Special Structures
Crane Runway Beams for Pre-Engineered Steel Buildings
Definition: A crane runway beam is a steel girder that runs the length of a building on brackets or columns and supports the rail of an overhead traveling crane, carrying wheel loads, lateral surge and longitudinal braking forces from the crane into the building frame and foundations.
Key facts
- Supports top-running bridge cranes on a rail, or underhung and monorail cranes on the bottom flange.
- Loads are moving and repeated, so fatigue is a core design check alongside strength and deflection.
- Crane class, capacity, span, wheel loads and duty cycle come from the crane supplier.
- Longitudinal crane forces need a dedicated bracing path to the foundations.
Role in the structure
Crane wheels apply moving vertical loads, impact, lateral thrust and longitudinal forces to the rail. The runway beam carries these along the building to brackets or crane columns, which pass the vertical load to the main frame columns or to separate crane columns. Lateral forces are taken by the main frames or by surge girders, and longitudinal forces are taken to the ground by crane bracing in the braced bays.
How do overhead cranes load a pre-engineered building?
An overhead crane applies its own weight, the lifted load and a dynamic allowance through its wheels. As the trolley travels across the bridge and the bridge travels along the runway, the wheel loads move, so every point on the runway sees repeated loading during the life of the building.
The crane also pushes sideways when the trolley accelerates or brakes and pushes along the building when the bridge brakes. These horizontal forces are smaller than the vertical loads but act at rail height, high on the columns, which makes them significant for column bending, frame drift and bracing.
Types of runway beams and supports
For lighter cranes, runway beams are often rolled or built-up I-sections sitting on brackets welded or bolted to the main frame columns. Heavier or high-duty cranes may use a cap channel or plate on the top flange, built-up girders with a wider top flange, or separate crane columns placed beside the main columns.
Underhung cranes and monorails hang from the bottom flange of a runway beam that is suspended from the roof structure. In that case the rafters and their connections must be designed for the crane loads, and the bottom flange is checked for local bending under the wheels.
Fatigue, deflection and alignment
Because a crane passes many times over each detail, welds, stiffeners and rail attachments must be detailed to avoid fatigue cracking. Continuous fillet welds, smooth transitions and avoidance of abrupt changes in section are typical good practice, and the required detail categories are set by the governing code.
Vertical and lateral deflection limits for runway beams are usually stricter than for other members so that the crane runs smoothly and the wheels do not bind. Rail alignment, rail splices and the gauge between runways must also be held within the tolerances given by the crane supplier and the applicable code.
Rails, clips and end stops
The crane rail is fixed to the top flange with clips or clamps that hold it in line while allowing for adjustment and replacement. Elastomeric pads may be placed under the rail to reduce noise and spread wheel loads.
End stops at each end of the runway are designed to absorb the impact of the crane bridge, usually with buffers. Conductor rails or festoon systems for crane power, walkways for maintenance and access ladders are coordinated with the runway layout.
Materials & coatings
- Hot-rolled or welded plate girder sections in structural steel grades to the specified code family
- Cap channels or reinforcing plates on the top flange where lateral loads are high
- Crane rails, rail clips, elastomeric pads and end stop buffers from the crane or rail supplier
- High-strength structural bolts for bracket and splice connections
Design considerations
- Obtain crane capacity, span, wheel loads, wheel spacing, class and duty from the crane supplier.
- Design for vertical impact, lateral surge and longitudinal braking forces as required by the code.
- Check fatigue at welds, stiffeners, bracket connections and rail attachments.
- Apply strict deflection limits and frame drift limits at rail level.
- Provide crane bracing to carry longitudinal forces to the foundations.
- Coordinate future crane upgrades so the runway and frames have spare capacity if needed.
Fabrication
- Girders are welded with continuous welds where fatigue design requires them and inspected to the specified level.
- Bearing stiffeners and bracket seats are fitted square to give full contact.
- Holes for rail clips and splices are drilled to template to maintain alignment.
- Camber, sweep and flatness of the top flange are checked before dispatch.
Erection
- Install runway beams after the main frames are plumbed and bracing is complete.
- Shim and align beams to achieve the specified gauge, level and straightness.
- Install rails, clips and pads, then fit end stops before the crane is commissioned.
Inspection & quality
- Survey rail gauge, elevation and straightness along the full runway length.
- Inspect welds at bracket and stiffener locations by the methods the specification requires.
- Verify bolt tightening at brackets, splices and crane bracing.
- Re-inspect connections and rail clips periodically during building use.
What to include in your RFQ
- Crane type: top-running, underhung, monorail or jib.
- Rated capacity, crane span and required hook height.
- Crane class or duty and expected number of cycles.
- Wheel loads and wheel spacing if the crane is already selected.
- Runway length, number of cranes per runway and any future capacity.
- Who supplies rails, stops and power conductors.
3D model & IFC of this component
Rotate the model, isolate the component and download its IFC4 file for your BIM coordination model.
IFC entity: IfcBeam. Illustrative geometry for coordination and learning. Final member sizes come from the project design.
Frequently Asked Questions
Can an overhead crane be added to a building later?
Only if the frames, foundations and bracing were designed for it or can be strengthened. Crane loads are significant, so a structural check by a qualified engineer is required before any crane is added.
Why are runway deflection limits so strict?
Excess deflection causes the crane to run uphill, wheels to bind and rails to wear quickly. Tight limits help the crane run smoothly and reduce maintenance.
Who designs the crane runway: the building supplier or the crane supplier?
Practice varies by project. Commonly the building supplier designs the runway beams and frames using crane data from the crane supplier, who supplies the crane, rails and end stops. Responsibilities should be stated in the contract.
Engineering content is general guidance. Every World Steel building is designed by qualified engineers to the code and loads of the project.
