One-way shear on circular mat foundation

[nicoga3000]

I've been investigating the best way to design mat foundations without the use of software (largely because we are a small firm and have not had time to really dig into STAAD or PCA Mats or any other software capable of this) and have run into a few pitfalls.

A little bit of info to make some sense...The mat foundation in question would be, say, 40' in diameter with a ringwall at a 12' radius. They are typically slope topped and, in the case of what I'm looking at now, 18" thick at the toe and 48" thick at the ringwall. The one-way shear is controlling the thickness here, and that's one reason why we need to find a better way to look at it.


First, as the thread title indicates, one-way shear checks outside of the ringwall are tough (it's sloped and it's a mat, so two things that make standard texts and references go out the window). Two-way checks are easy enough (and will seldomly control).

Also, the question of flexure checks come up. Outside of the ringwall (out to the toe), I'm considering one foot wide sections at the face of the ringwall and designing as a cantilevered beam. The transient loadings are being considered to act as a trapezoidal load over the section while the static loads are acting uniformly (as they should be). For inside steel, shear and moment diagrams suffice. In terms of circumferentially steel (assuming we lay the rebar out radially and circumferentially), hand calcs would probably lead to minimum steel, but I'm not sure this is the way we should consider it.

I guess my first question would be if anyone has any solid resources that detail mat foundation analysis. Second, does anyone know a good place I can go to read and learn about designing mat foundations through a FEM software? We have STAAD where I work, but we use it for proprietary software we had written for us by Bentley to design a specific structure we do quite often. I'd really appreciate any help and tips anyone has. Thanks!

 

[csd72]

stinlin,

a sketch would be useful as all this mention of ringwalls e.t.c. has gone straight over my head.

 

[ishvaaag]

I would say that for free form structures 3D FEM programs are a nicer tool than structural design software. Seeing this, quite likely it is best to use Autodesk Algor Simulation (the 2012 release has another name, I think to have seen) for your somewhat troncoconical foundation than one like Staad. Other thing is if you want the reinforcement be proportiones automatically, then the structural design software is far better but you may have to concede approximating the actual shape with steps etc. A design by hand may be as quick or more than any of the other two, and reasonable enough.

The structural design software packages use to be very much code oriented, and hypotheses may be set directly through them; those for free form use to be more oriented to one per case basis, even if they are also able to manage the number of hypothesis you want.

There are impressive packages the extent of which one most surely never will manage but seeing a free form shape properly loaded and then analyzed is something beautiful to see; as are complete and well integrated models on structural design software.

In my view, sooner or later you will be using the 3 ways, manual, structural design, and 3D FEM. Structural design is quite close to what you do by hand, and at most you need some rules on how to produce a model. Both structural design software and 3D FEM may rely on drawings made in other packages, say autocad, inventor, or spaceclaim; structural design software uses to have inside more competent modeling tools than 3D FEM for the respective problems.