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.
