Lizhong Jiang

Effects of friction-based fixed bearings on the seismic vulnerability of a high-speed railway continuous bridge

The fixed bearings of high-speed railway continuous bridges were vulnerable during earthquakes, since they transferred most of the seismic force between the superstructure and the piers. A type of friction-based fixed bearing was used and would slide during strong earthquakes. The influence of this sliding friction action on the seismic vulnerability curves of different components in the track-bridge system was analyzed in this article. Results show that the sliding friction action of the fixed bearings can protect other components from severe damage under earthquakes. This phenomenon is more significant when the friction coefficient on the friction-based fixed bearings is reduced. However, it increases the seismic relative displacement of the fixed bearings themselves. Finally, a sufficiently large displacement capacity and an appropriate friction coefficient between 0.2 and 0.3 are almost the best combination for the friction-based fixed bearings, which can effectively protect all components of the track-bridge system, including the track structure, piers, piles, and friction-based fixed bearings themselves.

Coupled Analysis of Slip and Deflection for Continuous Composite Beams of Steel and Concrete

Experimental results for eleven continuous composite beams of steel and concrete are presented in this paper, which includes laws of deflection and slip between the concrete and steel. Governing differential equations of slip and deflection for simply supported composite beams with different boundary conditions and different loads are established, and a set of numerical expressions for slip and deflection of continuous composite beams are established by the superposition method as well. The deflection and slip of seventeen continuous composite beams are calculated by the numerical expressions. The calculated results show good agreement with the experimental results. The numerical results show that the slip of continuous composite beams increases and approaches the slip of sandwich panels without shear connectors. At the same time, the degree of shear connection influences deflection to a certain extent. The degree of shear connection influences deflections little at full shear connection and the increment of deflection caused by slip is less than 5% when the degree of shear connection is between 60 to 100%. When the degree of shear connection is between 80 to 140%, the strain in the lower flange of the steel beam at the internal-support is influenced little.

Effects of uncertain characteristic periods of ground motions on seismic vulnerabilities of a continuous track–bridge system of high-speed railway

The high-speed railway in China has to pass through the site surrounded by several known faults. Different earthquake mechanics of those faults and propagation paths cause different ground motions, including different peak ground accelerations (PGA), durations and characteristic periods, acting on the high-speed railway bridges. However, the previous seismic vulnerability analysis mainly aimed at the influence of PGA instead of characteristic periods on the seismic fragilities of bridge structure rather than track–bridge system. By taking a typical and common continuous bridge recommended in Chinese criterion as example, the effects of the uncertain characteristic periods of ground motions on the seismic responses and fragilities of track–bridge system were analyzed based on a numerical method. The results indicate that the probabilities exceeding any damage state of most components, including the bridge and track parts, increase with the characteristic period of ground motions. The uncertain characteristic periods of ground motions should be fully considered for the seismic design of track–bridge system, especially when the uncertain characteristic periods change around a small value. In the seismic vulnerability analysis, the uncertain of the designed characteristic period of ground motions should be developed by considering the different earthquake mechanics of several known faults surrounding the bridge site and the complex propagation paths of ground motion waves through different soils. Using a constant characteristic period of ground motions only considering the soil profile at the local site of bridge possibly leads to an unsafe result in the current criterion.

Improved Finite Beam Element Method to Analyze the Natural Vibration of Steel-Concrete Composite Truss Beam

Based on Hamilton’s principle, this study has developed a continuous treatment for the steel-concrete composite truss beam (SCCTB). It has also deduced the SCCTB element stiffness matrix and mass matrix, which include the effects of interface slip, shear deformation, moment of inertia, and many other influencing factors. A finite beam element method (FBEM) program for SCCTB’s natural vibration frequency has been developed and used to calculate the natural vibration frequencies of several SCCTBs with different spans and different degrees of shear connections. The FBEM’s calculation results of several SCCTBs agree well with the results obtained from ANSYS. Based on the results of this study, the following conclusions can be drawn. For the SCCTB with high-order natural vibration frequency and with short span, the effect of the shear deformation is greater. Hence, the effect of the shear deformation on the SCCTB’s high-order natural vibration frequency cannot be ignored. On the other hand, the effect of the interface slip on the SCCTB’s high-order natural vibration frequency is insignificant. However, the effect of the interface slip on the SCCTB’s low-order natural vibration frequency cannot be ignored.

