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Assessment of damage to homes following a significant earthquake has found that the primary reason for major structural damage and failure is due to inadequate lateral bracing of cripple walls and inadequate sill bolting of the cripple wall to the foundation. Since the 1970s, methods to retrofit weak cripple walls and improve sill anchorage have been developed and implemented on many dwellings to improve their seismic performance, most notably available are the Federal Emergency Management Agency (FEMA) P-1100 guidelines. To assess the seismic vulnerability of existing and retrofitted cripple walls, experimental programs were performed and documentation of the evolution of damage during these experiments were produced and correlated to the structural capacity and residual drift of the specimens. Using the documented damage evolution, existing damage fragility functions were revised for wood lightframe sub-assemblies. In this article, an overview of the cripple wall experimental program is provided, including the variables investigated. Documentation of the damage evolution during these experiments is presented. Damage states based on repair triggers associated with imposed displacements of the experiments are defined. Finally, a discussion of how the damage observations were used to develop probabilistic component-level damage fragility functions for cripple-wall dwellings is provided. [ABSTRACT FROM AUTHOR]

As part of the Pacific Earthquake Engineering Research Center (PEER)-California Earthquake Authority (CEA) project, experimental programs were performed at UC San Diego and UC Berkeley, with the former focusing on small-component testing and the latter focusing on large-component testing. During the small-component testing program, a suite of 28 cripple wall-only specimens was tested under quasistatic reverse cyclic lateral loading with variations in exterior finishes, retrofit condition, cripple wall height, anchorage condition, boundary conditions, vertical load, and loading protocol. In the large-component testing program, cripple wall-first story specimens, load path connections, and combined materials in occupied stories were tested. The more easily performed small-component specimens facilitate comparison with the large-component specimens to allow the assessment of their potential to emulate large-scale specimen behavior, with a particular interest in cross-comparing their global hysteresis and physical damage evolution. This cross-comparison among small- and large-scale specimen test results is intended to offer best practices for the future design of cripple wall seismic retrofits in residential housing, with a particular interest in: (1) supporting the realistic design of small-component specimens that may capture the response of large-component specimens and (2) to qualitatively determine where the small-component tests fall in the range of lower- to upper-bound estimation of strength and deformation capacity for the purposes of numerical modeling. Data from both test programs were utilized in the PEER-CEA project to assist with validating numerical modeling tools, which in turn were used to generate 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. The objective of this article is to present an overview of the small- and large-component testing programs and key results pertaining to exterior finishes, boundary conditions, the FEMA P-1100 retrofit, and cripple wall height. [ABSTRACT FROM AUTHOR]