Behaviour of reinforced concrete skew slab under vertical loads

Abstract

The behaviour of skew slabs under vertical loads is reported in this thesis. All the slabs tested experimentally in the laboratory were 1/6th scale models of proto-type skew slabs having opposite edges simply supported. The same steel arrangement was used for all the test slabs. Main steel was parallel to free edges and distribution steel was parallel to support line. Two aspect ratio viz., 0.85 and 1.50 were considered. Centrally located single concentrated load and four point loads equally spaced across the mod-span were the two types of loading condition studied. Two different skew angles viz. 25° and 45° were the other parameters of study. A total of six model slabs were cast and tested in the laboratory and the observed behaviours were compared with corresponding response predicted by a nonlinear finite element computer programmmg. The experimental investigations were limited to measurement of deflections at some preselected nodal points, steel strains both for main and distribution steel and strains at the top and bottom surface of the concrete at some preselected (Gauss) points. Observations of cracking pattern and recording the cracking and ultimate loads were one for all the test slabs. The experimental records were compared with corresponding numerical predictions. The ultimate load carrying capacity of the experimental slabs compared well with the results obtained from numerical solutions. In other cases, the correlation was found to be fair. The behaviour of skew slabs were found to depend significantly upon two parameters of skew slabs namely skew angle (a) and aspect ratio (R). The effect of different reinforcement layout was not considered in this study. Slabs with higher skew angle and lower aspect ratio were found to have higher load carrying capacity and lower deflections compared to slabs having lower skew angle and higher aspect ratio. Empirical relations for determination of moments Mx, My and Mxy are suggested for hand computations. From these values, design moments M:. and M~ can be easily computed and reinforcement requirements in x and 'II directions determined. Step by step procedure for design of skew slabs using simple scientific calculator is suggested. Empirical relations for moments and deflection under two types of loading (studied here) have been formulated for elastic solutions. The values obtained using empirical formulations have been compared with linear finite element solution using a nonlinear programme tacitly. Good correlation is observed within the elastic range of solution for all the slabs including the test slabs. Empirical formulations for estimating the maximum deflection at central node have been suggested for both types of loading. Empirical predictions have been compared with both the numerically obtained deflections and recorded deflections for the test slabs. They compared well for all the test slabs especially with the experimental values.