Two major misconceptions about high-strength bolts
Two major misconceptions about high-strength bolts
High strength bolts are the most common construction content in steel structure construction. All steel structural engineer will feel too familiar. However, this may not be the case. Today, we will start with the most basic concepts and take you back to understanding high-strength bolts, which may overturn your most basic understanding.
01 What is high-strength bolt
High strength friction clamping bolts (referred to as hsfg). It can be seen that high-strength bolts in Chinese architecture are abbreviated as high-strength friction pre tensioned bolts. In daily communication, only the terms "friction" and "grip strength" are abbreviated, but many engineering and technical personnel have misunderstandings about the basic definition of high-strength bolts.
Myth 1: Is a bolt with a material grade exceeding 8.8 a "high-strength bolt"?
The core difference between high-strength bolts and ordinary bolts is not the strength of the materials used, but the form of stress. Its essence is whether to apply preload and use static friction to resist shear.
In fact, the hsfg bolts (BS EN 14399/astm a325&astm 490) mentioned in British and American standards only have grades 8.8 and 10.9, while ordinary bolts include grades 4.6, 5.6, 8.8, 10.9, 12.9, etc. Therefore, material strength is not the key to distinguishing high-strength bolts from ordinary bolts.
Myth 2: The bearing capacity of high-strength bolts is higher than that of ordinary bolts. Which one is' high-strength '?
From the calculation of a single bolt, it can be seen that the design strength of high-strength bolts in tension shear state is lower than that of ordinary bolts. The essence of its high strength is that relative sliding is not allowed during normal operation, which means small elastic-plastic deformation and high node stiffness.
It can be seen that under a given design node load, nodes designed with high-strength bolts may not necessarily save the number of bolts, but they have small deformation, high stiffness, and high safety reserves. Suitable for high stiffness parts such as main beams, in accordance with the basic seismic design principles of "strong nodes and weak components".
The strength of high-strength bolts is not due to their designed load-bearing capacity, but rather to their high stiffness, high safety performance, and strong resistance to damage.
High strength bolt specifications
The commonly used high-strength bolts in China are divided into two categories: ASTM and JIS. Usually, there are two types of ASTM high-strength bolts, A325 and A490.
