NCCER Tower Crane key terms

The load per unit area that a crane's foundation, mats, or track imposes on the soil beneath. It must stay below the soil's allowable capacity to prevent settlement, tipping, or collapse during lifting and travel.

The engineered support beneath a tower crane, such as a reinforced concrete pad, pile cap, or ballasted base, designed to carry vertical, moment, and shear loads. It must be designed for the specific crane and verified by a qualified person before erection.

Embedded or cast-in fasteners that secure the crane's base section or mast to its foundation. Their size, grade, embedment, and torque are specified by the manufacturer and must be inspected and verified before erection and climbing.

The horizontal distance from the crane's slewing center to the outermost point of the crane or load as it rotates. Operators and planners use it to keep the jib, counter-jib, and suspended loads clear of structures, power lines, and other cranes.

Electronic or mechanical devices that warn or stop crane movement when a crane approaches a preset limit, another crane, or a structure. They supplement, but never replace, the operator's judgment and the site's lift plan.

The manufacturer's table or graph giving the maximum allowable load for each radius, jib length, and configuration. It is the basis for lift planning and must match the crane's actual setup, counterweight, and reeving.

The maximum load a crane may lift under a given configuration and radius, as stated in the load chart. It already accounts for the crane's structural and stability limits but not for site-specific deductions like wind or dynamic effects.

The horizontal distance from the crane's slewing center to the center of gravity of the suspended load. Capacity decreases as radius increases, so the operator must know the radius for every pick before consulting the load chart.

An instrument that measures the load and radius and computes the crane's load moment, warning the operator and stopping movements when capacity is approached or exceeded. It must be calibrated and function-tested before use.

A device that stops or reverses a crane motion at a preset point, such as the hoist upper limit, trolley end stop, or slewing limit. Limit switches must be tested and never bypassed during operation.

A friction or disc brake that holds the hoist drum and suspended load when power is removed. It is a critical safety component and must be inspected and tested for holding capacity before lifts.

The large bearing that connects the crane's upper works to the mast or base and allows rotation. Its bolts and condition are inspected regularly because failure can cause catastrophic loss of the upper structure.

A prefabricated structural unit of the crane's vertical tower, usually a lattice of chords and bracing. Sections are stacked and pinned or bolted during erection and climbing, and each joint must be correctly fastened.

The process of raising a tower crane's mast or upper works using a climbing frame and hydraulic rams, adding mast sections as height increases. It requires a written procedure, trained crews, and careful load and wind monitoring.

A structural collar or cage that guides and supports the crane during climbing and holds the upper works while mast sections are inserted or removed. It must be inspected and correctly pinned before climbing begins.

The powered cylinder that raises the climbing frame or upper works during climbing. Rams, hoses, and valves must be inspected for leaks and damage, and the load must be mechanically secured before anyone works beneath it.

A connection between the crane mast and a building or independent structure that stabilizes the crane above a certain free-standing height. Tie-in spacing and design are specified by the manufacturer or a qualified engineer.

Weight added to the crane base or counterweight assembly to provide stability against overturning. Ballast quantity and placement are specified by the manufacturer and must never be altered without engineering approval.

The heavy blocks or plates mounted on the counter-jib to balance the load and jib. Their number and position are fixed by the load chart, and incorrect counterweight can cause overload or tipping.

The rearward arm of the crane that carries the counterweight, hoist machinery, and sometimes the operator's cab. It swings opposite the jib and must be kept clear of obstructions and people.

The forward horizontal or luffing arm of the crane from which the load is suspended. Its length, configuration, and reeving determine the crane's working radius and capacity.

The carriage that travels along the jib to position the hoist line at the desired radius. Trolley movement changes the load moment, so the operator must coordinate trolley and hoist motions to stay within capacity.

The wire rope that runs from the hoist drum over sheaves to the load hook. It must be inspected for broken wires, kinks, corrosion, and wear, and replaced according to manufacturer and regulatory criteria.

The path and number of rope parts between the hook block and the boom or jib. More parts increase capacity but reduce hoist speed, and the reeving must match the load chart's configuration.

The assembly containing the hook, sheaves, and weight that attaches the load to the hoist rope. Its capacity, sheave arrangement, and safety latch must be inspected before each lift.

The angle between a sling leg and the horizontal load surface, which determines the tension in each leg. As the angle flattens, tension rises sharply, so sling capacity and hardware must be rated for the actual angle.

A flexible assembly of wire rope, chain, or synthetic webbing used to connect the load to the hook. Slings must be rated, inspected, protected from sharp edges, and selected for the load's weight and shape.

A U-shaped connector with a pin or bolt used to join slings, hooks, and fittings. The shackle must be rated for the load, correctly oriented, and have its pin secured against rotation.

The collective term for shackles, hooks, links, swivels, turnbuckles, and other fittings used in a lift. Each item must have a legible capacity rating and be inspected for cracks, wear, and deformation.

The point at which a load's weight is balanced in all directions. Riggers must identify it to place the hook and slings correctly and prevent tilting, shifting, or uncontrolled rotation during the lift.

A rope attached to a load and controlled by a worker on the ground to prevent rotation and swinging. Tag lines keep the load stable and away from structures, and handlers must stay clear of pinch points.

A standardized arm and hand movement used to direct crane operations when radio communication is unavailable or as a backup. Only one designated signal person may give signals to the operator at a time.

The qualified worker who directs the crane operator using hand signals, radio, or other agreed means. The signal person must be competent, positioned with a clear view, and authorized to stop the operation at any time.

Two-way voice contact between the operator and signal person, often required when the load is out of sight. Clear channels and agreed terminology reduce misunderstandings, and lost communication requires the operator to stop.

The operator's management of hoist, trolley, and slew motions to keep the load stable, within capacity, and clear of obstructions. Smooth starts and stops reduce swing and dynamic loads on the crane and rigging.

The maximum wind speed at which the crane may operate, erect, climb, or dismantle, as specified by the manufacturer. Wind acting on the load and jib increases loads and must be monitored continuously.

Timber, steel, or engineered pads placed under crane supports to spread load over a larger soil area. Mats reduce ground bearing pressure and must be sized for the actual load and soil conditions.

A documented check of crane components, foundations, fasteners, and safety devices performed before erection begins. Defects found at this stage prevent failures during assembly and later operation.

A procedure that isolates energy sources and applies locks and tags before maintenance or repair. It prevents unexpected startup or movement of the crane while workers are exposed to hazardous energy.