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美国世贸中心倒塌报告

美国世贸中心倒塌报告
美国世贸中心倒塌报告

Executive Summary Following the September 11, 2001, attacks on New York City’s World T rade Center (WTC), the Federal Emergency Management Agency (FEMA) and the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE), in association with New York City and several other Federal agencies and professional organizations, deployed a team of civil, structural, and fire protection engineers to study the performance of buildings at the WTC site.

The events following the attacks in New York City were among the worst building disasters in history and resulted in the largest loss of life from any single building collapse in the United States. Of the 58,000 people estimated to be at the WTC Complex, 2,830 lost their lives that day, including 403 emergency responders. T wo commercial airliners were hijacked, and each was flown into one of the two 110-story towers. The structural damage sustained by each tower from the impact, combined with the ensuing fires, resulted in the total collapse of each building. As the towers collapsed, massive debris clouds consisting of crushed and broken building components fell onto and blew into surrounding structures, causing extensive collateral damage and, in some cases, igniting fires and causing additional collapses. In total, 10 major buildings experienced partial or total collapse and approximately 30 million square feet of commercial office space was removed from service, of which 12 million belonged to the WTC Complex.

The purpose of this study was to examine the damage caused by these events, collect data, develop an understanding of the response of each affected building, identify the causes of observed behavior, and identify studies that should be performed. The immediate effects of the aircraft impacts on each tower, the spread of fires following the crashes, the fire-induced reduction of structural strength, and the mechanism that led to the collapse of each tower were studied. Additionally, the performance of buildings in the immediate vicinity of the towers was studied to determine the effects of damage from falling debris and fires. Recommendations are presented for more detailed engineering studies, to complete the assessments and produce improved guidance and tools for building design and performance evaluation.

As each tower was struck, extensive structural damage, including localized collapse, occurred at the several floor levels directly impacted by the aircraft. Despite this massive localized damage, each structure remained standing. However, as each aircraft impacted a building, jet fuel on board ignited. Part of this fuel immediately burned off in the large fireballs that erupted at the impact floors. Remaining fuel flowed across the floors and down elevator and utility shafts, igniting intense fires throughout upper portions of the buildings. As these fires spread, they further weakened the steel-framed structures, eventually leading to total collapse.

The collapse of the towers astonished most observers, including knowledgeable structural engineers, and, in the immediate aftermath, a wide range of explanations were offered in an attempt to help the public understand these tragic events. However, the collapse of these symbolic buildings entailed a complex series

Executive Summary

of events that were not identical for each tower. T o determine the sequence of events, likely root causes, and methods or technologies that may improve or mitigate the building performance observed, FEMA and ASCE formed a Building Performance Study (BPS) T eam consisting of specialists in tall building design, steel and connection technology, fire and blast engineering, and structural investigation and analysis.

The T eam conducted field observations at the WTC site and steel salvage yards, removed and tested samples of the collapsed structures, viewed hundreds of hours of video and thousands of still photographs, conducted interviews with witnesses and persons involved in the design, construction, and maintenance of each of the affected buildings, reviewed construction documents, and conducted preliminary analyses of the damage to the WTC towers.

With the information and time available, the sequence of events leading to the collapse of each tower could not be definitively determined. However, the following observations and findings were made: The structural damage sustained by each of the two buildings as a result of the terrorist attacks was massive. The fact that the structures were able to sustain this level of damage and remain standing for an extended period of time is remarkable and is the reason that most building occupants were able to evacuate safely. Events of this type, resulting in such substantial damage, are generally not considered in building design, and the ability of these structures to successfully withstand such damage is noteworthy.

Preliminary analyses of the damaged structures, together with the fact the structures remained standing for an extended period of time, suggest that, absent other severe loading events such as a windstorm or earthquake, the buildings could have remained standing in their damaged states until subjected to some significant additional load. However, the structures were subjected to a second, simultaneous severe loading event in the form of the fires caused by the aircraft impacts.

