Structural Analysis

[n39]

Hi, I'm a fresh graduate in structural engineering. I realize that there are so many, way to many things to learn... I encounter some problem while learing stuff, such as:
1. What is two stage analysis, how do I use it, when do I use it (is it supposed when I had a basement?), I try to find these explanation on youtube or google, but it didn't help
2. I learnt about special moment frame, but about double moment frame, I know the shear wall resist most of the EQ load and the moment frame needed to be able to withstand 25% of the EQ load. But that's it, that's what I know. I don't know how to design it in ETABS, how do I control my design so that the moment frame can withstand 25% of the EQ load???
3. How do you calculate EQ load for basement?
4. I've learnt about special moment frames, but there is so much detailing... Usually I depends on the ETABS results (mostly PMM, long./shear reinforcement, B/C ratio, etc) but that's it. I rely on a software too much I think, I can calculate them actually, but it takes a lot of effort. I mean do you really need to understand all of those, or can you simply use ETABS results on designing a building?
5. I have some books, the seismic design handbook, seismic design of reinforced concrete, reinforced concrete mechanics and design. I try to read them. But the problem is, I don't know what to learn... It's like deadend to me

What I'm trying to say is that I'm kinda lost right now, because I felt like I don't have any clue on how to design a building despite all of my study... What should I do? How do you learn all this stuff?

Thank you, really appreciate for you guys who reply

 

[JAE]

Work under an experienced professional engineer for at least 4 years.

 

[phamENG]

Step 1: take a deep breath.

You don't come out of university as a fully formed engineer. It takes years and years of building up experience, and anyone who ever considers themselves "a fully formed engineer" is either lying to you or they are probably dangerous. We never stop learning.

Most of these are questions for your supervisor/mentor. If you don't have one, you need to get one. Somebody who understands that right now you just have a bunch of disparate theories and methods running around aimlessly in your head and wants to see you succeed.

I don't do much concrete or seismic, but I can answer a little bit:
1) For American codes (ASCE 7) It's used whenever you have a relatively flexible structure sitting on top of a very stiff structure. We have a lot of apartment buildings build on top of concrete parking garages. The concrete is very stiff, the light frame wood is flexible.

4)

I mean do you really need to understand all of those, or can you simply use ETABS results on designing a building?

I'll pose an alternative question: would you live in a building designed by ChatGPT, or perhaps a well trained monkey using ETABS correctly?

Of course you have to understand all of it! Why else does our profession exist? I hope you've heard of the garbage in => garbage out principle? The results from ETABS are only as good as the inputs and the interpretation. If you don't know what to put in, and you don't know how to interpret what comes out, how can you be sure there isn't a mistake?

5) This is why you need a mentor. They will help to guide you through the early parts of your career and get your feet under you.

 

[JoshPlumSE]

1. What is two stage analysis, how do I use it, when do I use it (is it supposed when I had a basement?), I try to find these explanation on youtube or google, but it didn't help

It depends on the context of where the term "two-staged" analysis is used. It can be related to when you have a superstructure of steel or wood on a concrete podium. The R value for the upper and lower portions of the structure are different. As such, you may analyze the structure with two different levels of seismic loads. One with a higher R value (meaning lower seismic force) for the upper structure. One with a lower R value (meaning a higher seismic force) for the lower structure.

Just as often it can be referring to "staged" construction. Meaning that certain loads are applied to one version of the structure (usually during construction), inducing stresses and deflections. And, other loads are applied to a 2nd version of the structure (after certain concrete members have cured or after other portions of the structure have been added or removed).

2. I learnt about special moment frame, but about double moment frame, I know the shear wall resist most of the EQ load and the moment frame needed to be able to withstand 25% of the EQ load. But that's it, that's what I know. I don't know how to design it in ETABS, how do I control my design so that the moment frame can withstand 25% of the EQ load???

Okay.... Some of this stuff is meant to be done or checked by hand. One thing you can do with computer analysis though is check to see how much of the shear is going to your moment frames compared to the shear walls. You might create a separate load case for the design of the moment frames where you scale up the seismic load so that those frames get designed to a higher shear load. It means you're using different Load Combinations for steel than you're using for concrete. But, that's pretty common.

3. How do you calculate EQ load for basement?

Someone else asked this question last week. There was a better discussion on it than I can summarize. Generally speaking, the foundation of a structure is not included in the seismic mass. Remember it's the inertial movement of the structure during an earthquake that causes the seismic loads. The foundation is generally assumed to move with the soil.

4. I've learnt about special moment frames, but there is so much detailing... Usually I depends on the ETABS results (mostly PMM, long./shear reinforcement, B/C ratio, etc) but that's it. I rely on a software too much I think, I can calculate them actually, but it takes a lot of effort. I mean do you really need to understand all of those, or can you simply use ETABS results on designing a building?

