Verification › V.03 Second-order (P-Delta) analysis

V.03.2Flagpole Cantilever

P-Delta within 0.3% of STAAD.Pro

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Problem

Compare the second-order (P-Delta) response, including the bowed moment along the member, with STAAD.Pro.

STAAD.Pro V8i SS6, the same input file run by Sutranet: linear analysis, PDELTA with SMALLDELTA, and the same model meshed into 10 members per member (for the moment along each member).

Vertical cantilever 10 m long, fixed at the base
20 kN lateral tip load and 5 kN/m lateral load along the member
Axial load 0.1 and 0.3 P_e (load cases 1 and 2)
Prismatic members: AX 0.01 m², IX 0.0002 m⁴, IY = IZ 0.0001 m⁴ unless stated; E 2 × 10⁸ kN/m²

Front view (X right, Y up). Joints numbered, supports marked ▲. Drawn from the project file.

Bending moment along the member (kN·m)

Result	First-order, STAAD.Pro	First-order, Sutranet	P-Delta, STAAD.Pro meshed	P-Delta, Sutranet	Difference
Moment at 0.1 L, 0.1 Pe (kN·m)	382.50	382.50	417.25	417.25	none
Moment at 0.1 L, 0.3 Pe (kN·m)	382.50	382.50	515.90	515.90	none

P-Delta support reactions

Result	STAAD.Pro SMALLDELTA	Sutranet	Difference
Base moment, 0.1 Pe (kN·m)	485.34	485.318	<0.01%

First-order displacements, reactions and end forces equal STAAD's linear run to its print precision; P-Delta joint results and end forces are within 0.3% of STAAD's SMALLDELTA run. STAAD reports the moment inside an unmeshed member without the P-δ bow, so the moment along the member is compared with the meshed model.

Open the project in the app (no sign-up needed), or download the file and open it with 📂 Import Job JSON in the File group.
Run Analysis (Static) with P-Delta Analysis ticked (unticked for the first-order result).

The app works in SI units; results in kip and inch are converted (1 kip = 4.448 kN, 1 kip-in = 0.1130 kN·m, 1 in = 25.4 mm).

Automated test: staad_pdelta.rs, run on every change.

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