The self-anchored suspension bridge is a kind of the flexible and redundant structural system. For this type of bridge, the current code only gives the overall seismic design principle, and there is little research on seismic fragility in the existing literature. Taking the three-tower self-anchored suspension bridge as the research object, the finite-element dynamic models with and without damping are established, respectively. Based on the strong earthquake database of PEER (Pacific Earthquake Engineering Research), 10 ground motion records are selected, and the seismic fragility curves of piers, bearings, towers, and slings are established by using the incremental dynamic analysis (IDA) method. The fragility curves of the bridge system were established by first-order reliability theory. In this study, the damage probability of bridge components under a seismic wave is studied. The results show that the damage exceedance probability of the damped connection system is reduced compared with the undamped fully floating structure system under the action of seismic waves. The damper device makes the seismic performance of the structure significantly improved, and the reduction effect of the damper device on high-intensity earthquakes is more obvious than that on low-intensity earthquakes.
In order to accurately simulate the position of the saddle in the analysis and calculation of a suspension bridge, and then obtain the accurate shape of the datum strand in the construction site, this paper puts forward a calculation method on the position of the saddle and the geometric shape of the datum strand on the basis of considering the friction between the main cable and the saddle. Firstly, the calculation method of friction between the main cable and cable saddle is proposed and the formula of the deviation between the coordinates of the initial position and that of the equilibrium position of the cable saddle is derived. Then, through theoretical derivation, the calculation program of cable geometric shape considering the change in saddle tangent point is compiled. Combined with the analytical algorithm, the concept of temperature telescopic bar is introduced, and a simulation method of the cable saddle and datum strand is given, which is suitable for the combination of finite element analysis and numerical algorithm. Finally, the reliability of the algorithm is verified by the comparison of a numerical example, and by changing the value of friction, the influence of friction on the saddle position and the datum strand geometric shape is analyzed.
As a common method, external prestressing widely informs rehabilitation in existing structures. This paper presents the total prebending moment calculation of external prestressing with different tendon profiles. Meanwhile, the external prestressing loss and original internal prestressing loss are considered in the calculation in both the theoretical method and the finite element method. Then, we discuss the reinforcement efficiency of different tendons profiles and provide the reinforcement distribution ratio. The results show that the theoretical method is similar to the finite element method, and it can quickly evaluate the reinforcement effect by using different tendon profiles in engineering. By comparing the reinforcement efficiency under different external tendon profiles, the reinforcement scheme is determined according to the local damage and the overall damage of the beam, which effectively decreases the cost of reinforcement.
The durability of a concrete bridge structure is a systematic problem composed of material, structure, natural environment, and service environment. Various factors are coupled, which affect each other, and single-factor research cannot fundamentally solve this problem. In this paper, the carbonation characteristics of RC beams with different loading states under the coupling action of carbonation and chloride erosion are studied. Through the experiment, the author tries to find the influence of stress state and chloride ion erosion on the carbonation of concrete and analyze the failure mode and the attenuation rules of the flexural and shearing capacity of the corroded RC beams under the coupling action. For this purpose, five groups of experiments under different working conditions were designed, including chloride ion erosion and carbonation experiments without external load of the cubic blocks, and chloride erosion and carbonation coupling experiments of RC beams under different stress states and stress levels. The carbonation rate of concrete can be reduced by 56%∼60% under the coupling action of chloride salt. Different loading states and stress levels have an obvious influence on carbonation and chloride ion corrosion, which further affects the corrosion rate of steel bars. Under a low corrosion rate, the bending and shear failure modes of the corroded beams are similar to those of the noncorroded beams, and the section strain distribution still approximately conforms to the plane section assumption. The relationship between the relative ultimate shear strength or the relative ultimate flexural strength and the average section-corrosion rate of the reinforcement is approximately linear.
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