The 2008 Wenchuan earthquake with a surface wave magnitude of 8.0 induced numerous landslides along the Longmen Mt. zone in Sichuan Province of China. The authors investigated into various influential factors on the slope stability of 119 landslides in Wenchuan prefecture, such as horizontal peak ground acceleration, slope angle, slope height, rock materials and geological structures. The authors developed hanging wall and footwall's acceleration attenuation formulae from 115 seismic stations and the formulae confirmed hanging-foot wall effect had notable influence on landslide distribution density and occurrence probability. The results of multivariable analysis clarified that slope height, horizontal peak ground acceleration and geological structures were more influential to sliding area and volume than slope angle and rock materials. Furthermore, the authors discussed the effectiveness of reinforcements on the slope stability and showed that anchor cable, frame beam and soil nailing wall had good anti-seismic property, however, shotcrete with bolts had limited ability to enhance slope stability during the earthquake.
A rheology originally proposed for high damping rubber bearing (HDRB) is applied to natural rubber bearing (RB) and lead rubber bearing (LRB) along with its simplified form. Comparing HDRB, the elastic-plastic equilibrium responses were found to be more dominant than the rate-dependent response due to viscosity for RB and LRB. Moreover, the overstress in loading/unloading was found to be analogous. The dependency of nonlinear viscosity on current strain was found to be weak in contrast to the existence of considerable nonlinearity in elastic response. The original rheology model considers the nonlinear elasto-plastic and viscosity induced rate-dependent behavior into account, while the viscosity effect is eliminated in the simplified version. The models are implemented in a finite element code. The modeling effects of bearings on the seismic responses of a multi-span continuous highway bridge are investigated via nonlinear dynamic analyses for two strong earthquake ground motions. Three analytical models of isolation bearings are considered for comparison: the conventional design models and the proposed two models. Model parameters for the bearings were determined for two temperature conditions: the room temperature (+23°C) and the low temperature (−20°C) based on experimental data. The implication of the rheology models for response prediction of a prototype bridge is studied by comparing the rotation of a plastic hinge in pier and shear strain at the top of the bearing. The comparison suggests that the modeling of RB and LRB considering rheology properties is important for rational prediction of the seismic response of highway bridges, particularly at low temperature condition.
This work deals with influence of bi-directional cyclic displacement loading on the ductility of hollow circular steel columns and to develop a seismic verification method for bridge piers, with pipe sections, when subjected to coupling action of two horizontal earthquake components. For this purpose, nonlinear numerical analyses are performed on Finite Element models by setting radius-thickness ratio and slenderness ratio as main design parameters. The strain-based ductility formulas are developed separately for uni- and bi-directional cyclic loadings, and based on these formulas a seismic verification method is proposed. To confirm this method, nonlinear dynamic analyses are carried out on three different beam element models of bridge piers. The deformation and strain performances are evaluated by displacement-based and strain-based methods. The comparative study shows that the strain-based seismic verification method is critical than displacement-based method. Further, comparison between allowable values given by past ultimate strain formula indicates that the formulas developed in the present study are more adequate for use in seismic verification of circular steel bridge piers when subjected to two directional earthquake components at the same time.
Given the different geology and earthquake activity, establishing a regional attenuation relationship is deemed important for the seismic design of structures. This paper presents a new equation in place of the relationship currently used in Vietnam for horizontal ground motion based on database sets compiled from strike-slip and shallow crustal earthquakes with magnitudes ranging from 3.0 ≤ Mw ≤ 6.9 and source distances of up to 300 km for northern Vietnam. This new equation estimates the ground motion in terms of moment magnitude, distance and site conditions for strike-slip earthquakes. The equation is derived based on a regression analysis of earthquake records; in this study, the database consists of earthquake records from Japan, Vietnam and adjacent areas. We also assume a few simple relationships, such as the relationship between Mw and Ms, the closest distance to the fault and the effects of shallow site conditions on the average shear-wave velocity in the upper 30 m to develop a comparison with existing relationships. The new equation for northern Vietnam corresponds better with other equations for near- and far-field distances than the equations currently used for seismic design in Vietnam.
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