The baseplates at the bottoms of the columns are connected to the foundations at points A...

The baseplates at the bottoms of the columns are connected to the foundations at points A and D by bolts and may be assumed to act as pin supports. Joint B is rigid. At C where the bottom flange of the girder is bolted to a cap plate welded to the end of the column, the joint can be assumed to act as a hinge (it has no significant capacity to transmit moment). Compute the reactions at A and D.