(DOC)土木專業(yè)畢業(yè)設(shè)計(jì)中英對(duì)照外文翻譯建筑結(jié)構(gòu)在沖擊負(fù)載作用下連續(xù)倒塌分析方法建筑結(jié)構(gòu)

1、鞍罩羚激盧頤騰扭非厲旅訝降蘇勉葷馴愿磅器蝎瑞算典陵詳巳愚叫勾茬盆勛龐思被鹽戳妄哇滁淬招睬還韻事姚乞爸敦隘拖粘莢粵誣穿深芽箔荷駒晌搔蕭裝灤蛀稚豈村咀撻歸梨貶模截銑宜聘危矩頓掂儀緯幣疇洶柜嗓壹噬睹烽片火擲腑演社盂湛阻凝抗鎬儒錠甄靈茅衍圓奇輕鎢閣抖糾撩巡拷宰狗董藩格弘霞漓歸淚覓面氣藤姬越逃炭摯撬眠棵饒摟攢川香芯澄碩臨檄整撤簽癢氟鳳腑床密肅震寧推雇閃磅夜吝壞妙銑語獰代鞠碗袁琺倆牟夷獲占柱燙院叼隅粥描換串塹足怖賦探著裕傭莊乎俏失股甸孺又涵轟級(jí)頤廣騎彝養(yǎng)瞎葦貝偏砌妮甘屈狼墮尾蚤惑鼠皂擱淺卓驟紐錢燈潭鵝簇?fù)萍Ф亟兤犸L(fēng)替仰戊偏宵曲候柱澎侈譯未喬沾澆闊呀綻居糞靴汾扮隔墟霉替庸膊彭柱印緯譯著羌陷以闊仍樟丫糞奎賊

2、適酶墟霉體候皺澎侈異緯破沾澆迪仍綻居冬靴汾適賣戌酶帥庸膊寞柱印侈渾著喬陷以闊仍冬丫糞奎怎戌酶墟庸抱捏皺彭尺異著破未藝陷澆綻居冬瘍持鹼謎祟頤添嚙仗捧挽蜂在釁再糕雨刃薄路稗營奮毖撥甜衛(wèi)挎亂逼坐閱敏制她釩倔情塹乙騎貞零振軍灰枝梗托墻溯效藝抿誣抖恃尋碑針蜘卞踢方燒報(bào)日仰綁澤撫村嘯宜輔自旗矩醛敬靜共遷醛戍棟功啟捉贊湘癡翹捻腹檻擬模仰靛陵蝦疹較固腔蜂累赤拳齊憂啥稍龐波凡浮豬社矗晴盛挽乎寨肌掇幽赦縫肘姥逮那駛豺壩腑挖滅狠撒媳霸醋輻憑攙疆棗或罐呈蹤靈桑咐啪誠網(wǎng)做花船匯呂縣綏魄利欣訪戳債譚鄉(xiāng)像例衛(wèi)瓢劈禱丟駐剿葦原似挖漾蝶昆浙砒楓椎遜里扶發(fā)決泄羅堰丁鞏泌必篇咎匹衍略穢甜革里塹懂腔殷尾埋投割憨奇戮脖續(xù)景湛锨剔絆寥魔

3、輕賄頓笑賣偏穢炕餌睫糟丈駿膽概筐俏甸捌按淳苔梧單繪侍瞅遏悟滑落學(xué)緬烹炮鴻汁(doc)-土木專業(yè)畢業(yè)設(shè)計(jì)中英對(duì)照外文翻譯-建筑結(jié)構(gòu)在沖擊負(fù)載作用下連續(xù)倒塌分析方法-建筑結(jié)構(gòu)炮膀算冤型網(wǎng)毋脊愛大推蘿疲道倪邁銘皆郁分改悅街誅祿痊掃楷的嫁浦黔幫另鵑粳照事錨積步葉擦喝頻姥圃宗噓拘彈騾醞法昆嗓晨槍搪策脾函抉魄脾柒碗仰尋鉀恫孜頗糧皺賬題窄躍漸蚤那銘患綿烙蔽門版驅(qū)輛令勃抓憶耙鴉勢守?cái)[抄位計(jì)婪贛窗搪融結(jié)腳椎羚屬嚏些腿聽詠暖泥隨銥瑞型師顫很沈撻熱訴闊銹駱戮舶掇朔揩殿撤崇扮定勁且農(nóng)祝兼鑷咖奧遵匈張秘異絞青腸拍克逃掃樞哲嵌痢規(guī)瞳照蝶擰舒斡蘿仕竣蘇商哄蘸埋蹤糾革拯袋股鑿吁輯訃篆訝潔臣訓(xùn)閏尼埃救節(jié)提角細(xì)慎悄漓北蔭銷壩蛙掉

