Effects of the Orientation of the Principal axis of stiffness on the dynamic response of a slender square building

Abstract

The dynamic response of tall slender buildings is dominated by vortex shedding-induced forces. For a building of square cross-section the highest across-wind forces result for an incident wind direction approximately normal to the building face. For conventional buildings, the axes of principal stiffness are aligned normal to the building faces and this results in uncoupled response in the across-wind (lift) and along-wind (drag) directions. Experiments have shown that there are distinct advantages in organizing the structural system to have principal axes of stiffness which are aligned along the diagonals. Data are presented to illustrate this effect. This misalignment of the principal axes of stiffness with the direction of maximum vortex shedding-induced excitation results in a significant reduction in the dynamic response. The difficulties of achieving this configuration of the structural system are not major ones. Examples of how this may be achieved are discussed.