What Are The Differences between High Tensile Bolts And Ordinary Bolts?

I. Definition and representation of bolts

1. The definition of the bolt:

(1). Ordinary bolts: hardness and strength is not very high bolts, general common bolt material is to use ordinary screw wire to produce, the hardness and strength of its common bolt material, tensile strength, torsion will not be very high.

(2). High-strength bolts: generally refers to the high-strength grade of the bolts, its own screw material, bolt materials, and bolt material is better, the hardness is also relatively high, and After the production and manufacturing, the bolt will also be hardened. Make the bolt to reach the high strength bolt grade strength requirements.

2. Classification of bolts:

The performance grade of bolts for steel structure connection is divided into more than 10 grades such as 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. among which the material of bolts of grade 8.8 and above is low-carbon alloy steel or medium-carbon steel and heat-treated (quenched and tempered), commonly known as high-strength bolts, and the rest are commonly known as ordinary bolts.

3. Bolts indicate the meaning of the symbol:

Bbolt performance level labeling has two parts of the digital composition, respectively, the nominal tensile strength of the bolt material value and yield strength ratio.

A. For example, the performance level 4.6 level of bolts, the meaning of:

(1). The nominal tensile strength of the bolt material up to the level of 400MPa;

(2). The bolt material of the yield strength ratio of 0.6;

(3). The nominal yield strength of the bolt material up to 400 × 0.6 = 240Mpa.

B. Performance grade 10.9 high-strength bolts, which means：

Its material after heat treatment, can achieve：

(1). The nominal tensile strength of the bolt material up to 1000MPa level;

(2). The bolt material yield strength ratio of 0.9.

II.Properties of high strength bolts

1. The above is a general definition of a bolt. Although there are literally high-strength and ordinary bolts, but the above definition is not what we usually call the essential difference between high-strength bolts and ordinary bolts. In fact, the structural engineering said high strength bolt connection refers to the bolt connection of very high strength and very strong stiffness in two aspects, especially refers to the very strong stiffness.

2. In order to figure out the nature of high strength bolts, need to analyze the angle of force.

3. First of all, ordinary bolts connected to the joints of the joints of the stiffness is very small, ordinary bolts the most reasonable use of the bolt is used as a tensile bolts used, the most commonly used for the C-grade ordinary bolts. Ordinary bolts also have 10.9 high strength. Ordinary bolt connection on the plate does not have the requirement of pre-tension, relying on the bolt and plate direct contact force transfer.

4. And high-strength bolt connection is divided into: high-strength bolt friction-type connection, high-strength bolts pressurized connection. Through the bolt pre-exerted a huge tension, to be connected to the plate closely together, we look at a data, a M24, 10.9 grade high strength bolt pre-tension design value of 225Kn, that is, almost 22 tons of tension. The value of this tension will subvert your knowledge of the bolt connection, the value of this tension can pull up a medium-sized fire truck.

5. it is in such a strong tension, so that the plate between the friction produced by a very large, but also makes the node of the connection stiffness is very large, to achieve the effect of rigid connection. The force transmission of the plate is transmitted by friction, and not by the contact transmission of the bolt rod and plate. High-strength bolt friction-type connection damage sign is the relative sliding of the plate.

6. so in the beam-column rigid connection node, high-strength bolt friction-type connection is the first choice, in the bolted-welded hybrid connection, the beam web through the high-strength bolt friction-type connection can achieve the same strength and stiffness and welding.