FAQ
What is the difference between Caltrans hinge and fiber hinge?
Extended Question: It appears that the Caltrans hinge and the fiber hinge are conceptually similar. They are both based on strain compatibility and equilibrium of forces. The Caltrans hinge can be idealized as elastic-perfectly plastic as shown in Figure 3.7 of Caltrans Seismic Design Criteria version 1.4 - does the mean that when the user specifies auto Caltrans hinge, the program always uses the idealized moment curvature, which would be the main difference between the two types of hinges?
Answer: The Caltrans hinge is a PMM type of hinge based on an interactions surface. The only thing that makes it a Caltrans hinge rather than any other PMM hinge is the idealized elastic-perfectly plastic behavior and how it is calculated. Like all PMM hinges, once the hinge yields, it locks onto a moment rotation curve based on the yield point. This curve include axial and rotational deformation based on the normal to the yield surface. It is a phenomenological approach. It works best for static loading without significant hysteresis.
The fiber hinge uses multiple axial stress-strain curves. It is more "realistic". Each fiber has its own hysteresis behavior, so it can track any PMM variation. It is computationally more intensive.
