Carlon External Load Calculation for Buried Conduit - Manual (Page 5)

EXTERNAL LOAD CALCULATIONS FOR DIRECT BURIED CONDUIT
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SIMULATES 180,000 lbs DUAL TANDEM GEAR ASSEMBLY. 26 INCH
SPACING BETWEEN TIRES AND 66 INCH CENTER-TO-CENTER SPACING
BETWEEN FORE AND AFT TIRES UNDER A RIGID PAVEMENT 12 INCHES
THICK + IMPACT.
* NEGLIGIBLE LIVE LOAD INFLUENCE.
ONCE THE DEAD LOAD AND LIVE LOAD ARE KNOWN THEY SHALL BE
ADDED TOGETHER TO OBTAIN THE TOTAL LOAD (TL = DL + LL). THE
TOTAL LOAD SHALL BE LESS THAN THE MAXIMUM LOAD.
SECTION 300-5 OF THE NATIONAL ELECTRICAL CODE (NEC) SPECIFIES
THE MINIMUM COVER REQUIREMENTS FOR CABLE, CONDUIT AND
OTHER RACEWAYS UP TO 600 VOLTS. TABLE 300.50 SPECIFIES THE
MINIMUM COVER REQUIREMENTS FOR APPLICATIONS OVER 600 VOLTS.
THE FOLLOWING IS A SAMPLE CALCULATION.
4” SCHEDULE 40 CONDUIT WILL BE BURIED 20 FEET BELOW A RAILWAY
IN TYPE I SOIL. 4” SCHEDULE 40 CONDUIT HAS AN OUTSIDE DIAMETER
OF 4.500” AND A MINIMUM WALL THICKNESS OF 0.237”.
1. CALCULATE THE MEAN RADIUS (r)
r = (O.D. -t)/2 = (4.500 in - 0.237 in)/2 = 2.132 in
2. CALCULATE THE MOMENT OF INERTIA (I)
I = t
3
/12 = (0.237 in)
3
/12 = 0.001 in
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3. CALCULATE THE PIPE STIFFNESS (PS)
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