计算结构首次穿越时间概率密度函数的新方法

本文在M adsen等提出的积分方程方法基础上,采用单点FORM方法计算结构首次穿越问题中的条件穿越率、联合穿越率及首次穿越时间概率密度。提出的新方法计算简单,结果精确,适于进行脆性结构的首次穿越破坏分析。     

基于IDA的层间隔震结构失效模式研究

层间隔震结构是由基础隔震结构发展而来的一种新型隔震结构。为研究层间隔震结构的倒塌,需先研究不同层间隔震结构的不同失效模式和失效位置,文章建立了3个不同结构参数的层间隔震结构有限元模型,选取20条与抗震规范反应谱吻合的地震动,采用增量动力分析（IDA）方法,分别对其失效模式和失效位置进行研究。研究表明:基于不同的结构参数,层间隔震的基本失效模式有三种,即隔震层水平位移超限导致结构失效、下部结构层间位移角超限导致结构失效、隔震层拉压应力超限导致结构失效;隔震层下部结构和隔震层最外边缘支座为结构的薄弱位置,应引起更多关注。此方法不仅可以研究结构的不同失效模式,还可以确定失效位置,可为下一步层间隔震结构的抗倒塌分析提供理论基础。     

高层钢结构地震失效模式控制的失效路径修正法

本文主要研究高层钢框架结构的地震失效模式及其控制方法。首先,给出了高层钢结构的地震失效模式的分析方法;其次,提出了根据结构的失效路径来加强构件对高层钢结构的地震失效模式进行控制的方法;然后,提出了结构整体抗震能力的分析方法以及分别相应于设计能力和屈服能力的能力储备分析方法;最后,通过对一座15层的钢框架结构进行典型地震动下的极限时程分析和极限pushover分析,得到高层钢框架结构的失效模式和整体抗震能力以及相应于最弱失效模式的能力储备,并验证了本文中地震失效模式控制方法的有效性。本文的研究表明,高层钢结构的地震失效模式控制可以采用结构失效路径修正(薄弱构件加强)来实现。     

在大震下 RC框架结构基于Pushover方法的失效相关性分析

目前,基于性能的建筑结构抗震设计成为世界各国土木工程界研究的热点之一.结构体系可靠度理论是进行结构性能分析的重要的理论基础.在结构体系可靠度的计算中,一个急待解决的问题是结构构件或截面间的失效相关性问题.本文基于pushover方法,采用Monte Carlo法和随机有限元法,在小震研究成果的基础上,进一步研究了钢筋混凝土框架结构在大震情况下的失效相关性问题,分别得出了框架梁、柱在大震作用下的部分失效相关性规律.     

多点冲击荷载作用下K6型单层球面网壳结构失效机理分析

为研究单层球面网壳结构在多点冲击荷载作用下的失效机理,在ANSYS/LS-DYNA中建立了60m跨度的Kiewitt 6型单层球面网壳结构的有限元模型,将整个网壳结构沿肋杆分成6个不同扇区,沿环杆分成5个不同环区,分别对网壳结构在同一环区和同一扇区受到多点冲击时的动力响应及冲击全过程能量传递的规律进行了分析研究。基于网壳结构失效变形特点,定义了多点冲击荷载作用下单层球面网壳结构的4类失效模式;根据整个冲击过程中能量的传递特点,揭示了单层球面网壳结构每类失效模式所对应的失效机理。     

关于建筑结构若干失效相关性问题的探讨分析

较深入地探讨了在“正常”和“异常”使用条件下，建筑结构和机电产品在失效相关理论上的一致性问题，讨论了多遇地震作用在“正常”或“异常”使用条件中的归属问题，并对失效模式相关性和约束状态相关性的相互关系进行了分析。     

罕遇地震下RC低矮框架失效相关性拟动力试验分析

为研究罕遇地震下低矮结构的失效相关性问题,设计了两榀钢筋混凝土对称与非对称三跨二层框架结构模型,通过拟动力试验,对低矮框架结构在罕遇地震作用下柱截面各约束的失效特点和相关规律进行了统计与分析,以期为低矮结构在罕遇地震作用下的失效相关性理论提供试验支持,文中指出钢筋材性的相对均匀性是造成罕遇地震下大量截面约束同时失效的主要原因。     

