should contain the minimum reinforcement indicated for solid slabs.
Ribbed or coffered slabs on linear supports
The span/effective depth ratio should not exceed the appropriate value from Table 16, multiplied by
the modification factor in Table 13.
b/b=1
b/b 0.3
Notes to Table 16
1. For spans in excess of 1Dm, the rotios should be multiplied by 1 0/Ispan in metresl.
2. b is the average width of the ribs.
3. b is the effective flange width.
4. For values of b/b between 1 and 0.3, interpolate lineay between the values in the Table.
The ratio of the longer span to the corresponding effective depth should not exceed the values for
slabs on linear supports multiplied by 0.90.
The shear force per metre width obtained from clause 4.2.3 should be multiplied by the spacing of the ribs
to obtain the shear force per rib.
The shear stress should be calculated from v =
ISiructE/ICE Rentorced concrete building structures 2nd edition
where v is the design shear stress in N/mm2
V is the design shear force arising from design ultimate loads per rib in kN
b is the avenge width of the rib in mm
If the shear stress v exceeds the permissible shear stress v in Table 15 then one of the following should be adopted:
Increase width of rib
Reduce spacing of ribs
Provide solid concrete at supports
Provide shear reinforcement only if none of the above is possible.
For ribbed and coffered flat slabs, solid areas should be provided at columns, and the punching shear stress
should be checked in a similar manner to the shear around columns in solid flat slabs.
Beam strips may be used to support ribbed md coffered slabs. The slabs should be designed as continuous,
and the beam strips should be designed as beams spanning between the columns. The shear around the
columns should be checked in a similar manner to the shear around columns in solid flat slabs.
Use of precast or semi-precast construction in an otherwise in situ reinforced concrete building is not
uncommon. There are various proprietary precast and prestressed concrete floors on the market. Precast
floors can be designed to act compositely with an in situ structural topping, although the precast element can
cany loads without reliance on the topping. Design using proprietary products should be carried out closely
in conjunction with the particular manufacturer. The notes below may be helpful to the designer:
The use of a structural topping should be considered but particularly to reduce the risk of cracking
in the sereed and finishes:
(a) when floors are required to resist heavy concentrated loads such as those due to storage racking
(b) when resistance to moving loads such as forklift trucks is required
or to provide diaphragm action when a floor is used which would otherwise have insufficient
capacity for transmitting in-plane shear. When used a structural topping should always incorporate
light fabric reinforcement
In selecting a floor, fire rating, durability and acoustic insulation need to be considered as well as
Precast components should be detailed to ensure a minimum bearing when constructed, of 75mm on
concrete beams and walls, but in eases where this bearing cannot be achieved reference should be
made to BS 8110 for more detailed guidance. Mechanical anchorage at the ends should be considered.
The design should eater for the tying requirements for accidental loading (see subsection 4.11)
Precast floor units, particularly those that are prestressed, have cambers that should be allowed for
in the thickness of finishes. When two adjoining units have different spans, any differential camber
could also be critical, and this has to be allowed for in the applied finishes (both top and bottom)
A ceiling to mask steps between adjoining units may be necessary
Holes required for services need to be planned
An in situ make-up strip should be provided to take up the tolerances between precast units and in
situ construction.
4.3 Sfructural frames
The moments, loads and shear forces to be used in the design of individual columns and beams of a frame
supporting vertical loads only may be derived from an elastic analysis of a series of sub-frames. Each subframe may be taken to consist of the beams at one level, together with the columns above and below. The
ends of the columns remote from the beams may generally be assumed to be fixed unless the assumption of
a pinned end is clearly more reasonable. Normally a maximum of only five beam spans need be considered
at a time. For larger buildings, several overlapping sub-frames should be used. Other than for end spans of
a frame, sub-frames should be arranged so that there is at least one beam span beyond that beam for which
bending moments and shear forces are sought.
The relative stiffliess of members may be based on the concrete section ignoring reinforcement.
For the purpose of calculating the stiffliess of flanged beams the flange width of T-beams should be taken
as 0.14 times the effective span plus the web width and for L-beams 0.07 times the effective span plus the
web width. If the actual flange width is less, this should be used.
The loading to be considered in the analyses should be that which provides the greater values of moments
and shears for the following two cases:
all spans with maximum ultimate load (l.4Gk + l.6Qk)
alternate spans with maximum ultimate load and all other spans with minimum ultimate loads (l.OGk).
The elastic bending moments should now be calculated.
The moments obtained from the elastic analysis of the frames may be redistributed up to a maximum of 30%
to produce members that are convenient to detail and construct
'Whether to redistribute and by how much to redistribute are thus matters of engineering judgment, not
analysis'8. Normally 15% redistribution could be taken as a reasonable limit.
The criteria to be observed are:
Equilibrium must be maintained for each load case
The design redistributed moment at any section should not be less than 70% of the elastic moment
The design moment for the columns should be the greater of the redistributed moment or the elastic
moment prior to redistribution.
A simple procedure may be adopted that will satis& the above criteria:
Alternate spans loaded
Move the moment diagram of the loaded span up or down bythe percentage redistribution required;
do not move moment diagram of the unloaded span (see Fig. 11).
Elastic diagram
moment for beam
(redistributed)
Redistributed diagram
(a) Downward distribution of span loaded diagram
// -J
(b) Upward movement of span loaded diagram
Fig. 11 Redistribution procedures for frames
All spans loaded
Move the moment diagram of the loaded spans up or down by the percentage redistribution
Shear calculations at the ultimate limit state may be based on the shear forces compatible with the bending
moments arising from the load combinations noted in clause 4.3.2 and any redistribution carried out in
accordance with clause 4.3.3.
This subsection describes the final design of beams of nonnal proportions and spans. Deep beams with a
clear span less than twice the effective depth are not considered.
check that the section complies with the requirements for fire resistance
check that cover and concrete comply with durability requirements
calculate bending moments and shear forces according to subsection 4.3 or clause 4.4.3(b)
cheek span/depth ratio and determine the compression steel (if any) required to limit deflection
calculate reinforcement.
The effective span of a simply supported beam should be taken as the smaller of the following:
the distance between the centres of bearings, or
the clear distance between supports plus the effective depth d of the beam.
The effective span of a beam continuous over its supports should normally be taken as the distance
between the centres of the supports.
The effective length of a cantilever beam should normally be taken as its length to the face of the
support plus half its effective depth. Where, however, it forms the end of a continuous beam, the length to
the centre of the support should be used.
Slenderness: The clear distance between adequate lateral restraints to a beam should not exceed the
lesser ofi 60k or 250b2/d where b is the width of the compression flange midway between the restraints.
(This is not usually a limitation on beams for which a slab provides the compression flange at midspan.) For
cantilevers, the length should not exceed the lesser of 25b or 1 OOb 2/d
In normal slab-and-beam or framed construction specific calculations for torsion are not usually
necessary torsional cracking being adequately controlled by shear reinforcement.
Where the arrangement of the structure is such that loads are imposed mainly on one face of a beam
without corresponding rotational restraints being provided, torsion may be a problem. BS 8110' should be
consuhed for design for torsion.
4.4.2.7 Fire resistance
The member sizes and reinforcement covers required to provide fife resistance are shown in Table 17.
