Structural Wind Tunnel Testing
Whether you’re a structural engineer, an architect, a planner or a construction engineer, Vipac’s Wind Tunnel Testing can help you determine the following dynamic properties of the building:
- Overturning moments
- Equivalent static load on towers.
Watch Vipac being interviewed by Channel 9 News here, highlighting the importance of Wind Tunnel Testing. Vipac’s prediction process considers all wind directions, thereby providing all of the wind load values needed to inform the structural design and potentially save significant structural engineering costs.
Combined with the data provided by structural engineers, our Wind Tunnel Test results offer a thorough understanding of the building’s dynamic behaviour, including any acceleration experienced by occupants caused by the building moving in the wind. Preventing this perceived motion is important both for code compliance and occupant comfort.
Results from our Wind Tunnel Tests enable us to assess whether additional dynamic controls, such as a damping system, is required. If so, we can offer services for dynamic control design and for monitoring the building in operation.
Why does it move?
There are two main types of wind forces on a structure – the first is the force measured along the wind direction and the second is its cross-wind response. Problems can occur if the regular frequency of the cross-wind vortex shedding coincides with the natural frequency of the structure.
Contrary to popular belief, wind can be problematic at low speeds (5 – 20 m/s) for this very reason. Testament to this is the famous failure at the Tacoma Narrows Bridge in Washington D.C. at only 18 m/s. In non-cyclonic areas, ‘design’ wind speeds are around 40m/s and in cyclonic or typhoon areas up at about 60m/s.
The Australian wind codes are some of the most developed in the world. They set guidelines by which buildings may be judged as candidates deserving ‘dynamic analysis’ or special wind tunnel testing. For these wind sensitive structures, it is an Australian code requirement that analysis be carried out to check for excessive response or for incipient instability. We can conduct wind tunnel testing on these buildings using a High Frequency Force Balance technique.
Approved by the ASCE and the AWES, the Force Balance Method measures the forces and the moments that are experienced by the building. This data is combined with the structural properties of the building to determine the dynamic response (motion) of the structure when subjected to these incoming forces.
Calculation results are floor-by-floor predicted forces, moments and building motions under service and ultimate wind conditions. Reworking after changes to the building properties is quick since the outside envelope of the building remains constant.