外文翻译--建筑结构在冲击负载作用下连续倒塌分析方法（中英文）

原文：Methods for Progressive Collapse Analysis of BuildingStructures Under Blast and Impact LoadsAbstract： Progressive collapse of building structures under blast and impact loads has attracted great attention all over the worldProgressive collapse analysis is essential for an economic and safe design of building structures against progressive collapse to blast and impact loads. Because of the catastrophic nature of progressive collapse and the potentially high cost of constructing or retrofitting buildings to resist it，it is imperative that the progressive collapse analysis methods be reliable. For engineers their methodology to carry out progressive collapse uation need not only be accurate and concise，but also be easily used and works fastThus，many researchers have been spending lots of effort in developing reliable，efficient and straightforward progressive collapse analysis methods recently. In the present paper，current progressive collapse analysis methods available in the literature are reviewedTheir suitability applicability and reliability are discussedOur recent proposed new method for progressive collapse analysis of reinforced concrete frames under blast loads is also introducedKeywords： progressive collapse analysis；building structures；blast load：impact load Progressive collapse is defined as“the spread of an initial local failure from element to element resulting in the collapse of an entire structure or a disproportionately large part of it”. It refers to the failure of one or a group of key structural loadcarrying members that give rise to a more widespread failure of the surrounding members and partial or complete structural collapseProgressive collapse of building structures might be induced by a series of accidental and intentional events such as false construction order，local failure due to accidental overload，damage of critical component by explosion and earthquakeThis paper only focuses on progressive collapse analysis of building structures induced by abnormal loads，such as blast and impact With the recent progressive collapse of Alfred PMurrah Federal Building and world Trade Center (WTC)researches are more focused than ever on constructing buildings safer from progressive collapse induced by blast and impact loadsProgressive collapse analysis is essential for an economic and safe design of building structures against progressive collapse to blast and impact loadsBecause of the catastrophic nature of progressive collapse and the potentially high cost of constructing or retrofitting buildings to resist it，it is imperative that the progressive collapse analysis methods be reliable For engineers，their methodology to carry out progressive collapse uation need not only to be accurate and concise，but also be easily used and works fastThus，many researchers have been spending lots of effort in developing reliable，efficient and straightforward progressive collapse analysis methods recently The current available methods in analyzing structural progressive collapse could be classified into two major categories，namely the direct simulation method，in which the blast loading effects on structural damage and building collapse are directly simulated，and uncoupled alternative load path method with analysis of the structure by simulating various levels of damage by the removal of key loadcarrying membersIn the present paper，the available progressive collapse analysis methods in the literature are reviewed according to their categoriesBoth advantages and disadvantages of each method are listedTheir suitability，applicability and reliability are also discussedOur recently proposed new method for progressive collapse analysis of reinforced concrete frames under blast 1oads is al so introduced1. Progressive collapse analysis methods for building structures. In