To build a truss bridge, you must decide what kind of truss bridge you need. For a short span bridge, use a king-post truss bridge. Choose your materials and connection. If you are using tubular steel, you will want to weld the connections. For I beam steel you will use bolt connectors. Prepare your abutments by excavating to the bedrock and pouring concrete. Add re-bar and anchor bolts to the concrete to attach the steel to. Build your trusses. They are a series of triangles that take the compression load across the bridge. You need 2 trusses, one on either side of the roadway. If the trusses were not built in place, then they will need to be craned into place. Install the cross members that attach the two trusses together. Apply the decking and the paving and you are done!