3-D shell analysis of cylindrical underground structures under seismic shear (S) wave action

The 3-D shell theory is employed in order to provide a new perspective to earthquake-induced strains in long cylindrical underground structures, when soil-structure interaction can be ignored. In this way, it is possible to derive analytical expressions for the distribution along the cross-section of axial, hoop and shear strains and also proceed to their consistent superposition in order to obtain the corresponding principal and von Mises strains. The resulting analytical solutions are verified against the results of 3-D dynamic FEM analyses. Seismic design strains are consequently established after optimization of the analytical solutions against the random angles which define the direction of wave propagation relative to the longitudinal structure axis, the direction of particle motion and the location on the structure cross-section. The basic approach is demonstrated herein for harmonic shear (S) waves with plane front, propagating in a homogeneous half-space or in a two layer profile, where soft soil overlays the bedrock.     

节理岩体地下洞室群的地震动力响应分析

节理岩体开挖后经常形成楔形体，对大型地下洞室顶拱和边墙的稳定笥构成威胁。地震的动力作用将加剧块体的运动，进而影响洞室的整体稳定性，合理地评价高烈度地区大型地下洞室的稳定性具有现实意义。节理岩体中地下结构的动力响应与稳定性分析目前研究较少。本文采用了动力离散元法分析了大型地下洞室群的动力响应，认为地下结构并不能完全免于震害，高烈度地震对于节理岩体中的地下结构有明显影响。     

爆炸地震波作用下地下结构动力响应数值分析

爆炸地震波荷载类似于天然地震波荷载，但又不完全相同。基于有效应力动力分析法，运用二维显式有限差分程序FLAC对地下结构在竖向和水平爆炸地震波荷载作用下的动力响应进行数值分析。编制了周围土体介质分析模型的程序模块并与FLAC接口。考虑了水平和竖向爆炸地震波荷载对地下结构的耦合效应，得出了一些定性的结论。     

地下厂房异型机墩结构动力分析

用三维有限元方法，对国外某水电站地下厂房的环梁三立柱式异型机墩及风罩、厂房墙体、楼板梁系统所组成的整体结构进行了动力分析；对厂房内各种振源频率与支承结构固有频率间的耦合共振情况进行了校核。结果表明，该异型机墩结构的动力设计是实际可行的，对以后该种机墩结构型式的推广应用有重要的参考价值。     

埋地双排复合式管体结构在SH波作用下的动力分析

以波动理论为基础,采用复变函数法,给出了地下双排复合式管体结构在SH波作用下的解析解。分析了入射波角度、频率变化,管体埋深、内管的厚度变化等参数对管体动应力集中的影响。结果表明:复合式管体内侧的动应力集中峰值明显高于外侧;高频入射时,双排管体在给定距离之间的相互影响较大,动应力集中峰值向邻侧偏移;复合式管体内管越薄,动应力集中峰值越大;垂直入射时,动应力集中峰值受埋深的影响呈周期性变化。     

Simplified 3-D dynamic analysis of structures with flexible diaphragms

A simplified method of 3-D dynamic analysis, named 3-D quasi-dynamic analysis, is presented. This method has been primarily used to evaluate stress states at identified times of peak dynamic responses of structures with flexible diaphragms. The quasi-dynamic analysis consists of extracting the accelerations predicted by the time-step integration analyses of two 2-D discrete MDOF dynamic models of a given structure (each discrete model corresponding to one of the principal orthogonal directions of the structure) at given times of interest. These accelerations are imposed on a 3-D representation of the structure (for example, a finite element mesh) as equivalent static forces. Accelerations at the diaphragms are assumed to act over the same tributary areas of the diaphragms considered in the 2-D discrete dynamic models. The study of the firehouse of Gilroy (an unreinforced masonry structure with flexible diaphragms) during the Loma Prieta Earthquake is presented to illustrate the 3-D quasi-dynamic seismic analysis. This method was compared to the more traditional 3-D modal time-step integration and 3-D response spectra analyses. The quasi-dynamic analysis had a general good agreement with the more formal, complex and computationally extensive modal time-step integration analysis. The 3-D response spectra analysis was very conservative and had a poor correlation with both the quasi-dynamic and the modal time-step integration analyses. The case study of the firehouse of Gilroy suggested that if 3-D effects have to be considered in the evaluation of a given structure, the quasi-dynamic analysis constitutes a reliable and computationally cheaper alternative to the more traditional methods of 3-D dynamic analysis.     

