GB/T 799 L-type Anchor Bolt Selection Guide

Standard Overview

GB/T 799-2020, Foundation Bolts, is the Chinese national standard issued on November 19, 2020, and implemented on June 1, 2021. It fully supersedes the previous GB/T 799-1988. The standard is administered by the National Fastener Standardization Technical Committee (SAC/TC 85), under the supervision of the China Machinery Industry Federation.

Scope: The standard applies to foundation bolts with thread sizes from M8 to M72, property grades 4.6 and 5.6, and product grade C. It specifies type dimensions, technical requirements, referenced standards, and marking methods.

Main technical changes in the 2020 edition (compared with the 1988 edition):

• Expanded the size range (1988 edition maxed out at M48; 2020 edition extends to M72)

• Added foundation bolt type dimensions (Chapter 3)

• Revised the length series

• Added general technical requirements (GB/T 16938)

• Upgraded property grades from 3.6 to 4.6 and 5.6

• Added hot-dip galvanizing requirements (GB/T 5267.3)

Note: The body of GB/T 799-2020 classifies foundation bolts into Type A, Type B, Type C, and other configurations for dimensional specification. The L-type (90° hook) foundation bolt is a typical configuration within this system, and its bend angle, hook length, and other characteristic parameters are specified as part of the type dimensions in the standard.

Key Technical Features

L-Type Hook Anchoring Mechanism

The 90° bent leg is the core anchoring structure of an L-type foundation bolt. The hook is embedded in the concrete foundation during pouring. When the bolt is subjected to an upward pull-out force, the hook forms a mechanical interlock with the concrete to resist extraction.

Hook length reference: For plain round foundation bolts, industry practice shows embedment depth is typically 25 times the bolt diameter, with a hook length of approximately 120 mm. Both the embedment depth and hook serve to ensure sufficient friction between the bolt and the foundation, preventing pull-out failure.

Metric Thread Sizes M12-M64

GB/T 799-2020 covers thread sizes from M8 to M72. Thread length parameters for common sizes are as follows (based on 1988 edition data; the 2020 edition dimensional system largely continues it):

Note: h is the distance from the hook end to the thread start. Refer to the 2020 edition standard text for actual dimensions.

Material Selection

Common industry materials include Q235, Q345, 45# steel, and 35CrMo. Material selection depends on design load, foundation conditions, and environmental corrosion exposure.

Property Grades and Surface Finishes

The mechanical property grades specified in the standard are 4.6 and 5.6. Grade 5.6 offers tensile strength in the 500 MPa class, nearly half again higher than the 330 MPa of the old Grade 3.6.

Surface finish options include:

• Plain (as-produced)

• Oxide treatment

• Electroplated zinc (per GB/T 5267.1)

• Hot-dip galvanized (per GB/T 5267.3, for outdoor damp environments)

Installation Methods

There are two primary methods for embedding foundation bolts:

Cast-in-place (pre-embedded): The bolt is embedded directly in position during concrete pouring. This suits towers, tall vessels, spherical tanks, and machinery with significant vibration.

Reserved hole with secondary grouting: A hole is reserved during pouring; after equipment positioning, the bolt is inserted and grouted in place. This suits horizontal vessels, heat exchangers, small vertical vessels, and other static equipment as well as low-vibration pumps.

Application Areas

Machinery Foundation Anchoring

The core application of GB/T 799 foundation bolts is securing various types of machinery to concrete foundations. Typical equipment includes:

• Pumps, fans, compressors

• Machine tools, stamping equipment

• Boilers, pressure vessels

• Tower equipment, heat exchangers

Steel Structures and Infrastructure

Widely used in railway, highway, power infrastructure, mining, bridges, tower cranes, and long-span steel structures.

Street Lighting and Traffic Infrastructure

Light poles, traffic signs, and signal poles widely use GB/T 799 foundation bolts in foundation embedment, with the L-type hook providing reliable anchoring capacity.

Petrochemical Equipment

Foundation bolt design for static petrochemical process equipment (towers, vessels, heat exchangers, etc.) can follow relevant design specifications, with the reserved hole grouting method being a common approach.

Selection and Installation Guidelines

Construction Notes

1. Verticality control: Foundation bolts should be installed vertically without tilt

2. Positioning and fixing: For high-precision requirements, first fabricate a bolt cage (thread through an embedded steel plate and tighten nuts), then tie it to the formwork before pouring

3. Construction records: Document bolt model and specifications in detail for future maintenance and replacement

Marking Method

Per GB/T 1237. Marking example:
For a foundation bolt with thread size d=M20, nominal length l=400 mm, property grade 4.6, Type A, plain finish, product grade C:
Foundation bolt GB/T 799 M20×400-A

Summary

GB/T 799-2020 is the Chinese national standard for foundation bolts, applicable to metric M8-M72sizes, property grades 4.6 and 5.6, and product grade C. Compared with the 1988 edition, the new standard extends the size range from M48 to M72, upgrades property grades from 3.6 to 4.6/5.6, and adds hot-dip galvanizing requirements. L-type foundation bolts achieve anchoring through mechanical interlock between the hook and concrete; industry practice sets embedment depth at 25 times the diameter with a hook length of approximately 120 mm. Material options include Q235, Q345, 45# steel, and 35CrMo, with surface finishes including plain, oxide, electroplated zinc, and hot-dip galvanized. These standard foundation bolts are widely used in machinery foundations, steel structures, street lighting and traffic infrastructure, and petrochemical equipment.