Reasons to Use Anchor Bolts

There are literally hundreds of types of bolts and fasteners used to anchor and hold buildings, structures, and other steel profiles to concrete pads.

In broad terms, they’re all known as foundation bolts; and the most common types, cast-in anchors, are typically templated into their set positions before the concrete is poured, leaving only their threaded ends exposed. These types of anchors are also manufactured in a virtually limitless range of sizes, forming methods, and thread pitches, making them ideal for loads that need large embedment lengths and high tensile strength.

If you’re considering hiring a contractor to fabricate or secure a structure for you, they’re undoubtedly already familiar with Australian Standard (AS) 5216 requirements for the design and installation of cast-in concrete fasteners. Knowing a little about them yourself, however, will help you to understand how the foundation work that your builder needs to perform corresponds to the stability and safety of your structure.

The Stability You Want With Cast-in Anchor Bolts


Depending on the job, cast-in foundation bolts are regarded as some of the strongest and simplest anchors used in construction; and you’ll typically find these types of heavy-duty hold-downs and anchor bolts used in minimum assemblies of 4 to ensure that there’s maximum load transfer from the structure’s frame to the foundation.

To fully understand the task that foundation bolts perform though, it’s important to recognize that structural foundations are more than just conveniently levelled surfaces to distribute weight on. They’re incredibly complex structures that, both during construction and after completion, are the counterweights for everything that’s bolted to them, including:

  • Concrete slabs;
  • Foundation walls;
  • Steel columns or girders;
  • Prefabricated structures; and,
  • Heavy machinery.

Cast-in anchor bolts and hold-down bolts are responsible for ensuring that all of these elements remain solidly tied to the foundation; and it’s a function that they’re required to perform flawlessly regardless of any winds, torsional forces, or vibration that they may encounter for decades to follows.

In short, regardless of whether you’re having an entire building erected or just an area light stood up, you want to know that the anchor bolts and hold-downs being used are up to the job. There are 3 main types of cast-in anchor bolts for sale that you’ll find being used in Australia, and each one has its own unique qualities.

Angled Anchor Bolts Still Get the Job Done


90° L-type and 135° J-type hold-down bolts have been the torchbearers for cast-in style foundation anchors for a long time. The radiused ends of these hold-downs are designed to be firmly encased in the setting concrete, while the threaded end remains above the top of the foundation, allowing for quick fastening of structural elements.

These Grade 8.8, high tensile steel foundation bolts can vary from M12 to M30 in diameter, typically boast lengths of up to 700mm, and are produced with a range of corrosion resistant coatings that include:

  • Hot dipped galvanizing;
  • Hobkote® plating; and,
  • Zinc plating.

And although research has found that angled hold downs tend to have less pullout strength than other types of cast-in foundation bolts, they continue to prove that they’re capable of handling incredible amounts of torque while still providing healthy amounts of resistance, when utilized correctly and allowed to set properly. Ideally, these hold down bolts are still perfectly suited for:

  • Bolting down heavy industrial equipment;
  • Fixing columns; and,
  • Attaching and stabilizing floor plates.

Hex-Headed Hold Downs Are the New Standard


Hex-headed type hold-down bolts are forged with a load-bearing square- or hex-headed appendage on their cast-in ends, making it possible for an additional square plate washer to be slid down onto it for even greater pullout resistance.

These hot rolled, Grade 36, 55, and 105 high tensile steel anchors are ordinarily available in M12 to M42 diameters and have become the new standard for cast-in hold downs for features that include:

  • Increased cost-effectiveness over other types of forged foundation anchors;
  • Significantly greater pullout resistance than angled hold downs; and,
  • Less space installation space required than angled hold downs.

Hex-headed hold downs have the same range of corrosion-resistant coatings that angled hold downs have, and their higher pullout strength makes them the preference for contractors who buy anchor bolts to mount objects such as:

  • Structural columns;
  • Precast concrete elements; and,
  • Wind turbines.

Custom Configurations With Threaded Anchor Bolts

Conceptually, threaded anchor bolts are almost identical to hex-headed hold downs, but with the exception that they’re made from either fully threaded, or dual-end threaded bar stock. Unlike the forged end of a hex-headed hold-down bolt, the cast-in end of a threaded anchor is fitted with a plated washer that’s friction locked between 2 nuts to prevent turning.

While materials, dimensions, and finishes are practically identical to hex-headed hold downs, threaded anchor bolts still have their own set of advantages, including:

  • The ready availability of heavy grade threaded rod stock almost anywhere;
  • The ability to configure custom the cast-in end hardware; and,
  • Inherently greater pullout resistance due to threaded bodies.

Threaded anchor bolts are ideal for all types of high-tension loaded foundations where time and cost are just as essential as reliability. It’s their versatility when it comes to using different nut and plate combinations, or the ability to weld or score them for even more pullout resistance, however, that makes them the anchor bolts Australia turns to for the biggest jobs.

The Final Word

At the end of the day, while there may be an array of choices available when it comes to cast-in foundation bolts, there’s no ambiguity about their function: to provide a counterweight that’s sufficient enough to prevent structural elements and equipment from incurring damage or catastrophic failure due to torsional or vibrational loading.

If you’re having work done that requires cast-in anchors, you want to pay close attention to how the foundation is being set, and you want to make sure that the hold-downs and anchor bolts being used are suitable for the job.