This model is similar to the Takeda model, but has additional parameters to control the degrading hysteretic loop. It is particularly well suited for reinforced concrete members, and is based on the observation that unloading and reverse loading tend to be directed toward specific points, called pivots points, in the action-deformation plane. The most common use of this model is for moment-rotation. This model is fully described in Dowell, Seible, and Wilson (1998). This model is not intended for unreinforced concrete. See the separate concrete model below.
The following additional parameters are specified for the Pivot model:
a1, which locates the pivot point for unloading to zero from positive force. Unloading occurs toward a point on the extension of the positive elastic line, but at a negative force value of a1;times the positive yield force.
a2, which locates the pivot point for unloading to zero from negative force. Unloading occurs toward a point on the extension of the negative elastic line, but at a positive force value of a2 times the negative yield force.
b1, which locates the pivot point for reverse loading from zero toward positive force. Reloading occurs toward a point on the positive elastic line at a force value of b1 times the positive yield force, where 0.0 < b1 < 1.0. Beyond that point, loading occurs along the secant to the point of maximum previous positive deformation on the backbone curve.
b2 , which locates the pivot point for reverse loading from zero toward negative force. Reloading occurs toward a point on the positive elastic line at a force value of b2 times the positive yield force, where 0.0 < b2 < 1.0. Beyond that point, loading occurs along the secant to the point of maximum previous negative deformation on the backbone curve.
h, which determines the amount of degradation of the elastic slopes after plastic deformation, where 0.0 < h < 1.0.
These parameters and the behavior are illustrated in the figures.
See Also: