ABSTRACT
The built-up plate girder scheme for a steel bridge structure, for example, may be economical for continuous spans up to about 800 ft (243.8 m), whereas for spans from 1000 to 1200 ft (305 to 366 m), a truss system may be the best solution. Finally, very large spans in the range of the present maximum of 4200 ft (1281 m) with predictable limits in the range of 10,000 ft (3048 m) would require a totally different system, such as a cable suspension structure, to make the project economically feasible. Similarly, structural engineering of tall buildings requires the use of different systems for different building heights. Each system, therefore, has an economical height range, beyond which a different system is required. The requirements of these systems and their ranges are somewhat imprecise because the demands imposed on the structure signifi cantly infl uence these systems. However, knowledge of different structural systems, their approximate ranges of application, and the premium that would result in extending their range is indispensable for a successful solution of a tall building project because engineers, like other human beings, are creatures of habit with a strong temptation to repeat concepts that were used successfully on earlier, similar projects. This is understandable because not only are the methods of analysis well established for these systems, but it also makes good business sense. Fortunately, in the design of high-rise structures, the engineer is not subject to this boredom and stagnation of using the same idea over and over again. Thanks to the architects for coming up with an array of new forms and daring concepts and to the ever-increasing building heights. The engineering challenge remains well and alive and promises to intensify in the future.