If the width of the beam is more than the minimum in Table 17 the cover may be decreased as below:
Where the cover to the outermost reinforcement exceeds 40mm special precautions against spalling may be
required, e.g. partial replacement by plaster, lightweight aggregate or the use of fabric as supplementaiy
Istructt/ICE Reinforced concrete building structures 2nd edition
Cover to main steel, mm
Minimum width, mm
a lower limit to the thickness of the cover to the reinforcement
good compaction, and
Values for (a), (b) and (c) which, in combination, will be adequate to ensure durability are given in Table 18
Characteristic concrete strength in the UK, N/mm2
Notes to Table 18
1. The cover to all reinforcement should not be less than the nominal maximum size of the aggregate.
2. The cover in mm to the main reinforcement should not be less than the bar size.
IStructE/ICE Reinforced concrete butding structures 2nd edition
Table 18 gives, in addition, the characteristic strengths that have to be specified in the UK to ensure that
The strengths quoted in Table 18 will often require cement contents that are higher than those given in
the Table. The potential problems of increased shrinkage arising from high cement and water contents should
The maximum values of the bending moments and shear forces at any section of a continuous beam may be
obtained by either:
consideration of the beam as part of a structural frame as described in subsection 4.3, or
as a beam that is continuous over its supports and capable of free rotation about them.
For beams that support substantially uniformly distributed loads over three or more spans that do not differ
in length by more than 15% of the longest span, and for which the characteristic imposed load does not
exceed the characteristic dead load, the values of the ultimate bending moments and shear forces should be
obtained from Table 19. No redistribution of moments should be made when using values obtained from this
Al tirst
At middle of
O.09F1
-0.11 F!
-0.08 F!
0.55 F
where / is the effective span and F = 1.4 Ok + 1.6 Ok
load on the cantilever and minimum load on the adjoining span must be checked.
The span/effective depth should not exceed the appropriate value in Table 20 multiplied by the modification
factor in Table 21. Compliance with these ratios will normally ensure that the total deflection does not exceed
span/250.
If the section is found to be inadequate, the span/depth ratio can be further modified using Table 22
which determines the percentage of compression steel required to limit deflections. If this percentage is
impractical, the section should be redesigned. Any compression reinforcement determined at this stage may
have to be increased to provide adequate strength (see clause 4.4.5.1).
b/b = I
Table 21 Modification factors for M/bd2 for beams
(f5=250) 167
= 460) 307
4otes to Tables 20 and 21
For spans in excess of 1 0m, the above ratios should be multiplied by 1 0/)span in metres). For exceptionally long spans the sparildepth ratio
may be exceeded it calculations of deflections are carried out according to BS 8110, Part 2.
2. M in the tables is to be taken as the moment at midspan, or for a cantilever at the support.
b is the effective width ot the compression tlange of a tlanged beam or the width of a rectangular beam.
t, is the average web width of the beam.
For values of b/b between 1 and 0.3, interpolate linearly between the values irs the Table.
4.4.5. 1 Bending
The most common beams have flanges at the top. At the supports they are designed as rectangular beams
and in the spans as flanged beams. For upstand beams, the reverse applies.
If the applied moment Mis less than the resistance moment M for the concrete, compression steel will
The resistance moments of concrete sections that are required to resist flexure only can be determined
from the formulas and Tables that are based on the stress diagram in Fig. 12. The lever arm is assumed to
be not greater than O.95d.
The effect of any small axial load on the beam can be ignored if the design ultimate axial force is less
than O.lfbd.
StrucfE/ICE Reinforced concrete building structures 2nd edition
f Stress block
TNeutral axis
Jepth=O.9x
d N---
Lever arm z= a1 d
----.4.
Fig. 12 Slress diagram
The procedure for the design of rectangular beams is as follows:
Calculate M for concrete = K'fbd2 where K' is obtained from Table 23.
Table 23 K' factors for beams
If M M for the concrete, the area oftension reinforcement A is calculated from:
where z is obtained from Table 24 for different values of K.
Table 24 Lever arm and neutral axis depth factors for beams
0.132 0.140 0.144 0.150 0.156
K=M/bd2f
0.05 0.06 0.07 0.08
Ci = (z/d)
0.94 0.93 0.91 0.90 0.89
0.13 0.16 0.19 0.22
0.100 0.104
0.110 0.119 0.130
If M> M for the concrete then compression reinforcement is needed. The area of compression steel
A's is calculated from:
M-M11
where d' is the depth of the compression steel from the compression face.
Ifd> 1
x,use7001 _)inlieuof0.95fy
The area of tension reinforcement A is calculated from:
0.95fz
For section design the effective width b of a flanged beam (see Fig. 13) should be taken as:
for T-beams: web width plus 0.21w or actual flange width if less
for L-beams: web width plus 0.11 or actual flange width if less
where 1 is the distance between points of zero moment, For a continuous beam this may be taken as 0.7
times the effective span.
Fig. 13 Beam secflons
The procedure for the design of flanged beams is as follows:
Check the position of the neutral axis by determining
using flange width b and selecting values of n and z from Table 24. Calculate x = nd.
If 0.9x h the neutral axis lies within the flange and A, is determined as for a rectangular beam, i.e.
If O.9x> h then the neutral axis lies outside the flange. Calculate the ultimate resistance moment of
the flange Mf from
MufzO.45fcu(b bw)hf (d 0.5h)
Calculate K =
M-Muf
fcu b d2
where b is the breadth of the web.
If K K', obtained from Table 23, then select the value of ai from Table 24 and calculate A, from
0.95f(d0.5h)
If Kf> K', redesign the section or consult BS 81101 for design of compression steel.
The areas of reinforcement derived from the previous calculations may have to be modified or supplemented
in accordance with the requirements below in order to prevent brittle failure and/or excessive cracking.
The minimum areas of tension reinforcement are given in Table 25.
f = 250N/mm2
Rectangular beams with overall dimensions b and h
00024 bh
0.002 bh
0.0035 bh
0.0024 bh
0.0048 bh
0.0036 bh
0.0026 bh
0.0015 ht per metre width
0.0015 hf
Flanged beams (web in tension)
b/b < 0.4
b/b 0.4
= 460N/mm2
Flanged beams (flange in tension over a continuous
Transverse reinforcement in flanges of flanged
beams (may be slab reinforcement)
per metre width
The minimum areas of compression reinforcement should be:
flanged beam web in compression
0.OO2bh
0.002b h
Neither the area of tension reinforcement, nor the area of compression reinforcement should exceed 0.04
Main bars in beams should normally be not less than size 16.
Minimum area of bars in the side face of beams (to control cracking)
Where the overall depth of the beam exceeds 500mm, longitudinal bars should be provided at a spacing not
exceeding 250mm. The size of the bars should not be less than:
for high yield bars (f = 460N/mm2)
for mild steel bars (f, = 250N/mm2)
where b is the width of the web for flanged beams and the beam width for rectangular beams. b need not
be assumed to be greater than 500mm.
Maximum spacing of tension bars
The clear space between main bars should not exceed the values in Table 26.
Table 26 Clear distance between bars in mm according to percentage
redisfributlon
Redistribution to or from section considered
The horizontal distance between bars should not be less than the bar size or the maximum size of the
aggregate plus 5mm.
Where there are two or more rows the gaps between corresponding bars in each row should be vertically
in line, and the vertical distance between bars should not be less than:
two-thirds the maximum size of the aggregate or
when the bar size is greater than the maximum aggregate size plus 5mm, a spacing less than the bar
size should be avoided.
