Anchor bolts play a key role in construction and industrial projects. They are used to connect structural and non-structural components to concrete, offering strength and stability. Choosing the right type of anchor bolt can make a big difference in the safety and durability of a project.
This article will walk you through the most common types of anchor bolts, their functions, and when to use each one.
What Is an Anchor Bolt?
An anchor bolt is a type of fastener used to attach structures or machinery to concrete surfaces. It provides a secure connection between the concrete and the object being fastened. Anchor bolts come in different shapes, materials, and strengths to match specific engineering needs.
There are two general categories:
- Cast-in-place anchor bolts (installed while concrete is being poured)
- Post-installed anchor bolts (installed after concrete has cured)
Now let’s take a closer look at the various types of anchor bolts available on the market.
1. L-Shaped Anchor Bolts
L-shaped anchor bolts are among the most widely used in structural applications. They are typically embedded into wet concrete during the casting process, with one leg of the “L” sticking out to hold structural steel or other components. The 90-degree bend at the bottom helps lock the bolt into place once the concrete sets, preventing it from pulling out under tension.
These bolts are often made from carbon steel or stainless steel and can be custom-fabricated to fit specific size requirements. They are commonly used in building columns, poles, heavy machinery bases, and structural steel frameworks where reliable anchorage is critical. This type of anchor bolt is valued for its simplicity, cost-efficiency, and strong mechanical retention within the concrete base.
2. Straight Anchor Bolts with Bottom Plate or Washer
Straight anchor bolts are long, straight rods with threads on the exposed end. To improve their hold within concrete, these bolts often have a welded plate, nut, or heavy washer fixed to the embedded end. The plate acts as a barrier that resists pull-out forces and distributes tension evenly across the concrete surface.
This type is frequently chosen for heavy structural connections, including industrial machinery foundations, bridge supports, and other high-load applications. The ability to fabricate the plate size and bolt length offers flexibility in custom designs. These bolts also allow for easy alignment and precision placement, which makes them a reliable option in settings that demand strict installation accuracy.
3. Headed Anchor Bolts
Headed anchor bolts are straight rods with a forged or welded head—usually hexagonal, square, or round, at one end. When the bolt is set into concrete, the head serves as a stop that anchors the bolt firmly. Unlike L-shaped types, there is no bending involved, which makes these bolts easier to produce in large volumes and standard sizes.
These bolts are often used in bridge construction, precast concrete installations, columns, heavy equipment bases, and transportation infrastructure. Because the bolt’s head sits flush within the concrete, it provides consistent load transfer and resistance to both shear and tensile forces. Headed anchor bolts are ideal when structural stability and ease of installation are equally important.
4. Sleeve Anchor Bolts
Sleeve anchors are post-installed anchors, meaning they are placed into hardened concrete using drilled holes. This type includes a threaded bolt surrounded by a metal sleeve. When the bolt is tightened, the sleeve expands outward and grips the concrete wall tightly, holding the anchor in place.
Sleeve anchor bolts are preferred in light- to medium-duty applications, such as mounting handrails, electrical boxes, HVAC brackets, and signs onto concrete, brick, or block walls. They are versatile because they can be installed without the need for pouring new concrete, making them suitable for renovation and retrofit work. These anchors are also adjustable after placement, which adds a layer of convenience during installation.
5. Wedge Anchor Bolts
Wedge anchors are another type of post-installed anchor that provides a high-strength connection to concrete. They consist of a steel rod with a tapered end and a small metal clip or wedge. When driven into a drilled hole and the nut is tightened, the wedge expands against the sides of the hole, locking the bolt in place.
Wedge anchor bolts are commonly used in industrial equipment installation, warehouse racking, structural supports, and safety barriers. They are ideal for static and heavy vertical loads. Their high holding power and reliability under tension make them one of the most dependable types of anchor bolts for permanent installations in solid concrete.
6. Expansion Anchor Bolts
Expansion anchors include a broad category of anchors that expand when a bolt or screw is inserted and tightened. These anchors often feature a sleeve, cone, or internal mechanism that pushes against the walls of the hole, creating strong friction and holding the anchor firmly in place.
They are suitable for medium-load installations such as cable trays, pipe supports, HVAC ducts, and light machinery. Expansion anchors are appreciated for their speed and ease of use, especially in maintenance work and field installations. Their performance may vary depending on the substrate material, so proper selection is crucial for long-term safety and stability.
7. Chemical or Epoxy Anchor Bolts
Chemical anchor bolts differ from mechanical types by using bonding agents such as epoxy or resin to fix the bolt in place. The anchor rod is inserted into a pre-drilled hole filled with adhesive, which then cures and forms a strong bond with the concrete. This type offers the advantage of zero expansion pressure, making it safer to use in delicate or cracked concrete.
These bolts are widely used in retrofitting work, structural repairs, seismic upgrades, and applications where precision and durability are critical. Because the resin fills all voids in the hole, it provides a very secure fit even under extreme stress or in corrosive environments. Chemical anchors also allow for longer anchoring depths and are well-suited for overhead or load-sensitive applications.
How to Choose the Right Anchor Bolt
When selecting an anchor bolt, consider the following:
- Load requirements: Understand both tensile and shear forces involved.
- Environmental exposure: Use stainless or galvanized steel for moisture-prone or corrosive areas.
- Installation timing: Decide between cast-in-place or post-installed based on project sequence.
- Substrate condition: Evaluate if the concrete is new, aged, or cracked.
- Code compliance: Always consult local regulations and engineering standards.
Proper selection not only improves safety but also extends the lifespan of the structure or equipment being supported.
Conclusion
Anchor bolts are small but essential parts in any concrete anchoring system. Each type, from L-shaped to epoxy anchors, offers unique benefits depending on the project’s needs and installation environment. By understanding how each anchor bolt functions, project owners and engineers can make smarter, safer choices.
If you’re looking for high-quality anchor bolt options for industrial or structural use, Karunia Utama offers dependable, custom-fabricated fasteners that meet strict quality standards.
FAQ
- Which type of anchor bolt is best for heavy machinery?
For heavy machinery, wedge anchor bolts or straight anchor bolts with a bottom plate are often recommended. These types offer strong load-bearing capacity and are designed to handle high stress under both tension and vibration.
- Can I use anchor bolts on brick or block walls?
Yes, certain types like sleeve anchor bolts and expansion anchors are suitable for brick or block installations. However, it’s important to check the load requirements and choose anchors specifically designed for hollow or less dense materials.
- How do I know what size anchor bolt to use?
Anchor bolt size depends on the weight of the object being secured, the type of material being anchored into, and any applicable building codes. Always consult with an engineer or refer to load tables provided by manufacturers for accurate sizing.
