Crane runway beams and brackets

What a crane runway system is

A crane runway is the pair of longitudinal beams, with rails, on which an overhead travelling crane moves along the building. In a pre-engineered building the runway beams normally sit on crane brackets welded or bolted to the rigid frame columns, or on separate crane columns or stepped columns for heavier cranes. The runway carries vertical wheel loads, lateral (side-thrust) forces from trolley movement, and longitudinal forces from crane acceleration and braking into the frames and the longitudinal bracing. Because these loads are repeated many thousands of times, runway design is governed by fatigue and serviceability as much as by strength. See crane buildings for the whole-building concept.

Crane types and how they load the building

The type of crane decides where the loads enter the structure and which members must be designed for them. Clarify the crane type with the owner and the crane supplier before the frames are designed.

Underhung and monorail systems are attractive in PEB because they avoid brackets and keep the floor clear, but they load the rafters directly. Their suspension points should be agreed early so that the rafters, flange braces and connection plates are designed for them rather than reinforced later.

Crane classes and load allowances

The crane's service class defines its duty and drives the fatigue design. In North America, top-running cranes are classified per CMAA 70 (multiple-girder) and CMAA 74 (single-girder) from Class A (standby) to Class F (continuous severe service). Australia uses AS 1418.1 and AS 1418.18, and Europe uses EN 1991-3 with crane classes per EN 13001 / ISO 4301.

Other codes use dynamic factors that depend on hoisting class and speed; the principle is the same but the values differ, so runway design must follow the code of the project location.

Classes from different systems do not map exactly to each other. For runway design, the structural engineer needs the crane supplier's data sheet: rated capacity, bridge and trolley weights, maximum and minimum wheel loads, wheel spacing, hook approach, speeds and the classification under the code that will be used for the building.

Beam and bracket types, sizing rules of thumb

• Runway beams: hot-rolled I-beams for light cranes; built-up plate girders, often with a channel cap or wider top flange to resist lateral loads, for heavier cranes. Simply supported spans equal to the bay spacing simplify fatigue design.
• Brackets: welded built-up or hot-rolled cantilever brackets on the frame column, commonly used for light to medium cranes (often up to about 10–20 t capacity, depending on span and duty).
• Stepped or independent crane columns for heavier cranes, high duty classes or where frame drift must be tightly controlled.
• Depth: runway beams are often in the range span/8 to span/12 for preliminary sizing, then checked for deflection and fatigue.
• Deflection: typical vertical limits are span/600 (CMAA Class A–C), span/800 (Class D) and span/1000 (Class E–F); lateral span/400 (AISC Design Guide 7).
• Frame drift at runway level: commonly about H/100 for pendant-operated and H/240 for cab-operated cranes (AISC Design Guide 3).

Rails, connections and fatigue detailing

Rails (ASCE or DIN/JIS profiles, or square bar for light cranes) are fixed with adjustable clips that allow alignment and permit replacement. Elastomeric pads reduce noise and wear. Runway beams are connected to brackets with bolts in slotted holes for alignment, and the top flange is tied to the column with a flexible connection that transfers lateral load but allows end rotation – rigid ties crack under fatigue. Welds subject to repeated stress, such as web-to-top-flange welds, should be complete joint penetration or properly sized fillets per the fatigue category, and stiffener ends should be detailed to avoid stress concentrations. End stops, conductor bar brackets and walkway supports are part of the runway package. Welding follows AWS D1.1, AS/NZS 1554.1 (with SP category where specified) or EN 1090-2 with execution class as specified – see connection design.

Erection tolerances and maintenance

Runway alignment is critical to crane performance: span between rails, rail straightness, level and step at joints must meet the crane manufacturer's and code tolerances (for example CMAA 70, AS 1418.18 and EN 1090-2 tables). Survey the runway after erection and before crane commissioning, and periodically thereafter. Inspect bolts, rail clips, end stops and welds for fatigue cracks; see erection tolerances.

World Steel fabricates runway girders, brackets, stops and rail fixings as part of its crane runway packages, designed together with the primary frame for the supplied crane data.