RisaFoundation - Adjusted Subgrade Modulus for Grade Beams

[TheDirtPounder]

All,

I've got a situation where I will be supporting a building on a series of grade beams. I've got a geotechnical report providing me the soils modulus of subgrade reaction (115 psi/in). For mat slabs or SOGs I adjust this value with respect to my foundation plan dimensions. For grade beams, the following image is from the RisaFoundation manual:

I've modeled the grade beams and applied the soil area to the extents of my foundation (see image below):

My question is, do I need to input an adjusted modulus of subgrade reaction or is RisaFoundation automictically adjusting it for my provided grade beam geometry? If I need to provide an adjusted reaction, can anyone point me towards a reference which addresses this task for grade beams?

Thank you,

 

[JoshPlumSE]

RISAFounation is only taking that modulus of subgrade reaction you entered and multiplying it by tributary contact area of each support spring. This is true for mats, spread footings or grade beams.

In your case, I believe, the program will use approximately 5 springs along the length of the grade beam (but, you'll want to confirm this yourself). That means each support spring is the width of the grade beam times the 1/4 the length of the beam (half that for the end support points because they only support 1/8 the length).

 

[JoshPlumSE]

Caveat: I used to work for RISA, but it's been a few years now. And, I mostly do not use the programs anymore (I actually work for a competing software program). Therefore, my knowledge may be dated and my opinions are somewhat biased.

 

[TheDirtPounder]

Thanks for the feedback Josh!