The large quantity of jet fuel carried by each aircraft ignited upon impact into each building. A significant portion of this fuel was consumed immediately in the ensuing fireballs. The remaining fuel is believed either to have flowed down through the buildings or to have burned off within a few minutes of the aircraft impact. The heat produced by this burning jet fuel does not by itself appear to have been

sufficient to initiate the structural collapses. However, as the burning jet fuel spread across several

floors of the buildings, it ignited much of the buildings’ contents, causing simultaneous fires across several floors of both buildings. The heat output from these fires is estimated to have been comparable to the power produced by a large commercial power generating station. Over a period of many minutes, this heat induced additional stresses into the damaged structural frames while simultaneously softening and weakening these frames. This additional loading and the resulting damage were sufficient to

induce the collapse of both structures.

The ability of the two towers to withstand aircraft impacts without immediate collapse was a direct function of their design and construction characteristics, as was the vulnerability of the two towers to collapse a result of the combined effects of the impacts and ensuing fires. Many buildings with other design and construction characteristics would have been more vulnerable to collapse in these events than the two towers, and few may have been less vulnerable. It was not the purpose of this study to assess the code-conformance of the building design and construction, or to judge the adequacy of

these features. However, during the course of this study, the structural and fire protection features of the buildings were examined. The study did not reveal any specific structural features that would be regarded as substandard, and, in fact, many structural and fire protection features of the design and construction were found to be superior to the minimum code requirements.

Executive Summary Several building design features have been identified as key to the buildings’ ability to remain

standing as long as they did and to allow the evacuation of most building occupants. These

included the following:

? robustness and redundancy of the steel framing system

? adequate egress stairways that were well marked and lighted

? conscientious implementation of emergency exiting training programs for building tenants

Similarly, several design features have been identified that may have played a role in allowing the

buildings to collapse in the manner that they did and in the inability of victims at and above the

impact floors to safely exit. These features should not be regarded either as design deficiencies or as features that should be prohibited in future building codes. Rather, these are features that should be subjected to more detailed evaluation, in order to understand their contribution to the performance of these buildings and how they may perform in other buildings. These include the following:

? the type of steel floor truss system present in these buildings and their structural robustness and

redundancy when compared to other structural systems

? use of impact-resistant enclosures around egress paths

? resistance of passive fire protection to blasts and impacts in buildings designed to provide resistance to such hazards

? grouping emergency egress stairways in the central building core, as opposed to dispersing them

throughout the structure

During the course of this study, the question of whether building codes should be changed in some way to make future buildings more resistant to such attacks was frequently explored. Depending on the size of the aircraft, it may not be technically feasible to develop design provisions that would

enable all structures to be designed and constructed to resist the effects of impacts by rapidly moving aircraft, and the ensuing fires, without collapse. In addition, the cost of constructing such structures might be so large as to make this type of design intent practically infeasible.

Although the attacks on the World T rade Center are a reason to question design philosophies, the BPS T eam believes there are insufficient data to determine whether there is a reasonable threat of attacks on specific buildings to recommend inclusion of such requirements in building codes. Some believe the likelihood of such attacks on any specific building is deemed sufficiently low to not be considered at all. However, individual building developers may wish to consider design provisions for improving redundancy and robustness for such unforeseen events, particularly for structures that, by nature of their design or occupancy, may be especially susceptible to such incidents. Although some conceptual changes to the building codes that could make buildings more resistant to fire or impact damage or more conducive to occupant egress were identified in the course of this study, the BPS Team felt that extensive technical, policy, and economic study of these concepts should be performed before any

specific code change recommendations are developed. This report specifically recommends such

additional studies. Future building code revisions may be considered after the technical details of the collapses and other building responses to damage are better understood.

Several other buildings, including the Marriott Hotel (WTC 3), the South Plaza building (WTC 4), the U.S. Customs building (WTC 6), and the Winter Garden, experienced severe damage as a result of the massive quantities of debris that fell on them when the two towers collapsed. The St. Nicholas Greek Orthodox Church just south of WTC 2 was completely destroyed by the debris that fell on it.

