A contractor is setting a massive W14x311 column on a concrete foundation for a heavy industrial facility.

Scenario: The concrete foundation is rarely perfectly level, and the heavy base plate (which is 3 inches thick) must be set to an exact elevation.

Solution: For large, heavy columns, it is impractical to manually shim the base plate perfectly level. Instead, the design utilizes leveling nuts.

The anchor rods are cast into the concrete. A "leveling nut" and washer are threaded onto each rod before the column is set down. The contractor uses a transit to adjust these lower nuts until they are all perfectly level at the correct elevation. The column and base plate are then lowered onto these nuts, and the top nuts are tightened down. Finally, high-strength, non-shrink grout is pumped into the gap between the concrete and the bottom of the base plate to provide continuous bearing.

A rigid frame building is designed to resist extreme lateral wind loads. The column bases must transfer significant shear force into the foundation.

Scenario: The calculated lateral shear force at the base of the column exceeds the combined shear capacity of the anchor rods and the friction between the base plate and the grout.

Solution: The anchor rods will fail in shear, or the concrete will fail in breakout, if relied upon alone.

The engineer specifies a shear lug. A shear lug is a heavy steel plate (or a piece of a structural shape like a WT) welded perpendicularly to the bottom of the base plate. A corresponding pocket or blockout is left in the concrete foundation. When the column is set and the pocket is grouted, the lateral shear force is transferred directly through bearing of the heavy shear lug against the solid concrete, safely bypassing the anchor rods.