A construction jack is a mechanical lifting tool that raises, holds or moves heavy loads with relatively little applied force. On site it is used to support beams, jack up buildings or position heavy elements. The device is also called a screw jack, hydraulic jack or simply jack.
How it works
A jack relies on force multiplication:
- Rack jack — a vertical rack is driven upward by a pinion gear. A long lever multiplies the operator’s force
- Screw jack — a large nut is turned over a vertical screw spindle, rising as it turns
- Hydraulic jack — a hand pump forces oil into a cylinder, pushing a piston with the load upward
A typical jack lifts 5 to 50 tonnes; industrial hydraulic versions go to hundreds of tonnes.
Use in construction
Construction jacks are essential for many jobs:
- Foundation repair — buildings with subsidence are lifted to install new supports
- Beam work — a sagging joist is brought back into position
- Moving heavy elements — concrete or steel beams are shifted centimetre by centimetre
- Heritage restoration — entire buildings are lifted to renew the foundation
- Bridge construction — for positioning girders onto abutments
Points to consider
- Stable base — the jack must stand on a flat, solid plate
- Safety stops — always add timber blocks or struts beneath the load
- Lift straight — angled loading can cause tipping
- Rated capacity — never exceed the maximum load
Related terms
- Screw jack
- Shoring
- Jacking up
- Foundation repair
- Winch
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