Successive sustained loading effect on the long-term deflection of flat slab

Abstract

The research work presents the experimental long-term behaviour of reinforced concrete (RC) flat slab specimens at 1:2 scale, subjected to uniformly distributed sustained load in successive phases up to 90 days. The sustained load was applied in two stages, in the first stage, it was 3 kN/m2 for 30 days, whereas in the second stage, it was increased from 3 kN/m2 to 6 kN/m2 for the next 60 days. Age-dependent strength of cement mortar and concrete as used in RC flat slabs has been determined using the method as per the Indian code of practice. The contribution of creep and shrinkage deflection in total deflection for the column strip, middle strip, and cantilever portion has been observed in the range of 34% to 42% at the end of 90 days. After the first 30 days, the mid panel deflection of the flat slabs was larger as compared to column strip and cantilever deflection. At 90 days, the cantilever portion experienced the highest deflection as compared to middle strip and column strip deflection. The measured deflection has also been compared with the IS code procedure and it is found that the code underestimates the long-term deflection of the flat slab. Further, the finite element modelling using ABAQUS has also been carried out on the RC flat slab to validate the experimental results of the same slab within the elastic range. The present study gives an idea to the designer for fixing the thickness of the slab by considering the long-term deflection criteria in the design of the RC flat slab based on its behaviour under sustained loading.