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[quote user="Electroliner 1935"]I have a question on a bridge with a flat floor (concrete), a vertical center truss above the floor and little arch to the floor. How does the tension to the floor address (handle) the vertical forces on the structure? [/quote] The bottom plate is the bottom chord of the truss, the roof plate the top chord. The top chord gets compressive stress, the bottom chord tensile stress. Concrete is not well suited for tensile stress. Its tensile strength is less predictable than compressive strength. Therefore in dimensioning is said (at least here in Germany) that all of the tensile stress has to be carried by reinforcement steel. But you can replace normal reinforcement with post-tensioning. As long as the compressive stress from post-tensioning is higher than the load tensile strength the bottom chord reacts as if concrete would be able to carry tensile stress like compressive strength. What I described is full post-tensioning. Partial tensioning is possible too but would go too far here. The post-tensioning reduces the deflection compared to standard reinforcement. [quote user="Electroliner 1935"]The stays had to be there to transfer the vertical loads from the span to the pylon.[/quote] The stays are not necessary if the truss is designed and analysed properly [quote user="Electroliner 1935"]Also, how was the center truss connected to the floor? That could be a stress point leading to cracking. [/quote] That is something that we don't know. The joints would be included in structural analysis and would be shown in the reinforcement drawings. They are critical points but doable. Regards, Volker
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