Structural Optimization to Limit Natural Periodsby Richard A. Henige, Jr., LeMessurier Consultants, Cambridge, United States,
Abstract: It is necessary to limit the natural periods of some structures to control their response to dynamic loads. Floor systems with natural periods greater than approximately 0.15 seconds may experience unacceptable vibration if used for dancing or aerobic exercise activities. Similarly, the critical period at which wind vortices are shed from a tall building is dependent on design wind velocity and building shape and width. The natural period of a tall building should be less than this critical period to avoid resonance with the forces induced by vortex shedding. Structural engineers are faced with the problem of how to efficiently distribute material throughout such structures to limit their periods and dynamic response. The Principle of Virtual Work is a simple but powerful tool which estimates the contribution of each member to the response of a structure. This principle may be used to optimize a structure by distributing material so that the virtual work density is the same for all members. This optimization method is simple enough for manual analysis and provides a designer with insight into the behavior of a structure. The Virtual Work Optimization procedure may also be estimated and integrated with analysis programs to optimize large, complex structures.
Subject Headings: Dynamic loads | Building design | Structural analysis | Dynamic response | Wind forces | Vortex shedding | Construction materials
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