外文翻譯--綠地中心主塔 結(jié)構(gòu)設(shè)計(jì)與建筑設(shè)計(jì)的完美結(jié)合

1、<p><b>　　中文5340字</b></p><p>　　綠地中心主塔: 結(jié)構(gòu)設(shè)計(jì)與建筑設(shè)計(jì)的完美結(jié)合</p><p>　　Guoyong Fu, Dennis Poon & Mark Dannettel</p><p>　　Thornton Tomasetti Inc.</p><p>　　51

2、 Madison Avenue</p><p>　　New York, NY</p><p><b>　　USA 10010</b></p><p>　　摘要：武漢綠地中心主樓共125層，總高度600米以上。主樓的結(jié)構(gòu)設(shè)計(jì)追求建筑和結(jié)構(gòu)的完美結(jié)合、結(jié)構(gòu)效率的最大化以及安全性的提升。 獨(dú)特的“風(fēng)槽”的設(shè)計(jì)有效降低了風(fēng)旋渦脫落效應(yīng)。在塔樓頂部，三腳

3、鋼桁架沿樓面邊緣向上呈匯聚式延伸，在頂部實(shí)現(xiàn)無縫對接，形成了一個(gè)造型別致的塔冠結(jié)構(gòu)。如何通過基于性能的設(shè)計(jì)評估建筑抗震性能、如何通過抗連續(xù)倒塌分析來評估結(jié)構(gòu)冗余度是本項(xiàng)目結(jié)構(gòu)設(shè)計(jì)的主要挑戰(zhàn)。通過對參數(shù)化模型的運(yùn)用，（建筑幕墻設(shè)計(jì)者）對平板玻璃現(xiàn)場冷彎的使用達(dá)到了最大化，盡可能地避免采用造價(jià)昂貴的曲面玻璃，從而減小外幕墻的建造成本。</p><p>　　關(guān)鍵詞: PBD、基于性能的設(shè)計(jì)、參數(shù)模型、桁架、帶狀桁架&l

4、t;/p><p><b>　　1 引言</b></p><p>　　中國對超高層建筑的追求浪潮始于東面沿岸城市，并逐漸向內(nèi)地發(fā)展。武漢綠地中心主塔將坐落于毗鄰長江的內(nèi)陸城市武漢。塔樓共125層，總高度達(dá)600米以上，是一個(gè)多功用的超高層建筑，建成后將成為世界第七高樓。主樓底層到69樓用于辦公室、70至89層為公寓、91層到頂樓為酒店、另有5層地下室作停車和容納機(jī)電設(shè)備之功

5、用。一個(gè)高61米的獨(dú)特塔冠和高35米的穹拱位于塔樓頂部，凸顯塔樓獨(dú)特的建筑風(fēng)格。</p><p>　　為了有效地承擔(dān)側(cè)向力(風(fēng)荷載和地震荷載)，武漢綠地中心主樓的主要結(jié)構(gòu)體系包括強(qiáng)大的組合剪力墻、微傾的巨型SRC組合柱和曲線型的環(huán)帶桁架。結(jié)構(gòu)構(gòu)件的位置和幾何形狀都經(jīng)過了精心地優(yōu)化以滿足強(qiáng)度和剛度的要求， 同時(shí)與建筑設(shè)計(jì)達(dá)到完美的結(jié)合。</p><p>　　1.1 減少塔群風(fēng)荷載</p

6、><p>　　如同其它的超高層建筑, 側(cè)向荷載（含風(fēng)荷載和地震荷載）在武漢綠地中心主樓的結(jié)構(gòu)設(shè)計(jì)中起至關(guān)重要的作用。根據(jù)中國《建筑抗震規(guī)范》(GB50011-2010)，武漢位于抗震設(shè)防烈度6度區(qū)，設(shè)計(jì)基本地震加速度值為0.05g, 其中設(shè)計(jì)基本地震定義為50年超越概率為10%的地震或回歸期為475年的地震。RWDI進(jìn)行風(fēng)洞試驗(yàn)以確定用于塔樓結(jié)構(gòu)強(qiáng)度設(shè)計(jì)和剛度設(shè)計(jì)的風(fēng)荷載。對于塔樓結(jié)構(gòu)構(gòu)件的強(qiáng)度設(shè)計(jì)，100年風(fēng)荷載和

