Flush end plate with minor axis moments.

[malikasal]

i have a flush end plate connection with M22 (Minor axis moment) with M33 and axial loads, AISC Design guide 4 only deals with major axis moment, does anyone have any idea about the effect of m22 on the connection???



“If you don't build your dream someone will hire you to help build theirs.”

Tony A. Gaskins Jr.

 

[KootK]

I don't know of any published example of this. Here's what I'd try:

1) Design for each moment independently. Make sure you're good there.
2) Dream up some equilibrium satisfying solution for the biaxial case and use your best judgement to work your way through it.

What are the magnitudes of the two moments? Can you provide a sketch?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[malikasal]

Thank you kootk.

i have Axial = 50KN , M33= 90KN.m , M22: 30KN.m .

What i did is a assumed that M22 will behave as a couple force system at 1/4 and 3/4 of the flange width, forcing the plate to bend between the flange and the interior bolt, i didn't account for and interaction between M22 and m33 because the failure path for prying caused by M33 and P is not the same as the bending failure path caused by the M22.

feel free to comment on my assumptions i could really use another engineer opinion.
i attached the detail.




“If you don't build your dream someone will hire you to help build theirs.”

Tony A. Gaskins Jr.

 

[KootK]

Thanks for the sketch Malikasal. It's a neat problem.

I'm surprised by your choice of stiffener location. I would have thought it advantageous to move them further from the flanges, allowing the bolts to be closer to the flanges and allowing the stiffeners to provide more effective stiffening to the inner bolt lines.

The way that I see it, under biaxial bending, there will be a bolt pair that receives tension from both major and minor axis bending simultaneously. In that respect, at least, interaction must be considered.

I'm also generally skeptical regarding your quarter point couple assumption for M22. It puts half of your bolts in compression under M22 alone when I'm fairly certain that all of your bolts would be in tension. [pre][/pre] I'd make your couple be from the centre of the section to somewhere near the flange tips.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[KootK]

Could you put bolts outside the flanges if you wanted to? It would make for cheaper construction and simpler design.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[KootK]

Or could you use standard flange / web plates as you would in a common beam splice?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[JoshPlumSE]

I might resolve the weak axis moment as a force couple between bolt lines. Then I've got a conservative tension force induced in the bolts from weak axis moment.

Then convert that to an equivalent axial force in the tension flange. Then use the AISC design guide procedure for considering axial forces in this type of connection.

Not a particular rigorous design procedure. But, it is rational and conservative.

I agree with KootK that your stiffener placement seems odd. I've seen the stiffener between bolts or on the other side of the tension bolts.

 

[KootK]

I'm now in favour of Josh's design method. Love it.

Why is there an impetus to assume that the resisting lever arm for the weak axis is the distance between bolt lines? That seems altogether arbitrary to me as there is no reason to expect the centre of compression to be at the bolt line.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[malikasal]

Kootk: the connection has to be flushed because of arch reasons, that is why i went with the option of flush end plate.

as i discussed in my previous post i assumed that m22 will cause bending in the plate between the flange and the bolt so i used a stiffener in that location, i have no issues regarding the area under the tension bolts because according to prying calculation the plate thickness is adequate.

in my point of view the effect of m22 will be at the flanges , that is why i went with couple force at each flange.

JoshPlum : i am ok with assuming the couple force between the bolt lines, it is not that far from my assumptions, but i can only treat it as an additional axial when designing the bolts, but when it comes to the plate i cannot just assume that it will cause a simple prying as if it was a pure axial , M22 will behave in a way that will try to bend the plate near the flanges (At least this is what i think will happen).



“If you don't build your dream someone will hire you to help build theirs.”

Tony A. Gaskins Jr.

 

[JoshPlumSE]

Typically with Bolted End Plate moment connections, the connection capacity based on the tension side. Either the yielding the of the plate, or the failure of the bolts in tension.

I tend to think that the primary behavior in this connection will be strong axis moment. And, that whatever forces I calculate for weak axis behavior are merely going to aggravate an existing strong axis failure mode.

Now, the design procedure I suggest is really just an idea that came into my brain upon reading your post. So, I make no claims that it is completely thorough. You should definitely add additional checks to it if you feel it necessary.

I believe what you are saying is that it is possible for the connection to fail more like a baseplate (where you get yielding on the compression side on the plate) if the combination of axial compression and weak axis bending is significant. Not sure if I fully agree with that argument for a beam to column connection. But, it is a valid argument and I get where you're coming from.