What Is Considered a Structural Bolt?

In the realm of construction and engineering, structural bolts are pivotal components that ensure the stability and integrity of various structures. These bolts are specifically designed to withstand significant loads and stresses, making them indispensable in the assembly of steel structure buildings and other critical infrastructure.

Understanding Structural Bolts

A structural bolt is a high-strength fastener used to join structural components, such as beams, columns, and trusses, in construction projects. They are engineered to bear heavy loads and resist shear forces, ensuring the safety and durability of the structure. Typically, these bolts are made from medium carbon steel or alloy steel and are heat-treated to achieve the necessary strength. The most common standards for structural bolts are ASTM A325 and ASTM A490, which define the mechanical properties and dimensions of these fasteners.

Types of Structural Bolts

Structural bolts come in various types, each suited for specific applications:

1. ASTM A325 Bolts

These are heavy hex structural bolts made from medium carbon steel. They are commonly used in structural steel joints in heavy construction and are available in diameters ranging from 1/2” up to 1-1/2”. A325 bolts come in two types:

• Type 1: Made from medium carbon steel and can be galvanized.

• Type 3: Made from weathering steel that offers atmospheric corrosion resistance similar to that of ASTM A242 or A588.

2. ASTM A490 Bolts

These are heavy hex structural bolts made from alloy steel. They are used in structural steel joints in heavy construction applications that require greater yield and tensile strengths than those of an A325 bolt. A490 bolts are available in diameters ranging from 1/2” up to 1-1/2”.

3. Tension Control (TC) Bolts

These bolts are designed for use in high-strength friction grip (HSFG) connections. They are installed using a special wrench that controls the tension applied to the bolt, ensuring consistent clamping force across all bolts in the connection.

4. High-Strength Friction Grip (HSFG) Bolts

HSFG bolts are used in slip-critical connections where the load is transferred through friction rather than bearing. These bolts are tightened to a specified tension to develop the necessary clamping force.

Applications in Steel Structure Buildings

In steel structure buildings, structural bolts play a crucial role in connecting various components:

• Beams and Columns: Bolts are used to connect horizontal beams to vertical columns, forming the skeletal framework of the building.

• Trusses: In roof and floor trusses, bolts secure the joints between members, distributing loads evenly.

• Bracing Systems: Bolts are integral in bracing systems that provide lateral stability to the structure.

• Connections to Foundations: Anchor bolts are used to secure the steel structure to the concrete foundation, preventing movement and ensuring stability.

The selection of the appropriate type of structural bolt depends on factors such as load requirements, environmental conditions, and the specific design of the structure.

Standards and Specifications

Structural bolts must adhere to specific standards to ensure their performance and reliability:

• ASTM A325: Specifies the requirements for medium carbon steel bolts, studs, and other fasteners.

• ASTM A490: Defines the requirements for high-strength alloy steel bolts.

• ASTM F3125: A consolidated standard that includes the requirements of A325 and A490 bolts.

• AISC Specification: Provides guidelines for the design and installation of structural joints using high-strength bolts.

Adherence to these standards ensures that structural bolts perform as intended under the expected loads and conditions.

Installation and Maintenance

Proper installation and maintenance of structural bolts are essential for the safety and longevity of the structure:

• Installation: Bolts should be tightened to the specified torque to achieve the required clamping force. This can be done using a calibrated torque wrench or a tension control device.

• Inspection: Regular inspections should be conducted to check for signs of corrosion, wear, or loosening.

• Maintenance: Damaged or corroded bolts should be replaced promptly to maintain the integrity of the structure.

In steel structure buildings, maintenance is particularly important due to the exposure to environmental factors that can affect the bolts' performance.

Comparative Overview

Conclusion

Structural bolts are integral components in the construction of steel structure buildings, providing the necessary strength and stability to ensure the safety and longevity of the structure. Understanding the different types of structural bolts and their applications allows engineers and builders to make informed decisions, ensuring that each connection is secure and reliable. Adhering to established standards and performing regular maintenance further guarantees the performance of these critical fasteners.