GB/T 6728-2025Cold forming sectional steel for general structure (English PDF)

3.1 Free edge

In open-sectional steel, an edge that only one end has a rounded corner (R-angle).

3.2 Non-free edge

In open-sectional steel, an edge that both ends have rounded corners (R-angle).

5.1 Closed-sectional steel is classified into square, rectangular, and circular shapes

according to its external shape. Their codes are as follows.

a) Square sectional steel (also known as square tube). F;

b) Rectangular sectional steel (also known as rectangular tube). J;

c) Circular sectional steel (also known as circular tube). Y (or phi).

5.2 Open-section sectional steel is classified into nine types according to the cross-

sectional shape. Their codes are as follows.

a) Cold forming equal angle steel. JD;

b) Cold forming unequal angle steel. JB;

c) Cold forming equal channel steel. CD;

d) Cold forming unequal channel steel. CB;

e) Cold forming inward-curled channel steel. CN;

f) Cold forming outward-curled channel steel. CW;

g) Cold forming Z-shaped steel. Z;

h) Cold forming rolled-edge Z-shaped steel. ZJ;

i) Cold forming rolled-edge equal angle steel. JJ.

6.1 Cross-section, dimensions and allowable deviations

6.1.1 Closed-sectional steel

6.1.1.1 The cross-sectional view of the square sectional steel is shown in Figure 1.The cross-sectional dimensions, allowable deviations, theoretical weight, cross-sectional area, and cross-sectional properties shall conform to the provisions of Table 1.The cross-sectional area, cross-sectional property parameters, and surface area per meter of length are for reference only.

6.1.1.2 The cross-sectional view of the rectangular sectional steel is shown in Figure 2.

The cross-sectional dimensions, allowable deviations, theoretical weight, cross- sectional area, and cross-sectional properties shall conform to the provisions of Table

6.1.1.4 The cross-sectional properties of closed-sectional steel can be calculated with

reference to Annex A. Sectional steels with dimensions and allowable deviations other than those specified in Tables 1, 2, and 3 may be provided upon negotiation between the supplier and the purchaser and as specified in the contract.

6.1.1.5 The allowable deviation of the wall thickness of closed-sectional steel shall

comply with the provisions of Annex B. ......