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Southern Alberta Canada | I think it's based on dynamic load over a period of time. In other words you could park as many 72 ton trucks on the bridge as will fit and it'll support them no problem but if you run 72 ton trucks over the bridge at speed it creates stresses and shock loads throughout the structure and it's been determined it'll last X number of years, increase it to 100 ton and the lifespan of the bridge will be significantly shortened.
So a couple 72 ton trucks occasionally will be no issue (unless posted as single unit only)
This railroad bridge is an example of that https://en.wikipedia.org/wiki/Lethbridge_Viaduct , it was designed for much smaller trains then cross it today, but they must cross at much slower speeds, I watched a couple loaded trains cross it and it took over an hour before the whole train was done. | |
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highway bridges ?
