Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

  • Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Spring Support Generation in STAAD.Pro

Status
Not open for further replies.

fleisher

Structural
Joined
Oct 10, 2002
Messages
73
Location
US
I am checking a mat foundation that was modeled in STAAD using springs. The engineer used the PLATE MAT feature in STAAD where it "multiplies the subgrade modulus by the influence area of each support node to determine the spring stiffness". I can see how the influence area may be calculated but how do I verify the subgrade modulus for the soil?
 
JE Bowles' book on Foundation Analysis and Design publishes typical values for some soil types. By cross checking the soil you got against the published values you will have an idea where you stand.

Failing that do a load test on soil.
 
For Mat foundations the Subgrade Modulus (k) can vary depending on the duration of the load. To be conservative, as far as moments are concerned, you can look up the typical value for k based on your soil conditions and divide it in half. For bearing pressure use the higher k, resulting in higher pressures. Basically, you will have an upper and a lowere bound for your k. If you don't have a soils report, this is about all you can do.
 
Firstly, I use the same approach to compute my spring value. Secondly subgrade modulus (k in pci) should really come from the geotechnical engineer. It is a tricky number and lots of people assume it. I also encountered geotechnical engineers who would give different values for (k). I would suggest to use a seasoned soils engineer not one who copies numbers from previous reports (oops.. I hope this does not upset any one).

Good luck.
 
[wink] Not me!

[blue]Lufti[/blue] is on the mark - the geotechnical engineer should be providing those values - and if the structure is "significant", you should work together to iteratively improve them. You see, there is no such thing as "the" k-value - it is a numerical convenience, not an intrinsic property.

[pacman]

Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor

Back
Top