Bolted Joints Calculator — Preload, Tightening Torque & Fatigue Safety (VDI 2230)

The primary calculation follows VDI 2230-1:2015 — the definitive German guideline for the systematic calculation of high-duty bolted joints. Thread geometry is per ISO 724 / DIN 13, and the unified inch sizes use those same ISO formulas for the pitch and minor diameters; the tensile stress area As uses the ISO 898-1 definition for metric and ASME B1.1’s 0.7854·(D − 0.9743/n)² (in²) for inch. Thread stripping runs wherever the thread's worst-material-condition limit dimensions are known: seven metric coarse sizes (M8–M30) are tabulated at 6g/6H, and for any other thread — a fine pitch, a unified inch size, or a different tolerance class — you enter those four dimensions for your own fit and the check runs on them — after confirming they can belong to that thread: a set on the wrong side of the ISO 724 basic profile, such as another size's values or a unit slip, is refused rather than computed. It covers clearance fits; interference-fit threads are outside it. They are not computed for you: this tool does not hold a verified source for the ISO 965-1 tolerance formulas, and it tests any candidate against the seven rows it already ships before trusting it. A limit dimension generated from an unverified formula is worse than none, because nothing on the page would show it was a guess. The fatigue check compares the alternating stress amplitude to the VDI 2230-1 §5.5.3 size-dependent endurance amplitude σ_ASV (rolled threads, class-independent). The governing formulas are cited in the generated PDF engineering report.

Yes. The pressure under the head or nut is computed on the annular bearing face, both as assembled and under load; an M12 property class 10.9 at full preload puts over 800 MPa on a plain hole, which is why washers exist — fitting one is modelled and drops it to around 200 MPa. The limiting pressure belongs to your clamped material, so the calculator reports the pressure always and gives a safety factor once you enter that limit; it does not invent an allowable for you. Thread stripping uses the shear area of each thread against its own material and reports which thread goes first plus the engagement depth needed to develop the bolt — the check that decides whether a bolt threaded into aluminium or cast iron strips before it breaks. For a tapped joint the calculator asks for the real engaged depth rather than assuming one. The check needs the thread's limit dimensions at the worst material condition; seven metric coarse sizes are tabulated at 6g/6H, and for every other thread you can enter your own four dimensions and have it run on those. Where they are not available the result says the check was NOT made — it is never assumed to pass.

Yes. Machined surfaces bed in under preload by a few micrometres — VDI 2230-1 §5.4.2.1 Table 5 gives the amount f_Z for the thread, each head or nut bearing face and each inner interface, by surface roughness and by whether the joint is loaded axially or in shear. That settlement is preload gone: F_Z = f_Z/(δ_S + δ_P), which on a short stiff joint is kilonewtons. The calculator takes it off the residual clamp load, so the friction-grip capacity and the margin before the interface opens both reflect it. The resilience it divides by comes from the joint geometry you enter (VDI 2230-1 §5.1), which also gives the load factor Φ instead of asking you to guess one.

The yield safety factor S_F = Rp0.2 / σ_red checks that the bolt does not yield during assembly or under the maximum working load — it uses the von Mises (combined tension + torsion) stress and must be ≥ 1.0, with ≥ 1.2 recommended. The fatigue safety factor S_D checks that the cyclic alternating stress amplitude carried through the bolt does not exceed the VDI 2230-1 §5.5.3 size-dependent endurance amplitude σ_ASV; it should be ≥ 1.5. A joint carrying no alternating load has no fatigue question to answer, and the calculator reports that check as not applicable rather than as a margin. Both must be satisfied simultaneously.

VDI 2230 assigns each tightening method two separate figures. The utilisation factor ν sets how much of the bolt's yield strength the permissible preload may use — 0.90 for torque-wrench, 0.95 for angle-controlled, 0.98 for hydraulic tensioning. The tightening factor α_A is the scatter of what you actually achieve, taken from Table A8: 1.4 for torque-controlled tightening, 1.2 for angle-controlled and for hydraulic with standard bolts and nuts. The permissible preload F_M,zul is the top of that band and the minimum is F_M,zul / α_A, so a more precise method delivers both a higher and a more consistent preload for the same bolt.

Yes, and under out-of-plane loads too. The bolt-pattern panel takes any bolt coordinates and sizes and any number of forces (at a point and height) and moments. Shear uses the elastic vector method (AISC Manual Part 7, checked against Shigley Example 8-7). Tension uses general unsymmetric bending including the product of inertia, which stays correct on asymmetric patterns where the common Ix/Iy-only shortcut is not. On a uniform bolt circle it reproduces the slewing-bearing makers' 4·M/(n·D). For a joint that is not preloaded, an exact rigid-plate contact model finds where the plate bears. It is badged as an engineering model because no standard prescribes it, and it does not include prying from plate bending. The most-loaded bolt can then be sent to the VDI 2230 check in one click.

You can run the full calculation during a free 30-minute preview with no sign-up required. A free 14-day account trial unlocks every calculator in the suite with no credit card needed. The branded PDF engineering report and saved calculations are included in the free 14-day trial and in every paid plan.