基于子集模拟法的非线性结构动力可靠度计算

子集模拟法是计算结构动力可靠度的新方法。该文在子集模拟法的基本思想上,适应性的选取子失效域的反应界限,合理的选取建议概率密度函数,应用修正的Metropolis算法产生计算条件失效概率时所需的随机变量样本,给出了所需样本的具体个数,并通过上述关键点总结给出了子集模拟法的具体计算步骤。最后应用子集模拟法首先计算了受平稳高斯白噪声作用的单自由度Duffing体系的失效概率,当确定落入失效域的样本时,需计算结构的非线性反应,该文采用迭代的数值逐步积分法进行计算;随后计算了受平稳高斯白噪声作用的采用三线型恢复力模型的三自由度结构的失效概率,结果表明:子集模拟法计算非线性结构动力可靠度时具有高效及高精度的特点,尤其适用于小失效概率的计算。     

非平稳随机激励下结构动力可靠度时域显式子集模拟法

基于动力响应显式表达式,时域显式随机模拟法可以通过减少单次样本计算时间有效提高动力可靠度的计算效率。然而,对于小失效概率问题,由于需要大量次样本计算,该法的计算量仍相当可观。为了克服上述困难,在时域显式随机模拟法基础上引入子集模拟法的基本思想,把小失效概率表示为一系列较大的条件概率的乘积,其中各条件概率采用时域显式随机模拟法计算,条件域内的样本采用Metropolis-Hastings抽样方法生成,从而实现了减少随机模拟所需的样本数,进一步提高了计算效率。算例结果表明改进的方法具有更高的计算效率,更适用于小失效概率和多自由度结构的动力可靠度问题。     

地下结构横截面地震反应拟静力计算方法对比研究

对目前地下结构横截面地震反应计算中广泛采用的地震系数法、自由场变形法、土-结构相互作用系数法、反应位移法、反应加速度法等多种拟静力方法进行介绍及分析。以大开地铁车站地震反应为例进行数值模拟,通过改变输入地震波、结构刚度、土层刚度以及结构埋深对各种拟静力计算方法的适用性进行了研究,将不同方法的计算结果与动力时程分析方法结果进行了对比。研究结果表明:反应加速度法与动力时程分析方法符合较好,表明该方法在常见地下结构环境条件下具有良好的适用性与计算精度,可以用于地下结构的抗震反应分析。     

多点激励下减震桥梁结构抗震可靠度分析的哈密顿蒙特卡洛子集模拟法

减震桥梁结构在地震激励下的可靠度分析为一典型的局部非线性动力可靠度问题。随机模拟法对于求解非线性动力可靠度问题具有普遍适用性,但对于实际工程问题,其应用存在计算工作量巨大的问题。随机模拟法计算时间主要取决于所需样本数目及单次样本计算效率。为提高减震桥梁结构抗震可靠度计算效率,基于精细时程积分法、Newton迭代法建立了多点激励下减震桥梁的运动方程及相应的时域显式降维迭代解格式,提高了单次样本的计算效率;引入基于哈密顿蒙特卡洛算法的子集模拟法,减少了所需样本个数。数值算例表明:与传统随机模拟法相比,所建立的方法可有效地提高减震桥梁结构非线性动力可靠度计算效率。     

地震作用下深厚土层-结构相互作用的高效分析方法

基于黏弹性边界和将场地反应转化为等效地震荷载的有限元直接法是目前进行地震作用下土-结构相互作用分析的常用时程分析方法之一。当土层厚度较深时,整个深厚土层-结构系统的有限元模型自由度数目较多,尤其对于三维问题,计算效率低。该文提出一种高效分析方法,即一维场地反应分析仍然针对整个深厚土层,在后续的土-结构相互作用分析中将土-结构计算模型的底面人工边界从深厚土层底面（基岩面）向上移动到接近结构的位置,通过缩减土-结构相互作用模型尺寸来提高计算效率。采用理论分析与数值算例,通过与采用整个深厚土层的传统土-结构相互作用分析结果对比,说明提出的高效分析方法能够满足精度要求,并且给出底面人工边界位置以及边界条件和地震动输入方式的建议。     

