Report - PEER - University of California, Berkeley

this paper, initial results of a research underway aimed at evaluating the seismicperformance of masonry structures is presented.2. SEISMIC DESIGN OF CONFINED MASONRY CONSTRUCTION2.1 Seismic BehaviorSeismic behavior of confined masonry walls has been studied through quasi-staticcyclic loading and via shaking table tests. Recently, cyclic loading experiments havebeen conducted on full-scale isolated walls and on 2D and 3D wall subassemblages.Typically, in such tests a drift-controlled cyclic program, with monotonicallyincreasingdrift amplitudes, has been applied. Variables studied have included wallsaspect ratio, wall flexural coupling (i.e., flexural-to-shear capacity ratio), wall verticalstresses applied to simulate gravity loads, type of unit (e.g., handmade solid clay,industrialized multiperforated clay, semi-industrialized cement), type of mortar, TCdetailing (e.g., percentage of transverse reinforcement), percentage of horizontalreinforcement along the mortar joints, and the size of a welded wire fabric connectedto the walls. Details of recent experimental programs and test results can be foundelsewhere (Aguilar, 1996; Alcocer and Meli, 1995; Alcocer, 1996; Alcocer et al.,1996; Alcocer and Zepeda, 1999). Shaking table tests have been carried out on smallscale specimens (Alcocer and Muria, 2000; Alcocer et al., 2004). Recently, half scaleone-, two- and three-story structures, which represented a prototype structure, weretested under recorded and artificial ground motions that represented credibleearthquakes probable to occur on the Mexican Pacific coast.Typical hysteresis curves of confined masonry walls with and without horizontalreinforcement along the mortar joints are shown in Fig. 1. Initial behavior is linearelastic until first inclined masonry cracking occurs. With further cycling at higherdrift levels, cracking concentrates near the diagonals (mainly in a wide, single crack)thus dividing the wall into triangular blocks limited by the main cracks. At this stage,wall stiffness has considerably decayed and strength (maximum load) is provided byfriction and brick/block interlock, and through shear resistance of TC’s ends. Afterthis stage, shear degradation of wall strength takes place because of brick crushingand spalling, and of shearing off of the TC ends. Confined masonry walls horizontallyreinforced with high-strength deformed wires generally exhibits a superior behaviorin terms of strength, energy dissipation and deformation capacity. At wall strength, anarray of widely distributed, fine cracking, suggests the formation of a diagonalcompression field, which is balanced, in the horizontal direction, by forces resisted bythe wires.2.2 General Requirements for Analysis and DesignMexican masonry standards allow the use of a simplified method of analysis todistribute the earthquake-induced lateral loads among the walls in symmetric and235