Effect of reinforcement orientation on ultimate flexural capacity of solid and biaxial voided RC slabs

A common observation is that flexural load carrying capacity of reinforced concrete slab from yield line analysis is lower than that from an experimental study. This capacity difference arises due to tensile membrane action developed at the post-yield stage. The orientation of reinforcement also plays a significant role in enhancing load carrying capacity, since the fracture moment exceeds moment capacity estimated using yield line analysis. It happens only when reinforcement in orthogonal directions is compelled to yield by diagonal fracture line. The present study investigates the load enhancement due to tensile membrane action and orientation of reinforcement in solid and biaxial voided slabs. Experimental results of 10 specimens (6 solid and 4 biaxial voided slab) were taken from literature. Two-way flexural capacity of those specimens was estimated by yield line analysis in conjunction with Indian code provisions (IS 456: 2000). Results from the experimental study are comparable with yield line analysis after considering the effects due to tensile membrane action and reinforcement orientation.