Обзор
This module designs and checks steel members per CSA S16-24. It supports I-Shapes, Т-образные формы, каналы, и разделы HSS (RHS, СВС, CHS), using standard Canadian sections or user-defined custom sections.
The module checks axial tension, осевое сжатие, bending about both principal axes, сдвиг, and the combined-action interactions between these effects. Compression checks include flexural, торсионный, и изгиб-промежуточный стрижка. Bending checks include lateral-torsional buckling for laterally unsupported members. Section classification for local buckling is performed automatically ahead of every resistance calculation.
Использование модуля
The module is available in SkyCiv Structural 3D Member Design. Выбирать CSA S16-24 as the Код дизайна. The previous edition, CSA S16-14, is still available in the same list.
Запустить дизайнер (the SkyCiv section optimizer) can be used with CSA S16-24 to find the most efficient section.
The settings (механизм) button opens the member design settings, which include a Report Mode option for the calculation report:
- Подробно (дефолт): shows the calculations in detail, with the formulas used at each step
- таблицы: only shows the relevant variables, in tables
Through the API, the design code is CSA_S16-24. Видеть S3D.design in the SkyCiv API documentation.
Классификация разделов
Before any resistance is calculated, the module classifies the section per Clause 11. The flange and web are classified independently. Each is checked against the Table 2 width-to-thickness limits for its governing stress distribution: сжатие, изгиб, или комбинация того и другого.
The resulting flange class and web class each drive which resistance formula applies to that element in Clauses 13.3 и 13.5. Класс 1 и 2 use plastic section properties. Класс 3 uses elastic section properties. Класс 4 triggers the effective-width reduction below.
Класс 4 Effective Properties
For a Class 4 элемент, the module computes an effective width for the compression flange and an effective height for the web, per the Clause 11 effective-width provisions. It then derives an effective area and an effective section modulus from these reduced dimensions.
These effective properties replace the gross properties before the compression and bending resistance are calculated. The same resistance clauses run regardless of class. Only the section properties fed into them change.
A section with both flange and web classified as Class 4, or a Class 4 element whose effective width or height reduces to zero or below, falls outside the module’s supported scope and halts calculation.
Web Slenderness Under Combined Axial and Bending
CSA S16-24’s Table 2 web classification limit, h/w ≤ (1900/√F<sub>y</sub>)(1 − 0.65x), использует x = C<sub>f</sub>/φC<sub>y</sub> as a proxy for the web’s actual stress gradient. This proxy decouples from the true gradient whenever the axial force is close to its capacity but the moment is small. The section then reads as nearly axial, even though its web is not actually near a uniform-compression stress state.
The module replaces x with the true elastic stress fraction, α = f<sub>a</sub>/(f<sub>a</sub> + f<sub>b</sub>) = C<sub>f</sub>·S/(C<sub>f</sub>·S + M<sub>f</sub>·A), где f<sub>a</sub> is the average axial stress and f<sub>b</sub> is the extreme-fibre bending stress. The web slenderness limit becomes:
h/w ≤ (1900/√F<sub>y</sub>) × [0.35 + 0.65(1 − α)²]
В α = 1 (pure axial compression), this reduces to 0.35 × 1900/√F<sub>y</sub> ≈ 670/√F<sub>y</sub>, CSA S16-24’s Table 1 предел. В α = 0 (pure bending), it gives the full 1900/√F<sub>y</sub> предел. Between the two, the quadratic term is calibrated against classical (Timoshenko) plate buckling theory, which is convex across the stress-gradient range rather than linear.
В 0.65 coefficient matches the base formula’s leading coefficient. It gives a small additional margin over the 0.62 value required for exact tangency to the theoretical curve.
Validation Against Plate Theory and CSA S16-24
The hypothesis: the quadratic-corrected limit stays conservative relative to both rigorous elastic plate buckling theory and CSA S16-24’s own Table 1 и таблица 2 limits, across the full stress-gradient range, not only at the pure-axial and pure-bending endpoints where the unmodified formula is already exact.
