Turkey Buildings Earthquake Standard-2018 (TBEC 2018) | Türkiye Bina Deprem Yönetmeliği 2018 – (TBDY 2018)

The procedure for calculating earthquake loads in the Turkish Building Earthquake Code (TBEC-2018) closely resembles that of ASCE-7-16.

Earthquake Ground Motion Levels – (TBEC-2018 – 2.2)

Ground Motion	Probability of Exceedance (in 50 Years)	Repetition Period	Definition
DD-1	2 %	2475	Maximum expected earthquake
DD-2	10 %	475	Standard design earthquake
DD-3	50 %	72	Frequent earthquake
DD-4	68 %	43	Service earthquake

Soil Classes – (TBEC-2018 – 16.4)

(V_S)₃₀: average shear wave velocity up to 30 m. depth
(N₆₀)₃₀: average number of standard penetration blows
(C_u)₃₀: average undrained shear strength

Turkey earthquake hazard map – (TBEC-2018 – 2.1.2)

By accessing the website “https://tdth.afad.gov.tr/” (AFAD Turkey earthquake maps interactive web application) and inputting parameters such as Earthquake Ground Motion Levels (DD-1 to DD-4), Soil Type (ZA to ZE), and the project location, users can obtain the following outputs:
S_S : Short period map spectral acceleration coefficient [dimensionless]
S₁ : Map spectral acceleration coefficient for 1.0 second period [dimensionless]
S_DS : Short-period design spectral acceleration coefficient [dimensionless]
S_D1 : Design spectral acceleration coefficient for 1.0 second period [dimensionless]
PGA : Maximum ground acceleration [g]
PGV : Maximum ground speed [cm/sec]

Local soil impact coefficients F_S and F₁ – (TBEC-2018 – 2.3.3)

F_S and F₁ represent the local soil class coefficients for the short-period region (TBEC-2018 – Table 2.1) and the 1.0 second period region (TBEC-2018 – Table 2.1), respectively. These coefficients are derived through the AFAD earthquake hazard map and the regulations outlined in the TBEC 2018, as detailed in the tables provided.

Design spectral acceleration coefficients S_DS and S_D1 – (TBEC-2018 – 2.3.2)

The map spectral acceleration coefficients Ss and S₁ are transformed into the design spectral acceleration coefficients S_DS and S_D1 as follows:

F_S and F₁: local soil impact coefficients

S_DS= S_s F_s   
S_D1= S₁ F₁                                         

The horizontal elastic acceleration spectrum – (TBEC-2018 – 2.3.4)

The Horizontal elastic design spectral acceleration S_ae(T) is defined from the formula 2.2 of the TBEC-2018.
T = Natural vibration period [s]
T_A = Horizontal elastic design acceleration spectrum corner period [s]
T_B = Horizontal elastic design acceleration spectrum corner period [s]
T_L = Transition period to the constant displacement region in the horizontal elastic design spectrum [s]

Building Categories

The seismic design guidelines in the TBEC 2018 Code integrate several key classifications, including:
– Building Occupancy Classes (BKS)
– Seismic Design Categories (DTS)
– Building Height Categories (BYS)

Building Occupancy Classes (BKS) and building importance factors (I) – (TBEC-2018 – 3.1)

Building Occupancy Classes (BOCs) outlined in Table 3.1 of TBEC–2018 categorize buildings based on their intended use. The building importance factors (I) are determined based on the different building occupancy classes.