Executive Summary

WTC 5, WTC 7, 90 West Street, the Bankers T rust building, the Verizon building, and World Financial Center 3 were impacted by large debris from the collapsing towers and suffered structural damage, but arrested collapse to localized areas. The performance of these buildings demonstrates the inherent ability of redundant steel-framed structures to withstand extensive damage from earthquakes, blasts, and other extreme events without progressive collapse.

The debris from the collapses of the WTC towers also initiated fires in surrounding buildings, including WTC 4, 5, 6, and 7; 90 West Street; and 130 Cedar Street. Many of the buildings suffered severe fire damage but remained standing. However, two steel-framed structures experienced fire-induced collapse. WTC 7 collapsed completely after burning unchecked for approximately 7 hours, and a partial collapse occurred in an interior section of WTC 5. Studies of WTC 7 indicate that the collapse began in the lower stories, either through failure of major load transfer members located above an electrical substation structure or in columns in the stories above the transfer structure. The collapse of WTC 7 caused damage to the Verizon building and 30 West Broadway. The partial collapse of WTC 5 was not initiated by debris and is possibly a result of fire-induced connection failures. The collapse of these structures is particularly significant in that, prior to these events, no protected steel-frame structure, the most common form of large commercial construction in the United States, had ever experienced a fire-induced collapse. Thus, these events may highlight new building vulnerabilities, not previously believed to exist.

In the study of the WTC towers and the surrounding buildings that were subsequently damaged by falling debris and fire, several issues were found to be critical to the observed building performance in one or more buildings.

These issues fall into several broad topics that should be considered for buildings that are being evaluated or designed for extreme events. It may be that some of these issues should be considered for all buildings; however, additional studies are required before general recommendations, if any, can be made for all buildings. The issues identified from this study of damaged buildings in or near the WTC site have been summarized into the following points:

a. Structural framing systems need redundancy and/or robustness, so that alternative paths or additional

capacity are available for transmitting loads when building damage occurs.

b. Fireproofing needs to adhere under impact and fire conditions that deform steel members, so that the

coatings remain on the steel and provide the intended protection.

c. Connection performance under impact loads and during fire loads needs to be analytically understood and

quantified for improved design capabilities and performance as critical components in structural frames. d. Fire protection ratings that include the use of sprinklers in buildings require a reliable and redundant

water supply. If the water supply is interrupted, the assumed fire protection is greatly reduced.

e. Egress systems currently in use should be evaluated for redundancy and robustness in providing egress

when building damage occurs, including the issues of transfer floors, stair spacing and locations, and stairwell enclosure impact resistance.

f. Fire protection ratings and safety factors for structural transfer systems should be evaluated for their

adequacy relative to the role of transfer systems in building stability.

The BPS Team has developed recommendations for specific issues, based on the study of the performance of the WTC towers and surrounding buildings in response to the impact and fire damage that occurred. These recommendations have a broader scope than the important issue of building concepts and design for mitigating damage from terrorist attacks, and also address the level at which resources should be expended for aircraft security, how the fire protection and structural engineering communities should

Executive Summary increase their interaction in building design and construction, possible considerations for improved egress in damaged structures, the public understanding of typical building design capacities, issues related to the study process and future activities, and issues for communities to consider when they are developing emergency response plans that include engineering response.

National Response. Resources should be directed primarily to aviation and other security measures rather than to hardening buildings against airplane impact. The relationship and cooperation between public and private organizations should be evaluated to determine the most effective mechanisms and approaches in the response of the nation to such disasters.

Interaction of Structural Elements and Fire. The existing prescriptive fire resistance rating method (ASTM E119) does not provide sufficient information to determine how long a building component in a structural system can be expected to perform in an actual fire. A method of assessing performance of structural members and connections as part of a structural system in building fires is needed for designers and emergency personnel.

