Estimating Out-of-Plane Strength of Cracked Masonry Infills

Abstract

The primary objective of the research project was to determine the transverse (out-of-plane) seismic strength of unreinforced masonry infill panels that have been cracked with in-plane lateral forces. The goal of the research was to develop a simple method that practicing engineers could use for evaluating strength of infill panels that have been damaged in earthquakes. In addition, the feasibility of using a low-cost repair or rehabilitation technique for improving transverse strength was examined. A total of 22 tests were run on eight large-scale masonry infill panels that were constructed in a single bay, single story reinforced concrete frame. Test panels were first subjected to in-plane load reversals to create a pre-existing cracked, damaged state for the subsequent out-of-plane tests which were done with an air bag. Following this test sequence, selected damaged panels were repaired and retested. Previous in-plane cracking was found to reduce out-of-plane strength by as much as a factor of two. However, transverse strength of a cracked masonry infill was found to be appreciable because of arching action. A simple equation was developed for out-of-plane strength based on the masonry compressive strength, the hit ratio, the amount of in-plane damage and the stiffness of the bounding frame. An evaluation procedure was developed based on this procedure.