The research progresses of steel bridge fatigue were systematically generalized and analyzed,and the innovative achievements of steel bridge fatigue load,fatigue mechanism,anti-fatigue design method,fatigue safety monitoring and evaluation,and fatigue safety maintenance and other aspects were summarized.The technical challenges were deeply discussed for steel bridge construction and service maintenance,and the development tendencies were explored for the innovative research of steel bridges.Research results show that(1)the developed vehicle,train,and temperature fatigue load models are matched with the characteristics of traffic loads at bridge sites,structural types and design service life,promoting the improvement of the anti-fatigue design theory for long-lasting steel bridges.(2)The actual fatigue damage of steel bridges can be better reflected by the surfing calculation model derived by the vehicle-temperature coupling fatigue stress.The cumulative fatigue damage under the coupling effect of temperature and vehicles is 10％-15％higher than when only considering the effect of vehicles.(3)A new paradigm of fatigue mechanism research,which integrates physical fatigue test,digital fatigue test and in-situ fatigue test techniques,has emerged,partially altering the traditional understanding of fatigue.The influence laws of distortion-induced deformation ratio and stress ratio on the distortion-induced fatigue behavior and detail fatigue strength were investigated.It is found that the fatigue strength of cable steel wires plummets under the condition of high stress ratio in actual bridges.The objective law is revealed that when the strength grade of cable steel wires increases from 1 670 MPa to 2 060 MPa,the fatigue strength first increases and then decreases.The objective fact is clarified that the fatigue strength of weathering steel bridge details does not decrease after the corrosion.(4)The construction of whole bridge multi-physical field,multi-scale,and multi-probability fatigue twin model has been gradually realized,promoting the advent of steel bridge fatigue metaverse technology characterized by data originality,data interaction,and the symbiosis of virtuality and reality.(5)To solve the design issues of steel bridge details working with fatigue cracks,it is necessary to take the fatigue cracks as the key technical index controlling the structural function and safety,and to adopt the damage tolerance theory for the anti-fatigue design of steel bridges.(6)To break through the technical bottlenecks of crack perception and load acquisition,it is necessary to deeply integrate new artificial intelligence technologies such as acoustic emission,digital filming/photography,computer vision technology,and deep learning,and to create a digital monitoring database for fatigue load and damage of steel bridges,providing comprehensive information for researching on the fatigue mechanisms,design,and evaluation methods of steel bridges.(7)To solve the technical issue that traditional linear cumulative damage evaluation models can not predict the fatigue life of cracked details,it is necessary to establish a digital fatigue evaluation model for steel bridges based on digital twin technology.This will enable precise digital description of fatigue cracks across scales and throughout the entire process,and build an integrated digital fatigue evaluation platform for steel bridges,consisting of intelligent monitoring,twin simulation,intelligent evaluation,and smart decision.(8)Cold reinforcement technique can realize targeted and efficient reinforcement for fatigue cracks in steel bridges with zero or minimal damage to the original structure,allowing implementation without interrupting traffic flow,and has a broad application prospects.(9)Cold reinforcement,hot reinforcement,and cold-hot hybrid reinforcement techniques can be utilized flexibly for steel bridges with different fatigue damage degrees,performance enhancement requirements,and life extension goals,to achieve toughening and light-weighting in the fatigue maintenance of steel bridges.1 tab,33 figs,174 refs.
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