Fatigue State Prediction Of Orthotropic Decks Of Steel Box Girder Based On Markov Chain

The steel box girder has been widely used in long-span bridges owing to its outstanding advantages,such as good structural stress performance,wind resistance,light weight,low steel consumption,and low cost.However,its own complex structure,numerous welds,and external factors such as vehicle load have led to prominent fatigue problems.In recent years,scholars at home and abroad have mainly used two methods to study the fatigue state of orthotropic decks,including finite element model methods using computers and experiments based on the use of full-scale models or scale models.With the development of technology,structural health monitoring has been widely adopted on long-span bridges.Monitoring data can be used to evaluate the state of the bridge.This paper took the Xihoumen Bridge as the research object,and analyzed the static and dynamic response and the fatigue state of orthotropic steel decks:(1)A multi-scale finite element model of two separated box girders of a long-span suspension bridge was established.The form-finding analysis of the cable system was performed to obtain the main cable shape and internal force.The main cable shape and internal force were compared with the field cable measurement results.Applying the multi-scale model theory,the simple beam model established first was refined.Under the vehicle load of different working conditions,the static and dynamic responses of the refined model were compared with the field experiments on the bridge to ensure that the finite model can fit the filed bridge situation.(2)When analyzing health monitoring data of long-span suspension bridges,the strain data are generated under the effects of multi-source loads in complex environments.In order to analyze the fatigue state of orthotropic steel decks,based on the wavelet analysis,the original stress time-history was layered according to the different frequencies affected by each load,and threshold denoising was performed at each decomposition level.Finally,the stress time-history affected by vehicle load and the temperature was obtained.(3)In the actual situation,the crack state at the last moment of the U-rib of the orthotropic deck is only related to the state at the previous moment,which is consistent with the Markov chain model.When analyzing the fatigue problem,the formula of the state transition matrix in the process is derived after setting the fatigue state index.(4)According to fracture mechanics,the calculation of the stress intensity factors of the three forms of cracks was analyzed.Based on the fatigue damage in this paper,the stress intensity factors of the critical positions of the orthotropic decks were obtained.Combining with the Markov chain model and the stress time-history,the fatigue state and crack propagation of the critical positions of the steel box girder of the Xihoumen Bridge were analyzed,which provides a reference for bridge management and maintenance.(5)According to the method of data fusion,a calculation framework was proposed to analyze the fatigue state with multiple data,which can include the weight of the multiple data.According to the multilevel analysis,the fatigue state of the region of the orthotropic steel decks can be obtained.