【正文】 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。 that is, one tube could be framed, while the other could be braced. In considering this system, is important to understand clearly the difference between the shear and the flexural ponents of deflection, the terms being taken from beam analogy. In a framed tube, the shear ponent of deflection is associated with the bending deformation of columns and girders (, the webs of the framed tube) while the flexural ponent is associated with the axial shortening and lengthening of columns (, the flanges of the framed tube). In a braced tube, the shear ponent of deflection is associated with the axial deformation of diagonals while the flexural ponent of deflection is associated with the axial shortening and lengthening of columns. Following beam analogy, if plane surfaces remain plane (, the floor slabs),then axial stresses in the columns of the outer tube, being farther form the neutral axis, will be substantially larger than the axial stresses in the inner tube. However, in the tubeintube design, when optimized, the axial stresses in the inner ring of columns may be as high, or