BoltIO 3D Bolted Connection (Huth + 6DOF)

Huth Joint Type

Two-Sheet Materials (Huth)

Huth stiffness models a fastener joining sheet 1 (thickness t₁ per bolt) to sheet 2 (thickness t₂). Moduli below are in ksi.

E₁ sheet 1 (ksi)

E₂ sheet 2 (ksi)

Ef fastener (ksi)

Manual override (advanced)

Shear Type

Bolts (pattern + per-bolt t₁/t₂/dia)

Loads at origin

3D Bolt Pattern, Applied Loads & Reactions

Technical Reference

BoltIO — 3D Bolt Pattern Load Solver

Huth shear stiffness + bolt-shank axial stiffness • Units: in, ksi (converted to psi internally), lb, lb-in

Model: A rigid plate at the pattern origin (0,0,0) is connected to ground through discrete bolt springs. Applied loads (forces and moments) act at the origin; bolt coordinates are relative to that point.

1. Huth Two-Sheet Joint

Each fastener joins sheet 1 (thickness t₁, modulus E₁) and sheet 2 (t₂, E₂). Huth Eq. 31 (1984) gives shear-transfer flexibility C; shear stiffness k_shear = 1/C.

C = ((t₁+t₂)/(2d))^a · (b/n) · [1/(t₁E₁) + 1/(nt₂E₂) + 2/(3t₁Ef) + 2/(3nt₂Ef)]

n = 1 single shear, n = 2 double shear
a, b depend on joint type (bolted metallic, riveted, composite)
Per-bolt d, t₁, t₂ allow mixed fastener sizes and grip lengths in one pattern

2. Axial Bolt Stiffness

Bolt tension/compression uses shank stiffness across the grip: k_axial = Ef · A / (t₁+t₂), with A = πd²/4. This is separate from Huth shear transfer.

3. 6-DOF Assembly

Plate motion: u(r) = u₀ + ω × r. Global 6×6 stiffness K is assembled from each bolt’s 3×3 K_global (local shear + axial, rotated to bolt axis).

K δ = F

Bolt displacement at (x,y,z): δ_bolt = δ_trans + ω × r. Reaction force: F = K_global δ_bolt, split into axial (along bolt axis) and shear (perpendicular).

4. Inputs & Outputs

Bolt axis — local Z of each fastener (X, Y, or Z global)
Loads — Fx, Fy, Fz (lb) and Mx, My, Mz (lb-in) at origin
Outputs — per-bolt tension, shear components, |F|, Huth k values, equilibrium residual

5. Limitations

Linear elastic, small displacement
Rigid connecting plate (no plate flexibility)
No bolt hole bearing redistribution or prying
No friction or slip at faying surfaces
Not a substitute for full FEM of the joint

Use for preliminary bolt-group proportioning, comparing fastener stiffnesses, and checking load split before detailed connection design.