Calculating Rebar diameter for Concrete Landing 5

[azonicbruce]

First of all, let me say, WOW! I can't believe the wealth of knowledge that can be found on this site. First time posting and hope to be able to contribute.

I'm supposed to be a design engineer, but manufacturing engineering is my background, so I'm VERY new to working with structural design.

Here's the problem. We are going to be putting in a new concrete landing on our site. Approximate size is 190' x 100' by 8" thick.

I'm wondering if there's a good beginning reference for calculating what size rebar we will need for reinforcement. Typical items being placed on this pad weigh about 400 tons. The contact patch they have with the concrete is small (about 36 sq. in. each footing, 4 footings).

I think were going to become more and more involved with foundation/concrete design, so what a good BEGINNER's reference?

Thanks

 

[dbuzz]

There is a reason that engineerning is taught and practiced in different disciplines - and this is a great example why!

I'm certain the civil, structural and geotechnical engineers in this thread and forum would baulk if their employer asked them to design a conveying system or select bearings, a housing and the lubricating oil! In fact, in my country it is against our professional body's Code of Ethics to practice outside an area of competency.

The slab design will be a relatively simple task for a suitably experienced structural engineer and recommend that you engage one in this case.

 

[CTW]

Your doing the right thing by taking the initiative to learn more about the proper way to design and construct this type of slab. It sounds like you don't have much say in the final design, but I wouldn't worry about it. Just use this opportunity to learn. Take notes during the construction phases about concrete strength, thickness, rebar size and spacing, location of rebar in slab, curing method, jointing, subbase/soil conditions, and anything else that may seem useful. Be sure to take plenty of pictures.
The good thing about this project is that the slab is not going to fall down.

 

[sacem1]

To dbuzz:

I'm sure that no engineer is going to answer or recomend something that they do not know or are in doubt of, however the truth is that in many situations an engineer has to develop other fields in order to be able to solve problems that arise in their work, thats why I agree completly with CTW in that azonicbruce should study and learn from this experience.
In my own experience, 31 years of profeeesional practice up to now, I have found that having a basic plan, layout or design helps a lot in refining and recalculating the final design.
I expected feed back for my recomendation either up or down from my values which are given by experience and studies as really I am an Industrial engineer wich also have studied civil engineering and done an specialization in machine design in Switzerland, right now I design machinery for heavy mining equipment and manage my own small manufacturing firm in wich we export a lot of finished components to the States, Chile, Panama Canal Authority, etc. and in the years of experience acumulated I had to solve several heavy foundation designs for the Ball and Rod Mills that we also manufacture and have to install for our customers.
Hope I did not trespass any ones turf, if I did sorry.
SACEM1

 

[azonicbruce]

Well, I thought I'd all let you know that it doesn't matter now. The contractors already came and are starting construction. I guess the least I could do is keep you updated as to what ends up happening with this situation. I'll be taking a lot of pictures during the construction to see how it is getting built and what types of things I can consider next time around.

Thanks again for all the help. It's nice to know that there are people that are willing to help. In fact, I know that I'm going to have a few Statics questions in the near future, so you'll probably see more posts from me.

 

[Focht3]

Did you decide the pavement thickness and design, or did someone else? (My money's on the successful bidder -)



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[DDS1]

Azonicbruce

My curiosity is with Focht3. I have been following the posts and was wondering who made the final decision. When I first read your post I was sure you were going to get "beat up" for practicing outside your area of competance. For the most part everyone was helpful and your honesty contributes to that. For thoes that like to play the "discipline" fiddle dont let it be a discourage. Accumulate good reference material, put in the time and effort to research your designs(against this material) and try to find an experienced engineer to bounce ideas(and designs) off of. If you have received a bs in engineering you should have the math and physics (the tools) to get a fundemental understanding of a variety of topics provided you do the proper research with good engineering reference material. It is of upmost importance to know when your in over your head and need outside assistance. Further formal education in areas as mentioned in a prior post is a great tool to broaden you areas of knowledge.

