## C h

Where w is the total design ultimate load per unit area in kN m2 h is the thickness of the slab at the column in mm. 4supp is the area supported by the column in m2 uc is column perimeter in mm. It should be noted that for slabs less than 200mm thick shear reinforcement is not effective. 4.8.7 Adequacy of chosen sections to accommodate the reinforcement The actual bar arrangement should be considered at an early stage particularly where the design is close to reinforcement limits.

## Combination of actions

Quasi-permanent combination of actions The combination of permanent and variable loads which is most likely to be present most of the time during the design working life of the structure. Frequent combination of actions The most likely highest combination of permanent and variable loads which is likely to occur during the design working life of the structure.

## Contents

1.4 Contents of the Manual 4 1.5 Notation and terminology 4 3 Design principles - reinforced concrete 8 3.2.1 Ultimate limit state (ULS) 9 3.2.2 Serviceability limit states (SLS) 10 4 Initial design - reinforced concrete 11 4.3 Material properties 12 4.4 Structural form and framing 12 4.8.3 Width of beams and ribs 15 4.8.4 Sizes and reinforcement of columns 15 4.8.6 Punching shear in flat slabs at columns 17 4.8.7 Adequacy of chosen sections to accommodate the reinforcement 18 4.8.7.1 Bending...

## Design principles reinforced concrete

The loads to be used in calculations are Characteristic permanent action (dead load), Gk the weight of the structure complete with finishes, fixtures and fixed partitions. The characteristic variable actions (live loads) Q where variable actions act simultaneously a leading variable action is chosen Qk1, and the other actions are reduced by the appropriate combination factor. Where it is not obvious which should be the leading variable action, each action should be checked in turn and the worse...

## Division into subframes

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 subframes. 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...

## Elastic analysis

Frames should be analysed for the most unfavourable arrangements of design loads. For frames subjected to predominantly uniformly distributed loads it will be sufficient to consider one the following arrangements of loads only for ultimate limit state verification i) a) Alternate spans carrying the maximum design permanent and variable load, i.e. (1.35Gk + 1.5Qk), other spans carrying the maximum design permanent load, i.e. 1.35Gk and b) Any two adjacent spans carrying the maximum design...

## Fig Basic control perimeters for loaded areas close to or at an edge

Fig 5.8 Shear perimeters for internal columns Fig 5.9 Control perimeter near an opening If the applied shear stress at the basic control perimeter is less than the permissible ultimate shear stress vRd1 (see Table 5.7) no further checks are required. If vEd > vRd c, the outer control perimeter, out, at which vEd G vRd c is then determined. Table 5.7 Ultimate shear stress vRd,c MPa Table 5.7 Ultimate shear stress vRd,c MPa The tabulated values apply for fck 30MPa. Approximate values for other...

## Fig Layout of flat slab shear reinforcement

The area of a link leg (or equivalent), Aswmin, is given by A . 15 H 0 08 Where sr is the spacing of shear links in the radial direction st is the spacing of shear links in the tangential direction. The distance between the face of a support, or the circumference of a loaded area, and the nearest shear reinforcement taken into account in the design should not exceed d 2. This distance should be taken at the level of the tensile reinforcement. Where proprietary products are used as shear...

## Final design reinforced concrete

Section 4 describes how the initial design of a reinforced concrete structure can be developed to the stage where preliminary plans and reinforcement estimates may be prepared. Now the approximate cost of the structure can be estimated. 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 further amendment, and it may be necessary to repeat this process until approval is given by all...

## Flat slabs

If a flat slab has at least three spans or bays 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 in each direction may be obtained from Table 5.4. This assumes 20 redistribution of bending moments. Where the conditions above do not apply, bending moments in flat slabs should be obtained by frame analysis (see Section 5.3). The structure should then be considered as being divided longitudinally and...

## General principles

This section outlines the general principles that apply to the design of both reinforced and prestressed concrete building structures, 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...

