Anchor Bolt

An Anchor Bolt (also known as a foundation bolt, anchor rod, or embedment bolt) is a high‑strength threaded fastener that is embedded in concrete or asphalt to provide a secure fixing point for AGL equipment. It is the primary means of attaching base plates, base cans, junction boxes, mounting rings, and other AGL components to the pavement structure, ensuring that they remain firmly in place under the extreme loads and vibrations experienced on an active airfield.

Key characteristics of anchor bolts include:

• High Strength: Made from high‑grade steel (typically Grade 8.8 or 10.9) to withstand tensile, shear, and bending loads from aircraft, vehicles, and environmental factors.
• Corrosion Protection: Hot‑dip galvanised, stainless steel, or coated to resist corrosion from moisture, de‑icing chemicals, and fuels.
• Precision Threading: Threaded to precise standards (metric or UNC) to ensure consistent torque and clamping force.
• Embedment Features: Often includes a hook, bent end, or plate at the embedded end to provide mechanical anchorage in the concrete.

Anchor bolts are used in a wide range of AGL applications, including:

• Base Plate Fixing: Securing base plates for elevated fixtures, signs, and junction boxes.
• Base Can Installation: Anchoring base cans into the pavement to prevent movement or uplift.
• Mounting Ring Fixing: Securing mounting rings inside base cans for inset fixtures.
• Junction Box Anchoring: Fixing underground or above‑ground junction boxes to the pavement.
• Earthing Connection Points: Providing a fixing point for earthing cables and connectors.

Anchor bolts are typically installed during the pavement construction process (cast‑in‑place) or retrofitted into existing pavement using epoxy or mechanical anchors (post‑installed). The selection of the bolt type, size, and embedment depth is critical to achieving the required load capacity and long‑term performance.

Every AGL fixture, base can, or junction box eventually has forces working to move it: aircraft jet-blast and wheel loads, thermal expansion of the pavement, frost heave, and years of vibration. The anchor bolt's purpose is to convert the pavement itself into the fixture's foundation, transferring tensile, shear, and bending loads from the fixed equipment down into the concrete so that the equipment cannot work loose, tilt, or lift over time. This matters operationally as much as structurally: a fixture that shifts even a few millimetres out of position can throw off its beam alignment enough to fail a photometric inspection, and a loosening anchor is often the first, hard-to-see stage of a failure that later shows up as a cracked base plate or a fixture that has worked itself proud of the pavement — a potential FOD and aircraft-tyre hazard. Correctly specified anchor bolts (grade, embedment depth, corrosion protection) are therefore a preventive measure as much as an installation step.

Anchor bolts are used throughout the airfield wherever AGL equipment needs to be securely fixed to the pavement or concrete foundations, including:

• Runway Lighting: Anchoring base plates and base cans for elevated runway edge lights, and securing mounting rings for inset runway lights.
• Taxiway Lighting: Fixing base plates, base cans, and mounting rings for taxiway edge and centreline lights.
• Approach Lighting: Anchoring base plates for approach light fixtures, barrettes, and flashing light units.
• Airfield Signage: Securing mandatory instruction signs, direction signs, and information signs to the pavement.
• Junction Boxes and Distribution Panels: Anchoring underground and above‑ground enclosures.
• Obstruction Lighting: Fixing base plates for obstruction lights on structures and poles.
• Earthing Systems: Providing fixing points for earthing connectors and cable lugs.

The bolt is selected based on the load requirements (tensile, shear, and combination), the type of base material (concrete or asphalt), and the environmental conditions. For critical applications, the bolt is designed to provide a safety factor of at least 2.0 against failure under maximum expected loads.

Anchor bolts are set into the concrete foundation at the same time it's poured (cast-in) or drilled and epoxied into cured concrete afterward, positioned to the base plate or base can's bolt-hole pattern so the fixture, pole, or equipment can be bolted down without adapting the hardware. Bolt embedment depth and edge distance from the foundation edge are set to the manufacturer's pull-out and shear rating, since these bolts carry the full wind and impact loading (or, for a frangible installation, the load that must be reliably exceeded to trigger the intended break) rather than just static weight. Anchor position is set out from the same survey used for the base can or plate itself, checked for level and pattern alignment before the concrete is poured or the epoxy is set, since a bolt pattern that's out of alignment can't be corrected afterward without redrilling.

An anchor bolt functions as a mechanical connection between the AGL equipment and the pavement structure. Its design ensures that loads are transferred safely from the equipment into the foundation:

• Load Transfer: The bolt transfers tensile, shear, and bending loads from the equipment (e.g., wind loads on a sign, aircraft loads on a light fixture) into the concrete or asphalt through mechanical interlock or adhesive bonding.
• Mechanical Anchorage: For cast‑in‑place bolts, the hook, bent end, or plate embedded in the concrete provides mechanical resistance against pull‑out. For post‑installed bolts, the expansion mechanism or adhesive bonding provides the anchorage.
• Clamping Force: When the nut is tightened, the bolt creates a clamping force that holds the equipment securely against the pavement, preventing movement or vibration.
• Alignment: The precise positioning of the anchor bolts (using a template or jig) ensures that the equipment is correctly aligned during installation.

The installation process varies depending on whether the bolt is cast‑in‑place or post‑installed:

• Cast‑in‑Place (Embedded): The bolt is positioned in the formwork before the concrete is poured, using a template to ensure accurate alignment. The bolt is held in place by the concrete after it cures. This method provides the highest load capacity and is used for critical equipment.
• Post‑Installed (Mechanical or Adhesive): A hole is drilled into the existing pavement, and the bolt is inserted using an expansion anchor (e.g., wedge anchor, sleeve anchor) or bonded with epoxy or polyester resin. This method is used for retrofits and repairs.

The bolt is designed to provide a service life of 20+ years, with regular inspection for corrosion, loosening, and damage. The torque on the nuts should be checked periodically to ensure that the clamping force is maintained.

The anchor bolt is the one genuinely permanent connection in the fixture's mechanical stack — everything bolted above it (base plate, base can, frangible coupling, fixture) is designed to be replaceable, and in a frangible installation, some of it is designed to fail on impact, but the anchor bolts themselves are meant to remain intact through that event and every normal load cycle before and after it. This is why anchor bolt sizing and embedment are calculated conservatively against the full range of loads the installation can see (wind, aircraft-induced pressure, impact), independent of whatever sits above: if the anchor bolts were ever the weakest point in the stack, an impact would pull the whole foundation apart rather than shearing cleanly at the frangible coupling as intended.

An anchor bolt is machined from carbon steel, stainless steel, or galvanised steel bar stock to the specified grade, with the embedded end formed as a hook, L-bend, or expansion mechanism depending on whether it is a cast-in-place or post-installed design, so the bolt develops its full tensile and shear capacity through mechanical interlock with the surrounding concrete or asphalt rather than relying on bond strength alone. The exposed end is threaded to the specified pitch and length to accept the nuts and washers that secure the base plate or equipment above, with the thread length sized to allow for levelling adjustment during installation. Corrosion protection is applied either as a hot-dip galvanised coating of a specified minimum thickness, a zinc-plated finish, or by specifying stainless steel bar stock outright, since anchor bolts remain permanently embedded in pavement exposed to moisture, de-icing chemicals, and freeze-thaw cycling for the life of the installation. Where used in seismic or high-vibration applications, the bolt's embedment depth and any additional anchor plate or washer at the embedded end are sized to develop the required pull-out and shear resistance in the specific concrete or asphalt strength being anchored into.