What are the requirements for ordinary bolt connections in steel structures
What are the requirements for ordinary bolt connections in steel structures
Firstly, let's understand the types of steel structural bolts and some common problems encountered:
1、 Grade A.B.C: A and B are refined bolts, while Grade C is rough bolts;
2、 Material grade: Grade 8.8 for A and B, Grade 4.6 or 4.8 for C;
3、 Processing: Grade A.B is precisely machined from rough parts on a lathe - refined; Grade C is made by pressing raw round steel - rough;
4、 Screw hole: Class A.B requires drilling with a jig (Class I hole), with a hole diameter about 0.3mm larger than the screw; Class C refers to the hole diameter that is 1.5~3.0mm larger than that of the screw, which can be punched in one shot or drilled without a drill jig (Class II hole)
5、 Stress: Class A.B has good stress performance, small connection deformation, and can withstand both tension and shear, used for important connections; The performance of C-grade bolt connections is not as good as that of A.B grade, mainly subjected to tension and used for secondary connections that bear static loads and indirectly dynamic loads.
6、 Cost: A.B grade bolts are expensive, while C-grade bolts are cheap. Places where C-grade bolts can be used do not require A.B grade bolts.
When ordinary bolts are used as permanent connection bolts, they should meet the following requirements:
① For general steel structure bolted connections, flat washers should be placed below the bolt head and nut to increase the bearing area.
② The number of washers placed under the steel structure bolt head should generally not exceed 2, and the number of washers placed under the nut head should generally exceed 1.
③ For bolts and anchor bolts that require relaxation in design, nuts or spring washers with relaxation devices should be used, or relaxation measures should be taken manually.
④ For bolted connections that bear dynamic loads or important parts, spring washers should be placed according to design requirements, and the spring washers must be set on one side of the nut.
⑤ For I-beam and channel steel types, diagonal washers should be used as much as possible to ensure that the bearing surface of the nut and bolt head is perpendicular to the screw.
