Free Tool · EN 1993-1-8:2005 §7

Tubular Joint Resistance Calculator

Calculate the design resistance of CHS and RHS/SHS tubular joints per EN 1993-1-8:2005 §7. K, N, T, X and Y joint types. Failure modes: chord face plastification (Eq. 7.1 / 7.20), chord punching shear (Eq. 7.3 / 7.22), chord side-wall buckling (Eq. 7.21), brace effective width (Eq. 7.23), chord gap shear (Eq. 7.4). Validity ranges per Tables 7.1 and 7.8. S235–S460 · EN/NL/DE/JA/ZH/HI.

g θ₁ θ₂ N₁ N₂ N₀ CHS chord
Joint Parameters
Angle between brace axis and chord axis. Range 30°–90°.
Compression is negative. Used for chord stress function kp/kn.

Worked example (K-joint CHS 219.1×10, braces CHS 139.7×6.3 @ 45°, g=20 mm, N_Ed=350 kN)

Results
Geometric parameters
β = d₁/d₀ (or b₁/b₀)0.638
γ = d₀/(2t₀)10.96
τ = t₁/t₀0.630
η = h₁/b₀0.638
Validity check
All validity conditions satisfied (Tables 7.1 / 7.8)
Failure mode resistances
ModeN₁,Rd (kN)
Chord face plastification
EN 1993-1-8 Table 7.2		 452.15
Chord punching shear
EN 1993-1-8 Table 7.2		 2659.72
Chord gap shear (K/N only) 0.117 — PASS
452.15
Governing resistance N₁,Rd (kN)
Joint efficiency η = N_Ed / N₁,Rd
77.4%
PASS EN 1993-1-8 Table 7.2
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Which joint types does this calculator cover?
T, Y, K, N and X joints for both CHS chords (§7.4 Tables 7.2–7.4) and RHS/SHS chords (§7.5 Tables 7.10–7.12). Each joint type has different failure modes that govern; the calculator checks all applicable modes and reports the minimum (governing) resistance.
What is chord face plastification?
The chord face can yield plastically when the brace pushes into it. For CHS, Eq. 7.1 gives N₁,Rd = kp · fy0 · t₀² · (2.8 + 14.2β²) / (sinθ · γM5). For RHS T/Y joints, Eq. 7.20 uses N₁,Rd = kn · fy0 · t₀² · (2η/(1−β) + 4√(1−β)) / (sinθ · γM5). These are usually the governing modes for lightly loaded chords.
When does chord side-wall buckling govern?
Side-wall buckling applies to RHS X joints (Eq. 7.21) and T/Y joints when β ≥ 0.85 (brace nearly fills the chord width). The chord side walls can buckle under the concentrated line loads from the brace. This mode becomes critical for wide braces on thin-walled chords.
What is the validity range for the EN 1993-1-8 §7 formulae?
For CHS: 0.2 ≤ β ≤ 1.0, γ ≤ 25, d₀/t₀ ≤ 50, d₁/t₁ ≤ 50, θ ≥ 30°. For RHS: 0.25 ≤ β ≤ 1.0, γ ≤ 25, b₀/t₀ ≤ 35, b₁/t₁ ≤ 35, θ ≥ 30°. Outside these limits the simplified formulae may be unconservative — a more detailed analysis is required.
What is γM5 and why is it 1.0?
EN 1993-1-8 §2.2(3) specifies γM5 = 1.0 for hollow section joint resistance. Unlike bolts (γM2 = 1.25) or welds (γM2 = 1.25), tubular joints rely on plastic redistribution that is captured in the joint efficiency formulae themselves. The safety is built into the semi-empirical equations validated against test data.
How is the chord stress function kp (or kn) computed?
The chord stress function accounts for the detrimental effect of chord compression. For CHS: kp = 1 − 0.3n(1+n) for n < 0 (compression), where n = σ₀,Ed / fy0. For RHS (kn): same form. For tension chords n ≥ 0 gives kp = kn = 1.0 — no reduction. This is defined in Tables 7.2 and 7.10 respectively.