The behavior of the structural system under fire conditions should be considered as an integral part of the structural design. Recommendations are to:

? Develop design tools, including an integrated model that predicts heating conditions produced by the fire, temperature rise of the structural component, and structural response.

? Provide interdisciplinary training in structures and fire protection for both structural engineers and fire protection engineers.

Performance criteria and test methods for fireproofing materials relative to their durability, adhesion, and cohesion when exposed to abrasion, shock, vibration, rapid temperature rise, and high-temperature exposures need further study.

Interaction of Professions in Design. The structural, fire protection, mechanical, architectural, blast, explosion, earthquake, and wind engineering communities need to work together to develop guidance for vulnerability assessment, retrofit, and the design of concrete and steel structures to mitigate or reduce the probability of progressive collapse under single- and multiple-hazard scenarios.

An improved level of interaction between structural and fire protection engineers is encouraged. Recommendations are to:

? Consider behavior of the structural system under fire as an integral part of the design process.

? Provide cross-training of fire protection and structural engineers in the performance of structures

and building fires.

Fire Protection Engineering Discipline. The continued development of a system for performance-based design is encouraged. Recommendations are to:

? Improve the existing models that simulate fire and spread in structures, as well as the impact of fire and smoke on structures and people.

? Improve the database on material burning behavior.

Building Evacuation. The following topics were not explicitly examined during this study, but are recognized as important aspects of designing buildings for impact and fire events. Recommendations for further study are to:

? Perform an analysis of occupant behavior during evacuation of the buildings at WTC to improve

the design of fire alarm and egress systems in high-rise buildings.

Executive Summary

? Perform an analysis of the design basis of evacuation systems in high-rise buildings to assess the

adequacy of the current design practice, which relies on phased evacuation.

? Evaluate the use of elevators as part of the means of egress for mobility-impaired people as well as

the general building population for the evacuation of high-rise buildings. In addition, the use of

elevators for access by emergency personnel needs to be evaluated.

Emergency Personnel. One of the most serious dangers firefighters and other emergency responders face is partial or total collapse of buildings. Recommended steps to provide better protection to emergency personnel are to:

? Have fire protection and structural engineers assist emergency personnel in developing pre-plans for buildings and structures to include more detailed assessments of hazards and response of

structural elements and performance of buildings during fires, including identification of critical structural elements.

? Develop training materials and courses for emergency personnel concerning the effects of fire on steel.

? Review collaboration efforts between the emergency personnel and engineering professions so that engineers may assist emergency personnel in assessments during an incident.

Education of Stakeholders. Stakeholders (e.g., owners, operators, tenants, authorities, designers) should be further educated about building codes, the minimum design loads typically addressed for building design, and the extreme events that are not addressed by building codes. Should stakeholders desire to address events not included in the building codes, they should understand the process of developing and implementing strategies to mitigate damage from extreme events.

Stakeholders should also be educated about the expected performance of their building when renovations, or changes in use or occupancy, occur and the building is subjected to different floor or fire loads. For instance, if the occupancy in a building changes to one with a higher fire hazard, stakeholders should have the fire protection systems reviewed to ensure there is adequate fire protection. Or, if the structural load is increased with a new occupancy, the structural support system should be reviewed to ensure it can carry the new load.

Study Process. This report benefited from a tremendous amount of professional volunteerism in response to this unprecedented national disaster. Improvements can be made that would aid the process for any future efforts. Recommendations are to:

? Provide resources that are proportional to the required level of effort.

? Provide better access to data, including building information, interviews, samples, site photos, and documentation.

