Construction Transport Platform

Overview

A construction transport platform, usually called a construction hoist or rack-and-pinion hoist, is a temporary lift fixed to the outside of a building under construction. It carries crew, tools, and materials between the ground and the working floors. On a tall building this is the workhorse of vertical logistics: a single or twin car climbing a tied mast at the edge of the structure, serving every floor as the building rises.

The hoist differs from a passenger lift in that it climbs a rack with pinions rather than hanging on ropes from a machine room, so it needs no overhead headroom and the mast simply extends as the building grows. Car capacity runs from about 1.5 t on a single car to over 3 t on large cars, carrying 12 to 20 people or a loaded material trolley. Travel speed is 24 to 65 m/min depending on the duty.

Base Enclosure

The Base Enclosure is the boarding station at ground level. Its Anchored Base Frame welded base is bolted to a concrete pad and anchors the mast. A Perimeter Mesh Fence mesh fence encloses the ground area so nobody can walk under the descending car, with access only through an Interlocked Entry Gate interlocked gate that the car cannot move past unless it is closed. A Loading Ramp loading ramp bridges the gap so trolleys roll on and off, and Bottom Buffer buffers at the base absorb the car if it ever overruns the bottom stop.

Tower Mast

The Tower Mast is built from bolted Mast Section lattice sections joined with Mast Section Bolt high-tensile bolts. Each section carries a Climbing Rack Strip hardened rack down one face, and the mast is built up from the car as the building grows: the crew rides to the top, adds a section and its rack, and the car climbs onto it. Because a tall mast cannot stand freely, Building Tie Frame tie frames anchor it to the structure every 6 to 9 m. The ties carry wind load and the bending the eccentric car load creates, so their design and anchor capacity are checked for each installation.

Transport Platform Car

The Transport Platform Car is the cage that climbs the mast. Its Car Structural Frame welded frame carries an anti-slip Anti-Slip Car Floor floor sized for trolleys and pallets, Mesh Side Wall mesh side walls, and a Protective Roof roof to protect crew from falling objects. Car Access Gate interlocked gates at each end prevent the car moving unless they are closed and aligned to a landing. Eight Mast Guide Roller guide rollers run on the mast to hold the car square under an off-centre load such as a stack of board at one end.

Rack-and-Pinion Drive

The Rack-and-Pinion Drive sits on the car. Two Drive Motor motors drive two Drive Gearbox gearboxes, each built from a Gearbox Housing casting, a Helical Gear Pair reduction, Ball Bearing bearings and an Oil Seal seal. Each gearbox turns a Climbing Pinion case-hardened pinion that meshes with the mast rack and walks the car up and down. Motor Brake spring-applied brakes hold the car at any landing on power loss.

The critical safety element is the Overspeed Safety Gear overspeed governor. It is an independent centrifugal device geared to the mast: if the car ever moves faster than its rated speed in either direction, the governor grips the rack and arrests the car mechanically, regardless of what the motors or brakes do. This is what makes a rack-and-pinion hoist safe to carry people without a rope and counterweight.

Landings and Access

The Landing Gates & Stops hardware gives safe access at every floor. Each level has a Interlocked Landing Gate interlocked landing gate that opens only when the car is present and stopped at that level, and a Landing Access Frame access frame bridging the building edge to the car deck. Levelling Cam levelling cams on the mast trigger the slow-down and stop so the car floor lines up with the landing. Final Limit Switch final limit switches cut power if the car ever passes the top or bottom of the intended travel.

The interlock chain is the heart of the safety case: the car cannot move unless every car gate, base gate and the relevant landing gate is closed, and a landing gate cannot open unless the car is there.

Control and Power

The Control & Safety System system manages calls and watches the interlocks. A Car Control Panel in the car selects the destination level; Landing Call Station call stations at each landing summon the car; a Control PLC PLC manages calls, levelling and the interlock chain; a Overload Sensor overload sensor blocks departure if the car is loaded past its rating; and Emergency Stop emergency stops cut all drive power.

Power reaches the car through the Electrical Supply system. A Power Supply site supply unit feeds a festooned Trailing Supply Cable that pays out as the car climbs, managed by a Cable Guide Collector guide collector, with Wire Bundle internal wiring and a Residual-Current Device residual-current device breaking supply on earth fault. Working wind limit is typically 20 m/s, above which the hoist is parked because the car and mast present a large sail area at height.