The span of an overhead crane is the horizontal distance between the centerlines of the two runway rails. It is a critical parameter that determines working coverage, prevents rail gnawing, and avoids structural interference.

1. Definition

Span $S$ (meters) = perpendicular distance between the left rail centerline and the right rail centerline.

2. Standard Formula

S = L - 2a

S=L−2aS=L−2aWhere:

• $L$ = Clear inside width of the building (between inner edges of columns), in meters

• $a$ = Safety margin from rail centerline to column inner edge (includes rail clamp, bumper, and clearance), typically 0.2 m – 0.5 m

Example: 

$$L=20\; m、a=0.3\; m、S=20-2\times 0.3=19.4\; m$$

3. Practical Adjustments

4. Step-by-Step Engineering Calculation

1. Measure accurately: Clear width $L$ between inner column edges (±10 mm). Do not use building axis distance.

2. Determine safety margin: Per GB/T 14405, $a\ge 200\text{mm}$.

3. Calculate preliminary span: $S=L-2a$.

4. Round to standard span: Refer to standard series (10.5, 13.5, 16.5, 19.5, 22.5, 25.5, 28.5 m, etc.). Select the nearest value not less than calculated $S$ (tolerance ±10 mm).

5. Final check: Minimum clearance from hook to column inner edge ≥ 100 mm.

5. Key Warnings

• ❌ Never use building axis distance instead of clear width $L$ (axis passes through column center).

• ❌ For outdoor cranes, ignore building dimensions – measure actual rail centerlines on site.

• ✅ For retrofits, directly use existing rail centerline distance as span.

Accurate span calculation eliminates rail gnawing, dead zones, and girder-column interference. Always have the crane manufacturer validate dimensions on site before final fabrication.