【正文】 he eccentric braced frame. Again, analysis can be by STRESS, STRUDL, or any one of a series of two –or three dimensional analysis puter programs. And again, centertocenter dimensions are used monly in the preliminary analysis. Shear walls The shear wall is yet another step forward along a progression of everstiffer structural systems. The system is characterized by relatively thin, generally (but not always) concrete elements that provide both structural strength and separation between building functions. In highrise buildings, shear wall systems tend to have a relatively high aspect ratio, that is, their height tends to be large pared to their width. Lacking tension in the foundation system, any structural element is limited in its ability to resist overturning moment by the width of the system and by the gravity load supported by the element. Limited to a narrow overturning, One obvious use of the system, which does have the needed width, is in the exterior walls of building, where the requirement for windows is kept small. Structural steel shear walls, generally stiffened against buckling by a concrete overlay, have found application where shear loads are high. The system, intrinsically more economical than steel bracing, is particularly effective in carrying shear loads down through the taller floors in the areas immediately above grade. The sys tem has the further advantage of having high ductility a feature of particular importance in areas of high seismicity. The analysis of shear wall systems is made plex because of the inevitable presence of large openings through these walls. Preliminary analysis can be by trussanalogy, by the finite element method, or by making use of a proprietary puter program designed to consider the interaction, or coupling, of shear walls. Framed or Braced Tubes Structures The concept of the framed or braced or braced tube erupted into the technology with the IBM Building in Pittsburgh, but was followed immediately with the twin 110story towers of the World Trade Center, New York and a number of other buildings .The system is characterized by three –dimensional frames, braced frames, or shear walls, forming a closed surface more or less cylindrical in nature, but of nearly any plan configuration. Because those columns that resist lateral forces are placed as far as possible from the cancroids of the system, the overall moment of inertia is increased and stiffness is very high. The analysis of tubular structures is done using threedimensional concepts, or by two dimensional analogy, where possible, whichever method is used, it must be capable of accounting for the effects of shear lag. The presence of shear lag, detected first in aircraft structures, is a serious limitation in the stiffness of framed tubes. The concept has limited recent applications of framed tubes to the shear of 60 stories. Designers have developed various techniques for reducing the effects of shear lag, most noticeably the use of belt trusses. This system finds application in buildings perhaps 40stories and higher. However, except for possible aesthetic considerations, belt trusses interfere with nearly every building function associated with the outside wall。 主要的結(jié)構(gòu)工作都集中在結(jié)構(gòu)布置中。事實(shí)上，這 種體系的重要特征就在于它既有堅(jiān)固的一面，也有脆弱的一面。 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。 環(huán)繞著建筑物布置了一個(gè)外筒。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。需要指出的是，如果把外部的柱子看成是一種從“帽”到基礎(chǔ)的直線體系，這將是不合適的；根據(jù)支撐核心的彈性曲線，這些柱子只發(fā)揮了剛度的 15%。 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。 根據(jù)梁的對(duì)比分析，如果平面保持原形（例如：厚樓板），那么外層筒中柱的軸心壓力就會(huì)與中心筒柱的軸心壓力相差甚遠(yuǎn)，而且穩(wěn)定的大于中心筒。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。由于其最佳位置正取決于所提供的桁架的數(shù)量，因此很多研究已經(jīng)試圖完善這些構(gòu)件的位置。設(shè)計(jì)者已經(jīng)開發(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。 在可能的情況