Archival Information. Archival information has been collected and provides the groundwork for continued study. It is recommended that a coordinated effort for the preservation of this and other relevant information be undertaken by a responsible organization or agency, capable of maintaining and managing such information. This effort would include:

? cataloging all photographic data collected to date

? enhancing video data collected for both quality and timeline

? conducting interviews with building occupants, witnesses, rescue workers, and any others who may provide valuable information

? initiating public requests for information

Executive Summary SEAoNY Structural Engineering Emergency Response Plan. As with any first-time event, difficulties were encountered at the beginning of the relationship between the volunteer engineering community and the local government agencies. Lessons learned in hindsight can be valuable to other engineering and professional organizations throughout the country. Appendix F presents recommendations that can be used as a basis for the development of other, similar plans.

Project 1世贸大楼倒塌事故的调查与原因分析

世贸大楼倒塌事故的调查与原因分析 尹航(6123310701),刘嘉磊(6123310702) 摘要: 美国纽约世界贸易中心在911事件中的倒塌不仅造成了巨大的人员、财产损失,也对全世界范围内土木工程设计产生了重要影响。本文通过参考多方调查数据以及对于大楼受爆炸冲击、火灾影响的数值分析,得出结论:“9·11”恐怖袭击事件造成纽约世贸大楼的内部竖向承重钢结构的防火保护层在爆炸中严重脱落,火灾高温使钢材强度大幅度降低,导致着火层群柱失稳,上部巨大的冲击荷载把下层柱逐层压,从而引发连续坍塌。最后对超高层建筑的结构从抗爆、耐火等方面提出相关设计建议。 关键词: 世贸大楼倒塌撞击爆炸影响火灾影响超高层建筑设计建议耐火性设计建议1.引言 2001年9月11日,恐怖分子劫持民航客机撞击美国纽约世贸中心双塔楼,随后的爆炸和火灾使大楼坍塌,造成3000余人死亡或失踪,经济损失无法估计。“9·11”事件留给人们无尽的思考,也给今后超高层钢结构设计带来严峻挑战。分析与总结人类用如此巨大的代价换来的教训与经验,对今后超高层钢结构设计具有重大意义。 2.世贸大楼倒塌事故的调查 美国国家标准技术研究所承担了本次事故世贸中心大楼倒塌原因的主要调查工作,经过了将近两年的时间于2004年6月19日发出总结报告:世贸大楼的设计者当初可能对该建筑的风力荷载量严重估计过低,导致大楼抵抗袭击的能力下降。同时塔楼打防火涂层和灭火设施未达到标准,没有对火灾达到良好的遏制,飞机撞击大楼后,世贸大楼内大火温度高达1093℃,所以即使是铜铸铁打也不能不塌。大火之所以摧毁大楼,是由于楼内的防火和灭火设施靠不住。在正常情况下,大楼的灭火系统应该可以控制火势。但是,飞机撞击损坏了楼内的防火层,切断了部分水管,碎屑粉尘堵塞了洒水装置,导致洒水装置无法运作,大火完全失控,使得火灾成为大楼坍塌的主要原因。下面是关于世贸大楼及911事件的调查数据统计: 2.1世贸中心工程概况数据 纽约世贸中心建成于1973年,由两栋110层的方形塔楼和裙房组成。塔楼地上部分为110层,高417m。平面尺寸为3.5m×63.5m,服务性核心区平面尺寸为42m×26.5m。标准层层高为3.66m。塔楼采用钢框筒结构体系。四周为密柱深梁型框筒,主要抵抗水平荷载。框筒由240根钢柱组成,柱距为1.02m(9层以上),柱截面为450mm×450mm 方钢管,其壁厚沿高度不等。窗裙梁截面高度为1320mm。框筒立面开洞率为24%。大楼底部(8层以下)三柱合一,柱距加大到3.06m,柱截面放大到686mm×813mm。内部核心区为47根钢柱组成的框架,用以抵抗竖向荷载。核心区的一般柱截面为450mm×450mm钢管。结构的外露表面喷涂石棉水泥进行防火保护,其厚度为30mm。 2.2飞机撞击情况数据

