Two misunderstandings of high strength bolt

High strength bolt is the most common construction content in steel structure construction. All steel engineers will find themselves too familiar. However, this may not be the case. Today, we start from the most basic concept, and take you to re understand the high strength bolt, which may subvert your most basic understanding.
01 what is high strength bolt
High strength friction clamp bolt (hsfg for short). It can be seen that the high-strength bolt in China is the abbreviation of high-strength friction pre tightening bolt. In daily communication, only the words "friction" and "grip strength" are abbreviated, but many engineers and technicians misunderstand the basic definition of high strength bolt.
Myth 1: bolts with material grade over 8.8 are "high strength bolts"?
The core difference between high strength bolt and common bolt is not the strength of the material used, but the form of stress. Its essence is whether to apply preloading and static friction to shear.
In fact, the hsfg bolts (BS EN 14399 / astm-a325 & amp; astm-490) mentioned in British standard and American Standard only have grade 8.8 and 10.9, while ordinary bolts include 4.6, 5.6, 8.8, 10.9, 12.9, etc., so the material strength is not the key to distinguish high strength bolts from ordinary bolts.

Misunderstanding 2: the bearing capacity of high strength bolt is higher than that of ordinary bolt, which is "high strength"?
From the calculation of single bolt, it can be seen that the design strength of high strength bolt in tension shear state is lower than that of ordinary bolt. The essence of its high strength is that relative sliding is not allowed in normal operation, that is, small elastic-plastic deformation and large joint stiffness.
It can be seen that under the given design node load, the joints designed with high strength bolts may not necessarily save the number of bolts, but they have small deformation, high stiffness and high safety reserve. It is suitable for high rigidity parts such as main beam, which conforms to the basic seismic design principle of "strong joint and weak component".
The strength of high strength bolt is not due to the design value of its bearing capacity, but because of its high rigidity, high safety performance and strong anti damage ability.
Specification of high strength bolt
High strength bolts commonly used in China are divided into ASTM and JIS. Generally, there are two types of ASTM high strength bolts, A325 and A490.
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