Horizontal Braces taking vertical load...

[mfstructural]

I am modeling a steel platform and have horizontal steel braces at two levels. The platform is 35' tall. I am specifying a one way load, but when I go to the load screen, it looks like the load per square foot is being applied to the horizontal brace. I tried to inactivate the horizontal braces for gravity load cases, but I get a warning about member end forces. Is there a way I can apply the gravity load without the braces taking it?

Also, on another note, I have vertical bracing in the same platform and when I inactivated all the bracing for gravity loads I got an warning about some instability at a joint and that a weak spring was added. The joint had a column running through it with two pinned beams framing into it and a brace. The brace was inactive for gravity and the beams are pinned to the column, so there shouldnt' be an instablity. The only thing I can think of is that the loading on the platform is unsymmetrical and is probably causing some leaning.

 

[mfstructural]

Anyone? Really struggling with this one.

 

[PAstructural08]

What program are you using?

When you say 'gravity load' do you mean selfweight of the structure or do you mean just vertical load?

 

[mfstructural]

Hey there, I mean all vertical load. What I did was create a group with all the members excluding the horz braces. I did some hand calcs to check my numbers I think it's ok.
I have another question about modeling for vertical loads and not including braces though.

I have two platforms, both unsymmetric in shape and loading (there is equipment and things like that). When I inactivate all the braces I get an instability. I just wanted to see if there is a way around this? Or in this case the bracing will be forced to carry some of the load because of the unbalanced load that caused the platform to lean.

 

[PAstructural08]

You are getting a instability because the entire structure is unstable; assuming you have simple shear connections and the bases of your columns pinned. You should keep the vertical braces active in the model. If the braces are simple x-bracing and are connected at a column and beam intersection node you will get minor load in them.

In reality you will get some load in your braces due how the brace is connected to a gusset which in turn is connected to the column and beam.

 

[mfstructural]

Right, I saw a discussion on this a couple months back on this forum...People argued for both ways. Inactivating the braces (even though your braces will take some load no matter what) or those that just left the braces and let it behave how it wanted. Both work, I'll just leave them and check the columns by hand. But yes that's what I have. Two levels with simple shear connections from both directions framing into the columns and braces/gussets. I attached a picture for info.

Thanks