Anchor Bolt Tensioning Requirements for Equipment and Structural Steel

1. Purpose – This article is about minimum requirements for tensioning of anchor bolts for equipment and structural steel.

2. Anchor Bolt Tensioning Requirements for Equipment and Structural Steel

The Installer contractor shall furnish all equipment, materials, and labor necessary to satisfy the contract anchor bolt tensioning requirements.
The anchor bolt tensioning may be required for, but not limited to, the following:
- Structural steel column base plates.
- Equipment bases.
- Column cans.
- Cold boxes.
- Vessels.
- Storage tanks.
Those bolts that require tensioning will be indicated on the foundation design drawings. As a general rule, bolt tensioning is required for dynamic loading conditions such as those associated with large compression equipment or tall vessels, cold boxes, and other structures.
Anchor bolt tensioning is not required on any field-installed mechanical fastener. Field-drilled mechanical anchor bolts shall be tensioned only to a snug-tight condition.

American National Standards Institute (ANSI)

ANSI B1.1 Unified Inch Screw Threads (UN and UNR Thread Form)

American Society of Testing Materials (ASTM)

ASTM A 36/ A36M Standard Specification for Carbon Structural Steel.

ASTM A 307 Standard Specification for Carbon Steel Bolts and Studs, 60000 psi Tensile Strength.

ASTM A 320/A320M Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for Low-Temperature Service.

Grout shall be installed in accordance with the requirements of Grouting of Equipment and Structural Steel. It is recommended that the grout under the base plate material shall cure for seven days before any anchor bolt tensioning.
The bolt sleeve shall be carefully cleaned of all debris, dried, and protected from the entry of any foreign material until the equipment or base plate is in place.
Bolt threads shall be clean and protected during concrete and grout placement activities.
For applications such as compressor installations, where shear transfer of lateral loads through the bolt is not required, the bolt sleeve shall be filled with elastomeric material or expanding urethane foam to prevent the annular space around the bolt from being filled with grout. Specific requirements are shown on the contract drawings.
For applications such as cold boxes or distillation columns, where shear transfer of lateral loads through the bolt is required, bolts should always be greased/waxed; sleeve is filled with grout, cured, and then preloaded/torqued. Specific requirements are shown on the contract drawings.

The most reliable way to ensure proper bolt tensioning is to use hydraulic jacks to stretch the bolt to the proper preload value. Torque methods though acceptable are much less reliable to ensure proper installation and are affected significantly by the frictional resistances developed between the connecting surfaces.
Bolts requiring tensioning that consist of ASTM A307 or A36 material shall be tensioned in accordance with the values listed in Table 1. UNC threads are assumed. Bolts requiring tensioning that consist of ASTM A320-L7 material and using UNC threads shall be tensioned in accordance with the values listed in Table 2. Bolts requiring tensioning that consist of ASTM A320-L7 material and using 8 thread series shall be tensioned in accordance with the values listed in Table 3.
All values for preload and corresponding torque are based on achieving a tensile stress in the bolt of 60 percent of the yield stress of the bolt material. All values are based on using friction factors of 0.1 for thread friction, 0.15 for contact surface friction, and using the tensile stress area of the bolt. Tensile stress area of the bolt (Ast) is calculated using the formula:

Ast = 0.7854 ( D – 0.9743/n)2 where D is the bolt diameter and n is number of threads

UNC Threads

UNC Threads

8 Thread Series – 8N