## Latin upper case letters AAccidental action

Ac Cross sectional area of concrete Ap Area of a prestressing tendon or reinforcement As min minimum cross sectional area of reinforcement Asw Cross sectional area of shear reinforcement Diameter of mandrel Fatigue damage factor Effect of action Tangent modulus of elasticity of normal weight concrete at a stress of vc 0 and at 28 days Effective modulus of elasticity of concrete elasticity of concrete Ecm Secant modulus of elasticity of concrete Ec(t) Tangent modulus of elasticity of normal...

## M fk bd ftd d

Is the area of the compression steel is the depth to its centroid is the width of the section is its effective depth. If, for flanged sections, M> 0.567 ck bf hf (d - 0.5hf) the section should be redesigned. bf and hf are the width and the thickness of the flange. hf should not be taken as more than 0.36d. It should be noted that where compression reinforcement is required transverse reinforcement should be provided to restrain the main reinforcement from buckling.

## Method

Another method is to use factors that convert the steel areas obtained from the initial design calculations to weights, e.g. kg m2 or kg m as appropriate to the element. If the weights are divided into practical bar diameters and shapes, this method can give a reasonably accurate assessment. The factors, however, do assume a degree of standardisation both of structural form and detailing. This method is likely to be the most flexible and relatively precise in practice, as it is based on...

## Oneway spanning slabs

For continuous slabs with a) substantially uniform loading b) dead load greater than or equal to imposed load and c) at least three spans that do not differ by more than 15 , the bending moments and shear forces may be calculated using the coefficients given in Table 5.2. Table 5.2 Bending moments and shear forces for one-way slabs a F is the total design ultimate load (1 b l is the span. Allowance has been made in the coefficients in Table 5.2 for 20 redistribution of moments. Allowance has...

## Redistribution of moments

The moments obtained from elastic analysis may be redistributed up to a maximum of 30 to produce members that are convenient to detail and construct, noting that the resulting distribution of moments remains in equilibrium with the applied load the design redistribution moment at any section should not be less than 70 of the elastic moment there are limitations on the depth of the neutral axis of the section depending on the percentage of redistribution (see Section 5.4.4.1), and the design...

## Serviceability limit states SLS

The appropriate serviceability limit state should be considered for each specific case. EC21 provides specific checks under characteristic, frequent and quasi-permanent loads the check required varies depending on the effect considered. The corresponding load cases are given in Table 3.3 and are obtained by multiplying the characteristic variable actions by appropriate reduction factors ( I or 2). The values of 1 and 2 are given in Table 3.4. The effects of these factors have been included,...

## Shear reinforcement

Asw fWTCOte (old) (for initial sizing cot6 is the design ultimate shear force at the critical section is the spacing of shear reinforcement is the effective depth is the design yield strength of the shear reinforcement. Bar arrangements When the areas of the main reinforcement in the members have been calculated, check that the bars can be 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...

## Solid singleway and twoway slabs

Shear reinforcement is not normally required provided the design ultimate shear force VEd does not exceed VRd c. VRd,c 012k (100fck) bwd but not less than Where k 1 + T G 2 and t G 0 02 Where Asl is the area of tensile reinforcement, which extends beyond the section considered taking account of the 'shift rule' (see Section 5.12.6). For heavy point loads the punching shear stress should be checked using the method for shear around columns in flat slabs.

## Ultimate limit state ULS

The design loads are obtained by multiplying the characteristic loads by the appropriate partial factor cf from Table 3.2. When more than one live load (variable action) is present the secondary live load may be reduced by the application of a combination factor 0 (see Table 3.4). The basic load combination for a typical building becomes Where Qk1, Qk2 and Qk3 etc. are the actions due to vertical imposed loads, wind loads and snow etc., Qk1 being the leading action for the situation considered....

