【正文】 g .1 represents the average unit weight of a conventional frame with increasing numbers of stories. Curve B represents the average steel weight if the frame is protected from all lateral loads. The gap between the upper boundary and the lower boundary represents the premium for height for the traditional columnandbeam engineers have developed structural systems with a view to eliminating this premium. Systems in steel. Tall buildings in steel developed as a result of several types of structural innovations. The innovations have been applied to the construction of both office and apartment buildings. Frame with rigid belt trusses. In order to tie the exterior columns of a frame structure to the interior vertical trusses,a system of rigid belt trusses at midheight and at the top of the building may be used. A good example of this system is the First Wisconsin Bank Building(1974) in Milwaukee. Framed tube. The maximum efficiency of the total structure of a tall building, for both strength and stiffness,to resist wind load can be achieved only if all column element can be connected to each other in such a way that the entire building acts as a hollow tube or rigid box in projecting out of the ground. This particular structural system was probably used for the first time in the 43story reinforced concrete DeWitt Chestnut Apartment Building in Chicago. The most significant use of this system is in the twin structural steel towers of the 110story World Trade Center building in New York Columndiagonal truss tube. The exterior columns of a building can be spaced reasonably far apart and yet be made to work together as a tube by connecting them with diagonal members interesting at the centre line of the columns and beams. This simple yet extremely efficient system was used for the first time on the John Hancock Centre in Chicago, using as much steel as is normally needed for a traditional 40story building. Bundled tube. With the continuing need for larger and taller buildings, the framed tube or the columndiagonal truss tube may be used in a bundled form to create larger tube envelopes while maintaining high efficiency. The 110story Sears Roebuck Headquarters Building in Chicago has nine tube, bundled at the base of the building in three rows. Some of these individual tubes terminate at different heights of the building, demonstrating the unlimited architectural possibilities of this latest structural concept. The Sears tower, at a height of 1450 ft(442m), is the world’s tallest building. Stressedskin tube system. The tube structural system was developed for improving the resistance to lateral forces (wind and earthquake) and the control of drift (lateral building movement ) in highrise building. The stressedskin tube takes the tube system a step further. The development of the stressedskin tube utilizes the fa?ade of the building as a structural element which acts with the framed tube, thus providing an efficient way of resisting lateral loads in highrise buildings, and resulting in costeffective columnfree interior space with a high ratio of to gross floor area. Because of the contribution of the stressedskin fa?ade, the framed members of the tube require less mass, and are thus lighter and less expensive. All the typical columns and spandrel beams are standard rolled shapes,minimizing the use and cost of special builtup members. The depth requirement for the perimeter spandrel beams is also reduced, and the need for upset beams above floors, which would encroach on valuable space, is minimized. The structural system has been used on the 54story One Mellon Bank Center in Pittburgh. Systems in concrete. While tall buildings constructed of steel had an early start, development of tall buildings of reinforced concrete progressed at a fast enough rate to provide a petitive chanllenge to structural steel systems for both office and apartment buildings. Framed tube. As discussed above, the first framed tube concept for tall buildings was used for the 43story DeWitt Chestnut Apartment Building. In this building ,exterior columns were spaced at () centers, and interior columns were used as needed to support the 8in . thick (20m) flatplate concrete slabs. Tube