SPECIFICATION LIBRARY

ASTM F959

ASTM F959 Specification Overview

ASTM F959 standard refers to the specifications for compressible-washer-type direct tension indicators (DTIs) for use with structural fasteners. These specialized washers are designed to indicate the achievement of a specified bolt tension in structural bolting applications.

Direct Tension Indicators (DTIs) are specialized washers used in structural bolting to ensure that bolts are tightened to the correct tension. They come in two main types: squirter DTIs and non-squirter DTIs. The primary difference between these two types lies in their tension-indicating mechanism.

Squirter DTI Washers

  • Mechanism: Squirter DTIs are equipped with a silicone-filled indicator protruding from the washer's surface. When the bolt is tightened to the specified tension, the silicone is forced out, creating a visible "squirt" that serves as an indication of proper tension.

  • Advantages: The most significant advantage of squirter DTIs is the clear, visual confirmation of proper bolt tensioning, making it easy for inspectors to verify from a distance.

  • Application: Ideal for use in large-scale construction projects where quick and efficient inspection of numerous bolted connections is required.

Non-Squirter DTI Washers

  • Mechanism: Non-squirter DTIs utilize protrusions or bumps on one side of the washer. As the bolt is tightened, these protrusions compress. The reduction in gap or height indicates that the bolt has been tensioned properly.

  • Advantages: Non-squirter DTIs are simpler in design and function without relying on a visual squirt indicator. They are often preferred in environments where the silicone extrusion of squirter DTIs could be problematic or where a more traditional inspection method is desired.

  • Application: Used in various structural bolting applications where direct physical or tool-based inspection is feasible and preferred.

Key Features of ASTM F959:

  • Purpose: DTIs are used to ensure that the correct amount of tension is applied to structural bolts, which is crucial for the integrity of bolted connections in structural applications.

  • Material: These washers are typically made from high-strength steel to withstand the compressive forces during bolt tightening.

  • Types: The standard categorizes DTIs based on the type of bolt they are used with, such as Type 325 for use with ASTM A325 bolts and Type 490 for ASTM A490 bolts.

Mechanical Properties:

ASTM F959 specifies the following mechanical properties for DTIs to ensure they function effectively:

  • Hardness: DTIs should have a hardness compatible with the bolt grade they are used with to prevent deformation under load.

  • Compressibility: The washers must compress at the appropriate bolt tension, providing a visual or tactile indication that the bolt has been properly tensioned.

Dimensional Tolerances:

Here is a table outlining typical dimensions for Direct Tension Indicator (DTI) washers, conforming to standards like ASTM F959. These dimensions ensure the DTIs function correctly, indicating when the necessary bolt tension has been achieved in structural bolting applications:

Bolt Diameter

DTI Washer ID (min)

DTI Washer OD (max)

DTI Washer Thickness (nominal)

1/2 inch

0.52 inch

1.36 inch

0.19 inch

5/8 inch

0.64 inch

1.56 inch

0.22 inch

3/4 inch

0.77 inch

1.88 inch

0.25 inch

7/8 inch

0.90 inch

2.13 inch

0.28 inch

1 inch

1.03 inch

2.50 inch

0.31 inch

1-1/8 inch

1.15 inch

2.75 inch

0.34 inch

1-1/4 inch

1.28 inch

3.00 inch

0.37 inch

1-3/8 inch

1.41 inch

3.25 inch

0.40 inch

1-1/2 inch

1.54 inch

3.50 inch

0.43 inch

Notes:

  • ID (Inner Diameter): Slightly larger than the bolt diameter to ensure the washer fits over the bolt without impeding its tensioning.

  • OD (Outer Diameter): Large enough to distribute the load and provide a sufficient indication area, yet sized to prevent interference with adjacent components.

  • Thickness: Provides the necessary structural integrity to allow the DTI to compress properly under load, indicating the achieved tension.

This table offers a general guide to the sizing of DTI washers for various bolt diameters. Actual product dimensions can vary based on manufacturer specifications and the requirements of specific applications. Always refer to the official ASTM specifications or manufacturer's data for precise dimensions and tolerances.

 Applications:

  • Structural Steelwork: Used in the construction of buildings, bridges, and other structures where bolted connections are critical for safety and performance.

  • Quality Assurance: Facilitates the inspection process by providing immediate feedback on bolt tension, improving the reliability of structural assemblies.

Quality Assurance and Compliance:

  • DTIs must undergo rigorous testing to confirm their mechanical properties and functionality.

  • Regular quality checks are essential to ensure that the DTIs comply with the ASTM F959 standard and are fit for use in structural applications.

 

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