What are the requirements for ordinary bolt connection of steel structure

       First of all, we should know what kinds of steel structure bolts are and some problems we often encounter

       1、Grade I, grade A.B.C: Grade A and B are refined bolts, grade C are rough bolts;

       2、 Material grade: Grade A and B are grade 8.8, grade C is grade 4.6 or 4.8;

       3、 Processing: grade A.B is made of blank accurately processed on lathe - refined; grade C is made by pressing round steel without machining - rough;

       4、 Screw hole: Class A and class B need to be drilled with a drilling die (type I hole), and the hole diameter is about 0.3mm larger than that of the screw; grade C is one-time punching or drilling without drilling die (type II hole), and the hole diameter is 1.5-3.0mm larger than that of the screw

       5、 Stress: grade A.B has good mechanical performance, small connection deformation, and can be used for important connection; grade C bolt connection performance is not as good as A.B grade, mainly tensile, used for secondary connection bearing static load and indirect dynamic load.

       6、 Cost: the cost of A.B grade is expensive, and the price of grade C bolt is cheap. Grade A.B bolt is not used where grade C bolt can be used.

       When ordinary bolts are used as permanent connecting bolts, they shall meet the following requirements:

      (1)For general steel structure bolt connection, flat washer should be placed under bolt head and nut to increase bearing area.

      (2) generally, the number of washers placed under the bolt head of steel structure shall not be more than 2, and that under the nut head shall be more than 1.

      (3) for the bolts and anchor bolts that are required to be loosened in design, nuts or spring washers with loosening devices shall be used, or the loosening measures shall be taken by manual methods.

      (4) for the bolt connection bearing dynamic load or important parts, the spring washer should be placed according to the design requirements, and the spring washer must be set on one side of the nut.

      (5) for I-beam and channel steel, oblique washer should be used as far as possible to make the bearing surface of nut and bolt head perpendicular to the screw.