Rebar Properties

Standard reinforcing bar sizes and steel grade mechanical properties — ASTM A615/A706, EN 10080, IS 1786.

ISO Metric Bar Sizes — EN 10080

Steel Grades — Mechanical Properties (EN 1992-1-1 Annex C / EN 10080)

ASTM A615 Bar Sizes

Steel Grades — Mechanical Properties (ASTM A615 / A706)

IS 1786 — TMT / Deformed Bar Sizes

Steel Grades — Mechanical Properties (IS 1786:2008)

Cross-Sectional Properties & Reinforcement Database Tables

This module presents comprehensive cross-sectional property tables for reinforcing steel bars under different international regulatory frameworks. The data matrix maps nominal bar diameters, total cross-sectional areas (A_s), and unit weights according to each specified design standard.

EN 10080 / ISO Metric Table: European metric bar designations ⌀8 mm to ⌀40 mm paired with ductility classes (Class A, B, C). Covers nominal diameters, cross-sectional areas (mm²), and unit weights (kg/m) for compliance with EN 1992-1-1 detailing rules on minimum reinforcement ratio and maximum bar spacing.
ASTM A615 Table: Standard US bar sizes No. 3 to No. 18 with corresponding nominal diameters (in/mm), cross-sectional areas (in²/mm²), and unit weights (lb/ft, kg/m). Covers Grade 60 (f_y = 414 MPa) and Grade 80 (f_y = 552 MPa) for evaluation of minimum reinforcement ratios (ρ_min) and spacing limits per ACI 318.
IS 1786 Table: Nominal dimensions and cross-sectional areas for Indian standard high-yield strength deformed (HYSD) bars — Fe 415, Fe 500, Fe 550, and Fe 600. Includes unit weights for immediate checking of tension and compression reinforcement areas under IS 456:2000 flexural and shear design provisions.

📚 Reinforcing Bar Properties — Background & Code References

Bar Designation Systems↑ Top

How Rebar Sizes Are Designated

Three parallel systems exist worldwide, each using different nominal diameter conventions. Despite the naming differences, the mechanical performance requirements — yield strength, elongation, and ductility class — are set by each country's standard and do not translate directly from one system to another.

Standard	Designation	Nominal diameter d_b	Strength grades
ASTM A615 / A706 (USA)	Bar No. = d_b in 1/8-inch increments (e.g. #8 = 1 in = 25.4 mm)	No.3 (9.5mm) – No.18 (57.3mm)	Grade 40, 60, 80, 100 (ASTM A615-22)
EN 10080 / ISO metric (Europe)	Ø + nominal diameter in mm (e.g. Ø12)	Ø6 – Ø40 mm	B500A, B500B, B500C (f_yk=500 MPa)
IS 1786:2008 (India)	Fe + yield strength in MPa (e.g. Fe500)	6 mm – 40 mm	Fe415, Fe500, Fe550, Fe600

Deformed vs Plain Bars

All modern structural rebar is deformed — it has surface ribs or lugs pressed onto the bar during rolling. These deformations create mechanical interlocking with the concrete, dramatically improving bond compared to plain round bars. Plain bars are now used only for stirrups and ties in some codes (they are bent into closed shapes so slip is not the primary concern), and for prestressed wire strands.

The cross-sectional area of a deformed bar is based on the nominal diameter — the diameter of a plain round bar of equal unit mass. The actual bar is slightly smaller at the core but the rib projections increase the outer diameter. This is why A_b = π·d_b²/4 always refers to the nominal, not measured, dimension.

Ductility Classes (EN 10080)

Eurocode rebar is classified by ductility, which governs the behaviour of the structure in the plastic range (seismic design) and determines whether moment redistribution is permitted:

Class	f_t/f_y (min)	ε_uk (min)	Application
Class A	1.05	2.5%	Non-seismic, lightly stressed
Class B	1.08	5.0%	General structural — most common
Class C	1.15–1.35	7.5%	Seismic DCH / DCM structures; moment redistribution >15%

Bond & Development Length↑ Top

Why Development Length Matters

Rebar carries tensile force. For that force to be transferred to and from the concrete, the bar must be embedded for a sufficient development length l_d. If a bar is cut short, the bar cannot develop its full yield strength — the failure mode is bar pull-out or splitting of the concrete cover, both brittle.

