What is the proper way to model hinges at the tops of piers in ADAPT-ABI?
Node hinges should be installed at the same step (day) as piers and supports. The node hinges should initially be set to R=3,3,3. This is essentially “Follow the Master” for X/Z translation and Y rotation. The hinges can then be modified to a roller or other condition in the appropriate step. This can be accomplished by simply clicking on that step and then changing the hinge properties. If hinges at pier tops are not modeled this way, you may receive an instability error in analysis (i.e. non-convergence) since the nodes that are located at the same position, as is the case with all hinges (the program creates two nodes at same location). In this scenerio the hinges are not connected by an element or restraint.
Also, at the location of hinges the program will automatically create fixed restraints (3,3,3) that connects the girder with the bearing location. In this scenerio, where nodes of the restraint and hinge are matching, the restraints are not necessary since a common master node is shared between a restraint and node hinge. This will lead to an erroneous solution. To overcome this, you can:
- manually modify the input file by deleting the restraint line at the appropriate step, or
- create a small offset between the top of pier and bottom of girder. In this case, the program correctly accounts for restraints and node hinges.
This video, ABI2009 Hinge Modeling (save as .wmv extension) shows how to properly model node hinges at tops of piers.