Retired) wrote that it did not seem many years ago that codes neglected negative pressure on roofs entirely, and they were still not fully satisfactory. The Paper was, therefore, very welcome.
61.Planning authorities should consider the effect of new buildings on the wind pressures upon existing structures. As stated, large suction forces were created on the lee of a bell tower and those were probably covered in design by other conditions of suction. It was the large pressures on the windward side which were not allowed for. For example, in the case of a 30" roof, the lee slope suction changed, at one point, from -0.55 to f0.9 on the windward side of a tower when built against the leeward side of the building.
62.Obstructions did not always act as expected. High hedges were used in the south of France to protect buildings from the mistral. Prof. Haddon had found, from models, that a 10-ft-high wall, 60 ft to windward of a 20-ft-high shed with a 30" slope roof, would change the average pressure on the windward slope from about -0.05 to -b 0.3, while with a diagonal wind, the peak suction could be increased to -3.0.
63.Results vary with different investigators: since velocity profile has a large effect on low slope roofs, height-breadth ratio is important, and if the model is not mounted on the tunnel floor, circulation might take place round the model increasing suction. In Table 10, were the results, which appeared high, given a 'factor of safety', or were the models not mounted upon the floor of a closed wind tunnel?
64.A rectangular prismatic shed with axial wind and side doors open near the windward end might have an internal pressure of -0.8, while rearward external pressure was only -0.
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