Steel bars: the "skeleton code" of concrete structures

As the core reinforcement material of concrete structure, steel bar is like the "skeleton" of the building. Its excellent tensile strength perfectly complements the compressive performance of concrete, and together they build the steel skeleton of modern projects such as skyscrapers, cross-river bridges, and underground tunnels. From the 6mm diameter floor distribution bar to the 50mm diameter bridge main force bar, steel bar carries the infinite imagination of human beings for space construction through precise strength grading and structural design.
1. Definition and classification system of steel bar
Definition: Steel bar refers to steel wire or rod used to bear tensile force in concrete structure. Its mechanical properties are optimized by carbon content regulation and alloy element addition. The surface usually has ribs to enhance the bonding with concrete. According to GB/T 1499.2-2018 standard, the yield strength of modern steel bar has been increased from 235MPa to more than 600MPa, achieving a technological leap of "doubling strength".
Classification by production process and surface morphology
Production process:
Hot-rolled steel bars: steel billets are heated to 1050-1150℃ and rolled, accounting for more than 90% of steel bar production;
Cold-rolled ribbed steel bars: cold-rolled into ribbed shape after hot rolling, with a strength increase of 15-20%, used for prefabricated components;
Residual heat treated steel bars: rapid cooling through water after hot rolling, surface hardening core toughness maintained, such as RRB400;
Heat treated steel bars: quenched + tempered, strength reaches 1470MPa, used for prestressed concrete.
Surface morphology:
Plain round steel bar (HPB): diameter 6-22mm, smooth surface, low bonding strength;
Crescent rib steel bar (HRB): ribs are crescent-shaped, angle 35-45°, and bonding strength is 40% higher than plain round steel bars;
Constant rib steel bar: rib height is consistent, used for coarse steel bars with diameter ≥28mm;
Epoxy coated steel bar: surface coated with 180-300μm epoxy layer, resistant to salt spray corrosion, used for marine engineering.
2. Production process and technological breakthroughs
Full process analysis
Steelmaking link:
Converter steelmaking: HRB400 steel bar adopts top and bottom double blowing converter, carbon content is controlled at 0.2-0.25%, manganese content is 1.2-1.6%, silicon content is 0.6-0.8%;
Refining process: High-end steel bars (such as HRB600) are refined by LF furnace, sulfur content ≤0.015%, phosphorus content ≤0.02%, to ensure toughness.
Continuous casting technology:
Small billet continuous casting (150mm×150mm): used to produce steel bars with a diameter of ≤32mm, with a pulling speed of 3-5m/min;
Electromagnetic stirring technology: applying an alternating magnetic field in the crystallizer to make the molten steel solidify evenly, reduce center segregation, and improve the ductility of the steel bars.
Rolling and controlled cooling:
High-speed wire rolling: φ6-12mm steel bars are produced by high-speed wire rolling mills at a speed of 120m/s, and the surface temperature is controlled at 850-900℃;
Controlled rolling and controlled cooling (TMCP): HRB500 steel bars are rolled at low temperature (900-950℃) + ultra-fast cooling (cooling rate ≥50℃/s), which refines the grains to less than 5μm and increases the strength by 20%;
Online residual heat quenching: After rolling, the steel bars are quickly cooled to 200-300℃ through a water-penetrating device, forming martensite on the surface, and ferrite + pearlite in the core. After tempering, the strength reaches more than 400MPa.
Cutting-edge technology cases
Headless rolling technology: Jingye Group uses headless rolling to produce HRB400 steel bars, eliminating the performance difference between the head and the tail, improving the dimensional accuracy to ±0.1mm, and increasing the yield rate by 3%;
Digital steel rolling: The intelligent steel bar rolling system deployed by Baowu Group predicts the rolling force and temperature through AI algorithms, and controls the strength fluctuation of φ20mm steel bars to ±15MPa;
Special steel bars for 3D printing: The 2.5mm diameter ultra-fine steel bars developed by MCC Construction Research Institute use the electroslag remelting process, with an oxygen content of ≤30ppm, and are used for micro-reinforcement of building 3D printing.
