Abstract:
Any satisfactory design requires the magnitude of deflection of structural components
of roof system at the service load to be within acceptable limit. Excessive deflections
of reinforced concrete roof structures can cause severe serviceability problems.
Although deflection is an important parameter in the design of structure, enough
emphasis is not usually given to the calculation of slab deflection. None of the several
methods presently available for the calculation of deflection of slabs provides the
designer any unified approach to readily estimate the slab deflection for any span ratio
and support condition. This study briefly reviews the methods available in literature
for calculation of slab deflection and attempts to develop a method to readily calculate
the deflection and moments of different types of slabs with various edge conditions.
With the aforesaid objective in mind, a software analysis technique (Using a general
purpose Finite Element software, ANSYS) has been used to study the behaviour of
different types of edge supported slabs. The results obtained from the Finite Element
(FE) models have been compared with those of the ACI moment coefficient method
in order to check the reliability of the method. The FE model has been used in the
parametric studies of deflection of slab with various edge conditions and span-ratios.
The results of parametric studies have been presented in tabular form that forms the
basis of an unified method for caltulating the slab deflection.
Moreover, the present study provides a method to compute the moment and deflection
of slabs with opening. Results obtained from the FE model have been used to develop
charts that relate the strip moments and deflection of such slabs with solid slabs.
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Using these charts it becomes possible to calculate the moments and the deflection of
such siabs by simply multiplying the moments and deflections of the appropriate solid
slab with a correction factor.
Finally, octagonal slabs with a few selected supporting states have been analysed. An
attempt is made to identify the geometric dimensions of the slab when it can be
treated as a rectangular slab for design purpose. Results are presented in tabular form
so that deflection and moments of any octagonal slab with the selected support
conditions can be computed.
