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Crawler crane designers continually extend the height of the machines. Models that reach over 500 feet high are commercially available. Of course, as the crane height increases, so do the hazards associated with tip-over accidents. Destabilizing tip-over moments are generated by the boom and the suspended payload when they extend beyond the base of support. Stabilizing moments are generated by the crane base and counterweights. Counterweights are normally secured by mechanical fasteners such as pins, bolts, or chains. However, some cranes use unrestrained counterweights that are held in place only with friction. This paper investigates the dynamic behavior of such unrestrained counterweights during tip-over accidents. The analysis shows that counterweight blocks can break free and slide off the crane when the tip angle is as small as 20 degrees. Scale-model testing of cranes with unsecured counterweights demonstrates that the fall path of the spilling counterweights on certain crane models intersects the operator cab and thus presents a deadly hazard.

Analysis of unrestrained crawler-crane counterweights during tip-over accidents