The shear stress v at any point should be calculated from:
IStructEIlCE Reinforced concrete building structures 2nd edition
is the ultimate shear force in kN
b is the width of the beam web in mm and
is the effective depth in mm.
or SN/mm2 even if shear reinforcement is provided.
In no case should v exceed O.8/
The shear stress, v, which the concrete on its own can be allowed to resist, is given in Table 27 for
various percentages of bending reinforcement and various effective depths for 30NIrnrn2 concrete.
Table 27 Ultimate shear sfresses v (N/mm2) for beams
1 OOA5
Note to Table 27
The tabulated values apply for f = 30N/mm2
For f 35N/mm2 the tabulated values should be multiplied by 1.053
For f = 40N/mm2 the tabulated values should be multiplied by 1.10
The term A relates to that area of longitudinal tension reinforcement that continues for a distance d beyond
the section being considered. At supports the full area of tension reinforcement at the section may be
considered, provided that the normal rules for curtailment and anchorage are met.
Shear reinforcement in the form of vertical links should be provided in accordance with the minimum
areas shown in Table 28.
The spacing of links in the direction of the span should not exceed 0.75d. At right-angles to the span the
horizontal spacing should be such that no longitudinal tension bar is more than 150mm from a tension leg
of a link; this spacing should in any case not exceed d.
For beams canying a generally uniform load or where the principal load is located further than 2d from the
face of the support, the shear stress may be calculated at a section a distanced from the face of the support.
If the corresponding amount of shear reinforcement is provided at sections closer to the support, then no
further check for shear at such sections is required.
Arrangement of links
For compression reinforcement in an outer layer, every corner bar and alternate bar should be supported by
a link passing round the bar and having an included angle of not more than 135. No bar within a
compression zone should be further than 150mm from a restrained bar.
Where slabs are supported at the bottom of the beams, the links should be designed to cany the reaction
from the slab in tension in addition to any shear forces.
IStruclE/ICE Reintorced concrete building structures 2nd edition
Area of shear reinforcement
Value of v N/mm2
Less than 0.5v0
Grade 250 (mild steel) links equal to 0.18% of the hotzontal section throughout the
beam, except in members of minor structural importance such as lintels
o.5v <, < )v+ 0.4)
Minimum links for whole length of beam
(Vc + 0.4) <V
Links only provided
o.4b ,
O.95f
A5> b Svv
Where b is the width in mm of the web of) the beam
S is the spacing of the links in mm
is the total cross-section of the link)s) in mm2 (2 legs for a single closed link, 4 legs for double closed links) and
is the charactetstic strength of the links in N/mm2
In locations where the design shear stress is less than the permissible stress, small openings not exceeding
0.25d in diameter can be permitted within the middle third of the depths of beams, without detailed
calculations. Where these conditions are not met, detailed calculations should be carried out.
This subsection describes the final design of stocky columns resisting axial loads and bending moments. A
method is given for biaxial bending. The general procedure to be adopted is as follows:
1. check that the column is not slender
2. check that section size and cover comply with requirements for fire resistance
3. check that cover and concrete comply with requirements for durability
4. calculate axial loads and moments according to subsection 4.5.3
5. design section and reinforcement.
The size of column, concrete grade and the cover to reinforcement should be determined by taking into
account the requirements of slenderness, fire and durability. To facilitate concreting the minimum dimension
ofa column should not be less than 200mm.
4.5.2.1 Slenderness
The ratio of the effective height of a stocky column to its least cross-sectional dimension should be 15 or
less. The effective height should be obtained by multiplying the clear height between the lateral restraints at
the two ends of the column by the factor obtained from Table 29.
End condition at bottom
Column connected monolithically to beams on each side that are at least as deep as the overall depth of the
column in the plane considered. Where the column is connected to a foundation this should be designed to carry
moment, in order to satisfy this condition.
Column connected monolithically to beams or slabs on each side that are shallower than the overall depth of the
column in the plane considered, but generally not less than half the column depth.
Column connected to members that do not provide more than nominal restraint to rotation.
Table 30 Fire resistance requirements for columns
Cover to main
Minimum dimensions and covers are given in Table 30.
Values for (a), (b) and (c) that, in combination, will be adequate to ensure durability are given in Table 31
(For definitions see Appendix C(
Characteristic strength in the UK, N/mm2
Note to Table 31
2. The cover in mm to the main reinforcement should not be less than the bar size
Table 31 gives, in addition, the characteristic strengths that have to be specified in the UK to ensure that
The strengths quoted in Table 31 will often require cement contents that are higher than those given in
4.5.3 Axia/ /oads and moments
The minimum design moment for any column in any plane should be obtained by multiplying the ultimate
design axial load by an eccentricity, which should be taken as 0.05 times the overall column dimension in
the relevant plane but not exceeding 20mm.
When column designs are required in the absence of a full frame analysis the following procedure may
The axial loads may generally be obtained by increasing by 10% the loads obtained on the
assumption that beams and slabs are simply supported. A higher increase may be required where
adjacent spans and the loadings on them are grossly dissimilar.
The moments in the columns may be obtained using the subframes shown in Fig. 14, subject to the
minimum design moments above.
Alternatively, axial loads and moments may be obtained from the frame analysis outlined in subsection 4.3.
Sections should normally be designed using the charts in Appendix D. Alternatively, the following simplified
procedures may be adopted where applicable.
IStructE/iCE Reinforced concrete buHding structures 2nd edition
1.4GK+ 160K
0.5Kri
0.5Kb2
- esK+K+o5Kb+osKb2
eK+K+05Kb
Mft=Me KL+ K+
Mft=Mes KL+ K5+ 0.5Kbl
Me = Fixed end beam moment
Mes = Total out of balance fixed end beam moment
MF5 = Framing moment in upper column
Mft = Framing moment in lower column
K5 = Stiffnessofuppercolumn
KL = Stiffness of lower column
Ku = Stiffness of left hand beam
Kb2 = Stiffness of right hand beam
Fig. M Subframes for column moments
In the case of columns where only the minimum design moment (see subsection 4.5.3) applies, the
ultimate axial load capacity in N of the colunm may be taken as
0.4f5 A O.8f A5
wheref is the characteristic concrete cube strength in N/mm2
A is the area of concrete in mm2
is the area of longitudinal reinforcement in mm2
f is the characteristic strength ofreinforcement in N/mm2
In the case of columns supporting an approximately symmetrical arrangement of beams (i.e. where
adjacent spans do not differ by more than 15%), subject to uniformly distributed loads, the ultimate
axial load capacity of the column may be taken as:
O.35f.&+0.7fA5
where the terms have the same definitions as above.
Where it is necessary to consider bending about both axes, a symmetrically reinforced rectangular column
section may be designed by increasing the moment about one of the axes using the procedure outlined
ih'the increased moment about the x x axis is M + /3 h'M
If M <i the increased moment about they y axis is M + /3b'M
rIVIy
Where b' and h' are the effective depths (see Fig. 15) and /3 is obtained from Table 32.
Fig. 15 Biaxial bending in columns
where N is the design ultimate axial load in Newtons (N) and band hare in mm (see Fig. 15).
The section should then be designed by the charts in Appendix D for the combination of N and the relevant
enhanced moment
Minimum area of reinforcement should be 0.4% of the gross cross-sectional area of concrete.
Longitudinal bars should not be less than size 12.
