Steel structure bolts are not only the “bond” that connects different steel parts, but also an important tool for bearing and dispersing forces to ensure the stability and safety of the structure. Through this blog, you will be able to:
- Learn more about the types, specifications and applications of steel structure bolts
- Choose bolts and accessories that suit project needs
- Master the installation skills and maintenance points of steel structure bolts
Whether you are an experienced engineer or a novice who has just entered the field of steel structure, this article will provide you with valuable reference. I hope that through these contents, you can make bolt selection and installation decisions in steel structure projects more confidently and ensure the smooth progress of the project.
What bolts are used for steel structures?
1. Ordinary Bolts (A307 Bolts)
| Feature | Ordinary Bolts (A307 Bolts) |
| Specifications | Diameter: M6 to M100 |
| Length: 1 inch to 12 inches | |
| Thread: Full or partial thread (customizable) | |
| Material | Low carbon steel, galvanized or hot-dip galvanized, strength grade Grade A or Grade B, tensile strength ~60,000 psi |
| Application Scenarios | Secondary structures, temporary connections, non-critical parts (e.g., brackets, platforms, stairs) |
| Advantages | Low cost, easy installation, high versatility, suitable for most non-high-stress applications |
| Disadvantages | Limited load-bearing capacity, poor anti-slip performance, not suitable for high-load or extreme environments |
2. High-strength Bolts (A325 and A490 Bolts)
| Feature | High-Strength Bolts (A325 and A490 Bolts) |
| Specifications | Diameter: M12 to M36 |
| Length: Customizable | |
| Thread: Full or partial thread options | |
| Material | Medium carbon steel or alloy steel, heat-treated for high strength, strength grades 8.8, 10.9, 12.9 |
| Application Scenarios | Main structural connections in bridges, high-rise buildings, and industrial facilities; parts under high loads and stresses |
| Advantages | High load-bearing capacity, excellent anti-slip performance, ASTM-compliant, ensures structural safety |
| Disadvantages | High cost, requires precise preload control, special tightening equipment needed |
3. Torsion shear bolt (TC bolt)
| Feature | Torsion Shear Bolts (TC Bolts) |
| Specifications | Diameter: M16 to M30 |
| Length: Customizable | |
| Design: Tail designed for torque control and stable connection | |
| Material | Alloy steel, heat-treated for enhanced strength, better shear and tensile resistance |
| Application Scenarios | Connections requiring anti-loosening or anti-slippage (e.g., steel structures, bridges, large equipment) |
| Advantages | Reliable connection, easy preload control, suitable for high-strength applications |
| Disadvantages | Requires precise torque control; incorrect tightening may cause connection failure |
4. Anchor bolts
| Feature | Anchor Bolts |
| Specifications | Diameter: M12 to M100 |
| Length: Customizable based on base and installation requirements | |
| Material | Mostly alloy steel or stainless steel, with strong corrosion resistance and durability |
| Application Scenarios | Foundation construction for fixing steel structures on concrete or ground (e.g., buildings, bridges, equipment foundations) |
| Advantages | Reliable fixation, strong corrosion resistance, suitable for harsh environments |
| Disadvantages | Complex installation, requires accurate drilling for optimal performance |
5. Heavy hexagonal bolts
| Feature | Heavy Hex Bolts |
| Specifications | Diameter: M16 to M36 |
| Length: 50mm to 200mm (customizable) | |
| Material | High-strength alloy steel or stainless steel, surface-treated (e.g., galvanizing, hot-dip galvanizing) |
| Application Scenarios | Connections bearing large static or dynamic loads (e.g., bridges, steel structures, industrial equipment) |
| Advantages | Strong load-bearing capacity, suitable for high-stress environments, stable installation |
| Disadvantages | More expensive than ordinary bolts, requires special tools for installation |
6. Other types of bolts
In addition to common ordinary bolts and high-strength bolts, there are some special-purpose bolts that also play an important role in certain specific engineering projects:
- Turnbuckle Bolts: Used to adjust the tension of steel cables or pull rods, commonly used in viaducts, tower cranes and other fields, and the specifications are usually M12 to M30.
- Eye Bolts: With a ring head, they are used for hoisting and lifting, and are widely used in industries such as ships and hoisting equipment. The specifications range from M6 to M50.
- U-Bolts: The shape is similar to the letter “U”, used to fix pipes, cables or other equipment, and are usually used in mechanical equipment, automobiles, pipeline installation, etc.
- Expansion Bolts: Commonly used in walls, concrete or masonry materials, widely used in construction and decoration, and the specifications can be adjusted according to different fixing requirements.
