I. Mechanical properties
The mechanical properties of steel bars are determined by tests. The mechanical properties used to measure steel bar quality standards include yield point, tensile strength, elongation, cold bending performance and other indicators.
(1) Yield point (fy)
When the stress of the steel bar exceeds the yield point, the tensile force does not increase but the deformation increases significantly, which will produce a large residual deformation. The tensile force per unit area of the steel bar obtained by dividing the tensile force at this time by the cross-sectional area of the steel bar is the yield point σs°
(2) Tensile strength (fu)
Tensile strength is the tensile force obtained by dividing the maximum tensile force that the steel bar can withstand before it breaks by the cross-sectional area of the steel bar. Tensile strength is also called ultimate strength. It is the maximum stress value in the stress-strain curve. Although it has no direct meaning in strength calculation, it is an essential guarantee item in the mechanical properties of steel bars. Because:
a. Tensile strength is the ultimate ability of steel bars to withstand static loads. It can indicate how much strength reserve the steel bar has after reaching the yield point. It is an important indicator of resistance to plastic failure.
b. Defects in the steel bars during the melting and rolling process, as well as unstable chemical composition of the steel bars, are often reflected in the tensile strength. When the carbon content is too high and the temperature at the end of rolling is too low, the tensile strength may be very high; when the carbon content is low and there are too many non-metallic inclusions in the steel, the tensile strength is low. c. The level of tensile strength has a direct impact on the ability of reinforced concrete structures to resist repeated loads. (3) Elongation Elongation is the maximum strain value when the specimen is broken in the stress-strain curve, also known as elongation. It is an indicator of the plasticity of steel bars. Like tensile strength, it is also an essential guarantee item in the mechanical properties of steel bars. The calculation of elongation is the percentage of the length of the elongated part of the steel bar when it breaks under tension. By putting the two broken sections of the specimen together, the length of the gauge section after fracture, L1, can be measured. Subtracting the original gauge length, L0, is the plastic deformation value. The ratio of this value to the original length is expressed as δ, that is, the larger the elongation δ value, the better the plasticity of the steel. The elongation is related to the gauge length. For hot-rolled steel bars, the gauge length is 10 times the diameter of the specimen as the measurement standard, and its elongation is expressed as δ10. For steel wire, the gauge length is 100mm as the measurement standard, expressed as δ100. For steel strands, it is δ200. (4) Cold bending performance Cold bending performance refers to the ability of steel bars to resist cracking when they are plastically deformed by cold processing (i.e. processing at room temperature). The cold bending test is a test to determine the ability of steel bars to withstand bending deformation at room temperature. During the test, the magnitude of stress should not be considered. Instead, a steel bar specimen with a diameter of d is bent to 180° or 90° around a bend with a diameter of D (D is specified as 1d, 3d, 4d, or 5d). The steel bar specimen is then inspected for cracks, scales, fractures, and other phenomena to determine whether its quality meets the requirements. The cold bending test is a more stringent test that can reveal defects such as uneven internal structure of the steel bar.
II. Mechanical properties
(1) The total elongation δgt of the steel bar under maximum force is not less than 2.5%. If the supplier can guarantee this, no test is required.
(2) According to the requirements of the purchaser, steel bars that meet the following conditions can be supplied:
a. The ratio of the measured tensile strength of the steel bar to the measured yield point is not less than 1.25;
b. The ratio of the measured yield point of the steel bar to the minimum yield point specified in the table above is not greater than 1.30.
III. Process performance
(1) Bending performance
After bending 180 degrees according to the bend diameter specified in the table below, no cracks shall occur on the surface of the bent part of the steel bar. Brand Nominal Diameter a
(2) Reverse Bending Performance
According to the requirements of the purchaser, the steel bar can be subjected to reverse bending performance test.
The bending center diameter of the reverse bending test is one steel bar diameter larger than that of the bending test. First bend 45 degrees forward, then bend 23 degrees in reverse, and then bend 23 degrees in reverse. After the reverse bending test, no cracks shall be generated on the surface of the steel bar at the bent part.

The mechanical properties of steel bars are the laws of reaction and change when the steel bar is subjected to force, including the yield strength of steel bars, the tensile strength of steel bars, the elongation of steel bars and the cold bending performance. The yield strength of steel bars is the stress generated by the steel bar to resist deformation, the tensile strength is the maximum bearing capacity of the steel bar, the elongation is the percentage of the extended part of the steel bar to the original length when it is broken, and the cold bending performance is the performance of the steel bar that can withstand bending without breaking at room temperature. Testing the mechanical properties of steel bars is one of the main tasks of construction engineering inspection personnel. By testing the mechanical properties of steel bars, the quality of the project can be effectively guaranteed and the occurrence of safety accidents can be prevented.

Answers

• 
  Rebar performance test? 19/09/2025 12:09:09
• 
  What is the welding performance of galvalume steel sheet? 19/09/2025 10:32:15
• 
  What is the difference between rebars without E and with E? 18/09/2025 09:12:20
• 
  What standards does S690QL steel plate comply with? 17/09/2025 14:19:56
• 
  What are the main aspects of rebar testing? 17/09/2025 07:27:08