Blowing the house down

Pioneering Canadian research into wind effects on low-rise buildings will use novel wind simulators being developed by Cambridge Consultants.

A new University of Western Ontario research centre – known as ‘The Three Little Pigs’ facility – will, for the first time, permit the controlled application of realistic wind loads to full-scale houses and other low rise buildings.

The research is expected to lead to more formalised techniques for weather-proofing low-rise buildings which – unlike their high-rise counterparts – are ‘non engineered’ and tend to use vaguely-defined structures.

“No one has attempted real-world wind simulation on this scale before, so much of the instrumentation will be developed specially for the application”, says Eric Wilkinson, head of Cambridge Consultants’ Products and Systems Business Unit. “One of the key challenges is the creation of a custom control system architecture to handle the large number of interconnected wind simulators, and deliver the real-time performance required.”

Realistic wind simulation will be provided by pressure boxes that are able to apply positive or negative wind forces over a +5 to -20 kilopascals range (5 kilopascals equates to a weight of around 500kg for every square metre of roof). This is combined with a fast-acting valve system that allows the simulated wind pressure to reverse direction at rates up to seven times a second.

The University of Western Ontario’s deep understanding of wind patterns will use this technology to create and apply realistic ‘wind profiles’ onto full-size structures – beginning with a full-size two-storey, pitched-roof dwelling. Surrounding the space for test structures is a reaction frame, which provides mountings for the pressure boxes.

All this equipment will be housed in a hangar-style building large enough to accommodate structures of up to three storeys, and which slides on rails to expose structures to the natural environment.

Cambridge Consultants won the development contract because of its expertise in this area, gained from work in the late 1980s on the UK Building Research Establishment (BRE) ‘Brerwulf’ project. At that time, working to a BRE design concept, the consultancy developed a large fan-driven wind simulation panel – measuring around 3 metres square – which provided a mechanism to test roofing systems and cladding.

The same basic wind generation technology – which uses high-performance fans – will be used in ‘The Three Little Pigs’ pressure boxes. However, for this application, a modular range of box sizes is being developed to enable complex building shapes to be handled.

Each box will additionally feature a sophisticated control and networking system that will allow the complex time- and spatially-varying wind effects of the real world to be realistically applied. This scheme will allow up to 100 interconnected pressure boxes to be controlled in real-time, supporting system sizes large enough to test complete low-rise buildings.

The leading wind-engineering consultancy RWDI-Anemos – whose Director Nicholas Cook was one of the designers of the seminal Brerwulf project – is helping Cambridge Consultants to develop the new pressure boxes and control scheme, by providing expert local advice on wind loading effects.

Paul Freathy, Managing Director of RWDI-Anemos, comments: “Damage to non-engineered buildings remains a significant financial burden on the economy. Although individual incidents are often minor, insurance statistics show that weather damage averages out to about £700 million per year in the UK alone.”

Cambridge Consultants will deliver the wind simulation pressure boxes in mid 2005.