Maximum area of reinforcement (other than at laps) should be 6% of the gross cross-sectional area of
concrete but 4% is generally preferable. At laps the maximum total percentage should be 10%.
Maximum spacing of main bars should not exceed 250mm.
Columns should be provided with links whose size should be the greater of one-quarter the size of the
largest longitudinal bar or size 6*.
Every corner bar and each alternate bar in an outer layer of reinforcement should have a link passing
around it. The included angle of the links should not be more than 1350 except for hoops or spirals in circular
columns. No bar within a compression zone should be further than 150mm from a bar restrained by a lmk.
The maximum spacing of links should be 12 times the size of the smallest compression bar but not more
than the smallest cross-sectional dimension of the column.
4.6 WaIls
This subsection describes the final design of stocky reinforced concrete walls that may provide the lateral
stability to reinforced concrete framed buildings. The general procedure to be adopted is as follows:
check that walls providing lateral stability are continuous through the height of the building and that
their shear centre coincides approximately with the line of the resultant of the applied horizontal
loads in two orthogonal directions; if not, calculate the resulting twisting moments and check that
they can be resisted
check that walls within any storey height are not slender
calculate axial loads and moments according to subsection 4.6.3
design section and reinforcement.
4.6.2. 1 Slenderness
The ratio of the effective height of stocky walls to their thickness should be 15 or less. The thickness should
not be less than 150mm, but to facilitate concreting 180mm is preferable. The effective height should be
obtained by multiplying the clear height between floors by the factor obtained from Table 33.
The minimum dimensions and covers should be obtained from Table 34.
4.6.2.3 Durabilily
Values for (a), (b) and (c) that, in combination, will be adequate to ensure durability are given in Table 35
This bar size may not be freely available
Wall connected monolithically to slabs on either side that are at least as deep as the overall thickness of the wall.
Where the wall is connected to a foundation, this should be designed to carry moment, in order to satisfy this
Wall connected monolithically to slabs on either side that are shallower than the overall thickness of the wall,
but not less than half the wall thickness.
Wall connected to members that do not provide more than nominal restraint to rotation.
Table 34 Fire resistance for walls
Cover to vertical
These walls may have less than 0.4% reinforcement
These walls to have between 0.4% and 1% reinforcement
These walls to have more than 1% reinforcement
Table 35 gives, in addition, the characteristic strengths that have to be specified in the UK to ensure that
The strengths quoted in Table 35 will often require cement contents that are higher than those given in
The axial load on the wall should be calculated to obtain the most onerous conditions using the partial safety
factors for loads in Table 1, and on the assumption that the beams and slabs transmitting forces into it are
The horizontal forces should be calculated in accordance with the provision of clause 2.6(e), and the inplane moments should be calculated for each lift of wall on the assumption that the walls act as cantilevers. The
moment to be resisted by any one wall should be in the same ratio to the total cantilever moment as the ratio of
Minimum cement content, kg/rn3
Notes to Table 35
The cover to all reinforcement should not be less than the nominal maximum size of the aggregate.
The cover in mm to the main reinforcement should not be less than the bar size.
its stiffness to the sum of the total stiffi3esses of all the walls resisting the horizontal forces in that direction.
The axial loads and in-plane moments should be determined as in clause 4.6.3.1. In addition, the moments
from horizontal forces acting at right-angles on the walls and from beams and slabs spanning monolithically
onto the walls should be calculated assuming full continuity at the intersection with the floor slab.
The stresses on the walls from the loads and moments should be obtained from the following expression:
extreme fibre stresses, f. =
where N is the ultimate axial load in N
M is the ultimate in-plane moment in Nnim
L is the length of wall in mm
h is the thickness of wall in mm
The ultimate compressive load per unit length equals hff N/mm. This should be equal to or less than the
ultimate load capacity:
O.35f A + O.7f
A is the area of concrete in mm2 per mm length of wall
A is the area of vertical reinforcement in mm2 per mm length of wall
f is the characteristic strength of reinforcement in N/mm2
The area of tension reinforcement if required should be obtained by calculating the total tensile force from
total tension = O.SftLth
whereJ is the extreme fibre stress in tension in N/mm2 and L is the length of the wall in mm where tension occurs.
The area of tension reinforcement should be placed within O.5L from the end of the wall where the
maximum tensile stress occurs.
The section should generally be designed on the assumption that the in-plane moments can act in both
directions and should be reinforced accordingly.
The section should firstly be designed for the case in clause 4.6.4.1. The section should then be checked f
transverse moments, treating each unit length as a colunm and additional reinforcement provided if necessary.
Where two walls intersect to form a core the interface shear may need to be checked.
The minimum area of vertical reinforcement in the wall should be 0.4% of the gross cross-sectional area of
the concrete on any unit length, and should be equally divided between the two faces of the wall.
The maximum area of vertical reinforcement should not exceed 4% of the gross cross-sectional area of
the concrete in a metre length.
When the vertical reinforcement does not exceed 2% of the gross cross-sectional area, the area of honzontal
reinforcement should not be less than 0.3% for steel off = 250N/mm2 and 0.25% forf = 460N/mm2.
The vertical bars should not be less than size 10, and the horizontal bars should not be less than size 6*
or one-quarter of the size of the vertical bars, whichever is the greater.
The maximum spacing of vertical bars should not exceed 250mm for stee1f = 250N/mm2 and 200mm
forf = 460N/mm2.
The maximum spacing of horizontal bars should not exceed 300mm.
For walls with vertical reinforcement exceeding 2% of the gross cross-sectional area the recommendations inBS 81101 should be used.
Door and service openings in shear walls introduce weaknesses that are not confined merely to the
consequential reduction in cross-section. Stress concentrations are developed at the corners, and adequate
reinforcement needs to be provided to cater for these. This reinforcement should take the form of diagonal
bars positioned at the corners of the openings as illustrated in Fig. 16. The reinforcement will generally be
adequate if it is designed to resist a tensile force equal to twice the shear force in the vertical components
of the wall as shown, but should not be less than two size 16 bars across each corner of the opening.
The reinforced concrete slab supporting the stair flights and landings should be designed generally in
accordance with the design information in subsection 4.2, except as indicated otherwise in this subsection.
*This bar size may not be freely available
Fig. 16 Reinforcement at openings in walls
When considering the dead loads for the flights, care should be taken to ensure that a sufficient
allowance is made to cater for the weight of the treads and fmishes as well as the increased loading on plan
occasioned by the inclination of the waist.
The member sizes, reinforcement covers and concrete grades to provide fire resistance and durability should
be obtained from Tables 7 and 8.
slabs and landings should be designed to support the most unfavourable arrangements of design
loads. Normally this requirement will be satisfied if staircase slabs and landings are designed to resist the
moments and shear forces arising from the single-load case of maximum design ultimate load on all spans.
Where a span is adjacent to a cantilever of length exceeding one-third of the span of the slab, the case
should be considered of maximum load on the cantilever and minimum load on the adjacent span.
Where staircases with open wells have two intersecting slabs at right-angles to each other, the loads on the
areas common to both spans may be divided equally between the spans.
4.7.4.1 Stairs spanning between beams or wa/ls
The effective span is the distance between centre-lines of supporting beams or walls.
The effective span is the distance between centre-lines of supporting landing slabs, or the distance between
the edges of the supporting slabs plus l.8m, whichever is the smaller.
