7 Critical Factors for an Earthquake-Safe Building
Türkiye sits in a first-degree seismic zone. Following the February 6, 2023 Kahramanmaraş earthquakes, enforcement of the Turkish Building Earthquake Regulation (TBDY 2018) has tightened significantly. This article summarizes the seven essentials of an earthquake-resistant structure.
1. Geotechnical Survey and the Right Foundation
It all starts with the soil. Geophysical and geotechnical surveys are mandatory and reveal:
- Soil class (ZA–ZE)
- Groundwater level
- Liquefaction risk
- Soil bearing capacity
- Site-specific earthquake spectrum
Based on soil class: mat foundation, pile foundation, or deep foundation. Pour standard pad foundations on bad soil and the best superstructure in the world will still fall.
2. Concrete Class: C
30 and Above
TBDY 2018 mandates a minimum of C25/30 for residential. Premium and high-rise buildings use C30/37 or C35/45. On site:
- Verify the ready-mix delivery slip
- Take cube/cylinder samples
- Run 28-day compressive strength tests
3. Adequate Reinforcement and Confinement
In columns and beams:
- Longitudinal reinforcement: S420 ribbed steel
- Confinement zones: at column ends and beam supports
- Stirrup diameter: minimum Ø8 mm
Stirrup confinement is the key to ductile behavior under seismic load. Sparsely tied columns fail brittlely.
4. Clean Geometry
Symmetry in plan and elevation is critical:
- Avoid soft stories (open ground floors)
- No short columns
- Compact forms — avoid L, T, U plans
- No torsional irregularity
5. Avoid Soft and Heavy Stories
Most building collapses in Türkiye involve shops on the ground floor and apartments above. Solutions:
- Sufficient shear walls on the ground floor
- Balanced mass distribution on upper levels
- Controlled roof and terrace loading
6. Use Shear Walls
In modern designs, reinforced concrete shear walls carry most of the seismic load. Properly placed, they:
- Resist 70%+ of horizontal forces
- Relieve column demand
- Shorten the building period
7. Workmanship and Inspection
Even the best design fails with bad workmanship. Critical control points:
- Quality of rebar tying
- Cover spacers in formwork (min. 25 mm cover)
- Vibrator use during pouring
- No cold joints
- Adequate curing (7 days minimum)
The building inspection firm's oversight at these points is non-negotiable.
Is My Existing Building Safe? Checklist
In an older building? Get a seismic performance assessment. Risk increases if:
- Built before 2000
- Ground floor has shops/garages (soft story)
- No shear walls except elevator core
- Visible cracks or corrosion
- Story added later
- Rebar corrosion visible
FAQ
How does building age relate to seismic safety?
Pre-1999 buildings typically follow the 1975 code (inadequate). 1999–2018 follow 1998/2007. Post-2018 follows TBDY 2018 — the safest category.
Retrofit or rebuild?
Depends on the assessment. If retrofit cost exceeds 60% of rebuild cost, demolishing and rebuilding usually makes more sense.
How can I check seismic specs?
Request the structural project (chamber-stamped), geotechnical report and inspection records. Get a civil engineer's second opinion to read them.
At Turallar Yapı İnşaat, every building we deliver fully complies with TBDY 2018 and TSE standards.
