Structural Design
Fork-Mounted Jib Crane
A demountable crane for a 3-tonne forklift: boom sections, pins, lifting lugs, fillet welds and bolted joints, with manufacturing drawings, a bill of materials and a user catalogue.
Overview
What profiles, pins, welds and bolts let the crane carry the forklift's allowable load at full reach and in its worst position, with a safety factor of 4.5 on the structure and 5 on the pins?
Approach
- Allowable hook load from the forklift's rated moment; inertia loads from the forklift's accelerations.
- Principal stresses on the critical element at the pin hole, horizontal and 45° positions.
- Pins in shear and bearing; fillet welds of the lugs and plates; bolt preload and tightening torque.
Results
| Larger beam, RHS 200 × 100 × 10, Tresca at FS = 4.5 | 209.5 MPa ≤ S_y = 235 MPa |
|---|---|
| Connecting pin, double shear at FS = 5 | Ø 17.12 mm required, Ø 18 mm selected |
| Lifting-lug welds, S_all = 94 MPa | 11.31 cm required per weld, 12 cm laid |
| Base-plate bolts, class 8.8 proof load | A_t = 33.5 mm² required → M8 (36.6 mm²) |
| Smaller beam | RHS 160 × 80 × 8, 1.4 m |
| Main / connecting pins | Ø 26 / 18 mm |
| Lifting gear | 3.25 t shackle and 3 t hook |
| Bolts | 4 × M8, class 8.8, 28.67 N·m |
| Cost | 385,310,000 rials (≈ 40 million tomans) |
From the report