## Secretary to the Task Group B Chan BScHons AMIMechE

Published by The Institution of Structural Engineers 11 Upper Belgrave Street, London SW1X 8BH, United Kingdom Telephone +44(0)20 7235 4535 Fax +44(0)20 7235 4294 Email mail istructe.org.uk Website www.istructe.org.uk 2006 The Institution of Structural Engineers The Institution of Structural Engineers and the members who served on the Task Group which produced this report have endeavoured to ensure the accuracy of its contents. However, the guidance and recommendations given should always be...

## Fig Redistribution procedures for frames

The effective span of a simply supported beam should normally be taken as the clear distance between the faces of supports plus one-third of the beam seating width at each end. However, where a bearing pad is provided between the slab and the support, the effective span should be taken as the distance between the centres of the bearing pads. 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...

## Sizes and reinforcement of columns

Where possible it will generally be best to use 'stocky columns' i.e. generally for typical columns for which the ratio of the effective height to the least lateral dimension does not exceed 15 as this will avoid the necessity of designing for the effects of slenderness. Slenderness effects can normally be neglected in non-sway structures where the ratio of the effective height to the least lateral dimension of the column is less than 15. For the purpose of initial design, the effective height...

## Division of moments between column and middle strips

The design moments obtained from analysis of the frames or from Table 5.4 should be divided between the column and middle strips in the proportions given in Table 5.5. Table 5.5 Distribution of design moments of flat slabs For the case where the width of column strip is taken as equal to that of the drop and the middle strip is thereby increased in width, the design moments to be resisted by the middle strip should be increased in proportion to its increased width. The design moments to be...

## Fig Corner reinforcement twoway spanning slabs

Column and middle strips should be reinforced to withstand the design moments obtained from Section 5.2.3.4. 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 column. The area of reinforcement in each direction should not be less than 0.00014 ck2 3bh or 0.0015bh Where h is the overall depth of the slab taken...

## Introduction

This Manual provides guidance on the design of reinforced and prestressed concrete building structures. Structures designed in accordance with this Manual will normally comply with BS EN 1992-1-1 20041 and BS EN 1992-1-2 20042. It is primarily related to those carrying out hand calculations and not necessarily relevant to computer analysis. However it is good practice that such hand analysis methods are used to verify the output of more sophisticated methods. The structural Eurocodes were...

## Fig Distribution of reactions from twoway slabs onto supports

Table 5.4 Bending moment and shear force coefficients for flat slab panels of three a F is the total design ultimate load b These moments may have to be reduced to be consistent with the capacity to transfer moments to the columns the midspan moments c must then be d The total column moment should be distributed equally between the columns e Moments at supports may be reduced by 0.15Fhc where hc is the effective diameter of the column or column head. Division of panels except in the region of...

## Section design ribbed and coffered slabs

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis, provided that the flange or structural topping and transverse ribs have sufficient torsional stiffness. This may be assumed provided that the rib spacing does not exceed 1500mm the depth of the rib below the flange does not exceed 4 times its width the depth of the flange is at least 1 10 of the clear distance between ribs or 50mm, whichever is the greater transverse ribs are provided at a clear...

## Beam strips in ribbed and coffered slabs

Beam strips may be used to support ribbed and 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. The shear in the ribs should be checked at the interface between the solid areas and the ribbed areas. If shear reinforcement is required in the ribs, these should be extended into the solid areas...

## Twoway spanning slabs on linear supports

Bending moments in two-way slabs may be calculated by any valid method provided the ratio between support and span moments are similar to those obtained by the use of elastic theory with appropriate redistribution. In slabs where the corners are prevented from lifting, the coefficients in Table 5.3 may be used to obtain bending moments per unit width msx and msy in the two directions for various edge conditions, i.e. Where bsx and bsy are the coefficients given in Table 5.3 n is the total...

## Initial design reinforced concrete

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, and without dimensions, but it is nevertheless expected that viable schemes be produced on which reliable cost estimates can...