In tunnel construction, there is a kind of equipment for starting and excavating called shield machine, which has the functions of excavating and cutting soil, conveying soil ballast, and assembling tunnel lining. When the segment is assembled, there is a screw that acts as a connection and fastening, and the assembly forms a cylindrical pipe, and the segment is a cylindrical wall; during excavation, it can effectively control the ground subsidence, reduce the impact on the ground buildings, and Underwater excavation does not affect the characteristics of water surface traffic, and the segments are combined together to form a pipeline. This design is a straight line or a certain arc-shaped fastening connector, which is the segment bolt. Segment bolts are divided into circumferential and longitudinal. In some designs, the circumferential and longitudinal specifications are the same. In some designs, two specifications, or even two strength levels, are used in the circumferential and longitudinal directions. In general, circumferential segment bolts are longer in length than longitudinal segment bolts.
Segment Bolt Type:
1. Double-ended straight segment bolts
2. Double-ended arc segment bolts
3. Hexagon head arc segment bolts
4. Hexagon head arc thread segment bolts
5. Hexagon flange face arc thread segment bolts
6. Non-standard segment bolts
High-strength bolts are one of the most representative products of special bolts. Compared with ordinary bolts, they have very high strength and long service life. Usually, high-strength bolts are quenched and tempered to increase their strength, and their organization is tempered martensite. Once the tensile strength of this tempered martensitic steel exceeds 1200MPa, the original grain boundary will be embrittled due to the action of trace hydrogen, and the phenomenon of delayed fracture during use becomes obvious.
The difference between high-strength bolts segment bolts and ordinary bolts:
High-strength bolts Segment bolts are made of high-strength materials. The screws, nuts and washers of high-strength bolts are all made of high-strength steel, commonly used in No. 45 steel, 40 boron steel, and 20 manganese titanium boron steel. General bolts are usually made of Q235 steel.
In terms of intensity level:
High-strength bolts are increasingly used. Two strength grades are commonly used, 8.8s and 10.9s, among which 10.9 is mostly. Generally, the strength level of bolts is lower, generally 4.4, 4.8, 5.6 and 8.8.
From the point of view of the force characteristics:
High-strength bolts apply pre-tension and transmit external force by resisting force. Generally, the bolt connection relies on the shear resistance of the bolt and the bearing of the hole wall to transmit the shear force. When the nut is tightened, the pre-tension is very small, and its influence can be ignored. In addition to its high material strength, high-strength bolts also impose a large amount of pre-tension on the bolts. The tensile force causes the extrusion force between the connecting components, so that there is a great resistance perpendicular to the direction of the screw, and the pre-tension force, anti-slip coefficient and steel type directly affect the bearing capacity of the high-strength bolt.
According to the force characteristics, it is divided into pressure type and conflict type. The calculation methods of the two are different. The minimum specification of high-strength bolts is M12, and M16~M30 is commonly used. The function of super-large bolts is unstable and should be used carefully in planning.