Inelastic dynamic analysis of RC bridges accounting for spatial variability of ground motion,site effects and soil–structure interaction phenomena. Part 1: Methodology and analytical tools     

Anastasios G. Sextos  Kyriazis D. Pitilakis  Andreas J. Kappos 《地震工程与结构动力学》2003,32(4):607-627

During strong ground motion it is expected that extended structures (such as bridges) are subjected to excitation that varies along their longitudinal axis in terms of arrival time, amplitude and frequency content, a fact primarily attributed to the wave passage effect, the loss of coherency and the role of local site conditions. Furthermore, the foundation interacts with the soil and the superstructure, thus significantly affecting the dynamic response of the bridge. A general methodology is therefore set up and implemented into a computer code for deriving sets of appropriately modified time histories and spring–dashpot coefficients at each support of a bridge with account for spatial variability, local site conditions and soil–foundation–superstructure interaction, for the purposes of inelastic dynamic analysis of RC bridges. In order to validate the methodology and code developed, each stage of the proposed procedure is verified using recorded data, finite‐element analyses, alternative computer programs, previous research studies, and closed‐form solutions wherever available. The results establish an adequate degree of confidence in the use of the proposed methodology and code in further parametric analyses and seismic design. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Inelastic dynamic analysis of RC bridges accounting for spatial variability of ground motion,site effects and soil–structure interaction phenomena. Part 2: Parametric study     

Anastasios G. Sextos  Andreas J. Kappos  Kyriazis D. Pitilakis 《地震工程与结构动力学》2003,32(4):629-652

The methodology for dealing with spatial variability of ground motion, site effects and soil–structure interaction phenomena in the context of inelastic dynamic analysis of bridge structures, and the associated analytical tools established and validated in a companion paper are used herein for a detailed parametric analysis, aiming to evaluate the importance of the above effects in seismic design. For a total of 20 bridge structures differing in terms of structural type (fundamental period, symmetry, regularity, abutment conditions, pier‐to‐deck connections), dimensions (span and overall length), and ground motion characteristics (earthquake frequency content and direction of excitation), the dynamic response corresponding to nine levels of increasing analysis complexity was calculated and compared with the ‘standard’ case of a fixed base, uniformly excited, elastic structure for which site effects were totally ignored. It is concluded that the dynamic response of RC bridges is indeed strongly affected by the coupling of the above phenomena that may adversely affect displacements and/or action effects under certain circumstances. Evidence is also presented that some bridge types are relatively more sensitive to the above phenomena, hence a more refined analysis approach should be considered in their case. Copyright @ 2003 John Wiley & Sons, Ltd.  相似文献   

A hybrid indirect boundary element—discrete wave number method applied to simulate the seismic response of stratified alluvial valleys     

S. A. Gil-Zepeda  J. C. Montalvo-Arrieta  R. Vai  F. J. Snchez-Sesma 《Soil Dynamics and Earthquake Engineering》2003,23(1):77-86

A hybrid indirect boundary element – discrete wavenumber method is presented and applied to model the ground motion on stratified alluvial valleys under incident plane SH waves from an elastic half-space. The method is based on the single-layer integral representation for diffracted waves. Refracted waves in the horizontally stratified region can be expressed as a linear superposition of solutions for a set of discrete wavenumbers. These solutions are obtained in terms of the Thomson–Haskell propagators formalism. Boundary conditions of continuity of displacements and tractions along the common boundary between the half-space and the stratified region lead to a system of equations for the sources strengths and the coefficients of the plane wave expansion. Although the regions share the boundary, the discretization schemes are different for both sides: for the exterior region, it is based on the numerical and analytical integration of exact Green's functions for displacements and tractions whereas for the layered part, a collocation approach is used. In order to validate this approach results are compared for well-known cases studied in the literature. A homogeneous trapezoidal valley and a parabolic stratified valley were studied and excellent agreement with previous computations was found. An example is given for a stratified inclusion model of an alluvial deposit with an irregular interface with the half-space. Results are displayed in both frequency and time domains. These results show the significant influence of lateral heterogeneity and the emergence of locally generated surface waves in the seismic response of alluvial valleys.  相似文献   

Simplified vibratory characterization of alluvial basins     

Jean-François Semblat  Roberto Paolucci  Anne-Marie Duval 《Comptes Rendus Geoscience》2003,335(4):365-370

