The bolted connection of the grid structure is the key connection method in the grid structure, and its specification requirements aim to ensure the reliability and durability of the connection. The main requirements include: bolt diameter, material, preload and installation accuracy. Bolt diameter should be in accordance with the design provisions, the material needs to meet the requirements of tensile strength and hardness, preload should be determined by calculation, and in the installation process to ensure that the position is correct. Should also comply with the relevant construction standards and acceptance procedures.
Specification requirements for bolting of mesh frame structures
1. Selection of bolt material and strength class
The reliability and safety of bolted connections are closely related to the choice of bolt materials. Generally speaking, bolt materials should be selected from high-strength steel, such as carbon steel and alloy steel. At the same time, according to the loading requirements of the structure and the characteristics of the use of the environment, choose the appropriate bolt strength grade, such as 4.8 grade, 8.8 grade, 10.9 grade and so on. When selecting the bolt material and strength grade, it is also necessary to consider the corrosion resistance and fatigue resistance of the bolt.
2. Control of preload and tightening force of bolts
The reliability and safety of a bolted connection depends mainly on the preload and tightening force of the bolts. Pre-tensioning force refers to the initial tensile force applied in the process of bolt connection, which can improve the stiffness and seismic performance of the connection. The tightening force refers to the actual stress state after the bolt connection, which should meet the structural loading requirements and the requirements of the design code. When making the bolt connection, it is necessary to control the pre-tensioning force and tightening force of the bolts to avoid over-tightening or over-loosening resulting in connection failure.
3. Geometrical requirements for bolted connections
The geometric requirements for bolted connections include the size and location of the bolt holes and the installation clearance of the bolts. The hole size and position of the bolts should meet the design requirements to ensure that the bolts can pass through the connection correctly and connect closely with the neighbouring components. The installation clearance of the bolts should be controlled within a reasonable range to avoid too large or too small resulting in connection failure or stress concentration.
4. Tightening sequence and torque control for bolted connections
The tightening sequence and torque control of bolted connections is an important part of ensuring the reliability and safety of the connection. When making bolt connections, the tightening sequence should be determined in accordance with the design requirements and specification requirements, and the torque control should be carried out using suitable tools and equipment. The purpose of torque control is to ensure that the tightening force of the bolts meets the design requirements, and to avoid over-tightening or over-loosening resulting in connection failure.
5. Basic requirements for bolted connections
Bolt tightening: Tighten the bolt to the appropriate position, ensuring that the bolt is stable and that there are no visible sleeve contact joints. WASHER USE: Flat washers should be placed under the head of the bolt and under the nut to increase the pressure-bearing area. There should generally be no more than 2 flat washers placed on the bolt head side and no more than 1 flat washer placed on the nut side. Anti-loosening device: for bolts whose design requires anti-loosening, nuts or spring washers with anti-loosening device should be used, and spring washers must be set on the nut side. Specific specifications and quality control measures for bolting: quality control: after the installation of the net frame structure, the longitudinal and transverse length of the net frame should be less than L/2000 and not less than or equal to 30mm, and the base offset of the bracket should be less than L/3000 and not more than 30mm. measuring tools: the quality inspector should prepare the measuring instruments such as latitude and longitude meter, level, steel ruler, etc., and keep abreast of the construction situation and make the necessary records. necessary records. Anti-loosening device: For bolted connections subject to dynamic loads or important parts, spring washers should be placed according to the design requirements, and the spring washers must be set on the nut side. Use of special materials: For I-beam and channel type steel using oblique connection, oblique washers should be used to make the supporting surface of the head of the nut and bolt perpendicular to the screw.