Building Use Class	Building Usage Purpose	Building Importance Factor
BKS = 1	Buildings that need to be used after an earthquake, buildings where people stay for a long time and intensely, buildings where valuable goods are stored and buildings containing dangerous substances a) Buildings that must be used immediately after an earthquake (Hospitals, dispensaries, health centers, fire brigade buildings, and facilities, PTT and other communication facilities, transportation stations and terminals, energy generation and distribution facilities, province, district, and municipality administration buildings, first aid and disaster planning stations)) b) Schools, other educational buildings and facilities, dormitories and dormitories, military barracks, prisons, etc. c) museums d) Toxic, explosive, flammable, etc. with features of buildings where substances are located or stored	1.5
BKS = 2	Shopping malls, sports facilities, cinemas, theatres, concert halls, places of worship, etc.	1.2
BKS = 3	Other buildings that are not included in the definitions given for BKS=I and BKS=2 (Houses, workplaces, hotels, building type industrial structures, etc.)	1.0

Seismic Design Categories (DTS) – (TBEC-2018 – 3.2)

Earthquake Design Classes (DTS), are determined according to the Tablo 3.2 of TBEC–2018.
DTS depends on the Building Use Classes and the short-period design spectral acceleration coefficient (S_DS) for the DD-2 earthquake ground motion level.

Building Height Classes (BYS) – (TBEC-2018 – 3.3)

In TBEC (2018), buildings are categorized into 8 Building Height Classes (BYS) according to their total height.

Building Performance Levels – (TBEC-2018 – 3.4)

While the fundamental design procedure adheres to a force-based approach in the 2018 Code, explicit definitions of building performance levels are provided to clarify design targets. These are summarized below.

– Continued Operation Performance (CO): Structural member damage is negligible.
– Limited Damage Performance (LD): Structural components experience limited damage, resulting in very limited inelastic behavior.
– Controlled Damage Performance (CD): Structural component damage is significant but repairable.
– Collapse Prevention Performance (CP): Structural component damage is severe; however, partial or total building collapse is prevented.

Building Design Targets and the Associated Design Procedures – (TBEC-2018 – 3.5)

Building design targets are determined based on a combination of target performances and ground motion levels considered in the design process.

Classification of Building Design Procedures:

Two main design procedures are mandated: Force-Based Design (FBD) and Performance-Based Assessment (PBD). FBD is used conventionally, while PBD is applied when necessary.

Performance Targets for Non-Tall Buildings:

Buildings not classified as tall have an ordinary performance target set to “Controlled Damage” under DD-2 or the 475-year design ground motion.

Advanced Performance Targets for Critical Buildings (DTS of 1a or 2a):

Performance-based procedures are used for DD-1 and DD-3 assessments, while force-based preliminary design is suggested for DD-2 design spectra.

Advanced performance targets include Limited Damage under DD-3 (43-year) and Controlled Damage under DD-1 (2475-year).

Design Procedure for Tall Buildings (BYS=1):

Tall buildings have a dual ordinary performance target.
They should remain linear elastic under DD-3 (43-year) and satisfy collapse prevention under DD-1 (2475-year).
Service level performance assessed by force-based analysis, while collapse prevention performance requires performance-based procedures involving nonlinear time history analysis.

The initial design can be force-based with a controlled damage target under the 475-year design earthquake.

Designers often prefer initial designs with forces obtained from the 43-year, DD-4 service earthquake spectrum instead of using the 475-year earthquake and adjusting forces with R factors, which are challenging to justify for tall buildings.
Initial design can be force-based with controlled damage target under the 475-year design earthquake.

• Table a: Relations between ground motion level, target performance, and design procedure.
  
• Table b: Relations for tall buildings regarding design procedures and performance targets.
  

Response reduction factors (R) – (TBEC-2018 – 4.3)

Equivalent Earthquake Load (EEL) Method – (TBEC-2018 – 4.7.1)

To implement the EEL method for buildings, compliance with the limits outlined in Table 4.4 of TBEC-2018 is necessary.

The total Equivalent Earthquake Load (EEL) in the earthquake direction is calculated according to Equation 4.16 in TBEC-2018.

m_t​: Represents the total mass of the building
S_aR: Reduced design spectral acceleration
T_p​^(X): Natural vibration period of the building in the x direction
g: Gravitational acceleration.

S_aR(T) is calculated according to Equation 4.8 in TBEC-2018.

Ra(T): Earthquake load reduction coefficient which is calculated according to Equation 4.1 in TBEC-2018.