Advanced Materials Research Vols. 163-167

Abstract: The dynamic analysis of earthquake responses of one simple bridge structure supported by hinged and rolled bearing and another simple bridge structure isolated by lead-core rubber bearings was described in elastic-plastic range. The relative displacements and accelerations of the structures were calculated under different amplitude earthquake waves in order to observe the influence of lead-core rubber bearing on earthquake- resistance of bridges. The availability of the analysis model, hysteretic model and relevant parameters adopted as well as the computation program developed are verified. According to the analysis of dynamic response data, the lead-core rubber bearings with proper parameters are used to improve the dynamic performance of the structures, the seismic response of the bridge deck and pier would therefore be greatly reduced, the safety and seismic performance of the structure are globally raised, earthquake- resistance could be increased, and rather good economic benefits have been achieved as well. The analysis can provide accurately the reference basis for construction design.

Abstract: According to anti-seismic design principle of strong column and weak beam, and of strong joint and weak member, reduced beam section (RSB) is often used to shift away plastic hinge from end of beam to the weaken region of the beam. The non-linear finite element models are established for concrete-filled steel square tubular column and reduced steel beam with holes in flange or in flange and web, considering geometric large deformation and material nonlinear. Comparison is made on load-displacement curves, the stress distribution of reduced beams, the ultimate load-carrying capacity, the ductility, and the energy-dissipating ability between analysis results of different RBS joints and experimental results. It shows that the stiffness and ultimate load-carrying capacity of new RBS joints are close to traditional RBS joint, the plastic hinge in the new joints with reduced beam section can be moved to the reduced region, and the new joints display good ductility, energy-dissipating ability and seismic behavior.

Abstract: The dynamic stress concentration on quadratic and U-shaped cavities in half space, which are similar to the cross-section of the tunnels, is solved in this paper impacted by SH-wave. The analytical solution for the cavity in elastic half space is gained by the complex function method. In the complex plane, the scattering wave which satisfies the zero-stress condition at the horizontal surface can be constructed, the problem can be inverted into a set of algebraic equations to solve coefficients of the constructed scattering wave by least square method. For the earthquake-resistance researches, the numerical examples of the dynamic stress concentration around the quadratic and U-shaped cavities impacted by SH-wave are given. The influences of the dynamic stress concentration by the incident wave number and angle, the depth and shape of the cavity are discussed. It is showed that the interaction among the wave, the surface and the shallow buried tunnels should be cared in half space. In this situation, the dynamic stress concentration around the tunnel is greater obvious than the whole space.

Abstract: Control of cable-stayed bridge flutter for earthquake and aerodynamic hazard mitigation represents a relatively new area of research. This paper proposes a new optimized smart control system to mitigate the cable-stayed bridge flutter due to seismic and aerodynamic vibration. A Magnetorheological (MR) fluid damper, which belongs to the class of controllable fluid dampers, is proposed for use in a control strategy for mitigating its effect on the cable-stayed bridge. Genetic algorithm is adopted to determine the flutter acceleration levels, and corresponding forces of MR dampers. The optimized forces values from MR dampers are studied under the effect of five strong earthquakes recorded, known as El-Centro, Mexico City, San Fernando, Ker Country, and Northridge earthquakes. The time delay between the monitoring system and the actuator response is also studied. The simulation and optimization results shows that the proposed control strategy using MR dampers is the promising one of the applicable control methods to reduce the seismic and aerodynamic flutter vibration of the stayed bridge.

Abstract: Taking Harbin west railway station as the researching object, the wind load distribution as well as its effects, which are widely used in practice, is investigated. First, wind pressure distribution on a rigid model is measured simultaneously in a wind tunnel. Some special characteristics of the measured wind pressure, especially its fluctuating component, are discussed. Then the fluctuating wind pressure field is reconstructed based on the synchronous multi-pressure scanning technique of wind tunnel tests and the proper orthogonal decomposition (POD) technique. The influence of lower RC structure on wind-induced vibration is investigated using non-linear time-history analysis. At last, a new method is introduced to obtain equivalent static wind load (ESWL) that reproduce all largest load effects at the same time. With the synthetic application of above methods, the problems such as: complex time and spatial distribution of fluctuating wind; multi-mode vibration of wind-induced response; multiple equivalent objectives for ESWL, can be solved efficiently.

