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RE: Slab On Grade STAAD Model

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I suggest using Staad for your application; model it through FE (finite element). To run the analysis Staad requires a sub grade modulus reaction (see below as an example in load input data). Caution with the units used you may need to convert as I just shown below.



*Subgrade modulus reaction is assumed 100pci (from geotech)

*for staad input (100pci*144in^2/ft^2*12in/ft)(kip/1000 lbs)=172.8

1 TO 2323 FIXED BUT KFX 172.8 KFY 172.8 KFZ 172.8



PC mat is a handy tool to use.


Good Luck!


Engr. Julius Micayas

P.E. license no.32969

Project Manager/Sr. Lead Structural Engineer

River Consulting LLC

111 Veterans Memorial Boulevard

               Suite 1600

Metairie, Louisiana 70005

Phone - 504-841-3014 (direct)

504 837-5275 (office)

Fax - 504-837-2986

E-mail: jmicayas(--nospam--at)


From: Bill Allen [mailto:T.W.Allen(--nospam--at)]
Sent: Friday, January 25, 2008 12:05 PM
To: seaint(--nospam--at)
Subject: Slab On Grade STAAD Model


I am having some difficulty modeling a slab on grade using STAAD. The slab is 20 ft. x 12 ft. x 3-1/2” thick. I am putting a point load (uplift) at one corner. I would also like to put another load at the middle of the long edge. I don’t model in STAAD very often, so I’m pretty sure I’m doing something wrong. I’m using Plate Mat foundation compression only supports, but I keep getting tension on some of the supports. When I put two corner loads and the load at the middle of the long edge (twice the corner load), the whole thing blows up even though the slab weight is greater than the uplift force.


If anyone has the time and inclination to look at my model, I would be most appreciative. FWIW, I’m using STAAD 2004. That’s how seldom I do modeling anymore.




T. William (Bill) Allen, S.E.


Consulting Structural Engineers
V (949) 248-8588 F(949) 209-2509