2015年4月25日尼泊尔廓尔喀M_S8.1级地震强地面运动     

王宏伟  徐培彬  温瑞智  任叶飞 《震灾防御技术》2015,10(2):201-210

2015年4月25日尼泊尔廓尔喀地区发生MS8.1级地震,本文分析了加德满都强震台站的强地震动记录特征,其水平向地震动表现为明显的脉冲地震动,脉冲周期约为6.0s,反映了近场地震动的方向性效应;处于深厚沉积层上的加德满都谷地对地震动有一定的放大作用,且主震的场地峰值频率向低频段偏移,出现明显的场地非线性反应;采用随机有限断层方法模拟的空间地震动分布与宏观地震烈度图符合较好,可以为分析宏观震害提供参考;通过与尼泊尔设计反应谱对比,得出在短周期与长周期段,加德满都台站的水平向地震动的反应谱远高于设计反应谱,说明即使严格按照尼泊尔建筑抗震规范设计施工的建筑结构也难以抵御此次地震的破坏。  相似文献   

Baseflow Recession Analysis for Flood‐Prone Black Sea Watersheds in Turkey          下载免费PDF全文

Hafzullah Aksoy  Hartmut Wittenberg 《洁净——土壤、空气、水》2015,43(6):857-866

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Comparison of 1D linear,equivalent-linear,and nonlinear site response models at six KiK-net validation sites     

《Soil Dynamics and Earthquake Engineering》2015

Vertical seismometer arrays represent a unique interaction between observed and predicted ground motions, and they are especially helpful for validating and comparing site response models. In this study, we perform comprehensive linear, equivalent-linear, and nonlinear site response analyses of 191 ground motions recorded at six validation sites in the Kiban–Kyoshin network (KiK-net) of vertical seismometer arrays in Japan. These sites, which span a range of geologic conditions, are selected because they meet the basic assumptions of one-dimensional (1D) wave propagation, and are therefore ideal for validating and calibrating 1D nonlinear soil models. We employ the equivalent-linear site response program SHAKE, the nonlinear site response program DEEPSOIL, and a nonlinear site response overlay model within the general finite element program Abaqus/Explicit. Using the results from this broad range of ground motions, we quantify the uncertainties of the alternative site response models, measure the strain levels at which the models break down, and provide general recommendations for performing site response analyses. Specifically, we find that at peak shear strains from 0.01% to 0.1%, linear site response models fail to accurately predict short-period ground motions; equivalent-linear and nonlinear models offer a significant improvement at strains beyond this level, with nonlinear models exhibiting a slight improvement over equivalent-linear models at strains greater than approximately 0.05%.  相似文献   

A pushover procedure for seismic assessment of buildings with bi-axial eccentricity under bi-directional seismic excitation     

《Soil Dynamics and Earthquake Engineering》2015

A new modal pushover procedure is proposed for seismic assessment of asymmetric-plan buildings under bi-directional ground motions. Although the proposed procedure is a multi-mode procedure and the effects of the higher and torsional modes are considered, the simplicity of the pushover procedure is kept and the method requires only a single-run pushover analysis for each direction of excitation. The effects of the frequency content of a specific ground motion and the interaction between modes at each direction are all considered in the single-run pushover analysis. For each direction, the load pattern is derived from the combined modal story shear and torque profiles. The pushover analysis is conducted independently for each direction of motion (x and y), and then the responses due to excitation in each direction are combined using SRSS (Square Roots of Sum of Squares) combination rule. Accuracy of the proposed procedure is evaluated through two low- and medium-rise buildings with 10% two-way eccentricity under different pairs of ground motions. The results show promising accuracy for the proposed method in predicting the peak seismic responses of the sample buildings.  相似文献   

Generalized failure envelope for caisson foundations in cohesive soil: Static and dynamic loading     

《Soil Dynamics and Earthquake Engineering》2015

The response of massive caisson foundations to combined vertical (N), horizontal (Q) and moment (M) loading is investigated parametrically by a series of three-dimensional finite element analyses. The study considers foundations in cohesive soil, with due consideration to the caisson-soil contact interface conditions. The ultimate limit states are presented by failure envelopes in dimensionless and normalized forms and the effects of the embedment ratio, vertical load and interface friction on the bearing capacity are studied in detail. Particular emphasis is given on the physical and geometrical interpretation of the kinematic mechanisms that accompany failure, with respect to the loading ratio M/Q. Exploiting the numerical results, analytical expressions are derived for the capacities under pure horizontal, moment and vertical loading, for certain conditions. For the case of fully bonded interface conditions, comparison is given with upper bound limit equilibrium solutions based on Brinch Hansen theory for the ultimate lateral soil reaction. A generalized closed-form expression for the failure envelope in M–Q–N space is then proposed and validated for all cases examined. It is shown that the incremental displacement vector of the caisson at failure follows an associated flow rule, with respect to the envelope, irrespective of: (a) the caisson geometry, and (b) the interface conditions. A simplified geometrical explanation and physical interpretation of the associativity in M-Q load space is also provided. Finally, the derived failure envelope is validated against low (0.67 Hz) and high frequency (5 Hz) dynamic loading tests and the role of radiation damping on the response of the caisson at near failure conditions is unraveled.  相似文献   

A numerical and experimental study of hollow steel pile in layered soil subjected to vertical dynamic loading     

《Soil Dynamics and Earthquake Engineering》2016

This paper presents an investigation of the nonlinear behaviour of single piles subjected to varying levels of vertical dynamic load. A good number of tests are performed for the understanding of the dynamic behaviour of single hollow steel piles embedded in layered soil. Experimental results are validated with results obtained from a nonlinear numerical analysis using commercially available Finite Element Method (FEM) based software. The results of numerical analysis and experimental investigations showed that the length of pile has significant influence on resonant frequency and amplitude of the pile foundation. It has also been found that the slippage of pile from the surrounding soil considerably affects the resonance frequency and amplitude of the soil–pile foundation system.  相似文献   