7、常遇地震荷載需要與重力荷載組合，其中常遇地震被定義為50年超越概率為63%的地震或回歸期為50年的地震。在海外的設(shè)計(jì)規(guī)范中，地震荷載不要求與風(fēng)荷載進(jìn)行組合。與其它海外的設(shè)計(jì)規(guī)范不同，《高層建筑混凝土結(jié)構(gòu)技術(shù)規(guī)程》(JGJ 3-2010)要求地震荷載與100年風(fēng)荷載進(jìn)行組合。表1列出了100年風(fēng)荷載和根據(jù)規(guī)范計(jì)算的常遇地震荷載數(shù)值并進(jìn)行了比較。根據(jù)表1，100年風(fēng)荷載下的基底剪力和傾覆力矩均遠(yuǎn)大于常遇地震下的數(shù)值。</p>

8、<p>　　表1.側(cè)向力比較. 風(fēng)荷載數(shù)值基于RWDI于2012年2月提供的風(fēng)荷載</p><p>　　為了獲得最佳的建筑功能和結(jié)構(gòu)性能，武漢中心主樓的建筑體量在設(shè)計(jì)過程中進(jìn)行了不斷地優(yōu)化，主要采取了以下四項(xiàng)措施：（沿豎向）逐漸縮進(jìn)的體型、穹拱式的塔冠、帶圓角的三角形樓層平面和散落在不同高度的風(fēng)槽（參見圖1）。由于這</p><p>　　些措施能夠有效減小作用于超高層建筑的不利風(fēng)

9、荷載效應(yīng)，所以結(jié)構(gòu)材料的用量可以得到節(jié)省，建造成本也會(huì)大幅降低。</p><p>　　從結(jié)構(gòu)的角度上看，每一幢超高層建筑均可視為沿豎向的懸臂梁。側(cè)向荷載（風(fēng)或地震）以及建造成本均會(huì)隨建筑高度的增加而急劇增加。逐漸縮進(jìn)的建筑體型已經(jīng)被證明可以有效地減小作用于塔樓的整體側(cè)向荷載，故被世界上許多超高層建筑所采用。從建筑的角度上看，逐漸縮進(jìn)的建筑體型有利于解決不同建筑體量對樓層面積的不同需求，避免傳統(tǒng)的呈階梯狀的樓層平面

10、突變。</p><p>　　超高層建筑項(xiàng)目通常具備多種建筑功能。在首層要對各類用戶及其通行加以區(qū)分。通常情況下，沿建筑高度方向樓層面積和出租樓面的跨度大小均逐漸減小。武漢綠地中心塔樓擁有三個(gè)功能分區(qū)：辦公、公寓和酒店。雖然一些超高層建筑通過樓層位置來區(qū)分租戶和訪客，本項(xiàng)目獨(dú)特的三角形平面允許租戶和訪客在首層擁有其獨(dú)立的入口。采用圓弧曲線加以修飾的（三角形平面的）角部以及位于塔頂?shù)膱A形拱頂創(chuàng)造出獨(dú)特的功用空間，它不

11、僅吸引更多的游客，更有助于減小風(fēng)荷載。為了進(jìn)一步減小塔樓風(fēng)荷載，以風(fēng)洞試驗(yàn)結(jié)果為指導(dǎo)，在塔樓某些部分開洞。（風(fēng)洞試驗(yàn)顧問）RWDI在風(fēng)洞中測試了三個(gè)建筑體量布置方案（參見圖2）。三個(gè)方案均擁</p><p>　　有逐漸收縮的體型。方案1在建筑立面沒有開洞。以方案1作為方案比較的基礎(chǔ)，方案2的特點(diǎn)是塔冠和穹拱之間存在空隙，并在建筑立面上存在局部開洞。方案3的特點(diǎn)是建筑立面上存在翼墻和豎向開槽。 表2列出了由風(fēng)洞試驗(yàn)

12、獲得的（三種方案下的）塔樓整體風(fēng)荷載。</p><p>　　表2.三種建筑豎向布置方案下的塔樓風(fēng)荷載比較. 基于2011年2月RWDI風(fēng)洞試驗(yàn)結(jié)果匯總</p><p>　　由表2可以看出，（與方案1相比）方案2中“X”向和“Y”向的風(fēng)荷載分別減小15%和6.6%，而方案3中的風(fēng)荷載沒有明顯的減小。從建筑上看，（方案2中）塔樓頂部處的開口把塔頂分成上部塔冠和下部穹拱兩個(gè)部分，此舉不僅減小了風(fēng)

