ABSTRACT
The calculations of girders determining their ultimate resistances may be found by the rational as well as by the empirical formulae : the rational is based upon reasoning, taking as axioms laws which are reasoned out in works upon Theoretical Mechanics; whilst the empirical is the application of analogy to the value of a given experimental result. Effective Span is the distance between the centres of the bearing surfaces of the girder on the supports, and is taken in the event of the camber of the girder preventing the bearing surface of the girder resting fairly on the stone template. The vertical shearing stress molecule of the vertical cross section of a beam is a couple, and therefore if a molecule is in equilibrium, as a couple can only be kept in equilibrium by couple, the sum of the horizontal shearing stresses throughout the depth of the section will form a couple having the moment of the vertical shearing stress.
