LBR Tabulated Calculations - FM 5-515

SUMMARY

This article will describe the calculations used for LBR Test.  CBR is calculated similarly but will use different division values.

SOLUTION

LOAD [L]

Recorded during test or manually entered by user.

PENETRATION [P]

Recorded during test or manually entered by user.

CORRECTED LOAD [CL]

CL = L- initial load + top cap weight.

CORRECTED PENETRATION [CP]

CP = P - initial displacement

STRESS ON PISTON [SP]

SP [psi] = CL [lbf] / 3

LBR PERCENTAGE [LBR]

PENETRATION INDEXES [PI] = 0.1 in.

LBR Values are calculated at closest CP to PI.

DIVISION VALUES [DV] per FM 5-515 =

800 @ 0.1 in

LBR @ PI = SP [psi] / CV * 100

DV is in PSI units.

CORRECTED LBR PERCENTAGE [CLBR]

Same as LBR but adjusted by correction line drawn.

From the correction line we get the correction lines Slope [S], Y-Int [B], and Corr [C].

Next, we need to determine the displacement offset of the line.  This is found with the line equation when y is zero.

CORRECTION LINE PENETRATION CORRECTION VALUE [C]

C = -B / S.  This is derived from y = mx +b and we are solving for x.

The closest matching P value for the PI is adjusted with C yielding the Adjusted Penetration value.

ADJUSTED PENETRATION [AP]

AP = CP + C

Finally, we determine where the AP value intersects with the curve.  A vertical line is used to determine intersection.  This will yield the ADJUSTED FORCE [AF] value.  

CLBR = AF / DV * 100