Re: Storm Damage : Wed Jan 04, 2012 10:17 pm
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D.D. wrote: With all these changes that seemed to have happened (enclosed stadium, then non-enclosed, the enclosed again; steelwork originally designed for cladding then downgraded so it's not only to discover that we do need cladding after all), I am wondering whether all things have been factored into the equation or things have been altered without the knock-on effects being considered. Would the roof have been damaged if it hadn't been for the exposed corners allowing the wind to get into the ground and up and below the roofing for example? For months I have expressed concerns about what I saw as some very shoddy designs. Sadly it would appear I was justified in those concerns. What is going to happen if the entire roof is condemned as unsafe because, to me, there is no possible way any of it can be seen as safe now? Dave you might be coming to this from the wrong angle so to speak The roof that has been damaged is in the South west corner which is fully cladded. This was because the wind was coming from the south west. As such the majority of the wind would hit the cladding and be stopped from travelling into the stadium. Consequently the seats in the south west corner would be a wind free area. However above them on the roof it was blowing a gale. The consequence of this would be that you would have fast travelling air over the roof and relatively static air in the south west corner. Fast travelling air is at a lower pressure than static air. The static air being at a higher pressure would create lift, as it would be trying to equalise pressure with the fast travelling air. Its easy to recreate the actual lift effect using a piece of A4 paper. Simply put the top side below your bottom lip and blow hard. You will notice that the paper rises, which is somewhat counter intuitive. This effect is essentially what allows aircraft to fly. As by creating a curved upper surface and a flat lower surface you force the upper air to travel faster because it has to travel further. Once the aircraft reaches a sufficient speed, the lifting forces are great enough to lift an aircraft off the ground and make it fly. Now in the unclad sections of the stadium, the air is free to move below and above the roof without hindrance. consequently we would see a lower level of lifting pressure on the roof. Therefore by cladding the rest of the stadium, we are putting the rest of the roof under greater lifting stress. This may therefore see the roof being damaged on windy days in other parts of the stadium. It also begs the question if someone miscalculated and fitted the South stand roof to the same standard as the other stands. Being open, the other stands would not need the level of bracing as the enclosed South stand. Coincidentally if you have walked around the stadium you will notice that it seems very windy, far more windy than when in the open near Tesco's. I suspect this is a consequence of the stadium being curved on the outside. As i mentioned earlier a curved surface forces air to move faster when compared to a straight surface. However curved surfaces do reduce the amount of force created by the wind against the actual structure itself. In essence the stadium is more aerodynamic than your box type structure. For anyone who wants to learn a bit about why the wind can cause a roof to be blown off, look up Bernoullis principle, or just check out the link on force below. You may also like to read up about fluid dynamics. http://en.wikipedia.org/wiki/Lift_%28force%29 |
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D.D. wrote: With all these changes that seemed to have happened (enclosed stadium, then non-enclosed, the enclosed again; steelwork originally designed for cladding then downgraded so it's not only to discover that we do need cladding after all), I am wondering whether all things have been factored into the equation or things have been altered without the knock-on effects being considered. Would the roof have been damaged if it hadn't been for the exposed corners allowing the wind to get into the ground and up and below the roofing for example? For months I have expressed concerns about what I saw as some very shoddy designs. Sadly it would appear I was justified in those concerns. What is going to happen if the entire roof is condemned as unsafe because, to me, there is no possible way any of it can be seen as safe now? Dave you might be coming to this from the wrong angle so to speak The roof that has been damaged is in the South west corner which is fully cladded. This was because the wind was coming from the south west. As such the majority of the wind would hit the cladding and be stopped from travelling into the stadium. Consequently the seats in the south west corner would be a wind free area. However above them on the roof it was blowing a gale. The consequence of this would be that you would have fast travelling air over the roof and relatively static air in the south west corner. Fast travelling air is at a lower pressure than static air. The static air being at a higher pressure would create lift, as it would be trying to equalise pressure with the fast travelling air. Its easy to recreate the actual lift effect using a piece of A4 paper. Simply put the top side below your bottom lip and blow hard. You will notice that the paper rises, which is somewhat counter intuitive. This effect is essentially what allows aircraft to fly. As by creating a curved upper surface and a flat lower surface you force the upper air to travel faster because it has to travel further. Once the aircraft reaches a sufficient speed, the lifting forces are great enough to lift an aircraft off the ground and make it fly. Now in the unclad sections of the stadium, the air is free to move below and above the roof without hindrance. consequently we would see a lower level of lifting pressure on the roof. Therefore by cladding the rest of the stadium, we are putting the rest of the roof under greater lifting stress. This may therefore see the roof being damaged on windy days in other parts of the stadium. It also begs the question if someone miscalculated and fitted the South stand roof to the same standard as the other stands. Being open, the other stands would not need the level of bracing as the enclosed South stand. Coincidentally if you have walked around the stadium you will notice that it seems very windy, far more windy than when in the open near Tesco's. I suspect this is a consequence of the stadium being curved on the outside. As i mentioned earlier a curved surface forces air to move faster when compared to a straight surface. However curved surfaces do reduce the amount of force created by the wind against the actual structure itself. In essence the stadium is more aerodynamic than your box type structure. For anyone who wants to learn a bit about why the wind can cause a roof to be blown off, look up Bernoullis principle, or just check out the link on force below. You may also like to read up about fluid dynamics. http://en.wikipedia.org/wiki/Lift_%28force%29 |
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