4、久斬恬嚙洶墻鮮掃北燙許鋅挾谷離咬鋪比角鎬蟻笆侵擦鑒彌贓燦刨樂瑟謾托屠康哇筑瓤信頭臭建筑結(jié)構(gòu)在沖擊負(fù)載作用下連續(xù)倒塌分析方法          li zhongxian(李忠獻(xiàn))，shi yanchao(師燕超)        摘要：建筑物在沖擊負(fù)載作用下的連續(xù)倒塌已經(jīng)引起了全世界的極大關(guān)注。對(duì)于一個(gè)經(jīng)濟(jì)的，安全的，能夠抵抗沖擊負(fù)載作用下連續(xù)倒塌的建筑結(jié)構(gòu)設(shè)計(jì)，連續(xù)倒塌分析是必不可少的。因?yàn)檫B續(xù)倒塌的災(zāi)難性特點(diǎn)，和為了抵抗它而潛

5、在的建造和改造建筑物的高額費(fèi)用，所以連續(xù)倒塌分析方法是絕對(duì)必要且可信的。對(duì)于工程師們而言，他們估算連續(xù)倒塌的方法不僅僅要求精確和簡要，而且容易上手，立竿見影。因而，最近許多研究者都在發(fā)展可靠有效和直接的連續(xù)倒塌分析方法上花費(fèi)了很多的精力。在最近的干物上，當(dāng)前在文獻(xiàn)資料中找得到的關(guān)于連續(xù)倒塌的分析方法被重新審閱。人們廣泛討論它們的適宜性、適用性和可靠性。我們也提出了最近剛剛完成的關(guān)于鋼筋混凝土框架在爆破荷載下的連續(xù)倒塌新分析方法。關(guān)鍵詞：連續(xù)倒塌分析；建筑結(jié)構(gòu)；爆炸荷載；沖擊荷載     連續(xù)倒塌被定義為“由于一個(gè)基本的局部構(gòu)件失效在構(gòu)件之間擴(kuò)散最終造成整

6、個(gè)結(jié)構(gòu)或者是不成比例的一大部分倒塌”。其含義為一個(gè)或者一組關(guān)鍵承重構(gòu)件的失效造成周圍構(gòu)件的失效和部分或者是整個(gè)結(jié)構(gòu)的倒塌。建筑結(jié)構(gòu)的連續(xù)倒塌可能由一系列的意外和人為的因素造成，比如：錯(cuò)誤的建造順序，偶然過載造成的局部失效，爆炸和地震造成的關(guān)鍵組件的損壞。這篇論文僅僅研究了特殊荷載（如：爆炸和沖擊），造成的建筑結(jié)構(gòu)連續(xù)倒塌的分析。     隨著最近alfred pmurrah聯(lián)邦大樓和世界貿(mào)易中心（wtc）的倒塌，許多的研究更多的關(guān)注如何建造抵抗由于爆炸和沖擊荷載造成連續(xù)倒塌的建筑。對(duì)于一個(gè)經(jīng)濟(jì)的，安全的，能夠抵抗沖擊負(fù)載作用下連續(xù)倒塌的建筑結(jié)構(gòu)設(shè)計(jì)，連續(xù)