Improved finite beam element method for analyzing the flexural natural vibration of thin-walled box girders:

This study establishes the improved element stiffness and mass matrices of the thin-walled box girder, using a cubic Hermite polynomial shape function and based on an improved displacement function for shear-lag warping meeting the axial equilibrium condition of shear-lag warping stress and the consistency requirements of the displacement function. The improved thin-walled box girder element comprehensively considers multiple influencing factors, such as the thin-walled box girder shear-lag effect, shear deformation, and rotational inertia. The element shape function has first-order continuity at the element interface and satisfies the calculation precision with relatively few degrees of freedom. A finite beam element method program that can be used to calculate the natural vibration frequencies of thin-walled box girders was compiled based on the improved thin-walled box girder element. This program was used to calculate the natural vibration frequencies of many thin-walled box girder samples with different span-width ratios, span-height ratios, and boundary conditions. After comprehensively considering the influencing factors, the calculation results obtained from finite beam element method are in good agreement with those obtained from an ANSYS finite element calculation, thus demonstrating the rationality and validity of the improved thin-walled box girder element stiffness matrix and mass matrix proposed in this study. Finally, factors influencing the thin-walled box girder shear-lag effect and shear deformation were analyzed, providing relevant reference for project designers.

An Analytical Study on Dynamic Response of Multiple Simply Supported Beam System Subjected to Moving Loads

Based on Euler–Bernoulli beam theory, first, partial differential equations were established for the vibration of multiple simply supported beams subjected to moving loads. Then, integral transforms were conducted on the spatial displacement coordinate and time in the partial differential equations, and the frequency-domain response of multiple simply supported beams subjected to moving loads was obtained. Next, by conducting the corresponding inverse transforms on the displacement frequency-domain responses of multiple simply supported beams, the spatial displacement time-domain responses were obtained. Finally, to validate the analytical method reported in this paper, the dynamic response of a typical double simply supported rail-bridge beam system of high-speed railway in China subjected to a moving load was carried out. The results show that the analytical solution proposed in this paper is consistent with the results obtained from a finite element analysis, validating and rationalizing the analytical solution. Moreover, the system parameters were analyzed for the dynamic response of double simply supported rail-bridge beam system in high-speed railway subjected to a moving load with different speeds; the conclusions can be beneficial for engineering practice.

Effects of friction-based fixed bearings on seismic performance of high-speed railway simply supported girder bridges and experimental validation

This study investigated the seismic performance of simply supported girder bridges with a span length of 32u2009m. Those bridges were a common part in China’s high-speed railway system and used spherical bearings to connect girders and piers. First, a finite element model of the scaled bridge with a geometrical similarity ratio of 1:8 was established by OpenSees. Second, five seismic damage states of fixed bearings and piers were defined based on the deformation failure criterion. Finally, an incremental dynamic analysis and a pseudo-dynamic test were performed to evaluate the effects of friction-based fixed bearings on the seismic response and damage state of bearings and piers. Results show that the sliding of friction-based fixed bearings effectively restricts the force transmitting between piers and girders, and reduces the seismic damage of piers. Those bearings with a small friction coefficient lead to a large relative displacement between piers and girders, while those bearings with a large friction coefficient cause a large seismic force exceeding the yield load of piers. Therefore, an appropriate friction coefficient of friction-based fixed bearing should be determined to achieve an optimal seismic performance of bridge according to the specific conditions of bridge and ground motion inputs.

Natural vibration analysis of steel–concrete composite box beam using improved finite beam element method:

Based on Hamilton’s principle and a cubic Hermite polynomial shape function, first the improved steel–concrete composite box beam element stiffness and mass matrixes with a few numbers of degree were derived by considering many influencing factors such as interface slip, shear lag, shear deformation, and rotational inertia, and then the finite beam element method program was established. The natural vibration frequencies of many steel–concrete composite box beam calculation samples with different spans, degrees of shear connection, and boundary conditions were calculated. The analysis results show that the finite beam element method calculation results are consistent with ANSYS’ calculation, thus demonstrating the rationality and validity of the improved steel–concrete composite box beam element stiffness and mass matrixes proposed in this study. Moreover, some meaningful conclusions to engineering design were drawn as follows: The effect of shear lag increases with the order of steel–concrete composite box beam’s natural vibration frequency and degree of shear connection. Shear deformation also increases with the order of steel–concrete composite box beam’s natural vibration frequency; thus, the shear deformation corresponding to the steel–concrete composite box beam’s high-order natural vibration frequency cannot be ignored. The interface slip of steel–concrete composite box beam’s high-order natural vibration frequency is negligible; however, the interface slip of steel–concrete composite box beam’s low-order natural vibration frequency cannot be ignored.