Crane Load Calculator — Mill-Building Frames That Carry the Hook
Turns the crane data-sheet numbers into the loads your steel frame actually feels: maximum / minimum wheel loads, the dynamic impact coefficient (α = 1.05 soft hook, 1.10 hard hook per GB 50009-2012 §6.3.1), the horizontal braking forces that run the runway beam into the frame, and the runway beam design moment from the governing wheel arrangement. A 30 t crane is not 300 kN on the frame — it is four wheel loads, a trolley position, two braking directions and a bumped buffer, each reaching the columns at a different time.
Wheel Loads & Runway Beam Effect
Enter the crane data-sheet values. The calculation follows the handbook method of GB 50009-2012 §6.3 in its essential steps, giving the design loads for the runway beam and the frame node forces for your workshop.
Inputs — Crane Data Sheet
Design vertical wheel load for the runway beam: P = α × Pmax = 146 kN (impact included). Horizontal force acts transverse to the rail at the rail-head level and couples into the frame as a horizontal node load at the cap.
How to read the results
Pmax/Pmin come from the crane data sheet — not from the rated load divided by wheels. With the trolley parked at the extreme position (Q + G0 concentrated at one rail), that rail carries the maximum wheel load; the other rail carries the bridge weight only. The formula:
Pmax = [G0·(Lk−a) + Q·(Lk−aQ)] / (n·Lk) + Gc/(2n)
per rail, where a is the trolley's extreme position from the far rail, aQ the hook line position at the extreme, and n the number of wheel pairs on the rail — the calculator uses the handbook approximations (trolley at the buffer stop, hook line 1.5 m from the rail) with the exact same order of magnitude as the data sheet, which always wins when available.
Impact: the dynamic coefficient α = 1.05 (soft hook) / 1.10 (hard hook, meltshop) multiplies the vertical wheel loads for the runway beam and its connections — the frame columns themselves take the effect through the fatigue and the dynamic preference in the member check. The braking force H = α'×(Q+G0)/nwheels along-rail (traction) and ~ 1/10 of (Q+G0) transverse (skew) couples into the frame bracing — the bracing of a crane bay is *the* member that sizes up for crane braking, not for wind.
Mmax is the runway beam maximum moment from the governing wheel group on the beam span — the classic "wheels arranged for max moment" placement — before section selection (plastic / elastic per GB 50017) and the deflection check (L/600 for crane runway typically, L/750 for heavy cranes). This number is what the runway beam section, the cap plate, the rail fastening fatigue and the welds at the seated connection all answer to.
Crane Data Points to Feed the Calculator
| Crane (Q t) | Span Lk (m) | Trolley G0 (t) | Bridge Gc (t) | Pmax (kN) | Wheels/rail |
|---|---|---|---|---|---|
| 5 t single-girder | 10.5 – 22.5 | 0.7 | 4.5 | 45 | 2 |
| 10 t double-girder | 10.5 – 28.5 | 1.2 | 11 | 82 | 2 |
| 20 t double-girder | 10.5 – 31.5 | 3.0 | 21 | 137 | 2 |
| 32 t double-girder | 10.5 – 31.5 | 4.8 | 32 | 198 | 2 |
| 50 t double-girder | 10.5 – 34.5 | 7.5 | 52 | 268 | 4 |
| 100 t — slab / melt shop | 19 – 34 | 12 | 88 | 490 | 4 |
Indicative values for preliminary sizing over 22.5 m span typical; always use the crane supplier data sheet for final design — that is why our quotes always say "preliminary, pending crane data sheet".
Worked example: 20 t bridge crane in a fabrication shop
Q = 20 t, G0 = 3.0 t, Gc = 21 t, Lk = 22.5 m, 2 wheels per rail, soft hook (α = 1.05). Trolley parked at the extreme (a = 1.5 m from rail): Pmax ≈ [3.0×21.0 + 20×21.0] / (2×22.5) + 21/(2×2) = (63 + 420)/45 + 5.25 ≈ 10.73 + 5.25 ≈ 16 t ≈ 157 kN; Pmin = Gc/(2n) ≈ 5.25 t ≈ 51 kN. Design vertical: P = 1.05×157 ≈ 165 kN; braking H ≈ 0.1×(20+3.0) ≈ 2.3 t ≈ 22.6 kN per rail end. On a 6 m runway beam span, Mmax ≈ 370 kN·m, which selects a welded asymmetric H runway beam (e.g. 500×250×10×16) — and the column at that frame gets a horizontal node load at the cap for the braking case. The calculator reproduces exactly this arithmetic; the sample inputs above are this very crane.
Why the runway beam is the fatigue member
Every hook cycle passes the wheels over the same rail seats: the runway beam is the one member in the building designed for fatigue (GB 50017 §16 for heavy cranes), not just strength. The welded splices are located away from the peak-moment zones, the bearing stiffeners at the seats are full-depth when the wheel load demands it, and the rail fastenings are sized for the braking forces with the crush plate protecting the beam flange. When a mill building outlives its first crane upgrade, it is the runway beam that decides — detail it with the fatigue regime in mind.
Crane Loads Into the Frame — Where They Land
- Vertical wheel loads sit on the runway beam, transfer through the cap plate at the column into the column (eccentricity = half the cap-plate width produces the cap moment), and into the foundation. The cap plate and its stiffeners are a welded detail unique to crane bays — and the most common place we see fatigue cracks in older shops.
- Transverse braking force acts at the rail head; the couple it forms with the reactions at both rails enters the frame as a horizontal force at the cap — the column, the knee joint and the crane-bay bracing all answer for it. In a long bay the bracing system transfers the braking to the ground; in a short bay the columns themselves must stand it.
- Along-rail traction is taken by the longitudinal bracing at the rail level and the crane girder stops / bumpers. The end stop and the buffer force are designed for the crane at rated speed with the buffer spring — a 30 t crane bumping the end stop delivers a peak that the end-frame anchorage must resist beyond the wheel loads alone.
- Combination with other loads: the crane cases combine with dead, live, snow and wind per the governing combination rules; crane-related cases are frequent-returning (fatigue) but not all simultaneous — the frame report lists the governing combination per member, and the runway beam has its own fatigue check set.
Send us the crane data sheet (Q, G0, Gc, span, hook type, rail) — we return the runway beam section, cap detail, bracing layout and frame node loads as part of the structural budget in 24 hours.
Explore the Full Calculator Suite
Wind Load Calculator
Characteristic pressure wk with exposure classes and shape factors per GB 50009.
Snow Load Calculator
Design snow load sk = μr·s0 with drift and asymmetric cases.
Seismic Load Calculator
Base shear FEk by GB 50011 from intensity, site class and fundamental period.
Steel Weight Calculator
Theoretical weight of H-beams, pipes, plates and angles for the frame budget.
Workshop Frame Sizing
Combine the crane case with wind / snow / seismic before the member check.
Crane-Runway Workshop Design
Runway beam, cap detail, bracing and frame node loads from your data sheet.
Workshops, Mill Buildings & Crane Bays Done Right
Send us the crane data sheet and the bay layout — we return the runway beam section, the cap and seat details, the bracing layout and the frame node loads, with the fatigue regime spelled out for the live crane.
Email: market@permanentsteelstructure.com | WhatsApp: +86 18621689980 | Phone: +86 516-83269982