FAQData: - "@type": "FAQPage" "mainEntity": - "@type": "Question" "name": "What is the most common error in CSA S16 Base Plate Design?" "acceptedAnswer": "@type": "Answer" "text": "The most common error in Canadian base plate design is using bolt hole diameters that are too small for erection tolerance. CSA S16 Table 2 specifies 4 mm oversize for M20-M24 bolts and 6 mm oversize for M27-M36. Using standard clearance results in field fit-up problems. The second most common error is omitting the lateral shear transfer mechanism — base plate friction alone (mu = 0.40 per CSA S16 Cl. 25.3.5) is insufficient for most lateral load combinations, requiring a weld-on shear key at the underside of the plate." - "@type": "Question" "name": "How do I handle uplift on base plates in Canadian steel design?" "acceptedAnswer": "@type": "Answer" "text": "For uplift cases (load combination 0.9D + 1.4W per NBCC 2020 ULS-7), the tension force Tf must be resisted by anchor rods in tension. Each anchor rod is checked for tensile rupture: Tr = 0.75 _ phi_ar _ Ase * Fu where phiar = 0.80 (CSA S16 Cl. 25.3.2) and A_se is the effective tensile stress area (ISO 898 thread root area). The plate is then checked for bending at the column flange line under the uplift prying action: tp >= sqrt(4 * Tf _ b' / (phi _ B * Fy)) where b' is the distance from anchor rod centre to the face of the column flange. Prying action must be considered when the anchor rod gauge exceeds the column width by more than 100 mm."

CSA S16 Base Plate Design — W310x86 Worked Example per CISC & A23.3

Complete design procedure for concentrically loaded steel column base plates per CSA S16:24 Clause 25, CSA A23.3-14 (concrete design), and CISC Handbook of Steel Construction 11th Edition. This page includes a complete worked example for a W310x86 column on a concrete pier foundation with four M24 ASTM F1554 Grade 36 anchor rods.

Quick access: CSA S16 Column Design → | Canadian Steel Sections → | Bolt Design Guide → | NBCC Load Combinations →

PRELIMINARY — NOT FOR CONSTRUCTION. All results are for educational and reference use only. Must be independently verified by a licensed Professional Engineer (P.Eng.) before use in any project.

Design Philosophy

Base plate design in Canadian practice follows the same mechanical model used worldwide: the plate acts as a cantilever extending from the column profile to the plate edge, bending under the uniform bearing pressure from the concrete below. The three design checks are:

1. Concrete bearing — ensure the plate area is large enough that the concrete bearing stress does not exceed the factored bearing resistance.
2. Plate thickness — ensure the plate does not yield in flexure at the line of the column flange or web.
3. Anchor rods — provide erection stability, resist uplift from wind/seismic, and transfer lateral shear to the foundation.

CSA S16:24 references CSA A23.3-14 (Design of Concrete Structures) for the concrete bearing check, not ACI 318. This is a critical jurisdictional difference.

Problem Statement — W310x86 Worked Example

A W310x86 column (G40.21 Grade 350W) supports a factored axial compression of Cf = 1,850 kN from the governing NBCC 2020 load combination ULS-2: 1.25D + 1.5L. The column base is a 600 mm square concrete pier with f'c = 30 MPa. Design the base plate using ASTM A36 plate material (Fy = 250 MPa) and ASTM F1554 Gr. 36 anchor rods.

Step 1 — Concrete Bearing Capacity (CSA A23.3 Cl. 10.8.4)

The factored bearing resistance of concrete under a base plate is:

Pr_max = 0.85 * phi_c * f'c * A1 * sqrt(A2 / A1)

where:

• phi_c = 0.65 (concrete bearing, CSA A23.3)
• f'c = 30 MPa
• A1 = base plate area = B x N (mm^2)
• A2 = maximum area of the supporting surface geometrically similar to and concentric with A1 (mm^2)
• sqrt(A2/A1) <= 2.0 (confinement cap, CSA A23.3 Cl. 10.8.4.3)

The pier is 600 mm square. For an initial guess, try a 460 mm x 310 mm plate:

Pr_max = 0.85 * 0.65 * 30 * 142,600 * sqrt(2.0)
       = 0.85 * 0.65 * 30 * 142,600 * 1.414
       = 3,345,000 N = 3,345 kN >> 1,850 kN  ✓

Bearing is not critical. The minimum plate area required is:

A1_min = Cf / (0.85 * phi_c * f'c * sqrt(2.0))
       = 1,850,000 / (0.85 * 0.65 * 30 * 1.414)
       = 1,850,000 / 23.46
       = 78,860 mm^2

Any plate larger than 281 mm x 281 mm satisfies bearing. The actual plate will be sized by the plate bending check.

Step 2 — Cantilever Dimensions m, n, lambda*n'

The base plate thickness is determined by the largest of three cantilever dimensions:

m = (N - 0.95 * d) / 2 — cantilever in the strong-axis direction

m = (460 - 0.95 * 310) / 2 = (460 - 294.5) / 2 = 82.8 mm

n = (B - 0.80 * bf) / 2 — cantilever in the weak-axis direction

n = (310 - 0.80 * 205) / 2 = (310 - 164) / 2 = 73.0 mm

lambda*n' — cantilever for H-shaped column profile (accounts for the column core area)

lambda = 2 * sqrt(X) / (1 + sqrt(1 - X))  where X = (4 * d * bf) / (d + bf)^2
       = 2 * sqrt(0.499) / (1 + sqrt(1 - 0.499))
       = 2 * 0.706 / (1 + 0.708) = 1.412 / 1.708 = 0.827

n' = sqrt(d * bf) / 4 = sqrt(310 * 205) / 4 = sqrt(63,550) / 4 = 252 / 4 = 63.0 mm
lambda * n' = 0.827 * 63.0 = 52.1 mm

Controlling cantilever = max(82.8, 73.0, 52.1) = 82.8 mm → m governs.

