A Database-Assisted Design Approach for the Assessment of Wind Induced Torsional Effects on Tall Buildings
I Venanzi, William P. Fritz
Structures subjected to wind loads experience torsional moments due to the eccentricity of the time-dependent resultant aerodynamic load with respect to the structures 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. The non-zero distance between the elastic center and the mass center causes coupling of responses in the x and y directions and in torsion. This paper describes the modal analysis of the freely vibrating system, which takes that distance into account, and the dynamic analysis of the system excited by the wind loading, as defined by the simultaneously recorded pressures obtained in the wind tunnel at a large number of taps over the building surface. The analysis yields the requisite wind-induced deflections, velocities, and accelerations of the system via the Database-assisted Design approach. This type of information is used by the structural engineer for serviceability design purposes. Information needed for safety design consists of internal forces and combinations thereof via interaction equations and specified load combinations. The paper includes such information for a select number of members in a 66 story building as a function of various mean recurrence intervals.