TBDY 2018 (Turkish Building Earthquake Code 2018), starting from Article 3.4 and the subsequent provisions, defines itself as a performance-based code by specifying the performance level that buildings are required to achieve under the relevant earthquake ground motion. For new buildings, the standard performance objective is KH (Controlled Damage), while DGT (Design Based on Strength), which is based on linear analysis, is prescribed as the design approach.
Performance analysis is the process of determining where damage is expected to occur in a building during a possible earthquake or the design earthquake—identifying which columns and beams will be affected and at which specific locations along these structural elements damage will occur. Considering that damage, in technical terms, can be expressed through deformation, performance analysis can essentially be described as calculating the deformations at the critical points of structural elements. In a reinforced concrete structure, performance analysis therefore involves calculating parameters such as compressive shortening of concrete and tensile elongation of reinforcing steel in columns and beams.
Chapter 4 of TBDY 2018 establishes the principles for the strength-based design and assessment of buildings under earthquake effects. New buildings are designed in accordance with this chapter. When Design Based on Strength is applied, deformations in structural elements—such as elongation of reinforcement and shortening of concrete in reinforced concrete structures—are not directly calculated. Instead, certain limiting force/stress values are defined, and the results of the structural analysis are compared against these limits.
When considered in detail, and given that deformation and damage must normally be known in a performance-based assessment, it may be argued that this type of calculation appears to conflict with the fundamental philosophy of performance-based design adopted by the code.
However, Chapter 4 of TBDY 2018 states that when a new building is designed according to Design Based on Strength and complies with the principles specified in this chapter, the building is deemed to satisfy the KH (Controlled Damage) performance level. In other words, the code provides this assurance to the engineer without requiring a separate deformation-based performance analysis.
Therefore, an additional performance analysis is not required for new buildings designed in accordance with Chapter 4.
Chapter 15 of TBDY 2018, on the other hand, covers the assessment and strengthening of existing buildings. Consequently, recalculating or reassessing a newly designed building as though it were an existing building by applying the provisions of Chapter 15 is an unnecessary practice.
In particular, the deformation-based assessment criteria specified in Chapter 15 differ from the criteria established in Chapter 4. Since these methods are based on different criteria and different fundamental principles, they should not necessarily be expected to produce identical results.
In this context, compliance with the relevant provisions of TBDY 2018 is both necessary and mandatory for structural design and assessment. Whether a building is existing, newly constructed, or being strengthened, it is sufficient to apply the relevant chapter of the code corresponding to its specific condition.
Treating a newly planned building designed according to Design Based on Strength as an existing building and attempting to apply the requirements of Chapter 15 in addition to Chapter 4 is therefore an unnecessary duplication of engineering work.
In conclusion, a new building designed on a strength basis in accordance with the principles of Chapter 4 of TBDY 2018 is considered to have achieved the KH (Controlled Damage) performance level. This assurance is provided directly by the provisions of the code.
Türkçe