# STAAD QUESTION



## StructuralPoke (Mar 5, 2009)

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...


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## TXengrChickPE (Mar 5, 2009)

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.


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## kevo_55 (Mar 5, 2009)

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:


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## StructuralPoke (Mar 5, 2009)

kevo_55 said:


> 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.
> ...


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...


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## kevo_55 (Mar 5, 2009)

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

Inquiring minds want to know.


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## StructuralPoke (Mar 5, 2009)

kevo_55 said:


> ^^ 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.


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## TXengrChickPE (Mar 5, 2009)

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


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## StructuralPoke (Mar 5, 2009)

TXengrChickPE said:


> 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.


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## TXengrChickPE (Mar 5, 2009)

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


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## StructuralPoke (Mar 5, 2009)

pinned base moment frames are stable - just much more flexible


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## StructuralPoke (Mar 5, 2009)

nm - double post


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## MA_PE (Mar 5, 2009)

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


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## StructuralPoke (Mar 5, 2009)

MA_PE said:


> 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.


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## TXengrChickPE (Mar 5, 2009)

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.


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## MA_PE (Mar 5, 2009)

StructuralPoke said:


> 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.



TXengrChickPE said:


> 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.


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## StructuralPoke (Mar 5, 2009)

MA_PE said:


> 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...


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## MA_PE (Mar 5, 2009)

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.


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## Vinsanity (Mar 5, 2009)

MA_PE said:


> 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.


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## StructuralPoke (Mar 5, 2009)

Vinsanity said:


> 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.


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## StructuralPoke (Mar 5, 2009)

MA_PE said:


> 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...


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## kevo_55 (Mar 7, 2009)

^^ Well, if you can sweet talk you boss into getting a few seats of RISA 3D I think you'll find that you can get MUCH more done.

Then again, that won't be cheap. But, it would be cheaper than getting a single seat of NASTRAN or ABAQUS.


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## Vinsanity (Mar 10, 2009)

Brick veneer? so in that case you can model it as an eight noded element a good model can by a 1x1x1 block and all you can get from STAAD are element stresses and deflection of course, based from this ouptput you can design the reinforcements needed, this the most exact method for this type of structure, I know this because I have studied this in MS courses and some seminars with STAAD and SAp 2000 and ETABS.

You can also model it as a shear wall type of structure.


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## StructuralPoke (Mar 11, 2009)

Vinsanity said:


> Brick veneer? so in that case you can model it as an eight noded element a good model can by a 1x1x1 block and all you can get from STAAD are element stresses and deflection of course, based from this ouptput you can design the reinforcements needed, this the most exact method for this type of structure, I know this because I have studied this in MS courses and some seminars with STAAD and SAp 2000 and ETABS.
> You can also model it as a shear wall type of structure.


It's just veneer - the inherent stiffness is neglected in favor of the steel frame doing all the work. The brick is simply held to the stud walls w/ brick ties. Nothing to transfer load to the brick or any way for the brick to resist the load.

And I can get the deflections of the frame out of STAAD -- it's the deflection-limiting criteria that is not working.

Still no answer from STAAD by the way...


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## kevo_55 (Mar 11, 2009)

Vinsanity said:


> Brick veneer? so in that case you can model it as an eight noded element a good model can by a 1x1x1 block and all you can get from STAAD are element stresses and deflection of course, based from this ouptput you can design the reinforcements needed, this the most exact method for this type of structure, I know this because I have studied this in MS courses and some seminars with STAAD and SAp 2000 and ETABS.
> You can also model it as a shear wall type of structure.


Vinsanity,

Why would you model the brick (cladding) with your building frame? The cladding is responsible to resist it's own loads, transfer them to the MFRS, and to be able to move with the building.

I have always seen that the gladding dead weight added to the MFRS and then neglected in all other calculations. I have never seen it modeled with the building to give it more "stiffness."


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## Vinsanity (Mar 11, 2009)

kevo,

no i'd didnt model the cladding on the building frame. i was thinking that the structure described here is made of bricks.

Struct...,

you might use the command in STAAD, Story Drift, with this command you can see the output based on limiting deflection that you are talking about, the story drift is calculated in very story of the building at a specific node.

hope this helps.


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## dastuff (Mar 11, 2009)

Risa has a STAAD convertor. Why don't you attach the file (minus relevant info for security sake, although a 2d frame I wouldn't consider any kind of security risk  ) have someone import it into RISA and give it a shot. 

I use staad (mainly for aluminum) and risa for everyone else, but haven't ever been very concerned w/ deflection limits sorry.


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## dastuff (Mar 11, 2009)

Although that will all change when RISA gets an AL check at the end of the year...

Then I'm going to give STAAD a quick kick in the pants out the window.... Freaking Fortran based systems... The amount of times a model of mine has failed because the stupid ";" was grayed out is incalculable. And do you know how hard that is to catch....

Really... Freaking.... Hard...


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## StructuralPoke (Mar 11, 2009)

Oh -- the actual check of the frame isn't the problem -- just STAAD's bastardized deflection check. It used to work, I swear...

Didn't know about "Story Drift" command. I shall try that in future models...


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## Vinsanity (Mar 11, 2009)

StructuralPoke said:


> Oh -- the actual check of the frame isn't the problem -- just STAAD's bastardized deflection check. It used to work, I swear...
> Didn't know about "Story Drift" command. I shall try that in future models...



Struct Poke,

this is an example of story drift output and it is close to your l/500 something that you specified, please see attached file.

hope this helps.


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## StructuralPoke (Mar 12, 2009)

Vinsanity said:


> Struct Poke,
> this is an example of story drift output and it is close to your l/500 something that you specified, please see attached file.
> 
> hope this helps.


That's quite a handy command. Thanks for that!


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## Vinsanity (Mar 12, 2009)

StructuralPoke said:


> That's quite a handy command. Thanks for that!



THis a video animation of 4 story building with lateral deflection captured from ETABS on its mode shape 3. This one of the projects Ive been working. Check this link.

http://www.youtube.com/watch?v=UidQcRh991Q


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