Wind Loads on Tall Building Structures / Building Motion Studies

Video of an aeroelastic model

Introduction

In modern building design it is now an important consideration to think about the effect wind induced motion towards tall, slender, flexible, and light-weight buildings, and the human perception of building motion.

It is important that all building structures with a height to breadth ratio of 5 or more be designed using dynamic analysis as per requirements of The Australian and New Zealand Wind Loading Standard, AS/NZS 1170.2:2011. A wind tunnel study can be used to accurately estimate the dynamic wind loads which means there is potential for considerable savings in the cost of the structure and rationalisation of the structure.

Wind tunnel modelling technique is also necessary to analyse wind loads of structures that are taller than 200m or with a natural frequency less than 0.2Hz as per the requirements of The Australian and New Zealand Wind Loading Standard, AS/NZS 1170.2:2011.

Methodology

Wind-induced base moments for the design of the structural frame can be measured using an aeroelastic test rig or a high-frequency base balance rig. Translational vibrations can be determined and assessed against various comfort criteria using this study. This study also allows to determine how any interference effects from nearby buildings can be identified and solved in order to alleviate any problems.

The high-frequency base balance technique can be applied to tall buildings and offers advantages to structural engineers. The advantages it offers to engineers is that they can easily update the results in case there is a change in the building’s stiffness, mass or natural frequency. The great thing about this technique is that it allows them to update the results promptly and have confidence in the accuracy of the results. Windtech Consultants use the modal analysis technique when using this setup. The great thing about this technique is that it allows for an analysis of wind tunnel results for buildings that have complex 3D coupled mode shapes. The effect of close natural frequencies between the modes of vibrations can be an issue but Windtech have developed a technique to account for such an effect.

The effect of rigid linkage on the load transfer between the two towers can be determined by a technique devised by Windtech which also allows them to determine appropriate load cases. This technique allows them to accurately determine where there is a rigid link between separate tower buildings so the rigid linkage effect can be determined.

Two leading wind tunnel laboratories have confirmed Windtech’s wind tunnel data for structural loads on tall buildings.