Verification › V.04 Dynamic analysis

V.04.17-Storey Steel Moment Frame: Natural Periods

All 7 periods match OpenSees to 5 decimals

Open in the app and solveNo sign-up needed: it runs in your browser.

Problem

Find the natural periods of the 7-storey frame of problem V.02.2 with a lumped mass on each floor.

OpenSeesPy documentation, example "PortalFrame2d" (5 decimals; SAP2000 Verification Manual Example 1 and SeismoStruct Example 11 print the same to 4).
STAAD.Pro V8i SS6, the same input file run by Sutranet.

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

Natural periods (s)

Mode	OpenSees	STAAD.Pro	Sutranet	Difference
1	1.27321	1.27321	1.2732111	none
2	0.43128	0.43128	0.4312785	none
3	0.24204	0.24204	0.2420432	none
4	0.16018	0.16018	0.1601789	none
5	0.11899	0.11899	0.1189896	none
6	0.09506	0.09506	0.0950639	none
7	0.07951	0.07951	0.0795148	none

Modal weight in X (kip) and participation (%)

Mode	Weight, STAAD.Pro	Weight, Sutranet	Participation, STAAD.Pro	Participation, Sutranet	Difference
1	1058.933	1058.9327	79.96	79.9627	none
2	150.1232	150.12322	11.34	11.3362	none
3	55.36824	55.368233	4.18	4.1810	<0.01%
4	28.00899	28.008990	2.12	2.1150	none
5	18.73272	18.732715	1.41	1.4146	none
6	9.004698	9.0046967	0.68	0.6800	<0.01%
7	4.113278	4.1132832	0.31	0.3106	<0.01%

STAAD prints the modal weights to 7 significant figures; four of them differ from ours by one unit or less in the 7th figure, so they match to 6 significant figures. Everything else matches to every printed digit.

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.
Modal Analysis.

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: opensees_portal_frame2d.rs, run on every change.

Run your own models the same way

Free account: build frames, trusses and towers, import STAAD .std files, and run IS 800 and AISC design checks in your browser.