Choosing Grúa Span and Lifting Height: The Two Numbers That Decide Whether Your Grúa Fits
Most crane buyers start with capacity — "I need 10 tons" — and treat span and lifting height as details to confirm later. In practice, span and hook height are the numbers that determine whether a crane physically fits your building, and getting them wrong is far more expensive to fix than getting capacity wrong. This guide covers how to specify both correctly, and where buyers most often lose clearance.
Span: Not the Same as Your Building Width
Span is the centre-to-centre distance between the crane runway rails, not the clear width of your building. For a top-running overhead crane, the relationship is:
- Span = building clear width − 2 × (rail offset + runway beam flange + clearance)
- Typical allowance: 500–750 mm per side for buildings up to about 30 m span
For an LD single-girder crane (0.5–20 t), the girder sits on top of the runway beams, so you need headroom above the rails. For an LH hoist double-girder (5–50 t) or QD universal double-girder (5–150 t), the end carriages sit on the rails and the hook travels between the two girders — this changes both the approach dimension and the required headroom.
Two practical checks before you commit:
- Measure the actual clear width between columns, not the nominal building width. Bracing, cable trays and sprinkler pipes all reduce usable span.
- Confirm the rail gauge with a laser or steel tape at several points along the runway. Runway beams installed out of parallel by more than about ±10 mm over the span will cause wheel flange wear and skewing.
Hook Height and the Approach Dimension
Altura de elevación (hook height) is the vertical distance from the floor to the hook saddle at its highest position. It is not the same as your building height, because you must subtract:
- Grúa structure depth (girder height plus end carriage)
- Hoist body height above the hook
- The approach dimension — the minimum horizontal distance from the hook centre to the face of the runway rail when the trolley is at its extreme position
The approach dimension is the number that catches people out. On a QD double-girder crane, the hook cannot reach the last 1–2 m of the building on each side because the trolley must stop before the end carriage. If your process requires lifting a load at the far wall — loading a truck bay, for example — you need either a longer span, a cantilever extension, or a jib crane (BZD pillar or BX wall-mount) to cover the dead zone.
For a 20 t QD crane with a 22.5 m span, a typical approach is around 1,500–2,000 mm per side. For an LD single-girder 5 t crane, it is closer to 800–1,200 mm. Always ask for the approach dimension on the specific model, not a rule of thumb.
Building Fit: Headroom, Wheel Load and Clearance
Three building-side constraints decide whether the crane can be installed at all:
- Headroom: For a top-running crane, the top of the girder plus the rail height must clear the lowest roof truss or purlin. If headroom is tight, consider an underslung or low-headroom configuration, or a gantry crane (MH single-girder or MG double-girder) running on ground-level rails.
- Wheel load: The maximum wheel load is not simply total weight ÷ 4. It depends on span, trolley position and dead weight. A 50 t MG gantry crane can impose 250–350 kN per wheel on the runway. Your runway beam and column foundations must be designed for this — check with a structural engineer before ordering.
- Side clearance: For grúas pórtico, the leg clearance and the rail gauge determine how close the crane can travel to walls or stockpiles. For RMG rail-mounted container cranes, the rail gauge and cantilever overhang are fixed by the container handling geometry.
Matching Span and Height to Grúa Tipo
Different crane families have different practical span ranges:
- LD single-girder (0.5–20 t): spans normalmente 7.5–22.5 m; best for light workshops with moderate headroom.
- LH hoist double-girder (5–50 t): spans 10.5–31.5 m; better hook approach and higher duty cycles than LD.
- QD universal double-girder (5–150 t): spans 10.5–40 m; the standard choice for heavy fabrication and steel mills.
- YZ metallurgical (5–125 t): spans matched to the ladle bay; designed for high temperature and heavy duty.
- MG double-girder gantry: spans 18–35 m; used where no runway building exists.
If your span requirement falls between standard models, do not simply round up — a longer span increases wheel load, girder weight and cost. Sometimes a smaller span with a transfer car or a jib crane at the end bay is cheaper and more practical.
What to Enviar for an Accurate Quote
To get a correct span and hook height recommendation, send:
- Building clear width between columns, and the rail gauge if runways exist
- Floor-to-lowest-obstruction height, and the required hook height
- Maximum load weight and the load's dimensions
- Duty cycle (how many lifts per hour, shifts per day)
- Any hazardous environment — dust, heat, humidity, explosive atmosphere
Chunhua Grúa supplies 81 standard models across five categories, built to GB/T 3811 with FEM 1.001, DIN 15018 or CMAA #70 on request, using Q345B/Q235B steel and Schneider, Siemens, ABB or SEW components. Certificaciones include CE, CCC, EAC (TR CU 010/020), GCC/SASO, SONCAP and KEBS. There is no MOQ, quotes are returned within 4 hours, production runs 30–45 days, and every crane carries a 12-month warranty.
Enviar your building dimensions and load data to WhatsApp +86 193 9277 7259 or yuhua0095@gmail.com and we will confirm the correct span, hook height and approach dimension for your bay before you commit to a runway design.