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Ma T.,State Key Laboratory of Disaster Reduction in Civil Engineering | Ge Y.,State Key Laboratory of Disaster Reduction in Civil Engineering
Journal of Structural Engineering (India) | Year: 2014

The design of long-span bridges requires accurate finite element (FE) models for reliable predictions of their dynamic characteristics and responses to loads, such as wind or earthquakes. There are inevitably deviations in dynamic characteristics resulted from different FE models with different modeling details. Firstly, the influence of modeling details on structural dynamic characteristics is investigated, including the beam-column joint modeling in tower, the choice of deck models and structural mass simulation. The optimal FE modeling details are proposed for bridges with different structural systems or different girder sections. Then, based on the nature of uncertainties of structural quantities and the characteristic of turbulent wind loading, the sensitivities of buffeting response prediction to structural quantities and wind spectra are both studied through two-dimensional buffeting analysis in frequency domain and three-dimensional buffeting analysis in time domain, respectively.

Shen Z.-Y.,Tongji University | Shen Z.-Y.,State Key Laboratory of Disaster Reduction in Civil Engineering | Lei M.,Tongji University | Li Y.-Q.,Tongji University | And 3 more authors.
Advances in Structural Engineering | Year: 2013

Concrete-filled L-shaped steel tube columns can be used to save architectural space at room corners, and may have many advantages of structural behavior of common concrete-filled steel tubes as columns. In this paper, the seismic behavior of concrete-filled L-shaped steel tube columns (CFLSTs) was investigated. Six specimens subjected to a constant axial load and cyclically varying lateral loading were tested to study the effects of width to depth ratio of section, depth to thickness ratio of steel tube and axial load level on the strength, as well as stiffness, ductility and energy dissipation of CFLST columns. Experimental results showed that the displacement ductility of CFLST columns decreased significantly with the increase of axial load level, and the strength and stiffness degradations of CFLST columns were more significant with higher axial load level. With the increase of depth-thickness ratio of steel tube and depth-width ratio of section, the ductility and the lateral ultimate load-carrying capacity of CFLST columns also decreased gradually. All CFLST columns exhibited favorable energy dissipation and ductility, even for the columns subjected to high axial load, which indicates that this type of composite columns is adoptable in practical engineering, especially in seismic regions.

Xie Q.,Tongji University | Xie Q.,State Key Laboratory of Disaster Reduction in Civil Engineering | Zhu R.,Tongji University
IEEE Power and Energy Magazine | Year: 2011

An Overview is Provided of the Damage to Electric Power grid infrastructure caused by three types of natural disasters that have taken place in the past few years in China: severe windstorms, ice and freezing rain, and earthquakes. Interruptions of electric service caused by these natural disasters have led to devastating economic losses in China and reduced the restoration and reconstruction speed of other related lifeline infrastructures, such as water supply systems and communication systems. The lessons learned from these disasters and their consequences for the Chinese power systems are described, as are actions taken to reduce the impact of such events in the future. © 2006 IEEE.

Jie L.,Tongji University | Jie L.,State Key Laboratory of Disaster Reduction in Civil Engineering | Xiaodan R.,Tongji University
Science China: Physics, Mechanics and Astronomy | Year: 2010

The research of modern mechanics reveals that the damage and failure of structures should be considered on different scales. The present paper is dedicated to establishing the multi-scale damage theory for the nonlinear structural analysis. Starting from the asymptotic expansion based homogenization theory, the multi-scale energy integration is proposed to bridge the gap between the micro and macro scales. By recalling the Helmholtz free energy based damage definition, the damage variable is represented by the multi-scale energy integration. Hence the damage evolution could be numerically simulated on the basis of the unit cell analysis rather than the experimental data identification. Finally the framework of the multi-scale damage theory is established by transforming the multi-scale damage evolution into the conventional continuum damage mechanics. The agreement between the simulated results and the benchmark results indicates the validity and effectiveness of the proposed theory. © Science China Press and Springer-Verlag Berlin Heidelberg 2010.

Yuanqi L.,State Key Laboratory of Disaster Reduction in Civil Engineering | Yuanqi L.,Tongji University | Wang L.,Tongji University | Shen Z.,State Key Laboratory of Disaster Reduction in Civil Engineering | And 2 more authors.
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2011

It is widely known that added mass has a significant influence on the natural frequency of membrane structures. Previously, the total added mass of a one-dimensional membrane has been investigated with theoretical analysis. However, no test result has been applied to verify results of the theoretical analysis. Furthermore, the distribution of the added mass is still unclear. In this study, first, thin-airfoil theory was applied to analyze the distribution of the added mass. The distribution of the added mass was found to be basically uniform for the first vibration mode of a one-dimensional membrane. Then, it was assumed that the added mass of one vibration region is independent of the added mass of another vibration region for higher vibration modes, where the vibration regions are the parts of the membrane separated by the nodal points (nodal lines for two-dimensional membranes) of the vibration mode. Based on the above analysis, a simplified added-mass model was proposed; i.e., for every vibration mode, the added mass of each vibration region is equivalent to the uniformly distributed air with a height of αml, where αm is the added mass coefficient and l is the diameter of the inscribed circle of the corresponding vibration region. To ascertain the added-mass coefficient and verify the simplified added-mass model, a vacuum chamber was designed to test the vibration of a circular flat membrane in still air with varying air pressures. The results showed that the simplified added-mass model was accurate when the added-mass coefficient was taken as 0.65. The efficiency of the proposed simplified added-mass model was further verified by an existing test of a three-sided membrane. © 2011 Elsevier Ltd.

