Verification
Results you can trust, and show.
The published ETABS and SAFE verification problems run as tests on every release. zspan was also compared against closed-form solutions and OpenSees, an independent research-grade finite-element program.
≤ 10−11
relative difference from OpenSees on frames
0.3 %
core-wall building vs. OpenSees shells
0.23 %
Scordelis–Lo roof benchmark
900+
automated tests gate every release
| Benchmark | Reference | Result |
|---|---|---|
| 3-D frames: static displacements, member forces, periods, ELF loads | OpenSees | ≤ 1×10⁻¹¹ relative |
| P-Delta (iterative, consistent geometric stiffness) | OpenSees / exact beam-column | ≤ 1×10⁻⁴ |
| Shell element: patch test, MacNeal beam, Cook's membrane, Navier plates, Scordelis–Lo roof | Closed form / published benchmarks | all pass, roof 0.23 % |
| Core-wall building: periods and lateral displacements | OpenSees ShellDKGQ | within 0.3 % |
| Cantilever shear wall: top drift | Timoshenko beam theory | within 1 % |
| NBC 2020 / ASCE 7-16 load generators and combinations | Hand calculations | 86 checks pass |
| CSA A23.3 and S16 member design | Hand calculations | 153 checks pass |
| Steel libraries (AISC, CSA, EN, IS, BS, AS/NZS) | Source tables and exact geometry | 292 checks pass |
Side-by-side with ETABS. The Windows app runs your installed ETABS on the same model and reports zspan's periods, base reactions, story shears and drifts next to ETABS's, value by value. Comparisons on beta firms' real buildings are under way and will be published here with their permission.
ETABS verification manual
The same problems ETABS is verified on.
CSI publishes the problems ETABS is verified against, with theoretical results or refined SAP2000 meshes as the reference. We rebuilt every linear one in zspan.
| Problem | Reference | ETABS | zspan |
|---|---|---|---|
| 1 · Plane frame with span loads: moments and shears | Theory | exact | exact |
| 2 · Three-storey frame: periods and mode shapes | Theory | exact | within 0.1 % |
| 3 · ASCE 7 equivalent static storey shears | Hand calculation | exact | within 0.01 % |
| 4, 5, 8 · 3-D frames and braced building: periods, modes, spectrum response | Theory / published | within 0.3 % | within 0.3 % |
| 6 · Nine-storey, ten-bay frame: eigenvalues | Published | within 0.1 % | identical to ETABS |
| 15 · Shear walls, coupled walls, wall on columns, E and flanged walls: lateral displacements and twists (24 values) | SAP2000 refined mesh | stiffer in 20 of 24, by up to 22 % | 17 of 24 within 1 %, 23 within 4 %, median 0.3 %* |
Why ETABS and the refined mesh differ on walls. In CSI's Example 15 the ETABS models use one element per wall panel per storey, which is stiffer than a converged mesh: up to 22 % on a one-storey wall, under 8 % on six storeys. zspan with a fine wall mesh lands on the refined result. With one element per panel, zspan comes within about 2 % (median) of ETABS’s published values (up to 12 % on the wall-on-columns case), so a difference between the two can be traced to the mesh.
*All values use zspan's default shell walls. The one value outside 4 % is a 0.0005-radian twist published to one significant figure.
*All values use zspan's default shell walls. The one value outside 4 % is a 0.0005-radian twist published to one significant figure.
SAFE verification manual
Slab design, checked the same way.
CSI's SAFE verification problems for plate analysis, punching shear, slab flexure and cracked deflection, rebuilt in zspan on SAFE's own meshes. Thin-plate results are shown; the thick-plate versions agree within 5%.
