ارزیابی شاخص خسارت پارک- انگ در سطوح عملکرد لرزه‌ای قابهای خمشی بتن مسلح

The main goal of seismic design is having safety while earthquake happens and making a structure repairable. For estimating the damages in the elements criterions are defined as damage indices.
Damage indices are functions consist of some damage variables and show the effect of those variables on the element’s damage. One of the most important damage indices is the Park-Ang damage index. It shows the damage of reinforced concrete elements as a linear combination of maximum deformations and absorbed cyclic energy. The analytical value of this damage index for the state of not having any damage will zero and for the collapse of the element should be equal one. The Park-Ang damage index has a non-negative factor shows the reduction of element’s resistance in cyclic loading and specifies the energy dissipation and the strength damage of the elements. This factor has been used for calibrating damage index and it has been found that the damage index is merged to one in the failure point. Applying this model in structural systems requires determination of an overall member’s deformation. Since inelastic behavior is limited to plastic zones adjacent to the ends of a member it is difficult to correlate, the relationship between overall member deformation, local plastic rotations and the damage index. So a modified version of this model developed by Kunnath and et al.
The most important difference between Kunnath model and Park-Ang model is representing this equation based on the moment-curvature diagram and replacing the non-dimensional factor with the strength deterioration factor in a hysteretic model. Supposing this factor as a constant will increase the diversion of the damage index in collapse prevention performance level.
In this paper, the Park-Ang damage index and its correctional relations for the various performance levels which contain immediate occupancy, life safety and the collapse prevention level has been evaluated and the values of damage index at these levels has been specified. For this purpose, three reinforced concrete frames with various numbers of stories have been designed for three levels of performances have been used for this purpose. Nonlinear dynamic analysis has been done with seven earthquake acceleration records and finally the damage analysis has been done for them. The damage index has been derived for all of these nine frames and the values of damage indices have been evaluated.
The beam damage indices are related directly to the rotation which happens in the plastic hinges. In components with immediate occupancy level, this linear characteistic is more clear but with increasing the rotation in the componenets or in the collapse prevention level, damage indices will more diverge. In this paper, it has been shown that this damage index needs to be investigated furtherer at the collapse prevention level and the second part of the damage index (strength damage) shall be determined by the element’s type and level of performance. The sensitivity of damage index is little to the column damages and the damage caused by the weak story is low and needs to be evaluated.