this section，the current methods for analyzing structural progressive collapse available in the literature are presented in two major categories，namely the direct simulation method and the alternative load path method1.1 Direct simulation method For the direct simulation method，the building structures，air，and explosive are all modeled in detailExplosion，blast wave propagation and its interaction with structures all need to be simulated，if not，blast and impact loads acting on the building structure should be derived and directly applied to structural componentsThe material nonlinear behavior and dynamic effects and damage due to blast or impact are mostly included in the simulationThis section will list typical applications of direct simulation method in progressive collapse analysis of building structures recently，each with its own characteristic.1.1.1 of building collapse under blast loads Luccioni et al carried out an analysis of structural collapse of an actual building，the AMIA (Israels Mutual Society of Argentina)building，which had suffered a terrorist attack and collapsedIn the analysis，the building was modeled using 3一dimensional solid elements， including the reinforced concrete columns，beams and masonry walls.The analysis of the structural collapse of the building was performed in two stagesThe first part of the analysis consisted of the simulation of the explosion itself from the detonation instant and the second part consisted of the analysis of the effect and interaction with the building of the blast wave generated by the explosionOnly the load produced by the air blast wave was considered in the analysisThe ground motion generated by the explosion was not taken into account Fig2 shows the numerical results of the collapsed buildingThe comparison of numerical results with photographs taken after the terrorist attack showed that the numerical analysis accurately reproduced the collapse of the building under the blast loadThe good agreement between actual damage and that one numerically obtained proves that the detailed simulation of the structure，materials and blast effects are needed for this type of analysis and nowadays represent the only way to successfully run a complete collapse analysis of an entire building This case represents a good example of using direct simulation method to carry out the progressive collapse analysis of structuresThat is，the method could successfully predict the progressive collapse process of the structure under blast and impact loadsHowever，this accuracy is achieved at great costIn order to derive the accurate material parameters，experiments should be carried out firstThe building structures，air，and，explosive should be modeled in detail，which need thousands of elementsSpecial algorithms and software were also needed to calculate the blast wave-structure interaction and to catch the damage and collapse behavior of the building structureTherefore，it is extremely time consuming，and requires a profound knowledge of structural dynamics，damage mechanics，dynamic material properties and computational skills112 Collapse analysis of the World Trade CenterQuan and Brinbaum carried out a 3-dimensiona1 computer simulation of impact and collapse of the WTC North Tower using AUT0DYN 3D computer program to numerically reproduce the entire event of impact and collapse of the North Tower of WTC on September l1.Their model included the entire building of the WTC North Tower and a Boeing 767 passenger jetThe threedimensional finite element model used in the simulation contained a total of 270 000 beam and shell elementsAll the columns on the perimeter wall as well as inside the central core were simplified，being modeled by beam elements instead of using solid elements or shell elementsFloors and roof were modeled by the AUTODYN shell solverThe Boeing 767 airplane was