Rebar – an indispensable building material in construction

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I. Diameter Specifications (Main Application Range) The diameter specifications of HRB400E rebar must strictly comply with the “Hot-rolled Ribbed Steel Bars for Reinforced Concrete” (GB/T 1499.2-2018). The nominal diameter range is 6mm-50mm, covering most stress scenarios in engineering. Different diameters correspond to different application requirements, as follows: Small diameter (6mm-12mm): Mainly used for small components, stirrups, and distribution bars, such as floor slab distribution bars, wall tie bars, lintel stirrups, etc. Common specifications are 6mm, 8mm, 10mm, and 12mm; Medium diameter (14mm-25mm): The most widely used, suitable for core stress-bearing components such as frame beams, frame columns, shear wall edge members, and pile caps. Mainstream specifications are 14mm, 16mm, 18mm, 20mm, 22mm, and 25mm; Large diameter (28mm- 50mm): It is mostly used in large-span structures, heavy components or high-load parts, such as large-section frame columns, bridge main beams, pile foundation steel cages, and large equipment foundation reinforcement. Common specifications are 28mm, 32mm, 36mm, 40mm and 50mm. II. External Dimensions and Rib Parameters (Mandatory Requirements)
The HRB400E rebar has a circular cross-section with ribs along its length. The ribs are divided into longitudinal ribs (parallel to the rebar axis) and transverse ribs (at a certain angle to the axis). The parameters must meet the following requirements to ensure bonding and anchorage performance with concrete:
Transverse Rib Design:
Angle: The angle β between the transverse rib and the rebar axis must be between 45° and 60°. When the rebar diameter d ≤ 12mm, the angle can be appropriately widened to 30°.
Spacing: The transverse rib spacing l must be adapted to the diameter. For example, l ≤ 12mm when d = 6mm, l ≤ 20mm when d = 25mm, and l ≤ 25mm when d = 50mm. The deviation of the transverse rib spacing for the same rebar must not exceed ±10%.
Height: The transverse rib height h must meet strength and bonding requirements. For example, h ≥ 0.8mm when d = 10mm, and h ≥ 0.8mm when d = 20mm. When h ≥ 1.5mm, and d = 40mm, h ≥ 2.4mm, and the actual measured height must not be less than 90% of the standard value. Longitudinal Rib Design: Quantity: Each rebar requires 2 symmetrically distributed longitudinal ribs. The width b of the longitudinal rib should match the diameter, e.g., b = 2.0mm when d = 16mm, b = 3.0mm when d = 32mm; Length: The longitudinal rib must run the entire length of the rebar without any partial gaps or interruptions, and the top of the longitudinal rib must smoothly transition to the top of the transverse rib to avoid stress concentration caused by sharp edges. Section Deviation: The actual diameter deviation of the rebar must be within ±0.4mm (e.g., for a rebar with a nominal diameter of 20mm, the actual measured diameter must be between 19.6mm and 20.4mm); The perimeter deviation of the section must not exceed ±2%, and the ellipticity (the difference between the maximum and minimum diameters of the section) must be ≤0.4mm to ensure a regular section shape and uniform stress distribution.