3. Mechanical properties and engineering applications
Building structure field
High-rise buildings:
Beijing China Zun Building (528m) uses HRB500E steel bars (φ32mm) as the main reinforcement of the core tube, with a yield strength of 540MPa, which reduces the steel consumption by 18% compared with HRB400;
Prefabricated building prefabricated composite panels use cold-rolled ribbed steel bars (CRB600H) welded mesh with a spacing of 150mm×150mm, and the construction efficiency is 3 times higher than that of traditional binding.
Foundation engineering:
The underground comprehensive pipeline corridor in Xiongan New Area uses HRB400E steel bars (φ22mm), and the reinforcement is optimized through BIM technology to reduce the collision rate of node steel bars by 90%;
The nuclear power plant containment uses Φ32mm 20MnNiMo steel bars, which are 100% ultrasonically inspected to ensure the integrity of the structure under the design basis accident.
Bridges and traffic engineering
Cross-river bridges:
The main tower of the Qingzhou Channel Bridge of the Hong Kong-Zhuhai-Macao Bridge uses HRB500 steel bars (φ40mm), and the tensile bearing capacity of a single steel bar reaches 628kN, which can withstand a 16-level typhoon;
The cable anchors of the Shanghai-Suzhou-Jiangyin Yangtze River Bridge use Φ70mm 40CrNiMoA alloy steel bars, which have a σb≥980MPa after quenching and tempering treatment, and a fatigue life of ≥2×10^6 times.
Railway transportation:
The HRB400E steel bars (φ16mm) are used for the shield tunnel segments of the subway, with a bending angle of 180° and no cracks, which meet the deformation requirements of the tunnel;
The Φ10mm CRB600H cold-rolled ribbed steel bars with a spacing of 100mm are used for the ballastless track slabs of the high-speed railway, which improve the anti-cracking performance of the track slabs.
Special environmental engineering
Marine engineering:
The Hainan Wenchang launch site pier uses epoxy coated steel bars (Φ25mm), zinc layer + epoxy composite protection, and salt spray test (5000 hours) without rust;
The South China Sea island reef building uses Φ18mm stainless steel bars (316L), which are resistant to chloride ion corrosion and have a service life of more than 100 years.
Municipal engineering:
The concrete stands of the "Ice Ribbon" speed skating hall of the Beijing Winter Olympics use HRB600 steel bars (Φ20mm), which are 50% stronger than HRB400 and realize large-span column-free space;
The Shanghai deep drainage tunnel uses Φ32mm sulfate-resistant steel bars, which resist sulfate ion (SO4^2-≤10000mg/L) corrosion by adding 0.3% vanadium.
Earthquake-resistant engineering applications
Buildings in high-intensity areas:
The Jiuzhaigou post-disaster reconstruction hospital in Sichuan uses HRB400E steel bars (Φ22mm), with a strength-to-yield ratio of 1.38 and an elongation of 19%, achieving "no collapse in a major earthquake" in the 8-degree fortification zone;
The terminal building of Kunming Changshui Airport in Yunnan uses Φ120mm low-yield point steel bars (LYP160) for buckling restraint bracing, with a yield strength of 160MPa, to absorb earthquake energy.
IV. Market structure and technology trends
Global industry status
Capacity distribution: In 2024, the global steel bar production will be about 420 million tons, of which China will account for 56% (Hebei, Jiangsu and Shandong will produce more than 50 million tons per year), followed by India (8%), the United States (5%) and Turkey (4%);
Price dynamics: The average price of HRB400E steel bar (Φ20mm) in 2024 will be about US$650/ton, which will be 7% higher than that in 2023 due to the price of iron ore (62% grade Australian ore is US$125/ton) and coke price (US$350/ton);
Import and export structure: China exports about 12 million tons of steel bars annually, mainly to Southeast Asia (accounting for 40%), and imports about 500,000 tons, mainly high-end stainless steel bars (such as SUS316L steel bars imported from Japan, which are 3 times more expensive than domestic ones).
Technology development direction
Green and low-carbon production:
Short-process steelmaking: Using scrap steel + electric arc furnace to produce steel bars, CO₂ emissions per ton of steel are reduced from 2.1 tons to 0.8 tons (such as the EAF+CSP process of Nucor in the United States);
Hydrogen energy steelmaking: The hydrogen-based vertical furnace developed by Hesteel Group produces HRB400 steel bars, using green hydrogen to replace coke to achieve "zero-carbon steelmaking";
Waste heat recovery: During the rolling process, waste heat from flue gas above 800℃ is recovered and used to preheat steel billets, saving more than 15% energy.
