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RE: Torsion in Wide Flange Beam
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- Subject: RE: Torsion in Wide Flange Beam
- From: "Rich Lewis" <seaint02(--nospam--at)lewisengineering.com>
- Date: Thu, 26 May 2005 23:19:35 -0500
Thanks for all who responded to this question. I'm still confused. I understand Warren's comment regarding developing the forces in the flange. That was helpful. I still have a hard time picturing a pinned end connection for torsion. ASIC Design Guide 9 shows one, and has the data for designing it. Like Bill Sherman, it seems to me the end needs to be fixed, or ideally should be. I assume the shear connection illustrated in the Design Guide should state that it needs to be designed for both vertical shear and a torsional force couple. If I have a uniform load that is eccentric, and is torsionally pinned at the end, it seems to me the maximum torsion then occurs at the mid span, analogous to a simply supported beam bending moment. But if there is a force couple at the end, then there is a torsional moment at the end, or is it not there? A sum of the forces would say there has to be an end torsion. So, is a torsionally pinned connection one that has torsional restraint, except for warping stresses? I don't understand why the Design Guide calls it "free torsional end condition". To me, that implies zero torsion. Why do all the strength books stop short of illustrating this? Rich -----Original Message----- From: Jones, Mark [mailto:MJones(--nospam--at)ssoe.com] Sent: Wednesday, May 25, 2005 11:55 AM To: seaint(--nospam--at)seaint.org Subject: RE: Torsion in Wide Flange Beam Uniform loads do not produce uniform torsional moments just like they do not produce uniform bending moments. Only a pure moment, either torsional or bending, will produce a uniform moment. You are correct, a uniform load will produce a torsional moment curve just the same as a bending moment curve and point loads will produce linearly varying moments. The parallel between bending and torsional moments hold. Each goes from a load to a shear to a moment. (assuming you don't have pure shears and pure moments.) While we typically think about torsion as just a moment, there is an induced torsional shear. A load inducing a torsion reaches equilibrium similarly to one in bending. Remember that when the load starts it is a pure load resisted by the restraints in the X, Y, Z directions. The moment is then induced INTERNALLY within the member, progressively resisted by the member properties. Assuming you have a bolted framed beam connection, then the load on the beam's flange will be externally resisted by a axial forces in the bolts acting as a couple. If you weld just the web of the beam then the resistance is axial forces in each of the welds. If one connects the flanges of the beam then a fixed (or semi-fixed) end is created and all of the above changes similarly to how a fixed end changes bending reactions. Mark ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ******** ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********
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