Hot-rolled ribbed bars
Hot-rolled ribbed bars, also known as hot-rolled shaped steel bars, are mainly used in reinforced concrete structures and prestressed concrete structures as reinforcing bars, prestressed rods and supports for railway sleepers, bridges and various large-scale project structures, as well as steel structures for ordinary buildings. GB/T 14981-1994 provides the specifications for hot-rolled ribbed bars. The mass per meter, dimensions, dimensions and allowable deviations, steel grades and mechanical properties, surface quality and technical requirements, test methods, inspection rules, packaging, marking and quality certificate of hot-rolled ribbed bars are specified .
Hot-rolled ribbed bars are divided into light-yield and high-yield ribbed bars according to their yield strengths. Light-yield ribbed bars mainly refer to hot-rolled ribbed bars with nominal diameter under 16mm. High-strength ribbed bars mainly refer to ribbed bars with nominal diameter over 14mm. According to the ribbing of hot-rolled ribbed bars, they are divided into ordinary ribs and the ribs with deformations. Generally, ordinary ribs refers to those ribs with a ribbing height of not more than 3.5mm. The higher of the ribbing height, the larger of the bond area between itself and concrete, which bring stronger anchorage effect. The ribs with deformations are ribbed bars whose ribs are formed with a special mold.
In terms of requirements for mass per meter, the mass per meter of hot-rolled light-yield ribbed bars is from 0.222kg/m to 1.968kg/m. The mass per meter of high-yield ribbed bars is from 8.0kg/m to 33.6 kg/m. In terms of the allowable deviation for mass per meter, the mass per meter should fall within the range of deviation specified in GB/T 14981-1994. According to the standard, the allowable deviation should be +/-3%.
In terms of dimensions, the nominal diameters of hot-rolled ribbed steel bars should be 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 20mm, 25mm, 28mm, 30mm, 32mm, 40mm, 50mm and 60mm. The allowable deviation for diameter should be (-0/+2%) in general, while the deviation could reach up to (-0/+3%) for 18mm and higher diameters based on some certain conditions.
The chemical compositions, requirements and test methods for chemical compositions of hot-rolled ribbed bars are specified in GB/T 1499-1998. In terms of requirements for mechanical properties, the yield strength of hot-rolled ribbed bars has different requirements according to their nominal diameters. For light-yield ribbed bars with nominal diameters below 16mm, the yield strength should reach 235MPa. For high-yield ribbed bars with nominal diameter equal to or above 14mm, the yield strength should reach 300MPa. According to GB/T 1499-1998, the tensile strength of hot-rolled ribbed bars should meet the requirements stated in the corresponding regulations. The allowable deviation for the elongation of hot-rolled ribbed bars should be within 16% in general.
The surface quality of hot-rolled ribbed bars should meet the requirements stated in the corresponding regulations. Any dirt, burning patches, scale, scratches, slit, rupture and rust should not exist on the surface of these hot-rolled ribbed bars when their nominal diameters are below 20mm; if the nominal diameter of steel bars is higher, there should not be any large and obvious burning patches, scale, rust and slit.
The technical requirements, test methods and inspection rules of hot-rolled ribbed bars are provided in the aforesaid Chinese standard. In terms of requirements for packaging, all of the hot-rolled ribbed bars should be packaged with bundles of equal mass and same size. The number of pieces per bundle for ordinary hot-rolled ribbed bars should not be fewer than 5000 or 500 pieces. For bars of different nominal diameters, the number of pieces per bundle should be specified in GB/T 14981-1994.
In terms of requirements for marking, all bars should have the nominal diameter and steel grade marked on them and the bundles should have the mass per bundle, steel grade and nominal diameters marked. In terms of the quality certificate, it should provide the name of manufacturer, Dimensions, steel grade, batch code, test results, number of bundles and total mass.
In conclusion, the specifications, mass per meter, dimensional, mechanical properties, surface quality, technical requirements and quality certificate requirements of hot-rolled ribbed bars are all provided in GB/T 14981-1994. This standard covers the requirements for hot-rolled light-yield and high-yield ribbed bars and helps to ensure the quality of these products.
