What is the difference between high-strength bolts and ordinary bolts?

1. What are high-strength bolts?

High-strength bolt (High-Strength Friction Grip Bolt), English literal translation is: high-strength friction pre-tightening bolt, English abbreviation: HSFG. It can be seen that the high-strength bolt we refer to in Chinese construction is the abbreviation of high-strength friction pre-tightening bolt.

Ordinary bolts

1. Ordinary bolts are divided into three types: A, B, and C. The first two are refined bolts and are rarely used. Ordinary bolts generally refer to grade C ordinary bolts.
2. In some temporary connections and connections that need to be disassembled, C-grade ordinary bolts are often used. Common ordinary bolts commonly used in building structures are M16, M20, and M24. Some mechanical industrial rough bolts may have a relatively large diameter and special uses.

High Strength Bolts

3. The material of high-strength bolts is different from that of ordinary bolts. High-strength bolts are generally used for permanent connections. Commonly used ones are M16~M30. The performance of oversized high-strength bolts is unstable and should be used with caution.
4. The bolt connection of the main components of the building structure is generally made of high-strength bolts.
5. The high-strength bolts shipped from the factory are not divided into pressure-bearing type or friction type.

6. Is it a friction type high-strength bolt or a pressure type high-strength bolt? In fact, there is a difference in the design and calculation methods:

(1) Friction type high-strength bolts take sliding between the plate layers as the ultimate state of bearing capacity.

(2) Pressure type high-strength bolts take sliding between the plate layers as the limit state of normal use, and connection failure as the ultimate state of bearing capacity.

7. Friction type high-strength bolts cannot fully utilize the potential of bolts. In practical applications, friction type high-strength bolts should be used for very important structures or structures that bear dynamic loads, especially when the load causes reverse stress. At this time, the unused potential of the bolts can be used as a safety reserve. In other places, pressure type high-strength bolts should be used to reduce the cost.

The difference between ordinary bolts and high-strength bolts

8. Ordinary bolts can be reused, but high-strength bolts cannot be reused.
9. Material: High-strength bolts are generally made of high-strength steel (45 steel (8.8s), 20MmTiB (10.9S), and are prestressed bolts. The friction type uses a torque wrench to apply the specified prestress, and the pressure-bearing type unscrews the plum head. Ordinary bolts are generally made of ordinary steel (Q235), and only need to be tightened.
10. Strength grade: Ordinary bolts are generally 4.4, 4.8, 5.6 and 8.8. High-strength bolts are generally 8.8 and 10.9, with 10.9 being the most common.
11. The screw holes of ordinary bolts are not necessarily larger than those of high-strength bolts. In fact, ordinary bolts screw holes are smaller.
12. Ordinary bolts A, B level screw holes are generally only 0.3 ~ 0.5mm larger than the bolt. C level screw holes are generally 1.0 ~ 1.5mm larger than the bolt.
13. Friction-type high-strength bolts rely on friction to transfer the load, so the difference between the screw and the screw hole can be up to 1.5 ~ 2.0mm.
14. Pressurized high-strength bolts transmission characteristics are to ensure that in normal use, the shear force does not exceed the friction, and friction-type high-strength bolts the same. When the load is increased, the connection plate will occur between the relative slip, connection depends on the screw shear and hole wall pressure to transfer the force, the same as ordinary bolts, so the difference between the screw and the screw hole is slightly smaller, for 1.0 ~ 1.5mm.

Column Foot Anchor Bolt

15. Anchor bolts have no grades, only materials: Q235 and Q345. The most commonly used anchor bolts in building structures are column anchor bolts.
16. Column anchor bolts are neither ordinary bolts nor high-strength bolts. Strictly speaking, they are not bolts. Column anchor bolts are generally M20 or M24.
17. The manufacturing standards of column anchor bolts should be the same as those of ordinary bolts. The embedded length of the column anchor bolt should be related to the friction between it and the concrete, as well as the form of the anchor bolt.

Expansion bolts and chemical bolts

18. Whether it is expansion anchor bolts or chemical anchor bolts, they are not the connection forms specified in the national standard. Such connections should be avoided, especially in important connections. All pre-embedded parts should be used.
19. Expansion anchor bolts mainly rely on the friction between the expansion tube and concrete to resist pullout. The magnitude of the pullout resistance is closely related to the construction process, and the human factor is large. It is useless to do tensile tests for random inspections.

20. Chemical anchor bolts are formed by punching holes with a punching machine, and then chemical slurry is poured in and the bolt rod is placed in order to achieve anchoring.
21. Expansion bolts and chemical bolts are actually anchor bolts. In some cases, expansion bolts or chemical anchor bolts are needed because there is no pre-embedded part. But this situation should be avoided in the design. Because anchor bolts should be pre-embedded. For example, column foot anchor bolts. Because only in this way can the best bonding and force be guaranteed. Moreover, punching holes afterwards often causes damage to the stress-bearing steel bars in the concrete and the concrete itself.
22. In the concrete specification, components embedded in concrete are called embedded parts. According to the document of the Ministry of Construction, expansion bolts shall not be used in curtain walls. In general, expansion anchor bolts are strictly prohibited for new construction projects, and embedded parts should be used instead.