What is a diaphragm and why are they used in girders?

When you have a system of one way girders located in parallel with each other, a point load on a single girder (e.g. from a truck wheel) needs to be shared between adjacent girders, in order for a single girder not to take all the load. read more

Main girders: These are the strong beams that carry the load from the superstructure to the substructure (columns). Cross girders: Typically these are the transverse beams (also very strong/stiff) which are provided for transverse stiffness. read more

In that case, the end diaphragm would not have an effect since all the beams would "pull" it the same amount, implying in a simple rigid-body translation, without any deformation on the diaphragm. That, however, would be in the perfect world, and that ain't ours. read more