Community Wet II, Руководство по эксплуатации и установке

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Community WET II - Operation and Installation Manual - Page 24
4. Threaded Fasteners
Threaded fasteners are often used in rigging and mounting systems. As with eyebolts, many of Community’s
optional mounting brackets, yokes, and rigging plates utilize threaded fasteners. The fasteners that come
with each Community rigging kit are load rated to a sufficient strength to be safe when used within their
specified parameters. If replacement bolts are needed, or if additional bolts are required for mounting a
bracket to a beam, wall, or ceiling etc., such bolts should be purchased from a reputable manufacturer with a
minimum Grade 5 rating. On hex-head bolts this can be readily identified by looking at the head. A Grade 5
bolt will be marked with three lines; a Grade 8 bolt, which is even stronger, with six lines. Allen drive
fasteners are often made of high-strength steel (Grade 5 or better) if they are purchased from an industrial
suppler. As with any other rigging component, check the rating on the box or the manufacturer’s
specification sheet to be sure.
5. Support Points & General Practices
A vital part of planning the mounting or suspension system is to first determine the strength of the
building’s support points. Nothing should be assumed, even for the lightest loads. A ten pound loudspeaker
falling from ten feet can maim or kill just as readily as a heavy loudspeaker array falling from thirty feet.
The services of a registered structural or professional engineer should be employed to determine if the
materials and design of the supporting structure are adequate to support the intended load, and how to best
install mounting brackets or derive suspension points.
Fasteners
As a general rule, lag bolts driven into wooden beams should be avoided whenever possible, as they can pull
out as the wood ages or swells due to changes in temperature and humidity. Safe riggers will instead utilize
machine bolts of Grade 5 ratings or higher, rated beam clamps, brackets fabricated and welded by certified
welders, wire rope wrapped around beams with cushioning materials, and so on.
Certain wooden beams, or trusses, made of many laminations (often called Glue Lams) are intolerant of
holes. These beams are commonly used in modern construction, particularly in tilt-up concrete industrial
buildings. Drilling a hole through such beams can set up internal fractures, resulting in total failure of the
beam. Alternatives to drilling include fabricating steel brackets to surround the beam, or wrapping the beam
with a steel sling and fabric cushions, to derive a hang point.
Concrete expansion bolts, such as Hilti Kwik-bolts or equivalent, can provide an excellent means of
attaching moderate loads to concrete surfaces. However, as they rely on an expanding wedge to obtain
their strength, they must always be used in strict accordance with the manufacturer’s instructions. Such
instructions specify the diameter and depth of the hole, the composition of the concrete, permissible
spacing of the anchors, and the torque of the bolts. As a general rule, they should only be used for sheer
loads, not tension loads.
6. Liability
When you install a loudspeaker that is mounted or suspended over people’s heads, it is your responsibility
and yours alone to insure that the installation is performed in a safe manner. Never take the word of
someone who tells you, “That beam is safe to drill into,” or “This point can handle the load,” or “I’ll take
responsibility if anything happens.” To paraphrase Harry Donovan from his excellent book on safe rigging
practices entitled
Entertainment Rigging , ‘How is it going to sound to the jury at your manslaughter trial
when you use such statements by others as your defense?’
Never do anything you aren’t 100% sure is safe. If a manufactured product looks poorly designed and built, it
probably
is
poorly designed and built. If you aren’t absolutely sure where the wire rope came from or how
strong it is, don’t touch it. If the bolt looks too flimsy to hold the load, it probably
is
too flimsy. Always use
your best judgment, just as you do when driving at high speeds in traffic. The life you save may be your own,
or that of your friend or colleague.