The variability of low building wind loads due to surrounding obstructions

Abstract

Most low buildings are sutuated in urban areas in the midst of neighbouring buildings, trees, fences, billboards and parks. These cluttered, undisciplined surroundings can have as much effect on the wind loads as do the details of the geometry of the building itself and often even more so.Studies in recent years have focussed primarily on the influence of turbulent boundary layer winds in open terrain relatively free of surrounding obstructions in which building geometry is a dominant factor. In this study, a new approach is proposed to study the interference of local obstructions on low building wind loads from a statistical point of view through wind tunnel experiments. An experimental wind tunnel simulation with randomized wind load parameters, especially random surroundings, is proposed. The generated data base, together with data from other relevant studies, can form the basis for a reliability analysis to predict wind loads for design codes.This paper outlines this approach and reports the exploratory tests on the effects of surroundings on area and local wind loads. The results show that wind loads in a realistic environment do not always follow the basic wind load characteristics of an isolated building because of interference by neighbouring buildings. The variation of wind loads with wind direction is less severe while the variability due to building location is large. Since expected values are considerably less than the ‘worst case’ data from isolated building tests, these results raise questions concerning the traditional approaches to choosing design loads.