where C is the centrifugal load per lineal foot, w is the equivalent live load per lineal foot, v is the velocity of train in feet per second, and R is the radius of the curve in feet.

All portions of the structure affected by the centrifugal load are to be figured to carry properly the stresses induced by the said load in addition to all other stresses to which they may be subjected.

No percentage of impact is to be added to centrifugal loads.

EFFECTS OF CHANGES OF TEMPERATURE.

In ordinary structures changes of temperature will not affect the stresses in the members, provided, of course, that proper precaution be taken to permit unrestricted expansion and contraction. But in all arches, excepting only those hinged at both ends and at the crown, the stresses caused by the assumed extreme changes of temperature must be computed and duly considered.

INTENSITIES OF WORKING-STRESSES.

The following intensities of working-stresses (i.e., pounds per square inch of cross-section) are to he used for all cases, except where wind loads are combined with other loads, under which conditions the said intensities are to be increased thirty (30) per cent. But when high steel is employed the metal is to be strained fifteen (15) per cent higher for all cases than herein specified, even after the said thirty (30) per cent has been added to allow for wind stresses.