单层连方型球面网壳与下部支承结构协同工作的强震失效研究

基于ABAQUS有限元分析,研究了单层连方型球面网壳结构在90种工况下的3种失效模式:弱支承结构失效模式、强支承结构失效模式和中等支承结构失效模式。不同失效模式下结构所能承受的极限加速度有较大差别。结构处于弱支承或强支承状态时失效极限荷载较低,处于中等支承时失效荷载较高;在由弱或强支承向中等支承过渡的区间,结构的失效荷载呈现逐渐增加的趋势。当上下部结构刚度比较匹配时,二者才能充分发挥抗震性能,同时结构的极限承载力也会相对较高。下支承柱刚度是影响结构失效模式和极限荷载的主要因素之一,研究结果表明,随着支承刚度的增加,结构极限荷载呈先增加后减小的趋势。随着屋面等效荷载的增加,结构的极限承载力将会降低,在地震中更容易发生破坏。     

建筑结构不同性能水平失效概率的合理比例关系研究

在基于性能的抗震设计中,为了使结构在整个生命周期内费用达到最小,不仅需要确定各个性能水平的目标失效概率,同时还需要确定不同性能水平目标失效概率之间的合理关系。本文针对这个问题。研究了在结构造价一定的情况下,不同性能水平失效概率的合理比例关系,使得在设计基准期内结构损失达到最小。在本文中,根据我国建筑抗震设计规范的条件,仅考虑“小震不坏”和“大震不倒”两个性能水平。     

高层钢框架结构的薄弱层加强与最弱失效模式控制

主要研究通过加强薄弱层的方法对高层钢框架结构的最弱失效模式进行控制的方法。首先,给出了结构的非线性计算模型和倒塌失效模式判别准则;然后,利用均匀损伤的概念,给出了高层钢框架结构的损伤模型及结构的变截面位置;最后,重点研究了高层钢框架结构的最弱失效模式中的薄弱层的加强准则。通过加强最弱失效模式中的薄弱层,可消除结构的最弱失效模式,验证了本文中地震失效模式控制方法的有效性。本文的研究表明,通过加强最弱失效模式中的薄弱层,可使高层钢框架结构的失效模式得到控制。     

Volume estimation of the 1998 flank collapse at Casita volcano,Nicaragua: a comparison of photogrammetric and conventional techniques

In October 1998 a precipitation‐triggered flank collapse occurred at Casita volcano, Nicaragua, leading to a devastating lahar. In this paper the failure volume was calculated using a range of methods. Several pre‐ and post‐failure digital elevation models (DEMs) were created, based on photogrammetric, cartometric and surveying data. The wide range in resulting volumes prompted an assessment of the accuracies and potential problems associated with each of the datasets and techniques used. The best estimate for the failure volume is 1·6 × 10⁶ m³. It is based on a vegetation‐corrected pre‐failure DEM, generated using automated digital photogrammetry, and a post‐failure surface based on a field survey carried out with a Total Station. The volume figure is approximately an order of magnitude higher than values reported in previous publications, all of which are based solely on field estimates. This demonstrates that values reported in the literature, if they are not based on rigorous quantitative analysis, must be regarded with caution. Copyright © 2002 John Wiley & Sons, Ltd.     

陕西地震前兆台网ZD9A-Ⅱ地电场仪故障及排除

通过对陕西地震前兆台网4个地震台的ZD9A-Ⅱ地电场仪的观测资料进行了分析,对该仪器的各项工作指标、观测记录的数据甄别出异常变化形态,找出观测过程中存在的主要问题和故障现象,分析发生仪器故障的原因及处理方法;对有关的电路及故障原因进行分析,并以实例对这些故障的检修进行了总结,提出了检修方法、步骤及改进措施。     

拜城地震台数字仪故障的检查与排除

对拜城地震台数据传输链路出现的现象、原因及网络故障,进行了检查和分析处理,为台站资料的连续、可靠提供保障。     

Modelling the fine-structure of the geoid: Methods,data requirements and some results

