Crane Type Identification and Applications Flashcards

A contractor needs to erect structural steel on a high-rise building in a dense urban core where the footprint is extremely limited and the crane must remain stationary for several months. Which crane configuration best satisfies all three constraints simultaneously?

Answer: A climbing tower crane anchored to the building's core with jump frames, configured as a top-slewing luffing-jib unit

A top-slewing luffing-jib tower crane climbing on the building's structural core addresses all three constraints: the luffing jib sweeps a reduced radius to avoid adjacent structures, the climbing mechanism eliminates the need for a large ground footprint, and anchoring to the core allows months-long stationary operation. A hammerhead with luffing jib is not a standard configuration; self-erecting cranes lack the height capacity for high-rise work; and a crawler with superlift requires significant adjacent ground space.

An offshore platform installation requires lifting a 900-ton module from a barge onto a fixed jacket structure in open sea with significant wave-induced motion. Which crane vessel type is specifically engineered for this dynamic loading environment, and what critical design feature differentiates it from a land-based equivalent?

Answer: A semi-submersible crane vessel (SSCV), because its pontoon-supported hull minimizes vessel motion through wave cancellation, protecting the lift from dynamic amplification

A semi-submersible crane vessel is the purpose-built solution for heavy offshore module lifts. The submerged pontoon hull sits below the wave action zone, dramatically reducing heave, pitch, and roll — the primary causes of dynamic load amplification that can exceed the static lift capacity. Jack-up barges work in shallow water only and require seabed penetration time; shearlegs are used for heavy lifts but do not address vessel motion; active heave compensation alone cannot cancel all six degrees of freedom for 900-ton lifts.

A boom truck (hydraulic truck crane) and a carry-deck crane are both on-site. A 4,200 lb HVAC unit must be set on a rooftop parapet 22 feet high, but the only available approach path is a narrow interior courtyard with a 9-foot-wide access gate and a 12-foot clearance overhead pipe rack at the entry. Which statement correctly identifies the limiting factor and the appropriate crane choice?

Answer: The carry-deck crane is preferred because its compact footprint fits the 9-foot gate, and its 360° rotation allows repositioning without moving the machine once inside

A carry-deck crane is specifically designed for confined interior work: typical widths are 5–8 feet, allowing passage through the 9-foot gate, and the 12-foot overhead rack is a non-issue since carry-decks travel with the boom lowered. Once inside the courtyard, its 360° swing eliminates repositioning. Boom trucks are typically 8–10+ feet wide and cannot deploy outriggers through a 9-foot gate; asymmetric outrigging reduces rated capacity dramatically and is rarely permitted for the full load. A material hoist cannot perform the lateral placement a crane provides.

When a conventional lattice-boom crawler crane is reconfigured with a fixed jib (also called a luffing jib or offset jib) offset at 30° from the main boom, which of the following operational changes is most critical for the operator to understand regarding load chart applicability?

Answer: The crane must now use the fixed-jib load chart, which accounts for the reduced structural capacity at the main boom tip caused by the jib's eccentric loading and the increased radius at the hook

A fixed jib creates a new configuration requiring its own dedicated load chart because: (1) the eccentric load at the main boom tip generates additional bending moments the main boom chart does not account for, (2) the true working radius at the hook is greater than the main boom radius alone, and (3) the jib angle and length combination are variables the manufacturer must have tested and certified. Using the main boom chart would be a serious safety violation and potentially fatal overload. A fixed jib is not the same as a luffing jib — luffing jibs are variable-angle hydraulically controlled attachments with their own distinct charts.

A railroad bridge rehabilitation project requires a crane to work from a flatcar within the rail corridor, lift spans weighing up to 180 tons from beneath the bridge, and travel under its own power between work sites along the track. Which specialized crane type is purpose-built for this exact scenario?

Answer: A Gottwald or similar rail-mounted portal crane with a self-propelled undercarriage running on standard-gauge track

A rail-mounted portal crane (such as those manufactured by Gottwald, Liebherr, or Kirow) is purpose-engineered for heavy bridge rehabilitation: it rides on standard-gauge or heavy-haul rail, self-propels between spans, can lift 100–350+ ton spans, and its portal legs straddle the existing track allowing train operations to continue. Standard crawler-to-rail conversions ('burro cranes') exist but are limited to lighter lifts and are not self-propelled in the same sense. A gantry on a transporter requires external power and is not a crane. A floating crane is only viable if the bridge crosses water.

An engineer specifies a 'derrick' for a shaft-sinking project 340 feet underground in a mine. The derrick must be permanently installed, rotate 360°, and hoist ore buckets on a single wire rope through a relatively small headframe opening. Which derrick subtype is most technically appropriate, and why does a stiff-leg derrick fail to meet this application?

Answer: A guy derrick is most appropriate because its 360° rotation under full load requires only a central mast and wire guys that can be anchored radially around the shaft collar; a stiff-leg derrick's rigid legs physically block the 360° swing path

A guy derrick is the historically validated choice for mine headframes and vertical shaft hoisting: its central vertical mast, rotating boom, and radially tensioned wire guys allow true 360° continuous rotation — essential for swinging ore buckets from the skip to the dump without repositioning. The guys are anchored to the surrounding headframe structure or ground anchors spaced around the collar. A stiff-leg derrick is fundamentally incapable of 360° rotation: its two rigid compression legs physically intersect the boom's path at approximately 120° of the swing arc, limiting rotation to roughly 270° maximum. The Chicago boom is a valid alternative for building cores but less suited to the isolated headframe structure described.