MIL-HDBK-1038
the boom should be installed with a slight upward slope towards the tip to
compensate for deflection under load.
4.1.9
Pillar Anchor Bolts. Freestanding pillars require an integral base with
a wide foot print for anchoring them to the concrete foundation. The preferred
installation of anchor bolts (ASTM A36 threaded rods) is to have them cast
directly into the concrete base. The embedded ends may be terminated with heavy
steel plates/washers with nuts on both sides. Anchor bolts with bent ends (J or L
bolts) are permitted only if recommended by the manufacturer of the standard
commercial crane. Installation of anchor bolts into drilled holes by means of
bonding compounds is an acceptable alternative for existing concrete foundations.
4.1.10
Portal and Floating Crane Truss Booms. The deep triangular truss booms
of older cranes are assembled from standard open structural shapes fastened with
rivets or bolts. There are few, if any, weldments on these booms. Every riveted
or bolted joint is susceptible to rusting at the faying surfaces and requires
frequent inspection and maintenance. A common design feature is the back-to-back
arrangement of lacing members separated by the width of the flange thickness of
another structural member. The narrow separation between the flat faces of such
lacings provides limited access to clean and preserve them against corrosion.
Many rivets corrode and loosen within their bores and must be replaced. The
commonly accepted replacement fasteners in place of rivets are the high strength
ASTM A325 bolts.
4.1.11
Portal and Floating Crane Lattice Booms. The lattice booms of newer
cranes are assembled from three or four all-welded sections bolted together at the
main chords. The ends of the main chords have heavy bolting plates welded,
gusseted, and machined for a close fit with the mating boom section. Each boom
section supports a walkway along the entire length of the boom to provide access
to all lighting fixtures, sheaves, rollers, and lubrication points. The walkway
is accessible from the machinery deck with the boom level.
Traditionally the main chords were required to be either structural
angles or wide flange beams. Tubular sections for main chords were avoided
because damage on them can be repaired only by cutting and welding, and because
the condition of the interior surface could not be known with certainty. Damage
on main chords of the open structural sections in most cases is easily repaired by
cold straightening. The tubular sections - either round, square, or rectangular
were permitted for lacing members because their convex shape minimizes the forming
of water pockets on the boom. Current NCC policy is to permit tubular sections for
all structural members of booms, provided they are capable of being weld repaired
in the field. The ends of tubular sections must always be seal welded to prevent
water intrusion.
The lower (foot) section of the boom is tapered in profile and terminates
with two hinges which may contain reinforced housings. The hinges should be
spread wider than the width of the basic boom structure to limit the wind loads
and inertia loads on the hinges. The hinge arrangements utilize bronze bushings,
which may be installed either in the boom foot section or the base supports. The
upper (tip) section of the boom is also tapered in profile and carries the whip
hoist sheave at its end, and inboard, the auxiliary hoist sheaves if the crane is
so equipped. The main hoist sheave nest and the outboard luffing hoist sheave nest
(or wire rope pendant connections from the strut) are usually built into the
outboard end of the
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