Tension Only Truss Members 1

I am working on the load rating of a historic truss bridge. All the diagonals are steel rods which can't take any compression. I tried to use RISA but the program can't handle Tension Only (even you turn on the Euler Buckling option) and keep the truss stable at the same time. Even worse, the program locked almost all the truss joints due to instability but DID NOT report the lock as it normally does for other models. I contacted the technical support at RISA and they told me the only way to let the model run is to let every truss member carry both tension and compression. I wonder if anyone here used other program to handle this type of problem? I have SAP2000 and ANSYS on my computer. ANSYS sure is powerful but the problem will be with the moving load generator. How about SAP? What do you do with tension only brace analysis uner building lateral forces?