Testing Study Of Fatigue And Local Optimization On The Detail Structure Of Steel Box Girder

Orthotropic steel bridge decks have been widely used in kinds of long-span bridges.They have many advantages, such as light weight, high carrying capacity, beautiful structureand convenient construction and so on. Because of their complex structure stresses,multiplicity structural forms, the residual stress of weldings and the errors of manufacturesand installations, they are easy to appear fatigue failure. The welded joints of typicalstructures of orthotropic steel bridge decks on Jiujiang Yangtze River Expressway Bridgewere investigated in this dissertation. The investigations contained the welded joint betweenthe U-rib and the deck, the joint between the deck and the longitudinal rib and thetransverse rib, the rounded welding region of the U-rib and the diaphragm. The main contentsare listed as follows:Firstly, the three local structures of the real bridge at which the crack was easy to initiatewere chose. Using the finite element software to analyze them, the changing curves ofstress-time in the interest point were gotten. In order to accurately analyze the local structureof the bridge, the finite element model of the sub-model in the point of interest was built.Based on the sub-model method, the stress state of the local structure was gotten. The state ofthe stress in the specimens should be similar to the real bridge in the corresponding place.Then the three kinds of specimens were designed.Secondly, the finite element model of the fatigue specimens was built, and based on theanalysis results, the strain gauges on the specimens were placed. The stress distributions ofthe interest points on specimens were known by analyzing. The static testing and fatiguetesting were finished respectively. Comparing the results of the static testing and the finiteelement results, the reasonableness of the specimen design was verified.Thirdly, the fatigue results of the specimens were analyzed respectively after the fatiguetesting. The S-N curves of the interest points in the real bridge were fitted, then the allowedstress amplitudes were obtained respectively. The crack types of three kinds of specimenswere analyzed to find out the rules of the crack initiation. The effects of the spot welding andthe surface roughness for fatigue life were also analyzed. The results can be used for the evaluation of the fatigue life, health detection, maintenance and repair of the bridge, whichcan also be referenced by other bridge design.Fourthly, the analysis of fatigue cracks and the hardness testing in the rounded weldingregion were finished. In order to improve the fatigue strength of the local structure, this regionwas optimized. By comparing and analyzing the three reasonable schemes, the optimizationscheme was suggested.