Given the inherently unpredictable nature of seismic loads, designing structures to remain entirely within the linear elastic range during earthquakes would result in uneconomically heavy structures. Consequently, modern building codes and design methodologies incorporate safe approaches that account for the inelastic behavior range of structures.
A robust approach for structural design that considers inelastic behavior is Performance-Based Design (PBD), which employs a multi-level methodology for designing structures under various seismic intensities. The contemporary PBD concept in various codes is founded on three fundamental principles:

No damage under low-intensity earthquakes
No structural damage but minor non-structural damage under moderate-intensity earthquakes
Collapse prevention with allowable structural and non-structural damage under high-intensity earthquakes

 
This seismic design philosophy is based on the principle that structures must satisfy different performance objectives when subjected to seismic hazards ranging from frequent, low-intensity events with short return periods to rare, high-intensity events with long return periods, thereby enhancing structural safety. In PBD, structural performance is explicitly defined as either a design objective or a design constraint.
According to design codes, structural members must be designed to withstand applied forces with appropriate safety margins that depend on the design methodology. As one of the most advanced seismic design approaches, performance-based design yields structures that are simultaneously economical, safe, and reliable.
When subjected to seismic excitation, structures experience varying degrees of structural and non-structural damage. The extent of damage depends on:

Input excitation characteristics (e.g., frequency content)
Site conditions and geological structure (e.g., distance from seismic source, local soil type)
Structural configuration (e.g., ductility capacity, building height)

 
The damage process initiates immediately upon loading and continues until structural collapse. This reality has led researchers to investigate not only complete collapse but also progressive damage and various damage levels. A key indicator of damage progression is the increasing deformations in structural members or the entire system, including:

Plastic rotation at critical sections
Inter-story drift ratios
Global lateral displacements relative to the base level

 
A fundamental question in damage assessment is determining how severely a structural member or system is damaged and how close it is to ultimate collapse. The Damage Index (DI) serves as a quantitative measure of the damage sustained by individual members, stories, or entire structures under applied loads. When damage is quantified through discrete damage levels, structural condition assessment becomes more realistic.
A primary objective of this research is to calculate damage indices for reinforced concrete structures. In recent years, quantitative damage assessment studies have grown significantly. Park and Ang (1985) proposed a widely-used damage index for seismic damage evaluation that remains extensively referenced in research. The purpose of this study is to evaluate the Park-Ang failure index in special bending frames of high-rise reinforced concrete buildings, designed based on performance. In this research, OpenSees software was used for modeling and analysis. This study consists of two basic steps. In the first step, 3 long reinforced concrete bending frames of 18, 24 and 30 floors were designed using push-over modal analysis based on ASCE41-17 and FEMA356 regulations in the framework of the performance-based design approach. In the second step, the evaluation of Park-Ang damage index in the frames designed in the first step has been obtained and discussed. It can be seen according to the obtained results that with the increase in the number of floors, the damage index of Ang-park in frames 18, 24 and 30 increases by 10%, 16%, and 34%, respectively. Also, according to the results obtained for the deterioration index of Ang Park, it can be seen that the performance-based design method causes the designed structures to be within the repairable range.