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[quote user="Paul_D_North_Jr"]It may surprise some here, but it's standard practice with most reinforced concrete structures to use less steel than would be necessary for a full utilization of the concrete's strength - say, 75% of the otherwise required steel as a typical figure - the technical term is "underreinforced". [/quote] It astonishes me. Here in the EU you would get your walking papers. I looked up "under reinforced" and found it recommended for single reinforced beams (rebars only in the tension zone, none in the compression zone). Is under reinforcing done on all concrete beams? Single reinforced beams are not allowed in the EU. Beams need a minimum of stirrups and reinforcement in the compression zone to fix them. I would say all European concrete beams are over reinforced according to American standards. Beside the stability proof that determines the amount of rebars we have to limit deflection and and the crack width. All might need additional reinforcement to comply with standards. [quote user="Paul_D_North_Jr"]The structure is still designed - even with the less steel - for full loading, so there's no safety issue. [/quote] The beam is designed for the full load, but as the safety factor is determined by deviding the yielding strength by the load stress you get a lowered safety factor. There was a good reason not to use the hardening after yielding for dimensioning. The beams to European standards are ductile and predictable. You realise overloading early enough through crack formation and growth. Looks like there are quite different dimensioning philosophies in our countries. [quote user="Paul_D_North_Jr"]Offhand, I can't think of any US freight railroad structures that are cable-stayed or use post-tensioned concrete - might be some, but not very many. In contrast, there are several in use for light-rail systems. [/quote] In the USA you find a number of pre-stressed freight railroad bridges. In Germany most of the railroad bridges on high-speed lines are post-tensioned continous concrete beams. You can find only few cable stayed railroad bridges around the world.
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