Product Overview
Structural Steel Bolts are high-strength fasteners specifically engineered for the erection of steel structures, including bridges, buildings, transmission towers, and heavy industrial frameworks. They are designed to carry shear and tensile loads in slip-critical and bearing-type connections, ensuring the integrity and safety of the overall structure. These bolts are used in conjunction with matched heavy hex nuts and hardened washers, and require controlled installation via calibrated torque or tensioning methods.
Key Features & Benefits
High Clamp Force & Preload: Designed to be tightened to a specified minimum preload (proof load), which is crucial for the performance of the bolted joint.
Shear Strength: Engineered to withstand significant shear forces, a primary load in structural connections.
Controlled Installation: Must be installed to a specific tension, often achieved using the turn-of-nut method, calibrated wrench, or direct tension indicators (DTIs).
Material & Dimensional Consistency: Manufactured to strict chemical, mechanical, and dimensional standards to ensure predictable performance and interchangeability.
Durability: Available with various coatings (e.g., hot-dip galvanizing) for long-term corrosion protection in exposed environments.
Material Specifications, Grades & Standards
Structural bolts are categorized by their material strength and intended service conditions. The most common standards are ASTM (USA) and ISO (International).
| Type / Standard | Grade / Class | Material & Process | Minimum Tensile Strength | Proof Load Stress | Marking |
|---|---|---|---|---|---|
| Heavy Hex Structural Bolt (ASTM A325) | Type 1 / Type 3 | Medium Carbon Steel (Type 1) or Weathering Steel (Type 3), Quenched & Tempered | 120 ksi (830 MPa) | 85 ksi (585 MPa) | A325 |
| High-Strength Heavy Hex Bolt (ASTM A490) | – | Alloy Steel, Quenched & Tempered | 150 ksi (1035 MPa) | 120 ksi (830 MPa) | A490 |
| Structural Bolt (ISO) | Property Class 8.8 / 10.9 | Medium Carbon or Alloy Steel, Quenched & Tempered | 800 MPa / 1040 MPa | 580 MPa / 830 MPa | 8.8 / 10.9 |
Common Configurations & Components
A complete structural bolt assembly typically includes:
Bolt: Heavy hex head, fully threaded or with a short unthreaded shank (grip length).
Nut: Heavy Hex Nut matching the bolt’s grade (e.g., ASTM A563 Gr. C/D for A325, Gr. DH for A490).
Washer: Hardened Circular Washer (e.g., ASTM F436) under both the bolt head and nut to distribute load and protect the connected material.
Surface Finishes & Corrosion Protection
The choice of finish depends on the environment and required friction coefficient for the joint.
| Finish Type | Standard / Specification | Characteristics & Application |
|---|---|---|
| Plain / Black (Oiled) | – | For indoor or painted structures. Lowest cost. |
| Hot-Dip Galvanized (HDG) | ASTM A153 / ISO 10684 | Most common for exposed steel. Thick, durable zinc coating for superior long-term corrosion resistance. May require special lubricants to achieve consistent preload. |
| Mechanically Galvanized | ASTM B695 | Uniform coating without hydrogen embrittlement risk. Good corrosion resistance. |
| Geomet® / Zinc-Flake Coating | Proprietary (e.g., Delta Protekt) | High-Performance. Provides excellent corrosion resistance (>1000 hrs salt spray), consistent friction coefficient, and is RoHS compliant. Used in demanding applications. |
| Weathering Steel (ASTM A325T) | – | The bolt itself is made from weathering steel (e.g., ASTM A588). Develops a protective patina for atmospheric corrosion resistance; often used unpainted. |
Installation & Tightening (Critical Process)
Proper installation is paramount. Common methods include:
Turn-of-Nut Method: A specified rotation (e.g., 1/2 to 2/3 turn) from a “snug-tight” condition.
Calibrated Wrench (Torque Control): Using a wrench set to a torque that correlates to the required bolt tension.
Direct Tension Indicating (DTI) Washers: Washers with protrusions that flatten to a specific gap when the correct tension is achieved.
Tension Control Bolts (TC Bolts): Feature a splined end that shears off when the proper tension is reached.
Quality Assurance & Traceability
Certifications: Manufactured under quality systems compliant with ISO 9001:2015 and often certified to specific construction standards.
Testing: Each production lot undergoes rigorous testing including tensile strength, proof load, hardness, and wedge tests per ASTM or ISO standards.
Traceability: Full Mill Test Reports (MTRs) with heat numbers are provided. Bolts, nuts, and washers are clearly marked with manufacturer’s ID and property class for complete traceability.
Inspection: Dimensional checks, thread verification, and visual inspections are standard.
Manufacturing Expertise
Our structural bolts are produced by Hebei Wohe Fastener Manufacturing Co., a manufacturer with dedicated capabilities in high-strength, large-diameter fastener production. Our integrated process includes controlled forging, precision thread rolling, and in-house heat treatment with strict atmosphere control to achieve the required mechanical properties. We supply certified structural bolt assemblies to steel fabricators and construction projects, ensuring compliance with international specifications for safety-critical applications.
Ordering & Specifications:
Product Identification: Specify Standard (ASTM/ISO), Grade, Diameter, Length, Finish, and Quantity.
Kitting: Available as individual components or pre-assembled kits (bolt, nut, two washers).
Customization: Non-standard lengths, special markings, and proprietary coatings can be accommodated.
Minimum Order Quantity (MOQ): Project-based, typically starting from 5,000 pieces per size/grade.
Lead Time: Standard specifications: 25-35 working days. Large project orders require advance planning.
Important Notice: Structural bolting is a specialized field. The selection, installation, and inspection of structural bolts must be performed in accordance with approved engineering designs and relevant construction codes (e.g., AISC, RCSC). The information provided here is for general reference only and does not constitute engineering advice.
