experimental high resolution analysis of the pressure
TRANSCRIPT
Cook, N. J. (1985). The Designer’s Guide To Wind Loading Of Building-Structures - Part1. Butterworths (for) Building Research Establishment, Department of the Environment, London.
Holmes, J. D. (1997, November). Equivalent time averaging in wind engineering. Journal of Wind Engineering and Industrial Aerodynamics 72, 411–419.
Lawson, T. (1980). Wind effect on buildings, Volume 1: Design applications. London: Applied Science Publishers
Lawson, T. V. (1976, January). The design of cladding. Building and Environment 11 (1), 37–38.
Lin, J. and D. Surry (1998). The variation of peak loads with tributary area near corners on flat low building roofs. Journal of Wind Engineering and Industrial Aerodynamics 77, 185–196
Surry, D. and T. Stathopoulos (1978). An experimental approach to the economical measurement of spatially-averaged wind loads. Journal of Wind Engineering and Industrial Aerodynamics 2 (4), 385–397.
Doctoral Programme in Mechanical Engineering
Experimental high resolution analysis of the pressure peaks on a building scale model façades
Doctoral Thesis of Luca Amerio – Supervisor Prof. Alberto Zasso, co-supervisor Dr. Andrew Allsop XXX Cycle, Dynamics and vibration of mechanical systems and vehicles
Objectives
Results
MeccPhD
Doctoral Programme in Mechanical Engineering
Programme Coordinator prof. Daniele Rocchi
Department of Mechanical Engineering
Via La Masa 1
20156 Milano
info and contact
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During wind tunnel cladding tests, pressure time histories are recorded in several points across the building surface. The design value, however, needs to be representative of the area-averaged value and should be purged by the contribution of localized phenomena. Lawson in (Lawson, 1976) and (Lawson, 1980) has suggested to obtain the correct area-averaged pressure filtering the local pressure using a moving average filter with a span equal to T=KL/V. This equation is commonly known as the “TVL formula”. This approach has benchmarked to assess its validity in computing area-averaged-equivalent results.
Despite being an established technique, wind tunnel testing results are still affected by a certain degree of uncertainty. During a typical wind tunnel cladding test, the pressure is measured in a limited set of discrete points and is then extrapolated on the remaining surface. In the present thesis work we investigated the space-time distribution of peak suction events occurring on the surface of a wind tunnel scale model in order to understand the best technique to evaluate the design value for cladding elements.
The results highlighted the presence of strong concentrated pressure spikes that does not obey the TVL formula prediction mixed with weaker, but more spread, pressure peaks. The two phenomena are not always clearly distinguishable in the time-domain. This proved how any time-filtering technique should be used with extreme caution.
A high-resolution space-time survey of the pressure fields acting on the surface of a high-rise building scale model has been performed. The results highlighted a poor correlation between the duration and the size of suction peak events, undermining the existing state-of-the-art methodology. A comparison between the real area averaged value and the one estimated with current techniques allowed to find the best value for the K parameter. An alternative cheap experimental solution has been proposed improving the precision of the area-averaged design value estimation and overcoming the need of an analytical solution to the problem.
Example of short-duration pressure spike
A study of the distribution of the K parameter of the TVL formula showed that its value strongly depends on the position in which the pressure is recorded. For windward measurements the value is close to the value of 1 prescribed by Holmes, while for leeward measurement this is close to the 4.5 value prescribed by Cook and Lawson. This suggests that, when a time-filtering technique is adopted, the filtering span should not be constant for all the pressure taps.
To overcome the difficulties in the analytical evaluation of area-averaged design pressure using single point measurement, a new experimental methodology has been proposed. The new measurement device is composed of a rigid porous panel enclosing an empty cavity inside which the area-averaged pressure is evaluated. The results have been beyond the expectations, with the pressure inside the cavity performing extremely well in estimating the area-averaged pressure on the porous surface, completely overcoming the need of an analytical formulation of an equivalent time-filter.
PDF of the K parameter of the TVL formula for different exposures
A prototype of the new experimental device
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