Advanced Materials Research Vols. 243-249

Abstract: A modified Hertz model with nonlinear damping (Hertz damp model) is proposed for capturing the seismic pounding response of adjacent structures. Relevant parameters in the model are theoretically derived and numerically verified. Then, this model is used to simulate pounding response of a base-isolated highway bridge subjected to near fault ground motions. At the same time, nonlinear viscous dampers are installed between bridge decks for pounding prevention. The appropriate damping coefficient of the dampers can be found by parametric studies. It is shown that nonlinear viscous dampers are effective in reducing the relative displacement between bridge decks. At last, the hysteresis curve, the maximal damper force and stroke are used to demonstrate the behavior of nonlinear viscous dampers. The results indicate that satisfied viscous dampers can be produced to eliminate pounding according to the current manufacturing skills.

Abstract: Microstructural properties such as pore structure and hydration play a decisive role in determining the properties of a concrete. This paper presents the investigation on pore structure and hydration process of high strength concrete. Pore structure study was conducted using mercury intrusion porosimetry and hydration progress was monitored using thermogravimetry analysis on various blended combinations of cementitious materials incorporating fly ash and silica fume as partial cement replacement. It was found that silica fume refined the pore structure efficiently and reduced the calcium hydroxide content as early as 1 day. All ternary blended systems containing fly ash and silica fume exhibited lower calcium hydroxide content and refined pore structure in comparison to their respective blended pastes.

Abstract: It is documented that some confusions about ground motion input and artificial boundary condition in present seismic analysis affect engineering anti-seismic security evaluation, and that different treatment effects on security are so lack of verification that they are must be checked, discussed and made clear to get consensus. A study was conducted with a typical example with large FEM software ANSYS and comparison was made between the results of various ground motion input and boundary treatment methods and those of theoretical correct analysis. Study shows that ground motion input and artificial boundary condition is greatly correlative and that correct results can’t be got unless ground motion input and artificial boundary condition can be treated and matched properly.

Abstract: In order to eliminate some problems of ordinary artificial boundary conditions in soil-structure dynamic interaction analysis at present, such as plenty amount of work required in establishing viscous boundary and viscous-elastic boundary and the expensive computing hours cost in traditional far-field artificial boundary condition, an equivalent far-field artificial boundary condition for dynamic analysis was proposed based on the wave propagating theory and the reflection and transmission principle of wave on the interface of medium by setting a fully-transmitting layer and lower the speed of wave considerably propagating within it. Then numerical simulations and studies of factors affecting accuracy for equivalent far-field artificial boundary condition were conducted with FEM. Researches show that equivalent far-field artificial boundary is as nearly accurate as viscous boundary; it can overcome the problems of viscous boundary, viscous-elastic boundary and traditional far-field boundary mentioned above; it is very convenient to operate and realize; it is very efficient and low-cost in workforce. The equivalent far-field boundary proposed can be applied to engineering dynamic field such as anti-seismic of structures, vibration and impact etc.

Abstract: Lateral spreading induced by earthquake liquefaction in soil layers is classified as a main cause of damage of pipeline structures. In this study, non-linear finite element method was applied for three-dimensional shell element analysis of continuous oil pipeline structures against transverse permanent ground deformation due to lateral spreading. The soil-structure interactions were simulated by soil-spring elements and the elastro-plastic of soil property was taken into accounted. Influential factors, such as width of lateral spreading, characteristics of pipe, on behavior of pipeline structures are examined by numerical analysis using finite element software ANSYS. According to the parameters analysis, some recommendations for safety design for oil pipeline across potential earthquake liquefaction areas are proposed.

