Study On Ultimate Load Bearing Capacity Of Trussed Arch Bridge With Defects And Damage

Most of the as-built reinforced concrete trussed arch bridges on highways in our contry have following defects:transverse crack in lower chord near arch spring; crack at the end nodes of chords; distortion of the truss pieces; vertical crack in straining beams, tie rods, and transverse diaphragms; crack even crush of deck slabs; breakage or lack of expansion and contraction joints; deflection of sidewalks; transverse crack in sidewalks and tie rods near the joint seams between two span. It is necessary to study the ultimate load bearing capacity of reinforced concrete trussed arch bridge in service which contains multiple defects and damage, and provide basis in order to determine the actual bearing capacity and conduct safety evaluation.This paper reviews research conditions of bearing capacity of arch bridge, and research outcome about the infection of defects and damage to the arch structure. Analysing and comparing the different analytical methods of ultimate load bearing capacity of trussed arch bridge. Under the background of one trussed arch bridge, the ultimate load bearing capacity of reinforced concrete trussed arch bridge with defects and damage has been studied.Because all staffs of RC trussed arch bridge mainly bear axial forces, and only bear very small bending moment near the nodes, so spatial beam cells can be adopted to simulate the structure in the paper; moreover based on the theory that the steel and concrete can work together and distort in phase, the steel and concrete of RC trussed structure can be equal to one ideal elastic-plastic combined material with dissymmetrical constitutive relation of stress-press, the constitutive relation deduced by the paper can benefit to the same kind of RC trussed structure. Furthermore, the reciprocity of peg and soil is equaled to pole-spring model. Three kinds of trussed arch bridges with different structural forms are contrasted and analyzed, considered linearity, geometric nonlinearity, and dual nonlinearity respectively(both geometric nonlinearity and material nonlinearity), and the nonlinear influence on the analysis effects of RC trussed multi-arch bridges is studied. The analysis effects indicate:In order to get accurate results, the influence of geometric and material nonlinearity must be considered when the ultimate load bearing capacity of RC trussed arch bridges is studied. Loading form of the arch bridge has great influence on ultimate load bearing capacity, given the structure failure process and damage model under different load operating forms, and sumed up the most two adverse load forms.By mathematical methods, from the conditional random variables, the randomly distributed modes of defects are deduced. Based on dual nonlinear analysis method, the ultimate load bearing capacity of trussed arch bridge with different distributive defects in plane and out plane is studied. For the three structural forms of the trussed arch bridge, the first buckling mode as the mode of defect distribution in plane and out plane, with the defect amplitude increase, the ultimate load bearing capacity of structure falls; when defect amplitude less than 1/1500 of the span, the defects have little effect on the ultimate load bearing capacity; when the defect amplitude more than 1/1500 of the span, along with the defect amplitude increases, the ultimate bearing capacity will be greatly decreased. Compared with the in-plane defects, when the defect amplitude less than the 1/500 of the span, to the same defect amplitude, the ultimate bearing capacity of the trussed bridge with out-plane defects is less than that with in-plane defects; However, when the defect amplitude more than the 1/500 of the span, to the same defect amplitude, the ultimate bearing capacity of the trussed bridge with out-plane defects is more than that with in-plane defects. Regardless of the distribution mode of in-plane defects or out-plane defects, eigenvalue buckling mode as the distribution mode of defects is not necessarily the most unfavorable distribution mode, such as the 6th-order distribution mode of random defects impacts more on the ultimate bearing capacity than that eigenvalue buckling distribution mode does. However, a high-level distribution mode of random defects happens almost impossible, on the other hand, eigenvalue buckling mode as the distribution impacts more on the ultimate bearing capacity than that the vast majority distribution modes of random defects, so in most cases, eigenvalue buckling mode as the distribution mode of defects is close to the most unfavorable distribution mode.Increament of damage degree leads to structural stiffness degrading, results in structural deformation increasing; and the larger the damage degree is, the bigger the increase rate of the structural deformation is. As the damage degree increasing, the ultimate bearing capacity declines linearly. Through the regularity analysis, damage ultimate live load factor of the structureλ=λ0(1-1.1×η)can be deduced. The comparison between simplify analysis and dual nonlinear analysis of the real trussed arch bridge with defects and damage shows that, the difference of calculation result by simplify analysis method and by dual nonlinear method is very small. The simplify analysis method dedued in this paper is exact, and can be adopted in the same kind of bridges'structure analysis. Three different definitions of stability assurance coefficient are discussed and the second definitions of stability assurance coefficient is suggested to measure the overall stability level of old RC trussed multi-arch bridges, its lowest allowance value of stability assurance coefficient is suggested to be 5 in the paper. the bias allowance of the arch rib construction is more conservative in " Technical Specifications for Construction of Highway Bridges and Culvers" (JTJ041-2000), and may be appropriate to relax, the horizontal axis deviation of the allowable range may be slightly larger than the vertical deviation of the allowable range.The research work benefits to learning about the process until the whole trussed arch bridge structure finally failures and many influence factor on the ultimate load bearing capacity of this kind of old trussed arch bridges; provides many useful experiences and advices on evaluation of ultimate load bearing capacity, overrunning capacity, security evaluation, and so on of trussed arch bridges with defects and damage in service for many years.