【正文】 ngs perhaps 40stories and higher. However, except for possible aesthetic considerations, belt trusses interfere with nearly every building function associated with the outside wall。T headquarters is an example of an astonishing array of interactive elements: 1. The structural system is 94 ft () wide, 196ft(59. 7m) long, and 601ft () high. 2. Two inner tubes are provided, each 31ft(9. 4m) by 40 ft (12. 2m), 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 steel plate 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 Towe r, 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 need not be similar in plan shape, It is not unmon that some of the individual tubes one of the strengths and one of the weaknesses of the system. This special weakness of this system, particularly in framed tubes, has to do with the concept of differential column shortening. The shortening of a column under load is given by the expression △ =Σ fL/E For buildings of 12 ft () floor tofloor distances and an average pressive stress of 15 ksi (138MPa), the shortening of a column under load is 15 (12)(12)/29, 000 or 0. 074in (1. 9mm ) per story. At 50 stories, the column will have shortened to in. (94mm) less than its unstressed length. Where one cell of a bundled tube system is, say, 50stories high and an adjacent cell is, say, 100stories high, those columns near the boundary bet ween . the two systems need to have this differential deflection reconciled. Major structural work has been found to be needed at such locations. In at least one building, the Rialto Project, Melbourne, the structural engineer found it necessary to vertically prestress the lower height columns so as to reconcile the differential deflections of columns in close proximity with the post tensioning of the shorter column simulating the weight to be added on to adjacent, higher columns. 抗側(cè)向荷載的結(jié)構(gòu)體系 常用的結(jié)構(gòu)體系 若已測出 荷載量達(dá)數(shù)千萬磅重，那么在高層建筑設(shè)計(jì)中就沒有多少可以進(jìn)行極其復(fù)雜的構(gòu)思余地了。 如果忽略一些與建筑材料密切相關(guān)的概念不談，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。 5． 筒中筒結(jié)構(gòu)。而且，就較高的建筑物而言，大多數(shù)都是由交互式構(gòu)件組成三維陳列。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)造出來了，然而，如果沒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。設(shè)計(jì)方法的本質(zhì)貫穿于整個(gè)討論中。 我們可以利用 STRESS， STRUDL 或者其他大量合適的計(jì)算機(jī)程序進(jìn)行結(jié)構(gòu)分析。這種體系以其結(jié)點(diǎn)處鉸接或則接的線性水平構(gòu)件、垂直構(gòu)件和斜撐構(gòu)件而 具特色，它通常與其他體系共同用于較高的建筑，并且作為一種獨(dú)立的體系用在低、中高度的建筑中。 剪力墻 剪力墻在加強(qiáng)結(jié)構(gòu)體系剛性的發(fā)展過程中又前進(jìn)了一步。由于剪力墻寬度狹狹窄受限，所以需要以某種方式加以擴(kuò)大，以便提從所需的抗傾覆能力。這種體系還具有高延性之優(yōu)點(diǎn)，這種特性在強(qiáng)震區(qū)特別重要。由于這些抵抗側(cè)向荷載的柱子差不多都被設(shè)置在整個(gè)系 統(tǒng)的中心，所以整體的慣性得到提高，剛度也是很大的。這種觀念已經(jīng)影響了筒體結(jié)構(gòu)在 60 層以上建筑中的應(yīng)用。但是，作為一個(gè)性價(jià)比較好的結(jié)構(gòu)體系，桁架能充分發(fā)揮它的性能，所以它會(huì)得到設(shè)計(jì)師們持續(xù)的支持。配置第二層柱的目的是增強(qiáng)抗顛覆能力和增大側(cè)移剛度。在支撐筒中，剪切構(gòu)件的偏角和對(duì)角線的軸心變形有關(guān)，而彎曲構(gòu)件的偏角則與柱子的軸心壓縮和延伸有關(guān)。這很容易去理解，內(nèi)筒可以看成是一個(gè)支撐（或者說是剪切剛性的）筒，而外筒可以看成是一個(gè)結(jié)構(gòu)（或者說是剪切彈性的）筒。在核心交互式結(jié)構(gòu)中，內(nèi)筒是一個(gè)支撐結(jié)構(gòu)，外筒沒有任何剪切剛度，而且兩種結(jié)構(gòu)體系能通過一個(gè)空間結(jié)構(gòu)或“帽”式結(jié)構(gòu)共同起作用。 把內(nèi)外筒相連接的空間結(jié)構(gòu)、懸臂梁或桁架經(jīng)常遵照一些規(guī)范來布置。 在短方向上內(nèi)筒被支撐起來，但是在長方向上沒有剪切剛度。 在建筑的底部布置了一個(gè)相似的空間桁 架結(jié)構(gòu)。一些單個(gè)的筒高于建筑一點(diǎn)或很多是很常見的。這些柱子在 50 層的時(shí)候和 100 層的時(shí)候的變形是不一樣的，位于這兩種體系之間接近于邊緣的那些柱需要使這種不均勻的變形得