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#26
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OT Screen cages, was Crawl spaces
On Apr 19, 9:25*am, Richard Casady
wrote: On Sun, 19 Apr 2009 05:36:11 -0700 (PDT), wrote: On Apr 18, 3:08*pm, wrote: On Sat, 18 Apr 2009 11:53:19 -0700 (PDT), wrote: On Apr 18, 12:38*pm, wrote: On Sat, 18 Apr 2009 11:44:05 -0400, "Eisboch" wrote: wrote in message .. . On Sat, 18 Apr 2009 08:02:46 -0400, "Eisboch" wrote: We also had a pool enclosure installed at that house. *By that time the code requirements were for 150 mph winds. It was installed by a reputable and licensed company but "Wilma" still pretty much destroyed it with 120 mph gusts. I was involved in some post mortem inspections of failed screen cages after Charley. It appears the first thing to fail is the cable stay system, then the screen cage just shakes itself apart. I really believe these should be designed more like a bi-plane than a bridge with more cable stays. The forces are more similar. One of the mitigation in the subsequent code was more diagonal bracing in the roof to give them better dimensional stability. I don't know if this is true or not, but it was suggested to me that in hurricanes, it is best to remove or open any doors on the pool enclosures. The screen sections are installed in a manner that is supposed to allow them to "blow out", reducing the surface that the wind can capture and thus reduces the loads on the aluminum frame and braces. *Leaving the doors open allows the wind "pressure" *to equalize within the structure. Eisboch We picked apart 5 failed cages of various vintages and none of them seemed to "blow out" the screen before the structure failed. The only real commonality was in every case there was an apparent failure of the cables in the section that failed first. Once one part fails, the rest comes down fairly fast if the wind keeps blowing. The "flat spline" patio material will hold screen until the screen itself fails. Round spline will pull out but that is not used here except in door and window frames. It is ironic that the old method of through bolting an eye bolt for the cable stay seems more robust than the new style angle corner bracket with 8-10 screws in it. The bracket itself fails. (all of the new cage failures) After this, I did add some additional cable stays to my cage and used the eye bolt method. Wilma didn't hurt it. After Charley we found a 40' mango tree on our cage, the oldest part. |
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