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Re: Repair of Aluminum Trusses

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Thanks Christopher.


----- Original Message ----- From: "Christopher Wright" <chrisw(--nospam--at)skypoint.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, March 17, 2005 6:31 PM
Subject: Re: Repair of Aluminum Trusses



On Mar 17, 2005, at 5:24 PM, Paul Feather wrote:

How do welded aluminum structures function? Are the connection capacities half the member strength due to weld zone influence? Are member splices typically over built to compensate?
Welding aluminum is really a different beast, but the weld design methodology is pretty much the same except that the allowable are lower. Much lower. The weld zone partially retempers itself as a result of the weld metal/base metal admixture. 6061-T6 is about the most common wrought structural alloy and it is strengthened by thermal treatment. In the T6 condition the yield strength is about 35 ksi and as welded the yield strength is 17 ksi. The welded strength is a good bit higher than the annealed yield strength, though.

The real tricks with aluminum design is to put welds in low stress areas, or use locally thickened areas called weld lands if your construction permits. There's also the issue of the effect of lower modulus on buckling strength. I've never had occasion to use limit design with aluminum, adn the equipment I get involved with is driven my service loading. It's non-linear and somewhat more susceptible to fatigue than ordinary structural steel becasue the strain levels tend to be higher so local stress concentrations accumulate plastic strain faster. It's not as tough as structural steel, but there's no ductie/brittle transition, either. There are a series of design guides with both working stress and LRFD-type design rules for sale at the Aluminum Association <http://www.aluminum.org/>

The biggest mistake you can make with aluminum is assuming it's just like steel only lighter. I've been involved in a couple of real brou-ha-ha's with some people who thought that.
Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/


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