Our bolts undergo strict material screening and quality control to ensure that each one can withstand high-intensity loads and stresses, thereby improving the durability and safety of the overall steel structure. Whether it is ordinary bolts, high-strength bolts, or other special types of bolts, we can provide them.
Application of Steel Structure Bolts
Building Structure
In steel structure buildings, bolts are used to connect beams to columns, nodes and supports. Bolted connections are not only quick to install, but also easy to adjust and maintain, and can effectively ensure structural stability.
Bridges
In bridge engineering, bolts are used to connect main beams, cross beams and bridge decks. They provide high load-bearing capacity and good vibration resistance, ensuring the safety of bridges in long-term use.
Industrial Facilities
In the installation of heavy machinery, equipment supports and pipe supports, bolts can adapt to high strength and dynamic loads to ensure the stable operation of industrial facilities.
Temporary Structures
Bolts are widely used in temporary supports, scaffolding and temporary bridges. Because they are easy to disassemble and reuse, they greatly facilitate the rapid construction and disassembly of construction sites.
Advantages of bolted connections
As a common method in steel structures, bolted connections have the following significant advantages:
Easy installation: Bolt connection is simpler than welding installation and does not require complex equipment and professional technicians, which can improve construction efficiency and save time and cost.
Flexibility: Bolted connections are easy to disassemble and modify, making them ideal for projects that require adjustments, expansions or relocations, providing great flexibility.
Quality control: The quality of bolted connections is easy to check and verify, which can ensure the reliability of the connection, especially suitable for projects with strict quality requirements.
Environmental protection: Compared with welding, bolted connections reduce on-site light pollution and gas emissions, and are more in line with low-carbon and environmentally friendly requirements.
Challenges and considerations of bolted connections
Although bolted connections have many advantages, there are also some challenges and considerations in practical applications. Understanding these issues will help you better select and use bolted connections.
Risk of loosening: Bolts may loosen when subjected to vibration or dynamic loads. Therefore, regular inspection and tightening are required. Auxiliary measures such as anti-loosening washers or double nuts can be used to enhance the stability of the connection.
Corrosion issues: Bolts are prone to corrosion in humid or corrosive environments. To improve corrosion resistance, galvanized or stainless steel bolts are often used to ensure long-term durability.
High cost: High-strength bolts and accessories (such as washers and nuts) are expensive. When choosing, you need to consider the budget and project requirements comprehensively to ensure that both economy and safety are given equal importance.
High installation accuracy requirements: Bolted connections require high hole position accuracy. Accurate alignment needs to be ensured during installation to avoid errors affecting the connection quality.
How to choose the right bolt accessories
Choosing the right bolt accessories is the key to ensuring structural safety, improving construction efficiency and reducing maintenance costs. The following are suggestions for choosing bolt accessories according to different situations. Of course, if you have any questions, our team can help you make the best choice based on your specific needs.
Load requirements
- High load scenarios: Choose high-strength bolts (such as A325, A490) or heavy hexagonal bolts to ensure that the connection can withstand greater loads, suitable for high-demand projects such as bridges and industrial facilities.
- Medium load scenarios: Ordinary high-strength bolts or torsion shear bolts are usually sufficient to meet the needs and are suitable for most building structures or non-critical parts.
Environmental factors
- Corrosive environment: In a humid or highly corrosive environment, choosing galvanized, hot-dip galvanized or stainless steel bolts can effectively extend the service life of the bolts and prevent corrosion from affecting structural safety.
- High temperature environment: Choose high-temperature resistant alloy steel bolts to ensure that the bolts can maintain stable performance under extreme temperatures, suitable for high-temperature equipment and industrial sites.
Installation conditions
- Limited space: If the installation space is limited, it is recommended to use torsion shear bolts. This type of bolt is easy to install, reduces the difficulty of manual operation, and is suitable for environments with small spaces.
- High precision requirements: For projects that require precise control of preload, the use of tension control bolts (such as TC bolts) can ensure installation accuracy and reduce later maintenance issues.
Cost and efficiency
- Limited budget: Ordinary high-strength bolts provide a cost-effective option, suitable for cost-constrained projects, ensuring connection performance while saving budget.
- Construction efficiency: Torsion shear bolts and heavy hexagonal bolts can greatly improve installation efficiency and reduce construction time, suitable for time-sensitive projects.
Whatever your project needs, our team can help you choose the most suitable bolt accessories according to your specific requirements, ensuring that you can meet technical requirements and optimize costs and efficiency during construction. Please feel free to contact us, we will provide you with professional advice and customized solutions.
Installation and tightening of steel structure bolts
The stability and safety of steel structures depend to a large extent on the correct installation and tightening of bolts.
