Deflection is often the governing factor in crane runway design. The CMAA (Crane Manufacturers Association of America) and AISC Design Guide 7 recommend specific limits based on the duty cycle of the crane.
L/450: Standard limit for light to medium duty cranes (Classes A, B, C). This prevents noticeable "sag" as the load moves.
L/600: Stricter limit for heavy duty (Class D) or mill duty cranes. This minimizes wear on the mechanical trolley components.
L/800 or L/1000: Used for severe service or when tight tolerances are required for automated systems.
S-Shapes vs. W-Shapes
While Wide Flange (W) beams are more efficient for bending, American Standard (S) beams are frequently used for monorails and underhung cranes.
Why? The S-shape has a tapered flange (approx 16.7% slope) which matches the tapered tread of many standard trolley wheels. Running a tapered wheel on a flat W-beam flange effectively creates a point load on the edge of the wheel, causing rapid wear. If using W-shapes for underhung cranes, ensure the trolley wheels are "flat tread" or compatible with wide flanges.
Impact Factors (CMAA 70)
Vertical loads must be increased to account for the sudden movement of lifting. This tool applies a multiplier to the Lifted Load + Hoist Weight (but not the Bridge Weight).
Pendant/Radio Control (10-15%): Smoother operation allows for a lower impact factor.
Cab Operated (25%): Higher speeds and aggressive acceleration typically require a 25% increase in vertical load design.