This section is from the book "Safe Building", by Louis De Coppet Berg. Also available from Amazon: Code Check: An Illustrated Guide to Building a Safe House.
(German Bruchcoefficient; French, Module de rupture.)
It has been found by actual tests that though the different fibres of materials under transverse strains are either in compression or tension, the ultimate resistance of the "extreme fibres" neither entirely agrees with their ultimate resistance to compression nor tension. Attempts have been made to account for this in many different ways; but the fact remains. It is usual, therefore, where the cross-section of the material is uniform above and below the neutral axis, to use a constant derived from actual tests of each material, and this constant (which should always be applied to the "extreme fibres," i. e., those along upper or lower edge) is called the modulus of rupture, and is usually expressed in pounds per square inch.
Modulus of Rupture. (See Tables IV and V.)