PEER has just published Report No. 2020/18: "Cripple Wall Small-Component Test Program: Wet Specimens II," 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 Brandon Schiller and Tara Hutchinson, University of California, San Diego; and Kelly Cobeen, Wiss, Janney, Elstner Associates Inc.
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.
This report is a product of Working Group 4 (WG4): Testing, whose central focus was to experimentally investigate the seismic performance of retrofitted and existing cripple walls. This report focuses stucco or “wet” exterior finishes. Paralleled by a large-component test program conducted at the University of California, Berkeley (UC Berkeley) [Cobeen et al. 2020], the present study involves two of multiple phases of small-component tests conducted at the University of California San Diego (UC San Diego). Details representative of era-specific construction, specifically the most vulnerable pre-1960s construction, are of predominant focus in the present effort. Parameters examined are cripple wall height, finish style, gravity load, boundary conditions, anchorage, and deterioration. This report addresses the third phase of testing, which consisted of eight specimens, as well as half of the fourth phase of testing, which consisted of six specimens where three will be discussed. Although conducted in different phases, their results are combined here to co-locate observations regarding the behavior of the second phase the wet (stucco) finished specimens. The results of first phase of wet specimen tests were presented in Schiller et al. [2020(a)]. Experiments involved imposition of combined vertical loading and quasi-static reversed cyclic lateral load onto ten cripple walls of 12 ft long and 2 or 6 ft high. One cripple wall was tested with a monotonic loading protocol. All specimens in this report were constructed with the same boundary conditions on the top and corners of the walls as well as being tested with the same vertical load. Parameters addressed in this report include: wet exterior finishes (stucco over framing, stucco over horizontal lumber sheathing, and stucco over diagonal lumber sheathing), cripple wall height, loading protocol, anchorage condition, boundary condition at the bottom of the walls, and the retrofitted condition. Details of the test specimens, testing protocol, including instrumentation; and measured as well as physical observations are summarized in this report. Companion reports present phases of the tests considering, amongst other variables, impacts of various boundary conditions, stucco (wet) and non-stucco (dry) finishes, vertical load, cripple wall height, and anchorage condition. Results from these experiments are intended to support advancement of numerical modeling tools, which ultimately will inform seismic loss models capable of quantifying the reduction of loss achieved by applying state-of-practice retrofit methods as identified in FEMA P-1100,Vulnerability-Base Seismic Assessment and Retrofit of One- and Two-Family Dwellings.