also modeled in detail using AUTODYN shell solver and Lagrange solver. The complete simulation consists of four stages：static equilibrium calculation to get the initial stresses and strains from gravity；simulation of a Boeing 767 airplane impacting the tower；the reduction of the strength and stiffness of the tower resulting from the post-impact fuel fire；and finally，the progressive collapse of the Tower driven by gravityFig4 gives one of the typical results，which presents the material location of the tower at 65 s after the impactAs can be seen，the building had already collapsed to half of its heightThe numerical results showed that a scientifically substantiated plausible scenario for the impact and collapse event of the North Tower could be obtained through the numerical simulationIn the progressive analysis，a reasonable simplification in the modeling such as using simple elements to represent complex behavior of structural members will not affect the accuracy of the results，while this might dramatically reduce the size of the mode1This could save lots of computer memories and computing time，especially for the complex structures，such as tall buildingsOf course， certain finite elements are still needed to be developed.1.1.3 DYN method in progressive analysis of RC flame Hao et ai proposed a DYN method based on the continuum damage mechanics theoryThe main difference between this method and other direct simulation methods is that the explosion initialization and blast wave propagation were not directly modeledInstead， blast loads acting on the structure were calculated firstusing the formulae given in TM51300 and Ref. Then they are directly applied on front，side，roof and rear of the building structure This method was used to analyze structural progressive collapse of a three-storey and two-span reinforced concrete（RC）frame structureComputer software LSDYNA with userdefined subroutines was used to perform the analysesFig5 gives the configuration of the RC frame and the explosive locationIn the analysis，the blast was assumed to be detonated on ground surfaceThe blast weight was chosen to be 1 000kg equivalent of TNT，while the scaled distance used was 17 mkg ，at which only the first floor middle column would collapse due to blast effects The fig shows the numerical results of the structural progressive collapse obtained from DYN method analysisAs can be seen，DYN method gives reasonable prediction of the RC frame collapse under critical blast loadIn their study，comparisons were also made between results from DYN method，GSA and DoD guidelines based alternative load path methodsIt was found both the GSA and DoD based alternative load path methods may not give reliable prediction of structural progressive collapse and usually underestimate the stress and strain response at the supporting joint above the blast damaged columns. As mentioned above，the great improvement of the DYN method is that，interaction between the blast wave and building structure，blast initial and blast wavepropagation are not needed to be directly simulatedIt uses the profound knowledge of blast load distribution to define the blast loads and then directly apply them to the structureThis could dramatically decrease the size of finite element model and increase the efficiency of the simulation To sum up，the direct simulation method can yield reliable predictions of structural collapse to blast and impact loads，but it is extremely time consuming，and requires a profound knowledge of structural dynamics，damage mechanics，dynamic material properties and computational skillsIt is therefore not practical for common engineering applicationThe practicability of this category of methods could be improved in the following way：1)Developing new finite element，which is not only simple to be established and calculated，but also can represent the complex behavior of structural components such as nonlinear and dynamic effects；2)Proposing new method of accurately predicting blast loads around the building structures in different blast scenariosWith the development of computer science，with the improvement of the finite element model and the progress of the load application method，the direct simulation method might become an accurate and efficient way in doing progressive collapse analysis of structural building under blast and impact loads.