High-strength bolt connection is through the great tighten pretension bolt rod inside the connection plate plate clamping piece, enough to produce a lot of friction, so as to improve the integrity and stiffness of connection, when the shear, in accordance with the requirements for the design and stress is different, can be divided into friction type high strength bolt connection and high strength bolt connecting two pressure type, is the essential difference between the two limit state is different, although it is the same kind of bolt, but the calculation method, requirements, scope of application is very different.In shear design, high-strength bolt friction connection refers to the maximum friction force that may be provided by bolt tightening force between the external shear force and the contact surface of the plate as the limit state, that is, to ensure that the internal and external shear force of the connection does not exceed the maximum friction force during the whole service period.There will be no relative slip deformation of the plate (the original void between the screw and the hole wall is always maintained).In shear design, pressure type high strength bolt connection is allowed in the external shear force exceeds the maximum friction force, the relative sliding between the connected plate deformation, until the bolt contact with the hole wall, then connection on bolt shaft shear and pressure on the hole wall and the friction between the contact surface panel joint force, finally to shaft shear or pressure on the hole wall damage as even accept shear limit state.In short, friction type high-strength bolts and pressure-bearing type high-strength bolts are actually the same kind of bolts, but the design is
Slippage is not considered.Friction type high-strength bolt can not slip, bolt does not bear shear force, once slip, the design is considered to reach the failure state, relatively mature in technology;High-strength pressure-bearing bolts can slide, and the bolts also bear shear force. The final damage is equivalent to that of ordinary bolts (bolt shear or steel plate crushing).From the perspective of use:
The bolt connection of the main member of the building structure is generally made of high-strength bolt.Common bolts can be reused, high strength bolts can not be reused.High strength bolts are generally used for permanent connections.
High-strength bolts are prestressed bolts, friction type with torque wrench to apply the prescribed prestress, pressure type screw off the plum head.Ordinary bolts have poor shear performance and can be used in secondary structural parts.Ordinary bolts need only be tightened.
Common bolts are generally class 4.4, class 4.8, class 5.6 and class 8.8.High strength bolts are generally 8.8 and 10.9, of which 10.9 is the majority.
8.8 is the same grade as 8.8S.The mechanical properties and calculation methods of ordinary bolt and high-strength bolt are different.The stress of high-strength bolt is first of all through the application of pretension P in its internal, and then the friction resistance between the contact surface of the connecting piece to bear the external load, and the ordinary bolt is directly bear the external load.
High strength bolt connection has the advantages of simple construction, good mechanical performance, dismountable, fatigue resistance, and under the action of dynamic load, which is a very promising connection method.
High strength bolt is to use a special wrench to tighten the nut, so that the bolt to produce a huge and controlled pretension, through the nut and the plate, to be connected by the same amount of prepressure.Under the action of pre-pressure, greater friction force will be generated along the surface of the connected piece. Obviously, as long as the axial force is less than this friction force, the member will not slip and the connection will not be damaged. This is the principle of high-strength bolt connection.
High strength bolt connection depends on the friction force between the contact surfaces of the connecting parts to prevent the mutual slip. In order to have enough friction force on the contact surfaces, it is necessary to increase the clamping force and friction coefficient of the contact surfaces of the members.The clamping force between the members is achieved by applying pretension to the bolts, so the bolts must be made of high-strength steel, which is why they are called high-strength bolt connections.
In the high strength bolt connection, the friction coefficient has great influence on the bearing capacity.The test shows that the friction coefficient is mainly affected by the form of contact surface and the material of component.In order to increase the friction coefficient of contact surface, methods such as sand blasting and wire brush cleaning are often used in construction to treat the contact surface of components within the connection range.
Post time: Jun-08-2019