超高层美国原世茂双塔

原世茂双塔 原世茂双塔效果图原世贸中心总平面图 世茂双塔,是美国世界贸易中心商业综合体的主体部分。整个综合体由世茂双塔、4幢7层办公楼和1幢22层的酒店组成。1966年开工,1973年竣工。双塔大楼高宽比为7:1,由密集的钢柱组成,钢柱之间的中心距离只有1米多。双塔可供5万人办公,并可接待9万来客。WTC1是北塔,WTC2是南塔。 (1)国别:美国 位置:哈得孙河口,曼哈顿闹市区南端,纽约海港旁。 (2)基本情况 ·综合体占地面积:65000平米 ·双塔总建筑面积:932000平米

·高度(至屋顶),北塔:417米 南塔:415米 ·层数,北塔:地上110层地下6层 南塔:地上110层地下6层 (5)双塔业态构成:办公、商业 (6)写字楼 ·单塔使用面积:350000平方米 ·标准层建筑面积:4032平方米 ·标准层使用面积:3700平方米 ·竖向位置:除地下及44、78、107层以外的全部楼层 (7)商业 ·建筑面积:_平米 ·标准层面积:4032平方米 ·竖向位置:地下一层为综合商场 44和78层设银行、邮局和公共食堂等服务设施 第107层是瞭望层 (8)技术服务楼层:7、8、41、42、75、76、108、109层,分别为两层楼高,等距分布在建筑物内。 (9)观光平台 ·室内观光台:南楼第107层(400米高处) ·室外观光台:南楼第110层(420米高处),可看到80千米外。

(10)电梯数:双塔198部 (11)停车位:2000 (12)建筑设计: 米诺儒?雅马萨奇(Minoru Yamasaki)事务所及特洛伊、密西根、埃默里?罗斯父子公司共同设计。 (13)开发商:纽约和新泽西州港务局 楼层平面图竖向布局图

世界贸易中心飞机撞击后倒塌过程的仿真分析

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世贸大厦倒塌的结构学分析

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911大楼倒塌的力学分析土木与建筑工程学院 专业:工程管理(2) 姓名:李明月 指导老师:阎利

911大楼倒塌的力学分析 摘要:9.11世贸大厦的倒塌因其重要的工程背景引起了国内外许多学者的注意,关于其倒塌的原因分析很多,但大多都是从爆炸冲击和火灾燃烧方面进行考虑和解释,同时国内对世贸大楼倒塌的原因的理论研究更是不少本文首次从塑性极限分析的角度来进行研究,假设大楼倒塌时结构内产生塑性铰,应用静力学极限分析的方法,计算出大楼倒塌所需要的极限静荷载,然后将大楼上部楼层自由落体与大楼下部楼层相互作用的冲击荷载与静荷载联系起来,得出大楼倒塌可能性与上下楼层完全刚性冲击作用时间的相关性。 最后,我们简单介绍了飞机撞击大楼后的爆炸当量死亡半径、财产损失半径等等,并对9.11以后未来高层建筑的发展趋势作了简单的展望。 关键词:世贸大厦塑性极限分析刚性冲击 正文: 1.塑性极限分析方法研究世贸大楼倒塌 1.1 世贸大厦概况 曼哈顿岛上的世贸中心是世界上最大的贸易机构,其主要建筑双塔楼是世界上最高的建筑之一,其中两座建筑南楼高1368英尺 110层,北楼1362英尺 110层,起标准层高为 3.676m。两座大楼都为方柱形体,且外形完全一样,每边宽200英尺,每幢塔楼面积达46.6×106m2约250000t,大楼的外墙每边又排列很密的59根钢柱组成,每根钢柱都是边长为14英寸的正方形,钢柱间的距离为3英尺4英寸,大楼外表包以银色铝板,在普通风力作用下,楼层摆幅能达到2.8m. 世贸大楼的建筑钢材坚固,结构设计合理,大楼不仅经历了许多年的风雨依然完好,而且这次飞机的巨大撞击也未能使之立即倾倒,恐怖分子劫持以撞击大楼的波音757飞机起飞重量为104t,波音767飞机起飞的重量为156t,它们的飞行速度是100km/h,据幸存者描述,飞机撞击大楼虽然震动幅度在1m左右,但大楼并未立即倒塌,这既为幸存者逃离大楼争取了宝贵的时间。也证明了飞机撞击