13、荷載，而且賦予塔樓一個(gè)獨(dú)特的建筑特征。另外，用于清洗穹拱的塔冠圍護(hù)設(shè)備或擦窗機(jī)也可以隱藏于塔冠之中。最終方案2被采用。</p><p>　　1.2 塔樓抗側(cè)力體系</p><p>　　經(jīng)過（設(shè)計(jì)者）精心地優(yōu)化，綠地中心主樓的結(jié)構(gòu)體系與建筑融為一體，以便最大限度地提高結(jié)構(gòu)效率和增強(qiáng)安全性。平面上呈“Y”型的混凝土核心筒（從其底區(qū)）從塔樓中心點(diǎn)到其最外邊的距離達(dá)31.3米。（這種對）核心筒的布

14、置不僅有利于區(qū)分辦公、旅館和公寓的功能，也為塔樓結(jié)構(gòu)提供巨大的結(jié)構(gòu)剛度和承載力以承擔(dān)側(cè)向力和重力荷載，同時(shí)增大了容納機(jī)電設(shè)備的空間和管井空間。</p><p>　　為了最大限度地發(fā)揮“Y”形平面的結(jié)構(gòu)剛度，在（Y形平面的）各肢最外端位置分別布置一對巨柱（SC1）。為了減小外周結(jié)構(gòu)構(gòu)件的跨度，在塔樓周圍每邊約在每個(gè)Y形平面的三分之一的位置 各布置2根巨柱（SC2）。巨柱的最大截面尺寸達(dá)3.3 m× 4.6

15、m左右并加入由鋼板焊接而成的組合鋼柱。兩至三層高的鋼外伸臂桁架把巨柱與核心筒相連。外伸臂桁架布置在第36層至39層、第67層至70層以及第101層至103層之間，另外在第121層至123層之間布置帽桁架。在塔樓高度方向沿建筑周邊布置十道鋼環(huán)帶桁架。外伸臂桁架和環(huán)帶桁架沿建筑高度方向接近均勻分布以最大限度地發(fā)揮結(jié)構(gòu)效率，同時(shí)所有桁架均布置于機(jī)電層或避難層以避免對出租面積的影響。平面上呈折線形的（環(huán)帶）桁架在重力荷載作用下有扭轉(zhuǎn)的傾向，故在

16、（環(huán)帶）桁架上下弦桿平面布置水平支撐體系以約束桁架的受扭。樓面水平支撐體系由樓面鋼梁和雙角鋼斜撐組成。</p><p>　　1.3 風(fēng)槽樓層位置的優(yōu)化</p><p>　　武漢綠地中心主樓的建筑外形在經(jīng)典的“Y”形平面基礎(chǔ)上逐步演化，最終成為具有優(yōu)雅曲線的獨(dú)特外形。在不同的建筑標(biāo)高位置，通過去掉局部樓面及位于建筑外周的部分結(jié)構(gòu)構(gòu)件形成建筑立面上的(開口)“風(fēng)槽”。這些“風(fēng)槽”既賦予建筑物與

17、眾不同的個(gè)性，又減小了由風(fēng)旋渦脫落引起的結(jié)構(gòu)風(fēng)荷載（參見圖3）。</p><p>　　“風(fēng)槽”的位置經(jīng)過了精心地選擇以避免結(jié)構(gòu)的不連續(xù)性。在設(shè)計(jì)初期，這些風(fēng)槽布置于機(jī)電層。由于空腹桁架沒有斜腹桿，便于更多氣流通過，所以位于風(fēng)槽層（即機(jī)電層）的環(huán)帶桁架采用空腹桁架的形式似乎是合理的選擇。然而空腹桁架有兩個(gè)主要缺點(diǎn)。首先，空腹桁架的結(jié)構(gòu)效率遠(yuǎn)不如帶斜腹桿的傳統(tǒng)桁架體系。其次，環(huán)帶桁架作為轉(zhuǎn)換桁架支承位于相鄰兩個(gè)環(huán)帶桁

