Large-Component Seismic Testing for Existing and Retrofitted Single-Family Wood-Frame Dwellings (PEER-CEA Project)

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.

Cripple Wall Small-Component - Test Program: Comparisons (PEER-CEA Project)

“…Observations and results from all tests included in this experimental investigation were provided in the three previous reports [Schiller et al 2020(a); 2020(b); 2020(c)]. It is noted that large-component tests were conducted within the scope of WG4; see Cobeen et al [2020]. To this end, a comprehensive report comparing like-specimens from the small-component test program with those within the large-component test program is available; see Schiller et al [2020(e)].…”

Cripple Wall Small-Component Test Program: Wet Specimens I (PEER-CEA Project)

“…The testing program of Working Group (WG) 4 focused on the first phase of an experimental investigation to study the seismic performance of existing 1 and retrofitted cripple walls with sill anchorage. Paralleled by a large-component test program conducted at University of California, Berkeley (UC Berkeley) [Cobeen et al 2020], the present study involves the first of multiple phases of small-component tests conducted at University of California San Diego (UC San Diego).…”

“…The experimental program within the PEER-CEA Project was executed at UC San Diego and UC Berkeley: (1) UC San Diego's program consisted of testing only cripple-wall assemblies denoted as the small-component testing program; and (2) UC Berkeley tested cripple wall and first-floor assemblies, denoted as the large-component testing program [Cobeen et al 2020]. Scaling of results from the small-component tests was undertaken to capture results for similarly detailed specimens from test results of the large-component tests [Cobeen et al 2020]. In addition, UC Berkeley tested load path connections between the foundation sill plate and the foundation, and between the cripple wall top plate and the floor framing above.…”

“…This report is a product of Working Group 4: Testing and focuses on the first phase of an experimental investigation to study the seismic performance of retrofitted and existing cripple walls with sill anchorage. Paralleled by a large-component test program conducted at the University of California [Cobeen et al 2020], the present study involves the first of multiple phases of small-component tests conducted at the UC San Diego. Details representative of era-specific construction, specifically the most vulnerable pre-1960s construction, are of predominant focus in the present effort.…”

Project Technical Summary (PEER-CEA Project)

“…The reader is referred to the individual reports prepared by the Working Groups for comprehensive information on the tasks, methodologies, and results of each report: Cobeen et al [2020]; Mazzoni et al [2020]; Reis [2020(a); (b)]; Schiller et al [2020(a); (b); (c); (d); (e)]; Vail et al [2020]; Welch and Deierlein [2020]; and Zareian and Lanning [2020].…”