Experimental study to evaluate short-term deflections for two-way RC slabs

Determination of deflection in structure is important from serviceability criteria. Codal provisions are available to calculate deflections in RC members in general. The codal provisions for calculation of short-term deflection in RC two-way slab are based on the effective moment of inertia (Ieff), The Ieff depends on the cracking moment (Mr) and maximum moment due to service load (M). Short-term deflections determined based on the provision for two-way RC slabs, are not comparable with experimental values. Even sometime negative deflection is obtained with the procedure. Present paper gives a method designated as Equivalent Load Method, in which equivalent load is calculated using Grashoff-Rankine formulae, and is considered to be acting on the slab. The deflection calculated using equivalent load method is found to be closer to experimental values. The negative deflection has been tackled in literature by applying a factor of 0.7 to cracking moment (Mr). The deflection thus calculated again differs considerably with the experimental values. In the paper, with the method, a procedure has been proposed in which instead of the factor 0.7 being applied to Mcr; cracking moment of inertia is proposed to be used in place of effective moment of inertia. The deflection thus calculated has been found to be comparable with experimental results. Experimental data obtained and data available in literature have been used to validate the procedure. Experimental work has been carried out for two end conditions i.e. fixed supported and simply supported two-way RC slab. Six separate specimens were casted for both end condition of different thickness, sizes and for different loads.