Dynamic centrifuge modeling on the superstructure-pile system considering pile-pile cap connections in dry sandy soils

In conventional designs, the pile and pile cap are typically considered rigid connections. However, this type of connection experiences a concentrated force during earthquakes, leading to frequent damage at the pile heads. To mitigate pile head damage, semirigid pile-pile cap connections are proposed. Centrifuge shaking table tests were conducted to investigate the seismic response of the superstructure-pile foundation system. Two layers of Toyoura sand, including a moderately dense upper layer and a denser bottom layer, were used as the foundation soil. The superstructure was simplified as lumped masses and columns with two different heights and periods. The foundation consisted of a 3 x 3 group of piles. Rigid and semirigid pile-pile cap connections were evaluated. The experiments investigated the effect of connection type on the distribution of bending moments in the piles and analyzed the acceleration and displacement responses of the superstructure under different pile-pile cap connections. According to the results, semirigid connections reduced the peak bending moment at the pile head by 50-70 %, especially for low-rise superstructure cases. The influence depth of the connection type on the pile bending moment reaches approximately 10 times the pile diameter. For low-rise superstructure cases, semirigid connections slightly reduced the natural frequency of the superstructure, leading to a decrease in the superstructure acceleration during earthquakes with a short dominant period. The semi-rigid connections reduce the rotation of foundations but promote the translational displacement of foundations. For the mid-rise superstructure cases, semirigid connections reduce the translational displacement and increase the rotational displacement of the foundation. These experiments provide insights into the seismic performance of superstructure-pile foundation systems with different pile-pile cap connections and can serve as a reference for seismic design in similar engineering practices.