美国世贸中心和五角大楼为什么会遭飞机撞击

美国世贸中心和五角大楼为什么会遭飞机撞击2001年9月11日,也就是俗称的“911”事件,恐怖分子劫持两架民航客机,分别撞击了处于纽约的世贸中心一二号楼,这两座建筑在遭到撞击后相继倒塌。9时左右,恐怖分子劫持另一架民航客机撞击了位于华盛顿的五角大楼,导致五角大楼的局部受损并发生坍塌。 但是,美国的建筑很多,为什么偏偏要选择世贸中心和五角大楼这两座建筑呢?作为恐怖分子,对于政治的敏感自然要高于我们,这个行动也是具有政治意义的。 首先说世贸中心的情况。世贸中心在一定程度上是经济的代名词,其中更是随时都有着大量的世界人才,也是金融流通的场所。而五角大楼,全称美国国防部五角大楼,是美国国防部的总部所在。同样的,在某种意义上,它代表的是美国国防部,甚至是美国军事当局。其中同样有着大量的人才和重要资料。 这样一来,恐怖分子撞击世贸中心和五角大楼的表层原因就昭然若揭了。其一,是对美国政府的公然挑战。世贸中心和五角大楼都是美国的代表性建筑,对其进行撞击就可以有效地打击美国的国际尊严。其次,是对美国造成极大的损失。世贸中心与五角大楼都是人才的汇聚之处,而这次撞击,致使其中的人员死亡,其中更是有大多数的人是重要人才,损失不可估量。此外,单单是固定资产,都是很答的损失。 但是,深层原因显然不止如此。

据美国政府表态及基地组织的残余资料表示,本拉登直接参与了对“911案件”的策划。那么,本拉登为什么要制造这次恐怖袭击呢? 这与美国的霸权主义是分不开的。二战以后,美国沿承了之前老牌强国的一贯做法,对伊斯兰国家进行了经济掠夺,低价买入石油资源。与此同时,美国向伊斯兰国家输出西方的价值体系与价值观念,使伊斯兰国家的文化体系遭到了冲击与破坏。美国还在政治和军事上不断对伊斯兰世界进行压抑和打击,甚至直接入侵。它长期支持以色列,压抑巴勒斯坦;长期对伊朗、伊拉克、利比亚、叙利亚等国家进行封锁和制裁;相继发动海湾战争、阿富汗战争、伊拉克战争,侵占伊斯兰领土,屠戮伊斯兰人民。因此,在本拉登所处的伊斯兰世界中,有着普遍的反美情绪。在其眼中,美国就是邪恶的象征。他们对其进行恐怖袭击,自然在他们眼中是“对罪恶的制裁”。 这样一来,所谓的“911事件”倒可以说是两个文化体系之间的碰撞。因此,之所以选择五角大楼和世贸中心,主要是想用这两个代表性的建筑物来表明伊斯兰国家——尤其以基地组织为代表的激进主义者对于美国霸主地位的不满。毕竟,这两个建筑是最显眼的。撞击了世贸中心与五角大楼,也就是所谓的杀鸡儆猴,可以有效地产生打击作用。 这,大概就是美国的世贸中心和五角大楼被撞击的原因了吧。

