PEER has just published Report No. 2020/20: "Large-Component Seismic Testing for Existing and Retrofitted Single-Family Wood-Frame Dwellings," a report for the "Quantifying the Performance of Retrofit of Cripple Walls and Sill Anchorage in Single-Family Wood-Frame Buildings" Project. It was authored by Kelly Cobeen, Wiss, Janney, Elstner, Associates, Inc.; Vahid Mahdavifar, University of California, Berkeley; Tara Hutchinson and Brandon Schiller, University of California, San Diego, David P. Welch, Stanford University; Grace S. Kang, Pacific Earthquake Engineering Research Center; and Yousef Bozorgnia, University of California, Los Angeles.
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Abstract
This report is one of a series of reports documenting the methods and findings of a multi-year, multi-disciplinary project coordinated by the Pacific Earthquake Engineering Research Center (PEER and funded by the California Earthquake Authority (CEA). The overall project is titled “Quantifying the Performance of Retrofit of Cripple Walls and Sill Anchorage in Single-Family Wood-Frame Buildings,” henceforth referred to as the “PEER–CEA Project.”
The overall objective of the PEER–CEA Project is to provide scientifically based information (e.g., testing, analysis, and resulting loss models) that measure and assess the effectiveness of seismic retrofit to reduce the risk of damage and associated losses (repair costs) of wood-frame houses with cripple wall and sill anchorage deficiencies as well as retrofitted conditions that address those deficiencies. Tasks that support and inform the loss-modeling effort are: (1) collecting and summarizing existing information and results of previous research on the performance of wood-frame houses; (2) identifying construction features to characterize alternative variants of wood-frame houses; (3) characterizing earthquake hazard and ground motions at representative sites in California; (4) developing cyclic loading protocols and conducting laboratory tests of cripple wall panels, wood-frame wall subassemblies, and sill anchorages to measure and document their response (strength and stiffness) under cyclic loading; and (5) the computer modeling, simulations, and the development of loss models as informed by a workshop with claims adjustors.
Quantifying the difference of seismic performance of un-retrofitted and retrofitted single-family wood-frame houses has become increasingly important in California due to the high seismicity of the state. Inadequate lateral bracing of cripple walls and inadequate sill bolting are the primary reasons for damage to residential homes, even in the event of moderate earthquakes.
Physical testing tasks were conducted by Working Group 4 (WG4), with testing carried out at the University of California San Diego (UCSD) and University of California Berkeley (UCB). The primary objectives of the testing were as follows: (1) development of descriptions of load-deflection behavior of components and connections for use by Working Group 5 in development of numerical modeling; and (2) collection of descriptions of damage at varying levels of peak transient drift for use by Working Group 6 in development of fragility functions. Both UCSD and UCB testing included companion specimens tested with and without retrofit. This report documents the portions of the WG4 testing conducted at UCB: two large-component cripple wall tests (Tests AL-1 and AL-2), one test of cripple wall load-path connections (Test B-1), and two tests of dwelling superstructure construction (Tests C-1 and C-2). Included in this report are details of specimen design and construction, instrumentation, loading protocols, test data, testing observations, discussion, and conclusions.