ICS77.140.70 H 44 NATIONAL STANDARD OF THE PEOPLE'S REPUBLIC OF CHINA 中华人民共和国国家标准 GB/T 6728-2002 Supersedes GB/T 6728-1986 Cold Formed Steel Hollow Sections for General Structure - Dimensions, Shapes, Weight and Permissible Deviations 结构用冷弯空心型钢尺寸、外形、重量及允许偏差 Issued on July 15, 2002 Implemented on January 1, 2002 Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
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ICS77.140.70 H 44
NATIONAL STANDARD
OF THE PEOPLE'S REPUBLIC OF CHINA
中华人民共和国国家标准 GB/T 6728-2002
Supersedes GB/T 6728-1986
Cold Formed Steel Hollow Sections for General Structure - Dimensions, Shapes, Weight and
Permissible Deviations 结构用冷弯空心型钢尺寸、外形、重量及允许偏差
Issued on July 15, 2002 Implemented on January 1, 2002 Issued by the General Administration of Quality Supervision, Inspection and
Foreword GB/T 6728 - 2002 "Cold Formed Steel Hollow Sections for General Structure - Dimensions, Shapes, Weight and Permissible Deviations" is a product variety standard of cold formed steel hollow sections for general structure in cold formed section series standards, and the related technical condition standard is GB/T 6725 - 2002 "Cold Formed Steel Sections". Square and rectangle cold formed steel hollow section specified in this standard correspond to European standard EN 10219-2-1997 "Cold Formed Welded Structural Hollow Sections of Non-alloy and Fine Grain Steels - Part 2: Tolerances, Dimensions and Sectional Properties", and specification for round Cold formed steel hollow section corresponds to ISO 4019:1982 "Structural Steels -- Cold-formed, Welded, Structural Hollow Sections -- Dimensions and Sectional Properties". The consistency of this standard, EN 10219-2-1997 and ISO 4019:1982 is not equivalent. This standard differs from EN 10219-2-1997 "Cold Formed Welded Structural Hollow Sections of Non-alloy and Fine Grain Steels - Part 2: Tolerances, Dimensions and Sectional Properties" in: - Specification for round cold formed steel hollow section with outside diameter 610 mm is added; — Class interval and specification of square and rectangle cold formed steel hollow section
are added; — The plane unevenness permissible deviation of square and rectangle cold formed steel
hollow section is added; — Bend angle permissible deviation of square and rectangle cold formed steel hollow section
is decreased; — Bending radius permissible deviation of square and rectangle cold formed steel hollow
section is decreased; — Class interval divisions of bend angle external arc semi-diameter R or (C1, C2) of square
and rectangle cold formed steel hollow section are different; — Type of special cold formed steel hollow section is added and specific shape and
dimension are not provided; — Permissible deviation of cold formed steel hollow section cut lengths is adjusted little; — Weight permissible deflection of cold formed steel hollow section is added. This standard differs from ISO 4019: 1982 "Structural Steels -- Cold-formed, Welded, Structural Hollow Sections -- Dimensions and Sectional Properties" in: — The outside diameter of round cold formed steel hollow section is adjusted little; — Specification for round cold formed steel hollow section with outside diameter 610 mm is
added; — Class interval and specification add square and rectangle cold formed steel hollow section
are added; — Overall size permissible deviation is added; — Minimum wall thickness permissible deviation of cold formed steel hollow section is
added; — Class interval division of bend angle external arc semi-diameter R or (C1, C2) of square
and rectangle cold formed steel hollow section is different, and different requirement in carbon steel and low alloy steel are specified respectively;
— Angular permissible deviation of square and rectangle cold formed steel hollow section is
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added; — Plane unevenness permissible deviation of square and rectangle cold formed steel hollow
section is added; — Type of special cold formed steel hollow section is added and specific shape and
dimension are not provided; — Specification in common fixing cutting permissible deviation of cold formed steel hollow
section is added; — Specification in weight permissible deviation of cold formed steel hollow section is
added; This standard replaces GB/T 6728 - 1986 "Cold Formed Steel Hollow Sections for General Structure - Dimensions, Shapes, Weight and Permissible Deviations" from the implementation date. Compared with GB/T 6728 - 1986, the following modifications are made in this standard: — Outside diameter 21.3 mm – 610 mm of round cold formed steel hollow section is added; — Specification scope of square cold formed steel hollow section is expanded, and side
lengths 170mmx170mm - 500mmx500mm are added; — specification scope of rectangle cold formed steel hollow section is expanded, and side
lengths 200mmx120mm - 600mmx400mm are added; - thickness 10 mm, 12 mm, 14 mm and 16 mm are added;
