huangyhg

connections for torsion.
i鈥檝e got a situation where i have torsion on an i-beam. at the end of the beams i have simple shear connections (i.e. angles and bolts). what i鈥檓 having a hard time deciding is: what to design the angles for (in terms of the load from torsion; throwing the (block) shear demands aside for a moment). intuitively, you鈥檇 design for a bearing force (tension or compression) on the angle (and the bolts) for the couple created by the torque. but this type of connection is torsionally 鈥減inned鈥?is it not? so, theoretically, it shouldn鈥檛 see any load from the torque. (but it actuality (as we all know) there really isn鈥檛 any such thing as a connection that is perfectly 鈥減inned鈥?or 鈥渞igid鈥?.
thoughts?
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i will be interested to hear some responses to this. i have always wondered how you have a connection that is pinned against torsion. in my mind, i imagine the beam just continually twisting around since the pin (for torsion) offers no rotational restraint (which is what torsion is).
a pinned torsion connection differentiates whether the section is free to warp at the supports, not whether it has any twisting moment. the torsion is still max at the supports and has to go somewhere. it isn't quite analagous to the flexural "pinned" and "fixed" terms we use.
i would try sizing an angle at the top and bottom flange for the torsion moment.
ucfse, when you say "i would try sizing an angle at the top and bottom flange for the torsion moment.", are you saying i should connect to the flanges? this is a beam to beam connection.
3doorsdwn,
virtually all the torsion resistance of an i beam is in the flanges, the web plays very little part. so any connection that does not connect rigidly to the flanges is not a torsion connection.
if you are saying that this is connected to a perpendicular beam then this is a difficult detail. you can either detail it so that there is negligible torsion transferred into the supporting beam, or you can brace the supporting beam (with fly braces e.t.c.)to take any torsion.
a flexible end plate is sometimes used that can transfer torsion (in plane) but is too flexible to transfer out of plane loads.
i would suggest you read the aisc design guide on this as this really is a complex topic.
csd
actually, i have the aisc design guide on this topic and (like most publications) doesn't specifically address this topic (accept to address what constitutes torsionally fixed and trosionally pinned connections (i.e. on p.9 & 107)). i have not addressed tensional connections (in the past) without some type of restraint for the flange (and it appears that that may be necessary for this case; perhaps (since it鈥檚 beam to beam) a full pen weld on each flange may be required).
repost, too many misspellings above:
actually, i have the aisc design guide on this topic and (like most publications) doesn't specifically address this topic (accept to address what constitutes torsionally fixed and torsionally pinned connections (i.e. on p.9 & 107)). i have not addressed torsion connections (in the past) without some type of restraint for the flange (and it appears that that may be necessary for this case; perhaps (since it鈥檚 beam to beam) a full pen weld on each flange may be required).
a lifetime ago, when i worked on nuclear power plant design, we did a lot of study and developed criteria and details for torsional connections.
if the connection is fully fixed, it's easy. if the member is ok, the connection is ok. but for a torsionally pinned connection, you can either check the angles or shear plates for the torsional shear forces or design a special connection. you'll find out pretty quickly that the angles or shear plates have to be very thick to carry any significant torsion. so we would put plates top and bottom with shear tabs on each side of the flange to carry the torsion. the top and bottom plates (only welded to the main member) can develop the couple. not too expensive, but not free either.
you didn't ask, but be sure to get your aisc torsional design guide to analyze the warping stresses on the
jed, i have enercalc for the analysis. when you say you designed for the "torsional shear forces" for simple shear connections (i.e. bolted angles) are you referring to resolving the torque into a couple (with the centroid at the center of the connection)?
i agree with jedclampett. and i think this type of connection can resist the torsion from the supported beam, without putting torsion into the supporting girder (due to the vertical end reaction of the supported beam). the girder will twist a little bit, but not enough to worry about.
i hope i am not muddying the waters.
daveatkins
when i mentioned angles, i was thinking beam to column connection. i suppose i would use plates for beam to beam.
note that torsion doesn't transfer from the twisting beam into it's support as torsion, usually. twisting in the beam usually becomes flexure in the supporting beam or column when it's orthogonal to the twisting beam. you get a concentrated moment into your support.

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