Стол 1 tests this against classical plate theory across the full gradient range, from pure bending to pure axial compression. Стол 2 tests it against the code’s Table 1 (axial-only) и таблица 2 (load-ratio) limits, sweeping combined axial and bending stress from 0 в φF<sub>y</sub>. Both use F<sub>y</sub> = 350 MPa, E = 200000 MPa, и ν = 0.3. In both, the module’s limit stays at or below the reference value. It is most conservative near the middle of the gradient range and converges to the code values at the pure-axial and pure-bending endpoints.
| Stress case | 1 − ψ | f1 | f2 = ψf1 | fa | fb | α | k(ψ) Timoshenko | h/w Timoshenko | h/w proposed | Margin |
|---|---|---|---|---|---|---|---|---|---|---|
| прогиб | 2.00 | 1 | −1.00 | 0.00 | 1.00 | 0.00 | 24.0 | 2082.86 | 1900.00 | 91% |
| 1.33 | 1 | −0.33 | 0.33 | 0.67 | 0.33 | 11.5 | 1441.79 | 1213.89 | 84% | |
| треугольный | 1.00 | 1 | 0.00 | 0.50 | 0.50 | 0.50 | 8.4 | 1232.23 | 973.75 | 79% |
| 0.80 | 1 | 0.20 | 0.60 | 0.40 | 0.60 | 7.1 | 1132.88 | 862.60 | 76% | |
| 0.67 | 1 | 0.33 | 0.67 | 0.33 | 0.67 | 6.1 | 1050.07 | 802.22 | 76% | |
| компрессия | 0.00 | 1 | 1.00 | 1.00 | 0.00 | 1.00 | 4.0 | 850.32 | 665.00 | 78% |
fa = Cf/A (МПа) | fb = Mf/S (МПа) | α | h/w Стол 1 | h/w Стол 2 | h/w proposed | Margin vs Table 1 | Margin vs Table 2 |
|---|---|---|---|---|---|---|---|
| 0 | 0 | 0.00 | 670.00 | 1900.00 | 1900.00 | 284% | 100% |
| 0 | 78.75 | 0.00 | 670.00 | 1900.00 | 1900.00 | 284% | 100% |
| 0 | 157.5 | 0.00 | 670.00 | 1900.00 | 1900.00 | 284% | 100% |
| 0 | 236.25 | 0.00 | 670.00 | 1900.00 | 1900.00 | 284% | 100% |
| 0 | 315 | 0.00 | 670.00 | 1900.00 | 1900.00 | 284% | 100% |
| 78.75 | 0 | 1.00 | 670.00 | 1591.25 | 665.00 | 99% | 42% |
| 78.75 | 78.75 | 0.50 | 670.00 | 1591.25 | 973.75 | 145% | 61% |
| 78.75 | 157.5 | 0.33 | 670.00 | 1591.25 | 1213.89 | 181% | 76% |
| 78.75 | 236.25 | 0.25 | 670.00 | 1591.25 | 1359.69 | 203% | 85% |
| 157.5 | 0 | 1.00 | 670.00 | 1282.50 | 665.00 | 99% | 52% |
| 157.5 | 78.75 | 0.67 | 670.00 | 1282.50 | 802.22 | 120% | 63% |
| 157.5 | 157.5 | 0.50 | 670.00 | 1282.50 | 973.75 | 145% | 76% |
| 236.25 | 0 | 1.00 | 670.00 | 973.75 | 665.00 | 99% | 68% |
| 236.25 | 78.75 | 0.75 | 670.00 | 973.75 | 742.19 | 111% | 76% |
| 315 | 0 | 1.00 | 670.00 | 665.00 | 665.00 | 99% | 100% |
Load Combinations and Reported Section Classification
The module checks the member against every load combination in the model, not a single load case. Классификация секций, and any Class 4 effective-property reduction, is repeated for each load combination. The governing stress gradient α depends on that combination’s axial force and moment, so it changes from combination to combination.
Each utility check (напряжение, сжатие, изгиб, сдвиг, combined actions) reports only its own governing load combination. That combination is whichever produces its highest utility ratio for that check. Different checks can be governed by different combinations.
The section classification and Table 2 slenderness result shown in the report do not follow this per-check governing logic. Вместо, they are taken from the load combination with the highest factored axial force, C<sub>f</sub>, across the model. This combination is not necessarily the one governing any individual utility check. A section could be reported as Class 3 based on its highest-C<sub>f</sub> combination. A different combination, with a smaller C<sub>f</sub> but a larger moment, could produce a less favourable α. That combination would classify the section as Class 4 if it were checked on its own.
