StruCla against SCIA Engineer: concrete frame with columns and beams
A space frame of two concrete columns (700×450 and 500×450) with beams and consoles on each floor, C16/20 with B400B reinforcement, 24 nodes and 16 members. Four load cases: self weight (BG1), pipes and friction (BG2), wind in X (BG3) and wind in Y (BG4). The same model was built in StruCla from the load tables of the SCIA output; every StruCla value comes from StruCla's own results and report. Project name, client, address and licence data have been removed from the SCIA output.
Green: equal within 1 % or 0.06 (kN, kNm), roughly the rounding of the SCIA output. Red: a larger difference; it is described below. Each cell shows SCIA on top and StruCla below. Forces and moments are compared as magnitudes: SCIA and StruCla use different local axes and signs.
1. Reactions (ULS), global axes: R in kN, M in kNm
| Support | Comb. | Rx | Ry | Rz | Mx | My | Mz |
|---|---|---|---|---|---|---|---|
| Sn2/K72 | 11/1 | −0.94 −0.95 | 8.76 8.75 | 217.29 217.22 | 0.00 0.00 | 1.41 1.39 | −2.09 −2.08 |
| Sn1/K5 | 2/2 | 0.00 0.00 | −0.24 −0.24 | 121.51 121.51 | 0.00 0.00 | 0.00 0.00 | 0.00 0.00 |
| Sn1/K5 | 12/3 | 17.44 17.44 | 8.28 8.27 | 97.27 97.29 | 0.00 0.00 | 142.25 142.09 | −2.13 −2.12 |
Combination keys (SCIA sheet 22): 11/1 = 0.90 G + 1.50 Q; 10/2 = 0.90 G; 12/3 = 0.90 G + 1.50 Wx + 1.50 Q. G = BG1, Q = BG2, Wx = BG3, Wy = BG4. The column feet are fixed except for the rotation about X (Mx = 0 in the SCIA output).
2. Capacity response check (SCIA sheet 22)
SCIA's "capacity response" check calculates the cracked section under the design load (concrete in compression only, bilinear concrete, reinforcement with a horizontal branch) and reports strains, stresses and a unity check. For beams the unity check also includes the compression zone limit of NEN-EN 1992-1-1+NB 6.1(9): xu/d ≤ εcu·10⁶/(εcu·10⁶ + 7 fyd), which is 500/(500 + fyd) for fck ≤ 50 MPa. StruCla uses the same section model and reports the same quantities. The load vector is the one printed by SCIA (N, My, Mz at the position and combination given), so this comparison does not depend on the analysis of the frame.
| Member, position, comb. | N, My, Mz kN, kNm | Unity check | x mm | σc N/mm² | εs ‰ | σs N/mm² | StruCla strength UC 3-D interaction |
|---|---|---|---|---|---|---|---|
| S3 0.383, /1 | -82.91 9.52 3.77 | 0.04 0.04 | 716 681 | 0.41 0.42 | 0 0 | 0.7 0.6 | 0.03 |
| S60 6.125, /2 | -176.59 5.45 -1.49 | 0.05 0.05 | 832 1741 | 0.49 0.49 | 0 0 | 0 0 | 0.04 |
| S57 1.500−, /2 | 0.00 -16.04 4.01 | 0.71 0.72 | 185 185 | 4.04 4.05 | 0.78 0.78 | 155.4 155.6 | 0.33 |
The unity check is the largest of the response checks (σc/fcd, εc/εcu, εs/εud, σs/fyd) and, for the beam S57, UC xu. For S57, xu = 151 mm against a limit of 209 mm (d = 355 mm), so UC xu = 0.72. The last column is StruCla's strength check: the ray from the origin through the load vector to the 3-D interaction surface N–My–Mz. SCIA does not print it on this sheet. The check of S57 is therefore governed by the compression zone limit, not by strength (0.33).
