Tower Cranes

Nothing goes up without the crane. The whole tower — steel, rebar, concrete, glass, chillers — passes through one hook.

The machine

A steel lattice mast; a slewing ring; a horizontal jib with a trolley that runs the hook in and out; a counter-jib with concrete ballast; and an operator in a cab at the top who often cannot see the load and works by radio with a signal person on the deck. Hammerhead cranes have the fixed jib; luffing cranes raise and lower the jib to work in tight sites where the jib cannot swing over the neighbours.

How it climbs

The crane builds itself. A hydraulic climbing frame lifts the slewing unit and jib one mast section's height; a new section is slid into the gap and bolted; the frame releases; repeat. Free-standing cranes are limited by their base; beyond that they are tied to the building every few floors. Internal-climbing cranes sit inside the core and jump up through it as the core rises, then are dismantled from the roof by a smaller derrick that is itself taken down by hand.

The load chart

Every crane has a chart: the further out the trolley, the less it can lift. Wind limits stop work — typically around 20 m/s at the hook. Every pick has a weight, a radius and a plan; the rigger chooses the slings and the hitch; the signal person owns the airspace.

The rules

A certified operator (NCCCO in the US), a qualified rigger and signal person for every lift, a daily inspection, an annual inspection, and an engineer's sign-off on every tie and every climb.

The trades

Crane operator, rigger, ironworker (erecting and dismantling the crane), electrician (its power), mechanic (its service), and every trade on site that waits for the hook.

Pay

Operators earn $60,000 to $120,000; the operator on a supertall is a specialist known by name across the industry.

See it: the scale crane on the table lifts a real load. Count the picks it takes to build one floor.