Seismic performance of a continuous bridge with winding rope device activated by a fluid viscous damper

The seismic requirements of piers with fixed bearings (the fixed pier) for continuous girder bridges are relatively high, while the potential seismic capabilities of piers with sliding bearings (the sliding piers) are not fully utilized. To solve this contradiction, a new type of winding rope shock absorption device activated by a fluid viscous damper (WRD-D) was proposed. The WRD-D was installed on the top of the sliding piers, and the both ends of a fluid viscous damper were connected to the superstructure by winding ropes. During an earthquake, the damping force rises with the increase of relative speed between the sliding piers and the superstructure, activating the WRD-D and producing large frictional resistance, subsequently causing the sliding piers and the fixed pier to bear the seismic load cooperatively. In this study, the working mechanism of the WRD-D was researched. The shaking table test of a scaled continuous girder bridge model employing the WRD-D was conducted. The test results reveal that the WRD-D can effectively reduce the seismic requirements of the fixed pier and the superstructure displacements.

Seismic Mitigation of Curved Continuous Girder Bridge Considering Collision Effect

Due to structural irregularity, curved bridgesaremore likely to cause non-uniform collisions and unseating between adjacent components when subjected to earthquakes. Based on the analysis of the collision response of curved bridges duringearthquakes, and according to the seismic characteristics of curved bridges, research was carried out on pounding mitigation and unseating prevention measures. A curved bridge with double column piers was taken as an engineering example, and a finite element model of curved bridges thatcould consider the non-uniform contact collision between adjacent components was built with ABAQUS software. Viscoelastic dampers, viscous dampers, and a lead rubber bearing were selected as the damping devices, and a steel wire rope-rubber mat was used as the pounding mitigation device to form the combinatorial seismic mitigation system. Based on the principle of energy dissipation combined with constraints, three kinds of combined seismic mitigation case were determined; a seismic response analysis was then performed. The results indicated that the three kinds of combined seismic case were effective atreducing the response topounding force, stress, damage, girder torsion and displacement, and achieved the goals of seismic mitigation and unseating prevention.

Mechanical Properties of Full-Scale Prestressed Concrete Beams with Thin Slab after Exposure to Actual Fire

To provide an effective basis and reference for applications of prestressed concrete thin-slab beams after a bridge fire, methods and principles of fire-resistant design, repair, and reinforcement of such beams were discussed. Taking a simple supported and continuous girder bridge of an expressway in service as a sample, appearance testing and nondestructive testing of the internal structure were carried out. Four representative full-scale prestressed concrete beams were selected. Through the comparative test of the ultimate bearing capacity of such beams, the laws of the deflection deformation, strain distribution, crack formation, and crack development were obtained. By combining with the finite element simulation and theoretical analysis, the ultimate bearing capacity, complex mechanical characteristics, and breakage feature and failure mechanism of such beams were studied. It was indicated by the results the following: (1) Prestress loss will cause height reduction of the concrete shear zone, which is one of the main reasons why the bending-shearing failure of such beams happened before the pure bending failure. (2) Under certain operating loads, brittle fracture is more likely to occur on the bottom surface of such beams when directly exposed to fire. (3) The bursting and spalling depth of concrete after being exposed to fire can be used as the characteristic parameters for the rapid identification of the bottom surface of such after-fire beams.

Influence of Water-Structure and Soil-Structure Interaction on Seismic Performance of Sea-Crossing Continuous Girder Bridge

Based on the Hong Kong-Zhuhai-Macao project, considering the fluid-structure interaction and soil-structure interaction, the seismic response of a sea-crossing continuous girder bridge is analyzed. Three-dimensional nonlinear numerical bridge model is developed, in which the hydrodynamic force is represented by added mass and pile-soil interaction is represented by p-y elements. Meanwhile, stratification of soil is considered in the free field analysis. Through the comparison of responses of the bridge cases, the effects of earthquake-induced hydrodynamic force and pile-soil interaction are studied. For the influence of hydrodynamic force, the results show that it is relatively slight as compared with pile-soil interaction; moreover pile foundation is more sensitive to it than other bridge components. The influence of pile-soil interaction is relatively significant. When both of the interactions are considered, the influence is not a simple superposition of acting alone, so it is recommended to consider both factors in dynamic analysis.

Finite Element Analysis and Preliminary Dynamic Tests of Laboratory Bridge Model

A preliminary dynamic test of a two-span continuous girder bridge is reported in this paper, including the design specifications, the numerical model, and the modal identification result. This laboratory bridge is made of aluminum plates and connected via bolts. The finite element method is applied to build a numerical model of the bridge to aid the design and test plan. Several ambient vibration tests are conducted to extract the modal parameters, e.g., modal frequencies, damping ratios, and mode shapes, of the constructed bridge, and the Bayesian FFT algorithm is used for modal identification. We compare the identified results with those predicted by the finite element model and vary the magnitude of load to investigate its potential influence on the modal parameters. Damage cases by loosening structure members are also considered, and significant changes are observed in modal frequencies. The constructed model will be used as a benchmark for damage identification, model updating, and condition assessment, etc.

Seismic Damage Probability Assessment of Isolated Girder Bridges Based on Performance under Near-Field Earthquakes

This paper presents a copula technique for developing seismic fragility curves for an RC (reinforced concrete) isolated continuous girder bridge, by considering earthquake damage indicators such as bridge piers, isolated bearing components, and the main girder of collision damage. The results of this method are compared with those of the limit method of the first-order reliability theory. Meanwhile, the incremental dynamic analysis of the bridge structure under different failure conditions is carried out, and the randomness of the near-fault ground motion and the structural parameters are accounted. Based on the damage index of the isolated bridge under different damage conditions, the seismic fragility curves of each component and the whole isolated bridge are obtained. The research shows that the safety control of the isolated continuous girder bridge structure is mainly affected by the seismic fragility of the isolated bearing, the influence of bridge pier seismic fragility is relatively small, and the probability of beam collision in an isolated bridge is lower than that of a general bridge without isolation bearing. By applying the isolation scheme, the probability of different damage state of the bridge structure is greatly reduced, thus the seismic performance is improved. It also verifies the efficiency and superiority of copula technology. The results will provide a reference for future seismic damage prediction.

Construction Stage Seismic Vulnerability Evaluation of a Continuous Girder Bridge with the Cast-in-Place Cantilever Construction Method

To evaluate the vulnerability of bridges at various construction stages under the action of strong earthquakes, the incremental dynamic analysis (IDA) method is applied, and the vulnerabilities of a continuous girder case study bridge with the cast-in-place cantilever construction method, which owns five main construction stages, are evaluated and compared. The results show the following: With the increase in the peak ground acceleration (PGA), the vulnerabilities of bridges at different construction stages all increase. The fragility and vulnerability are mainly determined by the structural mechanical system condition and the mode shapes but not the modal frequency. For the working condition of seismic PGA of 0.4 g, (1) the bridge at the substructure construction stage may only experience slight or moderate damage with the exceedance probability of 8% to 5% and the mean loss ratio being only about 5%; (2) the vulnerabilities of bridges at the middle cantilever construction stage and the long cantilever construction stage are similar, the collapse damage exceedance probability is about 80%, and the mean loss ratio is about 65%; and (3) the vulnerabilities of bridges at the middle span closure construction stage and the bridge completion construction stage are nearly the same, the collapse damage exceedance probability is about 98%, and the mean loss ratio can reach 80%. The research results explore a new method for evaluating the vulnerability of bridges at different construction stages, which can provide suggestions for seismic damage defense and seismic insurance risk evaluation.