Shear wall for wind etabs analysis 4

[Stuctural100]

Hello

I am trying to check the adequacy of a shear wall for wind load in Etabs.
I have started by tracing my model on a plan from AutoCAD.I then assigned my sections and materials. I have defined the loads including wind. I have assigned a diaghragm to each floor slab and a pier label to each wall. I have released the top of the columns because I do not want them to take any lateral shear.
When I run the analysis, I do not get the SFD and BMD I am expecting for the walls. The highest moments are on the first floor, while I expect them to be highest at base.
Any ideas on what might have gone wrong with the model?

 

[KootK]

Is there a basement modelled? If so then your results probably make sense. Look into the backstay effect: Link.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[StructuralAddict]

Hello KootK. I'd like to say that I am really impressed with your great knowledge in structural engineering. Your answers to all questions imply that you have an excellent experience in the structural engineering field. For me, I am a fresh graduate who strive to become a professional structural engineer. Can you please refer me to the sources that you provided you with such a great knowledge? And what is your advice to fresh graduates like me? Thanks in advance!

 

[jayrod12]

Monir87,

Koot has developed his skills through a combination of a few things. Years of experience being a large part but Koot also has this uncanny desire and interest in structural engineering that makes him excel more than most.

Most of us do non-engineering related things for fun, but I'm not so sure his brain ever turns off.

 

[Trenno]

Read Eng-tips daily.

Always question "why?"

Surround yourself with good mentors.

Learning doesn't stop at 5pm. You'll need to do research and study outside of work hours.

 

[StructuralAddict]

Thank you jayrod12 and Trenno for your thoughts and invaluable pieces of advices

 

[Stuctural100]

Thank you, makes sense

Also, the moment I get from etabs for the wall is much less than the one you'd calculate by hand for a typical cantilever. Is this because floor diaphragms provide some restraint to the wall?

 

[KootK]

I'd like to say that I am really impressed with your great knowledge in structural engineering. Your answers to all questions imply that you have an excellent experience in the structural engineering field.

Thanks Monir87, that's very kind of you to say.

Can you please refer me to the sources that you provided you with such a great knowledge?

For me, it's been mostly about books. I didn't get all that much out of graduate school. And, while I've had some excellent mentors, they mostly taught me about project management, efficient graphical communication, and business development. By the time that I was about three years into my career, I found that I had a pretty good handle on how buildings work in the real world and the purely technical mentoring that I was receiving slowed to a trickle.

The trick with the books is a) finding the time to read them and b) finding the right ones. There are oodles of textbooks out there that teach us how to design particular things. In my opinion, however, there are only a select few that have really helped me to think like a structural engineer. And those books have really helped me.

As far as I can tell, I read vastly more technical material on my own time than your average structural engineer. And, even at that, I only make it through about two structural engineering textbooks cover to cover each year (in addition to random articles etc). So one has to be selective. Here are a few of the publications that have been especially helpful to me:

- Structural Concepts and Systems for Architects and Engineers, TY Lin
- Building Structural Design Handbook, White & Salmon
- Reinforced Concrete Structures, Park & Paulay.
- Seismic Design of Reinforced Concrete and Masonry Buildings, Paulay & Priestley
- Structural Members and Frames, Theodore Galambos
- Design of Welded Structures, Omer Blodgett
- Structural Stability - Theory and Implementation, Chen & Lui
- Design of Prestressed Concrete Structure, TY Lin
- Reinforced Masonry Engineering Handbook, Amrhein
- Simplified Design of Building Foundations, Ambrose
- The Analysis of Irregular Shaped Structures - Diaphragms and Shear Walls, Malone & Rice

So there you have it. Just sit down and read 6000+ pages of material on your own time and you'll be all set. If you decide to do some reading, I'd recommend the two bolded texts to start. In my opinion, they're the best for understanding practical, holistic building design. And, oddly, almost nobody has these books anymore.

And what is your advice to fresh graduates like me?

In my estimation, these are the required skills for a brilliant career as a structural engineer, listed in order of importance:

1) Salesmanship. The ability to sell yourself, your ideas, and your firm to your clients.

2) Project/People Management. If you don't make money and hit deadlines, your competition will get the cool projects.

3) Technical prowess.

Do not underestimate the importance of items #1 and #2. Money has to be made and clients have to be kept happy at all costs. Our professors, our professional associations, and even other engineers will tell you that public safety (technical) supersedes all else. That's an incorrect portrayal of reality in my opinion. You have to pick your battles technically to ensure that you are tending to gardens #1 & #2 as well as ensuring safety on the truly critical items. If you're a hard-ass about everything technical, you'll find yourself designing garden sheds and sweating over the correct splicing of the diaphragm chords. Meanwhile, the engineer down the street who doesn't know what a diaphragm is will be turning out sky scrapers and giving seminars on how to generally be awesome.








I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

Also, the moment I get from etabs for the wall is much less than the one you'd calculate by hand for a typical cantilever. Is this because floor diaphragms provide some restraint to the wall?

The inadvertent moment connection between the above grade floor diaphragms and the shear wall may be causing the columns near the wall to act sort of like outriggers, drawing moment away from the wall. I would not expect this effect to be significant however in a building with a conventional wall/column layout. Normally, I would expect to be able to predict base level (main floor) moment quite accurately based on hand calcs treating the wall as cantilevered from the base.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[StructuralAddict]

Thank you sooooo much (KootK) for the time you spent to share your self-development experience, and for providing me with great pieces of advice as a fresh graduate!! I greatly appreciate it.
I would like also to express my gratitude for suggesting a list of useful references to explore. Based on your advice, I bought the "Structural Concepts and Systems for Architects and Engineers, TY Lin" book today. I intend to put some time every day to read it after the work hours. I hope this step will put me in the right track towards becoming a professional structural engineer (like you).
Thank you very much again

 

[KootK]

You won't regret the TY Lin book. It's a "page turner" by trade publication standards.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Stuctural100]

Thank you kootK, appreciated

 

[Ndarama1]

Monir I am equally a graduate engineer like you and I find Kootk's contributions really educative. Thank you Kootk and Monir.

 

[ahypek]

If you have a building frame system then I highly recommend modeling only your shear walls and assigning masses to define your diaphragm/exterior walls.