Anchoring Systems for Steel Structures

Anchoring secures your steel carport or garage to the earth, countering wind uplift and lateral forces. The type of anchor required depends entirely on the surface where the building is installed.

This guide reviews the three primary anchoring systems used to secure steel buildings.

Which Anchor Do I Need?

1. Concrete Expansion Wedge Anchors (e.g., Power-Stud SD1)

The standard anchoring system for flush or wide-margin concrete slabs, relying on radial friction.

• The Physics (ACI 318): Holes are drilled through the steel base rail into the concrete. Expansion wedge bolts are driven into the holes and torqued. As the nut turns, the tapered mandrel is drawn upward, forcing an expansion clip outward. This wedging mechanism exerts massive, permanent radial forces against the concrete.
• Edge Distance Blowout Risk: Because expansion anchors generate high internal stress fields, they are highly sensitive to edge distance. If placed too close to the edge of the slab, the radial expansion pressure will simply blow out the side of the concrete (edge spalling). ACI 318 requires a minimum edge distance of 5 times the anchor diameter.

2. Heavy-Duty Screw Anchors (e.g., Simpson Titen HD)

Used for heavy wide-span buildings or when anchor bolts must be placed close to the concrete edge.

• The Physics: Heavy-duty screw anchors function through mechanical interlock without generating expansion forces. They feature hardened, serrated carbon-steel cutting threads that slice directly into the concrete matrix as they are driven in with an impact wrench.
• The Edge Advantage: Because they eliminate outward radial wedging stresses, screw anchors can be installed at significantly smaller edge distances (e.g., as close as 1.75 inches for some sizes) compared to expansion wedges, making them ideal for flush-mount slabs.

2. Solid Steel Asphalt Pins

Used when structures are installed on paved asphalt driveways or parking areas.

• How they work: A 30-inch solid steel rebar pin with a welded collar is driven through the base rail, penetrating the asphalt layer and anchoring deep into the gravel subbase beneath.
• Engineering limits: Asphalt is flexible and can soften in summer heat, meaning asphalt pins provide lower uplift resistance than concrete anchors. They are excellent at preventing lateral sliding but are generally not certified for extreme wind uplift unless paired with specialized soil anchors.
• Precaution: Drilling through asphalt can lead to moisture infiltration. Sealing around the pin head with heavy-duty silicone or asphalt sealant is recommended.

4. Double Helical Ground/Soil Anchors (Earth Augers)

Required for installations on raw soil, compacted gravel pads, or agricultural land.

• How they work: Heavy steel shafts (e.g., Minute Man MMA-2, 650 EZDH anchors, typically 48 inches long) equipped with helical screw plates are driven into the ground using a motorized auger drive attached to a skid steer.
• Engineering limits (Pullout Strength): Helical anchors utilize the dead weight of the mobilized soil cone above the plates to resist tension. Under standard residential codes, earth augers used for certified carports must resist a minimum allowable working load of 3,150 pounds and an ultimate load of 4,725 pounds.
• Installation Verification: To guarantee this immense uplift capacity, contractors must drive the anchors deep enough to achieve a verifiable installation torque of at least 2,400 ft-lbs.

5. Rebar Anchors

A basic anchoring solution primarily used as a temporary or minimal-securing option on solid ground.

• How they work: Straight steel rebar pins are driven directly through the base rail and into the dirt.
• Engineering limits: Because they lack helical threading or concrete expansion mechanisms, they rely solely on soil friction. They offer the lowest uplift resistance and are typically not certified for high wind loads.

6. Anchoring and the 90 MPH Wind Warranty

Proper anchoring is not just a structural necessity—it is a strict warranty requirement.

To qualify for a manufacturer’s standard 90 MPH Wind Warranty, you must:

1. Purchase and install the specific anchor package (Mobile Home, Asphalt, or Concrete) certified for your foundation type. (Standard rebar anchors do not qualify).
2. Ensure that if a failure occurs during a certified wind event, it is due to the anchors failing. The warranty typically dictates that the base rail must be completely ripped out of the ground or concrete for coverage to apply.