Research On Fatigue Performance Evaluation Of Railway Orthotropic Steel Bridge Deck And UHPC Strengthening Technology

Orthotropic steel bridge decks have been widely used in railway bridge engineering in recent years because of their good mechanical properties.However,due to the repeated effects of the train load,the fatigue damage of the bridge deck structure accumulates with the increase of the using time.Therefore,the fatigue performance of the steel bridge deck should be evaluated regularly,and the reinforcement measures should be taken when the cracks appear.By taking Nanjing Dashengguan Yangtze River Bridge as the research object,this thesis carried out fatigue stress analysis and fatigue life evaluation of railway orthotropic steel bridge deck,followed by experimental research and numerical analysis on the fatigue stress characteristics of typical structural details.The reinforcement technology using UHPC has also been studied.The main research contents and conclusions are as follows:(1)Referring to the current bridge design specification,the fatigue life evaluation method of railway orthotropic steel bridge deck was systematically proposed.Nanjing Dashengguan Yangtze River Bridge was selected as the engineering object to carry out a real case analysis.The finite element model of the integral section of steel bridge deck between two truss joints was established by Abaqus software.The fatigue strength of five key structural details was checked under two fatigue limit states of fatigue I(infinite fatigue life)and fatigue II(finite fatigue life)by calculating the hot spot stress at the weld toe using extrapolation method.The results showed that the fatigue performance of all structural details meets the requirements of the design stage.On this basis,considering the existing fatigue damage accumulation,the residual fatigue life of the orthotropic steel bridge deck of the in-service uncracked railway was predicted,which can also meet the remaining service life requirements.By carrying out the fatigue performance evaluation,the U-rib weld toe of the rib-deck(RD)joint weld and the U-rib weld toe at the beam cutout were identified as sensitive areas for possible fatigue cracking in the future,which needs to be focused.(2)The rib-deck-beam(RDF)three-way joint node with high fatigue stress was extracted from the overall model of the bridge deck for special research.Two RDF node specimens were designed and manufactured to carry out hot spot stress test.One specimen was reinforced with ultra-high performance concrete(UHPC)before loading.The stress distribution of the extrapolated area near the weld toe was measured by gradient strain gauges,and the hot spot stress values were obtained based on the IIW extrapolation method.The test results showed that the maximum stress of the joint appears in the U-rib weld toe of the U-rib and beam welds and the opening area of the beam where stresses exhibits linear and quadratic parabolic distribution respectively.The hotspot stress in the key areas have been greatly reduced after the reinforcement of the decks by using UHPC.(3)The finite element models have been established respectively for unreinforced and reinforced RDF node with UHPC.The local stresses of the hot spot areas have been analyzed,and the results showed that the stress distributions near the weld toe and the corresponding hot spot stress values are consistent with the measured results.Therefore,the accuracy of the finite element models was verified.Based on the parametric analysis of how UHPC reinforcement layer thickness affects the hot spot stresses,it was found that increasing the UHPC thickness can reduce the stresses at the U-rib weld toe and the edge of the beam cutout.The research results of this thesis can provide references for fatigue stress analysis and fatigue performance evaluation of railway orthotropic steel bridge deck,and can also provide scientific basis for the UHPC-based steel bridge deck fatigue reinforcement method.