Seismic response of connections in indeterminate flat-slab subassemblies

[摘要] Recent earthquakes have shown the vulnerability of flat-slab structures to severe ground motion. The failure in such structures typically initiates at the slab-column connections in the form of a punching failure. This investigation was carried out to evaluate the adequacy of current procedures for the design of slab-column connections. The variables studied included the intensity of gravity loading, slab shear reinforcement at the column line, slab overhang and stiff edge beam at exterior connections, and the indeterminacy of the connection subassembly.Nine half scale slab-column subassemblies were tested under simulated earthquake loading. Seven of the subassemblies simulated a single floor of a two-bay flat-plate structure. Each subassembly consisted of one interior and two exterior slab-column connections. The remaining two specimens were individual interior and exterior connections. All specimens were subjected to the same predefined displacement routine which consisted of twenty cycles of incremental displacements increasing to a maximum of seven percent drift.Increased slab gravity load significantly reduced the drift capacity of both interior and exterior connections. To achieve a lateral drift level of 1.5 percent prior to failure, the ultimate direct shear on flat-plate connections must be limited to $Vsb{u} leq Csb{d}sqrt{fsb{c}spprime}bsb{o}d$, where $Csb{d}$ = 2.0 for exterior connections and $Csb{d}$ = 1.4 for interior connections.The ACI code design approach for interior connections was unconservative for higher gravity load levels. For the range of shear stress levels studied in these tests, the ACI Committee 352 recommendations that moment and shear be treated independently for design of exterior connections appears reasonable. The ultimate direct shear capacity of the exterior connections in this study was $Vsb{u} = 2sqrt{fsb{c}spprime}bsb{o}d$.Closed hoop stirrups enclosing the slab flexural reinforcement passing through the interior connection prevented punching shear failure and increased the ductility of the connection. A stiff edge beam or slab overhang at the exterior connections increased both the strength and ductility of these connections. The behavior of the combined specimens was similar to a summation of the individual connections especially at drift levels less than 1.5 percent.

[发布机构] Rice University

[效力级别] engineering