What is a high-strength bolt?

What is a high-strength bolt?

High-strength bolts, also called: high-strength friction pre-tightening bolts.English abbreviation: HSFG.

In daily communication, only the two words "Friction" and "Grip" are simply abbreviated, but this has caused many engineers and technicians to understand the basic definition of high-strength bolts and have misunderstood.

Misunderstanding 1

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A bolt with a material grade exceeding 8.8 is a "high-strength bolt"?

The core difference between high-strength bolts and ordinary bolts is not the strength of the material used, but the form of force. The essence is whether to apply pre-tightening force and use static friction to resist shear.

In fact, in the British Standard Specification, the high-strength bolts (HSFG BOLT) mentioned in the American Standard Specification have only two types (BS EN 14399 / ASTM-A325&ASTM-490) (BS EN 14399/ASTM-A325&ASTM-490), but ordinary bolts contain 4.6, 5.6, 8.8, 10.9, 12.9, etc. (BS 3692 11, Table 2); it can be seen that the strength of the material is not the key to distinguish high-strength bolts from ordinary bolts.

Misunderstanding 2

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The bearing capacity of high-strength bolts is higher than that of ordinary bolts. Is it "high-strength"?

From the calculation of a single bolt, it can be seen that the design strength of high-strength bolts in tensile and shear is lower than that of ordinary bolts. The essence of its high strength is that during normal operation, no relative slippage is allowed in the joints, that is, the elastoplastic deformation is small and the joint stiffness is large

It can be seen that in the case of a given design node load, a node designed with high-strength bolts may not necessarily save the number of bolts used, but its deformation is small, rigidity is large, and safety reserves are high. It is suitable for main beams, and other positions that require greater joint stiffness, and conforms to the basic seismic design principle of "strong joints, weak members".