An overhead bridge crane is a long-term investment. If undersized, it quickly becomes a bottleneck as load requirements change. If oversized, you pay for unused capacity. Proper sizing requires evaluating several interdependent variables and understanding the impact of errors in any of them.
Start With Rated Capacity — But Don't Stop There
Rated capacity is the maximum load the crane can lift. Use your heaviest anticipated load, not the average, as the starting point. Be sure to include the weight of rigging hardware, below-the-hook attachments, and the hoist in your calculation.
Standard practice is to include a buffer. For example, if your heaviest lift is 4,000 lbs, specify a 5-ton crane instead of a 2-ton model. This allows for future load increases, reduces routine operation near maximum capacity, and provides flexibility for additional attachments.
Consider the duty cycle. Cranes lifting near rated capacity frequently require a higher duty classification than those used for occasional light lifts. CMAA duty class ratings from A to F define the appropriate structural and mechanical specifications for your usage.
Span
Span is the horizontal distance between the rails on which the bridge crane travels. It determines the width of the coverage area. Measure the distance between the centerlines of the runway rails to determine the specified span.
Headroom, column locations, building structure, and required work area all influence your span. Longer spans need heavier bridge beams to limit deflection. Excessive deflection can cause the crane to roll toward the center under load, a condition that cannot be corrected without replacing the beam.
Spanco workstation bridge cranes offer spans and bridges up to 40 feet, enabling a single crane to cover large production areas. The ProTek workstation crane lineup features Spanco trussed bridge systems designed for various spans and capacities to suit different facility types.
Lift Height
Lift height is the distance from the floor to the maximum hook position. Account for your tallest load at its highest point, any fixtures or attachments below the hook, and include a safety margin above the tallest anticipated load.
Common errors include specifying lift height only from the floor to the highest hook position without considering load height, or overlooking pallets or fixtures below the hook block. For example, if a 60-inch-tall load must clear a 54-inch-tall machine, the required hook height is at least 114 inches, not 60.
Headroom
Headroom is the distance from the top of the rail to the underside of any overhead obstruction, such as the roof structure, lighting, or HVAC runs. This measurement determines which hoist and bridge configurations will fit in your building.
Low headroom configurations are available for buildings with limited clearance. Standard hoists need more vertical clearance between the rail and the roof structure than low-headroom models. If your building has limited headroom, specify a low headroom or underhung configuration during initial planning rather than retrofitting later.
Building Structure and Installation Limitations
For ceiling-mounted runways, the building structure must support the crane's load, its own weight, and applicable dynamic load factors. A structural engineer should evaluate the building before installing any overhead crane.
Freestanding systems, such as Spanco's workstation bridge cranes, are installed on columns anchored to engineered floor foundations. These systems do not rely on the building structure but require assessment of the floor slab and may need additional concrete work.
Planning for Future Expansion
Plan runway length with future expansion in mind. If your work area may grow, installing longer runways now is more cost-effective than extending them later. The same applies to capacity; if you may add a heavier hoist in the future, size the bridge beam and runway accordingly from the start.
ProTek Crane Solutions can help you work through these variables for your specific facility. Explore our full crane and workstation crane catalog or contact our team for sizing guidance.