Good Luck,

DDS1

 

[azonicbruce]

Focht3,

Here's the deal. I was asked to be in charge of determining what we would need to complete this project. As far as the actual design, I simply based my models on what I was told to make them. At first was told to make it 10" thick, but then the "maintenance" guy said we probably wouldn't need THAT much, so they told me to change it to 8". He also said we should use 3/4" rebar spaced 12" apart in a grid pattern. Then we should use 10guage wire mesh. I guess he had been in charge of other concrete projects, but whether or not he knew what he was doing I don't know. Then, the VP of engineering told me that we probably will want footings. So I added those in. He told me they should be about 36" deep and 18" inch wide.

Since the landing was going to be placed on a slight slope, I had to determine how much dirt would be needed to make it level. Armed with nothing but a laser level and a metal ruler, I was able to model up what the fill would look like.

So really my main responsibility was to determine how much concrete, rebar, and dirt fill it would take to complete the project. With my model I was able to determine how many cubic yards or dirt/concrete, how many feet of rebar, etc. So if the contractor comes up short on materials, I'll be willing to take responsibility for that. It wasn't until the contractor said we didn't need this or that that we started to question whether or design was correct or not.

So I started to investigate, started asking questions, and here I am getting feedback from professionals who really know. I've definitely learned a good lesson working in the "real world".

I guess what's frustrating is that because I'm just out of college, I'm really not "competent" in anything; I simply don't have the experience. Yet it seems that in the environment I work in, there is nobody who really knows what they're doing either, so there's nobody to guide me and let me know what I'm doing right, and what I'm doing wrong.

Like you said DDS1, I have a basic understanding of these concepts because of my education, and I have some knowledge/tools to give me place to start, but not much to help me see if I'm going about understanding/solving the problem correctly (except for places like here). What really stinks is that I got good grades in school, but can't seem to remember those things when I really need to! I took statics, dynamics, and material properties almost 3 years ago. Should I be remembering everything I learned? Or is it normal to not remember everything you learned in college?

Sorry for my long posts. Again I appreciate everyone’s help.

 

[DDS1]

Azonicbruce,

No, you shouldn't remember everthing you learned in college. Therefore the comment on good reference material. You hopefully have your college textbooks but this is only a start. One of my most valued possessions is the library of reference material I have accumulated through out my career. I had a couple mentors who "guided" me through the early years. I to was "insecure" once about what I knew or thought I was supposed to know or remember. Experience, Experience, Experience. But you've got the right attitude and you've got eng-tips and I can tell by many of the posts I have read on these forums that there are alot of people here who have also played the role of mentors in their daily professions to many up and coming engineers.

With that said, do the research if your name is associated with the design. You mentioned the "maintenance man". I have dealt with many maintenance men and contractors. As mentioned do you homework because the maintenance man and contractors who were so eager to guide you into failure will be the first ones to step back and say "Im not the engineer".

Your contractor that has suggested things you did or didnt need, does he have an engineer on staff. He may have and that engineer may have provided this information and may be someone you can speak with. When someone suggest something, question them as to what they are baseing their suggestions on. It will provide you insight as to if they have any idea what there talking about because youve done you homework or if not now have some to do. Keep you chin up and your ego down.

Good luck,

DDS1

 

[ERV]

azonicbruce,

It really is not important or is it possible to remeber everything that we learn throughout life, what is important is that we learn from our mistakes. That is something that can only be learned with experience. As an engineer of more than 30+ years, I call it a gut feeling and start from there. With no experience, a person does not have a starting point, so reliance on the gut feeling of others has to be the start. The difference between good engineering practices and bad engineering pratices is research. I think that you are off to a good start, honesty about what you don't know is a rare trait, never be afraid to ask questions about what you do not understand. No answer is far better than the wrong answer in engineering.

 

[Focht3]

I hate engineers that try to bluff their way through problems they clearly don't understand! Guys like that aren't very bright - trying to "buffalo" the real experts! It used to make me mad - now it makes me laugh!



Your honesty is refreshing. Stick with it!

I am much less concerned about pavement failure than I would be about a structure's failure - particularly since it's in your company's marshalling yard, and the design is in-house. Finally, I have a hard time seeing anyone hurt as a result of an inadequate design. Waste of money? Yes. But it isn't a fatal mistake; and it might work for some time.

Hang in there!



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.