Dynamic Response of Arbitrarily Shaped Foundations: Experimental Verification

Results of twenty‐one free vibration tests on surface model footings on moist sand having different base shapes and about equal base area have been reported by Stokoe and Erden (5,8). These tests are used here to verify the analytical method of the companion paper (3), for circular, square and rectangular base shapes with aspect ratios up to 6, and including vertical, torsional and coupled swaying‐rocking oscillations. Close agreement is found between predicted and measured frequencies in all cases, and also between damping ratios in vertical and torsional vibration. The experiments provide strong support for the vertical and torsional radiation damping graphs developed in Ref. 3, including verification of the increased damping ratios predicted for the longest footings. The accord is also reasonably good for damping in those swayingrocking tests in which rocking and material damping are dominant and the overall damping ratio is about 3%. However, the method of Ref. 3 overpredicts the measured swaying‐rocking damping ratios in those tests in which swaying and radiation damping are also important, and for which larger damping ratios are predicted (4% to 9%). This discrepancy between half‐space predicted swaying‐rocking damping and measured values is explained by the effect of boundary wave reflections on the test results.