Tower Crane Erection, Climbing, and Dismantling Flashcards

During a self-erecting tower crane's telescoping (climbing) operation, the hydraulic climbing frame has been extended and pinned, but the operator notices the mast section being lifted is binding asymmetrically against the climbing cage guides. What is the MOST likely cause and correct immediate action?

Answer: An internal climbing lug pin on the mast section is misaligned with the climbing frame pocket; retract the cylinder, reposition, and re-engage before continuing

Asymmetric binding during climbing typically indicates a misalignment between the mast climbing lug pin and the climbing frame pocket. The correct response is to retract the hydraulic cylinder, carefully reposition the mast section until the lug aligns properly with the climbing frame pocket, then re-engage. Continuing to force the cylinder risks damaging the climbing frame guides, the mast section, or causing a catastrophic drop. Wind loading causes overall deflection rather than asymmetric binding, and counterweight position affects slewing balance rather than climb mechanics.

A top-slewing tower crane is being dismantled using a mobile crane as the assist crane. After the top portion (slewing ring, cab, jib) has been removed, a technician discovers the mast anchor collars (ties) to the building structure were installed with the tie rod turnbuckles fully extended (maximum length). According to standard dismantling procedure, what is the significance of this condition?

Answer: Fully extended turnbuckles indicate the ties may be under high tension or were installed to compensate for mast lean; they must be inspected for overload and de-tensioned carefully before removal

Turnbuckles at maximum extension indicate they were either improperly installed or used to compensate for a mast that is out of plumb, meaning the ties may be carrying significant tension loads. Before removal, a competent person must inspect for signs of overload (bent rods, deformed brackets) and systematically de-tension each tie in the engineered sequence. Removing a highly tensioned tie suddenly can cause the mast to shift or snap back violently. Turnbuckle length is always significant and never irrelevant in dismantling operations.

During internal (floor-climbing) tower crane operation in a high-rise building, the crane must jump to the next floor. The engineer of record specifies that the crane's climbing frame must bear on two floors simultaneously during the jump sequence. At what point in the climbing sequence is the structure MOST critically loaded, and why?

Answer: When the mast is being lifted through the jump floor opening, because the climbing frame transfers the full crane load (dead load plus any dynamic amplification factor) to the two bearing floors while the mast is unsupported at mid-span

The most critical structural loading occurs while the mast is being hoisted through the jump floor opening. At this moment, the climbing frame straddles two floors and transfers the crane's entire dead load — plus any dynamic amplification from the hydraulic climbing motion — to both bearing floors simultaneously. The mast is effectively spanning between the two climbing frame support points with no other lateral restraint, meaning any eccentricity or dynamic spike is fully transferred to the building floors. This is why the engineer of record must approve the floor reinforcement scheme and the sequence of operations.

A tower crane manufacturer's erection manual specifies a maximum out-of-plumb tolerance of 1:500 for the mast (1 mm deviation per 500 mm of height). After erecting a 60-meter freestanding mast, a survey finds 130 mm of total out-of-plumb. Which statement BEST describes the required action and its underlying reason?

Answer: The crane exceeds tolerance (1:461 is worse than 1:500); the mast must be re-plumbed before commissioning because out-of-plumb compounds bending stress in the mast and shifts the center of gravity, reducing rated capacity safety margins

A 130 mm deviation over 60,000 mm yields a ratio of 1:461, which is worse (more out of plumb) than the 1:500 limit — the smaller the second number, the greater the lean per unit height. This out-of-plumb condition must be corrected before commissioning. The reason is that mast out-of-plumb introduces additional bending moment in the mast sections (P-delta effect), shifts the crane's center of gravity, and reduces the safety margin against overturning built into the rated capacity tables. Operational restrictions do not substitute for correct plumb, and the tolerance is not doubled for freestanding cranes unless explicitly stated in the manufacturer's documentation.

When dismantling a luffing jib tower crane, the erection supervisor plans to remove the luffing jib in a single piece using an assist crane. Before making the pick, which of the following conditions is the MOST critical to verify beyond basic rigging and load weight?

Answer: That the luffing rope and pendant ropes are completely slack and the jib pivot pins are removed before the assist crane takes load, to prevent the luffing rope drum from being back-driven

Before the assist crane takes load on the luffing jib, all luffing ropes and pendants must be fully slack and the jib pivot pins must be removed in the correct sequence. If the luffing rope still has tension when the assist crane lifts, the drum can be back-driven (rope feeds backward through the drum), potentially causing the rope to jump the sheave, overload the drum brakes, or create a catastrophic uncontrolled swing as the jib suddenly pivots. The manufacturer's sequence for pin removal and rope de-tensioning must be followed exactly. Rigging the jib at its geometric center is important but secondary to the rope management issue specific to luffing jib designs.

A tower crane is climbing inside a building and requires a temporary 'tie-in' anchor to the building floor slab during the climbing sequence. The structural engineer has specified cast-in anchors rated at 80 kN tension and 60 kN shear. During the climb, the crane's computerized monitoring system reports a combined anchor load of 72 kN tension and 48 kN shear. Using the linear interaction formula for combined loading (T/Tr + V/Vr ≤ 1.0), is this anchor within capacity?

Answer: No — the linear interaction value is 1.70; wait, calculating correctly: (72/80) + (48/60) = 0.90 + 0.80 = 1.70, so the anchor is overloaded

Applying the linear interaction formula: T/Tr + V/Vr = (72/80) + (48/60) = 0.90 + 0.80 = 1.70. Since 1.70 > 1.0, the anchor is overloaded despite both individual components being below their standalone ratings. This is a critical concept: combined loading is more severe than either load alone would suggest, because both loads simultaneously reduce the anchor's capacity for the other. The climb must be stopped, the engineer of record notified, and a remediation plan (additional anchors, reduced climbing loads) implemented before proceeding. There is no 25% overload allowance for combined loading on a temporary climbing anchor.