Effects of passive confinement on out-of-plane robustness of unreinforced masonry infill walls

Abstract

Unreinforced masonry (URM) walls are vulnerable to out-of-plane (OOP) collapse under lateral loads; however, URM structures are still popular in developing countries. Even in many countries classified as developed by the United Nations, URM walls are still commonly applied as exterior and interior infills in engineered buildings, resulting in severe OOP failure during strong earthquakes. The objectives of this study were: 1) to experimentally examine the OOP behavior and performance of URM infills with construction deficiencies commonly found in Asian countries, 2) to investigate the impact of construction quality on resistance to OOP collapse and 3) to propose a promising approach using passive confinement to improve the lateral resistance of URM infills and a method to evaluate their seismic performance. To attain these objectives, the study used two full-scale, single wythe, brick masonry specimens with specific boundary conditions at the top, a control specimen representing URM infills with construction flaws frequently found in Asian countries and a well-constructed specimen subjected to passive confinement under lateral excitation. A series of incremental dynamic shaking table tests was performed on both specimens under OOP unidirectional one-way bending. The test results revealed the positive effects of construction with passive confinement on OOP performance. The results indicated that the OOP robustness of infills can be improved without specific retrofit materials, leading to advantages such as simplicity, cost-effectiveness, and swift execution. Moreover, a theoretical method to evaluate the lateral resistance of infills was presented and verified for practical applications. This method can contribute to reducing the potential for earthquake damage in engineered buildings.