Bolt Pattern Force Calculator

Inputs

View results
How many equally spaced bolts are on the circle.
bolts
Diameter of the circle the bolts lie on; the radius R is half this.
mm
Torsional moment about the pattern centre, in the plane of the joint.
N·m
In-plane shear force carried by the whole joint (shared equally by the bolts).
N

Results

Default result
Edit inputs
Max shear per bolt (F_max)
1,000 N
Pass

1 kN · 0.102 t · 224.8 lbf

Worst-case shear demand per bolt — compare to the bolt’s shear capacity, not its tensile rating.

F_max = F_v + F_t — the worst-case demand to compare against the bolt’s shear capacity.

Also computed

Tangential force per bolt (F_t) 1,000 N

1 kN · 224.8 lbf

F_t = M / (N · R) — from the moment.

Direct shear per bolt (F_v) 0 N

0 kN · 0 lbf

F_v = V / N — the direct shear shared equally.

Method notes 4 notes
  • Elastic bolt-group (eccentric shear) method: the torsional moment is resisted by a tangential force on each bolt proportional to its distance from the pattern centroid. On one circle all bolts are equidistant, so each carries the same F_t = M / (N · R).
  • The direct shear is shared equally, F_v = V / N. The worst-case bolt is where the direct and tangential forces are collinear, so this adds them: F_max = F_v + F_t (conservative — it ignores the angle between them).
  • F_max is the shear demand per bolt; compare it to the bolt’s allowable shear (capacity), and check thread-vs-shank shear plane and any reduction for shear in threads.
  • Assumes rigid plates, equal-size bolts on a single concentric circle, and a moment applied about the pattern centre (no prying or out-of-plane load).

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