| Orthotropic steel bridge decks are widely used because of their light weight,strong loadbearing capacity,and fast construction speed.However,due to configutation and internal force state are more complicated,and the unreasonable shape design,some fatigue cracks appeared in the diaphragm arc cutout after a short-term operation period.The original shape of the arc cutout can be improved by using thermal cutting to release the stress concentration under vehicle loads.However,the thermal cutting improvement can also induce residual stress of high levels around the improved arc cutouts.Hence,the studies on the reseaon analysis of the fatigue cracking and fatigue maintenance for the diaphragm cutouts has become a difficulty in the field of bridge engineering.Aiming at the fatigue cracking problem of arc cutout,this paper proposes thermal-cold maintenance method of arc cutout.Established the temperature field and stress field distribution model of arc cutout thermal cutting.A fatigue assessment method for arc cutout considering the influence of residual stress is proposed.The main research contents and conclusions are as follows:(1)This writing introduces the application of steel bridge decks and summarizes the fatigue sickness within the domestic and overseas.The analysis standing of fatigue maintenance strategies,fatigue analysis strategies and thermal cutting residual stress field of orthotropic steel bridge decks within the domestic and overseas is summarized.It is pointed out that the research on fatigue cracking mechanism and fatigue maintenance method of diaphragm arc cutout is not thorough enough.(2)Aiming at the phenomenon of fatigue cracking of diaphragm arc cutout of steel bridge deck in engineering,a comprehensive fatigue maintenance scheme of arc cutout combining thermal and cold maintenance was put forward.The FEA model was created by ABAQUS,and the vehicle stress response before and after the arc cutout maintenance was calculated.The calculation results show that the way of thermal-cold maintenance will solve the strain concentration and reduce stress of auto.(3)The FEA model of the deck-Urib-diaphragm was created by ANSYS.Based on the thermal-structural sequence coupled FEA,the thermal cutting temperature field and residual stress field distribution model of the arc cutout was established.Maximum of the tangential residual tensile stress along the arc cutout is 376 MPa.Carried out the thermal cutting test of the full-scale component of the deck-Urib-diaphragm,and tested the temperature data during the component cutting process and the residual stress data after the arc cutout was cooled.And compared the test data with the simulation data to confirm the validity of the FEA.(4)According to the constitutive model of the steel,a coupling model of the vehicle stress and residual stress of the arc cutout is proposed.And the fatigue stress model at the arc cutout is obtained.Fatigue limit diagram is used to modify the stress amplitude obtained by rainflow counting with consideration of average stress.Based on the linear fatigue accumulated injury criterion and the S-N bight of steel,a way for predicting the fatigue lifetime of the arc cutout,considering the residual stress,is proposed.When the residual stress is not considered,the result will be insecure.When the residual stress is taken into account,the result of the original design arc cutout is about 7 years,which is consistent with the actual situation of the steel bridge studied in this paper.After the improvement of thermal cutting,the fatigue life of the arc cutout has been extended,but it is still less than the design service life of the bridge.The secondary fatigue maintenance with strengthened plate was used for the improved arc cutout of thermal cutting,the fatigue lifetime of the arc cutout is longer than the planning service lifetime of the bridge. |
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