Fatigue performance evaluation for composite OSD using UHPC under dynamic vehicle loading

A novel composite orthotropic steel deck (OSD) using ultra-high performance concrete (UHPC) is comprised of an OSD and a thin UHPC layer that are connected through shear connectors. The innovative composite OSD system has been increasingly applied to long-span bridges in China to overcome the defect of conventional OSD that frequently suffers from fatigue cracking. However, the fatigue performance of the composite OSD system is usually evaluated with the deterministic analysis in previous studies, which may lead to inaccurate evaluation as many uncertainties, including the statistical properties of dynamic vehicle loadings and fatigue-prone details, have not been considered rationally. In this paper, the fatigue performance of the composite OSD using UHPC was investigated using the reliability-based fatigue analysis and compared with the fatigue performance of conventional OSD system. A three-dimensional vehicle-bridge coupled system was adopted to obtain the stress time histories of fatigue-prone details in the bridge decks under the action of dynamic vehicle loading. The vehicle model was determined based on the fatigue load pattern adopted in the AASHTO standard specifications and finite element models (FEMs) of both the conventional OSD and the composite OSD using UHPC were built based on a girder segment adopted from the HuMen Bridge in China. Four key influence factors, namely, the road surface condition (RSC), length of bridge deck FEM, vehicle speed, and overloading, were taken into consideration. The fatigue life of six typical fatigue-prone details in these two deck systems was evaluated and compared. The results show that the composite OSD using UHPC can effectively extend the fatigue life of OSD by at least 60% and even eliminate the risk of fatigue cracking for most fatigue-prone details. Compared to the reliability method, the fatigue life of OSD determined based on the deterministic method would be overestimated by 65-110% if the very poor RSC is considered. Besides, the composite OSD using UHPC exhibits a better fatigue performance than the conventional OSD system under the action of overloaded trucks. The results from the study can provide a reference for the design and maintenance of the composite OSD using UHPC.