Crane runway beam
A simple-span W-shape, plain or with a cap channel, under the wheels of a top-running bridge crane, by AISC Design Guide 7, 3rd Edition (2019), Chapters 11, 12 and 14, with AISC 360-22 and the crane loads of ASCE 7-22 Section 4.9. The rail and its fastening are ILX Connection's crane rail fastening, which takes the forces found here.
Inputs of the crane runway beam #
- Runway beam: the W-shape, steel, simple span, rail and electrification load, unbraced length and Cb. The guide advises simple spans. It notes that a wheel on the top flange lowers lateral-torsional buckling strength; its examples use Cb = 1.0 at the full span.
- Crane: service class, rated capacity, bridge and trolley weights, the maximum wheel load from the manufacturer (0 takes it from the weights), and the wheels on this rail by distance from the first. Two cranes list the wheels of both at their closest.
- Impact: by ASCE 7-22 4.9.3 from the service class (25 % for D to F, 10 % for A to C), or entered. The guide's Example 14.1.1 uses 25 % for a class B cab-operated crane, which is ASCE 7-16's rule. ASCE 7-22 gives 10 %, so a new calculation may read lower than the guide.
- Lateral and longitudinal forces: 20 % of capacity plus trolley, over all the wheels of the crane; 10 % of the maximum wheel load (reported for the tieback, and not combined, as the guide's procedure). The lateral force is taken equally by both rails and all wheels, and acts at the top flange. ASCE 7-22 asks for "due regard" to lateral stiffness: where the rails differ, enter accordingly.
- Cap channel: the channel, steel, and the continuous fillet each side. With a weaker cap, lateral-torsional buckling and the weak axis use its Fy (14.1 step 5).
- Code options, all yours to change:
- Weak axis strength: the guide defines Mny on the top flange area; Example 14.1.1 reads the whole section's from a Manual table. The top flange is prefilled, the guide's definition and the lower of the two.
- Cr in web sidesway buckling: AISC 360-22 J10.4 defines My about the axis of bending, Fy Sx. The guide's examples use Fy Sy, which gives half the strength. The specification is prefilled.
- Deflection limits: the guide's span/600, 800, 1,000 by class and span/400 laterally, as entries.
- Fatigue: nSR by class (Table 11-1) or entered, and the tension flange's stress category. One crane passage can be several cycles (11.1): your value.
Auto-design varies the W-shape, lightest first, with optional depth limits, and the steel when unlocked. The cap channel, crane and span stay as you entered them.
Checks performed #
| Check | Basis |
|---|---|
| Wheel position | Largest moment under a wheel: every wheel and run of wheels on the span, midspan midway between the wheel and the resultant (14.1 step 2) |
| Tension flange, with impact | Eq. 14-1; Mn by F2, or Fy S1 with a cap (Eq. F5-10) |
| Compression flange, no impact, with Mry | Eq. 14-1; Mn by F2, or F5-1, F5-2 with a cap; Mny as selected, or Fy Zyt with a cap |
| Shear, with impact | AISC 360-22 G2 |
| Web sidesway buckling, under one wheel with impact | J10.4; does not apply past the slenderness limit |
| Cap channel weld | q = V Q / I, half each side, against J2.4; minimum size Table J2.4 |
| Vertical and lateral deflection | No impact; lateral on the top flange (half the Iy) or on the top flange and channel |
| Fatigue, tension flange | Appendix 3 Eq. A-3-1 on the wheel moment without impact (AIST TR-13 3.10.2.3, through the guide); peak stress 0.66 Fy; none at or below 20,000 cycles |
| Fatigue, cap weld | Eq. A-3-2, category F, shear on the throat |
| Cap on class E or F | An advisory: the guide says not to use them |
Limitations #
- Simple spans and W-shapes only; plate girders and continuous runways are not covered.
- The rail and its fastening, tiebacks, stiffeners and stops are not designed. Web local yielding and crippling under a wheel (J10.2, J10.3) are not checked. The guide's procedure does not list them either.
- Dead load moment and wheel moment add at their own maxima, as the guide does: slightly on the safe side.
- The AIST TR-13 load combinations and its increased lateral load at the top of the rail are not included. The guide offers them where the owner requires them; TR-13 itself is not on our shelf.
- Fatigue covers the tension flange and the cap weld. Compressive fluctuation is not counted, and the guide's warnings on web-to-flange and stiffener details belong to plate girders.
- J10.4 is written for one concentrated force. The guide says the criterion does not address several wheels, and knows of no problems from this use.
- Wheels are equal, and the same lateral force is used on each.
Verification examples #
Verification status: 62 values compared in 5 examples (4 published, 1 hand calculations from the cited equations): 54 within tolerance, 8 recorded deviations. Code basis: the provisions it uses were read in the target edition.
AISC Design Guide 7, 3rd Edition, Examples 14.1.1 to 14.1.4, on the Verification page with their pages. The examples run with the guide's own choices, as inputs: 25 % impact, whole-section Mny in 14.1.1, My = Fy Sy, and 50 ksi on the cap channel. Example 14.1.3 names an A36 cap and uses 50 ksi on it, against its own step 5.
Where we differ, documented on the Verification page:
- Lr with a cap channel. AISC 360-22 F5-5 gives 407 in. The guide's Table A-2 prints 457 in., which is Eq. F4-8, and puts it in Eq. F5-3. This calculation follows F5 and comes out 5 % lower on the lateral-torsional buckling moment, on the safe side. It reproduces the table's 457 in. by F4-8 as a separate value.
- Rounding. Example 14.1.1 rounds the slenderness ratio to 1.28 before cubing it, and Example 14.1.3 rounds 3,470 / 1.67 to 2,100 kip-in.: about 1 %.
- Weld shear in Example 14.1.3. It adds 75.0 and 2.74 kips where it found 76.2 kips: the weld demand stays within 1 %, as tested.
No published example: two cranes, fatigue, the weaker cap channel, by hand (tests/test_crane_runway.py). A worked fatigue example is in Fisher and Van de Pas (2002), which is not on our shelf.