Plate girder
A simply supported welded I-girder from its plates, to AISC 360-22: flexure (F4 or F5 with Rpc or Rpg), shear panel by panel with tension field action in interior panels, the intermediate stiffeners' rigidity, the bearing stiffeners at the supports, the flange-to-web welds, the proportion limits and the deflection.
What it adds over the steel beam. The steel beam's built-up I already has F4 / F5 flexure, G2 shear with tension field action, the G2.4 stiffener rigidity and the F13.2 limits (the same library). The plate girder adds the girder laid out panel by panel from the stiffener positions, each panel against its own required shear (end panels by G2.1), each stiffener's G2.4 rigidity with its own ρw, the bearing stiffeners (J10.8 column and J7 bearing, for what the web lacks or the full reaction), the flange-to-web welds for VQ/I, Cb on the governing unbraced segment and the deflection.
Inputs of the plate girder #
- Girder: the span, the web (h × tw) and the two flanges, the steel (A572 Gr. 50 or A36 plates).
- Loads and bracing: uniform and concentrated loads by type (ASCE 7-22 combinations), the girder's weight as dead load if D does not include it, the brace spacing of the compression flange (0 when braced continuously), Cb computed (Eq. F1-1 on the governing segment) or entered.
- Intermediate stiffeners: their positions from each support (mirrored about midspan; none for an unstiffened web), tension field action in interior panels, width, thickness, pairs or single, steel.
- Bearing stiffeners and welds: the bearing stiffener pair at each support, its corner clip, the bearing length, and whether it is sized for what the web lacks (J10) or the full reaction (your choice); the flange-to-web fillet size and FEXX; the deflection limit L/n on total or live load (your limit).
Auto-design varies the web and flange thicknesses, lightest first (equal flanges stay equal). Depth, widths, span, loads, stiffeners and bracing are kept.
Checks performed #
| Check | Basis |
|---|---|
| Flexure, compression flange yielding, LTB, local buckling, tension flange yielding | 360-22 F4 (Rpc) or F5 (Rpg); Cb by F1-1 |
| Proportion limits Iyc/Iy, aw, h/tw | F13.2 |
| Shear of each panel; interior panels with tension field action when a/h ≤ 3 | G2.1, G2.2 (Eqs. G2-6 to G2-8) |
| Intermediate stiffeners: (b/t)st, Ist with ρw | G2.4, Eqs. G2-16 to G2-19 |
| Bearing stiffeners as a column (two plates and a 12 tw strip, Lc = 0.75 h) | J10.8, J4.4 |
| Bearing of the fitted stiffeners | J7, Eq. J7-1 |
| Bearing stiffener thickness and width-to-thickness | J10.8(b), Table B4.1a |
| Flange-to-web welds for q = V Q/Ix, minimum size, web base metal | J2.4, Table J2.4, J4.2 |
| Deflection at most L/n | Your limit |
Limitations #
- Simple spans only; continuous girders, cover plates and holes in the tension flange (F13.1) are not covered.
- G2.3 (tension field action in end panels, new in 2022) is not built: end panels are taken by G2.1, as Design Examples G.8A and G.8B do.
- The web under concentrated loads is the concentrated forces type; stiffener welds, splices, fatigue and the bracing's design are not part of this calculation.
- The deflection is the midspan value of the superposed loads.
Verification examples #
Verification status: 16 values compared in 3 examples (2 published, 1 hand calculations from the cited equations): 16 within tolerance, 0 recorded deviations. Thin: only 2 published examples. Code basis: the provisions it uses were read in the target edition.
AISC Design Examples v16.0 F.14 (flexure, shear, weld shear flow, deflection) and G.8B (end and second panel shear with stiffeners at 42 and 132 in.). The stiffener rigidity and bearing stiffener values are hand calculations.