[CSB]

The amount of TNT needed to destroy a timber beam (applied externally) is:


P= D ^2 / 40

(That's P equals D squared, divided by 40)

Where:
P = Amount of TNT in pounds
D = Dimension of beam in inches

If the engineer can auger a big enough hole to the center of the timber,
the amount of TNT for an internal charge drops to:


P = D ^2 / 250

Notice how the constant divisor increased in size, decreasing the amount of TNT needed.

====================

For a bulk steel cutting charge, simply estimate the number of square inches
in the steel beam, then use:

P = 3/8 A

Where "P" = Pounds of TNT and "A" equals the Area of the structure in square inches.

For steel bars, cables and chains, simply use P =A. Sounds simple, but a 2 inch in diameter steel rod has a cross section of?

... Anyone? anyone?

Pi x R ^2 (The area of a circle) produces the area.

for a one inch radius (2 inch diameter) that's 1 x 1 x 3.14 = 3.14 inches cross section, yielding 3 1/4 lbs of TNT.