Cyclic loading of H-piles used for construction of integral abutment bridges.

摘要

Integral bridges are bridge structures that are built without expansion joints. In general, the girders and abutments of an integral bridge are cast "integrally" with one another and act as one unit. The loads and displacements from this system are then transferred to the soil via the abutment and also through piles (commonly steel H-piles) which support the abutment. Temperature induced (daily and seasonal) cyclic expansion and contraction of the bridge girders and deck subject the abutments to horizontal loads and movements. Because the girders, abutments, and piles are built integrally, and since there are no expansion joints, the H-piles supporting the abutments must accommodate this lateral movement. This can cause significant stresses to develop at the abutment-H-pile interface. Over the life-span of a bridge, there is a potential for degradation of the abutment-H-pile connection to occur due to cyclic loading caused by temperature variation. This degradation, if significant, could lead to increased and unacceptable levels of displacement in the abutment or an increased level of stress in other bridge components as a result of the decreased stiffness at the abutment-H-pile connection.;This research investigates how the magnitude of the stresses, caused by the daily and seasonal temperature variations, affects the interaction and performance of the abutment-H-pile connection. Specifically, this research investigates how the performances of identical abutment-H-pile connections differ, if each one is subjected to different levels of cyclic stress (i.e. stresses cycled to 35% of the weak-axis H-pile moment capacity compared to 75% or 120%). Four specimens were cast (three oriented for weak-axis bending and one for strong-axis bending), each tested at a various level of cyclic lateral load, and then monotonically loaded until yielding or failure.;The results indicate that the temperature induced cyclic stress did not produce significant degradation of the abutment-H-pile connections that were tested. The amount of degradation that was measured was very small with a less than 4% increase in deflection for a given load after 50 years of cyclic stress. The amount of degradation in the weak-axis abutment-H-pile connections did increase however, with increasing cyclic stress.;The abutment-H-pile connections that were tested remained robust throughout the duration of testing with no cracking or spalling of the concrete being noticed. In each case, the H-pile section yielded before any concrete failure was noticed.