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Engineering · Machine Design

Bolted Joint Stiffness and Load Fraction Calculator

Calculate ideal bolt/member axial stiffnesses and split an entered external tensile load using the classic joint stiffness fraction.

Engineering · Machine Design

Enter the engineering model

Explicit properties, geometry, units and assumptions
  1. 1EnterProvide the known values
  2. 2CalculateResults update automatically
  3. 3VerifyReview the details and units
Try an example
Visual modelSchematic · not to scale
Machine Design: fraction visual explanationA simplified diagram showing the relationship represented by the selected calculator mode. It is explanatory and not a fabrication, safety or scale drawing.bolt and member stiffness split external loadbolt increment + compression relief = applied load
The diagram explains the selected relationship only. Dimensions, symbols and proportions are illustrative; use the entered values and stated assumptions for the calculation.

Keep every unit basis, sign convention, property source and idealization consistent. Values stay in this browser.

Engineering calculation result

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Understand the machine model

What this calculator is for

A preloaded joint does not send every unit of external tensile load directly into the bolt. The bolt/member stiffness ratio controls bolt-load increase and member-compression relief before separation.

1Build both effective axial stiffnesses.
2Check the external-load reconciliation.
3Stop using the linear result once the compression output crosses zero.

Visual explanation

Picture the bolt and clamped members as two elastic paths. The stiffer the clamped members relative to the bolt, the smaller the ideal fraction C added to the bolt.

The governing relationship

kb=AbEb/Lb; km=AmEm/Lm; C=kb/(kb+km); bolt increment=C·P and member compression reduction=(1−C)P.

Keep the boundary visible

One-dimensional linear joint model only. Preload scatter, embedment, gasket behavior, prying, eccentricity, separation, fatigue and tightening procedure require a complete joint design.

Quick guide

How to use this calculator

  1. Choose the analysis mode that matches the physical model before entering values.
  2. Enter properties, geometry, loads, states and coefficients from one consistent unit and sign convention.
  3. Use the intermediate outputs to audit the relationship, then retain the stated idealization before applying it.

Calculation method

Transparent engineering model

kb=AbEb/Lb; km=AmEm/Lm; C=kb/(kb+km); bolt increment=C·P and member compression reduction=(1−C)P.

The calculator evaluates only the declared relationship and preserves visitor-entered assumptions rather than selecting materials, factors, components or standards.

Worked example

Worked example

Equal bolt and member stiffnesses produce C=0.5, so an ideal external tensile load is split equally between bolt-load increase and member-compression reduction.

kb=AbEb/Lb; km=AmEm/Lm; C=kb/(kb+km); bolt increment=C·P and member compression reduction=(1−C)P.

Supported inputs

Precision and limits

Analysis, not approval

One-dimensional linear joint model only. Preload scatter, embedment, gasket behavior, prying, eccentricity, separation, fatigue and tightening procedure require a complete joint design.

Standards and properties

Material properties, allowable values, load combinations, safety factors, correlations, manufacturer data, codes and jurisdictional requirements are not supplied automatically.

Units and precision

Use one consistent unit basis. Results retain working precision but cannot be more accurate than the entered measurements and properties.

Privacy

Entered engineering values and results stay in this browser and are not sent to analytics or third parties.