MethodWhat is calculated?
At the mid-web of a beam the bending stress is zero and the shear force produces pure shear; principal strains lie at ±45° with equal magnitude and opposite sign. Gauge pairs at 45° on both sides of the web, wired into a full bridge, measure shear force largely independent of bending moment – the shear-beam load-cell principle. Keil uses τ ≈ F/A_web for thin-walled sections.
Equations
τ_max ≈ F/A_Steg (Keil Gl. 10.42)
ε₁ = −ε₂ = τ(1+ν)/E
U_M/U_B = k/4·(4ε) = k·ε (Vollbrücke, Gl. 10.43)
ProcedureStep by step
- Enter shear force and web dimensions at the measuring section.
- For precise values use τ = F·S/(I·t) with the first moment of area and compare.
- Choose the circuit; the full bridge compensates bending and temperature.
Typical mistake
Using the whole section instead of the web area, or installing gauges off the neutral fibre where bending strain superimposes.
PracticeApplication and limits
Shear-beam load cells, shear-force measurement on beams, bearing-load determination on axles and crane runways, support reactions in civil engineering.
Mean shear stress of thin webs; for solid sections τ_max = 1.5·F/A (rectangle) or 4/3·F/A (circle). Gauges must sit in the neutral fibre.
SourceTechnical basis
Keil, Dehnungsmessstreifen, 2nd ed. 2017, sec. 10.2.4 shear-loaded objects, eqs. (10.42), (10.43).
The source supports the equation structure and worked examples; this calculator does not replace calibration of the measuring chain.
FAQFrequently asked questions
Why is shear measurement independent of bending?
In the neutral fibre bending strain is zero and the ±45° layout responds only to shear strain.
Can I design a load cell with it?
Yes, roughly: choose the web area so that ε at rated load is about 500–1000 µm/m.
What is the shear strain γ?
The angular distortion of the element; it equals the diameter of the strain circle, γ = ε₁ − ε₂ = 2ε₁.
In the same cluster
All strain-gauge calculators