Identification of diffusion parameters in a nonlinear convection–diffusion equation using the augmented Lagrangian method     

T. K. Nilssen  K. H. Karlsen  T. Mannseth  X.-C. Tai 《Computational Geosciences》2009,13(3):317-329

Numerical identification of diffusion parameters in a nonlinear convection–diffusion equation is studied. This partial differential equation arises as the saturation equation in the fractional flow formulation of the two-phase porous media flow equations. The forward problem is discretized with the finite difference method, and the identification problem is formulated as a constrained minimization problem. We utilize the augmented Lagrangian method and transform the minimization problem into a coupled system of nonlinear algebraic equations, which is solved efficiently with the nonlinear conjugate gradient method. Numerical experiments are presented and discussed. This work was partially supported by the Research Council of Norway (NFR), under grant 128224/431.  相似文献   

Modified fish-bone model: A simplified MDOF model for simulation of seismic responses of moment resisting frames     

《Soil Dynamics and Earthquake Engineering》2013

This paper presents a simplified Multi-Degree-Of-Freedom (MDOF) model through modification of fish-bone model (or generic frame). Modified Fish-Bone (MFB) model is developed through three enhancements: (i) the moment of inertia for half-beams is reduced slightly to modify the assumption of equal rotation at each story joints, (ii) a number of truss elements are inserted to the fish-bone model to simulate flexural deformation of moment frames due to axial elongation and contraction of columns, and (iii) moment–rotation relationship of representative rotational springs is supposed to be bilinear instead of trilinear in order to consider simultaneous yielding at both ends of the beam in moment frames. The proposed model is evaluated with respect to nonlinear dynamic analysis results of three classic moment resisting frames subjected to 94 records of FEMA-440 ground motion data set. Moreover, the adequacy of this model is compared with the fish-bone model and two predictors of nonlinear seismic demand. The statistical study of predicted interstory drift demonstrates the superiority of the proposed model over the fish-bone model and both seismic demand predictors.  相似文献   

Fission of a weakly nonlinear interfacial solitary wave at a step     

Roger Grimshaw  Efim Pelinovsky  Tatiana Talipova 《地球物理与天体物理流体动力学》2013,107(2):179-194

The transformation of a weakly nonlinear interfacial solitary wave in an ideal two-layer flow over a step is studied. In the vicinity of the step the wave transformation is described in the framework of the linear theory of long interfacial waves, and the coefficients of wave reflection and transmission are calculated. A strong transformation arises for propagation into shallower water, but a weak transformation for propagation into deeper water. Far from the step, the wave dynamics is described by the Korteweg-de Vries equation which is fully integrable. In the vicinity of the step, the reflected and transmitted waves have soliton-like shapes, but their parameters do not satisfy the steady-state soliton solutions. Using the inverse scattering technique it is shown that the reflected wave evolves into a single soliton and dispersing radiation if the wave propagates from deep to shallow water, and only dispersing radiation if the wave propagates from shallow to deep water. The dynamics of the transmitted wave is more complicated. In particular, if the coefficient of the nonlinear quadratic term in the Korteweg-de Vries equation is not changed in sign in the region after the step, the transmitted wave evolves into a group of solitons and radiation, a process similar to soliton fission for surface gravity waves at a step. But if the coefficient of the nonlinear term changes sign, the soliton is destroyed completely and transforms into radiation. The effects of cubic nonlinearity are studied in the framework of the extended Korteweg-de Vries (Gardner) equation which is also integrable. The higher-order nonlinear effects influence the amplitudes of the generated solitons if the amplitude of the transformed wave is comparable with the thickness of lower layer, but otherwise the process of soliton fission is qualitatively the same as in the framework of the Korteweg-de Vries equation.  相似文献   

Convection in rotating annular channels heated from below. Part 2. Transitions from steady flow to turbulence     

Yingli Chang  Xinhao Liao 《地球物理与天体物理流体动力学》2013,107(3):215-241

We report the results of fully three-dimensional numerical simulations of nonlinear convection in a Boussinesq fluid in an annular channel rotating about a vertical axis with lateral no-slip or stress-free sidewalls, stress-free top and bottom, uniformly heated from below, a problem first studied by Davies-Jones and Gilman (1971 Davies-Jones, RP and Gilman, PA. 1971. Convection in a rotating annulus uniformly heated from below.. J. Fluid Mech., 46: 65–81.  [Google Scholar]) and Gilman (1973 Gilman, PA. 1973. Convection in a rotating annulus uniformly heated from below. Part 2. Nonlinear results. J. Fluid Mech., 57: 381–400.  [Google Scholar]). A substantial range of the Rayleigh number R (R_c≤R≤O(100 R_c)), where R_c denotes the critical value at the onset of convection) is considered. It is found that the wall-localized convection mode, unaffected by the velocity boundary condition imposed on the sidewalls, is nonlinearly robust. Both directions of travelling waves, one propagating against the sense of rotation near the outer sidewall and the other propagating in the same sense as the rotation in the vicinity of the inner sidewall, are always present in the nonlinear solutions. In contrast to nonlinear convection in a rotating Bénard layer, neither convection rolls nor the Küpper–Lortz instability can exist in a rotating annular channel because of the effect of the sidewalls. It is the nonlinear interaction between the wall-localized modes and the internal mode that plays an essential role in determining the nonlinear properties of convection in a rotating annular channel. Our studies reveal systematically the various nonlinear phenomena, from steady travelling waves trapped in the vicinities of the sidewalls to convective turbulence exhibiting columnar structure.  相似文献