Wind loading - FRP onion dome 1

I would say it is much more likely that wind blowing up and over the top of the dome (which acts like an airfoil) created a low pressure zone which lifted and deflected the fiberglass.

Engineers,
Following up on the excellent response from cvg.....my question is now in regard to method for repair of the fiberglass panels of the wind-damaged onion skin dome. Please refer to the attached PDF for photographs. Is it feasible to repair the gaps between the panels in place? or... doest the entire dome need to be brought to the ground and repaired? I am leaning toward taking the entire dome down so that sealant can be applied from the top side of the panels, between the repaired gaps. Any ideas on what type of sealant to specify? Thank you for the assistance.
-jimjxs263

I'm not much of a fiberglass expert, but I doubt that wind has much to do with it. Wind might cause flexing, but the fiberglass would return to shape once the wind stops blowing. It is probably more about ageing, deterioration with UV exposure, and normal thermal issues. Fiberglass boats are all in one piece, not bolted together, so don't have this type separation issues. For repair, I would try to consult one of the manufacturers who make these things.

Looks like a very cheap, very jury-rigged piece of junk installation from a shoddy builder.

You've got your onion domes held on to a cantilevered angle iron spanning the cross-wise gaps across the rafters, then a single bolt (3/8 maybe ?) through the end of a (un-pressure-treated) junk 2x4 clamping (trying to clamp actually) the end-grain of the 2x2 (with some washers and some without) into a second angle iron on top of a stack of 2x4's to build a "bridge" up to the next level.

If ANY of that is in the builder's or architect's original drawings something is wrong. Get the architect AND the onion supplier back to the roof and get an idea of what THEY think they wanted installed. Immediately.

To fix: replace the angle iron (which itself doesn't look like it is tied down to anything!) checked for capacity against earthquake, snow, and wind uplift. AND wind "sidelift" around the dome. "Up" is probably much less that "out" (away from centerline) because the domes are not spherical, but have a nice sideways profile. That sideways wind loading will also tend to "balloon or split the seams sideways - which is what you are seeing.

Plan on adding a corrosion-resistant (stainless ?) steel backing plate to BOTH sides of every seam. What you would be doing with that is clamping the two plastic flanges together firmly. Then, you need to clamp the domes DOWN to the "bridge" structure that is clamped to the attic beams. Somewhere up there is something strong that won't blow away. You just need to find that "something" and attach the bottom of the domes to that "something" .

To further strengthen the onion joints - AFTER you unbolt each joint to add the reinforced backing plates - squeeze a long (continuous) bead of two-part, slow setting epoxy between the onion flanges.

Then, as you clamp the two backing plates with the bolts, the epoxy will both seal the gap against incidental water intrusion - though probably not completely block it - it will double the thickness of the effective FRP flange by gluing the two separate flanges into one.