Aerodynamic forces on the roofs of low-, mid- and high-rise buildings subject to transient winds

Michael Jesson,Mark Sterling,Chris Letchford,Chris Baker

doi:10.1016/j.jweia.2015.04.020

Michael Jesson, Mark Sterling + Show 2 more

Open Access

https://doi.org/10.1016/j.jweia.2015.04.020

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Abstract

Transient winds, such as thunderstorm downbursts, are the cause of design-load wind speeds in many countries. An understanding of the loading experienced by buildings during a downburst is therefore important to allow well designed and engineered buildings to be constructed. In contrast to boundary layer winds, the maximum wind speed in thunderstorm downbursts occurs as low as zm=30m above the ground, within the range of heights of man-made structures, suggesting that the wind loading will be dependent on the building eaves height relative to zm. In a novel set of experiments, the University of Birmingham Transient Wind Simulator (a 1m diameter impinging jet with aperture control) has been used to simulate a downburst striking buildings of different heights, ranging from below to above zm. Two forms of building have been used – a square-plan, flat-roofed structure, and a rectangular, portal-frame – at three angles (0°, 45° and 90°) relative to the radial wind direction. Pressure coefficients have been calculated (using eaves height velocity) over the roofs of these buildings, and are shown to be of greatest magnitude when the roof is above the region of maximum outflow velocity, with the exception of windward edges perpendicular to the flow, when they are generally greatest for the lowest building heights.

Highlights

Convection in thunderstorm cells can lead to the development of tornadoes or thunderstorm downbursts, i.e., transient wind events which have a short duration but which produce high wind speeds
This paper presents the findings of a research project aimed at quantifying the pressure field on low, mid- and high-rise structures in transient, downburst winds, and how the field varies with building height
Zm lies above the eaves high of low-rise buildings but below that of high-rise buildings, suggesting that there may be a difference in the roof wind loading due to a downburst in each case

Summary

Introduction

Convection in thunderstorm cells can lead to the development of tornadoes or thunderstorm downbursts, i.e., transient wind events which have a short duration but which produce high wind speeds. This paper presents the findings of a research project aimed at quantifying the pressure field on low-, mid- and high-rise structures in transient, downburst winds, and how the field varies with building height It extends the work of Jesson et al (2015) by varying the height of the model buildings subjected to a simulated downburst-type wind. The variation of the pressure field due to the building eaves height relative to zm is measured, and the pressure field due to a downburst elucidated for both lowand high-rise buildings

Experimental setup

Simulated flow field

Building models and pressure measurement

Aerodynamic pressure coefficients

Findings

Conclusions