Direct Answer
A column base plate is a steel plate welded to the bottom of a steel column and anchored to the concrete foundation with anchor bolts. It distributes the column's axial load, shear, and moment into the concrete. Base plates are typically A36 or A572 plate, sized by the engineer based on column loads and concrete bearing capacity, and are often grouted under after the column is plumbed.
Full Explanation
Base plate design per AISC Design Guide 1 considers: column load (axial, moment, shear), concrete bearing strength, anchor bolt pattern and capacity, and plate bending. The plate is shop-welded to the column using a four-sided weld around the column perimeter (or specific weld pattern per design). Anchor bolt holes in the plate must match the anchor bolt plan exactly — a mislocated hole in a base plate that's already welded to a column is an expensive repair. After erection, the space between the plate and foundation is filled with non-shrink grout.
What This Means for Your Shop
Base plate anchor bolt hole layout is a critical QC check. Verify each hole location against the approved anchor bolt plan before welding the plate to the column. An error discovered after assembly typically requires cutting off the plate — or, in the field, burning oversized holes — both costly.
Common Mistakes
Fabricating base plates before the anchor bolt plan is approved. Design changes to the anchor bolt pattern after base plates are fabricated require rework or replacement.
Recommended Process
Only fabricate base plates after the anchor bolt plan is approved for construction. Verify hole layout with a template against the approved drawing before welding. For columns with moment-resisting base plates, verify weld size and geometry carefully — these welds carry significant load.