Fatigue Assessment of Steel-Concrete Composite Bridge Girders Under Cyclic Loading

Abstract

Steel-concrete composite girders remain a common structural solution for medium-span highway bridges, yet fatigue-induced degradation at shear connector interfaces continues to raise durability concerns under sustained traffic loading. This study assesses fatigue behavior of composite girder specimens subjected to controlled cyclic loading regimes intended to approximate long-term traffic patterns observed on regional highway networks. Strain gauges and displacement transducers positioned at critical shear connector locations recorded interface slip and stress redistribution across successive loading cycles, allowing identification of degradation onset points prior to visible cracking. Findings indicate that interface slip accumulates in a distinct nonlinear pattern once a threshold cycle count is exceeded, after which stiffness degradation accelerates markedly compared to earlier loading stages. We compare observed degradation patterns against current fatigue design provisions, finding that existing detail categories may underestimate degradation rates for connector spacing configurations common in older bridge stock. The results support recommendations for more frequent inspection intervals on aging composite bridges with connector spacing outside optimal ranges, and inform ongoing efforts to update fatigue verification procedures for composite bridge rehabilitation projects.