— Type of special cold formed steel hollow section is added, and specific shape and dimension are not listed, and negotiated by the parties Negotiated by the parties;
— -In dimension permissible deviation, thickness deflection shall not be larger than the percentage of normal thickness;
— Upper and lower limits of bend angle arc semi-diameter are specified in dimension permissible deviation, as well as measuring method;
— Unevenness permissible level of section plane part is specified in dimension permissible deviation;
— General precision is canceled from dimensional precision; — Common fixing cutting length tolerance is specified more strictly in fixing cutting
precision; — Clear numerical value of non fixing cutting and undergauge pipe delivering proportion is
specified, and jointed pipe delivering mode is added; — Permissible value and measuring method of cold-rolled forming section twisting are
specified; — The inclination permissible value of cold-rolled forming section tip saw cutting is
specified; Appendix A hereto is informational appendix. This standard is proposed by China Iron and Steel Association. This standard is under the jurisdiction of National Technical Committee of Standardization for Steel. This standard is prepared by Baosteel Group Corporation Shanghai Steel Process Engineering Research Institute, Wu Steel Group Hankou Steel Rolling Plant and Guangzhou Steel Tubing Plant Co., Ltd. The standard is drafted by Qian Weizhong, Wang Daqi, Zhu Shaowen, Li Jianzhang and Zhang Xiufang. The first edition of this standard was issued in August of 1986.
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NOTE: The English version has been translated directly from the Chinese Standard GBT 6728-2002. In the event of any discrepancy in the process of implementation, the Chinese version shall prevail.
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Cold Formed Steel Hollow Sections for General Structure - Dimensions, Shapes, Weight and
Permissible Deviations 结构用冷弯空心型钢尺寸、外形、重量及允许偏差
1. Scope This standard specifies range, classification, code, technical requirement, dimension, shape, weight, permissible deviation and marking of cold formed steel hollow sections for general structure. The standard is applicable to cold forming cold rolled or hot-rolled tandem rolling steel plate and steel Strip, and cold-rolled forming section manufactured in continuous cold-roll-forming machine group. For cold formed steel hollow section specified by this standard, high frequency resistance welding is mainly adopted, and hydrogen arc welding or other welding methods may be adopted. This standard is not applicable to cold-rolled forming section manufactured through drawing, stamping, folding and so on. 2. Classification and Code According to shape, section steel is classified as round, square, rectangle and other special cold formed steel hollow sections. Codes for them are as following: Round cold formed steel hollow section, round tube is for short, and the code is Y Square cold formed steel hollow section, square tube is for short, and the code is F Rectangle cold formed steel hollow section, rectangle tube is for short, and the code is J Special cold formed steel hollow section, special tube is for short, and the code is YI 3. Sectional Dimension and Permissible Deviation 3.1 The sectional view of round cold formed steel hollow section is detailed in Figure 1, and sectional dimension, cross sectional area, theoretical weight and cross section feature shall correspond with specifications in Table 1. 3.2 The sectional view of square cold formed steel hollow section is detailed in Figure 2, and sectional dimension, cross sectional area, theoretical weight and cross section feature shall correspond with specifications in Table 2. 3.2 The sectional view of rectangle cold formed steel hollow section is detailed in Figure 3, and sectional dimension, cross sectional area, theoretical weight and cross section feature shall correspond with specifications in Table 3. 3.4 Sectional dimension and permissible deviation of special cold formed steel hollow section (special tube) refers to permissible deviation of square or rectangle cold formed steel hollow section. The shape is negotiated by the parties. 3.5 In view of demand side's requirements, cold-rolled forming sections may be supplied beyond the dimension scope specified by Table 1, Table 2 and Table 3, and the permissible
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deviation shall be selected from the deflection of adjacent small dimension specified in the table. 3.6 When the wall thickness is not larger than 10 mm, the wall thickness permissible deviation of cold-rolled forming section shall not be larger than ±10% of nominal wall thickness. When the wall thickness is larger than 10 mm, the wall thickness permissible deviation is ±8%, except wall thickness of bend angle and weld zone. 3.7 The bending angle deflection of cold-rolled forming section shall not be larger than ±1.5°.