18、架層之間的外周重力柱，當(dāng)環(huán)帶桁架下方某一樓層的外周重力柱失效時(shí)，（失效樓層以上的）重力柱作為吊桿把樓層荷載傳至（上方）環(huán)帶桁架，因此環(huán)帶桁架在抗連續(xù)倒塌體系中有至關(guān)重要的作用。經(jīng)過建筑師和結(jié)構(gòu)工程的協(xié)調(diào)配合，風(fēng)槽層被布置于環(huán)帶桁架層之下，這樣環(huán)帶桁架層可采用傳統(tǒng)的（帶斜腹桿的）桁架形式；與空腹桁架相比可節(jié)省建造成本。風(fēng)槽層也造成了某些次要周邊柱（在豎向）的不連續(xù)。在抗連續(xù)倒塌分析中，當(dāng)位于風(fēng)槽層下方樓層的非連續(xù)重力柱失效時(shí)，這些樓層的樓

19、面梁（被設(shè)計(jì)為）可以承擔(dān)原先由失效重力柱承擔(dān)的樓面荷載并把這些樓面荷載傳至相鄰柱子。</p><p>　　風(fēng)旋渦脫落被定義為發(fā)生在建筑物角部的紊流。它發(fā)生于物體的下風(fēng)向邊緣處，由低壓渦流（或風(fēng)旋渦）的交替產(chǎn)生和脫離造成。如果不加以控制，周期性的旋渦生成和脫離造成施加于建筑物上的周期性風(fēng)荷載，即橫向風(fēng)荷載。風(fēng)槽層能讓風(fēng)直接穿過建筑物角部到達(dá)下風(fēng)向一側(cè)，故可以抑制旋渦脫落的形成，從而減小旋渦脫落的影響。雖然作用在塔樓

20、上的總體順風(fēng)向荷載（拖力）不會(huì)因?yàn)榫植看嬖诘男★L(fēng)槽的影響而減小太多，但是這些風(fēng)槽肯定對減小局部的風(fēng)旋渦脫落有幫助。由于可以利用風(fēng)槽位置的優(yōu)化達(dá)到提高結(jié)構(gòu)效率的目的，風(fēng)槽得到了結(jié)構(gòu)工程師的歡迎，而建筑師則利用風(fēng)槽創(chuàng)造出獨(dú)特的空間和奇妙的景觀。</p><p>　　1.4 核心筒在罕遇地震下的性能</p><p>　　依據(jù)《高層建筑混凝土結(jié)構(gòu)技術(shù)規(guī)程》（JGJ3-2010），對于600米以上的

21、超高層建筑需要進(jìn)行罕遇地震下的彈塑性結(jié)構(gòu)分析以評估建筑物在地震中的性能。罕遇地震定義為50年內(nèi)超越概率為2%或2475年一遇的強(qiáng)震。遵循性能化設(shè)計(jì)原則和使用中國規(guī)范定義的材料非線性本構(gòu)關(guān)系曲線，結(jié)構(gòu)工程師利用分析軟件ABACUS創(chuàng)建數(shù)學(xué)模型，并輸入7套地震波進(jìn)行非線性時(shí)程分析。初步計(jì)算表明塔樓頂部樓層核心筒墻體單元進(jìn)入塑性的程度比較高，未能達(dá)到預(yù)期的性能水準(zhǔn)。對上部墻體損壞程度的運(yùn)算需要很長的時(shí)間才能達(dá)到收斂，每條地震波下的結(jié)構(gòu)分析需要

22、運(yùn)算長達(dá)近一個(gè)星期。計(jì)算結(jié)果表明該部分墻體性能的減弱明顯與91層的主核心筒的縮進(jìn)有關(guān)。這一縮進(jìn)顯著改變了核心筒的力學(xué)性能（參見圖4）。為了減小這一影響，建</p><p>　　筑師和結(jié)構(gòu)師相互協(xié)作，將原方案到91層就停止的部分核心筒墻體延伸到123 層，從而以最簡潔的方式保持了核心筒的力學(xué)性能（參見圖5）。延伸的墻體增加了塔樓核心筒的強(qiáng)度和剛度，降低了上部墻體在罕遇地震下的破壞，使核心筒達(dá)到了預(yù)期的性能水準(zhǔn)。這一

