A hot-rolled high-strength steel bar application technology content
Technical content of 1
High-strength steel bars refer to ordinary hot-rolled ribbed bars (HRB) and fine-grained hot-rolled ribbed bars (HRBF) with yield strengths of 400MPa and 500MPa, which are stipulated in the national standard "Steel for Reinforced Concrete Part 2: Hot-rolled Ribbed Bars" (GB 1499.2).
By adding vanadium (V), niobium (Nb) and other alloying elements for microalloying, the brand is HRB；; ; Through controlled rolling and controlled cooling process, the grain refinement grade of metallographic structure of steel bar is HRBF；; There is also the brand RRB, which is quenched by waste heat. Among these three kinds of high-strength steel bars, micro-alloyed steel bar (HRB) is the most reliable in terms of material mechanical properties, construction adaptability and weldability. The strength index and ductility of fine-grained steel bar (HRBF) meet the requirements, and its weldability is average. However, the ductility, weldability and machining adaptability of steel bars treated with waste heat are poor.
By comparing the application of high-strength steel bars in various structures, it is found that the application of high-strength steel bars can reduce the amount of steel bars by about 12%~ 18% on average, which has a good material saving effect. Considering the amount of steel bars saved by steel bar engineering in building construction, 25~38 yuan can be saved per square meter in civil engineering. Therefore, the economic benefits of popularizing and applying high-strength steel bars are also enormous.
The application of high-strength steel bars can obviously improve the reinforcement efficiency of structural members. In large public buildings, large column grids and long-span frame beams are widely used. If 400MPa and 500MPa high-strength steel bars are used for these long-span beams, the number of reinforcement can be effectively reduced, the reinforcement efficiency can be effectively improved, and the construction is convenient.
In the design of beam-column members, sometimes due to the influence of the number of steel bars, in order to ensure the proper spacing of steel bars, the cross-section width of the members has to be increased, which leads to the increase of concrete consumption in beam-column sections. If high-strength steel bars are used, the number of steel bars can be significantly reduced and the cross-sectional dimensions of beams and columns can be reasonably optimized.
2 technical indicators
The technical indexes of 400MPa and 500MPa grade high-strength steel bars should meet the national standard GB 1499.2, and the design strength and construction application indexes of steel bars should meet the relevant standards such as Code for Design of Concrete Structures (GB500 10), Code for Acceptance of Construction Quality of Concrete Structures (GB50204) and Code for Construction of Concrete Structures (GB50666).
According to Code for Design of Concrete Structures (GB500 10), the diameter of 400MPa and 500MPa high-strength steel bars is 6 ~ 50mm；; The yield strength, standard value of tensile strength and design value of tensile and compressive strength of 400MPa grade steel bars are 400N/mm2, 540N/mm2 and 360 N/mm2 respectively. The standard values of yield strength and tensile strength of 500MPa grade steel bars are 500N/mm2 and 630 N/mm2 respectively. The design value of tensile and compressive strength is 435N/mm2.
For structures with seismic fortification requirements, frames and supporting members designed according to the first, second and third seismic grades, the longitudinal stress of ordinary steel bars has further requirements on the strong yield ratio, super-strong yield ratio and ductility of steel bars, and its specifications shall meet the following requirements:
The ratio between the measured tensile strength and the measured yield strength of steel bars should not be less than1.25;
The ratio of the measured yield strength to the standard yield strength of steel bars should not be greater than1.30;
The total elongation measured under the maximum tension of steel bars shall not be less than 9%.
In order to ensure that the reinforcement material meets the seismic performance index, it is suggested to adopt hot-rolled ribbed reinforcement with suffix "E".
3 Scope of application
Priority should be given to using 400MPa grade high-strength steel bars as the main reinforcement of concrete structures, which are mainly used for longitudinal reinforcement of beams and columns, high-rise shear walls or long-span floors. Give full play to the characteristics of high strength and good ductility of 400MPa grade steel bars, and at the same time ensure and improve the structural safety performance, significantly reduce the amount of reinforcement compared with 335MPa grade steel bars.
500MPa-grade high-strength steel bars should be actively promoted, which are mainly applied to the longitudinal steel bars of columns, large column nets or heavy-duty beams in high-rise buildings, and can also be used in structural transfer stories and large foundation rafts of super-high-rise buildings, so as to achieve a better effect of reducing the amount of steel bars.