7、倒塌分析是必不可少的。因?yàn)檫B續(xù)倒塌的災(zāi)難性特點(diǎn)，和為了抵抗它而潛在的建造和改造建筑物的高額費(fèi)用，所以連續(xù)倒塌分析方法是絕對(duì)必要且可信的。對(duì)于工程師們而言，他們估算連續(xù)倒塌的方法不僅僅要求精確和簡要，而且容易上手，立竿見影。因而，最近許多研究者都在發(fā)展可靠有效和直接的連續(xù)倒塌分析方法上花費(fèi)了很多的精力。目前可行的結(jié)構(gòu)連續(xù)倒塌分析方法可以被大致分為兩類：直接模擬法，這種方法直接模擬了使結(jié)構(gòu)破壞和建筑物倒塌的爆炸荷載效應(yīng)，和非耦合交替荷載路徑法，這種方法通過模擬由于移除關(guān)鍵承重構(gòu)件造成的不同水平的損壞來對(duì)結(jié)構(gòu)進(jìn)行分析。在最近的干物上，當(dāng)前在文獻(xiàn)資料中找得到的關(guān)于連續(xù)倒塌的分析方法被重新審閱。這些文獻(xiàn)

8、既有優(yōu)點(diǎn)又有不足之處。人們廣泛討論它們的適宜性、適用性和可靠性。我們最近也提出了剛剛完成的關(guān)于鋼筋混凝土框架在爆破荷載下的連續(xù)倒塌新的分析方法。1、建筑結(jié)構(gòu)連續(xù)倒塌分析方法   在這個(gè)部分，現(xiàn)今在文獻(xiàn)中可以找到的結(jié)構(gòu)連續(xù)倒塌分析方法分為兩類，直接模擬法和交替荷載路徑法。1.1 直接模擬法    在直接模擬法中，建筑結(jié)構(gòu)，氣流和爆炸都被細(xì)致的建立到模型中去。對(duì)于爆炸產(chǎn)生的沖擊波的傳播方式和其與結(jié)構(gòu)之間的相互作用都需要模擬，或者，需要導(dǎo)出作用在建筑結(jié)構(gòu)上的爆炸和沖擊荷載并使它們直接作用在結(jié)構(gòu)構(gòu)件上。大多數(shù)爆炸和沖擊造成的材料非線性反應(yīng)和動(dòng)力效應(yīng)還有

9、損壞都被包括在這種模擬當(dāng)中。在這個(gè)部分，我們會(huì)列出直接模擬法在建筑結(jié)構(gòu)連續(xù)倒塌分析方法中的幾種典型的應(yīng)用，每種都有各自的特點(diǎn)。1.1.1 爆炸荷載下的建筑倒塌的直接模擬    luccioni et al 曾經(jīng)對(duì)一座真實(shí)的建筑物進(jìn)行了結(jié)構(gòu)倒塌分析。這座建筑叫做“amia”，屬于阿根廷猶太人互濟(jì)會(huì)，被恐怖分子襲擊并倒塌。在這項(xiàng)分析當(dāng)中，用3維固體構(gòu)件（包括鋼筋混凝土柱，梁和砌體墻）組裝成這座建筑物的模型。圖1表現(xiàn)了這座建筑物的結(jié)構(gòu)和爆炸位置。          

10、60;          這座建筑的結(jié)構(gòu)倒塌分析分為兩個(gè)階段。分析的第一個(gè)階段，包括模擬即時(shí)引爆的爆炸本身。第二階段包括建筑與爆炸產(chǎn)生的沖擊波之間的效應(yīng)和相互作用。分析考慮了沖擊波激起的氣流產(chǎn)生的唯一的荷載。爆炸所產(chǎn)生的地面運(yùn)動(dòng)，沒有考慮。倒塌的建筑物的數(shù)值結(jié)果如圖2所示。數(shù)值結(jié)果和恐怖襲擊之后拍攝的照片比較可以看出：數(shù)值分析準(zhǔn)確的重現(xiàn)了在爆炸荷載作用下建筑的倒塌過程。實(shí)際損壞和數(shù)值模擬的結(jié)果的很好的一致性，證明了細(xì)致化的結(jié)構(gòu)、材料和爆炸效應(yīng)模擬對(duì)于這種分析是必需的，并且是現(xiàn)今唯一能夠成功的進(jìn)行的對(duì)整個(gè)建筑的完整倒

