Stage Rigging 101
Apr 3, 2010 12:00 PM, Lawrence Graham
Fly tower and rigging
The area above the performing area of the stage is called the fly tower, and the part of the building that encloses the stage (the performing area and the wings) is called the stage house. The fly tower houses the stage-rigging system.
A fly tower may be configured in one of two ways: with or without a gridiron. A gridiron is a work floor, located high in the fly tower. It can be used to support the primary, upright rigging. Upright rigging utilizes the gridiron itself to hold the blocks that, in turn, support the live load on the system. Underhung rigging does not stand upright on the gridiron but is suspended from blocks attached below structural steel elements located seven or eight feet above the surface of the gridiron and just below the roof structure. In the design phase, it is possible to predict and control what the maximum loading on this kind of permanent rigging will be.
The gridiron also supports secondary rigging. Secondary rigging may consist of chain hoists or spot blocks that are temporarily installed to support point loads. These point loads might include heavy lighting trusses or any special rigging equipment associated with a particular production. Sometimes secondary rigging is used to actually fly performers, as in the musical Peter Pan. However, when designing the structure, it is not possible to predict or control what these point loads might be or where they will be placed.
The gridiron can also be used to support flexible stage-lighting cables. There are two types of these cables — those that are a part of the rigging and feed the electrical distribution strips and drop boxes, which provide additional flexible electrical connectivity to any of the pipe battens, light ladders, or booms that are used with portable fixtures to light the stage.
In the United States, the most commonly used type of rigging system is a manually operated counterweight system (see Fig. 1). In this system, the scenery or electrical system on the pipe batten is counterbalanced by steel weights. All the lift lines for a particular line set pass through a single pulley (called a head block) that is secured to the headwell. The load on the batten is transferred through the head block to counterbalancing steel weights placed in a frame called an arbor. When the counterweight arbor is raised and lowered, the pipe batten moves, or travels, in the opposite direction.
The arbor is raised and lowered by pulling on the operating line. The operating line passes through a brake and lock assembly. Whereas this device is used to prevent unwanted rigging movement, it is intended to work only when the rigging is in balance. As a result, it usually places no significant load on the building structure.
The loading gallery
When a pipe batten has been lowered to the stage floor in order to attach a load to it, the arbor will be located near the top of the fly tower. While the arbor is in this position, the counterbalancing weights are added to it. The loading gallery provides a place for personnel to carry out the operation. If there are no loads on the pipe battens in the system, the counterweights are stored on the loading gallery floor.
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