D - Outside diameter:
t - Wall thickness Figure 1: Round Cold Formed Steel Hollow Section
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B - Side length;
t - Wall thickness;
R - External Arc Semi-diameter
Figure 2: Square Cold Formed Steel Hollow Section
H - Long side;
B - Short side;
t - Wall thickness;
x - External Arc Semi-diameter
Figure 3: Rectangle Cold Formed Steel Hollow Section
6
Table 1: Section Dimension, Permissible Deviation, Cross Sectional Area, Theoretical Weight and Cross Section Feature of Round Cold Formed Steel Hollow Section
Outside
Diameter
D/
mm
Permissible
Deviation
mm
Wall
Thickness
t
mm
Theoretical
Weight
M/(kg/m)
Cross
Sectional
Area
A/cm2
Inertia
Moment
I/cm4
Radius of
Inertia
R/cm
Elastic
Modulus
Z/cm3
Plastic
modulus
S/cm3
Torsion constant
Surface
Area per
Unit
Length
As/m2 J/cm4 C/cm3
21.3
(21.3) ±0.5
1.2
1.5
1.75
2.0
2.5
3.0
0.59
0.73
0.84
0.95
1.16
1.35
0.76
0.93
1.07
1.21
1.48
1.72
0.38
0.46
0.52
0.57
0.66
0.74
0.712
0.702
0.694
0.686
0.671
0.655
0.36
0.43
0.49
0.54
0.62
0.70
0.49
0.59
0.67
0.75
0.89
1.01
0.77
0.92
1.04
1.14
1.33
1.48
0.72
0.86
0.97
1.07
1.25
1.39
0.067
0.067
0.067
0.067
0.067
0.067
26.8
(26.9) ±0.5
1.2
1.5
1.75
2.0
2.5
3.0
0.76
0.94
1.08
1.22
1.50
1.76
0.97
1.19
1.38
1.56
1.91
2.24
0.79
0.96
1.09
1.21
1.42
1.61
0.906
0.896
0.888
0.879
0.864
0.848
0.59
0.71
0.81
0.90
1.06
1.20
0.79
0.96
1.1
1.23
1.48
1.71
1.58
1.91
2.17
2.41
2.85
3.23
1.18
1.43
1.62
1.80
2.12
2.41
0.084
0.084
0.084
0.084
0.084
0.084
33.5
(33.7) ±0.5
1.5
2.0
2.5
3.0
3.5
4.0
1.18
1.55
1.91
2.26
2.59
2.91
1.51
1.98
2.43
2.87
3.29
3.71
1.93
2.46
2.94
3.37
3.76
4.11
1.132
1.116
1.099
1.084
1.068
1.053
1.15
1.47
1.76
2.01
2.24
2.45
1.54
1.99
2.41
2.80
3.16
3.50
3.87
4.93
5.89
6.75
7.52
8.21
2.31
2.94
3.51
4.03
4.49
4.90
0.105
0.105
0.105
0.105
0.105
0.105
42.3
(42.4) ±0.5
1.5
2.0
2.5
3.0
4.0
1.51
1.99
2.45
2.91
3.78
1.92
2.53
3.13
3.70
4.81
4.01
5. 15
6.21
7.19
8.92
1.443
1.427
1.410
1.394
1.361
1.89
2.44
2.94
3.40
4.22
2.50
3.25
3.97
4.64
5.89
8.01 10.31
12.43
14.39
17.84
3.79
4.87
5.88
6.80
8.44
0.133
0.133
0.133
0.133
0.133
48 (48.3) ±0. 5
1.5
2.0
2.5
3.0
4.0
5.0
1.72
2.27
2.81
3.33
4.34
5.30
2.19
2.89
3.57
4.24
5.53
6.75
5.93
7.66
9.28
10.78
13.49
15.82
1.645
1.628
1.611
1.594
1.562
1.530
2.47
3.19
3.86
4.49
5.62
6.59
3.24
4.23
