Fly system infrastructure consists of the relatively permanent load-bearing and load-transferring structures of a stage house. The infrastructure, generally fabricated of structural steel members, is sized by a structural engineer during the design of a new theatre, or theatre renovation. Rigging system infrastructure ultimately limits a fly system's capacity.
Building codes generally require that fly system beam design meets the L/360 rule: beams shall not deflect by more than the length of a span divided by 360. For example, a 30-foot head block beam should not deflect more than 1 inch under the system design's maximum loading condition. Beam design using the L/360 rule typically results in beams with a yield-strength significantly higher than the maximum loading condition, effectively providing a factor of safety.
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Linesets are manually operated from a locking rail such as this one.
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Loading bridge. Weights are seen on floor.
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Grid-less fly tower with catwalks. Battens (yellow), under-hung blocks and lift lines are visible.
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Channel-type grid with upright blocks and lift lines visible.
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Channel-type grid, viewed from below with drapes, battens, and electrics visible.
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Upright loft blocks on a channel-type grid.
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