23、措施也降低了上部墻體進(jìn)入塑性的程度，使得每條地震波的運(yùn)算時(shí)間大大減少，完成一條地震波的運(yùn)算縮減到兩天。建筑師通過調(diào)整樓梯布局以適應(yīng)增加的墻體，并且相應(yīng)減少了客房類型，這樣的建筑調(diào)整也受到了酒店運(yùn)營商的歡迎。</p><p>　　1.5 塔樓冠層結(jié)構(gòu)</p><p>　　武漢綠地中心主塔樓頂部集中表現(xiàn)了整座建筑的設(shè)計(jì)理念。隨著塔樓向上延伸，建筑表面逐漸分化為兩個(gè)建筑部分：主體和外殼。這種分離

24、設(shè)計(jì)有利于減輕塔頂?shù)娘L(fēng)荷載，從而顯著提高了建筑的性能。這一簡潔有力的設(shè)計(jì)證明了建筑和結(jié)構(gòu)在超高層設(shè)計(jì)互相協(xié)調(diào)的有效性，（該塔冠）為塔樓增添了最具標(biāo)志性的特征，無疑將使之成為武漢市天際線上的地標(biāo)。</p><p>　　隨著塔樓高度增加，塔樓翼緣逐漸錐化收縮，直到與塔樓中軸線在頂部匯聚為一點(diǎn)，形成一個(gè)61米高的塔冠（參見圖6）。而建筑表面另一角度的錐化收縮形成了35米高的穹頂。穹頂玻璃幕墻的清洗將由懸掛在塔冠上的擦窗

25、機(jī)完成。塔冠建筑外幕墻采用一個(gè)獨(dú)特的三腳架結(jié)構(gòu)體系支承。由于塔冠三腳架的桁架隱藏在不透明的幕墻內(nèi)，因此支承結(jié)構(gòu)的設(shè)計(jì)要盡量考慮節(jié)省材料并有利于施工。塔冠三腳架的每一個(gè)腳在豎向剖面上都呈半個(gè)拱形，橫截面為梯形。（三腳架的）每條支腿形成4個(gè)側(cè)面，每一側(cè)依建筑的表面形狀布置桁架。上/內(nèi)側(cè)和兩邊的三角形桁架提供了結(jié)構(gòu)的抗剪剛度，底/外側(cè)則布置無斜桿的空腹式桁架。桁架支承弦桿采用最大直徑500mm的鋼管，而桁架腹桿和斜桿選用小尺寸的鋼管。內(nèi)側(cè)桁架

26、斜桿的形式和三腳架支架中空的布置保證了內(nèi)部擦窗機(jī)的正常工作。兩側(cè)邊桁架逐漸收縮，在塔冠底部交匯為一點(diǎn)，支承在翼緣端部的巨柱上，并直接與巨柱內(nèi)的型鋼相連接，以保證荷載完全的傳遞到巨柱。</p><p>　　塔頂穹拱結(jié)構(gòu)是設(shè)計(jì)上的另外一個(gè)挑戰(zhàn)。穹拱幕墻是透明的，而且支承構(gòu)件有較大的跨度，承受較高的風(fēng)荷載。此外，建筑上還要求透過拱頂能夠仰視景觀。由于穹拱結(jié)構(gòu)在觀光層是可見的，因此穹拱的結(jié)構(gòu)設(shè)計(jì)需具有很強(qiáng)的空間雕塑美感。

27、 </p><p>　　結(jié)構(gòu)工程師提出多個(gè)結(jié)構(gòu)方案供建筑師選擇。方案包含全穹拱均勻分布式結(jié)構(gòu)體系、局部集中布置式結(jié)構(gòu)體系、水平支承式結(jié)構(gòu)體系和豎向支承式結(jié)構(gòu)體系。無論每一種結(jié)構(gòu)方案都綜合考慮到了構(gòu)件尺度對層次感與建筑美學(xué)的影響，結(jié)構(gòu)效率和施工可行性。為減小水平環(huán)梁的直徑，采用鋼吊桿懸掛的方式來降低重力方向上的跨度。由三弦桿桁架構(gòu)成的外露的三腳架支承來自環(huán)梁的風(fēng)荷載和吊桿的重力載。三腳架的內(nèi)側(cè)弦桿逐漸向外側(cè)

