Variable Mode Shape High-Frequency Force-Balance

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The serviceability limit state associated with occupant comfort under wind induced lateral and torsional motion is becoming an increasingly important consideration in the design of tall buildings. In some instances, structural modifications required to produce acceptable predicted response characteristics can cost hundreds for thousands of dollars or even millions of dollars. With these kinds of cost at stake it is imperative that predicted response levels be as accurate and reliable as possible. Aeroelastic model tests and high-frequency force-balance tests provide two means of estimating building response to winds. In most instances, aeroelastic model tests are impractical because of the time required to design and construct the models. Results obtained after completion of the normal design process cn produce cotly modificaiton or lively buildings where occupants must endure numerous instance of disturbing motion. Current high-frequency force-balance test can provide results in a fraction of the time required for aeroelastic model tests but incorporate linear mode shapes for sway and a uniform mode shape for torsion. Force-balance tests also do not provide information on possible aeroelastic effects which may increase or decrease loading and response. Research is proposed on second generation high-frequency force-balances and associated instrumentation which would overcome the model shape inaccuracies by allowing modal forces to be determined for various mode shapes. Badic research is also proposed on the influence of building motion on modal forces. The Principal Investigator is well qualified to conduct the research. The research will lead to improved force balance for use by commercial wind tunnel testing laboratories. Use of the improved balances will allow more accurate prediction of wind-induced response for complex structures where torsion is an important consideration and where mode shapes are not linear. Better understanding of aeroelastic effects will provide valuable information on limits to the application and force balance test