The multi-stage process of windward wall pressure admittance

This paper describes an investigation of the admittance processes for point and area averaged pressures on the windward walls of low-rise buildings. The idea that the admittance process for area pressures involves two-stages was investigated through an experimental study on a 1:50 scale model of the TTU test building. Experimental results presented in the form of admittance functions for point and area-averaged pressures at several locations on the windward wall show that point and area pressures exhibit different high frequency attenuation characteristics. In particular, the cut-off frequencies are distinctly different and area pressures are attenuated more than point pressures. It is shown that point pressure admittance, which is the first stage of area pressure admittance, is associated with the pressure field in front of the building and therefore the corresponding cut-off frequency relates to the size of the windward wall represented by the frontal wall area. Further attenuation observed for area pressures is due to the filtering effects of the integration process over the averaging area alone, as explained by lattice structure theory. Consequently, the cut-off frequency corresponding to the second stage corresponds to the size of the averaging area. It is also shown that attenuation levels are dependent upon the location on the wall and equations for predicting point and area pressure admittance functions are offered. Furthermore, it is demonstrated that building internal pressures are closely related to the area pressures over the extent of the opening and not with some point pressure at the opening as has been assumed in a number of studies in the past.