Assessment of axial force effect on improved damage index of confined RC beam-column members

In recent years, different damage indexes have been introduced in engineering literature. The most prominent one among other counterparts is the 1985 Park and Ang's damage index (DIPA), which demonstrates well calibration against experimental results. Hence, it has traditionally had broad application in the field of structural engineering. Commonly, in DIPA relevant parameters are assessed based on plastic-hinge approach, which is not well suited to consider the coupled response between stress resultants (axial force and flexural moment) especially in grossly nonlinear domain. The reason is that named approach is utilized constant shape plastic moment-curvature curve, which is not capable of varying the shape throughout loading history. Another drawback of plastic-hinge method is the difficulty of representing precisely partial yielding of the cross-section. To remedy the situation, the fiber discretization technique is used in this paper. Based on the fiber discretization strategy, not only have the stiffness and strength degradation been characterized more accurately, but also the distribution of plasticity along the plastic zone has been considered. Besides, the multi-directional effect of axial force and flexural moment is considered to assess DI parameters. Additionally, this strategy directly incorporates the effect of transverse confinement into cross sectional constitutive behaviour.