Fatigue Life Evaluation Of Typical Connection Details Of Orthotropic Steel Deck Based On Monitoring Data

Fatigue cracks are prone to occur in orthotropic steel decks（OSDs）due to long-term wheel loading with high cyclic stress and unavoidable manufacturing defects.This paper taking an in-service steel bridge as the engineering background,studied how to evaluate the fatigue damage and fatigue life of OSD by using the strain monitoring data of real bridge and the measured traffic flow data,based on the national key research and development project（2016YFC0701202）.The main contents and conclusions are as follows:2 weeks strain time history data of typical fatigue vulnerable details in OSD was obtained by strain monitoring on site,including rib-to-deck connection details,rib-to-diaphragm connection details and the cut-outs detail of diaphragm.The hot spot stress response of connection details was calculated by hot spot stress extrapolation formula.The fatigue damage degree and fatigue life of typical connection details were evaluated based on Miner’s rule and hot spot stress S-N curve of Eurocode.The results show that stress response of the typical connection details of OSD was high,among which the stress level of the cut-outs detail of diaphragm was highest,and the peak value of tensile stress reached 246 MPa.Fatigue life of the typical connection details of the monitored OSD was all less than 100 years under current traffic condition and structural state,and the fatigue life of the cut-outs detail of diaphragm was lowest,only 4.4 years.There was a significant risk of cracking in the OSD.Based on the WIM system,the sample data of traffic flow was obtained,and the probability distribution characteristics of traffic flow parameters were analyzed.A stochastic traffic flow model reflecting the statistical characteristics of actual traffic flow was established by using MC method.The hot spot stress influence surface loading method was used to obtain the stress response of connection details under the stochastic traffic flow,and the fatigue damage of typical connection details of the deck was also analyzed.The results show that the average daily damage degree of connection details in different lanes was different,and the damage degree of connection details in the middle lane of the half-width four-lane road was significantly higher than that in the side lanes,of which the fatigue damage of connection details under Lane 6 was the most serious.Among the details,the average daily damage degree of the cut-outs detail of diaphragm was the highest,up to 9.18×10^-4.Considering the randomness of the fatigue failure of the structure,the fatigue reliability of the OSD was studied in combination with the measured data.Based on the strain monitoring data and random traffic flow data,the probability distribution model of fatigue load effect was established.The fatigue life of the OSD was evaluated based on the target reliability index.In addition,the influence of the increase of traffic volume and vehicle weight on structural fatigue reliability was analyzed.The results show that the daily equivalent stress range S_eq has a single peak characteristic,and the lognormal distribution model can simulate its probability distribution well.The fatigue reliability of connection details decreases rapidly with the increase of traffic volume and vehicle weight,among which the increase of vehicle weight has a more notable impact on the fatigue damage of details.