Experimental Research of Fatigue Performance of OSDs with Severe Fatigue Cracking After Reinforcement Using UHPC Layer

Based on the newly developed technology proposed by our team, which involves reinforcing severely cracked orthotropic steel bridge decks (OSDs) with an ultra-high-performance concrete (UHPC) layer containing transverse steel-plate strips, this study conducted full-scale fatigue performance validation tests on the steel–UHPC composite bridge deck of the Junshan Yangtze River Bridge. To verify that the observed stress distribution reasonably reflects the actual structural behavior, finite-element modeling was used to derive the stress influence lines for both the actual bridge segment model and the laboratory-test specimen designed in this study across different fatigue details. The finite-element analysis showed good agreement between the model of the actual bridge segment and that of the laboratory-test specimen. The fatigue tests were conducted in three phases. In the first phase, fatigue cracks were initiated and monitored at specific critical details of the deck before reinforcement. The results indicated that cracks formed most easily and propagated most quickly at the intersections between the deck plate and U-ribs, as well as at the weld holes between U-ribs and transverse diaphragms. In the second phase, the propagation of these fatigue cracks and the changes in stress were compared before and after the UHPC layer reinforcement. The findings proved that the UHPC layer effectively suppressed crack growth and reduced the stress amplitude at fatigue-prone details (with reductions of up to 96% at the deck plate and U-ribs, and up to 57% at the U-ribs and diaphragm weld holes). In the third phase, the model underwent additional fatigue testing, including 1 million loading cycles at the diaphragm and 2 million two-point loading cycles at the mid-span, to verify the long-term fatigue resistance of the reinforced model throughout its entire service life. Data provided by the health monitoring system of the in-situ measurements on a real bridge further validated the effectiveness of the reinforcement measures in reducing stress amplitude at fatigue-sensitive locations (with stress amplitude reductions of up to 86% at the intersections of the deck plate, U-ribs, and transverse diaphragms). This study provides actionable insights into fatigue behaviors and reinforcement strategies, contributing valuable experience toward the maintenance and preservation of similar infrastructure.