隔震结构设计加速度反应谱的取值研究

本文分别采用中国、日本和美国三国规范中定义的等效线形化法和时程分析方法,基于单质点模型计算了不同周期隔震结构的地震反应。通过加速度反应和位移反应发现中国现行抗震设计规范中设计反应谱的长周期段反应谱偏大。文中根据加速度反应谱的时程分析结果,在现有设计反应谱的基础上提出了新的长周期段反应谱修正公式提案。文末采用新提案的设计反应谱,利用等效线形化法对隔震结构进行了地震反应分析,结果与时程分析法的分析结果一致,研究表明新提案的反应谱取值在进行隔震结构的地震反应分析时具有良好的计算精度。     

多点地震输入的反应谱法研究

提出了一种计算多点输入下结构最大地震内力的新反应谱法(MRSM-AD)。不同于以往的多点输入反应谱法,这种方法不再将结构的绝对位移反应分解成拟静力和动力分量,而是直接利用基于结构绝对位移反应的动力方程进行反应谱理论的分析,简化了多点输入反应谱法中的组合规则,提高了结构计算分析的效率。比较了结构算例的时程法计算结果和MRSM-AD法的分析结果,验证了MRSM-AD法的正确性。     

深埋盾构隧道结构抗震设计方法评价

分析评价了反应位移法、反应加速度法应用于深埋盾构隧道结构抗震设计的差异。采用平面弹性理论的复变函数方法,提出了深埋结构的土体弹簧的解析解法,可以应用于反应位移法。设定某地质条件下的深埋典型盾构隧道结构为基准模型,用反应位移法、反应加速度法和动力时程法计算基准模型的结构刚度变化时的结构内力和变形,评价前两种方法的适用性。结果表明：反应加速度法的结果一般比反应位移法更接近动力时程法;反应位移法的结果一般是偏于安全的;反应加速度法不适用于结构刚度较小时的情况。     

规则隔震结构等效简化模型的研究

在Kelly等人研究的基础上,以结构周期、总基底剪力和总基底弯矩相等为等效准则,将多自由度结构简化为与之等效的两自由度模型结构。通过对一些规则结构的数值模拟分析,给出了这个模型结构系统参数的简化计算公式。这样对简化后的等效模型结构应用振型分解反应谱法,可求出原结构考虑高阶振型影响的结构最大地震反应。其计算简单、可不依靠计算机进行。而将这种等效方法应用于高层隔震结构,可较准确的对其最大地震反应进行预测。计算实例也证明了,这种等效方法是简便可行的。这为高层隔震结构实用设计方法的研究提供了基础。     

单向偏心结构的简化增量动力分析方法

增量动力分析方法(IDA)可以较为全面的评估结构的抗震性能,但需对结构进行大量的非线性时程分析,计算量巨大.该文将单向偏心结构的等效二自由度模型(EDDOF)应用于增量动力时程分析,提出了单向偏心结构的简化增量动力分析方法.然后选取20条实际地震记录和一栋5层偏心结构,基于等效二自由度模型和原型模型分别进行了增量动力时...     

基于概率简单叠加法则的动力可靠度高效计算方法

基于计算单元失效域的重要抽样法和区域分解法是计算高维输入随机变量条件下小失效概率的高效算法。该文在此基础上,首先利用基于计算单元失效域的重要抽样法的思想,引入构成总失效域的由持时内的时间点划分出的单元失效域,其次利用区域分解法的思想,引入构成总失效域互斥的单元失效域,最后根据两种单元失效域的关系和概率简单叠加法则,即可计算总失效概率。其中关键问题是计算结构反应时单位脉冲响应函数的确定和落入各个互斥单元失效域的样本数的确定。算例部分对受高斯白噪声激励作用的单自由度线性体系和多自由度线性体系,分别应用该文方法、基于计算单元失效域的重要抽样法和区域分解法进行了计算,并用Monte-Carlo法进行了验证,结果表明计算动力可靠度,尤其是小失效概率时,该文方法对比Monte-Carlo法计算效率有明显提高,并同基于计算单元失效域的重要抽样法和区域分解法一样高效。     

