ASME B18.31.2 L-Type Anchor Bolt Selection Guide

Standard Overview

ASME B18.31.2-2014 is the American Society of Mechanical Engineers standard for inch-series studs, covering complete dimensional and general data for full-thread studs, double-end studs, and flange-bolting studs. The standard was reaffirmed in 2019 and remains active.

Important note: The body of ASME B18.31.2 specifies the dimensional system for stud-type products (full-thread studs, double-end studs, and flange-bolting studs). It does not list the bend angle, bend length, or other characteristic parameters of L-shaped anchor bolts as mandatory clauses. In practice, these parameters are customized by manufacturers based on industry practice and customer drawings.

On bend angle tolerance: Industry sources show that ASTM F1554 specifies a bend angle tolerance of ±5°, while some manufacturer product specifications list 90°±2°. The 90°±0.5° figure represents a higher-precision manufacturer's internal control standard, not a tolerance specified by the ASME standard itself. Always confirm with the drawing or manufacturer's specification sheet when purchasing.

Key Technical Features

L-Shaped Hook Anchoring Mechanism

The 90° bent leg is the core anchoring structure of an L-shaped anchor bolt. The bent portion is embedded in concrete 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: Industry practice shows the hook length is typically 4-6 times the bolt diameter. Some engineering specifications require embedment depth of 25 times the bolt diameter, minimum bolt spacing of 6d, and a minimum distance from bolt center to foundation edge of 4d.

Embedment Depth and Failure Modes

Academic research shows that the anchoring performance of L-shaped anchor bolts varies with embedment depth, exhibiting different failure modes:

Research suggests a concrete breakout capacity calculation method using a 35° cone spread angle for the CCD (Concrete Capacity Design) method.

Thread Specifications: UNC/UNF

ASME B18.31.2 covers both UNC (Unified Coarse) and UNF (Unified Fine) thread series. Common size correspondences are as follows:

UNC suits most general anchoring applications, while UNF is used where finer pitch and higher thread fit precision are required.

Material Selection

Carbon steel anchor bolts corrode in damp environments, so stainless steel should be preferred for outdoor or damp applications. Hot-dip galvanizing is the most common corrosion protection method for carbon steel anchor bolts.

Corrosion Protection: Hot-Dip Galvanizing

For carbon steel anchor bolts in outdoor or damp environments, hot-dip galvanizing is the preferred corrosion protection. Related specifications require a zinc coating weight of no less than 0.61 kg/m² (86 µm minimum thickness for workpieces over 5 mm thick), 0.46 kg/m² (64 µm) for workpieces 2-5 mm thick, and 0.33 kg/m² (47 µm) for workpieces under 2 mm thick.

Some manufacturer specifications require an average zinc layer thickness of ≥85 µm with a local minimum of ≥70 µm. After galvanizing, hammer testing verifies adhesion (no flaking), and threads must pass go/no-go gauge inspection.

Application Areas

Equipment Foundation Anchoring

The most typical application for L-shaped anchor bolts is securing small to medium-sized equipment to concrete foundations. They suit scenarios with low impact and vibration during operation, such as:

• Machine tools, punch presses, generator bases

• Pump and fan foundations

• Pipe supports and utility corridor foundations

Street Lighting and Traffic Infrastructure

Light poles, traffic signs, and outdoor advertising structures widely use L-shaped anchor bolts in their foundation embedment. These applications carry relatively light loads, and the simple L-shaped structure is reliable and cost-effective.

Steel Structure Column Bases

Light steel structure column bases can use L-shaped anchor bolts. Typical applications include:

• Factory building column bases

• Platform upright embedment

• Communication tower and lighting mast foundations

Other Infrastructure

• Lifting equipment: Gantry crane and overhead crane rail foundations

• Building curtain walls: Embedded parts systems

• Solar mounting: PV panel support structure foundations

• Seismic isolation: Building isolation bearing embedment

Selection and Installation Guidelines

Key Parameter Reference

Installation Methods

L-shaped anchor bolts are suited to the following construction methods:

Cast-in-place method: The bolt is embedded directly in position during concrete pouring. Once the concrete cures, the bolt is fixed. This is the most common method and requires accurate formwork positioning.

Reserved hole method: A hole is reserved in the concrete, the bolt is inserted after equipment positioning, and grout fixes it in place. This suits scenarios where equipment position requires on-site adjustment.

Common Installation Mistakes

Summary

The L-shaped anchor bolt under the ASME B18.31.2 system is a simple, easy-to-install concrete anchoring solution. Its 90° bend creates a mechanical interlock in the concrete to resist pull-out. UNC/UNF threads suit different precision requirements, and carbon steel galvanized or stainless steel materials are available for indoor and outdoor environments. Anchoring performance research shows that embedment depth is the key factor determining failure mode—shallow embedment leads mainly to concrete cone failure, while deep embedment shifts to bolt shank tensile failure. L-shaped anchor bolts are widely used in street lighting, traffic infrastructure, small to medium equipment foundations, and light steel structure column base anchoring. For heavy-load or high-vibration applications, consider movable anchor bolts or welded anchor plates for enhanced anchoring.

On 90°±0.5°: This tolerance represents a higher-precision manufacturer's internal control standard. The ASME B18.31.2 standard itself does not cover this tolerance; ASTM F1554 specifies a bend angle tolerance of ±5°. Always confirm with the specific drawing or supplier specification sheet when purchasing.