【正文】 that if a concrete rigid frame is designed in the conventional manner , without special care to produce higher ductility , it will not be able to withstand a catastrophic earthquake that can produce forces several times lerger than the code design earthquake forces . therefore , some believe that it may not have additional capacity possessed by steel rigid frames . But modern research and experience has indicated that concrete frames can be designed to be ductile , when sufficient stirrups and joinery reinforcement are designed in to the frame . Modern buildings codes have specifications for the socalled ductile concrete frames . However , at present , these codes often require excessive reinforcement at certain points in the frame so as to cause congestion and result in construction difficulties 。 Even so , concrete frame design can be both effective and economical 。 Structural Systems to resist lateral loads Omitting some concepts that are related strictly to the materials of construction, the most monly used structural systems used in highrise buildings can be categorized as follows: frames. frames, including eccentrically braced frames. walls, including steel plate shear walls. structures. structures. structures. or bundledtube systems. Particularly with the recent trend toward more plex forms, but in response also to the need for increased stiffness to resist the forces from wind and earthquake, most highrise buildings have structural systems built up of binations of frames, braced bents, shear walls, and related systems. Further, for the taller buildings, the majorities are posed of interactive elements in threedimensional arrays. The method of bining these elements is the very essence of the design process for highrise buildings. These binations need evolve in response to environmental, functional, and cost considerations so as to provide efficient structures that provoke the architectural development to new heights. This is not to say that imaginative structural design can create great architecture. To the contrary, many examples of fine architecture have been created with only moderate support from the structural engineer, while only fine structure, not great architecture, can be developed without the genius and the leadership of a talented architect. In any event, the best of both is needed to formulate a truly extraordinary design of a highrise building. Perhaps the most monly used system in lowto mediumrise buildings, the momentresisting frame, is characterized by linear horizontal and vertical members connected essentially rigidly at their joints. Such frames are used as a standalone system or in bination with other systems so as to provide the needed resistance to horizontal loads. In the taller of highrise buildings, the system is likely to be found inappropriate for a standalone system, this because of the difficulty in mobilizing sufficient stiffness under lateral forces. The braced frame, intrinsically stiffer than the moment –resisting frame, finds also greater application to higherrise buildings. The system is characterized by linear horizontal, vertical, and diagonal members, connected simply or rigidly at their joints. It is used monly in conjunction with other systems for taller buildings and as a standalone system in lowto mediumrise buildings. While the use of structural steel in braced frames is mon, concrete frames are more likely to be of the largerscale variety. Of special interest in areas of high seismicity is the use of the 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. 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 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, b