5.18
6.08
7.77
9.29
11.86
15.32
18.55
21.57
26.98
31.65
4.94
6.38
7.73
8.98
11.24
13.18
0.151
0.151
0.151
0.151
0.151
0.151
60 (60.3) ±0.6
2.0
2.5
3.0
4.0
5.0
2.86
3.55
4.22
5.52
6.78
3.64
4.52
5.37
7.04
8.64
15.34
18.70
21.88
27.73
32.94
2.052
2.035
2.018
1.985
1.953
5.11
6.23
7.29
9.24 10.98
6.73
8.27
9.76 12.56
15.17
30.68
37.40
43.76
55.45
65.88
10.23
12.47
14.58
18.48
21.96
0.188
0.188
0.188
0.188
0.188
75.5
(76.1) ±0.76
2.5
3.0
4.0
5.0
4.50
5.36
7.05
8.69
5.73
6.83
8.98
11.07
38.24
44.97
57.59
69.15
2.582
2.565
2.531
2.499
10.13
11.91
15.26
18.32
13.33
15. 78
20.47
24.89
76.47
89.94 115.
19 138.29
20.26
23.82
30.51
36.63
0.237
0.237
0.237
0.237
7
88.5 (88.
9) ±0.90
3.0
4.0
5.0
6.0
6.33
8.34
10.30
12.21
8.06
10.62 13.12
15.55
73.73
94.99
114.72
133. 00
3.025
2.991
2.957
2.925
16.66
21.46
25.93
30.06
21.94
28.58
34.90
40.91
147.45
189.97
229. 44
266.01
33.32
42.93
51.85
60.11
0.278
0.278
0.278
0.278
114
(114.3) + 1.15
4.0
5.0
6.0
10. 85 13.44
15.98
13.82
17.12
20.36
209.35
254. 81
297.73
3.892
3.858
3.824
36.73
44.70
52.23
48.42
59.45
70.06
418. 70
509.61
595. 46
73.46
89.41
104. 47
0.358
0.358
0.358
140
(139.7) ±1.40
4.0
5.0
6.0
13.42
16. 65 19.83
17.09
21.21
25.26
395.47
483. 76
568.03
4.810
4.776
4.742
56.50
69.11
85.15
74.01
91.17
107. 81
'790.94
967.52
1136.13
112.99
138.22
162.30
0.440
0,440
0.440
165
(168.3) + 1.65
4
5
6
8
15.88
19.73
23.53
30.97
20.23
25.13
29.97
39.46
655.94
805.04
948.47
1 218.92
5.69
5.66
5.63
5.56
79.51
97.58
114.97
147.75
103.71
128. 04
151.76
197.36
1 311.89
1 610. 07
1 896.93
2 437.84
159.02
195.16
229.93
295. 50
0.518
0.518
0.518
0.518
219.1
(219.1) ±2.20
5
6
8
10
26.4
31. 53
41.6
51.6
33.60
40.17
53.10
65.70
1 928
2 282
2 960
3 598
7.57
7.54
7.47
7.40
176
208
270
328
229
273
357
438
3 856
4 564
5 919
7 197
352
417
540
657
0.688
0.688
0.688
0.688
273 (273) ±2.75
5
6
8
10
33.0
39.5
52.3
64.9
42.1
50.3
66.6
82.6
3 781
4 487
5 852
7 154
9.48
9.44
9.37
9.31
277
329
429
524
359
428
562
692
7 562
8 974
11 700 14
310
554
657
857
1 048
0.858
0.858
0.858
0.858
325
(323.9) ±3.25
5
6
8
10
12
39.5
47.2
62.5
77.7
92.6
50.3
60.1
79.7
99.0
118.0
6 436
7 651
10 014
12 287
14 472
11.32
11.28
11.21
11.14
11.07
396
471
616
756
891
512
611
804
993
1 176
12 871
15 303
20 028
24 573
28 943
792
942
1 232
1 512
1 781
1.20
1.20
1.20
