UNREINFORCED BRICK MASONRY WALL COLLAPSE INVESTIGATION UNDER OUT-OF-PLANE DYNAMIC LOADING

Prieto J.A.; Aviram A.; Badillo J.W.; Jaramillo J.D. · World Conference on Earthquake Engineering proceedings (2021)

Resumen

Several analytical methodologies used for the collapse assessment of an unreinforced brick masonry (URM) wall subjected to out-of-plane dynamic loading are presented in this paper. The URM wall was constructed in an industrial facility in Medellin, Colombia, with intermediate, lightly-reinforced and widely-spaced concrete frames resulting in large masonry panels. Although the collapse occurred during a moderate wind storm, the analytical assessment considers an equivalent triangular force distribution that could also correspond to inertial forces produced under seismic excitation. The analytical models used to investigate the wall's response to out-of-plane loading include: 1) a rigid cantilever model of masonry panels; 2) a deformable cantilever model of concrete columns; 3) deformable frame models of intermediate concrete columns and beams at mid-height with and without masonry contribution to out-of-plane bending resistance; and 4) a finite element model with all concrete frame elements, masonry units and panel openings modeled explicitly. In the latter model, different boundary conditions are used to estimate peak force and deformation demands on main wall components. Comparison of analysis results between the different models is presented in terms of out-of-plane peak deflections at the wall top, as well as peak force and stress demand-to-capacity ratios on concrete frames and masonry elements, respectively. Past investigations on the performance of vulnerable URM walls under dynamic out-of-plane loading including wind, seismic, and blast demands, have been relatively scarce. Corresponding experimental data have primarily been derived from support motion simulating earthquakes, and quasi-static monotonic testing using airbags or multiple load points approximating distributed wind or blast pressures, or seismic inertial forces. In many of these studies, walls were not cantilevered but rather had two or more supports. Furthermore, tested walls had relatively small dimensions (i.e., length-to-width and height-to-thickness ratios) and were typically treated as rigid or semi-rigid components with idealized pinned supports. The current study is therefore a unique opportunity to evaluate the adequacy of simplified analytical methodologies to identify the collapse hazard of a long and slender URM wall under dynamic loading. Video evidence for the collapsed wall shows some degree of rotational restraint at the wall's base and significant curvatures prior to collapse in both horizontal and vertical bending directions, differing from the idealized boundary conditions and assumed deformed shapes used in past studies. Despite significant differences between the analytical models considered in the current study, recommended parameters and assumptions lead in all cases to the correct determination of the wall's imminent collapse under the estimated demands. Equivalent static force distributions, P-Delta effects, interaction and relative contribution to the out-of-plane bending resistance of concrete framing and masonry elements with either one-or two-way action are shown to be the main parameters affecting results and governing failure modes, in addition to model selection. Recommendations for the maximum allowable wall height resulting in stable behavior are made considering only wall geometry and anticipated peak dynamic demands. © The 17th World Conference on Earthquake Engineering.