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Re: Repair of Aluminum Trusses

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Well, don't heat straighten that Aluminum, you're likely to lose the temper - and that's where 60+% of the strength is. Welding is scary prospect - shop welding Al is dicey enough, field welding even moreso. Even the best TIG operator will get inclusions. Do you have any idea what grade and temper you're dealing with? If you don't, the first thing you should do is find out. Some common grades have ultimate stresses within 5 or 10% of yield, so there may be unseen damage in the members...ditto for any existing welded connections.

I'm probably in the minority, but for the most part I think welding of aluminum should be limited to bike frames, where the number of people killed when it fails will most likely be one (two if you count tandems), and the precipitating event is usually significant enough to kill the rider(s) regardless of the structural failure. I much prefer bolts and rivets, thankyouverymuch.

Jordan

Gary wrote:

A few days ago I went to view a pipe bridge which spanned over a
road.  It was a box truss fabricated from aluminum.  A dump truck
driver tried to drive under it with the box still up.  As a result of
the collision, several members have been bent or broken.  The chord
members have been bent as much as 15" out of alignment over a length
of 20'-0".  The diagonals have been bent or broken.

Although I have designed aluminum members before, I have never dealt
with a repair job.  Is it advisable to replace the bent members by
welding in new members or by trying to straighten them?  My gut
instinct is to weld in new members but I would appreciate comments
from list members who have more experience with aluminum design and
fabrication.  Photos available on request.

Thanks,
Gary


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