Comparisons Between Chinese and American Standards on Bolted Connection Design

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 ASTM A354 is equivalent to Grade 8.8 bolt and Grade BD bolt is equivalent to Grade 10.9 bolt. ASTM F3125 / F3125M also specified high-strength bolts of Grade A325 and Grade A490, which are equivalent to Grade 8.8 and 10.9. ASTM F3111 and ASTM F3043 specified high-strength bolt with the tensile strength of 1 380 MPa, which is higher than that of Grade 12.9 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 GB 500017—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 slip-critical 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.