1.20
1.20
355.6
(355.6) ±3.55
6
8
10
12
51.7
68.6
85.2
101.7
65.9
87.4
109.0
130.0
10 071
13 200
16 220
19 140
12.4
12.3
12.2
12.2
566
742
912
1 076
733
967
1 195
1 417
20 141
26 400
32 450
38 279
1 133
1 485
1 825
2 153
1.12
1.12
1.12
1.12
406.4
(406.4) + 4.10
8
10
12
78.6
97.8
116.7
100
125
149
19 870
24 480
28 937
14.1
14.0
14.0
978
1 205
1 424
1 270
1 572
1 867
39 750
48 950
57 874
1 956
2 409
2 848
1.28
1.28
1.28
457 (457) + 4.6
8
10
12
88.6
110.0
131.7
113
140
168
28 450
35 090
41 556
15.9
15.8
15.7
1 245
1 536
1 819
1 613
1 998
2 377
56 890
70 180
83 113
2 490
3 071
3 637
1.44
1.44
1.44
508 (508) ±5.10
8
10
12
98.6
123.0
146.8
126
156
187
39 280
48 520
57 536
17.7
17.6
17.5
1 546
1 910
2 265
2 000
2 480
2 953
78 560
97 040
115 072
3 093
3 621
4 530
1.60
1.60
1.60
610 ±6.10
8
10
12.5
16
118.8
148.0
184.2
234.4
151
189
235
299
68 552
84 847
104 755
131 782
21.3
21.2
21. 1
21.0
2 248
2 781
3 435
4 321
2 899
3 600
4 463
5 647
137 103
169 694
209 510
263 563
4 495
5 564
6 869
8 641
1.92
1.92
1.92
1,92
Note: values in brackets are specifications specified in ISO 4019.
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9
Table 2: Section Dimension, Permissible Deviation, Cross Sectional Area, Theoretical Weight and Cross Section Feature of Square Cold Formed Steel Hollow Section (Part 1)
Note: theoretical weight in the table is calculated according to density 7.85g/cm3.
3.8 Bend angle external arc semi-diameter R or (C1, C2) of cold-rolled forming section shall correspond with specifications in Table 4. Measuring method for R (C1, C2) shall be taken according to Figure 4 or through fillet gage.
Table 4: External Arc Semi-diameter R or (C1, C2)
Thickness t/mm
R or (C1, C2) Carbon Steel ( sσ ≤ 320 MPa) Low alloy steel ( sσ ≤ 320 MPa)
t ≤ 1.0~2.5 t 1.5~2.5 t 3<t ≤ 6 1.5~2.5 t 2.0~3.0 t 6<t ≤ 10 2.0~3.0 t 2.0~3.5 t t>10 2.0~3.5 t 2.5~4.0 t Note: value sσ is the minima specified in the standard.
19
Figure 4: Exterior Angle Section Plane of Square or Rectangle Cold Formed Steel Hollow Section
3.9 The convexo-concave of cold-rolled forming section sectional plane shall correspond with following specification: the convexo-concave shall not be larger than 0.6% of the side length, and the min value is 0.4 mm. The measuring method is detailed in Figure 5.
