NCCCO Tower Crane flashcards

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

Allowable ground bearing pressure

The maximum soil pressure a foundation can safely carry, expressed in kPa or psf. Crane base loads, counterweight, and overturning moments must be compared with this value before the foundation is built.

Mast out-of-plumb tolerance

Manufacturers commonly limit tower mast verticality to about 1 in 500 of measured height. Excess lean adds bending moment to the mast and must be corrected at the base before the crane is used.

Out-of-service wind case

The foundation and anchors are designed for a parked crane with the jib free to weathervane in the site's design storm wind. This case often governs over the maximum lifted load case.

Power line approach distances

OSHA 1926.1408 minimum approach distances are 10 ft for lines up to 50 kV, 15 ft for 50 to 200 kV, and 20 ft for 200 to 350 kV, with larger distances at higher voltages.

Zone of influence

The soil zone around an excavation that may move or lose support. A crane base should sit outside a line projected about 45 degrees up from the excavation toe unless engineered otherwise.

Full slewing clearance

The crane is positioned so jib and counter-jib can swing a complete circle clear of structures, other cranes, stockpiles, and power lines, including the arc swept while weathervaning out of service.

Base frame level tolerance

The base frame and anchor bolt template are set level and plumb within the manual's tolerance, typically about 1 mm per metre, so mast sections stack without inducing built-in bending.

Balanced climbing condition

Before jacking, the upper works' centre of gravity is brought directly over the mast by positioning trolley and hook exactly as the procedure shows. No load is on the hook during climbing.

Climbing pins and wedges

Mechanical supports that carry the upper works while hydraulic rams reposition the slewing unit. They must be fully engaged in the mast before ram pressure is released.

Free-standing height

The maximum mast height a tower crane may stand without being tied to a structure. Exceeding it risks mast failure, so tie frames are installed at the manufacturer's specified levels and spacing.

Tie frame structural check

Anchor frames transmit horizontal crane loads into the building. The structure at each tie level must be verified by a qualified engineer for those loads before the tie is installed.

Assembly director qualification

OSHA requires assembly and disassembly to be directed by a person meeting a defined qualification and to follow the manufacturer's instructions. The crane stays out of service until post-assembly inspection is complete.

Erection wind limit

Manufacturers usually prohibit assembling jib and counter-jib above roughly 10 to 12 m/s, about 22 to 27 mph, because partially assembled components have large sail area and little stability.

Post-climb verification items

After each climb, confirm mast bolts or pins installed and torqued, guide rollers adjusted, hydraulic pressure correct, and the load moment system and limit switches set for the new height.

Gross versus net capacity

Load charts rate the gross load. Subtract hook block, slings, shackles, spreader beam, and all other below-the-hook equipment to find the net capacity available for the payload.

Working radius definition

The horizontal distance from the crane's slewing centre to the vertical hoist line with the load applied. Radius grows as the trolley moves outward, and rated capacity falls with it.

Sling leg tension formula

For a symmetric two-leg sling, tension in each leg equals half the load divided by the sine of the leg angle above horizontal: T = W divided by 2 sin theta.

Sling angle load factors

Compared with a vertical leg, a leg at 60 degrees above horizontal carries 1.15 times its share, at 45 degrees 1.41 times, and at 30 degrees 2.0 times the share.

Load moment

Load multiplied by working radius. The load moment limiter compares measured moment to the rated moment for the current jib configuration and stops hoisting out or trolleying out before overload.

Sling design safety factors

ASME B30.9 minimum design factors are 5 to 1 for wire rope slings, 4 to 1 for alloy chain slings, and 5 to 1 for synthetic web slings, applied to the published rated capacity.

Tandem lift derating

In a multi-crane lift, each crane's share should not exceed 75 percent of its rated capacity at the working radius, and the total load should not exceed 75 percent of combined ratings.

Anti two-block device

A limit device that stops hoisting before the hook block contacts the jib or trolley. It must be function-tested before each shift and never used as a normal stopping point.

Load moment limiter action

The system warns as rated moment is approached and stops motions that would increase moment at or before the rated value. It may not be overridden or adjusted except by an authorized person.

Tag line purpose

A rope attached to the load and controlled from outside the fall zone to prevent rotation and swinging, keeping the load from striking the crane structure, nearby objects, or personnel.

Designated signalperson

Only one person directs the operator at a time. That person must be qualified, use standard hand signals or radios, and stay in clear view or continuous radio contact with the operator.

In-service wind limit

Manufacturers set a maximum in-service wind speed, often near 20 m/s or 45 mph at the jib, but capacity may be reduced at lower speeds for loads with large sail area.

Shift inspection scope

A visual and functional check by the operator before each shift covering wire rope, hooks, brakes, limit devices, the load moment system, and the anemometer. Deficiencies are recorded and the crane locked out if serious.

Annual inspection

A comprehensive inspection by a qualified person at least every 12 months, covering structural members, welds, pins, bolts, wire rope, and operational aids, with results documented in the crane records.

Wire rope removal criteria

Remove running rope with six or more randomly distributed broken wires in one lay, three broken wires in one strand in one lay, or any heat damage, kinking, bird-caging, or core protrusion.

Hook removal criteria

Remove a hook if the throat opening has increased more than 15 percent, if it is twisted more than 10 degrees out of plane, or if it shows cracks, excessive wear, or a faulty latch.

Anemometer requirement

Tower cranes must have a wind speed indicating device readable by the operator. Wind measured at jib height, not at ground level, governs whether lifting may safely continue.

High wind parking position

In the manufacturer's storm position the hook and trolley are placed as specified, the slewing brake is released so the jib can weathervane, and rail clamps or storm anchors are applied as required.