Mat Foundation 5

[hardyworld]

Greetings! I am new to the website and also relatively new to Engineering (I've worked as an EIT for 4 months now).

I am working on a project where I have to analyze the suggested Mat Foundation to be placed under a building addition. Our company only has 2 S.E. and they are out this week on vacation. I have never taken a foundation class and the local library doesn't provide any help besides explaining what a Mat Foundation is...

Are there any e-articles, free online scanned books, or code that can give me an example on how to decide what the foundation should look like??

Will an analysis of the Spread Footing and Wall Footings that would be included in the Mat Foundation be enough (ignoring all connected effects and additional support the mat foundation provides)???

All I can seem to find online are software programs that can do this for you...but I want to do a calculated analysis so that I can understand this suject better (and so my boss can see how I did the analysis). I can ususally work well from an example...just 1 example would be a GREAT help. Thanks in advance.

 

[JedClampett]

Someone in your office undoubtably has a foundation design book. Peck, Hanson and Thornburn, "Foundation Engineering" is good and pretty straight forward. Root around their offices and see what you can find.
If that's a total lost cause, go to your local bookstore and go buy a foundation engineering book. Try expensing it to the company. They're the ones leaving you to do designs without any tools. It might seem like a lot of money to dish out yourself, but eventually you're going to need one.
I wouldn't put a lot of hope on finding something on the internet. You might find some class notes or military standards on-line, but you really need some examples worked out, like in a text.

 

[chicopee]

Go on line. There are several sites on Mat foundations

 

[DaveAtkins]

hardyworld,

I am very impressed that you want to design this foundation by hand--I find most EIT's want to go straight to a computer program, without understanding what they are doing.

JedClampett made some good suggestions.

Basically, a mat foundation is a large spread footing. Take all your SERVICE column loads (use the appropriate load combinations per Code) and locate them on a plan view of the footing. Find the RESULTANT (sum up these loads), and the location of the resultant relative to the centroid of the footing. The soil pressure under the footing will equal the resultant load divided by the area of the footing (P/A), plus the resultant load times the eccentricity from the centroid divided by the section modulus of the footing (M/S) in each direction. Compare the soil pressure to the allowable bearing pressure.

This process is repeated, using ULTIMATE column loads. The footing thickness should be checked for punching shear, and the reinforcing in the footing should be designed for the bending in the footing between the columns (the upward soil pressure bends the footing between the downward column loads).

Note--the above method assumes the footing is infinitely stiff relative to the soil.

DaveAtkins

 

[Lion06]

hardyworld,

I am surprised your firm would let you spend the time to do it by hand. I would love to do more things by hand, but we have so many deadlines and our schedules are really pushed to the max. The only things we get to design by hand are what programs can't handle (or we don't have programs for). This amounts mostly to calcing out details by hand, and not much more. Kudos to your firm for allowing you to spend the time!

 

[DRC1]

Get acopy of J.E. Bowles "Foundation Design". Most geotechs have a copy in their office somewhere. He goes through step by step how to calculate.
Another resource for fast & good information is the Corp of Engineers design guides, downloadable at

http://www.usace.army.mil/publications/eng-manuals/cecw.htm

They probably have a manual that covers it.
Most libraries have copies of AIA Graphical Standards. This wont tell you how to design it per se, but will show lots of practical details and give you an idea of how it should look.

 

[JedClampett]

I think you should take this chance to design the foundation by hand before you cut loose using software. It's important to get the feel for the numbers involved before you trust the answers from a black box.

 

[josecastjr]

Go to Google.com and search Structural Engineering Freeware and you should find several foundation freeware programs that show basic footing foundation programs. The process is there just keep in mind current ACI 318 Code requirements. Good starting point if you do not find other sources. Best bet are the Foundation Engineering text books that have been recommended here.

 

[structuralaggie]

I agree with DRC1 about the Bowels book. I have found that a lot of Goetechs do have it, and they are often impressed when you tell them you have been reading it. I have the fifth edition which is the international edition. It covers about every topic you can think of.

The only problem with it is everything is in SI (aka communist) units. If you are like me, you will curse at the damn book a lot because following simple examples takes ten times longer due to the unit coversions. Over all a great book though. A geotech told me that the older versions are in the english units.

 

[swivel63]

i would venture to say that many structurals have the bowles, and at least the das books if not the peck and thornburn book. i'm not sure if the peck and thornburn book is still in print. but i'd love to have it because i have two das books (one on soils and the other on foundations) and the joseph bowles book.

oh yea, it's good that you wanna do it by hand. we have some engineers who actually have to do a small spread footing with just a moment and a load with a computer program. hell or even simple beams. setting up the damn thing would take longer than me just running some numbers. there needs to be more firms like this, because like my boss said....engineers are basically IT people these days.

daveatkins is right, but also check to see if you're eccentricity is in the middle third. if it's not, then there will be a higher bearing pressure because you get no tensile help from soil.