Double concentration

A term descriptive of the method of figuring stresses in bridges for a live load, consisting of a string of cars of uniform weight per lineal foot headed by an excess load equal to the difference between the total weight of an engine and tender and the product of the length of the two by the weight per lineal foot of the cars, and followed by another similar and equal excess load two panel lengths (about fifty feet) back of the head of the train. This type of live load is no longer used, as it has been replaced by the "equivalent uniform live load".