Importance

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Abstract

A jib is supported for its luffing movement by a luffing rope mounted to a longitudinally intermediate portion of the jib. The jib has a truss structure with upper and lower beam members respectively overhanging upward and downward of load action line which connects a lifting point with a support pin. Assuming that, when the burden of maximum load is lifted up, P is a load applied on the load action line from the tip of the jib; H is a width between upper and lower portions of the jib at a mounting point of the luffing rope; Eu and El are overhang eccentric lengths of the upper and lower beam members at the mounting point of the luffing rope with respect to the load action line, respectively; and Au and Al are cross-sectional areas of the upper and lower beam members, respectively, then cross-sectional areas Au and Al of the upper and lower beam members are determined depending upon overhang eccentric lengths Eu and El of the upper and lower beam members to satisfy ##EQU1## so that an upper portion of the jib is recurved toward a crane body when the burden of maximum load is lifted up.

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First Claim