A Database-Assisted Design Approach for the Assessment of Wind Induced Torsional Effects on Tall Buildings

Abstract

Structures subjected to wind loads experience torsional moments due to the eccentricity of the time-dependent resultant aerodynamic load with respect to the structure’s elastic center. We refer to such moments as aerodynamic torsional moments. In structures with significant dynamic response additional torsional moments arise if the center of mass does not coincide with the elastic center. Empirical information on aerodynamic torsional moments was developed from wind tunnel tests on building models by, among others, Greig [8], Lythe and Surry [11], Isyumov and Poole [10] (for results obtained by Isyumov see also [14, pp. 353-355]. Such moments appear to have been a main contributor to the serious damage experienced under strong winds by the 15-story Realty building and the 17-story Meyer-Kyser building in Miami [15]. It appears that the John Hancock Building in Boston has also performed poorly under aerodynamic torsional moments. To our knowledge, the first attempts to develop design criteria on aerodynamic torsional moments were reported in 1939; however, it was not until 1995 that provisions for such effects were included in a U.S. standard [1]. The dynamics associated with aerodynamic torsional moments on tall buildings was studied by Patrickson and Friedmann [12], Foutch and Safak [6], Hart et al., [9]. However, unlike in earthquake engineering, to our knowledge no methods have been developed for calculating windinduced effects on tall buildings, including effects associated with torsional moments due to the distance between the mass and elastic centers, in a manner that can be used confidently in structural design. Ad-hoc wind tunnel studies are therefore routinely being conducted, but to our knowledge they do not account for distance between centers of mass and elastic centers. For the majority of buildings, including very tall buildings, wind tunnel studies are performed on rigid models. Two approaches to performing such studies are available. In the first approach, called the High Frequency Force Balance (HFFB) approach, the wind tunnel operator records the time histories of the base shears and moments for two STRUCTURES 2006