The effective span and loads on each span are as indicated in Figs. 17 and 18. The arrangement of flight
supports shown in Figs. 17 and 18 is a special case where vertical support is provided at the ends of all
flights. Where this condition does not occur, the stair ifights should be designed for the full landing loads
and the effective spans should be in accordance with clauses 4.7.4.1 and 4.7.4.2.
both spans
Fig. 17 Stairs with open wells
wi = load/unit area for flights
w2 = load/unit area for landings
Fig. 18 Loading diagram
lSfructE/PCE Reinforced concrete building strucfures 2nd edifion
span/effective depth should not exceed the appropriate value from 'Table 36 multiplied by the
modification factor in Table 37.
Table 37 Modification factors for M/bd2 stairs
(f5 = 250) 167
(f5 = 460) 307
Notes to Tables 36 and 37
For spans in excess of 1 0m, the above ratios should be multiplied by 10 (span in metres).
2. M in Table 37 is the design ultimate moment at midspan or tar a cantilever at the support.
Where the stair flight occupies at least 60% of the span the permissible span/depth ratio may be increased by 15%.
The design of the landing slabs and flights should be carried out in accordance with the methods described
in subsection 4.2.5.
The overall depth of the flights should be taken as the minimum waist thickness measured perpendicular
to the soffit of the stair flight
There is normally no need to calculate shear stresses in staircases supported on beams or walls. For stair
landings, or beam strips supporting stair flights, the shear around columns should be checked in a similar
manner to the shear around columns in solid flat slab construction.
Non-suspended ground slabs are generally designed on an empirical basis. Successful design requires
attention to practical details. Thermal and moisture movements tend to produce the most critical stresses and
cracking particularly when the concrete is still green. Careful planning of joints and provision of suitable
reinforcement are essential.
Useful guidance can be obtained from reference 9.
The long strip method recommended in reference 9 is suitable for buildings where large areas of the
ground floor are free of structural walls (e.g. warehouse floors).
Where the layout of the building does not lend itself to long strip construction, the slab can be normally
cast in bays not exceeding 50m2 in area with the longer dimension of the bay limited to lOm. The slab
thickness and reinforcement can be obtained from reference 9.
This subsection describes the design of basement walls that form part of a reinforced concrete structure. The
general procedure to be adopted is as follows:
establish the requirements for the internal environment and follow the appropriate recommendations,
such as in the CIRIA guide on waterproof basements
make the walls at least 300mm thick and ensure that they comply with the slenderness provisions
in clause 4.6.2.1
check that walls comply with the requirements for fire resistance in clause 4.6.2.2
check that walls comply with the requirements for durability in clause 4.6.2.3.
The face exposed to the earth must be considered to be in a moderate environment, unless the soil is
aggressive, in which case BRE Digest 3631! should be complied with.
Bending maments and shear farces
The maximum values of the bending moments and shear forces at any section should be obtained by elastic
analysis using the appropriate ultimate loads noted in subsection 2.6*. A minimum vertical surcbarge of
lOkN!m2 should be considered where vehicular traffic could impose lateral loading on the wall.
Construction method and sequence could affect the design and should be considered early in the design process.
Any design requirements for temporary works (e.g. propping, sequence of backfllling and construction
of floors) should be stated on the drawings.
4.9.3 Sectian design
The sections should be designed in accordance with subsections 4.2 and 4.4 as appropriate. Where axial
loading is significant, the provisions of subsections 4.5 and 4.6 should be followed as appropriate.
4.9.4 Faundatian
The foundation or base slab should be designed as a strip footing under the action of the axial load and
bending moment from the wall. The base should be reinforced to ensure that the bending moments at the
base of the wall can be transmitted safely to the base slab.
The minimum area of reinforcement in each direction of the wall should be 0.4% of the gross cross-sectional
are&. The spacing of reinforcement should not exceed 300mm. Diagonal reinforcement should be provided
across the corners of any openings in the wall.
The design of the foundations is usually the fmal step. The type of foundation, the sizes and the provisional
formation levels depend on the results of the ground investigation. Until partial factors for bearing pressures
*For pressures arising from an accidental head of waler at ground level a parsial safety factor of 1.2 may be used.
lsfrucfE/ICE Reinforced concrete duilding sfrucfures 2nd edition
and pile resistances are codified it will be necessary to use the dead, imposed and wind loads on their own
(i.e. without multiplying them by the partial safety factors from Table I) for the proportioning of the
foundations. The factored loads are, however, required for determining the depths of foundations and for the
design of any reinforcement.
evaluate results of ground investigation and decide whether spread or piled foundations are to be used
examine existing and future levels around the structure, and taking into account the bearing strata
and ground water levels, determine the provisional formation levels
calculate the loads and moments, if any, on the individual foundations using the partial safety factors
in Table 1 and the imposed loading reduction in BS 6399 where appropriate
recalculate the loads and moments, if any, on the individual foundations without the partial safety
factors in Table 1, using the imposed loading reduction in BS 6399 where appropriate; in many
cases it may be sufficiently accurate to divide the factored loads and moments calculated in step 3
by 1.45
calculate the plan areas of spread footings or the number of piles to be used to support each column
or wall using the unfactored loads
calculate the depth required for each foundation and the reinforcement, if any, using the factored loads.
All foundations other than those in aggressive soil conditions are considered as being in moderate
environments (for definitions see Appendix C). cover to all reinforcement should be 50mm. For reinforced
foundations the minimum cement content should be 300kg/m3 and the maximum water/cement ratio 0.60.
The characteristic strength of the concrete for reinforced bases and pile caps should therefore be not less
than 35N/mm2. For unreinforced basesf = 20N/mm2 may be used, subject to a minimum cement content
of 220kg/m3. Where sulphates are present in significant concentrations in the soil and/or the ground water,
the recommendations of BRE Digest no. 363' should be followed.
The loads and moments imposed on foundations may be supported by any one of the following types.
Pad fooling
A square or rectangular footing supporting a single column
A long footing supporting a continuous wall
Combined fooling
A footing supporting two or more columns
Balanced fooling
A footing supporting two columns, one of which lies at or near one end
A foundation supporting a number of columns or loadbearing walls so as to transmit approximately uniform
loading to the soil
A foundation in the form of a pad, strip, combined or balanced footing in which the forces are transmitted
to the soil through a system of piles.
The plan area of the foundation should be proportioned on the following assumptions:
all forces are transmitted to the soil without exceeding the allowable bearing pressure
when the foundation is axially loaded, the reactions to the design loads are uniformly distributed per
unit area or per pile. A foundation may be treated as axially loaded if the eccentricity does not exceed
0.02 times the length in that direction
when the foundation is eccentrically loaded, the reactions vary linearly across the footing or across
the pile system. Footings should generally be so proportioned that zero pressure occurs only at one
edge. It should be noted that eccentricity of load can arise in two ways: the columns being located
eccentrically on the foundation; and/or the column transmitting a moment to the foundation. Both
should be taken into account and combined to give the maximum eccentricity
all parts of a footing in contact with the soil should be included in the assessment of contact pressure
it is preferable to maintain foundations at one level throughout.
4.10.5.1 Axially loaded unrein forced pad footings
For concrete withf = 20N/nun2 the ratio of the depth h to the projection from the column face a should be
not less than that given in Table 38 for different values of unlactored pressures, q, in kN!m2.