Differences. The two columns S3 and S60 are loaded to only 3 to 5 % of their capacity, so every value is small: the concrete stress is 0.42 and 0.49 N/mm² against 0.41 and 0.49 in SCIA and the unity checks round to 0.04 and 0.05 in both programs. The compression zone height x of such a section is not well defined (S60: 832 against 1741 mm). SCIA prints the strain of one fibre of the column section that is not necessarily the extreme fibre, so the concrete strain is not compared. The stress of a lightly loaded column depends strongly on the steel area, so the column reinforcement matters here: see section 4.
3. Section forces per row (SCIA sheets 12 to 14), kN and kNm
| Member | dx (m) | Comb. | N | Vy | Vz | Mx | My | Mz |
|---|---|---|---|---|---|---|---|---|
| S60 | 0 | 6/1 | −257.80 −257.71 | 8.84 8.83 | 0.94 −0.95 | −2.09 2.08 | 1.41 −1.39 | 0.00 0.00 |
| S3 | 9.5 | 2/2 | −50.49 −50.49 | −0.37 −0.37 | 0.00 0.00 | 0.00 0.00 | 0.00 0.00 | −0.99 −0.98 |
| S3 | 3.833+ | 1/3 | −119.85 −119.85 | −0.49 −0.49 | 0.00 0.00 | 0.00 0.00 | 0.00 0.00 | 1.48 1.48 |
| S3 | 0 | 7/4 | −137.78 −137.79 | 8.20 8.19 | −17.44 17.44 | −2.13 2.12 | 142.25 −142.08 | 0.00 0.00 |
| S3 | 3.833+ | 6/1 | −130.99 −131.14 | 8.03 8.02 | −0.43 0.43 | −2.91 2.92 | 6.81 −6.85 | −18.91 −19.15 |
| S60 | 3.833+ | 6/1 | −180.27 −180.05 | 9.01 9.01 | 0.43 −0.43 | −2.84 2.85 | 4.44 −4.47 | −21.87 −22.11 |
| S60 | 3.833- | 6/1 | −222.26 −222.19 | 8.84 8.83 | 0.94 −0.95 | −2.09 2.08 | 5.00 −5.04 | 33.88 33.84 |
| S59 | 2 | 2/2 | −9.52 −9.52 | −1.03 −1.04 | 0.00 0.00 | 0.00 0.00 | 0.00 0.00 | −1.33 −1.34 |
| S59 | 0 | 1/3 | −25.94 −25.93 | −1.38 −1.38 | 0.00 0.00 | 0.00 0.00 | 0.00 0.00 | 0.97 0.98 |
| S61 | 0 | 7/4 | −76.78 −76.58 | 4.76 4.78 | −5.80 5.79 | −0.65 0.66 | 14.19 −14.15 | −1.88 −2.19 |
| S55 | 0 | 6/1 | −65.12 −65.29 | 2.29 2.26 | 0.09 −0.09 | −0.81 0.81 | −4.73 4.75 | 1.22 0.98 |
| S59 | 0 | 6/1 | −33.96 −34.03 | −0.37 −0.37 | 0.13 −0.14 | −0.30 0.31 | −6.46 6.47 | 2.27 2.14 |
| S55 | 0 | 4/5 | −51.87 −51.87 | −1.24 −1.26 | −5.71 5.70 | 0.00 0.00 | 17.57 −17.52 | 1.55 1.59 |
| S61 | 2 | 6/1 | −63.54 −63.34 | 4.76 4.78 | −0.09 0.09 | −0.65 0.66 | −3.55 3.55 | 7.65 7.35 |
| S58 | 1.2+ | 6/1 | 0.00 0.00 | 1.22 −1.22 | −7.63 −7.63 | 0.00 0.00 | −3.79 −3.79 | 0.50 −0.50 |
| S56 | 1.5- | 6/1 | 0.00 0.00 | 0.51 −0.51 | −13.73 −13.73 | 0.00 0.00 | −10.30 −10.29 | 0.38 −0.38 |
| S57 | 1.5+ | 6/1 | 0.00 0.00 | −4.28 4.29 | 18.70 18.71 | 0.00 0.00 | −15.63 −15.63 | 3.69 −3.70 |
