Steel Plates in Structural Connections: Base Plates, Connection Plates and Ordering

Beams and columns are only half of a steel frame. The other half is the connections that join them to each other and to the foundations, and most of those are cut from steel plate. This article explains what column base plates and connection plates do, what matters on site, and how to order plate for connection parts.

What plates do in a steel connection

A plate in a connection carries force from one member to another. The base plate takes the column force into the concrete foundation; beam-to-column plates take the beam reaction into the column; splice plates join two lengths of column. Most of these parts are cut, drilled and welded to one member in the fabrication shop, then bolted or welded to the other member on site.

Plate size, thickness, grade and connection type are set by the structural engineer and shown on the shop drawings, under the design code of the project's country. This article does not replace that design; it covers the practical and purchasing side.

The column base plate

SteelConstruction.info, which describes itself as the free encyclopedia for UK steel construction information, describes the usual multi-storey column base as a single rectangular or square plate fillet-welded to the column end and fixed to the foundation with four holding-down bolts. The bolts sit in location tubes or cones in the concrete and carry anchor plates so they cannot pull out.

According to the same source, the column force is generally carried to the plate in direct bearing, while the bolts stabilise the column during erection and resist uplift in braced bays. For detailed design, the American Institute of Steel Construction (AISC) publishes Design Guide 1, "Base Connection Design for Steel Structures"; its third edition (2024) adds major updates on seismic design and embedded bases.

Anchor rods, oversized holes and leveling

Anchor rods are cast into the foundation before the steel arrives, so base plate holes are made larger than the rods. A June 2010 article in AISC's Modern Steel Construction notes that base plate holes are large and that a washer with a standard hole is often used. The same article makes several other points:

• Anchor rods cannot be pretensioned like high-strength bolts in a steel-to-steel joint, and they relax over time.
• Using anchor rods to transfer shear is not recommended and should be done only with caution.
• Four common leveling methods: leveling nuts and washers on the rods beneath the plate, leveling screws, shim stacks, and leveling plates that also serve as anchor rod templates.
• Any modification of anchor rods must be approved by the engineer of record (the article cites this as an OSHA requirement in the US).

It also warns that concrete tolerances are usually larger than steel erection tolerances, so the general contractor has to coordinate so that every trade knows which tolerances it must meet. In practice: check rod positions with a template before the pour.

Grout under the base plate

Once the column is leveled, the gap under the plate is filled. The AISC article says the general contractor places non-shrink grout between the base plate and the foundation, timed so steel erection can continue; SteelConstruction.info refers to high-strength grout poured below the plate. The aim is even bearing on the concrete.

Beam-to-column plates and column splices

In its guide to simple connections, SteelConstruction.info describes these plate types:

The source calls fin plates economical to fabricate and simple to erect. Its standard plate sizes belong to UK details and should not be carried into another project without design. For a comparison of box and double-beam columns, whose base details differ, see box column or double IPE.

Plate for connection parts

Connection parts are usually cut from hot-rolled plate. Ahan Assa's catalog lists S235JR plate and S355JR plate, both with dimensional tolerances to EN 10029, in thicknesses from 8 to 60 mm, with 1500×6000 and 2000×6000 mm as the main sheet sizes. The difference between the two grades is covered in S235JR vs S355JR.

The AISC article reminds readers that yield and tensile strength can change with thickness, so take grade and thickness together from the drawings and check them on the mill test certificate.

Ordering plate for connections

1. Take off every part from the drawings: base plates, connection plates, stiffeners and splice plates, with size, thickness, grade and quantity.
2. Group them by thickness and grade; each group is cut from one type of sheet.
3. Choose the sheet size that nests the parts best and allow for cutting waste.
4. Treat nominal weights as estimates: plate is sold on actual weight and can be ordered by kg, tonne or sheet.

Browse the sheet and plate category, and send your connection plate list through the contact form for a quotation.

Summary

Base plates and connection plates tie a steel frame together and to its foundations; most are shop-welded and site-bolted. At the column base, checking anchor rod positions before the pour, leveling the column and placing non-shrink grout are the key site steps. Size, thickness and grade come from the drawings; the buyer's job is to order exactly that, grouped by thickness and grade, with cutting waste and actual weight in mind.