Unfactored ground pressure q, kNfm2
For other concrete strengths
h >0.151
In no case should h/a be less than 1, nor should h be less than 300mm.
The design of axially loaded reinforced pad footings is carried out in three stages:
Detenmne the depth of the footing from the ratios of the overall depth h to the projection from the
column face a, given in Table 39 for different values of unfactored ground pressures q.
The effective depth d should not in any case be less than 300mm.
ISfrucfE/ICE Reinforced concrefe building sfrucfures 2nd edif ion
Check that the face shear
2(c+c)d
or 5N/mm2, where Nis the factored column load in kN, c,, and c are
does not exceed v,= 0.8
the column dimensions in mm and d is the effective depth in mm.
If v does exceed v increase the depth.
With the chosen depth (revised according to stage 2, if necessary) enter Table 39 and obtain the
corresponding reinforcement percentage.
Table 39 Reinforcement percentages, depth/projection ratios and ground pressures
for reinforced footings for f, = 460N/mm2
kN51m2
.._._.beused
The above percentages apply to reinforcement withf = 460N1mm2. Forf
reinforcement percentages by 1.85.
= 250N1mm2 multiply the above
The design of eccentrically loaded footings proceeds as follows:
determine initial depth of footing from Table 39 using maximum value of unfactored ground
check punching shear according to clauses 4.2.3.4 and 4.2.5.2
check face shear according to stage 2 in clause 4.10.5.2 using Veff from clause 4.2.3.4 in lieu of N
increase the depth if necessary to avoid shear reinforcement
with the chosen depth (revised according to stage 4, if necessary) enter Table 39 to obtain the
reinforcement percentage.
Strip footings should be designed as pad footings in the transverse direction and in the longitudinal direction
at free ends or return corners. If reinforcement is required in the transverse direction it should also be provided
in the longitudinal direction and should not be less than that obtained from the procedures in clause 4.10.5.2.
4.10.6.2 Combined footings ond balanced footings
Combined footings and balanced footings should be designed as reinforced pad footings except as extended
or modified by the following requirements:
Punching shear should additionally be checked for critical perimeters encompassing two or more
closely spaced columns according to clauses 4.2.3.4 and 4.2.5.2.
Bending moments should additionally be checked at the point of zero shear between the two
columns. Reinforcement should be provided in top and bottom faces tied together by links and may
be curtailed in accordance with the detailing rules in subsection 4.12.
Where a balanced footing consists of two pad footings joined by a beam, the beam may be designed
in accordance with subsection 4.4.
Steps in the top or bottom surface may be introduced if necessary provided that they are taken into
account in the design.
Where reinforcement is required it should be provided in two generally orthogonal directions. The areas in
each direction should not be less than 0.00 l3bh for Grade 460 or 0.0025bh for Gmde 250 reinforcement,
where b and h are the breadth and overall depth in mm, respectively. All reinforcement should extend the
thll length of the footing.
If 1 > 1 .5(c , + 3d), at least two-thirds of the reinforcement parallel to l should be concentrated in a
band width (c + 3d) centred at the column, where 1, and c are the footing and column dimensions in the
x-direction and l,, and c are the footing and column dimensions in they-direction. The same applies in the
transverse direction with suffixes x and y transposed.
Reinforcement should be anchored each side of all critical sections for bending. It is usually possible to
achieve this with straight bars.
The spacing between centres of reinforcement should not exceed 200mm for Grade 460 nor 300mm for
Grade 250. Reinforcement need nonnally not be provided in the side face nor in the top face, except for
balanced or combined foundations.
Starter bars should terminate in a 90 bend tied to the bottom reinforcement, or in the case of an
unreinforced footing spaced 75mm off the blinding.
4.10.8 Design of rafts
The design of a raft is analogous to that of an inverted flat slab (or beam-and-slab) system, with the important
difference that the column loads are known but the distribution of ground bearing pressure is not. A
distribution of ground bearing pressure has to be determined that:
satisfies equilibrium by matching the column loads
satisfies compatibility by matching the relative stiffiess of raft and soil
allows for the concentration of loads by slabs or beams continuous over supports, and
stays within the allowable bearing pressure determined from geotechnical considerations of strength
Provided that such a distribution can be determined or estimated realistically by simple methods, design as
a flat slab or beam-and-slab may be carried out In some cases, however, a realistic distribution cannot be
determined by simple methods, and a more complex analysis is required. Such methods are outside the scope
lsfructE/ICE Reinforced concrefe building structures 2nd edition
The design of pile caps should be carried out in accordance with the following general principles:
The spacing of piles should generally be three times the pile diameter
The piles should be grouped symmetrically under the loads
The load canied by each pile is equal to N/(no. of piles). When a moment is transmitted to the pile
cap the loads on the piles should be calculated to satisfy equilibrium
Pile caps should extend at least 150mm beyond the theoretical circumference of the piles
For pile caps supported on one or two piles only, a moment arising from a column eccentricity of
75mm should be resisted either by ground beams or by the piles.
Using the unfactored loads and moments calculate the number of piles required under each column
Proportion the pile caps on plan in accordance with the above general principles. Typical
arrangements are shown in Fig. 19 where S is the spacing of the piles
Determine the initial depth of the pile cap as equal to the horizontal distance from the centreline of
the column to the centreline of the pile furthest away
Check the face shear as for reinforced pad footings, using factored loads, and increase the depth if
Calculate the bending moments and the reinforcement in the pile caps using the factored loads.
rt---i
I__.__J___I
!5, S'
5, ._
f--_H-
Hg. 19 Typical arrangements of pile caps
All pile caps should generally be reinforced in two orthogonal directions on the top and bottom faces with
not less than 0.0013/j/i for Grade 460 or 0.0025bh for Grade 250 in each direction.
The bending moments and the reinforcement should be calculated on critical sections at the
column faces, assuming that the pile loads are concentrated at the pile centres. This reinforcement
should be continued past the piles and bent up vertically to provide full anchorage past the centreline
of each pile.
in addition, fully lapped, circumferential horizontal reinforcement consisting of bars not less than size
12 at a vertical spacing not more than 250mm should be provided.
If the recommendations of this Manual have been followed, a robust structure will have been designed,
subject to the reinforcement being properly detailed2.
However, in order to demonstrate that the requirements for robustness have been met, the reinforcement
already designed should be checked to ensure that it is sufficient to act as:
external colunm or wall ties
vertical ties.
The arrangement of these (notional) ties and the forces they should be capable of resisting are stated in
subsection 4.11.2.
Reinforcement considered as part of the above ties should have full tension laps throughout so as to be
effectively continuous. For the purpose of checking the adequacy of the ties, this reinforcement may be
assumed to be acting at its characteristic strength when resisting the forces stated below and no other forces
need to be considered in this check. Horizontal ties, i.e. (a), (b) and (c) above, should be present at each floor
level and at roof level.
Forces to be resisted by horizontal ties are derived from a 'tie force coefficient'
Fi=(20+4n)kNforn lO,or
F1=60kNforn> 10
where n is the number of storeys.
Peripheral ties should be located in zones within 1 .2m from the edges; they should be capable of resisting a
tie force of 1.0 F and should be fully anchored at all corners.
