What is the purpose of a steel column base plate?

A base plate distributes the load from a steel column over a large enough area of the concrete foundation to keep bearing stresses within acceptable limits. It also provides a level bearing surface for the column and, together with the holding down bolts, anchors the column against uplift and moment. Without a base plate, the concentrated column load would cause punching shear or bearing failure in the concrete.

What is the difference between a pinned base and a fixed base?

A pinned base is designed to transfer vertical load and horizontal shear to the foundation, but not significant bending moment. It uses a relatively thin base plate with holding down bolts positioned close to the column. A fixed base transfers moment as well as shear and vertical load, requiring a thicker base plate and holding down bolts set further apart or in a larger pattern to provide the lever arm for moment resistance. Portal frames typically use pinned bases for standard designs and fixed bases where moment transfer to the foundation is needed.

How thick should a base plate be?

Base plate thickness depends on the column size, loading, and base type. For simple axially loaded columns in standard buildings, 15mm to 25mm is a common range. For moment-resisting bases, 25mm to 40mm or more may be required depending on the plate projection beyond the column and the moment demand. Thickness must be confirmed by the structural engineer to BS EN 1993-1-8 using the T-stub equivalent model.

Why is grout used under a base plate?

Grout is placed under the base plate to fill the gap between the underside of the plate and the top of the concrete foundation. This ensures full, even bearing contact between the plate and the concrete, removing any voids or unevenness. Non-shrink cementitious grout is standard for structural steelwork. The grout is typically 25mm to 50mm thick, with the base plate temporarily packed and levelled during erection before final grouting.

Base Plate Sizes, Thickness and Weight

Base Plate Reference Data

Base plates provide the bearing surface between steel columns and concrete foundations. The configurations below are standard arrangements per BS EN 1993-1-8 and typical UK practice. Actual base plate sizing, thickness, and bolt layout must be confirmed by a structural engineer based on the specific loading and foundation design.

Base Plate Weight by Size

Plate weight in kilograms for common square and rectangular steel base plate sizes across standard thicknesses, calculated from steel density (7,850 kg/m³). Reference values to check before you order or detail. Weight = length × width × thickness × 7,850.

Plate size (mm)	10 mm	12 mm	15 mm	20 mm	25 mm	30 mm
150 × 150	1.77	2.12	2.65	3.53	4.42	5.30
200 × 200	3.14	3.77	4.71	6.28	7.85	9.42
250 × 250	4.91	5.89	7.36	9.81	12.27	14.72
300 × 200	4.71	5.65	7.07	9.42	11.78	14.13
300 × 300	7.07	8.48	10.60	14.13	17.66	21.20
350 × 350	9.62	11.54	14.42	19.23	24.04	28.85
400 × 300	9.42	11.30	14.13	18.84	23.55	28.26
400 × 400	12.56	15.07	18.84	25.12	31.40	37.68
450 × 450	15.90	19.08	23.84	31.79	39.74	47.69
500 × 500	19.63	23.55	29.44	39.25	49.06	58.88
600 × 600	28.26	33.91	42.39	56.52	70.65	84.78

Common base plate thicknesses are 10, 12, 15, 20, 25, 30 and 40 mm. Sizes shown are typical footprints; plates are cut to any size. Weights are nominal, for reference only.

Standard Configurations (BS EN 1993-1-8)

Column Serial Size	Typical Plate Size (mm)	Common Thicknesses (mm)	HD Bolt Pattern	HD Bolts

Base Plate Weight Calculator

Enter plate dimensions to calculate weight based on steel density (7850 kg/m³).

Length (mm):

Width (mm):

Thickness (mm):

Grout Thickness Guidance

Grout provides a level bearing surface and accommodates minor foundation irregularities.

Standard Grout Thickness	50–75 mm
Maximum Thickness	100 mm (requires structural design)
Grout Specification	Non-shrink cement-based grout, min. 40 MPa strength
Surface Preparation	Foundation must be level; base plate levelled with shims before grouting
Curing Time	Min. 7 days before applying load (check grout datasheet)

Reference data only. These are standard sizes and weights to look up, not a base plate sizing or design tool. Confirm all structural requirements with your engineer.