single angle prying action 3

[GBMRAO]

Dear Fellow friends,

Do you know any way of checking a single angle for prying action for uplift. Any spreadsheet or design example. i have a very small angle that i need to check for uplift and prying action.

I am tiring to use AISC but its mainly giving for T shape. I can use double angles and reduce the load to 3.7 kips and verify but still need any help or guide lines.

thanks and happy new year.

 

[DaveAtkins]

The problem with trying to use a single angle in uplift is the load will be eccentric from the resistance, causing a moment that must be resolved somehow. Part of the moment is taken by the angle leg through prying action, but the rest of the moment must be resisted by the member attached to the angle.

DaveAtkins

 

[JoelTXCive]

Here is some background info....

AISC had an article on it in Steelwise a few years ago.

 

[rb1957]

this is the usual way (I've seen) ...

another day in paradise, or is paradise one day closer ?

 

[KootK]

Thanks for the paper JoelTX, good stuff.

 

[JoshPlumSE]

JoelTXCive -

Great reference. I'm not sure that I've seen that before. I'm going to look at it more closely to see how it compares to what I've done in the past.

 

[JoelTXCive]

No problem!

Check out this guy's videos too. They look to be done by a mechanical engineer. He sets up the statics for all sorts of different loading directions:

https://www.youtube.com/user/stressebookllc/videos

Lastly, PCI has a brief discussion on it in their design manual...see attached..

 

[Settingsun]

Is it usual to push all the way to tensile strength rather than yield strength for plastic hinge formation? Joel's paper uses tensile strength.

 

[JoshPlumSE]

Is it usual to push all the way to tensile strength rather than yield strength for plastic hinge formation? Joel's paper uses tensile strength.

Remember that we're checking the bolts themselves. They're almost always checked vs ultimate tensile strength. There are checks you can do on the leg bending of the angle as well. Which are based on the angle's yield strength. But, that's a different (albeit related) topic.

 

[Settingsun]

Josh, still not clear to me. You say angle leg bending is based on yield strength but Joel's article takes leg capacity as when the angle hits ultimate tensile stress at two locations (angle corner and at the bolt), across the entire section thickness (Fu * plastic modulus).

 

[Settingsun]

Joel posted two articles. I'm referring to the first, from Steelwise.

Wouldn't having ultimate tensile stress at the two critical sections mean that yield stress is exceeded the full length from angle corner to bolt? The Steelwise method adds two mirrored cantilever models though with different effective width because of the bolt hole, so you'd get slightly less than Fu between the two critical sections as the hole reduction isn't applicable there.

 

[JoelTXCive]

Is it usual to push all the way to tensile strength rather than yield strength for plastic hinge formation? Joel's paper uses tensile strength.

I am re-reading the AISC article with the steel manual in front of me and I came across this in steel manual... I guess tensile strength is applicable in this scenario?

 

[Settingsun]

Thanks, Joel. Sounds as though it may have been Fy in older manuals. I wonder how much deformation occurs at Fu stress level. I don't have access to either of the referenced articles.

 

[GBMRAO]

Thanks to everyone for all your suggestions and the articles for references.
i will check the angle for prying action. and its supporting member.

 

[rb1957]

I would never have thought of a minimum thickness to prevent prying ? as though heavy angles don't pry ??

another day in paradise, or is paradise one day closer ?

 

[dauwerda]

rb1957, the key for the thicker, more rigid angles not to produce prying action lays in this statement: "the deformation of the connected tee flange or angle leg is assumed to be in double curvature." That is, the load is applied in such a way that the angle can't simply rotate about the toe of the angle. The prying action is happening due to local yielding of the leg (in double curvature) and the thicker angle prevents that yielding.
Here is the figure that the statement refers to:

 

[JoelTXCive]

What is fascinating to me is that in this instance prying action INCREASES the angle's capacity because the means of support change. As a plastic hinge forms at the angle's corner; you go from a cantilevered leg to a simply supported condition.

 

[rb1957]

prying force is, IMHO, "just" the static free body reaction. Thin or thick the reaction is the same, although the stresses in the flange are lower for the thick flange, of course.

The alternative is to say the fastener takes the offset moment in bending, again consider the free body (the direct load and reaction are off-set. And it could be that thick flanges have heavier fasteners (more capable of carrying the bending).

Now thin Tee flanges would limit prying, as the flange yields (although would that remove the pre-yield prying ? (I don't think so)

another day in paradise, or is paradise one day closer ?

 

[dik]

As attached... Need SMath...


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dauwerda]

AISC's definition requires deformation, their definition is as follows:
"Prying action is a phenomenon (in bolted construction only, and only in connections with tensile bolt forces) whereby the deformation of a connecting element under tensile force increases the tensile force in the bolt above that due to the direct tensile force alone."