I have created a STAAD model of a simply supported bridge superstructure. In the model I have used steel girder and diaphragms along with concrete plate elements for the deck. A few things I have noticed in particular:
1) There are bending moments at the the supports (which I can eliminate by using the offset command and releasing them at the supports)
2) The exterior girder away from the load shows negative moment when it should be possitive, as if the entire bridge is in torsion lifting up on the girder
3) Axial forces are present in the members (likely due to the vertical member offsets)
Does anyone know why I might be getting negative moments in the far exterior girder under vertical loading? What can I do to fix this? Also, the girders are broken down into 8 elements but I've noticed that the values of the moments do not equate when looking at the same node from two beam elements. Can I eliminate the axial forces in the girders so it doesn't create additional bending moments? I've attached the file. Any help would be greatly appreciated. Thanks.