Determining the seismic performance of a building is an uncompromising process based on the most concrete and clear rules of engineering science. In Turkey, this process is carried out in accordance with the standards of the Turkish Building Earthquake Code (TBDY-2018), and the results reflect the physical reality of the structure.

The stages of performance analysis, which reveal the actual condition of a building, consist of the following steps respectively:

1. Determination of the Existing Condition (As-Built Survey)

• The original architectural and structural drawings of the building are obtained, if available.

• If the drawings are not available or the current state of the building does not match the drawings, an on-site as-built survey of the building (structural system dimensions, column-beam layouts) is conducted. The existing physical condition (cracks, corrosion, subsequent interventions) is recorded.

2. Determination of Material Properties (Field Tests)

• Concrete Strength: Core samples are extracted from structural elements (columns and shear walls) using destructive methods, crushed in the laboratory, and the actual compressive strength of the concrete is calculated. This is supported by non-destructive methods (rebound hammer, ultrasonic pulse velocity, etc.).

• Reinforcement Detection: The diameter, quantity, and stirrup spacing of the rebars in columns and beams are determined using rebar scanning (X-ray/GPR) devices. Additionally, chipping (cover concrete removal) is performed in different areas in a quantity compliant with the code to observe the amount of corrosion (rusting) on the reinforcement.

3. Investigation of Soil Conditions (Geotechnical Study)

• The properties of the soil on which the structure rests are determined through drilling and seismic tests.

• The soil's bearing capacity, liquefaction risk, and potential for amplifying seismic waves (local site class) are identified and included in the report.

4. Modeling of the Structural System

• The acquired survey, material, and soil data are transferred into three-dimensional structural analysis software.

5. Definition of Seismic Effects and Analysis

• Seismic acceleration values are obtained from the AFAD Turkey Earthquake Hazard Map based on the building's coordinates and soil class.

• The behavior of the building under seismic forces is simulated using Linear or Non-linear (Pushover) analysis methods.

6. Determination of Damage Limits on an Element Basis

• As a result of the analysis, the damage that each column, beam, and shear wall constituting the structure will sustain is calculated.

• The elements are classified according to the strain they experience: Minimum Damage (MN), Significant Damage (BH), Severe Damage (İH), or Collapse (G).

7. Determination of Building Performance Level

• The holistic performance of the building is determined by combining the individual element damages. According to the code, the minimum standard a residential or commercial building must target is the Life Safety (CG) level.

• The results are grouped into 4 main categories:

  • Continuous Use / Immediate Occupancy (KK): The structure can be used immediately after the earthquake.

  • Life Safety (CG): The structure sustains damage but remains standing, allowing for the safe evacuation of its occupants. (The targeted result for standard buildings).

  • Collapse Prevention (GÖ): The structure is heavily damaged and becomes permanently unusable, but total collapse does not occur.

  • Collapse State (GD): The building cannot withstand the seismic loads and collapses.

8. Reporting and Final Decision

• If the analysis results in a Collapse State (GD), the structure is inadequate. At this stage, considering the economic life of the building and the costs involved, a decision is made either to prepare a retrofitting project or to proceed with the demolition (urban renewal) process.