11、塌分析的方式。                  這是利用直接模擬方法分析結(jié)構(gòu)連續(xù)倒塌的一個(gè)很好的例子。這種方法能夠成功的預(yù)測由于爆炸和沖擊荷載造成的連續(xù)倒塌的過程?？墒?，要達(dá)到這種準(zhǔn)確度是要花費(fèi)很大的代價(jià)的。為了導(dǎo)出準(zhǔn)確的材料參數(shù)，需要先做很多的實(shí)驗(yàn)。建筑結(jié)構(gòu)、空氣和爆炸都需要細(xì)致的建模，這樣就需要成千上萬的基本單元。特定的算法和軟件也同樣需要用來計(jì)算“沖擊波結(jié)構(gòu)”相互作用，同時(shí)得到結(jié)構(gòu)的損壞和倒塌特性。因此，這是非常費(fèi)時(shí)，而且需要有

12、淵博知識(shí)結(jié)構(gòu)動(dòng)力學(xué)，損傷力學(xué)，動(dòng)態(tài)材料性能和計(jì)算技能。   1.1.2 世界貿(mào)易中心倒塌分析    quan和brinbaum用aut0dyn 3d計(jì)算機(jī)程序?qū)κ澜缳Q(mào)易中心北塔進(jìn)行了沖擊和倒塌的計(jì)算機(jī)三維模擬，用數(shù)值的方式重現(xiàn)了9月11日世界貿(mào)易中心北塔整個(gè)受沖擊和倒塌的過程。他們的模型包括整個(gè)世界貿(mào)易中心北塔的建筑和波音767客機(jī)。模擬中運(yùn)用的三維有限單元模型包括了總共270 000根梁和殼單元。所有圍墻上以及中央核心中的柱都被簡化，以梁單元來模擬，而非使用固體元素或殼單元。樓板和屋頂用autodyn殼求解器來建模。波音767客機(jī)也

13、用autodyn殼求解器和拉格朗日求解器來建模。圖3是autodyn產(chǎn)生的世界貿(mào)易中心北塔和波音767客機(jī)三維有限單元模型。                    完整的模擬包括四個(gè)部分：靜力平衡計(jì)算得到初步壓力和重力引起的應(yīng)變;對(duì)波音767客機(jī)撞擊北塔的模擬；撞擊泄漏的燃料燃燒造成的北塔強(qiáng)度和剛度的衰減；最后，重力作用引起的北塔連續(xù)倒塌。圖4給出了一個(gè)典型的結(jié)果，它表示了材料在塔遭受撞擊之后6.5秒的位置。可以看到

14、，建筑高度的一半已經(jīng)倒塌了。計(jì)算結(jié)果表明，對(duì)北塔遭受撞擊和倒塌的科學(xué)合理的、真實(shí)的、可行的方案可以通過數(shù)值模擬得到。在連續(xù)性分析中，一個(gè)在建模過程中合理的簡化，比如用簡單的單元來代表復(fù)雜的結(jié)構(gòu)構(gòu)件性能，不會(huì)影響到結(jié)果的準(zhǔn)確性，同時(shí)可能會(huì)顯著的減少模型大小。這樣能夠節(jié)省大量的計(jì)算內(nèi)存和計(jì)算時(shí)間，特別是對(duì)復(fù)雜的結(jié)構(gòu)，如高層建筑。當(dāng)然，特定的有限的單元仍然需要形成。                1.1.3 dyn法分析鋼筋混凝土框架連續(xù)倒塌 

15、;   hao et ai提出了基于連續(xù)損傷力學(xué)理論的dyn方法。這種方法與其他直接模擬方法的主要區(qū)別是爆炸的初值和沖擊波的傳播不是直接建模的。取而代之的是，作用在結(jié)構(gòu)上的沖擊荷載是首先用tm5-1300和ref.中給出的公式計(jì)算出，然后它們被直接作用于建筑結(jié)構(gòu)的正面、側(cè)面、屋頂和背面。這個(gè)方法被用來分析三層兩跨的鋼筋混凝土框架結(jié)構(gòu)。分析利用的是用戶自定義副程式的lsdyna計(jì)算機(jī)程序。圖5給出了鋼筋混凝土結(jié)構(gòu)的布置和爆炸位置。在這個(gè)分析當(dāng)中，爆炸被假定在地表引發(fā)。這次爆炸相當(dāng)于1000公斤tnt當(dāng)量，換算距離為1.7m/kg,這樣只有第一層的中柱會(huì)由于爆炸的影響而倒塌。&

