Wind Engineering: Vibration and Dynamic Response Analysis on Structures

27 August 2018

An entire science has built up around this single doctrine. In short, when the wind blows, structures are influenced by its force. Trees sway in the wind because of this principle. If they were hard but inelastic, then they’d break as soon as the first heavy gust blew. It’s the same for man-made structures. Steel and other structural alloys are hard, yet they’re also simultaneously flexible.

The Science behind Wind Engineering

This isn’t meteorology speak or some debate about climate change. No, these are behavioural analysis patterns, which extrapolate wind loads and shear forces, as created by the air currents that live in and around our tallest structures. The buildings rise above urban areas, they’re exposed to nature’s naked energies, and they bend. They sway and oscillate. Dynamic response analysis is employed here so that these oscillations remain safely managed. Otherwise, well, the effects of a particularly powerful storm, one carrying gale force winds, could overcome a structure’s inbuilt dampening mechanism.

Vibration and Dynamic Response Analysis

On structures, this scientifically oriented set of engineering disciplines are used to model wind loads and their effects on a particular structure. Unfortunately, Mother Nature has made sure wind forces are chaotic and unpredictable. If this were an air conditioning system, travelling air force calculations would be a breeze (no pun intended). But chaos science, which is a real topic, determines the wind’s impact. However, engineers can call upon the services of dynamic response analysis tools. With this science, they mathematically model the kinetics of this airborne force. Differential equations, past meteorological records, and modal analysis techniques, all of these variables and constants combine to generate a conceptual model.

Defining the Primary Engineering Variables

Putting the complex mathematics to the side, let’s determine the key variables that impact this field of science. First of all, the structure has a natural sway frequency, which is measured according to a time-based study. The rigidity of the steel beams and their heat treated ductility combine with architectural elements to further refine this sway rate. Elsewhere in this equation, differential equations represent a conceptual model of the wind’s energies, including their vectors and oscillating frequencies. The task now is to see whether the modelled structure, which is however many metres tall, has enough inbuilt dampening power to offset a peak wind load.

There are many forces in play around a tall structure. Seismic vibrations cause sway and massive vibrations. Elsewhere, perhaps at a higher altitude, strong winds put stress on high-rise structures. Heat treated structural steels are designed to offset such dynamic forces. However, should the math indicate otherwise, a supplementary force dampening mechanism may be required.

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