Controlling the onset of numerical fracture in parallelized implementations of the material point method (MPM) with convective particle domain interpolation (CPDI) domain scaling

The material point method is well suited for large‐deformation problems in solid mechanics but requires modification to avoid cell‐crossing errors as well as extension instabilities that lead to numerical (nonphysical) fracture. A promising solution is convected particle domain interpolation (CPDI), in which the integration domain used to map data between particles and the background grid deforms with the particle, based on the material deformation gradient. While eliminating the extension instability can be a benefit, it is often desirable to allow material separation to avoid nonphysical stretching. Additionally, large stretches in material points can complicate parallel implementation of CPDI if a single particle domain spans multiple computational patches. A straightforward modification to the CPDI algorithm allows a user‐specified scaling of the particle integration domain to control the numerical fracture response, which facilitates parallelization. Combined with particle splitting, the method can accommodate materials with arbitrarily large failure strains. Used with a smeared damage/softening model, this approach will prevent nonphysical numerical fracture in situations where the material should remain intact, but the effect of a single velocity field on localization may still produce errors in the post‐failure response. Details are given for both 2‐D and 3‐D implementations of the scaling algorithm. Copyright © 2015 John Wiley & Sons, Ltd.     

Micro-mechanical analysis of splitting failure in concrete reinforced with fiber reinforced plastic rods

The present investigation provides a micro-mechanical model for the splitting failure analysis of fiber reinforced plastic (FRP) reinforced concrete members subjected to longitudinal tensile stresses. The model consists of three co-axial cylinders: (a) the inner elastic FRP rod; (b) the mid cracked part of concrete; and (c) the outer elastic part of concrete. The anisotropic properties of reinforcement, the compatibility of longitudinal strain at interface and the effect of Poisson's ratio of concrete are taken into account in the analysis. The method can be used to predict the stress distributions in the hybrid structure and the relations between the growth of cracks and the applied end forces. It is found that the number of splitting cracks and the material properties of the anisotropic FRP rods are not the dominant factors in splitting failure. It is also observed that neglecting Poisson's ratio of cracked concrete may under-estimate stresses in the hybrid structure.     

基于Legendre正交多项式逼近法的结构可靠性分析

提出了结构可靠性分析的Legendre正交多项式逼近法。主要是基于数值逼近原理,以Legendre正交函数族做基,利用功能函数的高阶矩信息,通过计算功能函数概率密度函数的逼近表达式,然后根据工程结构可靠性的一般表达式来计算结构的失效概率,进行可靠性分析。通过数值检验,证明该方法可以很好地逼近各种经典理论分布曲线(正态分布、指数分布等6种经典分布)。文后给出了结构构件失效概率的实例计算,并和其它几种常用方法进行对比,进一步表明了Legendre正交多项式数值逼近法在结构可靠性分析理论上的正确性和实用性。     

Fault tree conditioning methods to trace system configuration changes for the application to low-power/shutdown PSA

There have been few Probabilistic Safety Assessments (PSAs) for a whole low power and shutdown (LPSD) period since the difficulties and the cost for these assessments are considerable when compared with those for a normal operation period. The frequent changes in system configurations and the reactor coolant system (RCS) states make it difficult to estimate a risk for the LPSD period.We propose a new fault tree (FT) construction method for the LPSD PSA by using reference FTs, usually for a full-power mode, and by applying conditioning methods to the reference FTs. The conditioning method includes a condition gate function, an alternative FT structure, and the substitutions of an event to a reference FT.We used the FT of a full power PSA as the starting point to maintain a consistency between the full-power and the LPSD PSA model. Maintaining the original structure of the FT for a full-power PSA and providing flexibility to the developed FT for the LPSD are the key factors of the present study.The developed method was applied to the LPSD PSA model of the UCN 3&4 units in Korea, which showed that the FTs for the LPSD PSA model of a nuclear power plant (NPP) can be generated easily from those for a full-power mode as well as maintaining a consistency between the two models.     