Figure 5: Measurement for Convexo-concave of Square or Rectangle Cold Formed Steel
Hollow Section Plane 3.10 The dimension of cold-rolled forming section shall be measured not less than 100 mm away from the tip. 4. Length and Permissible Deviation 4.1 The normal delivery length of cold-rolled forming section is 4000 mm – 12000 mm. Cold-rolled forming section with others lengths may be negotiated by the parties. 4.2 Cold-rolled forming sections are delivered according to cut or multiple lengths, specifications shall be marked in the contract. The length tolerance shall correspond with specifications in Table 5.
4.3 Cold-rolled forming section of not less than 2000 mm undergauge and non fixing cutting are allowed to be delivered. Products may be delivered in the form of jointed tube, but the jointed position shall be cut off when the demand side uses them. The weight of undergauge and non fixing cutting products shall not larger than 5% of delivered weight, and for cold-rolled forming section which theoretical weight is larger than 20 kg/m, the weight of undergauge and non fixing cutting products shall not be larger than 10% of total delivered weight. 5. Shape 5.1 The bending radius of cold-rolled forming section shall be larger than 2 mm per m, and the total bending radius shall not be larger than 0.2% of total length. The measuring method is detailed in Figure 6.
Figure 6: Measurement for Bending Radius
5.2 Negotiated by the parties, and marked in the contract, the torsion degree of cold-rolled forming section may be measured. The measurement shall be taken on the platform, and the measuring method shall be taken according to Figure 7. The measured values shall be less than v value, and calculated according to formula (1).
v=2+L X 0.5/1000 (1)
Where, L - Length, mm; V - Degree of torsion, mm.
21
Figure 7: Torsion of Square or Rectangle Cold Formed Steel Hollow Section
5.3 The tip of cold-rolled forming section shall be cut as rectitude, and the saw cutting inclination shall not be larger than specifications in Table 6. Little deformation and burr caused by cutting are allowable.
6. Weight 6.1 cold-rolled forming section shall be delivered according to actual weight. 6.2 the permissible deviation of actual weight and theoretical weight for cold-rolled forming
section shall be 106
+− %.
7 Marking Demonstration Cold forming rectangular tube, which is made of Carbon Structural Steels Q 235, and the dimension is 150mmX100mmX6mm shall be marked as:
1988-700 GB/T-Q2352002-6728 GB/T J150x100x6Tube)ar (RectangulSection Hollow Steel Formed Cold
22
Appendix A (Informative)
Formulae for Section Characteristic Calculation Table 1, Table 2 and Table 3 of this standard specify nominal section Characteristic of round and square, rectangle cold formed hollow section with standard dimension scope, and nominal section Characteristic of round and square, rectangle cold formed hollow section with other dimension and thickness may be calculated in accordance with Table A.1 and Table A.2.
Table A.1: Round Hollow Section Steel
Item Symbol Unit Computing formula
Nominal Excircle Diameter D mm -
Normal Thickness T mm
Nominal Inner Circle Diameter d mm d=D-2t
Surface area per m length As m2/m As=π D/103
Cross Sectional Area A cm2 A=π (D2-d4
)/(4× 102)
Weight per unit weight M kg/m M=0.785 × A
Inertia Moment I cm4 I=π (D4-d4
)/(64× 104)
Gyration radius R cm R=(I/A)1/2
Elastic Modulus Z cm3 Z=(2I× 10)/D
Plastic modulus S cm3 S=(D3-d3)/(6× 103)
Twisting inertia J cm1 J=2I
Modulus of torsion C cm3 C=2Z
23
Table A.2: Square and Rectangle Hollow Section Steel Item Symbol Unit Computing formula
Nominal Length of Short Side
Face
B mm
Nominal Length of Long Side
Face
H mm -
Normal Thickness t mm -
Nominal Exterior Angle
Semi-diameter
R mm If t ≤ 6 mm, R=2.0t
If 6<t ≤ 10 mm, R=2.5t
If t>10 mm, R=3.0t
Nominal Interior Angle
Semi-diameter
r mm r=R-t
Weight per unit length M kg/m M=0.785A
Cross Sectional Area A cm2 A=[2t(B+H-2t)-(t-π )(R2-r2)]/102
Surface area per m length As mm2/m As=2(H+B-4R+π R)