1 — Wind (BS EN 1991-1-4 + UK NA)

V_b = V_b,map × C_alt × C_prob × C_season

= 21.0 × 1.05 × 0.83 × 1.0 = 18.30 m/s

q_b = 0.613 × V_b² = 0.613 × 18.30² = 205.3 N/m²

C_e(z) [town >2 km, z = 12 m] = 1.56

q_p = C_e × q_b = 1.56 × 0.205 = 0.320 kN/m²

2 — Suggested configuration (engine output)

10 bays × 2.0 m  |  5 lifts × 2.5 m (= 12.5 m)  |  5 boards / 1.138 m wide

Transom spacing = 1.0 m  |  Ties: 4.0 m horiz × 2.5 m vert (every lift)

3 — Member checks (permissible = characteristic / 1.65)

Tube S355 48.3×3.2: A = 453.4 mm², S = 6520 mm³

M_r = f_y·S/1.65 = 355×6520×10⁻⁹/1.65 = 1.403 kNm

Board (1.0 m span):

w = 2.0×0.225 + 0.25 = 0.70 kN/m

M = wL²/8 = 0.090 kNm = 0.70×1.0²/8 = 0.0875 kNm vs 0.48 kNm (18%) ✓

Transom (1.138 m):

w = 2.0×1.0 + 0.036 = 2.036 kN/m

M = 2.036×1.138²/8 = 0.330 kNm vs 1.403 (23%) ✓

Ledger (pattern loading, 2-span: c_f1=0.213, c_f2=1.25):

P = transom reaction = 2.036×1.138/2 = 1.158 kN

M = 0.213×1.158×2.0 = 0.493 kNm vs 1.403 (35%) ✓

Coupler = 1.25×1.158 = 1.448 kN vs 6.10 kN RAC slip (24%) ✓

Standard compression (EC3 curve c, f_y=355):

N_Ed = 6.48 kN vs P_c(L_e=2.5 m) = 18.39 kN (35%) ✓

M+N interaction (e = 48 mm coupler eccentricity): 0.575 ≤ 1.0 ✓

Tie force:

1.56 kN ≤ 6.1 kN (light-duty tie) ✓ PASS

All members, couplers, buckling, interaction & ties reproduce hand calc. S355 λ₁ normalisation correct — classic +30–38% unconservative error fixed. ✓ ALL MATCH