Numerical modelling of edge supported slab response

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. v 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.