Early on Christmas Day, we had high winds in Seattle. Steady 30mph winds, but gusts to over 50mph. And if there is anything that can wreak havoc with Christmas light displays, it’s wind. We build our display expecting this type of weather, though.
We did not escape unaffected.
The wind took out the topper on the mega tree. And it didn’t just pop out of its socket.
The wind managed to snap the topper off at the connection with the top of the mega tree.
As is the case with extreme weather, you usually find out where the weakest link in the structure resides.
The topper connected with a PVC 1″-to-3/4″ male adapter which was screwed into a 3/4″ female connection at the top of the tree. This has always been the weakest connection point, however it has held up in 30mph winds. It’s been the same one in use for the past 3 years.
So, what went wrong? Well, for starters, the adapter could not sustain winds at 50+ mph. To be fair, those winds are atypical and designing the topper for that scenario seemed over-the-top. Ah well, now we know our threshold we should accommodate.
So, knowing this is our weakest point (we have to attach the tree topper in some manner), how can we connect the tree topper in a way that minimizes the stress on the connection point? Easy — we spread the stress.
The adapter threads were the single weak point in the connection. Any force on the topper is transferred to the threaded adapter. The threaded portion of the adapter is approximately 3/4″ in length, and is hollow throughout. Once a strong enough gust hit the topper, the stress point was exceeded in the adapter, and it broke away from the tree.
To counteract this in the future, we need to alleviate the stress that can occur at the adapter. To do this, we want to spread it out — push the stress along other less faulty points in the structure. We can accomplish this by running a metal rod (such as rebar) through the center of the topper and down into the mega tree. We will continue to use a PVC adapter, but by pushing a support bar through the connection, any force on the topper must also extend force on support rebar. Support rebar, anywhere from 36″ to 48″, should extend up into the tree topper and down into the mega tree sufficiently to handle wind gusts in the 50mph range.
Unfortunately, that won’t happen until next year. We had to pull down the topper this year, and it’s been removed from the show. Alas, we’ve learned our lesson this year. Hey, another Christmas gift! 