Theatre Design & Technology - Summer 1984 - 19

Materials for this project were limited to wood products and to steel tubing. While there may certainly be great
advantages to other materials, it was
not within the scope of the project to
examine every possible combination of
products. There was no value judgment
as to the viability of wood and steel in
platform construction. The project accepted these materials as long-time
choices of scene shop staffs, and set out
to explore various platform configurations in an attempt to provide some
guidance.
There was also a matter of testing
limitations as directly influenced by finances, time, and my own lack of an engineering background. While a considerable amount of structural engineering
research went into the project, it cannot, in all honesty, be deemed a platform engineering research project. Outside advice on testing procedure ranged
from methods based solely on lab work
to methods strictly limited to computer
analysis of platform structures. In the
end, I decided to use a lab testing method while developing sample structures
based on accepted building practices.
Methods and procedure were not infallible and were not definitive for determining total strength of platform structures. Yet with all these project limitations, the results of the work are nonetheless quite valuable for theatres seeking feasible solutions to steel-framed
stock platforming.
The first consideration in this study
was the choice of topping for the platforming. Most materials for decking
offer some severe drawback. Particle
board is unsuitable because of its excessive weight and lack of strength.
Tongue and groove lumber is unsuitable primarily because its appliction is
time-consuming. A new "honeycomb
core panel" was considered, but availability is a drawback since it is not a material stocked by local lumber yards and
ordering it from manufacturers is a
problem because of the high cost of
shipping oversized items. In its most
advantageous form (with a thin skin on
each side) the honeycomb core panel
surface is not substantial enough for
nailing, bolting, and screwing on other
pieces of scenery. Plywood and concrete are the current building standards
for flooring, but concrete can be ruled
out for stage work. Plywood meets

most of the requirements for theatrical
materials-it is relatively inexpensive,
readily available, light in weight, strong,
time-saving and durable-so it was selected as the decking material for the
platform system. Two thicknesses that
were selected for investigation and testing were V2" and 314".
Square and rectangular section tubing are, by and large, the theatrical standard for steel platform construction.
Although there are countless other steel
configurations available to the scene
shop for scenic construction, there is a
long list of advantages for selecting
square and rectangular tubing-fundamentally a repeat of the requirements
for any theatrical material as cited
above. A chief advantage of square
tubing over pipe and various structural
steels is its ease of fitting and assembly.
Over the years, there has emerged a
preference for I" X I" X # 16 gauge
square tubing for theatre construction.
This tubing is perhaps the most readily
available in local steel yards. It is very
light in weight and relatively inexpensive at about 25(1: per foot in large quantities. The optimum wall thickness is
remarkably strong and borders on the
brink of weldability with common AC
arc welders. Thinner gauges invariably
develop burn-throughs, especially with
novice workers. The expensive gas metal arc welders, however, generally solve
the problem. With all the advantages
of I" X I" tubing, it must be pointed out
that it is a poor candidate as a material
for stock platforming. Experience with
I" x I" shows that it must be used in
conjunction with large numbers of legs
and substantial cross-bracing to sufficiently distribute the surface load. This
means that legging is a time-consuming
effort. So, while I" x I" is perfect for
platform trusses and non-stock units,
its use for stock plat forming is not
advised.
In an effort to maintain some uniformity in sizes of stock steel tubing,
only tubing measured in even inches
was explored. This decision was partly
a matter of time and money limitations
since it was not feasible to examine every size of steel tubing. There was also
a question of availability, since local
yards do not often carry a complete selection. Such sizes as I" x 2" and 2" x 2"
were easily located in the # 16 gauge wall
thickness. These sizes were suggested

by several area steel suppliers after a
discussion of the needs of theatre platform construction. It seemed that these
sizes were as strong as required as well
as reasonably priced in comparison to
wood 2" x 4"s. Several lengths of both
sizes were purchased for testing.
The first step in the development of
the plat forming was the examination of
wood stock platforming. It was hoped
that a steel platform could be designed
that was stronger and at the same time
comparable in weight and price. Admittedly, any steel construction is more
time-consuming than nailing wooden
units together, but the advantages
greatly offset this problem. The stock
wood unit examined weighed 126
pounds and consisted of a clear fir
frame of 2"x4" and a deck of 314" CD
plywood. The plywood weighed 72
pounds and the frame weighed 34
pounds with the remaining made up of
nails, glue, padding, a canvas cover,
and paint. The frame and the plywood
totalled 106 pounds. 1 This weight became a goal to achieve with steel. It was
also decided to limit frame designs to 50
pounds, a goal that seemed reasonable
in view of the steel weights of 1.26
pounds per foot for I" x 2" tubing and
1.71 pounds per foot for 2"x2".
With a goal in mind for weight, a
series of possible design configurations
for the frames was developed. To keep
under the ideal weight, the designs were
limited to 40 I of I" x 2" tubing and 30 I
of 2"x2". This limit immediately
posed a problem with the 2"x2" as
only one feasible frame could be so designed. The limitation was extended to
35 I of 2" x 2" which yielded a weight of
almost 60 pounds. While combinations
of many different sizes of tubing were
quite possible, it was decided not to explore them at the time. With the limitations of the project, it was necessary to
keep a carefully controlled range of designs for testing. In developing the
frame designs, several commercial standards and some theatre rules of thumb
were kept in mind. As a general rule, no
point on 314" plywood should be farther
than 12" from a support, while no point
on V2" plywood should be farther than
8" from a support. This theatre practice was confirmed by a number of
commercial construction guidelines. In
practice, this means the framing for 314"
plywood topped platforms should be

USITT /Summer I984/Theatre Design & Technology

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