Tower Crane Tie-In and Wind-Monitoring Findings
A 12-ton tower crane with a 180-ft jib has been climbed to a 160-ft height and tied to a concrete core at 100 ft. During a periodic inspection, you find that four bolts at the tie-in collar can be turned by hand, one tie-rod clevis is bent, and the climbing ladder access gate is missing. The anemometer is inoperative, and the slew brake allows the jib to drift about 3 ft at the tip when the controller is centered. The crew wants to make a 4,000-lb pick at a 100-ft radius; the chart allows 6,800 lb at that radius. The wind forecast is 20 mph with gusts to 28 mph. The crane's manufacturer lists a 20-mph maximum for picks with the panel being used. You are the inspector.
1. Which findings affect structural integrity or safe operation, and what is your serviceability decision?
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Structural and safe-operation findings: the hand-turnable tie-in bolts mean the tie-in collar is not carrying load as designed; the bent tie-rod clevis indicates damage or overload; the missing climbing gate is a fall hazard; the inoperative anemometer removes the required wind monitor; and the slew-brake drift affects control and load positioning. The 4,000-lb load is below the 6,800-lb chart value, but chart capacity assumes a properly tied, plumb, and maintained crane. With the tie-in loose and a bent clevis, the crane should be removed from service until repaired and verified. The wind forecast also exceeds the manufacturer's 20-mph limit for the panel, so the planned pick is not acceptable.
2. The site wants to complete the pick before repairing the anemometer because the forecast is 'only 20 mph.' Evaluate this position.
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Do not make the pick. A 20-mph forecast with 28-mph gusts is already at or above the manufacturer's 20-mph maximum, and wind at 160 ft can be stronger than at ground level. Without a working anemometer, the operator cannot verify actual conditions at the jib. The loose tie-in and bent clevis are independent reasons to stop. Waiting for the anemometer repair is not extra caution; it is restoring a required safety device. The load chart does not override wind limits or structural damage.
3. What repair, verification, and documentation are required before the crane returns to service?
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Lock and tag out the crane. Have the manufacturer or a structural engineer review the tie-in and bent clevis; replace the clevis and the affected bolts, torque the tie-in to the specified value, and verify alignment and plumb. Replace the climbing gate. Repair or replace the anemometer and the slew brake, then function-test them. A qualified person should perform a post-repair inspection, and any load test or NDT required by the manufacturer should be completed. Record the repairs, torque values, parts, test results, and return-to-service authorization in the crane log.