中美建筑钢结构设计方法比较——螺栓连接

Comparisons Between Chinese and American Standards on Bolted Connection Design

螺栓连接具有传力可靠、施工方便、可拆装等优势,是钢结构连接的主要形式。目前装配式钢结构和装配式组合结构的现场施工安装主要采用螺栓连接。美国钢结构协会颁布的AISC 360-16《建筑钢结构设计规范》和中国标准GB 50017—2017《钢结构设计标准》对钢结构螺栓连接形式、材料性能、承载力计算方法、构造要求都做出了详细规定。分析和比较了GB 50017—2017和AISC 360-16在螺栓连接设计规定方面的差异性和相近性,为钢结构设计人员准确理解及应用GB 50017—2017和AISC 360-16提供了参考,同时对进一步改进和完善GB 50017—2017提出了建议。主要内容包括:1)AISC 360-16和GB 50017—2017根据螺栓材料不同分成普通螺栓和高强度螺栓,中国的普通螺栓常采用4.6级和4.8级,也称为C级螺栓。美国ASTM A307标准规定的螺栓相当于4.6级或4.8级普通螺栓。中国的高强度螺栓有8.8级和10.9级,分为大六角头螺栓和扭剪型螺栓。美国的高强度螺栓也分为大六角头和扭剪型,ASTM A354标准规定的BC级螺栓相当于8.8级螺栓、BD级螺栓相当于10.9级螺栓。ASTM F3125/F3125M标准规定的A325级和A490级螺栓也相当于8.8级和10.9级,ASTM F3111和ASTM F3043标准还规定了抗拉强度等级为1380 MPa的高强度螺栓,其强度等级高于中国的12.9级螺栓。2)AISC 360-16和GB 50017—2017中设计普通螺栓连接时都不需要施加预拉力,安装时手动拧紧即可。GB50017—2017规定采用高强度螺栓时必须施加设计规定的预拉力,AISC 360-16允许结构设计人员决定对高强度螺栓是否施加预拉力。AISC 360-16规定的螺栓预拉力值比GB 50017—2017的规定值约大15%。3)AISC 360-16和GB 50017—2017中设计螺栓连接时分别考虑螺栓连接受剪、螺栓连接受拉、螺栓连接受拉剪联合作用的受力状况。当螺栓连接受到剪力作用时,普通螺栓按承压型连接设计,高强度螺栓可以按承压型连接设计或摩擦型连接设计,按照摩擦型连接设计的高强度螺栓必须施加规定的预拉力值并确定接触面抗滑移系数。GB 50017—2017规定的抗滑移系数与接触面表面处理方法和连接钢板的强度等级有关,而AISC 360-16规定抗滑移系数只与接触面表面处理方法有关,AISC 360-16和GB 50017—2017的抗滑移系数取值基本接近,都在0.3~0.5范围内。4)AISC 360-16和GB 50017—2017对螺栓连接的螺栓排布和构造要求都做出了明确规定,要求限制螺栓孔的最大和最小端距和边距,限制螺栓孔的最大和最小间距。AISC 360-16和GB 50017—2017规定了标准螺栓孔径比螺栓直径大2~3 mm的匹配要求,并允许按摩擦型连接设计的高强度螺栓采用大圆孔或槽孔。5)在计算不同受力状况的螺栓连接承载力时,AISC 360-16和GB 50017—2017都要求分别计算螺栓的承载力和连接板的承载力。对于承受剪力作用的长螺栓接头都要考虑螺栓内力分布不均匀的影响,对抗剪承载力进行适当折减。

Bolt connections with the advantages of high reliability,fast fabrication and easy disassembly,have become the primary connection method in steel and composite construction.AISC 360-16 Specification for Structural Steel Buildings published by American Institute of Steel Construction,GB 50017—2017 Standard for Design of Steel Structures released by Chinese government have specified the bolt types,material property,bolt resistance and structural requirements of bolted connections.This paper analyzes and compares the differences and similarities between GB 50017—2017 and AISC 360-16,and provides a reference for structural engineers to understand and apply GB 50017—2017 and AISC 360-16 efficiently.Further improvements and revisions on GB 50017—2017 are also recommended.The main contents of this paper include:1)There are two types of bolts recommended in AISC 360-16 and GB 50017—2017,ordinary bolts and highstrength bolts.The ordinary bolts used in China are Grade 4.6 and 4.8,also known as Grade C bolts.The bolts specified in ASTM A307 are equivalent to Grade 4.6 or 4.8 ordinary bolts.The high-strength bolts in China are Grade 8.8 and 10.9,which could be heavy hex bolts or twist-off bolts.AISC 360-16 also recommended highstrength bolts of heavy hex or twist-off type.Grade BC bolt specified in ASTMA354 is equivalent to Grade 8.8 bolt and Grade BD bolt is equivalent to Grade 10.9 bolt.ASTMF3125/F3125 Malso specified high-strength bolts of Grade A325 and Grade A490,which are equivalent to Grade 8.8 and 10.9.ASTMF3111 and ASTMF3043 specified high-strength bolt with the tensile strength of 1380 MPa,which is higher than that of Grade12.9 bolt in China.2)When applying ordinary bolts,the pretension is not required and bolts can be snug-tightened during installation.Whenever high-strength bolts are applied,the pretension should be specified as required by GB500017—2017.AISC 360-16 allows structural designers to decide whether or not the pretension applied to the high-strength bolts.The pretension of high strength bolts specified in AISC 360-16 is about 15%higher than that specified in GB 50017—2017.3)The bolted connections can be designed to resist shear force,tensile force,combined shear and tensile force.When the bolted connection is subject to shear force,the connections can be designed as bearing type or slipcritical type.The pretension should be applied when high-strength bolt is designed as slip-critical type,and the slip factor of faying surface should be designated.The slip factors recommended in GB 50017—2017 is relevant to the surface treatment and steel grade of connected steel plate,while the slip factors specified in AISC 360-16 is only relevant to the surface treatment.The values of slip factors given in AISC 360-16 and GB 50017—2017 are more or less similar,and in the range of 0.3~0.5.4)AISC 360-16 and GB 50017—2017 have specified the bolt spacing limits and bolt hole sizes.The maximum and minimum end distance and edge distance of bolt holes,and the maximum and minimum spacing of bolt holes should be limited.AISC 360-16 and GB 50017—2017 require that the standard bolt hole size should be larger than the bolt diameter about 2~3 mm,and oversize hole or slot hole is permitted for the high-strength bolt in slip-critical connections.5)AISC 360-16 and GB 50017—2017 require that the resistance of bolts and connecting plates should be determined respectively when designing the bolted connections under different loading conditions.For the long joints subject to shear force,the reduction factor is introduced to consider the uneven distributions of bolt shear forces.