28、弦桿縮進(jìn)，在穹拱底部與塔冠三腳架交匯于翼端的巨柱，與上部塔冠渾然一體，而施工時(shí)，穹拱與塔冠是分別進(jìn)行吊裝并連接在一起的（參見圖7）。若穹拱三腳架向上延伸并通過受壓節(jié)點(diǎn)在頂點(diǎn)交匯，則無法實(shí)現(xiàn)透過穹頂仰視景觀，需另想辦法。因此結(jié)構(gòu)工程師在接近穹頂?shù)奈恢貌捎靡粋€(gè)平面桁架將三腳架三條腿固定在一起，因而留出頂端的空間。這樣便形成了一個(gè)具有相當(dāng)抗側(cè)剛度的空間結(jié)構(gòu)體系。</p><p>　　塔冠和穹拱的結(jié)構(gòu)設(shè)計(jì)與建筑設(shè)計(jì)完美結(jié)

29、合，實(shí)現(xiàn)了流暢的建筑外立面效果，巧妙解決了核心筒墻體、塔冠和穹拱之間的過渡關(guān)系，同時(shí)實(shí)現(xiàn)了頂層的無柱大空間，利于游客觀光。從整體上看，塔冠實(shí)化，清晰可見，重點(diǎn)突出，而穹拱虛化，與塔冠相呼應(yīng)。穹拱內(nèi)部三腳架具有較好的尺度空間感，加上小尺寸的環(huán)梁支承玻璃幕墻，最大限度的實(shí)現(xiàn)了穹拱的通透效果。塔冠和穹拱上的全部荷載都傳遞到了巨柱上，傳力路徑簡潔明確，連接可靠性高。</p><p><b>　　1.6 結(jié)語&l

30、t;/b></p><p>　　武漢綠地中心主塔樓是建筑師、結(jié)構(gòu)工程師和幕墻設(shè)計(jì)師通過高效協(xié)作共同完成的建筑杰作。它的每一部分，從幾米尺度的板到600米尺度超高層，都是建筑美學(xué)、建筑功能、荷載抵抗和施工可行性的智慧結(jié)晶。</p><p>　　出處：Guoyong Fu, Dennis Poon & Mark Dannettel. Wuhan Greenland Center

31、Main Tower: Seamlessly Integrating Structure and Architecture</p><p>　　Wuhan Greenland Center Main Tower: Seamlessly Integrating </p><p>　　Structure and Architecture</p><p>　　Guoyon

32、g Fu, Dennis Poon & Mark Dannettel</p><p>　　Thornton Tomasetti Inc.</p><p>　　51 Madison Avenue</p><p>　　New York, NY</p><p><b>　　USA 10010</b></p>

33、<p>　　Abstract: Wuhan Greenland Center Main Tower is a 125-story, 600+ meter mega-tower in China. The tower structural system has been developed to harmonize with the architecture as an integrated whole to maximiz

34、e efficiency and enhance safety. The distinctive floor “slots” help reduce the vortex shedding effect. Slot locations were coordinated to avoid causing structural discontinuities. Above the roof, steel trussed tripod leg

35、s rise from tower plan wing tips to seamlessly complete the building form</p><p>　　Key words: PBD, Performance Based Design, Parametric Modeling, Outrigger, Belt Truss</p><p>　　Introuduction<

36、/p><p>　　The wave of Mega-Tall building construction in China started with cities along the east coast and is now moving inland. Located in Wuhan, an inland city adjacent to the Yangtze River, the Wuhan Greenla

37、nd Center Main Tower is a 125-story, 600+ meter mega-tower on track to be the 7th tallest building in the world, a mixed-use skyscraper with offices up through the 69th floor, apartments at the 70th to 89th floors, a hot

38、el from the 91st floor to the top floor and a five (5)-story deep basement hous</p><p>　　The major structural system of Wuhan Greenland Center Main Tower consisting of robust composite walls, giant slightly

39、sloping composite SRC columns and curved belt trusses, is adopted to resist the lateral loads ( wind or seismic ) effectively. The locations and geometry of structural components have been carefully optimized to not only

40、 provide enough strengths and stiffness but integrate with the architecture seamlessly. </p><p>　　1.1 Tower Massing to Reduce the Wind Load</p><p>　　Like other super tall buildings, the lateral

41、loads, wind and seismic, play the most important role in the structural design of Wuhan Greenland Center Main Tower.According to China “Code for Seismic Design of Buildings “ (GB 50011-2010), Wuhan is located in the Seis

