STAAD QUESTION

[StructuralPoke]

I've got a STAAD model that's a 3-story simple moment frame. See the screen cap attached.

Let's look at the column on the right. I've specified that I need to keep deflection to h/500 as follows

DJ1 1 MEMB 1 TO 3
 DJ2 4 MEMB 1 TO 3
 DFF 500 MEMB 1 TO 9

It is my understanding that's how it's supposed to be specified. Node 4 is 425" up, so 425"/500 = .85" max deflection. However, I get node 4 moving ~2.5" and the unity check says it is deflection controlled but passes. What am I doing wrong here?

STAAD Tech support is being especially slow today for the same question...

 

[TXengrChickPE]

I'm mostly just going to bump this up for you. Hopefully someone else will see it and be able to answer your question. I have never been successful at getting the deflection stuff to work.

 

[kevo_55]

Here's another bump .

Honestly, I'm a RISA guy myself but I'm thinking that your individual member lateral deflection is meeting the L/500 criteria but for whatever reason you don't have the total frame being checked.

Also, I wouldn't pin your end reactions. You'll never get your MF to work for L/500 unless you use a crazy amount of steel.

Just my :2cents:

 

[StructuralPoke]

Here's another bump .
Honestly, I'm a RISA guy myself but I'm thinking that your individual member lateral deflection is meeting the L/500 criteria but for whatever reason you don't have the total frame being checked.

Also, I wouldn't pin your end reactions. You'll never get your MF to work for L/500 unless you use a crazy amount of steel.

Just my :2cents:

Oh yeah -- pinned bases are helping to kill this frame, but the sizes of steel I have should be adequate enough and in the scope of the project aren't out of line.

bump bump bump. I've got the question in to Staad's help line and they are being painfully slow in responding. Nothing like pushing up towards the end of a project and needing an answer and the response taking longer than you hope...

 

[kevo_55]

^^ What was the deal? Is STAAD able to take care of a frame lateral deflection limit?

Inquiring minds want to know.

 

[StructuralPoke]

^^ What was the deal? Is STAAD able to take care of a frame lateral deflection limit?
Inquiring minds want to know.

No response yet. If I let STAAD design the members (instead of analyzing my sizes), I get a deflection of ~4.4". I honestly don't know what is correct. I don't think I believe the deflection -- I believe the unity check more, but geez! Something is just completely wrong.

 

[TXengrChickPE]

Have you tried making one of those pins a fixed connection? That, or stick a knee brace in there somewhere.

 

[StructuralPoke]

Have you tried making one of those pins a fixed connection? That, or stick a knee brace in there somewhere.

The architecture won't allow a brace. We'd prefer to not fix the base (yet at least...) but it may come to that.

 

[TXengrChickPE]

You are going to HAVE to fix at LEAST one base. The way it is right now, it isn't stable.

 

[StructuralPoke]

pinned base moment frames are stable - just much more flexible

 

[StructuralPoke]

nm - double post

 

[MA_PE]

don't lie. you've got a support in the Z-direction somewhere or that'll just flop right over. opcorn:

 

[StructuralPoke]

don't lie. you've got a support in the Z-direction somewhere or that'll just flop right over. opcorn:

It's a STAAD "plane" model. Or yes, it would sit-and-spin w/o a z-support.

 

[TXengrChickPE]

OK. I rarely do anything that isn't "3D", so I've probably never used a "plane" model.

Regardless, I think fixing one support location will give you a better idea of how the members will work. As it is, most of your deflection is due to the pin rotation, not the member bending.

 

[MA_PE]

It's a STAAD "plane" model. Or yes, it would sit-and-spin w/o a z-support.

I figured you had that covered and was really just busting your chops.

Of course with iso picture and release specification in the 3 moment directions, it wasn't apparent to me that it was a PLANE model.

OK. I rarely do anything that isn't "3D", so I've probably never used a "plane" model.
Regardless, I think fixing one support location will give you a better idea of how the members will work. As it is, most of your deflection is due to the pin rotation, not the member bending.

I respectfully disagree. The pinned bases will certianly contribute to the flexibility but I believe that the framed connections are all full moment connections, so the caculated displacement is entirely dependent on the member stiffness/bending.

 

[StructuralPoke]

I respectfully disagree. The pinned bases will certianly contribute to the flexibility but I believe that the framed connections are all full moment connections, so the caculated displacement is entirely dependent on the member stiffness/bending.

:true:

And no worries about busting my chops. I know STAAD isn't typical for structural design and didn't know if you knew the program or not. I wish we had RISA or (even better) something like etabs. I've only used a trial of etabs, but I liked it... Probably not any easier to use in the long run, but I liked what I was doing...

 

[MA_PE]

SP:

We used to use STAAD for basic analysis here. We found some problems with some of the fancier functions years ago and switched to RISA for frames. Most of our important analysis is done using FEM with NASTRAN or ABAQUS.

 

[Vinsanity]

SP:We used to use STAAD for basic analysis here. We found some problems with some of the fancier functions years ago and switched to RISA for frames. Most of our important analysis is done using FEM with NASTRAN or ABAQUS.

based on your model, and your editor you have specified that all your deflections are limited to this l//500, but this is way too conservative, your structure is not ductile, steel is usually ductile 180 to 360 would be fine, as for my judgement, you dont have to specfiy it to be L/500, just let if deflect based on loads applied on it. design it if it can satistfy deflection requirements from L/180 to L/360. Hope this helps.

 

[StructuralPoke]

based on your model, and your editor you have specified that all your deflections are limited to this l//500, but this is way too conservative, your structure is not ductile, steel is usually ductile 180 to 360 would be fine, as for my judgement, you dont have to specfiy it to be L/500, just let if deflect based on loads applied on it. design it if it can satistfy deflection requirements from L/180 to L/360. Hope this helps.

h/500 is for the brick veneer. Sorry -- I never gave the full story I guess.

 

[StructuralPoke]

SP:We used to use STAAD for basic analysis here. We found some problems with some of the fancier functions years ago and switched to RISA for frames. Most of our important analysis is done using FEM with NASTRAN or ABAQUS.

I'm leaning more and more to not using STAAD anymore, but it's what we've got. Well, I take that back, we do have RAM Advanse, but that program's learning curve is just a bit too steep. If I ever had any free time (heh) I'd try to figure it out...