Lateral load tests of houses damaged in the Christchurch earthquakes –preliminary findings

H. Morris & D. Carradine

In 2010 and 2011 major earthquake accelerations were experienced in Christchurch, New Zealand. Timber framed houses generally performed well but thousands suffered damage. A series of four lateral load tests were conducted on houses with minor seismic damage. The initial two tests were uni-directional to measure the stiffness and residual strength of the light timber framed houses above the foundations. 130kN of horizontal load was applied and was well in excess of the earthquake loads but deformations of only 10.8mm were measured on a 1983 house and 27mm on the softer side of a house built in 1947. After these damaging loads the houses still had residual strength and performance well in excess of code requirements. Further tests included the foundations in the whole house performance. A 1970’s house had reversing loads of up to 120kN applied with hydraulic actuators and included dynamic snap-back tests. The final test applied reversing loads of up to 200kN to a 1923 house and snap-back tests. Further tests were conducted after a typical repair strategy was applied. This series of full-scale tests on houses provided evidence that New Zealand timber framed houses are very stiff, even after being subjected to loads in excess of code level requirements, and still maintained significant residual seismic resistance. Potential serviceability damage should be considered as a criterion for future house designs, and for evaluations of the damage potential of existing houses, fragility curves need to be developed that relate to house loading.

TDJ 22-2

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