翻译：建筑结构在冲击负载作用下连续倒塌分析方法摘要：建筑物在冲击负载作用下的连续倒塌已经引起了全世界的极大关注。对于一个经济的，安全的，能够抵抗冲击负载作用下连续倒塌的建筑结构设计，连续倒塌分析是必不可少的。因为连续倒塌的灾难性特点，和为了抵抗它而潜在的建造和改造建筑物的高额费用，所以连续倒塌分析方法是绝对必要且可信的。对于工程师们而言，他们估算连续倒塌的方法不仅仅要求精确和简要，而且容易上手，立竿见影。因而，最近许多研究者都在发展可靠有效和直接的连续倒塌分析方法上花费了很多的精力。在最近的干物上，当前在文献资料中找得到的关于连续倒塌的分析方法被重新审阅。人们广泛讨论它们的适宜性、适用性和可靠性。我们也提出了最近刚刚完成的关于钢筋混凝土框架在爆破荷载下的连续倒塌新分析方法。关键词：连续倒塌分析；建筑结构；爆炸荷载；冲击荷载连续倒塌被定义为“由于一个基本的局部构件失效在构件之间扩散最终造成整个结构或者是不成比例的一大部分倒塌”。其含义为一个或者一组关键承重构件的失效造成周围构件的失效和部分或者是整个结构的倒塌。建筑结构的连续倒塌可能由一系列的意外和人为的因素造成，比如：错误的建造顺序，偶然过载造成的局部失效，爆炸和地震造成的关键组件的损坏。这篇论文仅仅研究了特殊荷载（如：爆炸和冲击），造成的建筑结构连续倒塌的分析。 随着最近Alfred PMurrah联邦大楼和世界贸易中心（WTC）的倒塌，许多的研究更多的关注如何建造抵抗由于爆炸和冲击荷载造成连续倒塌的建筑。对于一个经济的，安全的，能够抵抗冲击负载作用下连续倒塌的建筑结构设计，连续倒塌分析是必不可少的。因为连续倒塌的灾难性特点，和为了抵抗它而潜在的建造和改造建筑物的高额费用，所以连续倒塌分析方法是绝对必要且可信的。对于工程师们而言，他们估算连续倒塌的方法不仅仅要求精确和简要，而且容易上手，立竿见影。因而，最近许多研究者都在发展可靠有效和直接的连续倒塌分析方法上花费了很多的精力。目前可行的结构连续倒塌分析方法可以被大致分为两类：直接模拟法，这种方法直接模拟了使结构破坏和建筑物倒塌的爆炸荷载效应，和非耦合交替荷载路径法，这种方法通过模拟由于移除关键承重构件造成的不同水平的损坏来对结构进行分析。在最近的干物上，当前在文献资料中找得到的关于连续倒塌的分析方法被重新审阅。这些文献既有优点又有不足之处。人们广泛讨论它们的适宜性、适用性和可靠性。我们最近也提出了刚刚完成的关于钢筋混凝土框架在爆破荷载下的连续倒塌新的分析方法。1、建筑结构连续倒塌分析方法在这个部分，现今在文献中可以找到的结构连续倒塌分析方法分为两类，直接模拟法和交替荷载路径法。1.1 直接模拟法在直接模拟法中，建筑结构，气流和爆炸都被细致的建立到模型中去。对于爆炸产生的冲击波的传播方式和其与结构之间的相互作用都需要模拟，或者，需要导出作用在建筑结构上的爆炸和冲击荷载并使它们直接作用在结构构件上。大多数爆炸和冲击造成的材料非线性反应和动力效应还有损坏都被包括在这种模拟当中。在这个部分，我们会列出直接模拟法在建筑结构连续倒塌分析方法中的几种典型的应用，每种都有各自的特点。1.1.1 爆炸荷载下的建筑倒塌的直接模拟 Luccioni et al 曾经对一座真实的建筑物进行了结构倒塌分析。这座建筑叫做“AMIA”，属于阿根廷犹太人互济会，被恐怖分子袭击并倒塌。在这项分析当中，用3维固体构件（包括钢筋混凝土柱，梁和砌体墙）组装成这座建筑物的模型。 这座建筑的结构倒塌分析分为两个阶段。分析的第一个阶段，包括模拟即时引爆的爆炸本身。第二阶段包括建筑与爆炸产生的冲击波之间的效应和相互作用。分析考虑了冲击波激起的气流产生的唯一的荷载。爆炸所产生的地面运动，没有考虑。倒塌的建筑物的数值结果如图2所示。数值结果和恐怖袭击之后拍摄的照片比较可以看出：数值分析准确的重现了在爆炸荷载作用下建筑的倒塌过程。实际损坏和数值模拟的结果的很好的一致性，证明了细致化的结构、材料和爆炸效应模拟对于这种分析是必需的，并且是现今唯一能够成功的进行的对整个建筑的完整倒塌分析的方式。这是利用直接模拟方法分析结构连续倒塌的一个很好的例子。这种方法能够成功的预测由于爆炸和冲击荷载造成的连续倒塌的过程。可是，要达到这种准确度是要花费很大的代价的。为了导出准确的材料参数，需要先做很多的实验。建筑结构、空气和爆炸都需要细致的建模，这样就需要成千上万的基本单元。特定的算法和软件也同样需要用来计算“冲击波结构”相互作用，同时得到结构的损坏和倒塌特性。因此，这是非常费时，而且需要有渊博知识结构动力学，损伤力学，动态材料性能和计算技能。1.1.2 世界贸易中心倒塌分析 Quan和Brinbaum用AUT0DYN 3D计算机程序对世界贸易中心北塔进行了冲击和倒塌的计算机三维模拟，用数值的方式重现了9月11日世界贸易中心北塔整个受冲击和倒塌的过程。他们的模型包括整个世界贸易中心北塔的建筑和波音767客机。模拟中运用的三维有限单元模型包括了总共270 000根梁和壳单元。所有围墙上以及中央核心中的柱都被简化，以梁单元来模拟，而非使用固体元素或壳单元。楼板和屋顶用AUTODYN壳求解器来建模。波音767客机也用AUTODYN壳求解器和拉格朗日求解器来建模。完整的模拟包括四个部分：静力平衡计算得到初步压力和重力引起的应变;对波音767客机撞击北塔的模拟；撞击泄漏的燃料燃烧造成的北塔强度和刚度的衰减；最后，重力作用引起的北塔连续倒塌。图4给出了一个典型的结果，它表示了材料在塔遭受撞击之后6.5秒的位置。可以看到，建筑高度的一半已经倒塌了。计算结果表明，对北塔遭受撞击和倒塌的科学合理的、真实的、可行的方案可以通过数值模拟得到。在连续性分析中，一个在建模过程中合理的简化，比如用简单的单元来代表复杂的结构构件性能，不会影响到结果的准确性，同时可能会显著的减少模型大小。这样能够节省大量的计算内存和计算时间，特别是对复杂的结构，如高层建筑。当然，特定的有限的单元仍然需要形成。1.1.3 DYN法分析钢筋混凝土框架连续倒塌Hao et ai提出了基于连续损伤力学理论的DYN方法。这种方法与其他直接模拟方法的主要区别是爆炸的初值和冲击波的传播不是直接建模的。取而代之的是，作用在结构上的冲击荷载是首先用TM5-1300和Ref.中给出的公式计算出，然后它们被直接作用于建筑结构的正面、侧面、屋顶和背面。这个方法被用来分析三层两跨的钢筋混凝土框架结构。分析利用的是用户自定义副程式的LSDYNA计算机程序。图5给出了钢筋混凝土结构的布置和爆炸位置。在这个分析当中，爆炸被假定在地表引发。这次爆炸相当于1000公斤TNT当量，换算距离为1.7m/kg,这样只有第一层的中柱会由于爆炸的影响而倒塌。中显示了DYN分析方法得到的结构连续倒塌的数值结果。从中可以看出，DYN方法给出了合理的钢筋混凝土框架在临界冲击荷载作用下倒塌预测值。在他们的研究中，同样比较了DYN方法、GSA和基于交替荷载路径法的DoD指导方针得出的结果。基于交替荷载路径法的GSA和DoD被发现可能给不出可靠的结构连续倒塌预测并且常常低估爆炸破坏的柱子顶部支撑节点的应力和应变。上面提到DYN方法最为巨大的改进是冲击波和建筑结构之间的相互作用，最初的爆炸和冲击波传播并不需要直接模拟。它运用深厚的爆炸荷载分布理论来定义爆炸荷载然后把它们直接作用在结构上。这能够可观的减少有限单元模型的尺寸，同时增加模拟的效率。总得来说，直接模拟法能够产生可信的结构在爆炸和冲击荷载作用下倒塌的预测结果，但是那是以大量的时间投入，渊博的结构动力学、损伤力学、动态材料特性和计算技巧为基础的。因此，它不适用于实际工程应用。这类方法的可行性可以按照以下的方法进行改：1）开发新的有限单元，不仅仅要易于建立和计算，并且能够描述复杂的结构构件特性，如非线性和动力特性；2）提出新的方法，准确预测负荷爆炸周围建筑结构的不同的爆炸情景。随着计算机科学的发展，与改善有限元模型和荷载运用方法的进步，直接模拟方法有可能成为进行爆炸和冲击荷载作用下结构连续倒塌分析的一种准确有效的方法。