Seismic member checks
The member requirements of AISC 341-22 for a W-shape beam or column of a seismic force-resisting system: the width-to-thickness limits of moderately and highly ductile members, the stability bracing of beams, the column's required axial strength with the overstrength seismic load, and strong-column weak-beam at special moment frame joints. The member's own strength under the analysis load effects is designed by the steel beam and column types.
Inputs of the seismic member #
- Member: beam or column, the W-shape, its steel and Ry (Table A3.2 unless you enter it), the ductility the system's chapter designates, and whether the member is in a moment frame (Table D1.1b Case 11 for webs) or another system (Case 13).
- Column: the dead, live and seismic axial forces from your analysis, Ω0 of the system (ASCE 7-22 Table 12.2-1), SDS for Ev, the live load factor of the seismic combination, and K and L about each axis.
- Strong-column weak-beam (SMF): the columns at the joint (the column above taken as the same shape), the beams framing in, their steel, Ze at the hinge (ZRBS for a reduced beam section) and Mv per beam from your connection design (AISC 358); an E3.4a exception as your statement.
- Beam: its axial force and the spacing of its stability bracing.
Auto-design varies the member's W-shape, lightest first, within 15 % of the given nominal depth. The loads, system, beams and bracing are kept.
Checks performed #
| Check | Basis |
|---|---|
| Flange b/t at most 0.30 or 0.38 √(E/(Ry Fy)) | 341-22 Table D1.1b Case 7 |
| Web h/tw by Ca = αs Pr/(Ry Fy Ag) | Table D1.1b Case 11 (moment frames), Case 13 |
| Column compression and tension with Ω0 QE and Ev, moments neglected | D1.4a(b); ASCE 7-22 2.3.6, 2.4.5; 360-22 E3, D2 |
| ΣM*pc/ΣM*be > 1.0, Mpr = Cpr Ry Fy Ze | E3.4a, Eqs. E3-1 to E3-3; AISC 358 2.4.3 |
| Beam bracing spacing at most 0.17 or 0.086 ry E/(Ry Fy) | D1.2a, D1.2b, Eq. D1-2 |
| Required brace strength and stiffness (note), special bracing at hinges | D1.2a(b), Eq. D1-1; 360-22 App. 6.3.1a; Eq. D1-4 |
| Protected zones (note) | D1.3 |
Limitations #
- W, S, M and HP shapes only; HSS, built-up boxes, composite members, braces and links are not covered.
- The column required strength from the system's own analysis (D1.4a(a)) and intersecting frames are your analysis.
- Connections, panel zones and splices are not designed; Mv is your entry.
- Cpr and the Appendix 6 bracing stiffness are taken as cited without the AISC 358 and 360 text read here (to confirm against the code text).
Verification examples #
Verification status: 9 values compared in 3 examples (0 published, 3 hand calculations from the cited equations): 9 within tolerance, 0 recorded deviations. No published example: every value is a hand calculation. That checks the program against this reading of the code, not the reading itself. Code basis: the provisions it uses were read in the target edition.
No published worked example of these checks is in the free library (the AISC Seismic Design Manual is not on disk): hand calculations of the cited equations.