Experimental investigation of resistance function of RC beam considering membrane effects

Membrane actions commonly exist in reinforced concrete (RC) elements under flexural deformation, which could significantly increase the ultimate flexural load-bearing capacity and potentially influence the damage mode of the RC element. Most design codes only treat membrane actions as a “hidden” safety factor without considering its influence on the resistance functions and failure modes. In this paper, an experimental investigation is conducted to study the membrane actions on the resistance behaviors of restrained RC beams. It is found that compressive membrane effect occurred at early stage of a fully restrained RC beam, which leads to amplified flexural bending resistance capacity. Diagonal shear crack is developed since the designed shear resistance is lower than the amplified flexural bending capacity. Under membrane actions, the damaged beam with shear crack could still carry the imposed load and develop further tensile membrane action until eventual failure. The resistance function of the restrained beam under combined membrane and shear damage is significantly altered as compared to the un-restrained reference beam that failed in flexural bending. A modified theoretical resistance function is proposed to consider both the membrane effects and diagonal shear damage. Comparison with testing data shows that the proposed model could accurately describe the resistance of fully restrained RC beams under combined shear and membrane actions.Membrane actions commonly exist in reinforced concrete (RC) elements under flexural deformation, which could significantly increase the ultimate flexural load-bearing capacity and potentially influence the damage mode of the RC element. Most design codes only treat membrane actions as a “hidden” safety factor without considering its influence on the resistance functions and failure modes. In this paper, an experimental investigation is conducted to study the membrane actions on the resistance behaviors of restrained RC beams. It is found that compressive membrane effect occurred at early stage of a fully restrained RC beam, which leads to amplified flexural bending resistance capacity. Diagonal shear crack is developed since the designed shear resistance is lower than the amplified flexural bending capacity. Under membrane actions, the damaged beam with shear crack could still carry the imposed load and develop further tensile membrane action until eventual failure. The resistance function of the restrained beam under combined membrane and shear damage is significantly altered as compared to the un-restrained reference beam that failed in flexural bending. A modified theoretical resistance function is proposed to consider both the membrane effects and diagonal shear damage. Comparison with testing data shows that the proposed model could accurately describe the resistance of fully restrained RC beams under combined shear and membrane actions