Xie Q.,Tongji University | Xie Q.,State Key Laboratory of Disaster Reduction in Civil Engineering | Sun L.,Tongji University
Gaodianya Jishu/High Voltage Engineering | Year: 2010

In order to study the failure pattern and collapse mechanism of transmission tower under ice loading, a one-panel and a two-panel tower subassemblages of a typical 500 kV transmission tower which were severely damaged during the ice disasters were fabricated. Both of two subassemblages were tested under simulated ice loading statically. The mechanical behavior, failure pattern, strain and deformation of substructures were investigated. The FEM software ANSYS was employed to analyze the behavior of two subassemblages by using shell elements. The experimental results showed that buckling of main leg was the basic failure mode of the structures, although the strains of the diagonal braces were relatively small. The out-of-plane deformations in the joints of the diagonal braces of the structures were considerable, and would significantly weaken the lateral constraining for main member of the structure. The effective length of the main angles would be increased. Meanwhile, the instability modes would exhibit obvious torsional-flexural buckling. The corresponding load-carrying capacity would be decreased notably. It can be concluded that restraining the out-of-plane deformation of the cross-bracings is one of the effective methods to enhance the ice load-carrying capacity of transmission tower.

Xie Q.,Tongji University | Xie Q.,State Key Laboratory of Disaster Reduction in Civil Engineering | Wang W.,Tongji University | Li H.,Tongji University
Zhongguo Tiedao Kexue/China Railway Science | Year: 2012

A 2:1 scale model of the contact wire applied to China high-speed railway was made to carry out a wind tunnel test. The test was to measure along-wind drag force, crosswind lift force and vertical torsion moment at different wind velocities and in different turbulent flow fields. The change laws of the model's drag coefficient, lift coefficient and torque coefficient under different wind attack angles were analyzed. The influences of the model's section groove on its aerodynamic characteristics were studied. Den Hartog vertical vibration theory was used to analyze the galloping stability of the model. The results show that the aerodynamic drag force of the model increases obviously near -45° and 45° wind attack angles, because the wind direction is nearly perpendicular to the hypotenuse of the model's section groove. The aerodynamic stability of contact wire drops with the increase of turbulence flow field, and it shows a nonlinear relationship. Under no icing condition, the torsion moment of the model is very small, which suggests that the galloping of contact wire is caused by the change of crosswind lift force. The critical wind speed of contact wire galloping is proportional to its natural vibration circular frequency and mechanical damping.

Tian H.-W.,Tongji University | Li Y.-Q.,Tongji University | Li Y.-Q.,State Key Laboratory of Disaster Reduction in Civil Engineering | Yu C.,University of North Texas
Thin-Walled Structures | Year: 2015

This research is focused on the behavior of a novel cold-formed steel (CFS) shear wall system- steel sheathed cold-formed steel trussed shear wall (SSCFSTSW), which is different in skeleton configuration compared to conventional steel sheathed CFS framed shear wall. A test program was conducted on shear walls of various configurations. The walls differed in sheathing, chord studs and skeleton configurations. The results indicated that SSCFSTSW gave a significantly higher ultimate strength than that obtained from conventional shear walls. Based on the results, detailed discussion of the influence of different configurations on the performance of shear walls is given. © 2015 Elsevier Ltd. All rights reserved.

Wang D.,Tongji University | Li J.,Tongji University | Li J.,State Key Laboratory of Disaster Reduction in Civil Engineering
Science China Technological Sciences | Year: 2011

A physical random function model of ground motions for engineering purposes is presented with verification of sample level. Firstly, we derive the Fourier spectral transfer form of the solution to the definition problem, which describes the one-dimensional seismic wave field. Then based on the special models of the source, path and local site, the physical random function model of ground motions is obtained whose physical parameters are random variables. The superposition method of narrow-band harmonic wave groups is improved to synthesize ground motion samples. Finally, an application of this model to simulate ground motion records in 1995 Kobe earthquake is described. The resulting accelerograms have the frequency-domain and non-stationary characteristics that are in full agreement with the realistic ground motion records. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.

Wang D.,Tongji University | Li J.,Tongji University | Li J.,State Key Laboratory of Disaster Reduction in Civil Engineering
Science China Technological Sciences | Year: 2012

This paper presents a random physical model of seismic ground motion field on a specific local engineering site. With this model, artificial ground motions which are consistent with realistic records at SMART-1 array on spatial correlation are synthesized. A two-scale modeling method of seismic random field is proposed. In large scale, the seismic ground motion field on bedrock surface is simplified to a two-dimensional spherical wave field based on the seismic point source and homogeneous isotropic media model. In small scale, the seismic ground motion field on the engineering site has a plane waveform. By introducing the physical models of seismic source, path and local site and considering the randomness of the basic physical parameters, the random model of seismic ground motion field is completed in a random functional form. This model is applied to simulation of the acceleration records at SMART-1 array by using the superposition method of wave group. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.

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