Effect of In-Plane Damage on Out-of-Plane Response of FRCM Strengthened Masonry Infilled RC Frames

Abstract

The out-of-plane (OP) strength of masonry infills is reduced when damaged under the action of the in-plane (IP) forces. A strengthening approach using a fabric-reinforced cementitious matrix (FRCM) was proposed for improving the OP strength of damaged infill walls. A finite-element (FE) model of a reinforced concrete (RC) frame, infilled with FRCM-strengthened masonry, was developed and validated using experimental results and analytical predictions. Interaction curves representing the interplay between in-plane damage and out-of-plane response were generated for unstrengthened (ordinary) and FRCM-strengthened infill walls using FE analysis. Results of the FE analysis showed that FRCM-strengthened infills had greater OP strength in the undamaged state and suffered less strength degradation at high-damage states compared to unstrengthened infills. Anchoring of the fabric proved effective in utilizing the strength and ductility of the FRCM reinforcement. The fabric with ±45° orientation contributed more in resisting the diagonal tension under in-plane shear but was not as effective as 0°–90° orientation in resisting the OP flexural stresses corresponding to in-plane damage at 2.2% drift level. A novel definition of damage state was introduced for fragility analysis that can consider the effect of in-plane damage and out-of-plane strength using interaction curves. A four-bay, five-story masonry infilled RC frame was analyzed using the capacity spectrum method, and fragility curves were developed for unstrengthened and FRCM-strengthened infills. The effect of variation in out-of-plane demand and in-plane damage on each floor was included in the analysis. The RC frame using FRCM strengthened infills exhibited a smaller probability of exceedance of the performance limit than the unstrengthened infills. The proposed methodology helped identify critical infills that require strengthening.