| S56 | 0 | 4/5 | −3.07 −3.06 | 0.00 0.00 | 0.00 0.00 | 0.00 0.00 | 0.00 0.00 | 0.00 0.00 |
| S67 | 0 | 2/2 | 0.13 0.13 | 0.00 0.00 | 4.97 4.96 | 0.00 0.00 | −2.02 −2.02 | 0.00 0.00 |
| S66 | 3 | 6/1 | 0.74 0.77 | 0.51 −0.52 | −25.43 −25.43 | 0.56 −0.56 | −31.09 −31.09 | 0.73 −0.74 |
| S66 | 0 | 1/3 | 0.75 0.77 | 0.00 0.00 | 6.62 6.62 | 0.00 0.00 | −2.87 −2.89 | 0.00 0.00 |
| S67 | 0 | 6/1 | 0.18 0.17 | 0.51 −0.52 | 41.99 42.13 | 0.56 −0.57 | −55.75 −55.94 | −0.75 0.77 |
| S67 | 3 | 11/6 | 0.13 0.13 | 0.51 −0.52 | 30.40 30.55 | 0.56 −0.57 | 51.03 51.22 | 0.78 −0.80 |
| S66 | 0 | 11/6 | 0.56 0.57 | 0.51 −0.52 | −13.85 −13.85 | 0.56 −0.56 | 26.06 26.04 | −0.81 0.83 |
| S69 | 0 | 1/3 | 0.13 0.12 | 0.00 0.00 | 3.86 3.86 | 0.00 0.00 | −1.90 −1.91 | 0.00 0.00 |
| S68 | 0 | 6/1 | −1.38 −1.39 | −0.13 0.14 | 6.07 5.99 | 0.10 −0.10 | −5.10 −4.98 | 0.23 −0.23 |
| S68 | 3 | 1/3 | −1.38 −1.38 | 0.00 0.00 | −3.86 −3.86 | 0.00 0.00 | −1.78 −1.79 | 0.00 0.00 |
| S69 | 0 | 6/1 | 0.02 0.00 | 0.05 −0.04 | 7.48 7.37 | 0.13 −0.13 | −7.33 −7.18 | −0.04 0.04 |
| S69 | 3 | 11/6 | −0.02 −0.03 | 0.05 −0.04 | 0.72 0.62 | 0.13 −0.13 | 4.00 3.83 | 0.10 −0.10 |
| S68 | 3 | 6/1 | −1.38 −1.39 | −0.13 0.14 | −1.65 −1.73 | 0.10 −0.10 | 1.54 1.41 | −0.17 0.18 |
Combination keys (SCIA sheet 14): 6/1 = 1.20 G + 1.50 Q; 2/2 = 0.90 G; 1/3 = 1.20 G; 7/4 = 1.20 G + 1.50 Wx + 1.50 Q; 4/5 = 1.20 G + 1.50 Wx; 11/6 = 0.90 G + 1.50 Q.
Differences. 10 of the 30 rows differ in at least one value by more than 1 % or 0.06. They are the weak-axis moments Mz of the columns (1.1 to 3.9 % for values above 5; 0.1 to 0.3 kNm for the small values at the foot of S55 and S61 and the top of S59) and the shear force and moment of the small beams S68 and S69 (1.3 to 2.4 % for values above 5; 0.1 kN on the small shear forces). We have not traced these to a cause. One input is known to be incomplete in the printed output: the wind load BG3 also contains a line load of 0.62 kN/m on the two columns that is in the SCIA file and not in the printed tables; it is included in the StruCla model.
4. Model and reinforcement
- Concrete C16/20 (E = 28 600 N/mm², 2500 kg/m³), reinforcement B400B, γc = 1.5, γs = 1.15, αcc = 1.0, bilinear concrete diagram.
- Sections h×b: S3 and S60 700×450, S55, S59, S61 and S65 500×450, S56, S57, S58, S62, S63 and S64 400×250, S66 and S67 500×300, S68 and S69 350×250 mm.
- Nodes K5 and K72 fixed in five degrees of freedom (rotation about X free); all other connections rigid.