High-performance innovation:
HRB700 grade steel bar: By adding vanadium-titanium microalloy + controlled rolling and controlled cooling, the yield strength reaches 700MPa, which is used in super-high-rise buildings over 600 meters, reducing the amount of steel by 30%;
Intelligent monitoring steel bar: Φ20mm steel bar with built-in optical fiber sensor can monitor stress and strain in real time, which is used for bridge health monitoring;
Self-repairing steel bar: The surface is coated with microcapsule self-repairing coating. When the coating is damaged, the capsule ruptures and releases the repair agent to automatically heal the microcracks.
Intelligent manufacturing:
Unmanned steel rolling workshop: The steel bar intelligent workshop deployed by Shagang Group adopts 5G + industrial robots to realize the unmanned process from rolling to packaging, and the efficiency is increased by 40%;
Digital twin technology: Baowu Group has established a digital twin system for steel bar rolling, simulating temperature and stress fields, and reducing the trial and error cost by 70%;
Blockchain traceability: Jingye Group applies blockchain technology to exported steel bars, tracing the whole process from steelmaking to use, meeting the traceability requirements of EU CE certification.
Functional surface treatment:
Graphene enhanced coating: Adding 0.5% graphene to the epoxy coating improves the salt spray resistance from 1000 hours to 3000 hours, and is used in coastal projects;
Bionic anti-skid ribs: simulate the steel bar ribs of the octopus suction cup structure, and the bonding strength is 25% higher than that of the traditional crescent ribs, and is used for large diameter steel bars;
Nano zinc aluminum magnesium coating: replaces traditional galvanizing, and the thickness of 20μm can achieve the anti-rust effect of hot-dip galvanizing 85μm, and the cost is reduced by 20%.
V. Selection Guide and Maintenance Points
Selection Decision Factors
Structural Safety Level:
First safety level (important structure): select HRB400E/HRB500E, strength-to-yield ratio ≥1.25, elongation ≥17%;
Second safety level: select HRB400/HRB500, elongation ≥16%;
Temporary structure: HPB300 can be selected, and the cost is 15% lower than HRB400.
Environmental corrosion level:
Indoor dry environment: ordinary HRB400 steel bar, concrete protective layer thickness 20mm;
Wet environment (such as bathroom): HRB400 + epoxy coating, protective layer thickness 30mm;
Marine environment: 316L stainless steel bar or zinc-aluminum alloy coated steel bar, protective layer thickness 50mm.
Construction process requirements:
Mechanical connection (straight thread sleeve): select HRB400E/HRB500E, diameter ≥16mm;
Welding connection: select HRB400, carbon content ≤0.25%, avoid welding cracks;
Prefabricated components: select CRB600H cold-rolled ribbed steel bar, high strength and high dimensional accuracy.
Storage and maintenance technology
Rust-proof storage:
Open-air storage: Raise the height by more than 300mm, cover with waterproof canvas, lay ventilation pipes at the bottom, and keep humidity ≤60% RH;
Warehouse storage: Overhead stacking, spacing ≥500mm, install dehumidifier (humidity ≤45% RH), and spray water-soluble rust inhibitor regularly;
Sea transportation protection: The whole bundle of steel bars is wrapped with heat shrink film, and VCI gas phase rust prevention bags (dosage 100g/ton) are built in to prevent salt spray erosion.
Construction protection:
Rebar binding: Avoid contact with soil, clean with a wire brush after contamination, and return if rust is severe (rust is flaky);
Concrete pouring: Avoid direct contact with steel bars during vibration to prevent damage to the coating, and use plastic clamps for protective layer pads (spacing ≤600mm);
Construction in rainy season: If the tied steel bars are rusted, use mechanical sandblasting to remove rust (Sa2.5 level), and then apply steel bar rust inhibitor.
Post-maintenance:
Carbonization repair: When the carbonization depth of concrete is greater than the protective layer, electrochemical re-alkalization technology is used to restore the pH value of the steel bar surface to above 12.5;
Rust repair: Locally corroded steel bars can be protected by anode protection, and the steel bars can be made cathodes through an external power supply to prevent further corrosion;
Structural reinforcement: When the bearing capacity is insufficient, carbon fiber cloth (CFRP) or external steel plates are used for reinforcement to work together with the original steel bars.