42、mic Fortification Zone #6, with design ground acceleration specified as 0.05g under moderate earthquake, which is defined as a earthquake with “10% Exceedance Probability in 50-year” or an earthquake with 475-year return

43、 period. RWDI p</p><p>　　Architectural massing of the Wuhan Greenland Center Main Tower was developed to optimize both the structural and programmatic performance of the building. Four primary design solutio

44、ns were implemented to deal with both of these issues: a tapered profile, a dome top, triangular floor plans with rounded soft corners and the vent slots (see Figure 1). Since all of these elements help to minimize the n

45、egative effects of wind acting on Supertall buildings, they allowed the quantity of structural mat</p><p>　　Table 1. Lateral Load Comparison. Based on wind load data from RWDI, February 2012.</p><

46、p>　　From a structural perspective, every Supertall building is a cantilever beam in vertical direction, with lateral loads (wind or seismic) and construction costs increasing dramatically as the building height increa

47、ses. A tapered profile has been proved effective in reducing overall tower lateral loads and has been adopted for many Supertall buildings around the world. Architecturally, the tapering shape also helps to resolve diffe

48、rent floor plate size requirements for varied program elements with</p><p>　　Programmatically, Supertall buildings are usually developed as mixed-use projects. Multiple entrances at Ground Level distinguish

49、each type of user and control access. Floor plates typically reduce in size and lease span as the building rises into the sky. The Wuhan Greenland Center Main Tower provides spaces for three distinctive functions: office

50、, apartment and hotel. While some mixed-use towers separate users by levels, the triangular floor plan of this building allows for the tenants or visi</p><p>　　had tapered profiles. Option 1 featured a solid

51、 surface and served as the baseline option. Option 2 featured an opening between the crown and dome plus slotted floors at multiple elevations. Option 3 featured wing walls and vertical slots. The overall tower wind load

52、s for three options from the wind tunnel test are listed in Table 2.</p><p>　　From Table 2, Option 2 reduced the overall wind load by 15% and 6.6% along “X” and “Y” respectively, while Option 3 did not show

53、a significant wind load reduction. The wind tunnel consultant considered that, the opening at the tower top made a great contribution to wind load reduction. Architecturally, an opening at the tower top would separate th

54、e whole tower top into an upper crown and a lower dome. So, in addition to reducing the wind load at tower top, the opening at tower top would give the</p><p>　　Table 2. Tower Wind Load Comparison for Differ

55、ent Massing Options. Based on wind load data from RWDI, February 2011</p><p>　　1.2 Tower Lateral System</p><p>　　The structural system of Greenland Center Main Tower has been carefully developed

56、 to harmonize with the architecture as an integrated whole, to maximize efficiency and to enhance safety. The central “Y” plan concrete core extends 31.3m in plan from the tower center to its far ends at lower zones, and

57、 sets back twice at Levels 70 and 91. The core was organized to provide multiple benefits across different disciplines: separating office, hotel and apartment operational functions, providing signifi</p><p>

58、　　To maximize the structural stiffness given by a “Y” shape plan, a pair of massive super columns (SC1) is located at the tip of each tower wing. Two additional super columns (SC2) are spaced at approximately one-third p

59、oints along each face and serve to reduce the spans of perimeter structural members. The super columns are Steel Reinforced Concrete (SRC) columns, with welded built-up steel column shapes embedded within large concrete

60、columns up to 3.3m X 4.6m in plan dimension. Steel outrigger t</p><p>　　1.3 Optimization of Slotted Floor Location</p><p>　　Wuhan Greenland Center Main Tower’s unique architectural shape evolved

61、 from a classic tapered tower with “Y” plan shape into an elegant curvilinear figure. By locally omitting portions of floors and perimeter framing at different elevations, “slots” are created in the building envelope to

62、provide a distinctive architectural personality while reducing wind loads on the structure from vortex shedding. (see Figure 3).</p><p>　　Slot locations were carefully coordinated to avoid causing structural

63、 discontinuities. Originally, the slots are located at mechanical levels. A Vierendeel truss system would seem to be a natural structural solution at slotted floors, since the lack of diagonals would allow the most air f

64、low. However, Vierendeel truss systems have two major drawbacks. First, structural efficiency is much less than for traditional truss systems with diagonal members. Second, as they serve as transfer trusses supp</p>

