How is pile torsional capacity calculated?

The selected FHWA-OR-RD-16-14 method (Florida District 7 or CDOT) provides the ultimate shaft and optional toe components. Project-supplied θ50 values then mobilize those components along an elastically twisting solid circular shaft to produce the monotonic torque–rotation and depth-transfer response.

What structures need a torsion check?

Anything with eccentric lateral load about the foundation axis: cantilever sign structures, mast-arm traffic signals, sound walls, and monopoles under asymmetric wind. AASHTO sign-structure practice requires the check explicitly.

Does the model include cyclic or combined loading?

The model is monotonic. The public report calls for more research on generalized transfer curves, cyclic behavior, and combined loading, so PileCalc rejects those requests explicitly rather than guessing. Only the Florida District 7 cohesionless-toe normal-force term consumes a nonzero axial load.

FHWA-OR-RD-16-14 · Florida District 7 / CDOT methods

Torsional resistance and calibrated twist, layer by layer.

Separate shaft and toe ultimate resistance, then solve monotonic torque–rotation and depth transfer with explicit θ50 calibration and elastic GJ compatibility.

Try it free

PileCalc implements the Florida District 7 and CDOT ultimate shaft/toe equations documented in FHWA-OR-RD-16-14, including their distinct surface exclusions and cohesive/sand resistance rules.

The monotonic response requires a documented θ50 for every layer and included toe. The solver couples those project-specific hyperbolas to solid-circular elastic shaft twist, checks equilibrium, and repeats at half mesh resolution.

Shaft and toe methods

Florida District 7 or CDOT ultimate components, method-specific surface exclusions, and explicit factor-of-safety semantics.

Calibrated torque–rotation

User-supplied layer/toe θ50 values drive monotonic hyperbolic transfer; no hidden generic calibration.

Depth transfer and service stiffness

Elastic GJ compatibility returns internal torque/rotation with service secant and centered tangent stiffness.

Explicit scope

Generic cyclic degradation, rock, unsupported geometry, and generalized axial–torsional interaction are rejected explicitly rather than approximated.

Validated against published benchmarks

Every figure below is produced by the engine on the cited published problem — closed-form solutions, design-manual tables, or independent codes — and reproduced by the test suite on every release.

FHWA-OR-RD-16-14 Florida District 7/CDOT ultimate resistance with user-calibrated monotonic transfer

Quantity	PileCalc	Reference	Agreement
TDSFB frictionless-base shaft ultimate torqueFHWA-OR-RD-16-14 Table 5.3 (rounded published value)	≈139 kN·m	139 kN·m	within published rounding
Rigid-shaft limit of the calibrated hyperbolic transfer responseAnalytical limiting case with GJ → ∞	Tu·θ/(θ50+θ)	independent analytical hyperbola	within 0.25%
Same physical nonlinear capacity, service rotation, and stiffness in SI and US unitsPhysical SI/US twin with explicit unit convention	conversion-equivalent	conversion-equivalent	within solver tolerance

See the full per-tool validation report

The numbers, published

PileCalc's engine is checked term-by-term against the reference codes. A representative sample of the benchmarks — every intermediate value is visible in the app so you can reproduce them yourself.

Benchmark

Quantity

PileCalc

Reference

Agreement

Free-head pile (EI 1.43×10⁶, D 1 m, L 24.4 m)Liang et al. (2014) exact solution / RSPile

Max moment

792.2 kN·m

792.1 kN·m (exact)

within 0.1%

Fixed-head pile (EI 1.43×10⁶, D 1 m, L 24.4 m)Liang et al. (2014) exact solution / RSPile

Head moment

−581.1 kN·m

−581.0 kN·m (exact)

within 0.1%

Cantilever pile (EI 320, D 0.1 m, L 5.25 m)Liang et al. (2014) exact solution / RSPile

Head deflection

8.75 mm

8.750 mm (exact)

within 0.1%

Cantilever pile (EI 320, D 0.1 m, L 5.25 m)Liang et al. (2014) exact solution / RSPile

Max moment

2.335 kN·m

2.334 kN·m (exact)

within 0.1%

Circular pile, API sand (D 0.5 m, L 10 m, H 100 kN)RSPile verification manual

Deflection & moment profile

RSPile 2018 problems #1/#2/#8/#15

chart-reading tolerance

within 1–3%

Steel pile, multi-layer slope stabilization (17 m)RSPile / TZPile / LPile

Lateral resistance

607 kN

582 kN

within ~4%

Read how we validate — and why against two independent codes

Torsional load transfer: common questions

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