Report - PEER - University of California, Berkeley

limited possibilities of overcoming the situation due to a more constrainedeconomical position.The structural system most widely used consists of load-bearing masonry wallswith cast-in-place (or prefabricated) reinforced concrete (RC) slabs. Confinedmasonry is the preferred masonry system in Mexico, used to build houses rangingfrom low-cost to expensive and architecturally sophisticated residences. Confinedmasonry walls are confined vertically and horizontally with tie-columns, TCs, andbond beams, BBs, respectively. In Mexican buildings, such elements have very smallcross-sectional dimensions, typically equal to the wall thickness. Confining elementsare intended to tie structural walls and floor/roof systems together, and to improvewall energy dissipation and deformation capacities. When properly designed anddetailed, an increase in lateral strength can be quantified. Walls are built withhandmade or industrialized brick units, which may be made either of cement or clay,and which may be solid or hollow; handmade solid clay units prevail.1.2 Earthquake Performance of Confined Masonry HousesSeismic behavior of masonry buildings in Mexico City has been generally satisfactorydue to the low drift and acceleration demands in the soft-soil area, where most ofconstruction is located, because of the distinctly different fundamental period ofvibration of the buildings as compared to the fundamental frequency of the groundmotion. In near-epicentral regions, however, large damages have been observedduring strong ground shaking in inadequately confined masonry structures. Incontrast, well-confined masonry structures, with a reasonable symmetric wall layout,have shown excellent performance, with no damage even in brittle finishes. Lossestimations after recent earthquakes (Alcocer et al., 2001; Lopez et al., 2001)indicated that approximately one-third of the total losses, including direct and indirectlosses, have occurred in the housing sector. Loss estimations after disasters are quiterecent in Mexico, and information is not detailed enough to differentiate betweenstructural and non-structural damages.1.3 Research SignificanceAny effort to improve performance, through the development of design andassessment methodologies, and by tailoring capacities (structural and nonstructural) toseismic hazard regions in the country (demands), is well justified, from the social andeconomical stand point, because: (1) important differences are observed in thestructural design criteria used in housing projects (e.g., ratios of ultimate strengths todesign loads); (2) in some cases, architectural considerations are of primaryimportance whereas structural and nonstructural performances are unimportant; (3)70% of the housing construction does not comply with construction codes and isdeveloped without the participation of trained engineering professionals (Meli andAlcocer, 2004); and (4) a house is the most important and cherished family asset. In234