Abstract: Wind is an important and complex load and an important basis in the structural analysis and the design of high-rise structure. Based on Davenport wind spectrum, multi-dimensional fluctuating wind and random wind load of tall building structure are simulated by using harmonic wave superposition method. To investigate the coupling effect of wind loads, wind-structure system is solved with Wilson-θ step-by-step numerical integration method, and the wind load of Tall building structure subjected to fluid-structure interaction. Turbulence intensity and its variation are presented in this paper.

Abstract: Study the calculation method of equivalent damping ratio in Capacity Spectrum Method. Analyzing the feature of several methods for the calculation of equivalent damping ratio in the world, from the numeral example, the numeral results of several calculation methods of equivalent damping ratio are compared to the results of time course method. The follow conclusions are reached: Secant stiffness method overestimate the value of equivalent damping ratio for steel structure, therefore, underestimate the supreme seismic reaction. The level of underestimate is interrelate to yield still coefficient; Under the medium earthquakes effect, all the method can fairly good forecast the supreme seismic reaction; But Under the large earthquakes effect, only the Kwan (EP) method can give the best result. The conclusions has impotent value for the perfect of Performance-Based Seismic Design Methods.

Abstract: Base on the elastic-plastic analytical theory, an elastic-plastic time-history analysis of self-anchored cable-stayed suspension bridge, which engineering background is Dalian Gulf Cross-sea Bridge program, is performed by using general finite element software Midas/Civil. The material nonlinearity of structure is considered with reinforcement concrete fiber model, and distributed hinge type is adopted to simulate for plastic hinge. Compared with the results of an elastic time-history analysis, it is shown that for the structure into the elastic-plastic stage, because of the production of plastic hinge, the input seismic energy is dissipated partially, and the internal forces of structural elements are reduced. The bending moments and axial forces occur mainly in the main tower root. Furthermore, the rotation properties of the plastic hinge causes displacement increasing of certain parts of the structure, which assumes mainly the vertical displacement present on the top of main tower and the main beam. In conclusion, it is proposed that caging devices are set in the design.

Abstract: Earthquake input energy and structural energy dissipation are key indicators to assess the seismic performance of structures. To study the rules of distribution of hysteretic energy within structures, a 6-storey regular reinforced concrete frame structure model is analyzed through elasto-plastic time-history dynamic analysis using the El Centro and Northridge accelerograms. Based on the comparison between numerical results for the earthquake input energy and structural hysteretic energy under the minor, moderate and major earthquakes of Grade 8 and 9, the distribution of the ratio of the storey hysteretic energy to the total hysteretic energy through the height was further studied. It shows that the computed results corresponding to the two earthquake records are in good agreement under different ground motion severity. And the percentage of structural hysteretic energy to input energy is basically stable. The distribution pattern of storey hysteretic energy through the height is that the value of the upper stories is smaller than the value of the lower stories. And the ground motion severity has a minor influence on the distribution pattern when the plasticity of structure develops more sufficiently.

Abstract: The wind environment simulation analysis on planning scheme with computer is still in the exploratory phase. In this paper, the research took years of average meteorological factors of Shanghai as initial conditions to simulate the wind environment around the Wenyuan Building with a flow field simulation analysis of Fluent Airpak [1]. The simulation results were used to analyze the distribution of whirlpool, wind shadow zone, etc and the influence they had made. The experiment indicates that it has a practical value and the guidance meaning for architectural complex planning to simulate the building’s surrounding microscopic climate with Fluent Airpak.