世贸大厦的倒塌

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从技术上讲,典型的容灾系统一般包括2个主要的功能部分: 数据复制和应用切换。数据复制是指,在异地之间保证各个系统关键数据和状态参数的一致,其实现可以是软件的方式,也可以是硬件的方式; 应用切换是指,当某个具体应用在一个系统中失效之后,可以在另外一个系统中自动启动并接管该网络服务,这要求系统必须配置有相应的软件。 Morgan Stanley公司的主要系统中心建在世贸大厦内,同时在新泽西的Teaneck市建有一个容灾中心。其内部配备有与主系统基本一致的硬件和软件系统,与主系统一样具有强大的信息处理能力。最重要的是,该容灾系统时刻复制主系统中产生的数据,这不仅使得灾难发生后公司的关键数据不会丢失,而且,还能很快接管主系统的工作任务,向全球营业部提供原来由主系统所提供的服务能力。也正是这个容灾系统的出色表现,把Morgan Stanley公司在这次恐怖事件中的损失降到最低。全球的正常业务也基本没有停滞。 数据保护 前边已经提到,容灾系统主要包括数据保护和应用切换两大方面。目前,

世贸大厦倒塌原因

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纽约新世贸中心2号楼(2WTC)平面图1至19层

2 WORLD TRADE CENTER 200 GREENWICH STREET

FLOOR PLATES & LEASE SPANS The stepping boxes of the tower provide various sizes of floor plates from roughly 63.000 GSF to 31.000 GSF. Due to the stepping of the core the lower floors have very large lease spans to the east of more than 100 feet creating flexibility and communication for either trading floors or creative companies. The upper levels provide a more typical floor plan layout with a center core and regular lease spans to all sides. VERTICAL TRANSPORTATION Interior vertical circulation for the building will be provided in eight distinct zones. Podium floors are served by seperate elevator banks for high density floor plates. All other floors are connceted through crossover floors for each elevator bank. Additional amenity stops can be provided within the peformance calculations of the elevator banks. VERTICAL CIRCULATION 4059395838573756365535543453335232513150304929482847274626452544244323422230212920281927182617251624152314221321122011M 111910189178167614VERTICAL STACK _ VARIETY OF FLOOR PLATE SIZES 63,46 GSF / 76,334 RSF Z O N E 6 Z O N E 5 Z O N E 4Z O N E 3 Z O N E 2Z O N E 1 ELEVATOR BANK F ELEVATOR BANK E ELEVATOR BANK D ELEVATOR BANK H ELEVATOR BANK B ELEVATOR BANK J GREENWICH STREET 405939583857 3756365535543453335232 51 31503049294828472746264525442443 23422230212920281927 182617251624152314221321 1220 11M 1119101891781676 14

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点。4.与物证的取证调查结果不符。一)政府销毁物证灾难发生后,世贸中心现场被立即封锁。人们仅仅想对“现场零点”拍照也遭到逮捕的威胁。几乎全部钢材残骸都被运到海外(中国,印度)的熔化炉里销毁。急管局对倒塌原因作前期调查的建筑表现评估专家小组也不能进入“现场零点”。对於官方理论极为重要的建筑设计资料至今未能为公众所知。如果根据官方报告中对大楼结构的描述,将有达20%的已知被用于构建双塔的钢材不知所踪。急管局报告出台之际,“现场零点”已经清理完毕。 [ 转自铁血社区https://www.wendangku.net/doc/3c13640708.html,/ ] ?二)双塔的设计能承受大型飞机撞击事实上,世贸双塔的原设计是可以承受一架载有约70多吨汽油的波音707-340飞机的撞击和随之而起的大火的双重打击的。9/11当天撞击双塔的波音767-200飞机有着类似的体型,只载油约30多吨。每一栋大楼都是由钢柱组成的外墙和由47根巨型钢柱组成的中心区提供支撑力,地板横梁通过多重锁扣和直接焊接将中心区与外墙的钢柱紧密相连,形成所谓“筒中筒”的结构。这种当时首创的设计模式在现代的摩天大楼中广泛采用。就象所有大型钢铁建筑一样,双塔是过度建构数倍于可预见的承载,以抵抗如炸弹,火灾,台风等灾害的打击的。飞机的撞击,只切断了北塔,南塔240根外围钢柱的33和24根,即约14% 和10%的外围支撑结构。南塔飞机撞击的轨迹更

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