基于概率密度演化理论的结构抗震可靠性分析

运用随机过程的正交展开方法,将地震动加速度过程表示为由10个左右的独立随机变量所调制的确定性函数的线性组合形式。结合概率密度演化方法和等价极值事件的基本思想,研究了非线性结构的抗震可靠度分析问题。以具有滞回特性的非线性结构为例,对某一多自由度的剪切型框架结构进行了抗震可靠性分析。结果表明：按照复杂失效准则计算的结构抗震可靠度较之结构各层抗震可靠度均低。这一研究为基于概率密度函数的、精细化的抗震可靠度计算提供了新的途径。     

基于非线性本构关系的复合材料风机叶片有限元极限分析与设计

为了研究具有三维复杂构形的复合材料风机叶片的逐次破坏过程和极限承载能力, 将复合材料细观力学非线性本构理论桥联模型与有限元软件ABAQUS通过用户子程序UGENS结合起来对风力发电机叶片结构进行极限强度分析。只需提供纤维和基体的材料性能参数、 纤维体积含量以及蒙皮和增强筋的铺层数据包括铺设角、 层厚和铺层数, 就可预报出复合材料复杂叶片结构的整体承载能力以及叶片破坏所处的位置, 为正确评估和合理设计风机叶片结构提供了一种简便有效的分析方法。以一种20kW风机叶片为例, 用此方法实现了新型复合材料叶片结构的极限分析和合理设计, 提高了叶片的强度和刚度, 有效降低了叶片的重量。本文中的方法同样适用于其它复合材料复杂结构的极限分析与强度设计。      

Experimental Study on Ultrasonic Monitoring of Splitting Failure in Reinforced Concrete

This paper investigates inspection of reinforced concrete elements sensitive to the splitting failure. The behaviour of a reinforced concrete specimen subjected to a tensile stress is considered. The damage detection procedure is based on the ultrasonic wave propagation technique. The piezoelectric transducers are located on both ends of the specimen and the measurements are taken periodically during the incrementally increased loading. The features of measured signals in time and frequency domains as well as wavelet transforms before and after the splitting failure are studied. The experimental results show that proposed method can be used for monitoring of damage evolution in concrete elements. The method makes possible detection of the moment just before the splitting failure occurs.     

Reliability analysis of structures using neural network method

In order to predict the failure probability of a complicated structure, the structural responses usually need to be estimated by a numerical procedure, such as finite element method. To reduce the computational effort required for reliability analysis, response surface method could be used. However the conventional response surface method is still time consuming especially when the number of random variables is large. In this paper, an artificial neural network (ANN)-based response surface method is proposed. In this method, the relation between the random variables (input) and structural responses is established using ANN models. ANN model is then connected to a reliability method, such as first order and second moment (FORM), or Monte Carlo simulation method (MCS), to predict the failure probability. The proposed method is applied to four examples to validate its accuracy and efficiency. The obtained results show that the ANN-based response surface method is more efficient and accurate than the conventional response surface method.     

The dimension splitting reproducing kernel particle method for three-dimensional potential problems

In this paper, the dimension splitting reproducing kernel particle method (DSRKPM) for three-dimensional (3D) potential problems is presented. In the DSRKPM, a 3D potential problem can be transformed into a series of two-dimensional (2D) ones in the dimension splitting direction. The reproducing kernel particle method (RKPM) is used to solve each 2D problem, the essential boundary conditions are imposed by penalty method, and the discretized equation is obtained from Galerkin weak form of potential problems. Finite difference method is used in the dimension splitting direction. Then, by combining a series of the equations of the RKPM for solving 2D problems, the final equation of the DSRKPM for 3D potential problems is obtained. Five example problems on regular or irregular domains are selected to show that the DSRKPM has higher computational efficiency than the RKPM and the improved element-free Galerkin method for 3D potential problems.