Abstract: A comprehensive study of displacement-based design for reinforced concrete bridge columns is conducted. Section analysis software UC-Fyber is used to analyze the bending moment and curvature performance of columns’ sections, based on this, a new calculation method of target displacement of RC bridge columns is educed. Elastic displacement response spectrum, inelastic displacement response spectrum and inelastic demand spectrum are educed from acceleration spectra of Chinese Code JTG/T B02-01-2008; three simplified methods for displacement demand determination are developed. Example of the displacement-based design of bridge column was studied and checked by dynamic inelastic time-history analysis to clarify the reasonableness of the developed methods. Research shows that target displacement of RC bridge columns is relevant with concrete strength grade, longitudinal reinforcement ratio, height and the section form, etc; equivalent linearization method and inelastic displacement response spectrum method are based on the design response spectrum, could reach the target displacement and consider structure safety requirement; demand spectrum method is a simple and direct way to show design with graphics mode, with deficiency of structure capacity spectrum curve from pushover analysis differing from the reality.

Abstract: This study is aimed at evaluating the safety implications of near-fault directivity effect on nuclear structure and facilities designed according to the Chinese code. To this end, a set of near-fault ground motions at rock site with typical forward-directivity effect is examined with emphasis on several key parameters and response spectra. The bi-normalized response spectra in terms of different corner periods are utilized to derive nuclear design spectra. It was concluded that nuclear design spectra on rock site derived from typical directivity records are significantly influenced by both magnitude and distance. The nuclear design spectra specified in the code need to be adjusted to reflect the near-fault directivity effect of large earthquakes.

Abstract: Many field investigations of earthquake disaster cases confirm that earthquake-induced liquefaction is a main factor resulting in large damages to dyke. Consequently to ensure seismic safety of dyke on the liquefiable foundation, the research on seismic performances of dyke is of great importance. Herein seismic responses of dyke on the liquefiable soils were discussed by means of three dimension effective stress analysis method using a multiple shear mechanism model and liquefaction front. Two numerical models, in which the liquefiable foundation both consisted of saturated fine silica sand of 30% relative density and scenario waves with peak amplitude of 0.8056 and 3.133 m/s² were used input waves, were conducted to investigate the distribution principles and the changing rules of deformation, acceleration, express pore water pressure, and shear dilatancy behavior in the dyke and the liquefiable foundation. The computed results do good agreements with the measured results from centrifuge tests. And these results may be of theoretical and realistic significance for seismic design of dyke on liquefiable soils.

Abstract: In order to research the optimal parameters of dampers linking adjacent structures for seismic mitigation, two SDOF systems connected with visco-elastic damper (VED) are taken as research object and the primary structural vibration frequency ratio, connection stiffness and linking damping ratio as research parameters. Modified Kanai-Tajimi spectrum is selected to model the earthquake excitation. The peak distribution of power spectral density curves are analyzed, then the formulas of structural mean squared displacement (MSD) and research parameters is derived based on random vibration theory. Then the relationship of the adjacent structural seismic response versus the research parameters was presented. The optimal value of the linking visco-elastic damper damping ratio and stiffness ratio are investigated. Finally, the seismic responses of example structures with or without connecting dampers are contrastively analyzed. The dependence of response mitigation effective on research parameters is highlighted. The results indicate fine earthquake-reduction effectiveness of dampers connecting adjacent structures. It is also shows that optimal parameters of damper cannot reduce the seismic responses of the primary structures connected to the best extent simultaneously. The damper parameters should be determined according to the best seismic mitigation effectiveness of the primary, auxiliary structure or the combined structure system.

Abstract: This paper analyzed the dynamic characteristics and the random seismic response of a super large hyperbolic cooling tower using 3-D FEM method. The results showed that the tower was very flexible. And it’s meridian direction axial force RMS was relatively bigger in the range of 40m-120m high, the maximum value of annular axial force RMS was at the top of the shell. Furthermore, using the principle of first passage failure mechanism, the dynamic reliability under 7 seismic intensity and different site conditions were analyzed and calculated, in which the structural drift at the height of 40m was considered as the failure criterion, and the dynamic reliability of the tower during the design reference period was obtained. Otherwise, the results of dynamic reliability under a seismic load based on Poisson hypothesis and Morkov hypothesis were also discussed.