Bracing for Dual Systems

[jenofstructures]

Hello fellow engineers

I would like to ask, when modeling ETABS, how can you tell the program to analyze a building in Steel eccentrically braced?

Because when I run an analysis on the program, ETABS just stated that the building is just special moment frame and not a braced frame

in addition, do I need to do some thing in the model so that ETABS will compute a structure as bracings?

Thank you


Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds

 

[BAretired]

jen,

I can honestly say that I do not have the faintest idea of what you just asked.

I would like to ask, when modeling ETABS, how can you tell the program to analyze a building in Steel eccentrically braced?

Even if I had any understanding of ETABS, which I do not, I would not understand your question.

Your last two statements are equally dumbfounding.

I believe that you are a person who should not be using computers in analysing engineering problems because I get the impression that you do not know what you are doing.

If I am wrong, then perhaps I am getting too old to understand the modern way of looking at structures.

BA

 

[ToadJones]

BA-
Im glad you spoke. ( I was afraid to say anything lest I have dhengr sit me down..kidding)

I was trying to think of how I could relate this to STAAD and how I could "make STAAD realize what I wanted"

 

[BAretired]

Toad,

I sincerely hope I am wrong. I am hoping that jenofstructures is using computer-speak which, presumably, the younger generation understands. I certainly don't understand it but I am waiting to hear what it all means. And, by the way, Toad, I don't know anything about STAAD either.

Maybe it is time for a few words from dhengr.

BA

 

[ToadJones]

NO!
I can't take it. I'm going to bed!

I use STAAD a lot and I am probably a part of that younger group. STAAD outputs some version of what I input. It doesn't know if it is a car frame, a building frame or a picture frame.

I also hope it is a communication error we are dealing with.

No offense meant to anyone.
Ill be happy to help if I can.

 

[BAretired]

Well, folks...Toad has gone to bed...I bet he sleeps on a lily pad somewhere on the pond, croaking to his fellow toads. That leaves us to ponder the problem amongst ourselves without Toad assistance. Perhaps we need the intervention of someone so powerful, so knowledgable and so wise, someone who could sort this thing out once and for all...I know...dhengr!!!

Let's hear it for the KING!!!

BA

 

[dhengr]

Boy, oh boy, now even BA is funnin me!? You actually only have to capitalize the first letter of my title, not all four letters, when you address me.

Amen...., and peace sisters and brothers. Is that enough? That’s about all I can muster, and it seems to keep me out of trouble too. Finally, it certainly is more expeditious than what I have been doing.

On the other hand, I wonder if this doesn’t make my case (our case, two of us). Putting computer programs before a good sound understanding of the structural fundamentals, seems a very dangerous recipe to me. Now, if we dig out the cook books (I mean the latest AISC manuals) lets whip us up a building.

I mean no disrespect Jen, but you happen to have walked into a little three man tiff about computer use, or probably more accurately the three of us happen to walk into your thread, with our tiff in hand.

Jen... can you draw us a sketch of a few bays, and a few levels, of your eccentrically braced frame, and tell us about how you think it works to brace the bldg? Some approx. dimensions, loads, etc. would be helpful too. It seems to me that you have to know about how this structure works or you won’t know how to model it, whatever FEA program or frame program you are using. And, this is about what Toad said in his last post, you tell the program what to do by the way you model your bldg., and that better darn well represent the way you want the bldg. to act. Or else it’s just the old GIGO. Your model must show it’s an eccentrically braced frame, then the computer will give you the forces, moment, shears, etc. on that frame. The program doesn’t care what you call the frame and it won’t tell you what kind of frame it is, the codes make some of those distinctions based on experience, testing, new framing methods, etc.

BA.... Your and my first cut at this problem would be the cantilever method, exactly the method we were trying to sell on that truss without any diags. in the center panel. Except the center panel area on an eccentrically braced frame acts complex enough that even you and I would want a computer program to analyze that area. You’re an hour earlier than I am, turn out the lights when you leave.

 

[jenofstructures]

ETABS manually calculate base shear based from the Response modification factor that you will be putting for the "define static load case". But of course you know that the base shear is not only based from the R as describe by the ASCE 7-05 table 12.2-1, but also based from the importance factor, its total weight and so on since you are already using STAAD and other software for some time now.

You see, my design is not permitted to have only special steel frame (according again to the ASCE 7-05) since it surpassed the limitation of only 160ft. So I used the Dual Systems as prescribed by the table and put bracing in it (since I said its a special steel concentrically braced frames)

But when I run the program and check its "steel check" (its part of the ETABS too) the comment says the building is a "special steel frame". So even I put some bracing there, the program is still computing the whole building as "special steel frame" and not a dual system. That is why I am asking here if there's some method or input to use so that the ETABS will finally analyze the building as a dual system.

Maybe I am just using these software for 2 years now, but I know how to check if the ETABS is computing it correctly. (At least I know GIGO and also RIRO if your in Brit). Another, is that it is my first time to use ETABS for steel framing since I'm only using it for concrete design, while I am using STAAD for steel. The reason why I am asking here, because I know that there is SOMETHING WRONG.

Another sir, I believe that this site was created also for those people who wants to learn from other "experienced" professionals.








Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds

 

[rowingengineer]

thread802-237349

I believe you are posting in the wrong forum, such that a few of my colleges would not have any idea of what you are talking about, mainly because of the language e-tabs and similar programs use. maybe best reviewing the above post and if you have not defined your system this way ask your question in the Computers and Structures: ETABS Forum.

ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION.”

 

[dhengr]

Jen:
This should most certainly be a place for younger engineers to come for advice in furthering their abilities and knowledge about our profession. And, there are some mighty sharp and experienced people here willing to offer help. But, one hopes that they come with ‘the horse before the cart’ and not with the ‘cart before the horse’ so to speak. Because we should not be teaching basic structural concepts here, that should be gotten at the Uni. or by self study so it really sinks in. And, that they ask their question in the clearest possible way, maybe with sketches, etc. If you’ve been using ETABS for two years, that is two more than I have, I’ve never used it.

One of the sharp people understood your question, and rowingengineer’s link would seem to answer your questions and mine; that is, that ‘dual system’ has a special meaning in the way ETABS works and a switch to turn it on and off, or some such, and then you input to the program accordingly, whatever that is. My take on your question was the same as ATOOMUS’ in the link, just release the columns which were not part of some bracing system, and go to it.

Here again, the bldg. codes come into play, not the exact computer program being used, don’t they? They might tell you which various bracing systems can be used together, and under what conditions; as a function of the different bracing system’s characteristics and compatibility in the same bldg., or put some limitations on what each can do. You people who work in earthquake country are far smarter on this than I am.

 

[jenofstructures]

@rowingengineer, thanks for the link....before posting question, I usually search for it in the whole site. But my search yesterday returns to zero so I made a new thread regarding the topic. Sorry if I posted it in a wrong thread, it is because I think that some of us have no time visiting some threads that is why they tend to overlook some questions there.





Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds

 

[jenofstructures]

and another, ETABS is not part of our curriculum in college. Trainings and seminars for this software did not cover much of it programs and sometimes if the it is not a hands-on you can't absorb it much.

I therefore conclude that RESPECT is not varies directly with age or how many years are you in the business, it actually varies from how you do to make this PROFESSION a better field to live in

 

[BAretired]

jen,

I agree with your last statement about respect. Truce?

BA