Buckling Behavior of Steel H-piles Supporting Integral Abutments Bridges (IABs): Numerical and Analytical Investigation

Integral abutment bridges (IABs) have been gaining wide popularity in the United States and neighboring countries due to the rapid increase in maintenance costs associated with conventional bridges. IABs are jointless bridges where the superstructure is monolithically connected to the abutment wall without expansion joints or bearing devices. The design of IABs focuses on encasing the problematic locations within the abutment diaphragm, preventing structural elements degradation, and promoting long-term serviceability. The elimination of expansion joints in IABs allows the thermally induced lateral demand in the superstructure to be transferred to the supporting piles. Despite the well-established benefits of IABs, there is a lack of standardized national guidelines governing their design and construction. Instead, individual states in the US have developed their own design limitations based on engineering judgment and performance of previously constructed bridges. Piles in IABs are susceptible to fatigue due to bridge cyclic movement caused by temperature fluctuations. This research aims to quantify the behavior of steel H-piles supporting IABs through numerical and analytical approaches. Nonlinear finite element models (NLFEM) were calibrated and validated against available experimental data. Subsequently, a total of 30 models were established to examine the effect of various parameters (pile size, pile orientation, pile material yield strength, pile equivalent cantilever length, and axial compressive load) on piles supporting jointless bridges subjected to a combined axial load and lateral cyclic displacement amplitude. The analysis revealed that local buckling was the dominant failure mode for all specimens. Furthermore, this research reiterates the various parameters and assesses their influence through a statistical regression analysis to develop an empirical formula for calculating the lateral buckling capacity. The developed equation correlates material properties and section geometries with lateral loading capacity. The rationality of the developed formula was examined and tested with existing experimental data and its validity was supported by a high coefficient of determination and a low coefficient of variance. Moreover, extending bridge length limits can reduce the construction and maintenance costs for many structures that cannot currently be built using this structural system. The absence of a defined allowable pile ductility in jointless bridges creates a critical gap in determining the maximum permissible safe bridge length. The study further introduces a design aid procedure and offers practical tools in the form of a flowchart to aid engineers in establishing the maximum safe bridge length. The validity of the developed design aid procedure was examined and tested with existing experimental and numerical results. It was determined that the design aid procedure reasonably estimates the buckling response of a pile. Based on displacement buckling capacities of HP sections, length limits for IABs were estimated and compared with existing studies and the current practice of the US Department of Transportations.