Step 3 — Plate Thickness tp

The required plate thickness for a concentrically loaded base plate is:

tp = m * sqrt(2 * Cf / (phi * B * N * Fy))

where phi = 0.90 for steel flexure per CSA S16 Cl. 13.1.

tp = 82.8 * sqrt(2 * 1,850,000 / (0.90 * 310 * 460 * 250))
    = 82.8 * sqrt(3,700,000 / 32,085,000)
    = 82.8 * sqrt(0.1153)
    = 82.8 * 0.3396
    = 28.1 mm

Use tp = 30 mm plate. Check actual plate dimension: 310 x 460 x 30 mm in ASTM A36 / G40.21 38W.

Revised Plate Geometry Check

With tp = 30 mm, the base plate properties are:

Step 4 — Anchor Rod Design

Tension (Uplift Case)

For the uplift combination NBCC ULS-7: 0.9D + 1.4W, assume the column may experience a factored tension Tf = 280 kN from wind uplift.

For ASTM F1554 Gr. 36 (Fu = 400 MPa), M24 anchor rod:

Effective tensile stress area A_se for M24 (ISO metric thread, coarse pitch 3.0 mm):

• A*se = (pi/4) * (d - 0.9382 _ p)^2 = 0.7854 _ (24 - 0.9382 _ 3.0)^2 = 0.7854 * (21.19)^2 = 353 mm^2

Tensile resistance per anchor rod (CSA S16 Cl. 25.3.2):

Tr = 0.75 * phi_ar * A_se * Fu   where phi_ar = 0.80
Tr = 0.75 * 0.80 * 353 * 400 / 1000 = 84.7 kN per rod

For 4 rods: Tr_total = 4 * 84.7 = 338.8 kN > 280 kN ✓

Shear Transfer

The lateral shear at the column base Vf = 95 kN from NBCC ULS-6 (wind + gravity). Do not rely on friction alone — provide a shear key.

Base plate friction check (CSA S16 Cl. 25.3.5):

• mu = 0.40 (steel on grout)
• Vr*friction = mu * Cf = 0.40 _ 1,850 = 740 kN >> 95 kN ✓ (friction alone is adequate at ULS)

However, for SLS wind drift, anchor rods in oversized holes will slip. A 10 mm fillet weld shear key (50 x 50 x 10 mm flat bar) welded to the underside of the base plate and cast into a 70 mm deep pocket in the grout provides positive shear transfer regardless of bolt hole clearance.

Step 5 — Anchor Rod Embedment (CSA A23.3 Annex D)

For a headed anchor rod (heavy hex nut + washer at the embedded end), the concrete breakout strength in tension per CSA A23.3 Annex D, Clause D.6:

For a single M24 anchor, cast-in-place, with 300 mm embedment (12d):

For 30 MPa concrete, the concrete breakout capacity for a single anchor exceeds the steel rod tensile capacity — steel governs, which is the preferred design condition. Always detail anchor rods such that the steel rod yields before concrete breakout occurs (ductile failure mode).

Anchor Rod Layout — Typical Canadian Detail

For W310 columns, the standard anchor rod layout uses 4-M24 rods spaced at:

Anchor rod schedule on drawing: 4-M24 x 400 lg. ASTM F1554 Gr. 36 with double nuts, galvanized option if exposed.

Summary — W310x86 Base Plate Final Design

Frequently Asked Questions

Why use the 0.95 factor on column depth d?

The 0.95 * d factor in the cantilever dimension m accounts for the fillet radius at the flange-web junction. The effective bearing footprint of the column on the plate is slightly less than the nominal depth because the web-to-flange fillet does not transfer bearing pressure to the plate. The CISC Handbook (11th Ed., Part 4) recommends 0.95d for W shapes and 0.80bf for the flange width. Some designers use 0.95d and 0.80bf conservatively; using the full dimensions is acceptable for column base plates where bearing pressure is uniform and low.

When should I use a stiffened base plate?

A stiffened base plate (vertical gusset plates welded between the flanges and the base plate) is needed when:

• Plate thickness exceeds 50 mm (cost and welding concerns)
• Uplift forces are large (Tf > 500 kN per flange)
• Moment-resisting bases with significant bending in the plate
• Cantilever dimension m or n exceeds 120 mm (uneconomical unstiffened plate)
• HSS column bases where the plate span between tube walls is large

Stiffened base plates reduce the effective cantilever from the column edge to the gusset instead of to the plate edge, reducing required tp by 40-60%. The gusset thickness is typically 12-20 mm, full-penetration welded to the column and fillet welded to the base plate.

What is the difference between ASTM F1554 Gr. 36, Gr. 55, and Gr. 105?

Grade 36 is the standard for Canadian structural anchor rods. It has 20% minimum elongation, good weldability, and predictable behaviour in tension. Grade 55 is used where fewer or smaller anchor rods are needed to reduce congestion. Grade 105 requires project-specific welding procedure qualification and is rarely used in building construction.

Related pages: CSA S16 Column Design → | Canadian Steel Sections → | Bolt Design per CSA S16 → | NBCC Load Combinations → | Base Plate Code Comparison →