HPB300 steel bar replaces HPB235 steel bar, and 300(335)MPa steel bar is used as auxiliary steel bar. 300(335)MPa grade steel bars are required for structural reinforcement of members, stirrups of general beams and columns, reinforcement of general span floors and reinforcement of walls. Among them, HPB300 round steel is more suitable for stirrups of beams and columns of small components and welding nets between floors and walls. For high-strength steel bars with simple production process and cheap waste heat treatment process, such as RRB400 steel bars, due to their poor ductility, weldability and machinability, the Code for Design of Concrete Structures GB500 10 suggests that they be used in structural members and parts with low ductility of steel bars, such as foundation slabs, floors and secondary structural members of mass concrete, so as to make full use of them.
.4 engineering case
400MPa grade steel bars are widely used in high-rise buildings and large public buildings in China. Typical projects include: Beijing Olympic Games Project, Shanghai World Expo Project, Sutong Yangtze River Highway Bridge, etc. 500MPa grade steel bars are used in the new research building of China Institute of Building Research, Hualin Home in Zhengzhou, Hebei Construction Service Center and other projects.
Second, the application technology of high-strength cold-rolled ribbed steel bar
Technical content of 1
CRB600H high-strength cold-rolled ribbed bar (CRB600H high-strength bar for short) is a new type of cold-rolled ribbed bar developed in China in recent years. CRB600H high-strength steel bar is developed on the basis of traditional cold-rolled ribbed steel bar CRB550. After many technical improvements, product performance, product quality, production efficiency and economic benefits have been significantly improved. The biggest advantage of CRB600H high-strength steel bar is that ordinary Q235 wire rod is used as raw material. The production line has realized automatic, continuous and high-speed operation through cold rolling, online heat treatment and online performance control, without adding any microalloying elements.
CRB600H high-strength steel bar has the same price as HRB400 steel bar, but its strength is higher. After application, it can save steel 10%. The application of tons of steel can save alloy 19kg and standard coal 9.7kg. At present, CRB600H high-strength steel bars are widely used in construction projects in more than ten provinces and cities such as Henan, Hebei, Hubei, Hunan, Anhui, Shandong and Chongqing, with remarkable material saving and comprehensive economic effects.
2 technical indicators
The technical indexes of CRB600H high-strength steel bars shall conform to the current industry standard YB/T4260 and national standard GB 13788, and the design, construction and acceptance shall conform to the current industry standard "Technical Specification for Cold Rolled Ribbed Reinforced Concrete Structures" JGJ 95-201. The standards of China Engineering Construction Association, CRB600H steel bar application technical specification, high-strength steel bar application technical guide and local standards of Henan, Hebei and Shandong were compiled.
The diameter range of CRB600H high-strength steel bar is 5~ 12mm, the standard value of tensile strength is 600N/mm2, the standard value of yield strength is 520N/mm2, the elongation at break is 14%, the maximum uniform elongation is 5%, and the design value of strength is 4 15N/mm2 (360 higher than that of HRB400 steel bar.
3 Scope of application
CRB600H high-strength steel bars are suitable for industrial and civil buildings and general structures, and the specific scope is as follows: stressed steel bars in plate members (strength design value is 415n/mm2); Vertical and horizontal distribution of steel bars in shear walls and stirrups in edge members, excluding longitudinal steel bars in edge members; Beam-column stirrups have good economic benefits in the application of various plate and wall components because the diameter of CRB600H steel bar ranges from 5~ 12mm and the strength design value is high.
4 engineering cases
Mainly used in various public buildings, houses and high-speed rail projects. Typical projects include: Hebei University of Engineering New Campus, Wuhan Optics Valley Xingcheng Complex, Yichang Xinhuayuan Residential Area, Zhengzhou He Yi Medical University First Affiliated Hospital Complex, Xinzheng Port Civil Aviation International Xinyuan Large Residential Area, Anyang Comprehensive Commercial and Residential Area and other residential and public buildings; Track slabs in high-speed rail projects such as Zhengzhou Passenger Dedicated Line, Shanghai-Kunming Passenger Dedicated Line, Baolan Passenger Dedicated Line and Xicheng Passenger Dedicated Line.
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