Shear Center Again
Shear Center Again
(OP)
When you design a channel do you load it with the actual loading PLUS a torsional load which equals the actual loading multiplied by an eccentricity of the distance from the center of flange to the shear center?
I've designed many channels without considering this and no other engineers checking my work have mentioned it. I just wanted to get some other opinions.
I've designed many channels without considering this and no other engineers checking my work have mentioned it. I just wanted to get some other opinions.






RE: Shear Center Again
The only time I considered it was when I designed the catwalks for a performing arts center. There I did consider the shear center in how I detailed the catwalks as the major framing beams were channels.
Mike McCann
MMC Engineering
RE: Shear Center Again
As is often the case with torsion, I deal with it through detailing rather than calculation.
Consider two most common situations:
1) Something frames into the side of your channel. Even if it's just a shear tab connection, it probably offers significant torsional restraint to the channel.
2) Something frames over top of your channel. When the channel begins to rotate as a result of the torque, the point of loading will shift towards the heel of the channel flange, much closer to the shear center. Additionaly, if the framing passing above the channel is is welded or bolted to the channel flange, you've got some torsional restraint once again.
RE: Shear Center Again
Sometimes it can be a driving factor in the design.
RE: Shear Center Again
Personally I just frame into back of the web side of the channel every opportunity I get. I am also a fan of using 4-bolt connections at the ends to try give a measure of torsional rigidity to the end connections.
I would echo the previous comments: Avoid it whenever possible, detail it out when it's not, and if you really can't do anything else and (as an impromptu rule of thumb) if the load/capacity ratio is more than .8, include the effects. And if you're loading from above and nothing imparts the (very minimal necessary, refer to AdamP's post) don't forget to check the twisting deflection too... You'd be surprised just how much a channel can twist!
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: Shear Center Again
RE: Shear Center Again
RE: Shear Center Again
I believe this is why most folks get away with not considering the torsion. (As was typed in the vaporized thread: THANKS Moderator for deleting useful info.)
As I typed before also, I find that the deflection is usually what causes the problem for open sections with torsion. For example, consider what happens if a spandrel beam rotates and this translates into additional brick deflection.