Performance Of Steel Pipe Pile To Concrete Bent Cap Connections Subject To Seismic Or High Transverse Loading

A preliminary investigation was conducted on the behavior of steel pipe pile to concrete pile cap connections for bridge structures subjected to extreme seismic and ice forces. This investigation consisted of reviewing available information on the analysis, design, and performance of steel pipe pile to concrete pile cap connections, setting up a finite element model for analyzing the behavior of these connections, and investigating a method for experimentally testing these connections. Only limited information on the behavior of steel pipe pile to concrete pile cap was found during the literature search. Therefore, a finite element model was developed to study connection behavior. The model, developed in ANSYS, consisted of a typical bridge bent (comprised of steel pipe piles topped with a concrete pile cap) and superstructure. The concrete and steel were represented with 3D brick and link elements. All materials were modeled as linear and elastic. Inelastic material behavior was studied in some detail, and issues that need to be addressed in future analyses in modeling such behaviors were identified. The finite element model was used to study the behavior of the pipe pile to concrete pile cap connection in different situations. The model was loaded with a horizontally directed inertial body force of 1 g to study the behavior of the connection under lateral seismic loads. Ice loads were applied as pressures acting directly on the pile cap (high water case) and on the lead pile in a bent. These pressures varied from 0 to 200 psi (0 to 1379 kPa). In general, large stresses and strains were predicted in the pile to pile cap connection under seismic loads. The predicted strains exceeded the elastic limit of the materials, suggesting that large deformations and significant damage may occur in the pile and cap under seismic loads. The stresses and strains predicted in the ice load analyses were significantly lower than those predicted in the seismic analyses, and only minor damage would be expected in the pile and cap under ice loads. Parametric calculations were performed to estimate the effect of deck support conditions, pile height, pile embedment, and pile reinforcement on connection response. Performance of the finite element model was validated by comparing its results with the results of simple hand calculations and with the results of a test on a physical model of a pile and pile cap. The hand calculations were performed using a simple 2D frame model of a typical bent. The physical test was performed on a 1/2 size model of an interior section of a typical bent. Further calculations need to be done that realistically consider the inelastic response of the pile and cap materials under seismic loads. The objectives of such calculations would be (a) to precisely determine the vulnerability (strength and ductility) of these connections under seismic loads, (b) to develop retrofit strategies for existing connections, and (c) to develop design approaches for new connections, as necessary.