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1950-51 Theatre Catalog, 9th Edition, Page 117 (97)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 117
Page 117

1950-51 Theatre Catalog, 9th Edition, Page 117

block beams to buckle, since there is considerable side pull that must be taken up by the flanges of these beams. Wideflange beams are, therefore, most practical for this purpose.

The necessity of providing a bracer beam (as shown in Fig. 3) on a stage with considerable depth to offset this tendency to buckle has also been proved. The question of whether a beam or a channel is used depends on the load involved and the span. In any event, the bracer beam should not touch the bottom of the top flange of the head-block beam, and the on-stage flange of the bracer beam should not interfere with the cable leading from the head block to the first loft-block well. The two headblock beams should be connected by diaphragms at approximately 8' spacing so as to distribute this load over both beams.

Avoidance of Drilling

The foregoing again brings up the importance of properly designing the carrying beams for the stage equipment. When the engineer determines the size of the beams to be used, he does not take into consideration the drilling of numerous holes in the beams, a step which, of course, has a tendency to weaken them. The stage equipment manufacturer has this same thought in mind when he builds his equipment to clamp on the beamstto avoid this extra drilling. Hence, it is always best to allow proper clearance for the flanges on both the loftblock wells and head-block beams in order that the equipment may be clamped into place rather than to resort to drilling, a practice which not only weakens the beams, but materially increases the cost of installation as well.

Setting Off-Stage Head Block

In setting the off-stage head-block beam (the one nearest the wall), it is good practice to allow a 5" minimum clearance between the flange of the beam



and the wall. In using the 5" clearance between the flange of the off-stage headblock beam and the wall, the construction of the side wall underneath these head-block beams all the way to the stage floor should be taken into consideration. If the wall is perfectly smooth, and there are no projections, the 5" clearance is ample to receive the guide tracks, carriages, etc., with relation to the blocks overhead. However, if there are projections of any type on this wall, the 5" clearance should be taken from the projection, and not from the wall proper, to insure a clear space for the installation and operation of the counterweight system. No ducts, pipes, or other equipment should be hung on this wall. The counterweight equipment will occupy a depth of approximately 26" from the wall on stage.

Use of Supporting Hangers

In Fig. 1 (Method #2) supporting hangers carrying part of the load of the gridiron and attached to roof beams overhead are shown. This is good construction, provided the roof beams are available to attachment of the hangers. In this type of construction the steel in the gridiron proper can be cut approximately in half, a factor of considerable importance in three ways: (1) approximately half of the cost of the steel may be saved; (2) the actual load imposed by the gridiron itself is cut in half, and there is less weight to support on the side walls and overhead trusses; and (3) the cost of erection will be considerably less. This possibility in stage construction is one that is not taken advantage of in proportion to its importance.

Head Clearance

The question often arises as to how much head clearance to allow above the gridiron. Obviously, there should be enough to permit a man to stand up straight, but, since the roof beams or trusses usually run on and off stage

(across stage), it is satisfactory to base this clearance on the height from the gridiron floor to the top of the roof beams or trusses (underside of roof), while bearing in mind that it is desirable to cut the cost of construction at this point as much as possible.

Loading Platform

On any modern size stage a loading platform should be provided as per Fig. 4, and it should be figured to carry a load of approximately 100 lbs. per square foot. It is understood, of course, that only a part of the counterweights will be taken off and put on frequently, so the platform need not be figured to carry the entire counterweight load. The drawing shows a practical, inexpensive loading platform.

Problem of Accessibility

In the past it has been common practice to provide ladders up the side wall

'for accessibility to the gridiron. These

ladders, usually 60' to 80' high, are very hard to climb, and for that reason no one ever visits the gridiron, unless he is compelled to do so. This disadvantage does not permit proper service of the operating equipment.

Occasionally the design of the building will permit breaking up this ladder height to simplify climbing greatly. In any event, the ladder method of reaching the gridiron is coming up for more consideration in the future because safety inspectors are offering serious objections to these long, open type ladders.

One of the best methods for obtaining ready access to the gridiron is a circular stair, which should be placed against the back wall and just in front of the loading platform. This not only provides a convenient means of access to the gridiron, but also meets the requirements of safety regulations. If the stairs are placed in .the proper position, it is possible to operate sets in the same area without interference from the stairs, At
1950-51 Theatre Catalog, 9th Edition, Page 117