Document bakbNYMdMDy6KoMgb0dENNwwg

STRAP BLOCK DEAD END GOOSENECK GUDGEON, BOOM BAND STRAP BLOCK SHEAVE BLOCK SWIVEL HOOK BOOM PLATE PIN IN BOOM SEAT FOOT BLOCK MAST STEP FOOT BLOCK IRON MAST STEP SHEAVE STIFF LEG CONNECTION Fig 20-14 -- Diagram of stiff-leg derrick shows names of various parts Courtesy Travelers Insurance Co load on the boom, sandbags, cast iron weights, or concrete blocks are used to hold down the stiff-legs The hoist engines for both stiff-leg and A-frame derricks usually are bolted to the sills or ground members On smaller der ricks, the suspended loads may be slewed by being pushed manually The boom of a large derrick may be swung by a "bull-wheel" to which cables from another drum on the hoist engine are attached Since a loaded cable may whip consider ably and cause severe injury, the horizontal cables between the hoist engine and the boom hinge should be barricaded, and work men should be prohibited from crossing over or under them The guy derrick (Fig 20-15) is used largely for erection of the structural steel of tall buildings, especially those over 10 stones high that cannot be reached by the boom of a crawler crane operating on the ground Such demcks usually are of lat ticed steel and have an odd number of equally spaced wire rope guys, each equipped with a tumbuckle and attached to the steel beams or columns on the erection floor (Fig 20-16) If the demck is erected on the ground, the guys should be secured to heavy steel anchors buned deep in the ground, with ad ditional weights placed on the anchorages Heavy timbers, 12 by 12 in or 12 by 16 in , should be placed on the floor beams to sup port the foot of the mast These foot blocks must be braced against the stubs of the building columns to prevent their being "kicked" out of position when a heavy load is picked up with the boom at a low angle 553