RJR posted:I beg to differ. Years ago when involved in railroad relocations I encountered analyses of bridges that considered steam impact.
I would refer you to the Bridge Engineering Handbook, edited by Wai-Fah Chen & Lian Duan, sections 23.1.1 and 23.5.3.3.
See also Coping with the Older Railroad Steel Bridges, published by IMA Infrastructure Engineering Inc., Edmonton, Alberta, CANADA, September 2005.
I believe you are correct. The engineering design of railroad bridges as per the AREMA Manual of Railway Engineering requires consideration of dynamic forces. This is not limited to steam equipment. Speed, load, wheel spacing, and span length all contribute to the load. The bridge response depends on the natural frequency of the structure based on it's stiffness and mass, and damping characteristics. The load component consists of vertical forces from unbalanced drivers and reciprocating components (dynamic augment), uneven track, flat wheels, or wheels with other irregularities. There are also horizontal rocking forces that contribute a vertical dynamic component of force which can be applied to either rail as a moment couple force. For ordinary, simple steel bridges and speeds less than 90 mph, a simple set of equations reduces the vertical effect to a percentage of the live load. But it is often a significant percentage of the live load when both direct vertical forces, and vertical forces due to rocking are added together. These plug into the Cooper E rating.
