Steel section selection
Finds the lightest rolled W-shape that passes every check of a steel beam or a steel column calculation, optionally within a maximum depth and a list of nominal depths, and lists the lightest few passing shapes with their governing ratio.
Inputs of the section selection #
- Selection: beam or column; the steel (A992, A572 Gr. 50, A913 Gr. 65, A36); the maximum actual depth d (0 = no limit); the acceptable nominal depths in the US designation (W14 = 14, also for the metric W360), blank for any; how many passing shapes to list.
- Beam inputs: the inputs of the steel beam (length, supports, line and point loads, self-weight, bracing, Cb, deflection limits); see Inputs of the steel beam.
- Column inputs: the inputs of the steel column (lengths and K factors, loads, second-order effects, Cb, tension connection); see Inputs of the steel column.
Auto-design: the selection is itself the auto-design search of the steel beam or steel column (the same W-shape candidates, prefilter and weight objective; see Auto-design), so this calculation has no separate Auto-design button. To let auto-design vary the steel grade or use the depth objective, open the selected shape as a steel beam or steel column calculation.
Checks performed #
| Check | Basis |
|---|---|
| A W-shape passes | Each candidate is designed by the steel beam or steel column calculation itself, every check included |
| Checks of the selected shape | Exactly the checks of a steel beam or steel column calculation of that shape |
| Search | The auto-design search of the steel beam or steel column: candidates prefiltered by necessary properties from a reference design (beam: Zx from the flexural demand and Ix from the deflection ratio; column: Ag, Zx, Zy), with a 15 % margin for the self-weight change; designed lightest first (equal weights: shallower first) |
The key results list the selected shape and the lightest passing shapes (weight, depth, governing ratio and check), weight and depth in the units of the calculation (plf and in., or kg/m and mm). The diagrams are those of the selected shape.
Drawings #
The drawing sheet of the selection is the sheet of the selected shape exactly as the steel beam or steel column calculation draws it (elevation, section and diagrams), with a note that the shape is the lightest W-shape that passes every check within the depth limits, and the next lightest passing shapes listed as alternates in the design summary. Nothing is drawn when no shape passes.
Limitations #
- W-shapes only (the shapes the beam calculation designs). HSS and pipe columns are designed one at a time in the steel column calculation.
- At most 1,500 designs per selection (the auto-design evaluation cap, more than there are W-shapes, so every candidate within the limits can be designed). There is no time limit: the same input always selects the same shape. When no candidate passes the result is not feasible and says how many shapes were designed.
- Weight is the only criterion; depth, availability and connection needs are the engineer's.
Verification examples #
AISC Design Examples v16.0 selection examples, LRFD and ASD:
| Example | Selection | Published | ILX Calcs |
|---|---|---|---|
| F.1-1A | Beam, 35 ft, nominal depth ≤ 18 in., live load L/360 | W18×50, φMp = 379 kip-ft | W18×50, 378.8 |
| F.4 | Beam, 30 ft, live load deflection 1.00 in. (L/360) | W24×55, φMp = 503 kip-ft | W24×55, 503.1 |
| E.1A | Column, W14, pinned, 30 ft | W14×132, φcPn = 893 kips | W14×132, 893.2 |
Selections read from the AISC Steel Construction Manual, 16th Ed. (the lightest tabulated shape that covers the required strength, LRFD and ASD):
| Table | Selection | Published | ILX Calcs |
|---|---|---|---|
| 3-2 (p. 3-25) | Beam, 30 ft, continuously braced, Mu = 405 / Ma = 270 kip-ft | W21×50, φbMpx = 413, Mpx/Ωb = 274 kip-ft | W21×50, 412.5, 274.5 |
| 4-1a (p. 4-16) | W14 column, Lc = 20 ft, Pu = 1,400 / Pa = 938 kips | W14×145, 1,470 / 980 kips | W14×145, 1,473 / 980.0 |
| 4-1a | W14 column, Lc = 16 ft, Pu = 1,000 / Pa = 675 kips | W14×99, 1,080 / 716 kips | W14×99, 1,077 / 716.3 |
A behaviour test designs every lighter shape within the limits and confirms that each fails, so the selection is the lightest.