For the analysis of seismic wave amplification, modal methods are interesting tools to study the modal properties of geological structures. Modal approaches mainly lead to information on such parameters as fundamental frequencies and eigenmodes of alluvial basins. For a specific alluvial deposit in Nice (France), a simplified modal approach involving the Rayleigh method is considered. This approach assumes a set of admissible shape functions for the eigenmodes and allows a fast estimation of the fundamental frequency of the basin. The agreement with other numerical results (Boundary Element Method) and experimental ones is fully satisfactory. The simplified modal method then appears as an efficient mean for the global vibratory characterization of geological structures towards resonance. To cite this article: J.-F. Semblat et al., C. R. Geoscience 335 (2003).  相似文献   

The impact of decentralised forest management on charcoal production practices in Eastern Senegal     

Johan Post  Maaike Snel 《Geoforum》2003,34(1):85-98

In accordance with Senegal’s decentralisation policy, important forest management tasks, including the right to allocate charcoal production rights, have been transferred to rural councils. This paper investigates the impact of these institutional reforms on charcoal production practices using the environmental entitlement framework developed by Leach et al. [Environmental entitlements: dynamics and institutions in community-based natural resource management. World Development 27 (2) (1999) 225]. The councils have not been able to turn their new endowments into entitlements because they lack sufficient strength and legitimacy. Informal institutions, notably the coalition between merchants, state agents and village chiefs, continue to run the charcoal business and are hardly affected by decentralisation efforts. Most rural people, especially those relying solely on agriculture for sustenance, do not benefit at all from the charcoal trade. They do suffer from the environmental costs it brings with it, however. Although tensions between pro-exploitation actors and pro-conservation actors are evident, the pro-exploitation actors’ firm grip on the informal institutions will probably lead to a prolonged subversion of the laws that seek to enhance local control and to sustain the forest.  相似文献   

青藏高原东北侧一次MCC环境流场特征分析   总被引：1，自引：0，他引：1  

张列锐  侯建忠  郑泳宜 《干旱气象》1997,(2)

对１９９１年７月２８日青藏高原东北侧发生的一次中尺度对流复合体天气过程进行了环境和要素场分析，给出该类天气过程预报提示。  相似文献   

新疆南天山环境应力场特征   总被引：3，自引：0，他引：3  

吕桂林  陈培善 《内陆地震》1997,11(3):212-217

基于新疆强震固定台和流动观测记录的主要和余震加速度资料，选用了三个分向记录都完整的３７次地震。震级范围为１．８－６．８级，震中距为几至几十公里。根据用位错理论二维断裂力学模式推导的震源峰值、加速度与环境剪应力场关系式计算了新疆南天山环境剪应力值。计算结果表明，新疆南天山环境应力平均值偏高，这与新疆处于特殊构造环境条件有关。  相似文献   

论环境流场切应变率对台风移动的作用     

李小凡 《热带气象学报》1997,13(1):26-31

利用浅水波正压环境流场切应变率对台风移动的影响，得到的结果是：在环境流场切应变率空间不均匀条件下，正切应变率引起的台风偏差路径比负切应变率引起的偏差路径要长，特别在正切应变率的区域，正切应变率要比相对涡度梯度对台风移动有更大的影响。  相似文献   

香港的土地利用与环境保护   总被引：1，自引：0，他引：1  

陈朝辉 《热带地理》1997,17(2):149-156

香港地区地域狭小，地形崎岖，可利用地少，人口众多，用地紧张，但严谨的用地政策、规划用地和严格管地，使城镇有序，城乡结合协调，基础设施完善，做到合理用地，有效用地和高效用地，从而成为一座名副其实、整洁、美丽的现代化国际大都市。  相似文献   

新疆阿拉尔花岗岩MFC过程的微量元素综合效应     

刘伟 《地质论评》1997,43(5):465-475

新疆阿拉尔花岗岩的微量元素比相关图显示了线性样点列与幂函数曲线形式的样点列相 复杂图型。该图型用简单混合或者单一结果分异模型都不能解释。本文建立了混合－结晶分异复合过程的微量元素综合效应模型。模型１：从初始混合线引起害虫函数曲线束形式的结晶分异线。特殊情况有结晶分异线简化为通过原点的直线束形式或者与初始混合线重合。  相似文献