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Modeling Grade Beams in RisaFoundation

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CCox

CCox

Structural
Dec 6, 2010
72
I am trying to design grade beams in Risa Foundation. In the past, I have used Risa3D for this. I modeled discrete compression only springs that had a stiffness equal to the soil subgrade modulus times the tributary area of that spring. Check the reaction at the springs and make sure allowable bearing pressure is not exceeded.

I was trying to use the beam option in Risa Foundation and found that it really wasn't allowing me to design grade beams in this way. I even added discrete springs underneath the grade beam. Maybe my definition of "grade beam" is different? It appears that the beam option in Risa Foundation is for attaching independent wall footings or spread footings in a strap footing method.

So, then I modeled the grade beam as a slab. I assigned a soil definition under the slab and it calculated soil bearing pressures, deflections, etc. and output gave me required reinforcement.

Is this how people are modeling grade beams in Risa Foundation?
 
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You can do grade beams either with beams or small slabs. In either case, you don't need to manually define your soil springs. They should get created automatically.

The one problem I can see is that RISAFoundation is geared towards larger systems, so modeling a single grade beam probably doesn't work. That's because it's unstable for rotation about it's axis and RISAFoundation probably isn't smart enough to correct for that issue automatically. It's probably also not generalized enough of an interface to allow you to manually correct that instability.




 
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Thanks Josh. I think that was the case. In RISA3D, I would restrain the out of plane and torsional degrees of freedom to get the analysis to converge.
 
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