20.2 Controlled Rotation, Upending and Multiple-Crane Lifts

A moving load requires a changing force model

Rotation changes load orientation. Upending turns a load toward an upright position, often with a temporary ground support or tailing system. A multiple-crane lift has more than one crane supporting the same load. These activities require a planned sequence because sling angles, support reactions, CG position and crane radius may change during motion.

A rotation plan identifies attachment points, the load's ability to withstand changing reactions, controlling equipment, clearances and the supported final condition. Two hoists do not automatically provide equal sharing, and adding a tailing crane does not automatically halve demand. Calculate or otherwise establish forces at all governing stages, including the transition from ground support to full suspension.

Do not assume the load transfers entirely to one hook at a particular angle. Transfer depends on connection geometry, force directions, contact and control sequence. A kinematic drawing should show where each pick and support moves, rather than depicting only the starting and ending orientations.

Suspended rotation with separate controls

For a load rotated between two independently controlled hoists, establish which hoist raises or lowers at each stage and the expected reaction at each attachment. Verify stroke, chain/rope travel, capacity and anchor strength. The hoists must remain within their permitted load directions; a chain fall cannot be side loaded simply because it provides fine adjustment.

Plan against slackening a required retaining leg or allowing a sling to slide off a corner. A member's CG can pass outside a support or suspension arrangement, making the system unstable. The load may rotate rapidly if one restraint unexpectedly releases. Keep people outside the complete swept envelope and use the designed control points.

The CCO practical frame rotation has its own specified equipment, indicators and 90-degree task. It does not approve using the same simplified course arrangement on a different field load. Field drawings, lifting points and equipment limitations control the actual operation.

Ground-pivot illustration

Consider a simplified rigid 10-foot member with 10,000-lb weight, CG 6 feet from a ground pivot, and a vertical lifting force at its far end. The pivot remains in position and provides the other vertical reaction. At the horizontal start, moment balance gives:

$$F(10)=10{,}000(6),\qquad F=6{,}000\text{ lb}$$

The remaining vertical reaction is 4,000 lb. At an angle $\alpha$ from horizontal, if the same ideal geometry and vertical forces remain, both moment arms contain $\cos\alpha$:

$$F(10\cos\alpha)=10{,}000(6\cos\alpha)$$

For angles short of 90 degrees where that factor is nonzero, the model still gives 6,000 lb. It does not predict a gradual increase to 10,000 lb simply from the angle. At exactly upright the moment equation loses those lever arms and cannot determine the sharing by itself. Contact behavior, restraint and the intended support-transfer stage must be assessed separately.

This is a teaching model, not a field upending procedure. An actual pick may move, the pivot may slide, the force may incline, the member may flex, or contact may end. Each change requires a new force model. When the member becomes fully suspended from one hook, that system must carry the complete applicable suspended load.

Plan the multiple-crane operation

OSHA 1926.1432 requires the operation to be planned by a qualified person before more than one crane or derrick supports the load. The plan must ensure the applicable Subpart CC requirements are met. Where the qualified person determines engineering expertise is needed, the employer must provide it.

The operation must be directed by someone meeting both competent- and qualified-person criteria, or a competent person assisted by one or more qualified persons. The lift director reviews the plan with all involved workers. A Level II rigger certificate alone does not establish every qualification for that role.

There is no universal 75% tandem-crane chart limit in 1926.1432. An employer, project or engineered plan may impose a utilization limit, but it must be identified as that requirement. Never replace actual reactions and crane charts with an assumed derating percentage.

Sharing and radius example

A rigid load weighs 20,000 lb, has vertical picks 20 feet apart and a CG 8 feet from pick A. In the simplified two-support model, A carries 12,000 lb and B carries 8,000 lb. Each crane also carries its applicable rigging and equipment inventory. Assigning 10,000 lb to each crane would understate A's payload reaction by 2,000 lb.

As motion changes a crane's radius, capacity can fall even when its load share remains unchanged. Lateral movement can also incline connections, increase tension or introduce unapproved side pull. Evaluate the limiting stage for each crane separately and coordinate motions to preserve the approved geometry.

Signals and stop conditions

OSHA 1926.1419 permits one ordinary signal source at a time for each crane and allows anyone to give a safety stop. Commands to coordinated cranes must identify the equipment before the function. A shared dedicated radio channel may be used for coordination under 1926.1420. Do not assume that “one voice for the entire site” is the complete legal requirement.

Stop for unexpected rotation, shifting ground support, abnormal tension, loss of communication or a change outside the approved plan. Land or stabilize through the prescribed contingency rather than improvising a compensating motion. Once the load is secured in its final position, unload tailing and lifting connections in the planned sequence, confirming stability before release.

Sources: OSHA multiple-crane lifts, OSHA signals, OSHA electronic transmission, CCO reference manual.