Classification of Anchor Bolts

Anchor bolts, as an indispensable part of construction and engineering structures, play a crucial role in ensuring the safety and stability of projects. In this article, we will delve into the two main classifications of anchor bolts: based on performance grades and based on their shapes.

Anchor Bolt Types Based on Performance Grades

Anchor bolts primarily bear axial tension, making the classification based on performance grades reasonable and crucial. Performance grades mainly refer to tensile strength, and standards specify a range of grades, including 4.8, 6.8, 8.8 hot-dip galvanized bolts with matching nuts, and, under specific conditions, 10.9-grade bolts can be used. The first digit in the grade indicates the bolt's tensile strength, represented as 1/100 of the specific strength value, and the subsequent digit is the yield-to-tensile ratio, representing the ratio of the bolt's yield strength to its tensile strength.

The yield-to-tensile ratio is a critical indicator, and excessively high ratios may lead to structural brittle failure that is difficult to predict. Understanding performance grade markings can be illustrated through an example: if a bolt has a nominal tensile strength of 600 MPa and a yield-to-tensile ratio of 0.8, its performance grade marking would be "8.8."

Anchor Bolt Types Based on Shapes

The construction of anchor bolts includes a rod, nut, washer, and end anchoring component. Considering the variety of end anchoring forms affecting the anchoring force, anchor bolts can be classified into several main types based on end anchoring forms: J-type, T-type, cleat-type, and double-headed anchor bolts.

J-type Anchor Bolt: Simple in structure and easy to manufacture, suitable for towers with relatively small loads. It features a 180° hook at the end for enhanced anchoring in concrete. J-type is recommended for 4.6-grade anchor bolts with specifications controlled at M36 and below.

T-type Anchor Bolt: Easy to assemble, facilitates vertical positioning, and suitable for towers with smaller load capacities. The end anchoring uses an anchor plate, with four reinforcing plates evenly distributed and welded to the anchor plate and bolt. The heat generated during welding may weaken the bolt's strength to some extent. Considering the low material strength, low load-bearing capacity, and weldability of 4.6-grade anchor bolts, T-type anchoring is recommended for 4.6-grade anchor bolts, with specifications controlled at M42 and above, considering smaller T-type anchor bolts might not be easy to weld, and factors such as weakened strength due to reinforcing plate welding.

Cleat-type Anchor Bolt: The end anchoring uses a cleat-type form, with three hooked rebars evenly distributed and welded to the bolt. Heat generated during the welding of the hooked rebars may affect the bolt's strength. Suitable for towers with higher load capacities. Design considerations should include the distance between the cleats and surrounding stirrups to avoid collisions. Cleat-type is recommended for 5.6-grade anchor bolts.

Double-headed Anchor Bolt: Both ends have threads, facilitating easy assembly and having a higher load-bearing capacity. The anchoring part uses an anchor hole plate to enhance pull-out resistance. Double-headed anchor bolts are recommended for 6.8-grade and 8.8-grade anchor bolts.

By gaining an in-depth understanding of these classifications, we can better select the types of anchor bolts that are suitable for specific engineering requirements, ensuring the stability and safety of structures.