Yes, you may be relying on software too much. You really NEED to understand seismic detailing if you're going to be designing buildings and producing construction documents. Best to have conversations with your EOR about any detailing provisions you don't understand. It can be a little overwhelming at first. But, keep learning....

5. I have some books, the seismic design handbook, seismic design of reinforced concrete, reinforced concrete mechanics and design. I try to read them. But the problem is, I don't know what to learn... It's like deadend to me

You've got the right references. I like the seismic design handbook (the one edited by Farzad Naeim, right?). It's chapters are all pretty independent. So, you can read a chapter on steel or concrete detailing without having to fully understand any of the other chapters on seismic ground motion or such.

Note: That the Seismic Design Handbook is (in my opinion) very good at explaining the concepts of seismic design, you will have to take this knowledge to understand the latest seismic code provisions.

SEAoC has a number of seismic design manuals that can be helpful with the newer codes. These are less explanatory and more practical step by step examples of how to apply the seismic design codes.

 

[BulbTheBuilder]

I was recently a student like you so I understand how overwhelming all these can be. You aren't expected to know it all after school and even after a while. People often pick certain areas of structural design and focus on them (other might be excellent at seismic and steel but "clueless" at timber). I hope that gives you some comfort.

If you work with steel structures I would recommend AISC education youtube channel, It helped and still helps me a lot.
htt[url=https://www.youtube.com/user/AISCEducation]ps://www.youtube.com/user/AISCEducation[/url]

To your question,

1. What is two stage analysis, how do I use it, when do I use it (is it supposed when I had a basement?), I try to find these explanation on youtube or google, but it didn't help

I am not into seismic, but this has to do with seismic design of structures typically with podium (flexible structure supported by rigid structure).

2. I learnt about special moment frame, but about double moment frame, I know the shear wall resist most of the EQ load and the moment frame needed to be able to withstand 25% of the EQ load. But that's it, that's what I know. I don't know how to design it in ETABS, how do I control my design so that the moment frame can withstand 25% of the EQ load???

Do you understand the basics and fundamentals of load path for lateral forces, shear wall design, and can you produce a simple hand calc for some of these? If no, then you're honestly nowhere near using ETABs to do this analysis since you can't verify the results and output you will be getting. How would you interpret the results? How would you know you made a mistake or omitted something?

4. I've learnt about special moment frames, but there is so much detailing... Usually I depends on the ETABS results (mostly PMM, long./shear reinforcement, B/C ratio, etc) but that's it. I rely on a software too much I think, I can calculate them actually, but it takes a lot of effort. I mean do you really need to understand all of those, or can you simply use ETABS results on designing a building?

I know this feeling, quite often things are moving so quickly in the office you are "instructed" to run numbers through a software or spreadsheet rather than having a senior engineer walking you through the concept and helping you understand things. I'd recommend you talk to your head or supervisor about having some training. Relying solely on the software can be catastrophic.

5. I have some books, the seismic design handbook, seismic design of reinforced concrete, reinforced concrete mechanics and design. I try to read them. But the problem is, I don't know what to learn... It's like deadend to me

1.Start with a book on loads. ASCE has a good book...a little pricey but maybe you can convince your office to buy oneLink
How do you compute seismic loads - ASCE 7 chapter 12? What does the R- factors mean and how does it affect your structure? How does your load get transferred through your horizontal braces to vertical members to the foundation?
2. You can review a book on design of the elements taking your load. How do you design your diaphragm and horizontal braces? What are the principles behind?
3. Repeat this step for other elements like shear walls

PS: You don't have to necessarily go into details. Having a good understanding of the basics is a good start. Later you can come and dive deeper into each concept from time to time based on the demand of the project you are working on.

 

[Luceid]

I'm in my first few years working in consulting - and all of my colleagues at the same level feel the same way (folks who graduated at the top or bottom of my class - the whole range). The first month of working was daunting - could I even design a steel beam on my own despite learning it in school? Slowly you just realize that everyone else A) feels pretty similar and B) leverage the people around them to build confidence (by asking questions, receiving reviews, etc.) so they improve their skills. I'll leave the specific questions to the experienced folks - but if you give yourself time, you'll start to feel more confident and independent quicker than you might expect. Engineers with more experience than you are typically the greatest resource for the vast majority of things in the field.

Also - I understand your frustration in not knowing where/what to learn once you leave school. This gets a little easier once you start working, since you tend to learn what is needed to work on the project you are working on. On the other hand - it can feel more rewarding to understand what things you like doing the most (detailing, seismic design, specific materials, on-site activity, etc.) so you can learn more to be the best at those things. I haven't quite figured out the best way to learn "off the job" myself, other than attending presentations by my local engineering association and occasionally deep diving into a topic.