65、;<p>　　Vortex shedding is defined as an unsteady flow that occurs at building corners due to the formation and detachment of alternating low –pressure vortices or wind whirlpools on the leeward side of the edge of

66、 an object. Cyclic formation and shedding of vortices applies cyclic wind loads to a building that can generate large crosswind movements if not suppressed. Floor slots let some wind pass through building corners to the

67、leeward side, inhibiting the formation of vortices and reducing the effect</p><p>　　While the slots were welcomed by the structural engineer as a way to achieve an efficient structure through optimized floor

68、 slot locations, the Architect took advantage of the slot voids and created fantastic view opportunities at the unique spaces.</p><p>　　1.4 Performance of Core Wall Under Severe Earthquake</p><p&g

69、t;　　For a building taller than 600 meters, a nonlinear structural analysis to check building performance under a severe earthquake, defined as “2% Exceedance Probability in 50 years” or a 2475-year earthquake, is mandato

70、ry in China per the Technical Specification for Concrete Structures of Tall Building (JGJ 3-2010). Following the principles of Performance-Based Design and using the material constitutive relationship curves specified in

71、 China codes to define material nonlinearity, the structural eng</p><p>　　alleviate predicted wall damage, the Architect and structural engineer jointly decided to reduce the change in core properties by hav

72、ing smaller wall setbacks, simply extending some core wall portions to Level 123 that were originally stopping at Level 91 (see Figure 5). Extending those wall segments increased tower core strength and stiffness, reduce

73、d predicted wall damage under the severe earthquake case and helped the core structure achieve performance level goals. Reduced wall nonlinear beha</p><p>　　1.5 Tower Crown Structure</p><p>　　Th

74、e top of the Wuhan Greenland Center Main Tower is an expression of the project design philosophy. As the tower reaches into the sky, the cladding splits at the line between two architectural components known as the body

75、and the shield. This separation was created to help alleviate tower top wind forces and thus significantly improve building behavior. This simple but powerful statement about the effectiveness of coordinating architectur

76、e and structure in Supertall building design has become th</p><p>　　Rising from gently tapering tower wing tips, the taper steadily and continuously increases to the point that the tips converge on the tower

77、 centerline to form a unique 61m tall crown (see Figure 6). Tapering of other building surfaces defines a 35m tall dome. Cleaning of the dome glass will be performed by equipment suspended from the crown above. Cladding

78、of the outer crown is supported by a special tripod structural system. Because crown tripod leg framing is concealed within opaque cladding, </p><p>　　structural design was based on material efficiency and c

79、onstructability. Each crown tripod leg, a half-arch in profile, is trapezoidal in cross-section or plan. The four faces of each leg are trusses following simple surfaces, with the upper/outer and side trusses triangulate

80、d for shear stiffness and the lower/inner truss a Vierendeel without diagonals. Pipes up to 500 mm diameter are used for truss chords and smaller diameter pipes are used for web members and braces. The inner truss Vieren

81、deel</p><p>　　The tower dome structure posed different design challenges. Dome cladding is transparent but substantial cladding support framing is required at long spans and high wind pressures. Viewing up t

82、hrough the peak of the dome is desired. Dome structural framing will be visible to visitors so a dramatic sculptural appearance is desired.</p><p>　　Multiple structural schemes were proposed by the structura

83、l engineer for consideration by the architect. Systems included support framing distributed along all faces, framing concentrated at discrete locations, horizontal spanning schemes and vertically spanning schemes. For ea

84、ch scheme the relative hierarchy of framing sizes and functionswas considered for aesthetic intent, structural efficiency and constructability. The selected system has horizontal curved pipe girts to support the tower sk

85、in</p><p>　　The tower crown and dome structures were integrated with the architectural design to provide a seamless envelope transition from walls to crown and dome cladding while providing a column free spa

86、ce for visitors. The clad crown trusses are visually solid objects for reading clearly on the skyline. The exposed dome trusses read as sculpture to visitors within the transparent dome, with minimal visual obstruction b

87、y girts. All loads from the tower crown and dome flow directly onto the super columns</p><p>　　1.6 Conclusions</p><p>　　The Wuhan Greenland Center Main Tower illustrates ways that collaboration

88、between architect, structural engineer and skin consultant achieves a final design that addresses aesthetics, functionality, load resistance and constructability in a seamless way at all scales, from a 600+m cantilever t