Verification Model
A three-storey frame and shell-slab model compared between AutoCalcs and a separate OpenSees ASDShellQ4 reference model for linear static and modal analyses.
The slab mesh and frame members share nodes along the beam lines, so the comparison is focused on frame stiffness, shell stiffness, applied loading, modal mass, and geometric-stiffness behaviour rather than beam-to-shell coupling assumptions.
Model Definition
The same model was run in AutoCalcs and in a separate OpenSees model (elastic beam-column members and ASDShellQ4 slabs) built from the same input. A check passes when the two solvers agree within 2%.
| Geometry | 3 x 2 bays at 6 m, 3 storeys at 3.6 m, fixed column bases |
| Columns (steel) | A = 0.24 m², I = 4.8 x 10⁻³ m⁴ about both axes, J = 8.0 x 10⁻³ m⁴ |
| Beams (steel) | A = 0.15 m², I = 4.0 x 10⁻³ m⁴ (vertical bending) and 2.2 x 10⁻³ m⁴ (horizontal bending), J = 3.0 x 10⁻³ m⁴ |
| Steel | E = 200 GPa, ν = 0.3, ρ = 7,850 kg/m³ |
| Slabs (concrete shells) | 200 mm thick, E = 30 GPa, ν = 0.2, ρ = 2,400 kg/m³, 3 m mesh (6 x 4 panels per floor) sharing nodes with the beams |
| G | 20 kPa pressure on every slab panel |
| E | Lateral floor loads of 40, 80 and 120 kN at levels 1, 2 and 3, spread over the floor nodes |
| Modal mass | Self-weight of members and slabs |
Plate result note: the numeric plate comparison below uses raw element resultants from AutoCalcs and the ASDShellQ4 OpenSees reference run. The browser app defaults to smoothed plate contours for display and reporting because smoothing gives a more usable engineering contour field across a mesh. Smoothing is post-processing, so it is not used as the comparison value here.
Concrete slabs are modelled as linear-elastic shell elements for solver verification. The reported slab deformations are FEA displacement results, not code-based reinforced-concrete serviceability deflection checks with cracking, creep, shrinkage, or long-term modifiers.
OpenSees is third-party research software from UC Berkeley/PEER. AutoCalcs is not affiliated with, certified by, or endorsed by OpenSees, UC Berkeley, or PEER, and OpenSees is not distributed as part of AutoCalcs.
Node and Deformation Results
Maximum node deformations reported directly from the two solvers.
| Check | AutoCalcs | OpenSees | Difference |
|---|---|---|---|
Max vertical node displacement, GSlab deformation reported from the shell nodes at the upper floor. | -0.657 mm | -0.657 mm | <0.01% |
Max lateral node displacement, ERoof-level lateral displacement under the lateral load case. | 0.465 mm | 0.465 mm | <0.01% |
Member Results
Maximum absolute member response checks by force category, using resultant shear and bending values at member ends.
| Check | AutoCalcs | OpenSees | Difference |
|---|---|---|---|
Max column axial force, G + EBase-to-level-1 column at grid x=1, z=1; compression reported as positive in this comparison. | 2280.994 kN | 2280.994 kN | <0.01% |
Max column shear resultant, G + EColumn from level 2 to level 3 at grid x=3, z=1; lower-end resultant shear. | 95.810 kN | 95.810 kN | <0.01% |
Max column bending moment, G + EColumn from level 2 to level 3 at grid x=3, z=1; top-end resultant bending moment. | 202.100 kN-m | 202.100 kN-m | <0.01% |
Max beam bending moment, G + EZ-direction beam on level 3 at grid x=2; start-end resultant bending moment. | 83.933 kN-m | 83.933 kN-m | <0.01% |
Plate Results
Maximum raw shell recovery values compared element-by-element before contour smoothing. Plate deformation is reported above as nodal displacement.
| Check | AutoCalcs | OpenSees | Difference |
|---|---|---|---|
Max raw slab bending Mx, GMaximum element-centre bending value before contour smoothing. | 2.912 kN-m/m | 2.912 kN-m/m | <0.01% |
Max raw slab membrane stress Sy, GMaximum element-centre membrane stress before contour smoothing. | -40.872 kN/m2 | -40.872 kN/m2 | <0.01% |
Max raw slab transverse shear Qx, GMaximum element-centre transverse shear before contour smoothing. | -29.585 kN/m | -29.585 kN/m | <0.01% |
Modal Mode Results
First five natural frequencies from the runnable public sample compared against OpenSees ASDShellQ4. Modal mass is driven by the self-weight load case, LC: 3 - Mass - self-weight.
| Check | AutoCalcs | OpenSees | Difference |
|---|---|---|---|
Mode 1 | 4.6514 Hz | 4.6517 Hz | <0.01% |
Mode 2 | 4.7819 Hz | 4.7822 Hz | <0.01% |
Mode 3 | 5.4951 Hz | 5.4371 Hz | 1.07% |
Mode 4 | 15.1904 Hz | 15.1972 Hz | 0.04% |
Mode 5 | 15.4962 Hz | 15.5050 Hz | 0.06% |