Effective shear stiffness of diagonally cracked reinforced concrete beams

Beam deflections in cases of diagonal and bending cracking of reinforced concrete (RC) beams can be attributed equally to shear and flexural deformations. However, the extent of contribution by shear deformation is hard to quantify and is often underestimated in practical design. To address this, a quantitative analysis of the effect of shear deformation was conducted, considering the effect of tension stiffening after diagonal cracking, and a formula to derive effective shear stiffness is proposed. Five RC beams, comprising of three RC T-section beams with thin web and two RC rectangular beams, were tested to verify the theoretical models with minimum crack angle and total deflection as key points of comparison. The fully cracked responses were analyzed using truss model analogies while exact models applied depended on the crack angle. Results show that shear contribution to the total deflection in the diagonally cracked RC beam is significant.