Study On Fatigue Behaviors Of Tipical Welded Details Of Orthotropic Steel Decks By UHPC Reinforced

The orthotropic steel bridge deck is composed of U-ribs,roof and beams.The three are perpendicular to each other and work together by welding.It can not only bear the direct load of the bridge deck,but also participate in the work of the main beam.It has the advantages of light weight,steel saving,and high bearing capacity,so it is widely used in bridges around the world.But at the same time,due to complex forces,many welds,initial defects,and direct bearing of vehicle loads,fatigue cracks and damage to orthotropic steel bridge decks are common.Based on full-scale tests and numerical simulations,this paper studies the mechanical properties of orthotropic steel bridge decks.The main research contents and conclusions are as follows:(1)Six specimens are designed,which are divided into RDF and RDFUHPC.Each type of specimen is divided into single wheel loading specimen and double wheel loading specimen.Firstly,the static load is applied,and the stress distribution law in the hot spot area is obtained by gradient strain gauge and unidirectional strain gauge.Then,the high cycle fatigue test is carried out.The fatigue load amplitude is determined according to the stress ratio and stress level,and the crack development,vertical displacement and stiffness degradation of the specimen during the loading process are observed.(2)The stress distribution is obtained by static loading,and the stress at the toe or the edge of the opening is extrapolated by quadratic function.It is found that the stress drop of the key test points of UHPC strengthened specimens is more than 40%,and the effect of reducing the hot spot stress is significant.(3)The finite element software abqus is used to establish the same model as the test for numerical simulation,and the theoretical analysis results are compared with the actual test data.The results show that the simulated stress distribution of single wheel loading and double wheel loading is very consistent with the test stress distribution,and most of the key test points are within 5%.In the single wheel loading specimen,the improvement of the hot spot stress in the U-rib weld toe area by UHPC pavement is less than 1 / 2 of that in the beam opening area,while in the double wheel loading specimen,the decrease of the hot spot stress in the Urib area is more than 2 times of that in the beam opening area.(4)The failure mode of RDF joint is studied by fatigue loading.The results show that the failure process can be divided into four stages: crack initiation,stable development,through-u-rib wall thickness and specimen stiffness failure.(5)Under the same load condition,observe the cracking time,crack development rule and stiffness decline of the specimen.It is found that the cracking time of the specimen strengthened by UHPC is delayed,and the stiffness decline speed and amplitude of the specimen are reduced.In addition,after the crack penetrates the wall thickness of the U-rib,the stiffness decline rate of the specimen remains a stable trend.