Dynamic analysis of 3-D flexible embedded foundations by a frequency domain BEM-FEM

A study on the dynamic response of three-dimensional flexible foundations of arbitrary shape, embedded in a homogenous, isotropic and linear elastic half-space is presented. Both massive and massless foundations are considered. The soil-foundation system is subjected to externally applied forces, and/or to obliquely incident seismic waves. The numerical method employed is a combination of the frequency domain Boundary Element Method, which is used to simulate the elastic soil medium, and the Finite Element Method, on the basis of which the stiffness matrix of the foundation is obtained. The foundation and soil media are combined by enforcing compatibility and equilibrium conditions at their common interface. Both relaxed and completely bonded boundary conditions are considered. The accuracy of the proposed methodology is partially verified through comparison studies with results reported in the literature for rigid embedded foundations.     

P波作用下埋地管道的相互作用动力分析

建立了波动理论计算公式,给出了地下管道在平面P 波作用下动力响应问题的解析近似解答.对地下多管道体系的动力相互作用进行了分析.结果表明:当埋地管道之间的距离较近时,管道之间的波往复反射作用增强,相互作用明显,动应力集中具有显著的放大效应;随着管道中心距离的增加,动应力集中峰值振荡逐渐平稳;当中心距达到约100倍的管道内径时,相互作用消失,结果退化为单个管道的结果.     

Dynamic behaviors of underground structures in E-Defense shaking experiments

In mitigating disasters, underground structures are required to play an important role because they generally perform well even under large seismic loads and can be used as bases for reconstructing damaged cities. Underground structures compose a network, and therefore, disconnections caused by localized damage may induce critical malfunctions. To investigate this problem, a series of shake table tests using large-scale soil-underground structure models was performed at E-Defense, Japan in 2012. The intent of the tests was to capture detailed localized behaviors of underground structures around inground joints and boundaries between two different soil strata. In the experiments, significant failure developed at an inground joint due to displacement of the surrounding soil. In addition, noticeable localized behaviors, such as conversion of horizontal ground displacement to vertical bending of a tunnel appeared around the inground joints. Also, it was found that a flexible segment along underground structures is effective in mitigating damage to those underground structures, but only in its immediate vicinity.     

考虑时空耦联的等效惯性加速度加载的地下结构pushover分析

地下结构的薄弱环节在地震作用下可能发生破坏,进而影响整个结构体系的整体稳定性,地下结构的抗震能力成为结构工程领域研究的热点问题之一.在借鉴已有地下结构pushover分析方法的基础上,本文提出了一种考虑时空耦合的等效惯性加速度分布模式,详细介绍了该分布模式的求解步骤与基本特点,采用该方法对日本神户大开地铁车站进行了pu...     

煤矿井下槽波三维数值模拟及频散分析

采用交错网格高阶有限差分法编制了地震波场三维正演模拟软件,设计了基于镜像法原理处理煤矿井下近水平和起伏巷道特殊空间的算法;模拟了煤矿井下含巷道和不含巷道情况下煤层中传播的地震波场,并分析其频散特征.结果发现:由于巷道的影响,巷道壁上产生很强的巷道振型槽波,煤层中则出现了以Love型为主的槽波,据此分析了实际槽波记录的形成机理,研究结果对今后煤矿井下巷道地震超前探测和工作面弹性波透视等具有重要的理论意义和实际价值.     

Transient elastodynamic analysis by time domain bem in cylindrical coordinates

A time domain boundary element in a cylindrical coordinate system is developed for the analysis of wave propagation in a half space. The integral formulation is based on Graffi's dynamic reciprocal theorem and Stokes' fundamental solutions. The field quantities (displacements and tractions) are expressed as products of Fourier series in the tangential direction and linear polynomials in the other spatial directions. Gaussian integration is used to integrate the non-singular parts of the integral equations, whereas the integration of the singular components, which are either of order 1/r or 1/r², is handled by special numerical schemes. In the time marching aspect, the field quantities are assumed to vary linearly in the temporal direction as well. Examples for wave propagation due to various forms of surface excitations are reported to demonstrate the accuracy of the method.     