ACI 318-25 §25.5.1 — Development length for straight deformed bars in tension

l_d = (3f_y/(40λ√f'c))·(ψ_t·ψ_e·ψ_s·ψ_g/((c_b+K_tr)/d_b))·d_b ≥ 300 mm
where: ψ_t = top bar factor, ψ_e = epoxy factor, ψ_s = size factor, ψ_g = grade factor
(c_b+K_tr)/d_b ≤ 2.5 (confinement limit)

The development length is proportional to d_b and f_y, and inversely proportional to √f'c. A Ø32 bar in Grade 60 steel with poor cover can require l_d > 1.5 m.

EC2 §8.4.2 — Design anchorage length

l_bd = α₁·α₂·α₃·α₄·α₅·l_b,rqd ≥ l_b,min
l_b,rqd = (d_b/4)·(σ_sd/f_bd) where f_bd = 2.25·η₁·η₂·f_ctd
α-factors account for bar shape, concrete cover, transverse reinforcement, and transverse pressure

Hooks and Bends

Standard 90° or 180° hooks at the end of a bar can reduce the required straight embedment length by providing mechanical anchorage. ACI §25.3 and EC2 §8.3 define the minimum bend diameters (function of d_b) to avoid fracturing the bar during bending.

Bar size	ACI min. bend diameter (ties/stirrups)	ACI min. bend diameter (main bars)
Ø6–Ø16 / #3–#5	4d_b	6d_b
Ø19–Ø25 / #6–#8	—	6d_b
Ø29–Ø36 / #9–#11	—	8d_b
Ø43–Ø57 / #14–#18	—	10d_b

Detailing Rules↑ Top

Minimum Spacing — ACI 318-25 §25.8.1

Bars must be spaced far enough apart to allow concrete to flow between them during casting and to achieve adequate bond. The clear distance between parallel bars must be the greatest of:

25 mm (1 in)
d_b (bar diameter)
4/3 × d_agg (nominal maximum aggregate size)

Concrete Cover — ACI 318-25 §20.6.1 (Non-prestressed, Cast-in-Place)

Exposure condition	Minimum cover
Not exposed to weather, #6–#18 bars	38 mm (1.5 in)
Not exposed to weather, #5 and smaller	19 mm (0.75 in)
Exposed to weather, #6–#18 bars	50 mm (2 in)
Exposed to weather, #5 and smaller	38 mm (1.5 in)
Cast against earth permanently	75 mm (3 in)

Maximum Bar Spacing — Crack Control

Distributing reinforcement using many smaller bars at closer spacing reduces crack widths better than a few large bars. ACI §24.3.2 limits the centre-to-centre spacing of flexural reinforcement:

ACI 318-25 §24.3.2 — Maximum spacing for flexural steel

s ≤ min(380×(280/f_s) − 2.5·c_c, 300×(280/f_s))
where f_s = 2f_y/3 (service stress), c_c = clear cover to bar surface

For f_y=420MPa (Grade 60): f_s=280MPa → s_max = min(380−2.5c_c, 300) mm. With c_c=40mm: s_max = min(280, 300) = 280mm.

Lap Splice Length

When bar length from the mill is insufficient to span the full member, bars are overlapped in a lap splice. The splice length is a multiple of l_d (typically 1.0–1.3×l_d depending on the fraction of bars spliced at one location). Lap splices are NOT permitted for bars larger than Ø36 (ASTM #11) in tension — mechanical couplers or welded splices must be used instead.

References↑ Top

[1]
ASTM A615/A615M-22 — Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement. ASTM International, 2022.
[2]
ASTM A706/A706M-22 — Standard Specification for Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement (for weldability and seismic applications).
[3]
EN 10080:2005 — Steel for the Reinforcement of Concrete — Weldable Reinforcing Steel. CEN, Brussels. Ductility classes A, B, C.
[4]
IS 1786:2008 — High Strength Deformed Steel Bars and Wires for Concrete Reinforcement. Bureau of Indian Standards, New Delhi.
[5]
ACI 318-25 §25.5 (Development of deformed bars), §25.8 (Bar spacing), §20.6 (Cover requirements). ACI, 2025.
[6]
EN 1992-1-1:2004 §8.3 (Bend diameters), §8.4 (Anchorage of longitudinal bars), §8.7 (Laps). CEN, Brussels.