The requirements for precise geoid models on local and regional scales have increased in recent years, primarily due to the ongoing developments in height determination by GPS on land, but also due to oceanographic requirements in using satellite altimetry for recovering dynamic sea-surface topography. Suitable methods for geoid computations from gravity data include Stokes integration, FFT methods, and least-squares collocation. Especially the FFT methods are efficient in handling large amounts of gravity data, and new variants of the methods taking earth curvature rigorously into account provide attractive methods for obtaining continental-scale, high-resolution geoid models. The accuracy of such models may be from 2–5 cm locally, to 50–100 cm on regional scales, depending on gravity data coverage, long wave-length gravity field errors, and datum problems. When approaching the cm-level geoid basic geoid definition questions (geoid or quasigeoid?) become very significant, especially in rugged areas. In the paper the geoid modelling methods and problems are reviewed, and some investigations on local data requirements for cm-level geoid prediction are presented. Some actual results are presented from Scandinavia, where a recent regional high-resolution geoid model yields apparent accuracies of 2–10 cm over GPS baselines of 50 to 2000 km.     

Comparison of derivative-free optimization methods for groundwater supply and hydraulic capture community problems

Management decisions involving groundwater supply and remediation often rely on optimization techniques to determine an effective strategy. We introduce several derivative-free sampling methods for solving constrained optimization problems that have not yet been considered in this field, and we include a genetic algorithm for completeness. Two well-documented community problems are used for illustration purposes: a groundwater supply problem and a hydraulic capture problem. The community problems were found to be challenging applications due to the objective functions being nonsmooth, nonlinear, and having many local minima. Because the results were found to be sensitive to initial iterates for some methods, guidance is provided in selecting initial iterates for these problems that improve the likelihood of achieving significant reductions in the objective function to be minimized. In addition, we suggest some potentially fruitful areas for future research.     

Dynamic theory of rigid-plasticity

This paper deals with an analysis method for the response and motion of soil-like rigid-plastic bodies under seismic loading conditions. A continuity condition to determine the acceleration distribution within the rigid-plastic body when the failure occurs during seismic motions is proposed. Combining this continuity condition of acceleration and the ‘Generalized Limit Equilibrium Method (GLEM)’, the responses of the earth structure during seismic motions as well as the permanent displacements can be obtained, where GLEM is one of the limit equilibrium methods proposed by the authors for static problems and providing the approximate solution for Kötter's equation. The theoretical formulation of the method, the illustrative examples, and some comparisons between the analytical and experimental results are demonstrated.     

A Review Of Environmental Applications Of Quasi-Stationary Electromagnetic Techniques

Electromagnetic (EM) techniques are the most commonly used geophysical methods in mineral exploration. However, the use of EM measurements for environmental and engineering applications like the detection of contaminant plumes or the exploration of waste sites is relatively new.The reason for the success of the application of EM methods to environmental problems lies in the variation of conductivity caused by different geometry of pore fluids and clay contents in rocks, and by the presence of organic and inorganic contaminants.Many EM methods/instruments used for mapping near surface geology exist and nowadays they play a central role in environmental geophysics. In general, these methods can be classified in two blocks: EM methods using a plane wave source of excitation and EM methods using a controlled source like a magnetic dipole or a loop source. The Very Low Frequency (VLF, VLF-R) and Radiomagnetotelluric (RMT) methods are chosen as representative methods for plane wave techniques, while horizontal loop EM methods operating in low induction numbers (EM31, EM34) and Transient Electromagnetic methods (TEM) are chosen as representatives of magnetic dipole or loop source techniques. Basic principles, advantages and disadvantages of each technique as well as their connection to specific environmental problems will be discussed.Different successful applications of these methods are reported in the literature. However, this review will focus on three major subjects: waste site exploration, detection of contaminated earth layers, and groundwater exploration. Case histories are presented illustrating the suitability of EM methods for solving such problems.     

不同变形失稳模式下隧道围岩稳定性判据研究的进展

计算机模拟隧道围岩失稳研究的困难在于失稳模型不清楚、失稳判据不明确。本文综合分析了目前国内外应用的隧道稳定性判别方法,总结了不同变形失稳机制下的计算模型及其量化的破坏判据,分析了各种方法的研究进展和存在局限,为围岩稳定性数值模拟提供快速、合理、可操作的判据。     

基于结构能量分析的抗震设计新方法的研究

概要介绍了多自由度结构能量分析方法，根据单自由度体系得到的输入能量谱，研究分析了多自由度与单自由度输入能量和耗能的等效性问题，并对一座钢筋混凝土框架结构算例进行了能量计算，对计算结果进行了分析，为能量分析设计方法应用于结构抗震设计进行有益的探索。