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We also provide powered scaffold
consulting, but a powered scaffold
is completely useless without the necessary suspension equipment that
supports the platform when it is used to access the building
facade.
We have provided the following equipment definitions below please feel
free to read through them. (For more information read through
the Resources
section see OPOS
& high
rise access engineering).
Powered Platforms
The Stage
A powered platform, “swing stage” or ‘stage”,
is a work platform, whose
frame is typically constructed of aluminum.
The stage is vertically propelled using
electrically powered motor(s),
either traction hoist or drum type, on board.
Compressed air powered hoists are occasionally
used in lieu of
electrical power. The platform,
suspended by at least two independent wire ropes of 5/16 inch diameter
or
greater, may be as short as three feet for a single man cage, or as
long as
forty feet, carrying three men plus tools, equipment and supplies.
Whether “ground rigged” or “roof rigged”, the
stage and its electrical
cord are suspended from one of several types of roof top supports,
including:
davits; rolling roof carriage; outriggers; “drop through” sleeves;
monorail track;
parapet clamps or parapet hooks. Each of
these supporting devices are elaborated upon in subsequent paragraphs.
There are two basic construction styles for
work platforms, a “ladder
board” with handrails or a truss type that incorporates the handrail
within the
truss design. The “ladder board” variety
utilizes an “off-the-shelf” unit constructed of “I” beam rails held
together
with tubular rungs molded through the beam’s web, then covered with a
perforated decking. Bracket clips are
bolted to the webs at multiple positions along the stage’s length to
support
handrail stanchions.
The truss type stage is an all welded frame
with vertical and diagonal
members forming a triangular shaped truss.
The truss’ top cord becomes the handrail’s top
rail and the truss’ lower
cord is used to support cross members that span the stage’s width. A non-slip flooring covers the cross members
to complete the walk area. Design
conditions elaborated upon above for ladder stages should also be
considered in
the design of a truss stage.
Metal mesh or screening is used to enclose the
sides of the stage for
both types of construction, ladder or truss.
The screening helps keep tools or materials
form falling out of the
stage, a safety requirement on permanent equipment design, in
consideration for
the general public below who may be at risk.
Due to a building’s geometry or its roof
structural grid, one elevation
may require different length stages on the same roof.
It is impractical of an owner to purchase
numerous stages or for a window cleaning contractor to bring different
length
stages to the same building. The custom
designed and fabricated stage is therefore often made to be modular,
utilizing
stage sections that couple together in various lengths as needed for
any of the
building’s roof top areas. To accomplish
this, the stage is constructed in modular lengths from as short as two
feet to
as long as twenty feet. The stage’s end
sections contain the power units and the center sections pin together
to create
various lengths, like adding leaves to a dining room table. Both the truss type and the ladder board
variety of stages can incorporate the modular design.
Hoist Motors
There are two basic varieties of powered
hoists used to lift and lower a
powered work platform, the drum hoist or traction hoist.
All hoists used in the industry are “man
rated”, requiring a primary and secondary brake and an “over speed”
protection
device.
The drum hoist, powered by electricity,
collects wire on a traditional
flanged drum located under or just behind the stage work area. The support wire rope has its end clamped off
to the flange for protection against the rope accidentally spooling off
the
drum.
Traction hoists, usually powered by
electricity but occasionally powered
by compressed air, incorporated mechanical rope gripping, spring loaded
paws or
roller chain that encircle a sheave inside the hoist’s housing. The wire rope, fitted with a “bullet” end, is
fed into the mechanism, passing between the sheave’s hub and the spring
loaded
chain or paws.
With their “power feeding” of the wire rope,
traction hoists are great
for ground rigging. One interesting
feature of a traction hoist is that the greater the load on the wire
rope, the
greater the grip exerted on the rope by the roller chain.
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