Results.
| Example | Reference | Records | Largest deviation |
|---|---|---|---|
| Five-storey office building, rigid diaphragm | Independent program | 12 | 1.39% |
| Five-storey office building, semi-rigid diaphragm | Independent program | 12 | 1.41% |
Problem. A five-storey reinforced concrete office building with a core and walls on its short sides is solved separately with MindFEM and with ETABS. The building is solved once with a rigid diaphragm at the floors and once with the in-plane stiffness of the slab itself (semi-rigid diaphragm). The modes, the roof displacement under lateral load, the share of the base shear between the walls and the columns, and the axial force of a column under vertical load are compared.
Reference document. The reference is the same building modelled in ETABS 20.1.0 with its own objects. The walls and the slabs are divided by the same 0.5 m mesh in both programs.
Numerical model. The plan is 36 × 18 m with 6 m bays, the ground storey is 4.0 m high and the other storeys 3.2 m. The walls are 25 cm, the columns 50 × 50 cm, the beams 30 × 60 cm and the slabs 20 cm, the base is fixed, and the lateral load in X and Y (EX, EY) is applied at the column heads of every storey in proportion to the storey level.
Five-storey office building, rigid diaphragm
Parameters. mesh size [m] = 0.5
Independent calculation. ETABS 20.1.0, the same building modelled with ETABS's own objects on the same mesh
| Quantity | Reference | Computed | Deviation |
|---|---|---|---|
| Mode 1 frequency [Hz] | 2.94953 | 2.94164 | 0.268% |
| Mode 1 mass participation ratio, X | 0.645659 | 0.644286 | 0.213% |
| Mode 2 frequency [Hz] | 3.72792 | 3.72363 | 0.115% |
| Mode 2 mass participation ratio, Y | 0.365827 | 0.362131 | 1.01% |
| Mode 3 frequency [Hz] | 4.29501 | 4.2922 | 0.0654% |
| Mode 3 mass participation ratio, Y | 0.369025 | 0.374152 | 1.39% |
| Roof corner (36; 18) displacement under EX [mm] | 0.453244 | 0.456181 | 0.648% |
| Roof corner (36; 18) displacement under EY [mm] | 0.332886 | 0.334185 | 0.390% |
| EY base shear, core [kN] | 176.039 | 176.305 | 0.151% |
| EY base shear, end walls [kN] | 121.343 | 121.164 | 0.147% |
| EY base shear, columns [kN] | 12.1416 | 12.0547 | 0.716% |
| Base axial force of the interior column (24; 6) under self weight [kN] | 1,740.77 | 1,741.24 | 0.0272% |
Note. The wall and slab mesh is the same in both programs. As ETABS does not mesh straight walls without openings by default, the walls are built as panels of the mesh size, and the slabs are given the "Mesh N1 x N2" meshing. The beams are 0.5 m objects and the automatic end zones of the frames are switched off, so that mass and weight are computed over the axis length in both programs. The mass is the self weight, a 2 kPa finish and 0.3 times the live load.
Five-storey office building, semi-rigid diaphragm
Parameters. mesh size [m] = 0.5
Independent calculation. ETABS 20.1.0, the same building modelled with ETABS's own objects on the same mesh
| Quantity | Reference | Computed | Deviation |
|---|---|---|---|
| Mode 1 frequency [Hz] | 2.92674 | 2.9185 | 0.281% |
| Mode 1 mass participation ratio, X | 0.655184 | 0.652962 | 0.339% |
| Mode 2 frequency [Hz] | 3.69198 | 3.68675 | 0.142% |
| Mode 2 mass participation ratio, Y | 0.360879 | 0.356888 | 1.11% |
| Mode 3 frequency [Hz] | 4.26333 | 4.25966 | 0.0859% |
| Mode 3 mass participation ratio, Y | 0.376402 | 0.381709 | 1.41% |
| Roof corner (36; 18) displacement under EX [mm] | 0.459857 | 0.462775 | 0.635% |
| Roof corner (36; 18) displacement under EY [mm] | 0.341512 | 0.342904 | 0.408% |
| EY base shear, core [kN] | 187.059 | 187.394 | 0.179% |
| EY base shear, end walls [kN] | 109.602 | 109.369 | 0.213% |
| EY base shear, columns [kN] | 12.8627 | 12.761 | 0.790% |
| Base axial force of the interior column (24; 6) under self weight [kN] | 1,741.63 | 1,743.05 | 0.0813% |
Note. The modelling rules are those of the rigid-diaphragm example. With a semi-rigid diaphragm the slab deforms in its plane with the stiffness of its shell elements. Under EY the slab flexes between the core and the end walls, and part of the base shear moves from the end walls to the core.
Model files
The ETABS models behind the tables can be downloaded. They open in ETABS 20 and later with
File > Import > ETABS .e2k File.