Torsional Moments of Tall Buildings with various Planform Shapes

Abstract

Mean and fluctuating torsional moments of tall buildings with various planform shapes have been measured in wind tunnel boundary layer flows for suburban terrain. The cause of the high torsional moments are seen to be the combination of a sharp-edged separation from a building edge providing a significant moment arm, and the building surface in the wake producing complementary areas with low pressures. The torsional moments are hence normalised in coefficient form with the maximum projected width and the maximum projected area of the building. These torsional moment coefficients are shown to be related to the ratio, f, of minimum projected width to the maximum projected width of the building planform in two categories: the slab-like structures (f<0.3) and the non-slab type (f>0.3). For non-slab structures, the torsional moment coefficients are shown to vary with building planform shapes within the range of values for circular and rectangular planform to those for triangular planform. For slab type structures, the mean and fluctuating torsional moment coefficients are approximately 0.1 and 0.07 respectively.