Crane Type Identification and Applications Flashcards

A contractor needs to erect structural steel on a high-rise building in a congested urban site where the crane must remain stationary for several months and lift capacity must increase as the building rises. Which crane configuration is most appropriate?

Answer: A climbing tower crane mounted inside the building's core with a through-deck climbing frame

An internal climbing tower crane is specifically engineered to 'jump' upward through openings in the floor slabs as the structure rises, keeping the jib near the top of construction. This eliminates the need for ever-taller mast sections and maximizes hook height relative to the building as it grows. Luffing jibs are preferred in congested airspace but do not inherently solve the climbing requirement. Self-erecting cranes are low-capacity units unsuitable for structural steel. Guy wires on a hammerhead do not allow height progression.

On a marine construction project, a barge-mounted crane is being used to place riprap and must reposition frequently along a jetty. The crane has a 360° swing capability but the barge has no propulsion. What type of crane system describes this arrangement, and what is the primary operational limitation compared to a spud barge setup?

Answer: Floating crane; repositioning requires tug assistance and anchor re-setting, increasing cycle time

A crane mounted on a non-self-propelled barge without spuds is classified as a floating crane arrangement. Because the barge cannot anchor itself in position via spud poles, every repositioning event requires tug assistance to move the barge and then re-setting of anchor lines or winches, dramatically increasing cycle time compared to a spud barge that can 'walk' along a structure by raising and re-driving its spuds. Derrick barges typically use fixed boom geometries. Crawlers on deck barges require outrigger pads but this doesn't describe the primary limitation of the stated scenario.

A refinery turnaround requires picks inside a process unit where overhead obstructions limit hook height to 35 feet, loads up to 12 tons must be moved horizontally 80 feet, and the crane must operate within a 20-foot-wide aisle. Which crane type is the most operationally correct solution?

Answer: A gantry crane with adjustable-height legs straddling the aisle

A gantry crane with adjustable-height legs can be sized to straddle the 20-foot aisle, its legs set to clear obstructions, and the trolley traverses the full 80-foot horizontal distance without the crane itself relocating. An overhead bridge crane requires permanent installation on structural beams that may not exist or be rated for the load. A telescoping boom RT crane cannot achieve 80 feet of horizontal travel at a fixed hook height of 35 feet with restricted aisle width. A pick-and-carry RT crane could travel the aisle but would require multiple boom repositioning moves and cannot maintain a fixed 35-foot hook height while traveling under obstructions.

What is the defining structural characteristic that differentiates a stiff-leg derrick from a guy derrick, and in which application does the stiff-leg configuration provide a critical operational advantage?

Answer: A stiff-leg derrick uses rigid compression struts instead of wire rope guys to resist mast overturning; this allows full 360° rotation without guys crossing work areas or requiring re-rigging

A stiff-leg derrick replaces the wire rope guys of a conventional guy derrick with rigid steel compression struts (stiff legs) anchored to a structural frame. Because the restraining members are solid struts attached at fixed points on a base frame rather than radiating wire ropes staked to the ground, the mast can rotate up to approximately 270–300° (or full 360° depending on design) without the boom or load line fouling guy wires. This is a critical advantage on construction sites or industrial facilities where wire rope guys would obstruct travel lanes or working areas. The boom of a stiff-leg derrick does luff; it is not fixed.

A wind turbine installation project requires lifting a 72-meter blade weighing 14 metric tons to a hub height of 100 meters. The site terrain limits crane positioning so that the maximum permissible lift radius is 18 meters. After consulting load charts, the crane operator determines the chart capacity at 18 m radius and 100 m hook height is 16.5 metric tons. Which additional factor is MOST likely to require a crane with a higher rated capacity than what the load chart alone suggests?

Answer: The weight of the lifting beam and spreader hardware adding to the total lifted weight

The load chart capacity must account for the total suspended load, which includes not only the blade itself (14 MT) but also the custom spreader bar, lifting beams, slings, shackles, and any tag line rigging hardware — often 1–3+ metric tons on large wind turbine blade lifts. If this rigging hardware adds 2.5 MT, the total becomes 16.5 MT, exactly matching the chart's margin with no safety buffer. Wind loading (Answer A) is a real concern but is addressed through weather windows and de-rating factors, not a direct addition to chart load comparison. Sheave friction affects line tension but not the chart's gross capacity comparison. Ground bearing pressure affects crane positioning and may force a greater radius (worsening the situation) but is a separate analysis from chart capacity.

A heavy-lift contractor is evaluating crane types for a 600-ton reactor vessel pick in a petrochemical plant with very limited laydown area. They are considering a Liebherr LTM 11200-9.1 (mobile telescoping boom) versus a Manitowoc 31000 (crawler with lattice boom). Under which specific condition would the mobile telescoping crane be technically DISQUALIFIED from performing this lift even if its chart shows adequate capacity?

Answer: If the hook path requires simultaneous boom extension and load swing at maximum radius

On a telescoping hydraulic boom crane, simultaneous operation of boom extension (telescoping) and load swing while at or near maximum radius is prohibited by most manufacturers because the dynamic interaction of these motions can cause structural stress concentrations in the boom sections and telescope cylinder that are not accounted for in static load charts. The load chart capacity is derived from static or quasi-static conditions; dynamic combined motions at maximum radius create unpredictable load amplification. A lattice boom crawler crane, by contrast, does not telescope — its radius changes only through luffing, which is a geometrically simpler and more predictable motion. Outrigger bearing capacity (Answer B) is a site engineering issue affecting both crane types equally. Travel with load (Answer A) is restricted for all crane types by chart conditions, not a disqualifier unique to telescoping cranes. Hydraulic hold time (Answer C) is not a standard manufacturer disqualification criterion for capacity.