Gust Factors, Turbulence Intensities, Roughness Lengths, and Wind Direction Factors of Typhoon Winds in the Philippines

The exposure of a location against winds in the wind design provisions from the National Structural Code of the Philippines is mainly dependent on the topography and the degree of vegetation and urbanization. The wind exposure includes the vertical wind profile, the gust factors, and angles of approach. The current code provisions on the parameters for wind exposure are mainly dependent on surface roughness, which has been derived from steady wind conditions. However, winds from typhoons, the extreme winds being designed against, are, in fact, unsteady winds. The current code provisions also cover only area-based exposure, which assumes that wind exposure is constant. The provisions do not cover feature-based wind exposure, where winds can vary over short distances depending on the placement of the buildings and the angle of approach. To evaluate the exposure parameters at these conditions, two typhoon events are simulated using an unsteady-state CFD analysis. Wind exposure for typhoon winds reveals higher local gusts factors, which are related to the direction of the local wind and change in elevation. The upper limit of the surface roughness is determined by the building density and average roof height of the buildings, while its variation is dependent on the wind flow channeling, separation, and reattachment.