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RE: Single or Double angle bending member

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I see that torsion must be checked in the boundary stability of the lintel angle, but for the design of the angle, hopefully the vertical leg will not have much differential rotation. And the differential rotation is what will induce the torsional shear stresses. I can see there being bending in the vertical leg from it resisting torsion, the same type of bending induced in the horizontal leg from transferring the weight of the block to the vertical leg.

Maybe there is a small amount of rotation difference of the angle between anchor locations. But I don't think you have to design for the full torsion, only that which overcomes the normal friction between the block and the horizontal leg.

How many loose brick lintel angles have you ever seen? If torsion was such a large factor, wouldn't the angles twist right out? I'm not saying disregard it as a stability check, but I'm not sure if it is a big design issue. I wouldn't know where to start designing an angle for torsion either.

Will

>From: "Michael L. Hemstad" <hemstad.ml(--nospam--at)tkda.com>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: <seaint(--nospam--at)seaint.org>
>Subject: Single or Double angle bending member
>Date: Thu, 28 Apr 2005 13:29:10 -0500
>
>The distinguishing feature of a double angle is that the two pieces
>counter each other's tendency to rotate torsionally.
>
>Let me add a distinction here:  in designing a single angle member, it's
>not enough to consider LTB per se.  You also have to consider torsion.
>An unbraced wideflange beam centrally loaded will fail in LTB, but has
>no torsion.  A single angle will have torsion unless you take some very
>extreme steps to eliminate it.  You have to factor that torsion into all
>your analyses.  It really complicates a LTB analysis if you have torsion
>to start with.
>
>So, two angles back to back, connected every so often, and centrally
>loaded, don't have torsion.  Two angles toe to toe don't either, if they
>are connected adequately.  I don't have a quantitative answer for what
>"adequately" is, but to me it would involve bars about as thick as the
>angle, welded all the way across both horizontal legs, every couple of
>feet.  Just having a block wall between the angles doesn't cut it;
>putting expansion anchors though the angles into the block doesn't
>either, because that system is neither strong enough or stiff enough.
>Maybe a series of horizontal through bolts would be adequate if it
>pinched the angles tightly against the block.
>
>Assuming the angles are connected adequately, now you can analyze the
>vertical legs for LTB failure.
>
>Charley Hamilton was asking the right questions, in my opinion.  Bill,
>does your MathCad worksheet take the actual torsion into account?
>That's what's always scared me about single-angle lintels.
>
>Mike Hemstad, P.E.
>TKDA
>St. Paul, Minnesota
>
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