Installation method and preload control
- Torque method: Use a torque wrench to control the preload of the bolts, which is suitable for most standard bolts. This method is simple and reliable, and can accurately control the tightening force.
- Angle method: Control the preload by the rotation angle, which is usually used in uneven loads or special circumstances to ensure uniform connection tightening.
- Tension control method: Use torsion shear bolts (TC bolts) to accurately control the preload by twisting off the tail, which is suitable for connections with high strength requirements.
Preload is the key to ensuring the stability and anti-slip performance of bolt connections. Controlling the appropriate preload can effectively prevent the bolts from loosening and ensure the reliability of the connection. The arrangement of the bolts should also be adapted to the load type to ensure the stability of the connection.
- Parallel arrangement: Suitable for uniform loads.
- Staggered arrangement: Suitable for uneven loads to increase the stability of the connection.
Secondary tightening
Why secondary tightening
Even if the bolts are tightened to the specified preload during initial installation, they may loosen due to vibration or load changes as the structure ages. Therefore, secondary tightening after a certain period of time helps ensure the long-term stability of the bolted connection.
How to perform secondary tightening
It is usually recommended to perform secondary tightening within a few hours or days after the bolts are installed. During this process, the tightness of the bolts needs to be checked again and the preload needs to be readjusted by the torque method or the angle method.
Inspection and maintenance
Regular inspection: Check the bolted connection regularly to ensure that the bolts are not loose, corroded or damaged. Especially in environments with high temperature, humidity or high vibration, inspections should be strengthened.
Maintenance measures: Lubricate the bolts regularly to prevent rust and corrosion and extend the service life of the bolts. For environments prone to corrosion, galvanized, hot-dip galvanized or stainless steel bolts can be selected to better cope with the challenges of harsh environments.
We strictly follow ASTM A325, A490, F3125 and ISO 17025 quality control specifications to ensure that bolt products meet global and regional requirements, thereby ensuring the safety and stability of your steel structure projects.
If you have any questions or need help choosing the most suitable steel structure bolts, please contact our team and we will provide you with professional advice and support based on your specific needs.
Bolt Connection vs Welded Connection
| Criteria | Welded Connection | Bolt Connection |
| Strength & Rigidity | Higher strength and rigidity, ideal for heavy-load structures. | Lower strength but more flexible, suitable for adjustable structures. |
| Aesthetics | Neat appearance, suitable for exposed structures. | Rougher appearance, best for concealed structures. |
| Cost & Time | High initial cost but low maintenance cost. | Low initial cost, but may require more maintenance. |
If you’re planning a steel structure project, choosing the right bolts and connection methods is critical to ensuring safety, stability, and efficiency. We offer a wide range of bolts to meet your specific needs, including high-strength bolts, U-bolts, anchors, and more.
Our products meet global standards, ensuring your project complies with the latest regulations. Plus, our team of experts is always available to guide you through the selection and installation process. Project success starts with the right connections. Let’s build something strong together!
FAQs
How to determine the size of steel structure bolts?
The size of steel structure bolts depends on factors such as bearing capacity requirements, steel plate thickness, connection type, design standards, etc. Common bolt diameters range from 12mm to 24mm, and the length is usually twice or more than the thickness of the steel plate.
What strength grade is required for steel structure bolts?
The strength grades of steel structure bolts are usually 8.8, 10.9, 12.9, etc. 8.8-grade bolts are suitable for general steel structures, and 10.9 or higher strength grades are suitable for occasions that need to withstand large loads or high strength requirements. The strength grade of the bolt should be selected according to the needs of the structural design.
What are the requirements for the material of the bolt?
Steel structure bolts are usually made of high-strength steel, and common materials include Q235, Q345, etc. For corrosive environments, bolts need to use anti-corrosion materials or coatings (such as hot-dip galvanizing, spray painting, etc.). In special environments, such as high temperature, high humidity or marine environments, corrosion-resistant or high-temperature alloy materials are also required.
Do steel structure bolts need anti-loosening measures?
In some occasions subject to vibration or impact, bolts need to take anti-loosening measures, such as anti-loosening washers, double nuts, locking nuts, etc.
How long is the service life of steel structure bolts?
The service life of steel structure bolts depends on the material, environmental conditions and maintenance. Under normal conditions, galvanized bolts can be used for decades, but in highly corrosive environments, the life of the bolts may be shorter. Regular inspection and timely replacement of damaged bolts can extend the service life of the structure.
What to do if the bolts are loose?
If the steel structure bolts are found to be loose, the bolts should be checked and tightened in time. If necessary, the damaged bolts should be replaced or checked for other connection problems. For high-strength bolts, standard torque should be used when tightening to ensure that they are tightened in place.
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