弦支穹顶结构动力反应分析

以天津开发区商务中心大堂的弦支穹顶为研究对象,分析了弦支穹顶结构体系的自振特性,分别运用随机模拟风振分析方法和时间历程分析方法,对其进行了风振和地震反应分析,得到了结构在动力荷载作用下的响应时程,并对分析结果进行了频谱分析和统计分析。研究发现弦支穹顶结构的自振频率呈密集型分布,且振型复杂;结构的风振响应基本以受迫振动为主,没有出现明显的峰值共振现象;结构的地震响应在前几阶基频处出现了较为明显的峰值共振现象;从振动的幅值角度看,风荷载的动力作用效应相对于地震荷载要显著。     

Finite element versus simplified methods in the seismic analysis of underground structures

Seismic analysis of buried tunnels is considered herein. A comparison of results is carried out between a detailed finite element analysis and several simplified models for hand calculation. The finite element analysis is conducted by superimposing the free field motions and the interaction motions. The latter are calculated in a plane strain geometry taking into account the influence of adjacent structures with an approximation for 3-D effects and for soil non-linearities. Simplified models give, in general, conservative results, although better approximations are obtained by modelling the tunnel bends, where stress concentration occurs.     

Dynamic analysis of prismatic structures surrounded by an infinite fluid medium

For coupled vibration analyses of prismatic shell structures immersed in an infinite fluid medium, a composite element consisting of a semi-analytical infinite fluid element and a cylindrical shell strip element is proposed in this paper. The behaviour in the infinite direction can be accurately modelled with minimum effort and great saving in computational cost is achieved using this element. Unlike many other methods which tend to take advantage of axisymmetry to simplify the analysis, this method may be used to analyse the dynamic behaviour of prismatic shell structures with arbitrary cross-sections in offshore engineering.     

Dynamic analysis of structures with Maxwell model

A numerical method has been developed for the dynamic analysis of a tall building structure with viscous dampers. Viscous dampers are installed between the top of an inverted V‐shaped brace and the upper beam on each storey to reduce vibrations during strong disturbances like earthquakes. Analytically, it is modelled as a multi‐degree‐of freedom (MDOF) system with the Maxwell models. First, the computational method is formulated in the time domain by introducing a finite element of the Maxwell model into the equation of motion in the discrete‐time system, which is based on the direct numerical integration. Next, analyses for numerical stability and accuracy of the proposed method are discussed. The results show its numerical stability. Finally, the proposed method is applied to the numerical analysis of a realistic building structure to demonstrate its practical validity.     

垃圾填埋场渗漏污染三维分布式电学监测系统研制及应用

垃圾填埋场建设期将电极传感器网状布设于防渗层下方,垃圾场启用后通过预设电极实现观测区自然电位和地下介质电阻率测试.对比不同时期实测自然电位和视电阻率剖面特征变化,确定垃圾场渗漏与否、渗漏点的位置、数量及渗滤液形成羽状体的空间分布和扩散过程.三维分布式电学监测系统就是基于上述理念设计研制的,包括采集站、供电控制器及传感器系统,可同时完成多个位置点电位测量.粉砂层中渗滤液扩散过程的原位三维电学监测结果显示渗滤液污染区呈现自然电位负异常和低阻特征,低阻异常区分布范围和实际污染区具有良好的对应关系,污染区扩散特征可通过分析低阻异常区变化来确定.     

悬摆隔震结构动力分析方法初探

本文对悬摆隔震结构力学模型作等效处理,探索利用常规计算程序对其进行动力分析的有效方法,同时验证了悬摆隔震指施对于减弱结构地震反应的效果是明显的。     

Dynamic analysis of structures using lanczos co-ordinates

A procedure for deriving the Lanczos vectors is explained and their use in structural dynamics analysis as an alternative to modal co-ordinates is discussed. The vectors are obtained by an inverse iteration procedure in which orthogonality is imposed between the vectors resulting from successive iteration cycles. Using these Lanczos vectors the equations of motion are transformed to tridiagonal form, which provides for a very efficient time-stepping solution. The effectiveness of the method is demonstrated by a numerical example.