Free Tool · EN 1993-1-8 §6.2.5 + EN 1992-1-1 §3.1.6

Column Baseplate Design Calculator

Compute bearing strength fjd, T-stub effective area Aeff, compression resistance Nc,Rd, anchor bolt tension Nt,Rd and moment capacity MRd per EN 1993-1-8 §6.2.5. Live results, no sign-up.

B (plate width) L (plate length) Column A_eff Anchor
Column Profile
Plate Dimensions
Concrete & National Annex
Anchor Bolts
Applied Loads
Results
2453.3
Nc,Rd (kN) — compression resistance
Governing η 20.4% PASS ✓
fjd (§6.2.5)15.33 N/mm²
kj (Eq 6.6)1.15
c (Eq 6.5)88.9 mm
Aeff160,000 mm² (capped)
Nc,Rd2453.3 kN
Nt,Rd (2×bolt)282.2 kN (steel)
MRd56.4 kNm
tmin 30.6 mm ✓
aw,req (§4.5.3)3 mm
GoverningBearing N/N_c,Rd
1. f_cd (EN 1992-1-1 §3.1.6)
α_cc = 1 | γ_C = 1.5
f_cd = α_cc × f_ck / γ_C = 20 N/mm²

2. k_j (EN 1993-1-8 Eq 6.6)
A_c0 = B × L = 160000 mm² | A_c1 = 211600 mm²
k_j = √(A_c1/A_c0) = 1.15 (capped at 3.0)

3. f_jd (§6.2.5(7))
β_j = 2/3 (grouted base) | k_j = 1.15
f_jd = β_j × k_j × f_cd = 15.33 N/mm²

4. Overhang c (Eq 6.5)
c = t × √(f_y/(3·f_jd·γM0)) = 88.9 mm

5. A_eff (T-stub, §6.2.5(4))
A_eff = 160,000 mm² (capped at plate area)

6. N_c,Rd (Eq 6.4)
N_c,Rd = f_jd × A_eff = 2453.3 kN

7. Anchor resistance
F_t,Rd (steel) = 141.12 kN/bolt
N_Rd,c (cone) = 189.74 kN/bolt → governs: steel
N_t,Rd = 2 × min(...) = 282.2 kN

8. Utilisation
η_N = 20.4%  η_M = 0.0%  η_T = 0.0%
Governing η = 20.4% → PASS ✓
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Want the full design tables? Get the EN 1993-1-8 §6.2.5 cheatsheet → — M16–M36 bolt table, NL/DE/BE NA comparison, HEB 300 worked example.
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Baseplate Cheatsheet PDF Beam Moment Capacity Column Buckling Section Classification Weld Sizing Baseplate Design (detailed) Anchor Bolt Design (EN 1992-4)

FAQ

What is the T-stub effective area method in EN 1993-1-8?
The T-stub effective area method (§6.2.5) models the base plate as a T-stub that cantilevers beyond the column profile and bears on the grout/concrete. The overhang c = t_p × √(f_y/(3·f_jd·γM0)) is the maximum width that participates in bearing before the plate yields in bending. A_eff is the area of two flanges plus web footprint each expanded by c on all sides, capped at the plate area B×L. Larger plate thickness → larger c → larger A_eff → higher N_c,Rd.
What is f_jd and how is it calculated?
f_jd is the design bearing strength of the grout/concrete joint (EN 1993-1-8 §6.2.5(7)). It equals β_j × k_j × f_cd, where: f_cd = α_cc × f_ck / γ_C is the concrete design strength (EN 1992-1-1 §3.1.6); β_j = 2/3 is the joint coefficient for grouted bases; k_j ≤ 3.0 accounts for load spreading through grout to a larger area (Eq 6.6). The NA affects both α_cc (0.85 in NL/DE vs 1.0 in EN) and γ_M2 (1.1 in DE vs 1.25 in EN).
When does an anchor bolt carry tension?
Under pure compression (M_Ed = 0) no bolt carries net tension — N_Ed spreads across A_eff. Under combined N+M, the side of the plate away from the moment compressive zone lifts, and anchor bolts resist the overturning force. This tool uses a simplified lever-arm model: T_Ed = max(0, M_Ed/z − N_Ed/2), where z = L/2. The rigorous §6.2.8 model with actual bolt position should be verified for large moments.
What governs anchor bolt tension — steel failure or concrete cone?
Both modes are checked: F_t,Rd (steel) = 0.9 × f_ub × A_s / γ_M2; N_Rd,c (concrete cone, EN 1992-4 §7.2 simplified) = 10 × √f_ck × h_ef^1.5 / γ_Mc. For M20 8.8 anchors with h_ef = 300 mm in C30/37: F_t,Rd ≈ 141 kN (steel); N_Rd,c ≈ 97 kN (concrete cone governs). Increasing h_ef or moving to a higher concrete class is the most effective fix when concrete cone governs.
How is the minimum plate thickness determined?
The T-stub overhang c is derived from t (Eq 6.5). For a given plate geometry, the required overhang equals the physical overhang on each side: e_overhang = (B − b_c)/2 or (L − h_c)/2. Rearranging: t_min = e_max / √(f_y/(3·f_jd·γM0)). If t < t_min, the plate is too thin to mobilise its full overhang in bearing. Increase t_p until t ≥ t_min.
Why use S355 instead of S275 for the plate?
S355 gives a higher f_y which directly increases overhang c = t_p × √(f_y/(3·f_jd·γM0)), meaning more bearing area A_eff for the same plate thickness. This is especially beneficial when space is tight (column close to plate edge) or when the bearing stress demand is high. S275 is adequate for lightly loaded axial-only cases; upgrade when moment-induced anchor tensions are high or η_N exceeds 0.8.