Concrete & Steel Material Properties — TS 500 and TS 708

1. Concrete Grades — TS 500 Table 2

TS 500:2000 Table 2 defines concrete classes by their characteristic cylinder compressive strength f_ck at 28 days (150 × 300 mm cylinder). The class notation C_ck/C_cube follows the Eurocode convention where the first number is the cylinder strength and the second is the 150 mm cube strength (approximately f_cube = 1.25 · f_ck).

Tensile Strength f_ctk

TS 500 §4.2 gives the characteristic tensile strength as:

The tensile strength governs shear capacity (V_cr), punching shear, and splitting in development length calculations. It is not used directly for flexural design.

2. Concrete Modulus and Creep

This formula gives the initial tangent modulus. For deflection calculations in TS 500, the effective modulus accounts for creep:

Where h₀ is the notional size = 2A_c/u (A_c = cross-section area, u = perimeter exposed to drying). Turkey's Mediterranean coastal climate typically falls in RH 55–70%, placing creep coefficients in the range φ = 2.0–3.0 for typical members.

Comparison with Other Standards

TS 500's modulus formula gives values close to Eurocode 2 for normal-strength concrete (C20–C35), while ACI 318 yields notably lower stiffness predictions for the same cylinder strength.

3. Reinforcement — TS 708:2010

TS 708:2010 classifies reinforcing steel by yield strength and ductility class. The letter suffix (A, B, C) indicates ductility — Class C has the highest ductility and is mandatory in seismic zones per TSC 2018.

TSC 2018 Seismic Requirements for Reinforcement (§5.4)

• All longitudinal and transverse reinforcement in seismic systems must be Class C ductility (B420C or B500C).
• The upper bound on f_uk/f_yk ≤ 1.35 is critical — excessively high actual strength would increase capacity shear demands unexpectedly.
• B500C has become the standard specification in Turkish practice, replacing B420C for most new construction since the mid-2010s. The higher yield strength reduces steel quantities but requires careful crack width verification at serviceability.
• Smooth bars (plain round) are not permitted for longitudinal reinforcement in structural elements per TSC 2018.

4. Structural Steel — TS EN 10025

For steel structures designed per TS EN 1993 (Eurocode 3 adopted by TSE), the material standard is TS EN 10025 for hot-rolled sections and plates.

S355 is the dominant grade for structural frames in Turkey, preferred for its balance of strength and weldability. For seismic applications, TSC 2018 Chapter 9 specifies additional requirements: toughness grades (S355J2 or ML), and limits on yield-to-tensile ratio f_y/f_u ≤ 0.80 to ensure adequate plastic rotation capacity.

5. Partial Safety Factors

6. TSC 2018 Material Requirements

TSC 2018 §5.4 imposes mandatory material quality requirements that supplement TS 500 for all elements in the seismic force-resisting system:

• Minimum concrete class: C25/30 for all structural elements (f_ck ≥ 25 MPa). Higher grades (C30/37 or above) are recommended for columns in DTS 1/2 buildings.
• Reinforcement ductility class: Class C mandatory — this means B420C or B500C only. B500C is the standard choice in modern practice.
• Welded wire mesh: Only Class A or B welded fabric — not used for longitudinal bars in seismic members. May be used for secondary slab reinforcement with TSC acceptance.
• Overstrength bound: For capacity design calculations, TSC §5.4.3 defines the overstrength factor D = f_yk,actual/f_yk,nominal. The design capacity forces amplified by D must be checked to ensure critical elements (columns, connections) remain elastic.

Material Properties for Capacity Design

When TSC 2018 requires capacity design (e.g., column design in §7.3, foundation design in §16), the expected material strengths replace design values:

These expected strengths are used to compute probable flexural capacities (M_pr) of beams, which in turn determine the design shear of columns via the strong column–weak beam mechanism.

7. Comparison: TS 500 vs EN 1992 vs ACI 318

Practical Implications

• Concrete E_c: TS 500 gives slightly lower stiffness than EN 1992, leading to slightly larger computed deflections — conservative for serviceability. ACI's formula yields the lowest modulus of the three.
• Rebar strength: B500C (f_yd=435 MPa) vs ACI Grade 60 (f_y=420 MPa, with φ=0.90 → φf_y=378 MPa) means TS 500/Eurocode designs use approximately 15% less steel for the same moment demand.
• Concrete strain: EN 1992's ε_cu2=0.0035 vs TS 500's ε_cu=0.003 means neutral axis depth limits differ slightly. TS 500 is marginally more conservative in the maximum permissible moment capacity.