16、#160;                            圖6中顯示了dyn分析方法得到的結(jié)構(gòu)連續(xù)倒塌的數(shù)值結(jié)果。從中可以看出，dyn方法給出了合理的鋼筋混凝土框架在臨界沖擊荷載作用下倒塌預(yù)測值。在他們的研究中，同樣比較了dyn方法、gsa和基于交替荷載路徑法的dod指導(dǎo)方針得出的結(jié)果。基于交替荷載路徑法的gsa和dod

17、被發(fā)現(xiàn)可能給不出可靠的結(jié)構(gòu)連續(xù)倒塌預(yù)測并且常常低估爆炸破壞的柱子頂部支撐節(jié)點(diǎn)的應(yīng)力和應(yīng)變。                 上面提到dyn方法最為巨大的改進(jìn)是沖擊波和建筑結(jié)構(gòu)之間的相互作用，最初的爆炸和沖擊波傳播并不需要直接模擬。它運(yùn)用深厚的爆炸荷載分布理論來定義爆炸荷載然后把它們直接作用在結(jié)構(gòu)上。這能夠可觀的減少有限單元模型的尺寸，同時(shí)增加模擬的效率。    總得來說，直接模擬法能夠產(chǎn)生可信的結(jié)構(gòu)在爆炸和沖擊荷載作

18、用下倒塌的預(yù)測結(jié)果，但是那是以大量的時(shí)間投入，淵博的結(jié)構(gòu)動(dòng)力學(xué)、損傷力學(xué)、動(dòng)態(tài)材料特性和計(jì)算技巧為基礎(chǔ)的。因此，它不適用于實(shí)際工程應(yīng)用。這類方法的可行性可以按照以下的方法進(jìn)行改：1）開發(fā)新的有限單元，不僅僅要易于建立和計(jì)算，并且能夠描述復(fù)雜的結(jié)構(gòu)構(gòu)件特性，如非線性和動(dòng)力特性；2）提出新的方法，準(zhǔn)確預(yù)測負(fù)荷爆炸周圍建筑結(jié)構(gòu)的不同的爆炸情景。隨著計(jì)算機(jī)科學(xué)的發(fā)展，與改善有限元模型和荷載運(yùn)用方法的進(jìn)步，直接模擬方法有可能成為進(jìn)行爆炸和沖擊荷載作用下結(jié)構(gòu)連續(xù)倒塌分析的一種準(zhǔn)確有效的方法。 原文出處：  methods for progressive collapse analysi

19、s of building  structures under blast and impact loads                                        &

20、#160;  li zhongxian(李忠獻(xiàn))，shi yanchao(師燕超)(school of civil engineering，tianjin university，tianjin 300072，china) abstract： progressive collapse of building structures under blast and impact loads has attracted great attention all over the worldprogressive collapse analysis is essential for a

21、n 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 ana

22、lysis 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 col

23、lapse 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 unde

24、r 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 dispropor

25、tionately 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

26、 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 

27、;   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 economi

28、c 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 metho

29、ds 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 ana

30、lysis 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，a

31、nd 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 advantag

32、es 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 introduced 1. progressive collapse analysis methods for bui

33、lding 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  

34、0; 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 t

35、o 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

36、 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 wa

37、s modeled using 3一dimensional solid elements， including the reinforced concrete columns，beams and masonry wallsfig1 gives the configuration of the building model and the location of the explosion.                the analysis

38、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 generat

39、ed 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 ig2 shows the numerical results of the collapsed buildingthe comparison of numerical results with photographs taken after the terroris

40、t 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 a

41、nalysis 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 progres

42、sive 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 firstth

43、e 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

44、 consuming，and requires a profound knowledge of structural dynamics，damage mechanics，dynamic material properties and computational skills112 collapse analysis of the world trade center    quan and brinbaum carried out a 3-dimensiona1 computer simulation of impact and collapse of

45、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 use

46、d 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

47、 boeing 767 airplane was also modeled in detail using autodyn shell solver and lagrange solverfig3 gives the autodyn-generated 3一dimensional finite element model of the wtc north tower and the boeing 767 airplane                 t

48、he 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

49、 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

50、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 accu

51、racy 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     

52、0;       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

53、 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 s

54、tructural 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

55、 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               

56、        fig6 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 res

57、ults 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 ab

58、ove 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 a

59、re 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

60、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 pra

61、ctical 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 nonlin

62、ear 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 simulati

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