Home / Simulations / Torsion-Shear Interaction
🔄 Torsion-Shear Interaction
Shear and torsion both produce diagonal tension in the web, and on one face they add. A beam comfortably adequate for each action alone can fail under a modest combination of both — which is why they are checked together on a circular interaction surface, never independently. Move the point and watch it cross the envelope.
Demands
Capacities
Live Result
—
Interaction ratio (V/Vr)²+(T/Tr)²—
Shear utilization alone—
Torsion utilization alone—
Torsional capacity Tr (space truss)—
Max torsion at this shear—
Longitudinal torsion steel required—
Powered by the circular interaction rule and the
space-truss analogy (
engine/torsion-shear.js). Verified before
publishing: the interaction surface returns EXACTLY 1.000 at both the
pure-shear and pure-torsion capacity limits, every point on the computed
allowable-torsion envelope is confirmed to lie exactly on the interaction
surface, and the envelope is cross-checked against the closed form
√(1−(V/Vr)²). A deliberate test pins the engineering point: 75%
shear + 75% torsion gives 1.125 and FAILS, though each action alone is safe.Method
TS 500 / EC2(Vd/Vr)² + (Td/Tr)² ≤ 1 — quadratic because the two actions superpose as diagonal tension on the critical web face.
Space trussTr = 2·Ae·(Ao/s)·fywd·cotθ — only CLOSED stirrups carry the circulating shear flow.
Longitudinal steelTorsion also requires longitudinal reinforcement, Asl = Td·ph·cotθ/(2Aefyd) — frequently overlooked in practice.
Scope: the engine cannot tell whether torsion is equilibrium-required or compatibility-induced (and therefore redistributable). That judgement, and the decision to neglect torsion below Tcr, remain with the engineer.