【正文】 stiffness of the system is close to zero. The space structures of outrigger girders or trusses, that connect the inner tube to the outer tube, are located often at several levels in the building. The ATamp。 the trusses are placed often at mechanical floors, mush to the disapproval of the designers of the mechanical systems. Nevertheless, as a costeffective structural system, the belt truss works well and will likely find continued approval from designers. Numerous studies have sought to optimize the location of these trusses, with the optimum location very dependent on the number of trusses provided. Experience would indicate, however, that the location of these trusses is provided by the optimization of mechanical systems and by aesthetic considerations, as the economics of the structural system is not highly sensitive to belt truss location. TubeinTube Structures The tubular framing system mobilizes every column in the exterior wall in resisting overturning and shearing forces. The term?tubeintube?is largely selfexplanatory in that a second ring of columns, the ring surrounding the central service core of the building, is used as an inner framed or braced tube. The purpose of the second tube is to increase resistance to over turning and to increase lateral stiffness. The tubes need not be of the same character。 這種體系的脆弱，特別是在結(jié)構(gòu)筒中，與柱子的壓縮變形有很大的關(guān)系，柱子的壓縮變形有下式計(jì)算： △ =Σ fL/E 對(duì)于那些層高為 米左右和平均壓力為 138MPa 的建筑，在荷載作用下每層柱子的壓縮變形為 15（ 12） /29000 或 毫米。 外筒是一 個(gè)瞬時(shí)抵抗結(jié)構(gòu)，但是在每個(gè)長(zhǎng)方向的中心 米都沒(méi)有剪切剛度。同樣需要指出的是，內(nèi)柱中與側(cè)向力有關(guān)的軸向 力沿筒高度由拉力變?yōu)閴毫?，同時(shí)變化點(diǎn)位于筒高度的約 5/8 處。但是在筒中筒結(jié)構(gòu)的設(shè)計(jì)中，當(dāng)發(fā)展到極限時(shí)，內(nèi)部軸心壓力會(huì)很高的，甚至遠(yuǎn)遠(yuǎn)大于外部的柱子。實(shí)驗(yàn)表明：由于這種結(jié)構(gòu)體系的經(jīng)濟(jì)性并不十分受桁架位置的影響，所以這些桁架的位置主要取決于機(jī)械系統(tǒng)的完善，審美的要求， 筒中筒結(jié)構(gòu)： 筒體結(jié)構(gòu)系統(tǒng)能使外墻中的柱具有靈活性，用以抵抗傾覆和剪切力。不管應(yīng)用那種方法，都必須考慮剪力滯后的影響。 鋼結(jié)構(gòu)剪力墻通常由混凝土覆蓋層來(lái)加強(qiáng)以抵抗失穩(wěn)，這在剪切荷載大的地方已得到應(yīng)用。 此外，可以利用應(yīng)力分析、結(jié)構(gòu)設(shè)計(jì)軟件或一系列二維或三維計(jì)算機(jī)分析程序中的任何一種進(jìn)行結(jié)構(gòu)分析。對(duì)于較高的高層建筑，可能會(huì)發(fā)現(xiàn)該本系不宜作為獨(dú)立體系，這是因?yàn)樵趥?cè)向力的作用下難以調(diào)動(dòng)足夠的剛度。 將這些構(gòu)件結(jié)合起來(lái)的方法正是高層建筑設(shè)計(jì)方法的本質(zhì)。 如果忽略一 些與建筑材料密切相關(guān)的概念，高層建筑里最為常用的結(jié)構(gòu)體系便可分為如下幾類： 1． 抗彎矩框架。 Whittier,J. S. 。 4． 框架或支撐式筒體結(jié)構(gòu) 5． 筒中筒結(jié)構(gòu)。正相反，有許多例優(yōu)美的建筑僅得到結(jié)構(gòu)工程師適當(dāng)?shù)闹С志捅粍?chuàng)造出來(lái)了，然而，如果沒(méi)有天賦甚厚的建筑師的創(chuàng)造力的指導(dǎo)，那么，得以發(fā)展的就只能是好的結(jié)構(gòu)，并非是偉大的建筑。 由于柱梁節(jié)點(diǎn)固有柔性，并且由于初步設(shè)計(jì)應(yīng)該力求解決體系的突出弱點(diǎn)，所以在初析中使用框架的中心線尺寸設(shè)計(jì)是常見(jiàn)的。該體 系的特點(diǎn)是具有相當(dāng)薄的，通常是（而不總是）混凝土的構(gòu)件，這種構(gòu)件既可提供結(jié)構(gòu)強(qiáng)度，又可提供建筑物功能上的分隔。 由于這些墻內(nèi)必然出同一些大孔，使得剪力墻體系分析變得錯(cuò)綜復(fù)雜。設(shè)計(jì)者已經(jīng)開(kāi)發(fā)出了很多的技術(shù)，用以減小剪力滯后的影響，這其中最有 名的是桁架的應(yīng)用。這些筒體具有不同的特點(diǎn)，也就是說(shuō)，有些筒體是框架結(jié)構(gòu)的，而有些筒體是用來(lái)支撐的。 核心交互式結(jié)構(gòu)： 核心交互式結(jié)構(gòu)屬于兩個(gè)筒與某些形式的三維空間框架相配合的筒中筒特殊情況。美國(guó)電話電報(bào)總局就是一個(gè)布置交互式構(gòu)件的生動(dòng)例子。 由于外筒的剪切剛度在建筑的底部接近零，整個(gè)建筑基本上由兩個(gè)鋼板筒來(lái)支持。 主要的結(jié)構(gòu)工作都集中在結(jié)構(gòu)布置中。T headquarters is an example of an astonishing array of interactive elements: 1. The structural system is 94 ft () wide, 196ft() long, and 601ft () high. 2. Two inner tubes are provided, each 31ft() by 40 ft (), centered 90 ft () apart in the long direction of the building. 3. The inner tubes are braced in the short direction, but with zero shear stiffness in the long direction. 4. A single outer tube is supplied, which encircles the building perimeter. 5. The outer tube is a momentresisting frame, but with zero shear stiffness for the center50ft () of each of the long sides. 6. A spacetruss hat structure is provided at the top of the building. 7. A similar space truss is located near the bottom of the building 8. The entire assembly is laterally supported at the base on twin steelplate tubes, because the shear stiffness of the outer tube goes to zero at the base of the building. Cellular structures A classic example of a cellular structure is the Sears Tower, Chicago, a bundled tube structure of nine separate tubes. While the Sears Tower contains nine nearly identical tubes, the basic structural system has special application for buildings of irregular shape, as the several tubes