HEO Tower Crane NC III flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Wire rope discard criteria

Replace running rope when broken wires exceed 10 in any 6d length or 5 in any 30d length for a single lay, or when kinks, bird-caging, or severe corrosion are present.

Hook throat opening limit

Discard a hook when the throat opening has increased more than 15 percent, wear exceeds 10 percent of the original dimension, or the hook is bent or twisted more than 10 degrees.

Sling angle tension formula

Tension per leg equals load divided by (number of legs × sine of the angle from horizontal). At 30 degrees each leg carries the full load; at 60 degrees, 0.58 of it.

Choked hitch derating

A choked (choker) hitch reduces wire rope sling capacity by roughly 20 percent compared with a vertical hitch, because the rope is bent around itself and the load.

Ground bearing pressure

Pad pressure equals total crane ground load divided by total pad area. Compare the result with the geotechnical allowable bearing pressure before setting up outriggers or a crane base.

Overhead line clearance

Maintain at least 3 m clearance from power lines up to 50 kV, with greater distances for higher voltages, and use goalposts or barriers to prevent contact.

Mast verticality tolerance

Tower crane mast verticality is typically checked to 1/1000 of height, with a maximum deviation specified in the manufacturer's manual, commonly 200 to 300 mm at the top.

Erection sequence order

Typical order: foundation check, mast sections, slewing unit, cab, jib and counter-jib, counterweights and ballast, wiring and limit switch commissioning, then load test.

Free-standing height limit

The manufacturer sets a maximum free-standing height; beyond it the crane must be tied to the building with wall ties at specified intervals and calculated tie forces.

Climbing operation wind limit

Jacking or climbing is stopped when wind exceeds the manufacturer's limit, commonly 10 to 13 m/s, and no personnel may remain on the jib during the climb.

Ballast and load chart link

Counterweight and ballast must match the load chart configuration exactly; changing ballast changes the rated moment and invalidates the chart used for lifting.

Post-erection load test

After erection or climbing, a competent person load-tests the crane and verifies the load moment limiter and all limit switches before handover to service.

Load moment limiter function

The LML compares actual load moment (load × radius) with the rated moment and stops hoisting or boom-out at the limit; it must never be bypassed.

Slewing side-load effect

Slewing a suspended load creates centrifugal and side forces on the jib; keep slewing slow, keep the load below the jib, and avoid combined motions unless permitted.

Anti-two-block device

The anti-two-block device prevents the hook block from contacting the jib tip; it must be function-tested before each shift and the hoist limit must stop before contact.

Shock loading risk

Sudden pick-up or snatching a load can multiply the static load several times; take up slack slowly and use soft-start on the hoist to avoid overload.

Personnel platform lift rule

Lifting people is allowed only with a certified personnel platform, a written risk assessment, and an authorized permit; never lift a person on the hook or slings.

Emergency stop hand signal

Both arms raised with palms forward is the emergency stop signal; anyone on site may give it, and the operator must stop immediately regardless of who signals.

Single designated signaler

Only one designated signaler gives commands to a crane operator, except that any person may give an emergency stop at any time to prevent injury or damage.

Radio lift protocol

Identify crane and station, use short clear phrases, acknowledge every command, and confirm the load is clear before slewing or travelling.

Loss of communication rule

If radio or visual contact is lost, the operator stops and holds the load until contact is restored or the load is landed under a pre-agreed procedure.

Blind lift arrangement

When the operator cannot see the load, a signaler at the load position relays commands, and the lift plan states who signals and on which radio channel.

Rated capacity definition

Rated capacity is the lesser of the load chart value at the working radius and the structural or rigging limit; it already accounts for hook block and slings where stated.

Working radius measurement

Working radius is the horizontal distance from the slewing center to the centerline of the hook; increasing radius reduces capacity as the moment arm grows.

Load moment formula

Load moment in tonne-metres equals load in tonnes multiplied by radius in metres; the crane's rated moment is fixed for a given configuration.

Net payload calculation

Net payload equals the chart capacity at radius minus the weight of hook block, slings, and lifting beam. Example: 5 t chart minus 0.6 t rigging gives 4.4 t.

Critical lift threshold

A lift is critical when it exceeds 75 percent of chart capacity, involves tandem cranes, passes over occupied areas, or uses unusual rigging; it needs an engineered plan.

Hierarchy of controls

Controls rank from elimination, substitution, engineering controls, and administrative controls down to PPE, which is the last line of defense.

Thorough examination interval

Lifting equipment requires periodic thorough examination by a competent person, commonly every 6 or 12 months depending on equipment type and jurisdiction, separate from daily checks.

Lockout tagout purpose

LOTO isolates electrical, hydraulic, and gravitational energy before maintenance, with locks and tags applied and energy verified absent before work begins.

Brake holding test

Test the hoist brake by lifting a test load slightly and holding it, checking for drift; the brake must hold the rated load without slipping.

Crane shutdown procedure

Land and secure the load, park the jib in the specified position, apply the slewing brake, switch off power, lock the cab, and record the shutdown in the log.