Seismic Performance of Concrete Tilt-up Buildings: Current Wall-to-Slab Connections

Abstract eng:
Low rise buildings are commonly constructed in Canada and the US by casting concrete walls on the ground and then tilting them upright. Solid tilt-up walls are inherently stiff and strong. The wall strength and inelastic response is controlled by the connections to these elements. The connection between wall panels and the base slab is the focus of the current study. In order to determine the interaction between vertical uplift on the connector and horizontal shear capacity of the connector, a series of 20 tests are being conducted. The detailed results from three specimens on monotonic uplift, cyclic uplift and reverse cyclic shear with 50 mm uplift are presented. The current procedure used to weld together the plate embedded in the wall to the steel angle embedded in the concrete slab was found to result in a weld failure after only a few cycles of uplift. A revised welding detail is being developed and will be tested. Failure of the wall-to-slab connection may lead to sliding or rocking of the wall on the foundation. To explore the nonlinear system performance of sliding and rocking tilt-up buildings after connection failure, three-dimensional nonlinear response history analyses were conducted using Perform-3D. The wall rocking mechanism generally results in much larger (e.g., four times larger) maximum roof drifts compared to the wall sliding mechanism. About 80% of the energy dissipated in the rocking mechanism is due to movement of building mass, while in the sliding mechanism, about 70% of dissipated energy is due to sliding. Despite the larger displacement demands, the rocking mechanism is felt to be more practical because the complex geometry of real buildings may not allow sliding, and unlike the sliding mechanism, rocking never results in significant residual displacements.

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