Advanced Materials Research Vols. 163-167

Abstract: Based on practice engineering and model test, and considering different bridge elevation, elevation of sea bed, and the different wave factor, the author uses the 2D numerical wave tank based on the software ANSYS FLUENT which is established by ourselves to carry on the numerical simulation to various models, and compares with the corresponding experimental values. The author verified that all the forces are descending with the increase of bridge elevation. The most dangerous bridge elevation under wave action exists in bridge design, so it should be avoided. The optimum elevation of the bridge deck is recommended +5.5 m, and some advices on practice design engineering are presented.

Abstract: In this paper, seismic elastic and plastic responses of base-isolated structure are investigated, in which the bilinear restore-force model is employed for the isolation equipment. The mutual influences of both damping matrices and stiffness matrices are decoupled by using transition matrix. Based on the increment-dimensional precise integration method (PIM), the increment -dimensional blocks PIM is developed to separate structure characteristics and external forces, which can avoid the calculation of exponential matrices by PIM in each integration step. The results of numerical examples show that the efficiency of the new algorithm is very high in comparing with old method. The advantages of the new algorithm appear more obvious when the characteristics of large-scale structure have slightly changed, and only the external forces vary.

Abstract: In this paper, the spatial analysis model of non-symmetrical special-shaped column is established in ANSYS, and then, the translational and rotational component of the seismic wave was input to the frame structural model, taking account of stiffness enhancement of the floor on the beam, and carried out the elastic-plastic time-history analysis. Simulations show that the trend of development of displacement basically the same way on two horizontal components and torsional acceleration component, and the displacement on two horizontal components and torsional acceleration component increases significantly compared with one horizontal component; because of the presence of the floor, the intensity of beam is enhanced, leading to some columns more strain than the beam, so the floor should be fully considered in the design of the beam.

Abstract: Wind-induced response was investigated on the chimney of a 100MW solar thermal power station. Firstly, dynamic characteristic of the chimney was analyzed and the first eight vibration mode shapes and frequencies were obtained. Wind velocity time-history simulation was then conducted utilizing harmonic superposition method with Fast Fourier Transformation. Followed that, transient dynamic analysis was carried out to obtain the wind-induced response and the wind vibration displacement coefficient calculated. Numerical results indicate that the maximal displacement and acceleration of the chimney appear on the top with a value of 0.5593m and 0.1933m/s2 respectively. Wind vibration displacement coefficient on the chimney increases with height with an average value of 2.303.

Abstract: Long-span flexible bridges are always challenged by fierce wind load, and the wind with extreme-attack-angle may be a potential danger to threaten the bridge security. The three-component coefficients at extreme attack angles of the section model of one flat streamlined box-girder and central slotted box-girder are investigated through the wind tunnel test, and the detailed explanation are made. The results show that lift and pitch coefficients change approximately linearly between stall angles, and the coefficients display significant nonlinearity and a certain pulsation phenomenon when the attack angle exceeds stall angles, and the stall angles should not be less than ±10° for the sake of the safety of bridges.

Abstract: The vortex resonance characteristics of one typical streamlined bridge girder are studied using surface pressure measuring technique. Based on the testing results in smooth and turbulent flows with different attack angles, the means, standard deviations, power spectra of fluctuated pressures, as well as the correlations between local and total aerodynamic forces are comprehensively analyzed, and the torsional vortex vibration mechanism is disclosed. The research results indicate that, for the vortex resonance case, the flow separation at upper and lower surfaces is more severe than that of non-vortex case. The upper surface pressure fluctuation at the middle and downstream region is most obvious, which is incurred by the flow separation at the upper surface upstream tip. At the middle and downstream region, the aerodynamic forces keep good correlations with the total forces, and they provide the major torsional moment for vortex resonance. Vortex vibration depends on both fluctuation intensity and peak location. For the vortex resonance case, the surface fluctuated pressures are locked in the same frequencies.

Abstract: Active Mass Damper has been proven to be efficient in suppressing structure vibration. Previous studies of AMD have been concentrated on the vibration control of buildings under earthquake excitation, whereas few investigation of wind-induced bridge vibration control has been conducted. In consideration of the characteristics of one suspension pipeline bridge which behaves dramatic lateral and torsional response under fluctuating wind action, a two-DOFs TMD/AMD system for suppressing both lateral and torsional responses was proposed. The bridge is modeled using Ansys and the buffeting responses of the bridge under TMD, AMD control are respectively simulated and analyzed by MATLAB/Simulink. The efficiency of different control system has been studied. The results show that two-DOFs AMD system has a better performance in suppressing the buffeting response of lateral bending and torsion. In addition, AMD system can be applicable to a wider range of frequency and therefore manifests the more stable performance than TMD under fluctuating wind loads which contain various frequency components.

Abstract: Nonlinear eddy viscosity models have received significant interest because of the shortcomings of linear eddy viscosity models used in the numerical simulation of flow around building structures. There are many kinds of nonlinear eddy viscosity models. This paper adopts one of them to simulate backward facing step flow, which aims to evaluate the properties of this turbulence model. Compared with linear eddy viscosity model and experimental measurements, the simulation of nonlinear eddy viscosity model gives better results, especially for the reattachment length and pressure coefficient values. For this reason, this nonlinear eddy viscosity model is more suitable for numerical simulation of complex flow around building structures than linear eddy viscosity model.

Abstract: Long-span structure is a more common structural style in the public buildings, and its seismic response often differs from other structures because of the long-span characteristic, and thereby the multi-support earthquake excitation, such as the displacement model and acceleration model, need to be adopted in the seismic analysis. However, relative researches have proved that there exists certain problem in the displacement model. According to previous works, the error causes of displacement model are described firstly and expression is also given to estimate the magnitude of error. Then, the influencing factors on the error of displacement model are also given and analyzed. In the end, numerical studies are carried out to verify the viewpoint proposed in this paper.

Abstract: In Wenchuan Earthquake, masonry-infilled frames have the quite critical failures. In this paper, the reason of the failure phenomenon is analyzed and the influence of the infilled wall to performance of the frame is highlighted. An improved three-strut model for masonry-infilled frame structures is presented. Then, two RC frame specimens, which are modeled by the presented three-strut model and force-based beam-column element combined with fiber section considering compression-bending coupling in Opensees, are analyzed. The analytical results agree well with the experimental results. It is shown that the presented three-strut model is sufficient to simulate the performance of the infilled wall.