Bolt Pattern Calculator — mm, kN
How to use this calculator
Choose a bolt pattern layout (circular or rectangular), enter the bolt circle diameter or row/column spacing, then select bolt size (M12–M30), property class, and connection category. The tool returns the design shear and tension resistance per bolt and for the whole group per EN 1993-1-8. Tap any dimension on the diagram to jump to its input.
Grades — 8.8 (fub=800 MPa) and 10.9 (fub=1000 MPa).
Connection type — Bearing (Category A/D), slip-critical (Category B/C, μ=0.4), or tension (Category D/E).
Saved Calculations
| Time | Pattern | Bolts | Grade | Shear kN | Tension kN | Cost |
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How to Calculate Bolt Pattern Capacity (Eurocode)
This calculator determines shear and tension resistance of bolt groups per EN 1993-1-8. Select the bolt size (M12–M30), property class (8.8 or 10.9), connection category, and pattern layout. The calculator uses tensile stress area As and partial safety factor γM2=1.25 for resistance calculations.
Formulas
Shear (threads in plane): Fv,Rd = αv × fub × As / γM2, where αv = 0.6 for grades 4.6/5.6/8.8 and 0.5 for 10.9 (Table 3.4). Shear (shank in plane): Fv,Rd = 0.6 × fub × A / γM2. Tension: Ft,Rd = 0.9 × fub × As / γM2 with γM2 = 1.25. Slip-critical Category B/C: Fs,Rd = ks × n × μ × Fp,C / γM3 with Fp,C = 0.7 × fub × As, ks = 1.0 (normal round holes), μ = 0.4 (Class A), γM3 = 1.25. Anchor rods 4.6 / 5.6 are not preloaded, so the slip-critical case is treated as bearing N. Minimum spacing p1/p2 = 2.4·d0 (3·d0 preferred) and edge distance e1/e2 = 1.2·d0 per Table 3.3.
FAQ
What tensile stress area is used? The calculator uses standard tensile stress areas per ISO 898-1: M12=84.3, M16=157, M20=245, M22=303, M24=353, M27=459, M30=561 mm². Gross area A is used when threads are excluded from the shear plane.
What is the difference between categories? Category A: bearing at ULS (snug-tight permitted). Category B: slip-critical at serviceability (preloaded). Category C: slip-critical at ULS. Category D: tension, non-preloaded (typical for anchor rods Gr 4.6/5.6). Category E: tension, preloaded (Gr 8.8/10.9).
Is bolt bearing or tear-out on the plate included? No — this tool sizes the bolt group only. Check bearing Fb,Rd, block tearing and net section after you set the end-plate or gusset thickness, then verify the framing member with the beam and column calculators. For holding-down bolts cast into a concrete plinth, design the reinforcement with the rebar calculator and size the pier with the concrete beam calculator.
On install day
Three things fabricators forget. Preloading — Category B/C and Category E joints must be preloaded to Fp,C with HRC (twist-off), turn-of-nut, or DTI washers per EN 1090-2 §8.5; snug-tight Category A bearing joints are quicker but cannot be used where slip would govern. Faying surface class — Class A (μ = 0.5 per EN 1090-2 Table 18, conservatively 0.4 in EN 1993-1-8) needs blast cleaning to Sa 2½ or alkali-zinc-silicate paint; mill scale, ordinary primer, or HDG without roughening drops μ to 0.10–0.20. Edge distance — for M20 the minimum e1 is 1.2·d0 ≈ 26 mm; specify 1.5·d0 on shop drawings to keep the bearing check in hand. Typical 2025 European pricing: M20×65 8.8 HDG runs €1.20–1.80 per assembly delivered, 10.9 about 1.4× that, M24 Gr 4.6 anchor rods €6–12 per metre depending on length and finish.
