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Selecting Set Construction Materials Originally published at TheatreFace.com, Technical Direction Discussion Group, Rules of Thumb for Set Construction Materials, 2010-01-20.
A key element in the selection of materials should be the quantifiable structural strength properties they possess. Set pieces that will carry the weight of performers and/or crew must be strong enough to safely support the live loads imposed upon them. This involves both the bracing and flat materials as well as the fasteners that hold them together. A solid steel bar supported by a ¼” wooden dowel is just about as useless as an oak beam supported by a #6 sheet-rock screw. Platforms, ladders, stairs, and other creations that carry live loads must be designed to meet relevant building codes regardless of the length of time they will be in use. Unlike a dropped potato chip with a ‘five-second rule’, a structure must carry the expected working load regardless of its time in-service be it a five minute vignette or a five year Broadway run. If weight is a concern, then consider lightweight materials of appropriate strength. Aluminum or fiberglass beams in lieu of 2x4’s, space frames in lieu of post & beam structures, and aluminum tubing and SpeedRail fittings in lieu of the more conventional 1½” i.d. schedule 40 steel pipe. Fasteners can be lightweight, too. High strength aluminum and titanium bolts are available and for mission-critical objects that must be lightweight and can provide significant holding power. Structural adhesives can be very useful, as well, but be sure to live-load sand-bag test the final results before climbing on them or hanging from them. Be sure to check them regularly for de-lamination failures, just as you would check metal for fatigue cracks and wood for splitting and cracking. Bolted joints can be as strong as welded joints and do not require the welding skills of steel and aluminum. They also offer the benefit of disassembly after the set-piece is out of service. Become familiar with the ISO, SAE, and ASTM fastener (nut, bolt, & washer) strength grading systems and how they are represented on the components. Using a hardware store pot-metal nut on a Grade 8 Bolt does not make a Grade 8 rated assembly. It is also important to understand the difference between the axial loading strength of a bolted connection vs. the shear loading strength. Wood screws have very little axial loading strength (they are mostly 'nails with tread'), and typically not very good shear strength, either (the wood can sometimes split before the screw bends or breaks). With a coat of paint, any material can be made to look like any other material (well, except maybe clear items). Another point to be considered is that all materials used for scenery must be treated with fire retardants or be inherently incombustible (Ref: NFPA 101 - Life Safety Code, Sections 12.4.5.11). The cost of intumescent paint must be added to the cost of wood and plastic materials, where metal structural elements can remain untreated. Lastly, the cost of recycling the materials should be considered. Wood and plastic typically just goes to the dump (sadly, no one will buy your used wood, and used plastic is of extremely low value), where metal parts can typically be reused and / or recycled.
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