北美规范与中国规范关于冷弯薄壁型钢C形截面受弯构件设计的比较

对比了北美规范CSA S136-07和中国规范GB 50018-2002关于冷弯薄壁型钢C形截面受弯构件的名义抗弯强度。首先介绍了2本规范计算名义抗弯强度的方法，然后分析了控制构件名义抗弯强度的2个主要参数，即弯扭屈曲应力和有效截面模量，并对2本规范进行了深入对比，最后对典型的6 m跨长的C形托梁构件进行了名义抗弯强度比较。研究结果表明：依据GB 50018-2002计算的弯扭屈曲应力不小于依据CSA S136-07规范计算的结果，而根据GB 50018-2002计算的翼缘有效宽度则远远小于根据CSA S136-07规范计算的结果；2本规范名义抗弯强度的不同主要由C形截面翼缘尺寸和构件所受荷载类型控制；当翼缘尺寸较小，名义抗弯强度主要由弯扭屈曲而非局部屈曲控制时，如果构件用于均布荷载，则GB 50018-2002的计算结果大于 CSA S136-07规范的结果，但是当构件用于抵抗均布弯矩时，则没有区别；当翼缘尺寸较大，名义抗弯强度主要由局部屈曲而非弯扭屈曲控制时，在2种工况下GB 50018-2002的计算结果均小于CSA S136-07规范的计算结果。

On North American and Chinese Standards for Design of Cold-formed Steel C-section Flexural Members

Nominal flexural strengths of cold-formed steel C-sections evaluated by the North American standard CSA S136-07 and the Chinese standard GB 50018-2002 were investigated . To quantify the differences of the nominal flexural strength between the two standards ,6 m span joists with typical C-sections subjected to the uniformly distributed load and uniform bending mo-ment were investigated .The study results show that discrepancies between the two standards are resulted from both the difference in evaluating the effective section modulus and the difference in computing the lateral-torsional buckling stress . T he lateral-torsional buckling stress evaluated based on GB 50018-2002 is generally not less than that of CSA S 136-07 w hereas the flange effec-tive width of C-section calculated by GB 50018-2002 is much smaller than that of CSA S136-07 . T he adequacy of flange to prevent lateral-torsional buckling and the applied load patterns are the important factors resulting the differences of the nominal flexural strength between the two standards .If the flange is inadequate to resist later-torsional buckling and local buckling does not govern ,the strength associated with GB 50018-2002 is greater than that of CSA S136-07 if members are subjected to the uniformly distributed load but there is no difference for case of uni-form bending moment ;in the case that flange is adequate to resist later-torsional buckling but lo-cal buckling governs the strength ,then the nominal flexural strength obtained from GB 50018-2002 becomes less than that of CSA S136-07 in both foregoing applied load patterns .