Guide to Different Types of Anchor Bolts

Anchor bolts are a staple in all types of construction. They attach structural elements to masonry or concrete by embedding one end in the material and threading the opposite end to secure structural support. There are several types and sizes of anchor bolts, and each has an application based on the size and scope of the project.

Different Types of Anchor Bolts

Anchor bolt applications vary, but the four most common anchor bolts include swedge anchor bolts, headed anchor bolts, L-shaped anchor bolts and double-end rods with plate anchor bolts. Each has its merits depending on the intended use. Before choosing the anchor bolt you use for your project, ascertain whether it's the most applicable.

1. L-Shaped Anchor Bolts

L-shaped anchor bolts — also known as masonry anchors or foundation bolts — vary in size, shape and material depending on the intended application. They all consist of a threaded end for maximum load-bearing capability, where you can attach a hex nut and flat washer. L-shaped anchor bolts are frequently used in structural, masonry and concrete applications.

Some of their many uses include the following:

• Support structural elements in buildings, including beams, ledges and plates. 
• Balance signage and other structures erected on masonry or concrete.
• Embed in walls to support steel plates and beams in non-load-bearing and load-bearing walls. 

2. Double-End Rods With Plate Anchor Bolts

Double-end rods with plates are also known as anchor rods or threaded studs, among other terms. These double-end rods have a plate washer on one end, which can be welded to the anchor bolt or tack-welded to a nut inside the concrete. They are often used to anchor a structure to its foundation.

Applications for this robust alternative commonly include the following:

• Anchor traffic signal poles.
• Stabilize large buildings.
• Construct columns for buildings.

3. Headed Anchor Bolts

Headed anchor bolts differ from other anchor bolts and rods, as they have a non-threaded end with a square head, forged or heavy hex. The headed end is embedded into the foundations to secure a variety of structures in place. The primary application for headed anchor bolts is permanent installations. In general, they do not need maintenance once the installation is complete.

The most common applications for headed anchor bolts include:

• Secure structural steel columns.
• Attach bridge rails.
• Affix light poles.

4. Swedge Anchor Bolts

Many consider swedge anchor bolts the strongest variety of anchor bolts. They consist of round bars of steel, threaded on one end and swedged on the other. “Swedge” refers to multiple indentations on the non-threaded end to allow the concrete to settle within the grooves and increase pull-out resistance.

In general, a press adds the indentations — they must never be cut into the swedge anchor, or they will affect the part's integrity. Your provider can configure the indentations based on the application of the project to ensure maximum strength. Swedge anchor bolts are also available in several different materials and fall under the domestic classification.

Typical swedge bolt uses include the following:

• Connect piers and girders.
• Stabilize highway work.
• Augment Department of Transport projects.

Choose the Right Anchor Bolt for Your Build

While there are many critical factors to consider when choosing what anchor bolt is best for you, the two most important considerations are the size of the hole for fixtures and the length of the bolt. Other factors include the following:

• Fastener length: There is a formula you can use here. Add the thickness of the material you plan to fasten to the minimum embedment depth for the anchor bolt's diameter. Then, add the washer and nut thickness if applicable. The combined number will give you an indication of how long your fastener needs to be.
• Hole size: The hole in the fixture determines the size of the hole you'll need to drill into the concrete. You may need to size down to ensure the bolt can fit through the hole fixture.
• Concrete thickness: The smaller the diameter of the anchor bolt, the less depth you need when drilling a hole in your concrete. Calculating your minimum embedment will give you a better idea of which anchor bolt is most appropriate for your application.
• Weight of fastening: Positioning your anchor bolt near the bottom of the concrete can put undue pressure on the structure. Consider where you plan to position your anchor bolt concerning the weight of the item you are fastening. The anchor bolts must be able to hold the load without impacting the soundness of the structure.
• Structural integrity: The anchor bolt is the weakest point in a structure. In this regard, the bigger, the better. The strongest, widest and deepest embedded anchor bolts can handle the most weight safely.
• Concrete pounds per square inch (PSI): Knowing how much pressure your concrete can handle is essential before commencing your project. Concrete PSI depends on the concrete mixture, but the age of the concrete is also crucial. The older the concrete, the harder the consistency, which can be challenging to drill.
• Anchor bolt positioning: Your anchor bolt must perform different functions depending on where you place your fixture. For example, the anchor bolt best suited to wall fastening may not be the right option for overhead fixtures.
• Professional assistance: If you are unsure which anchor bolt is best for your project, consult a professional tools and equipment supplier. Explain the scope of the application, and they can help you choose the safest and most reliable anchor bolt for the job.

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