Seismic responses of abutment steel piles in integral skewed bridges

A three-dimensional structural model of a integral skewed bridge was established by using finite element analysis software SAP2000, and the interactions of abutment-soil behind the abutment and H-shaped steel pile-soil around the pile were simulated through a discrete nonlinear spring element. Through nonlinear time-history analysis under a series of bi-directional seismic actions, the influence rules of pile orientation, stiffness of the soil around the pile, and rotational stiffness of pile head on the seismic responses of the H-shaped steel pile in the skewed integral abutment bridge were studied. Research results show that under bi-directional seismic actions, the transverse displacement of the H-shaped steel pile is significantly greater than the longitudinal displacement, and greatly affected by the pile orientation. The bending moments around the strong and weak axes distribute in both positive and negative directions. The maximum values of yield surface function are generally located at the pile top, while the other peak values are located at the 2-4 m where the pile body is buried. When the steel pile is arranged around strong axis bending, the longitudinal displacement at the pile top reduces by 18.2% compared with that around weak axis bending, but the transverse displacement increases by 47.7%. The bending moment around the strong axis at the pile top increases by about 3.9 times, while the bending moment peak value of reverse strong axis of the pile body decreases by about 67.0%. The bending moment around the weak axis at the pile top basically unchanges, while the bending moment peak value around the reverse weak axis of the pile body increases by about 1.0 times. With the decrease in the stiffness of the soil around the pile, the longitudinal and transverse displacements at the pile top improve, and the yield surface function value at the pile top reduces slightly, while the peak value of the yield surface function of the pile body increases. The pile body is difficult to be elastic. When a flexible connection is adopted at the pile head, the longitudinal and transverse displacements at the pile top both rise. The yield surface function value at the pile top decreases, and the pile head can be protected effectively, but the peak value of the yield surface function of the pile body increases. When the rotational stiffness of the pile head is too low, the peak value of the yield surface function of the pile body may be higher than the value at the pile top, and thus the pile body may enter the plastic stage first under rare earthquakes.