BRE DG520 PDF

INTRODUCTION

The wind flow around buildings can have a major impact on pedestrian comfort and safety. A pleasant (and safe) pedestrian-level wind environment is a crucial requirement of good building design. If this is ignored, it can lead to financial or amenity loss due to people avoiding windy areas or, in the most extreme cases, can lead to serious injury or even loss of life if people are blown over by the wind^[1]. The pedestrian-level wind environment is governed by the layout and massing of buildings. Tall buildings can cause strong downward currents of air and are a major cause of wind problems at pedestrian level.

In the UK, the issue of unpleasant pedestrian-level wind speeds started to come to prominence during the 1960s when, due to advances in structural engineering and changes in urban planning, increasing numbers of tower blocks were built. These were often located in city centres and surrounded by open public-realm areas used for seating, markets, restaurants, gardens, etc. However, all too often the planned attraction of these areas was nullified by exposure to strong winds deflected downwards by the nearby tall buildings.

At about the same time, wind tunnels that accurately modelled the earth's atmospheric boundary layer (boundary-layer wind tunnels) were starting to be used for investigating building aerodynamics at model scale. By the 1970s, these wind tunnels, pioneered in the UK by BRE, were routinely used for measuring pedestrian-level wind speeds. At the present time, the wind tunnel is still the principal tool for quantitative measurement of wind speeds around buildings, although computational techniques have improved to the point where they can provide a viable alternative in some circumstances. However, the wind speed alone is not sufficient to determine whether the outdoor environment is suitable for the chosen pedestrian activity; the wind speeds must be assessed against defined comfort criteria using probabilistic methods. Unlike other wind effects, such as wind loading or pollutant dispersal, there are no national codes, standards or statutory requirements in the UK for pedestrian wind comfort. There are, however, established criteria for assessing the comfort and safety of pedestrians, and these are discussed in this Digest.