Estimation of elastic deflection of flat plate

Abstract

A satisfactory design of flat plate roof system requires the magnitude of deflection at service load to be within the acceptable limit. Excessive deflection of reinforced concrete flat plate can cause severe serviceability problems. Although deflection is an important parameter in the design of structure, enough emphasis is not usually given in the calculation of slab deflection as well as there is a tendency among designer to reduce slab thickness to save volume of concrete and dead load of structure that also increase serviceability deflection. Determination of flexural capacity with calculated deflection magnitude within permissible limit may permit use of shallower section for flat plate. The present study briefly reviews the methods available in literature for calculation of deflection of flat plate and attempts have been taken to develop a method to calculate the elastic deflection of flat plate for various end conditions. With the aforesaid objectives in mind, a software analysis technique (using Finite Element software, SAFE) has been used to study the behavior of deflection of flat plates. The results obtained form the Finite Element (FE) models have been compared with the ACI direct design method in order to check the reliability of the method. The FE model has been used in the parametric studies of deflections and span ratios. The results of parametric studies have been presented graphically as a basis of a unified method for calculation of the deflection of flat plate for different end conditions. Few test results arc available that were conducted to determine the immediate deflection of flat plate. The deflection calculations of flat plate by the proposed method have been validated by comparing against those test results. A range of ratios proposed to determine the long term deflection of flat plate comparing the available long term deflection of practical building with the elastic deflection determined the proposed method.