Effect of super-structure frequency on the seismic behavior of pile-raft foundation using physical modeling

This paper presents the results of two physical test series, including shaking table and centrifuge modeling, on two super-structures with different frequencies and supported by piled raft foundations in a dry sand bed. While the height and weight of two super-structures were kept constant, the axial force and bending moment of piles, as well as horizontal displacement of super-structures were recorded during seismic loadings. The input seismic loadings were given different amplitudes and frequencies. The shaking table and the centrifuge test results indicated that the super-structure frequency strongly affected the pile-raft system responses. Based on the centrifuge test results, the super-structure had larger horizontal displacement, when the excitation frequency was close to system frequency with low base acceleration (0.14 g), while subsequently, axial force and bending moment of piles increased. In high input base acceleration (0.4 g), excitation frequency dominated the super-structure response, and larger responses occurred at smaller (1 Hz) input excitation frequency.