NEES@UCSB

One of the greatest overall seismic risks in the United States is the risk of collapse of older concrete buildings in a major urban earthquake, yet there are no solutions to how to address this in a cost-effective manner. This multi-institution and multi-disciplinary project brings together engineers, educators and policy makers to assess the extent of the risk and develop cost-effective ways to prioritize addressing it. For many years it was the practice in structural engineering design to ignore the effects of soil conditions on the seismic behavior of buildings by performing seismic response analysis with a fixed-based condition. This can be especially problematic for stiff structures, such as reinforced concrete frame buildings with shear walls. When a fixed base is assumed, then the stiffest part of the structure, the shear wall, will attract most of the lateral load. These effects can only be properly accounted for with the use of appropriate engineering models to represent the foundation-soil interaction. A configurable 1/5-scale test structure has been constructed to represent a simple slab-on-grade system. This test structure will be tested in three different base/soil situations to evaluate a range of soil-structure systems. The three conditions are:

• Fixed-base, on the strong floor at the UCLA structures laboratory
• Very soft soil, on a poured slab at the NEES@UCSB Wildlife Permanent Field Site
• Soft soil, on a poured slab at the NEES@UCSB Garner Valley Permanent Field Site

Testing will be done using shakers from NEES@UCLA and NEES@UTexas and instrumentation from both NEES@UCSB and NEES@UCLA. Data from linear and nonlinear testing will be used to develop a master SSI model that will be applied to the broader NEESR-GC Vulnerable Concrete Buildings project.