PTI design equations for expansive soil moment and shear in grade beam

[ProLuke]

Hello,

I am designing to footings for a two-story wood framed house.

The house has a rectangular footprint 20' x 60'.

The soil is expansive clay.

I am trying to calculate the maximum moment and shear in the grade beams during edge-lift and center-lift

I have a soils report that recommends I use the PTI DC10.1-08 design method for calculating the moment and shear to use conventionally reinforced grade beams, with a structural slab (with voidspace). There are not going to be any deep piers, just the grade beams and structural slab.

I am trying to use the PTI equations 6-13, 6-18, 6-24, and 6-25 to calculate the max moment and shear in my grade beams.

Question:
What are the units and values of the variables in these equations?

The units: some I think I know, and have filled in.
L = lenght (feet)
S = ?
h = ?
P = perimeter load (lbs/foot)
y_m = max differential soil movment (inches)
e_m = edge moisture variation (feet)

Does anyone know the ones I have missing, or if I have the others correct? Is this a good method to calculate the moment and shear in a gradebeam supported on expansive soil?

Thank you!
--Luke

These are the values from the soil report, for reference:
Allowable Net Bearing Capacity (dead): 1000 psf
Allowable Net Bearing Capacity (dead + live): 1500 psf
Slab subgrade coefficient: 0.75
Edge moisture variation, e_m, feet:
Edge lift: 4.8
Center lift: 8.3
Differential Swell, y_m, inches
Edge lift: 1.0
Center lift: 1.2
Effective Plasticity Index (PI): 27
Support Index: 0.91
Minimum unconfined compressive strength: 2480 psf
climatic rating: 26


--Luke

 

[EricCA]

Appendix A.1 of PTI "Design of PT SOG" Version 3 shows

h = Total depth of stiffening rib, measured from top surface of slab to bottom of rib, in.

S = Interior stiffening rib spacing, ft.

All others look good to me.

 

[ProLuke]

Thank you Ericca!

So it is correct that I don't need to convert any units?

My Total load is 1165 plf on the perimeter grade beams.

I am planning to do the grade beams 12"x24", so I use 24" for "h"

The spacing across of the ribs is 12'.

Using the PTI equation for center lift, I get 7.9 kip-feet
and 5.3 kip-feet for edge lift.

But using the BRAB method, I get 22 kip feet.

Are my values for the PTI method correct?

I have attached the excel spread sheet I made using the formulas.

Does anyone have software to check my result?

--Luke