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 Definition of width of effective moment transfer strip be on plan
The maximum design moment that can be transferred to a column by this strip is given by Where d is the effective depth for the top reinforcement in the column strip, and fck G 35MPa. Where the transfer moment at an edge column obtained from Table 5.4 is greater than Mmax a further moment redistribution G 10 may be carried out. Where the elastic transfer moment at an edge column obtained from a frame analysis is greater than Mmax moment redistribution G 50 may be carried out. Where the slab is...
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...
Effective shear forces in flat slabs
Generally the critical consideration for shear in flat slab structures is that of punching shear around the columns. This should be checked in accordance with Section 5.2.4.2 except that the shear forces should be increased to allow for the effects of moment transfer as indicated below. The design effective shear force Veff at the perimeter of the column should be taken as Veff 1.15 VEd for internal columns with approximately equal spans 1.4 VEd for edge columns 1.5 VEd for corner columns Where...
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...
Notes on the use of precast floors
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 carry loads without reliance on the topping. Design using proprietary products should be carried out closely in conjunction with the particular manufacturer and in accordance with...
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...