Tower Crane Erection, Climbing, and Dismantling Flashcards

During a hydraulic climbing operation, the operator notices that one climbing pawl on the climbing frame fails to engage its ratchet notch after a climbing stroke. What is the correct immediate action?

Answer: Retract the climbing cylinder, lower the crane back to the last secured mast section, and halt climbing until the pawl is inspected and repaired

A failed climbing pawl means the crane lacks a critical redundant support point during the climbing stroke. The safe procedure is to immediately retract the cylinder to return the crane to a fully supported position on the last secured mast section and stop all climbing operations until the pawl mechanism is repaired and inspected. Continuing to climb with a failed pawl risks catastrophic loss of support if the functioning pawls are also stressed beyond capacity.

When erecting a tower crane on a foundation that is embedded in a structure's floor slab rather than a dedicated pad footing, which condition MOST critically affects the permissible freestanding height before the first tie-in anchor is required?

Answer: The compressive strength of the floor slab and the verified anchor bolt embedment depth

When a tower crane is anchored to a floor slab rather than a purpose-built foundation, the slab's compressive strength and the actual embedment depth of anchor bolts determine the true load transfer capacity. The manufacturer's standard freestanding table assumes a properly designed foundation with verified soil bearing capacity. A slab installation requires a site-specific engineering analysis; if slab strength or embedment is inadequate, the permissible freestanding height must be reduced regardless of what the standard table indicates.

A self-erecting top-slewing tower crane's manufacturer specifies a maximum out-of-service wind speed of 130 km/h. During a dismantling operation scheduled for the following morning, the forecast shows a cold front arriving with gusts up to 95 km/h. Which factor should MOST influence the decision to proceed or postpone dismantling?

Answer: Dismantling creates a transitional in-service condition with reduced structural redundancy, so the applicable limit is the lower in-service wind speed, not the out-of-service limit

During dismantling, the crane passes through intermediate configurations that are neither fully assembled nor fully disassembled. These transitional states often have lower structural capacity than either endpoint. The out-of-service wind rating applies to a fully assembled crane in weathervaning mode; during active dismantling, the crane is partially loaded, sections may be temporarily unsupported, and counterweights may be in non-standard positions. The applicable wind limit reverts to the in-service limit (typically 45–72 km/h depending on manufacturer) during active dismantling operations.

After adding a mast section during a climbing sequence, the erection crew measures the crane's plumb and finds a 1:450 lean toward the heavy-load side. The manufacturer's tolerance states maximum 1:500. What is the CORRECT course of action before resuming normal crane operations?

Answer: Halt operations, adjust the mast connection shimming or slew-ring leveling bolts per the manufacturer's procedure to bring plumb within tolerance, then re-verify before resuming

A plumb measurement of 1:450 exceeds the manufacturer's stated tolerance of 1:500 (a stricter ratio means less allowable lean). Operating out-of-plumb beyond tolerance increases eccentric loading on mast connections and the foundation, potentially accelerating fatigue cracking and reducing rated capacity margins. The correct action is to halt operations immediately and correct the plumb using manufacturer-specified adjustment methods (shimming, slew-ring leveling bolts, or mast connection adjustments) before resuming. Operating under a 'reduced radius' workaround is not an approved substitution for correcting an out-of-tolerance plumb condition.

During the dismantling of a top-slewing tower crane, the crew is preparing to remove the counter-jib. The load line is still reeved through the main jib sheaves with a hook block attached. What must be done BEFORE the counterweight blocks are removed from the counter-jib?

Answer: The hoist rope must be completely de-reeved and the hook block removed from the crane to eliminate asymmetric loading on the slewing ring during counterweight removal

With the hook block and hoist rope still reeved, removing counterweight from the counter-jib shifts the crane's rotational balance point dramatically toward the main-jib side. This can induce a sudden and uncontrolled rotation of the upper works or overturn the crane before the crane body can be secured. The manufacturer's dismantling sequence typically requires the load hoist rope to be fully de-reeved and the hook block physically removed — not merely landed — before counterweights are disturbed, eliminating the eccentric moment that a suspended hook block would create.

A climbing frame designed for a specific mast cross-section is being used on a replacement mast section from the same manufacturer but purchased two years later. The mast section dimensions appear visually identical. Before using this climbing frame, what verification is MOST critical?

Answer: Verify through manufacturer documentation that the replacement mast section's chord and diagonal geometry is confirmed compatible with the climbing frame's pawl engagement geometry and load path

Manufacturers occasionally revise mast section designs between production runs — even when outer dimensions appear unchanged, internal chord profiles, diagonal angles, or ratchet notch geometry may differ subtly. The climbing frame's pawls, guide rollers, and support beams are engineered to precise dimensional tolerances of the original mast geometry. A mismatch — even millimeters — in notch position or chord profile can cause pawl misengagement or unintended load transfer paths during a climb. Visual similarity is not sufficient; only manufacturer-confirmed dimensional compatibility documentation authorizes using a specific climbing frame with a specific mast section variant.