Infill panel system for seismic strengthening of flat-plate buildings
Humay, Francis Kam
Durrani, Ahmad J.
Doctor of Philosophy
Many existing flat-plate buildings are seismically deficient and pose a threat to life safety if subjected to ground motions of even low to moderate intensity. Failure in such structures is typically the result of punching failure at the slab-column connection. Because of this, performance-based retrofit procedures are needed to upgrade these non-ductile buildings. This investigation evaluated the use of lightweight pumice stone concrete (LWPSC) infill panels as a retrofit alternative for flat-plate buildings. Six four-tenth-scale slab-column subassemblies were designed and detailed based on ACI 318-63 and current performance-based testing requirements. Except for one bare frame specimen, all the subassemblies were retrofitted with prefabricated LWPSC infill panels and subjected to quasi-static loading conforming to FEMA 273. The geometry of the individual units was governed by weight limitations for handling and erection. Among the variables studied were connections between the slabs and the infill wall and the addition of uniformly distributed perforations (circular and rectangular openings). All of the retrofitted specimens had significant increases in both strength and stiffness over that of the bare frame. The behavior of the specimen with the infill panels not attached to the slabs was similar to that of a masonry wall without any connections to the frame. Although diagonal tension cracks formed within the recessed region, ultimate failure of the infill did not occur. Instead, frame-wall interaction transmitted large concentrated shear forces into the column that eventually contributed to failure of the longitudinal tension splice. The remaining subassemblies all had connections to the slabs and perforations within the wall. Specimens with circular holes experienced uniformly distributed cracking throughout the entire area of the infill wall. The chosen configuration, however, did not sufficiently weaken the wall, and shear failure of the column stopped the test. Because of its ductility and energy dissipation mechanism, the most promising infill panel configuration contained rectangular perforations. Two different reinforcement patterns were tested using rectangular openings. The addition of diagonal reinforcement between openings had the effect of increasing the yield strength of the wall as well as better maintaining post-yield deterioration.