Internal ties should be present in two directions approximately at right-angles to each other. Provided that
the floor spans do not exceed 5m and the total characteristic load does not exceed 7.5kNIm2, the ties in each
direction should be capable of resisting a tie force of 1.0 F1 kN per metre width. If the spans exceed 5m
SiructE/ICE Reinforced concrete building structures 2nd edition
and/or the total load exceeds 7.5 kN/m2, the tie force to be resisted should be increasedpm rata. Internal ties
may be spread evenly in the slabs or may be concentrated at beams or other locations, spaced at not more
than 1.5 times the span. They should be anchored to the peripheral ties at each end.
In spine or crosswall construction the length of the loadbearing wall between lateral supports should be
considered in lieu of the spans when determining the force to be resisted by the internal ties in the direction
External column or wall ties
External columns and loadbearing walls should be tied to the floor structure. Corner colunms should be tied
in both directions. Provided that the clear floor-to-ceiling height does not exceed 2.5m, the tie force for each
column and for each metre length of wall is 1 OF1. For floor-to-ceiling heights greater than 2.5m, the tie forces
should be increased pro rata, up to a maximum of 2.0Ff. The tie force should in no case be assumed less than
3% of the total design ultimate load carried by the coiunm or wall. This reinforcement should be fully
anchored in both vertical and horizontal elements.
Vertical ties should be present in each column and loadbearing wall. They should be capable of resisting a
tensile force equal to the maximum total design ultimate load received by the column or wall from any one
Where effectively continuous vertical ties cannot be provided (e.g. in some precast construction), the
effect of each colunm or loadbearing wall being removed in turn should be considered in accordance with
the provisions of BS 8110, Part 21.
Certain aspects of reinforcement detailing may influence the design. The most common of these are outlined
Local bond stress may be ignored, provided that the force in the bar can be developed by the appropriate
anchorage length (see Table 40).
A link may be considered fully anchored if it is detailed in accordance with Fig. 20.
Laps and splices should generally be positioned away from zones of high stress and should preferably be
staggered. When bars in tension are lapped the length should be at least equal to the design tension anchorage
length necessaiy to develop the required stress in the reinforcement. Lap lengths for unequal size bars (or
wires in fabric) may be based on the smaller bar. The following provisions also apply:
Where a lap occurs at the top of a section as cast and the minimum cover is less than twice the size
of the lapped reinforcement, the lap length should be multiplied by a factor of 1.4
Where a lap occurs at the corner of a section and the minimum cover to either face is less than twice
the size of the lapped reinforcement or where the clear distance between adjacent laps is less than
75mm or six times the size of the lapped reinforcement, whichever is the greater, the lap length
should be multiplied by a factor of 1.4
In cases where both conditihos (a) and (b) apply, the lap length should be multiplied by a factor of 2.0.
Table 40 Ultimate anchorage bond lengths and lap lengths as multiples of
f, N/mm2
Tension anchorage and
1.4 x tension lap
2.0 x tension lap
Compression lap length
These lengths have been calculated assuming the reinforcement is acting at its design strength (095 f5). It the
reinforcement acts at a lower stress the length may be reduced proportionately. The minimum lap length for bar
reinforcement should not be less than 15 times the bar size or 300mm, whichever is the greater, and for fabric
reinforcement should not be less than 250mm.
deformed bars type 2
welded fabric complying with BS 448312
Fig. 20 Anchorage of links
Where bars in compression are lapped the length should be at least 25% greater than the compression
anchorage length necessary to develop the required stress in the reinforcement. Lap lengths for unequal size
bars (or wires in fabric) may be based on the smaller bar.
Values for lap length are given in Table 40 as multiples of bar size.
Mechanical splices may be used in lieu of laps in order to reduce congestion of reinforcement. For
further information specialist literature should be consulted.
The minimum radii to which reinforcement may be bent may govern certain aspects of design, e.g. depths
of bearings and choice of bar size for a given thickness of slab. Table 4113 gives these dimensions, together
with effective anchorage lengths for bends and hooks.
Table 41 Minimum radii, bend and hook sizes and effect
Grade 250 bars
Grade 460 bars
Notes to Table 41
*Bar size may not be freely available
Values of rand Amy comply with BS 8666: 200013
Effective anchorage lengths are based on BS 81101
Effective anchorage lengths are given as multiples of bar size
Where a bar is fully stressed through the length of a bend, greater bending radii may be required to limit
the compressive stress on the inside of the bend.
4.12.5 Curtoilment of reinforcement
In every flexural member except at end supports every bar should extend beyond the point at which it is no
longer needed, for a distance at least equal to the greater of:
the effective depth of the member or
twelve times the bar size
and in addition, for a bar in the tension zone, one of the following distances for all arrangements of design
an anchorage length appropriate to its design strength (0.95f) from the point at which it is no longer
required to assist in resisting the bending moment
to the point where the design shear capacity of the section is greater than twice the design shear force
at that section or
to the point where other bars continuing past that point provide double the area required to resist the
design bending moment at that section.
The point at which a bar is no longer required is the point where the design resistance moment of the section,
considering only the continuing bars, is equal to the design moment.
As curtailment of substantial areas of reinforcement at a single section can lead to the development of
large cracks at that point, it is essential to stagger the curtailment points.
Alternatively, bars may be curtailed as shown in Figs. 21 to 25 for cases where:
the loading is predominantly uniformly distributed and
for continuous beams and slabs the spans do not differ by more than 15% of the longest span.
These should be designed and detailed in accordance with the appropriate clauses in the precast concrete
section of BS 8110'. Care should be taken to assess adequately the horizontal forces arising from restrained
temperature and moisture movements as these will often govern the design.
L__50%
,4JO.O8le
le = effective span
Effective anchorage length
Fig. 21 Simply supported beams and slabs
(StructE/ICE Reintorced concrete bC(ding strucCres 2nd eddor,
0.25le
(0.1 le for end support)
Fig. 22 Continuous beams
0.3le
Fig. 23 Continuous slab
Full tension anchorage length
Reinforcement curtailed
as shown in Fig 20
Fig. 24 Beams and slabs monolithic with support beam or wall (designed as simply supported)
Fig. 25 Cantilever beams and slabs
BS 8110: Structural use of concrete, Part 1: 1997. Code ofpractice for design and construction, Part 2:
1985. Code ofpractice for special circumstances. London, British Standards Institution.
The Institution of Structural Engineers and The Concrete Society. Standard method of detailing
structural concrete. London, The Institution of Structural Engineers, 1985
BS 648: Schedule of weights of building materials. London, British Standards Institution, 1964
BS 6399: Loadings for buildings, Part 1: Code of practice for dead and imposed loads. London,
British Standards Institution, 1996
BS 6399: Loading for buildings, Part 2: Code ofpractice for wind loads. London, British Standards
Institution, 2000
BS 8002: Code of practice for earth retaining structures. London, British Standards Institution,
Coordinated Project Information. SMM7 Standard method of measurement of building works, 7th
revised ed. CPI, 1979
Beeby, A. W.: The analysis of beams inplaneframes according to CP 110. Development Report no. 1.
Slough, Cement & Concrete Association, 1978
Concrete Society. Concrete industrial groundfloors a guide to their design and construction, 2nd
edn. Technical Report no. 34. Slough, Concrete Society, 1994
Mott MacDonald Special Services Division. Water-resisting basement construction a guide
safeguarding new and existing basements against water and dampness. CIRIA Report 139. London:
Building Research Establishment. Sulfate and acid resistance of concrete in the ground, BRE Digest
363. Watford, BRE, 1996
BS 4483: Steel fabricfor the reinforcement of concrete, London, British Standards Institution, 1998.
