Flexural behavior of reinforced concrete masonry walls under out-of-plane monotonic loads

This paper presents the test results of an investigation carried out to study the behavior and flexural strength of vertically spanned reinforced concrete block masonry walls under out-of-plane monotonic loading. The study presented in this paper which is part of the U.S.-Japan Coordinated Program on Masonry Building Research, addresses the elastic and inelastic behavior of reinforced block masonry walls. Six walls were tested to determine the effects of percentage and location of vertical reinforcement, block size, and extent of grouting. The behavior included cracking patterns and cracking moments, load-deflection curves up to and beyond the peak load and displacement ductility. Test results showed that the-percentage and location of vertical steel (centrally located versus staggered) had a significant effect on wall load-deflection curves, strength, and ductility. The extent of grouting (partially versus fully grouted) affected cracking load and consequently, flexural rigidity and deflection under service loads. The extent of grouting, however; did not show an adverse effect on wall stability in the inelastic range. The specified value of the modulus of rupture in the UBC-94 code is much lower than the experimental values of maximum tensile stress at first crack obtained for fully greeted walls. The theoretical analysis for the ultimate strength based on the Whitney stress block method that is included in the UBC-94 code showed a good correlation with the experimental results. Displacement ductility ratios ranged from 1.79 for the wall with 0.44 per cent vertical steel to 16 for the wall with 0.19 percent steel. As expected, the displacement ductility of the wall panels decreased as the percentage of vertical reinforcement increased.