- Point loads on nodes and members as on SCIA sheets 7 to 11; combination factors as printed on SCIA sheets 14 and 22.
- Reinforcement (table below) from the present-reinforcement input screens on sheets 24 to 27 of the SCIA output and the SCIA file: stirrups Ø8-300. For S3 and S60 sheet 24 gives 2Ø28 per y-edge and 1Ø12 per z-edge as basic bars and 2Ø26 per z-edge as fixed additional (corner) bars; the positions follow from that (4Ø26 in the corners, 2Ø28 at the thirds of each y-edge, 1Ø12 at mid-height of each z-edge, 30 mm cover). With this layout StruCla reproduces SCIA's concrete stress in both columns, which supports it. S66 and S67: 3Ø22 top and bottom (sheet 26). For S55, S59, S61 and S65 the output does not show the reinforcement, so none was entered and the StruCla report does not check them. The comparison of forces and reactions does not depend on reinforcement.
| Member | Section h×b (mm) | Longitudinal reinforcement | Stirrups |
|---|---|---|---|
| S3 | 700×450 | 4Ø26 + 4Ø28 + 2Ø12 | Ø8-300, 2 legs |
| S60 | 700×450 | 4Ø26 + 4Ø28 + 2Ø12 | Ø8-300, 2 legs |
| S56 | 400×250 | 2Ø10 + 3Ø14 | Ø8-300, 2 legs |
| S57 | 400×250 | 2Ø10 + 3Ø14 | Ø8-300, 2 legs |
| S58 | 400×250 | 2Ø10 + 3Ø14 | Ø8-300, 2 legs |
| S62 | 400×250 | 2Ø10 + 3Ø14 | Ø8-300, 2 legs |
| S63 | 400×250 | 2Ø10 + 3Ø14 | Ø8-300, 2 legs |
| S64 | 400×250 | 2Ø10 + 3Ø14 | Ø8-300, 2 legs |
| S66 | 500×300 | 3Ø22 + 3Ø22 | Ø8-300, 2 legs |
| S67 | 500×300 | 3Ø22 + 3Ø22 | Ø8-300, 2 legs |
| S68 | 350×250 | 3Ø10 + 3Ø10 | Ø8-300, 2 legs |
| S69 | 350×250 | 3Ø10 + 3Ø10 | Ø8-300, 2 legs |
5. What the SCIA output contains and where it is in the StruCla report
| SCIA output (sheet) | In the StruCla report |
|---|---|
| Internal forces N, Vy, Vz, Mx, My, Mz per member, extremes with the combination (12 to 14) | Section 7: "Section forces: extremes per member over all ULS combinations" (value, combination and position per component), "Results per combination" and the force diagrams |
| Support reactions Rx, Ry, Rz, Mx, My, Mz and the eccentricities ex, ey per combination (21, 22) | Section 7: "Support reactions per ULS combination" with e, and the envelope per support |
| Capacity response check: N, MEd, x, εc, σc, εs, σs, unity check (22) | Section 8: "Capacity response check" for every concrete member (columns and beams), and in each member calculation (governing section) with the four response unity checks and, for beams, UC xu |
| Provided longitudinal reinforcement per direction (21) | Section 8: "Provided longitudinal reinforcement" (bars and the area on each side of the centre) and the input of each member calculation |
| Deformations per load case (18, 19) | Section 7: displacement per combination and the deflection and sway check (SLS). SCIA lists displacements at chosen points for BG1; StruCla lists the maximum per combination and the member deflections |
| Steel check EC3 (20) | Not calculated in the SCIA output (error E-C04); no steel members in this model |
StruCla reports more than this: shear, torsion, detailing (8.2, 9.2, 9.5) and the interaction diagrams are in each member calculation. SCIA prints none of these in this output, so they cannot be compared.
6. Notes on the SCIA output
Project name, licence holder, author, organisation and logo have been removed from the SCIA sheets (white areas). Nothing else in the output was changed.
Reference: NEN-EN 1992-1-1:2005+A1:2015+NB:2016, 6.1(2), 6.1(3)P, 6.1(9) NB and 3.2.7(2).