BS 8666: Spec/Ication for scheduling, dimensioning, bending and cutting of steel reinforcementfor
concrete. London, British Standards Institution, 2000
Appendix A Reinforcement quantities
This appendix contains Tables Al, A2, A3, A4 and A5 referred to in method 2 of subsection 3.9.
The factors for converting reinforcement areas into unit weights of reinforcement assume that:
The reinforcement areas are those of practical bar arrangements, e.g. standard sizes at realistic
spacings in beams; an even number of bars in columns.
The detailing is in accordance with reference 2.
high yield steel 0.13% of gross cross-section
mild steel 0.24% of gross cross-section
Flat slabs on
A , required
Minimum steel or
001 25Asx*
(0.8d) (0.95f5)
(0.8d) (0.95fy)
0.8 (d 20) 0.95f5
0.8 (d 20) 0.95f
M is the maximum
bending moment per
anywhere in the slab
0011 IA'sx+A'sy)
0.011 lA'5 + A, I
M and M are the
moments per metre
width in each
M and M5 are the
mean )of the column
and middle strip)
width in each direction
'This includes weight of distribution steel
Notes to Table Al
All the bending moments are the design ultimate moments.
2 A and A are areas of reinforcement required in two orthogonal directions.
A',, and A,5 are areas at reinforcement un mm2l selected per metre width in two orthogonal directions.
Consistent units must be used in the formulas for obtaining areas of reinforcement.
lStructE/CE Reinforced concrete building structures 2nd edition
Ribs: high yield steel 0.25% b h
mild steel 0.50% b h
where b is the average width of the ribs and h is the overall depth of the slab
high yield steel 0.13% of gross cross-section of topping
mild steel 0.24% of gross cross-section of topping
required (in each
direction for two-way and
flat slabs), mm2
0.95f (d 0.5hf)
1.25 x wt/m2
b anywhere in the
slob'
For loose bar
0.009 (sum of bar
areas per m
0.02 A'
0.95fy(d 10 0.5h)
0.95f (d 0.5h)
0.013 (A'sx + A's)
As for one-way
rib in the two
M5 and M are the
mean (of the
middle strips)
moments per rib in
0.95fy(d 20 0.5hf)
Note to Table A2
c is the spacing of ribs in metres.
Consistent units should be used in the formulas for obtaining areas of reinforcement.
As, A'sx and Asy are the areas lin mm2l of bars selected per rib.
StructE/CE Reinforced concrete building structures 2nd edition
high yield steel 025% b h
Longitudinal steel:
where b is the width of beam and h is the overall depth of beam
mild steel: 0.25% of a horizontal section through the web
high yield steel: 0.12% of horizontal section through web
At midspan for T- and L-beams (and
at supports for upstand beams)
0.01 1A'
A' is the area (in mm2) of
selected at midspan or
supports whichever is
0.95fy(d 0.5hf)
For rectangular beams and at
supports tori- and I-beams (and at
M is the design ultimate
midspans for upstand beams)
0.95f (0.75d)
Shear stress design
Single links (i.e. two legs)
U.LJIOOW+
H is the depth of beam in
Double links (i.e. four legs)
If v > 0.6N/mm2
A'sv - bw(v -0.6)
A' is the area selected
0.016(1 .5B+ 2H) V for one leg of a link in
S is the selected
Treble links (i.e. four legs)
spacing of links in metres
If v 0.6N/mm2 choose
A' and Sv to satisfy
0.016 (2Bw + 3H)
Longitudinal steel: 1% of the necessary concrete area
Links make the choice to satisty the following:
size at least one-quarter of the biggest longitudinal bar
spacing: 12 x size of smallest longitudinal bar but not more than 300mm
every corner and each alternate longitudinal bar should be restrained by a link in each direction
Weight kg per m
Main steel 0.011 A1
A area of all vertical bars (mm2)
b and h are dimensions of column cross-section in metres
0.016 (b h) A
A is the cross-sectional area of one leg of a link in mm2
S3 is the spacing of links in metres
For sausage links (shape code 3313) b is the dimension parallel to the link
0.016b--
Table A5 Walls
Vertically 0.4% of cross-sectional area
Horizontally 0.2% of cross-sectional area
Weight of reinforcement in kg/m2 of wall elevation
0.011 (A53 + Ash)
where A. and Ash are areas of reinforcement in mm2 selected per metre width and height
Note: Consistent units must be used in obtaining areas at reinforcement
iStructE/ICE Reintorced concrete building structures 2nd edit ion
Appendix B Design data
General description, intended use, unusual environmental conditions
Durabffity
Soil conditions and foundation design
Ground slab construction
ISfrucfE/ICE Reinforced concrefe building sfrucfures 2nd edifion
The exposure conditions in service to be considered when determining the covers and grades of concrete to
be used for all members are as follows:
concrete surfaces protected against weather or aggressive conditions
concrete surfaces sheltered from severe rain or freezing while wet
concrete subject to condensation
concrete surfaces continuously under water
concrete in contact with non-aggressive soil
concrete surfaces exposed to:
severe rain; alternate wetting and diying or occasional freezing; or severe
deicing salts, directly or indirectly
corrosive fumes, or
severe freezing conditions while wet
concrete surfaces exposed to abrasive action by:
sea water carrying solids
flowing water with pH <4.5, or
machinery or vehicles
Appendix D Column design charts
This appendix contains design charts for stocky symmetrically reinforced rectangular and circular columns.
The charts for the rectangular columns are drawn for dlh values of 0.95, 0.90, 0.85, 0.80 and 0.75, while
those for circular columns are for h!h values of 0.9, 0.8, 0.7 and 0.6.
IStrucfE/ICE Reinforced concrefe building sfructures 2nd edifion
M/bh2f
p = A,Jbh
in calculating A3
M!bh2f
p = AJbh
Bars incudd
MIbh2f
p = A5/bh
in calculatingA6
in calculating A56
Bars inck.K$ed
IZ0.8
in calculathg
Ba included
4,_d
f/f=1 . 4
&/bh
in ca'culatingA8
=_0.80
\ NN \ \
\ N..______
,\ ) )
10i,
0.6 - ____ ____ ____ ____ ____ ____ ____
N .- ___ ___ ___
N N N ___ ___ ___
p =AJbh
d/h = 0.75
t-b---
M/h3f
p = 4A/ith
)r____
pf/fc=1
= Total area
Manual for the design of reinforced
In 1985 the Institution of Structural Engineers published its 'green' book, the
Manual for the design of reinforced concrete building structures, which was
drafted jointly with the Institution of Civil Engineers. Written by and for
practising designers, in a concise format, it reflects the logical sequence of
operations which a designer follows, and was compatible with British
Standard BS 8110 at that time.
This revised 2nd edition encapsulates changes arising from:
Amendments to BS 8110, which was republished in 1997 and further
amended in 2001;
The publication of BS 8002 for the design of earth retaining structures: and
As a result of feedback from practising engineers, some span/depth values for
initial design have also been modified.
The general scope of the Manual remains unchanged in that it still covers the
majority of reinforced concrete buildings. It continues to offer practical
guidance on how to design safe, robust and durable structures.
T +44 (0)20 7235 4535
F +44 (0)20 7235 4294
mail@isfructe.org.uk
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