Study Of Fatigue Performance For Detail Welding Structure Of Steel Bridge Decks Under Vehicle Loading

The maintenance and safety evaluation of the steel bridge are the issues of concern bythe bridge management department. Much damage of steel bridge is caused by the fatiguedamage of the bridge key components. The safety and durability of the bridge are mainlydetermined by the fatigue status of the key components, so the fatigue analysis on the safetyof the bridge operation is important. To study the fatigue performance of the orthotropic steelbridge deck weld structure, a steel box girder of a highway bridge on the Yangtze River waschosen as the research object.According to the orthotropic steel bridge deck construction and mechanicalcharacteristics, the weld structure of U-rib with cover, U-rib with diaphragm plate and coverand diaphragm plate with U-rib of the orthotropic steel bridge deck was chosen as researchobjects. The Δσ-N curves of the weld structure were obtained by the fatigue test, which failureprobabilities were50%and2.3%, respectively. The fatigue curves were extended to thelong-life span, and adequate fatigue design curves and calculation equation were proposed forthe weld structure following the specification of BS5400and EC.3. Meanwhile, According tothe steel-concrete bridge composite structure, the steel-concrete test samples were designedto test the ultimate shearing strength and the fatigue performance. The mechanical propertiessuch as ultimate shearing strength, load-sliding curve and the S-N curves of the shear studswere all obtained.The traffic flow was investigated on the bridge and18types of typical vehicles andproportions were gotten. Based on the equivalent axle load and average wheelbase, the typicalvehicle spectrum composed by7types typical vehicles were proposed to calculate thenominal stress spectrum of the focus points of the welding structures. With the nominal stressspectrum and calculation equations, the cumulative fatigue damage of the welding structureswas calculated, and the fatigue damage of the bridge that caused by overloaded vehicles wasdiscussed. The effects on the fatigue life that caused by the spot welding, the surface qualityof the samples, the welding quality, the assembled error and the value of the deflection error of U-rib and diaphragm plate were also discussed.In order to get full consideration to the fatigue risk of the bridge caused by the weight ofthe vehicles, the vehicle load distribution spectrum composed by18kinds of the typicalvehicles were obtained based on the actual survey traffic flow data. The stress-time curvesand the nominal stress spectrum were calculated by using the vehicle load distributionspectrum. Based on two cases with or without considering the traffic growth, the cumulativefatigue damage of welding structures were calculated by using the nominal stress spectrumand the calculation equations, in which the reliabilitys were50%and97.7%, respectively.Combined with considering the uniform corrosion, the fatigue life of the welding structureswas calculated by using the same method, in which the reliability was also the same.The components of the bridge which need maintenance and repair are mainly introduced.In the above two cases with or without considering the traffic growth, the maintenance plansof the welding structures were suggested based on the cumulative fatigue damage of thewelding structures, in which the reliability was97.7%. Meanwhile, according to the linearelastic fracture mechanics theory, the fatigue reliability assessment method was developed forsteel bridge cover and U-rib welding structure. The limit state function was established byusing the Paris equation, and reasonable parameters were chosen to do the fatigue reliabilityassessment and put forward the specific maintenance plans.