| Problem | Quantity | SAFE / hand calculation | zspan |
|---|---|---|---|
| CSA A23.3-14 RC-PN-001 · flat plate, interior column | Punching stress / resistance / D/C | 1.792 / 1.127 MPa / 1.59 | 1.792 / 1.127 MPa / 1.59 |
| ACI 318-14 RC-PN-001 · flat plate, interior column | Punching stress / resistance / D/C | 0.193 / 0.158 ksi / 1.22 | 0.193 / 0.158 ksi / 1.22 |
| CSA A23.3-14 RC-SL-001 · one-way slab, 1 m strip | Strip moment / bottom steel | 25.00 kN·m / 5.414 cm² | 25.00 kN·m / 5.406 cm² |
| Example 1 · simply supported plate, uniform / point / line load | 12 deflections and 12 strip moments | all within 0.4% of SAFE | |
| Example 2 · plate with fixed edges, point load | Centre deflection | 0.0598 in | 0.0598 in |
| Example 3 · plate with mixed edge conditions | Free-edge deflection | 0.5502 in | 0.5502 in |
| Example 4 · plate on flexible edge beams | Centre deflection / beam moment | 0.1854 in / 1,120.4 kip-in | 0.1854 in / 1,120.4 kip-in |
| Example 5 · infinite flat plate on columns | 7 deflections and 8 strip moments | all within 0.5% of SAFE | |
| Example 6 · infinite plate on elastic subgrade | Deflection under load / moment | 0.05405 in / 37.99 kip-in/in | 0.05405 in / 37.99 kip-in/in |
| Example 7 · skew plate, free obtuse edge | Free-edge deflection / max moment | 1.510 in / 12.03 kip-in/in | 1.511 in / 12.34 kip-in/in† |
| Example 16 · cracked slab deflection, creep and shrinkage | Short-term / long-term deflection | 13.55 / 24.51 mm (hand 14.4 / 23.9) | 13.40 / 23.84 mm |
| Flat plate, 3 × 8 m bays · statics across all strips | Midspan + mean support moment = w·l2·l1²/8 | 2,973.6 kN·m | 2,973.6 kN·m |
| Beam on elastic foundation (Hetényi), point load | Deflection under the load | 0.931 mm (closed form) | 0.934 mm |
| Footing with uplift, e > B/6, compression-only soil | Maximum soil pressure | 266.7 kPa (closed form) | 265.6 kPa |
† The thin-plate moment is singular at the obtuse corner; zspan's value converges toward the theory (11.84) as the mesh is refined.
Release 1.8.32 · 2026-10-13
Every release passes these first.
Each deploy runs the benchmark problems above as tests that fail outside their tolerance, together with the unit-test suites. Largest deviation is from the reference answer (for SAFE's point-load example, from SAFE on the same mesh).
| Suite | Passed | Tolerance | Largest deviation |
|---|---|---|---|
| CSI ETABS frame verification (vs published reference) | 58 / 58 | 0.5% | 0.53% |
| CSI ETABS wall verification (fine mesh vs SAP2000) | 37 / 37 | per quantity | 6.53% |
| CSI ETABS membrane C and E walls vs ETABS (same mesh) | 12 / 12 | per quantity | 2.53% |
| SAFE plate analysis verification (vs published reference) | 67 / 67 | 5.0% | 4.23% |
| SAFE thick plates (DKMQ vs SAFE, same mesh) | 27 / 27 | 5.0% | 4.58% |
| SAFE example 6, point load (vs SAFE, same mesh) | 15 / 15 | 1.0% | 0.74% |
| SAFE / CSI punching verification | 11 / 11 | 1.0% | 0.82% |
| SAFE strip verification | 3 / 3 | 0.5% | 0.14% |
| SAFE cracked-section deflection | 2 / 2 | 5.0% | 2.72% |
| Soil / foundation benchmarks (vs theory) | 6 / 6 | per quantity | 10.00% |
| Solver, elements and loads (closed-form and equilibrium checks) | 464 / 464 | — | — |
| NBC 2020 / ASCE 7 load generators | 95 / 95 | — | — |
| CSA A23.3 concrete design | 128 / 128 | — | — |
| CSA S16 steel design | 34 / 34 | — | — |
On every run
A hand-check report with every analysis
Beyond release testing, each analysis recomputes the main load-case totals independently of the solver (gravity totals, code base shear, wind pressures, spectrum scaling) and checks drift, deflection, uplift and wall cracking against their limits, citing the clause for each.
Your numbers
Compare it with your own results.
Bring an ETABS model and we'll help you compare.