Funded by the California Universities for Research in Earthquake Engineering. Investigators – Y. H. Chai, T. C. Hutchinson and S. K. Vukazich.
Although modern residential buildings are commonly founded on concrete slab-on-grade, older buildings constructed prior to 1960 were typically built on raised foundations or supported on cripple walls of short wooden studs between the foundation and first floor framing. These old buildings were found to perform rather poorly in recent earthquakes. Typical failures involved large lateral displacement of the upper story framing over the soft cripple wall, resulting in a vertical drop of the building causing fracture of sewer, water and gas lines. Failures or damage to hillside homes supported on stepped cripple walls were also extensively observed in recent earthquakes. Limited research has been conducted to-date on the seismic response of cripple walls, particularly for stepped cripple walls. In this project, both level and stepped cripple walls will be tested under a combined axial compression and reversed cyclic lateral displacement. Results from level cripple wall tests are geared towards the retrofit of older homes, whereas results from stepped cripple wall tests are relevant for both retrofit and new construction of hillside homes. Parameters investigated include wall height-to-width ratios, percentage of bracing for walls, axial load levels, slopes of stepped cripple walls, influence of cement plaster on wall lateral strength, and effects of loading history on the lateral response of cripple walls. A total of 26 cripple walls were tested in this project, with 12 tests on level cripple walls and 14 tests on stepped cripple walls. Two heights (2′ and 4′) were investigated for level cripple walls, and two slopes (3 horizontal to 1 vertical, and 2 horizontal to 1 vertical) were investigated for stepped cripple walls.
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Key Publications:
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Y. H. Chai and Tara C. Hutchinson (2003), “Seismic Damage Characteristics of Cripple Walls”, Earthquake Spectra, Vol. 19, No. 4, pp. 753-778.
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Y. H. Chai, Tara C. Hutchinson and Steven M. Vukazich (2003), “Quasi-Static Reversed Cyclic Response of Level and Stepped Cripple Walls”, Journal of Structural Engineering, ASCE, Vol. 129, No. 5, pp. 567-575.