> > > >

1950-51 Theatre Catalog, 9th Edition, Page 118 (98)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 118
Page 118

1950-51 Theatre Catalog, 9th Edition, Page 118

any rate, if a loading platform is used, it is good practice to discontinue the ladder or the stairs at the loading platform. A short ladder can then be placed on the loading platform leading up to the gridiron.

Underhang Type

The preceding discussion has had to do entirely with the upright or conventional type of gridiron which should be provided for in any modern equipped house. There is, however, what is known as the Underhang type of gridiron, in which the stage equipment is attached to the under side of I-beams running up and down stage in approximately the same position as the Wells and headblock beams on the upright type gridiron with the loads correspondingly distributed. There are cases where this is the only type of suspension practical, but the so-called Underhamg type of gridiron is only make-shift at best and has many disadvantages.

First of all, the beams are figured to carry not only the static load of the stage equipment, but also the floor or roof above. It follows, therefore, that if the floor above becomes overloaded, or the roof carries an exceptionally heavy snow load, the load upon the beams is changed accordingly. These conditions are very difficult to anticipate. Occasionally these beams are supplemented with other beams to carry the roof load, but in most cases the other beams are lighter and, therefore, subject to greater deflection. Thus the bulk of .the load, in turn, is transferred on to the stage equipment beams. If one also considers at the same time that considerable more stage equipment may be added than that which the architect originally figured on, an unsafe condition develops.

Secondly, once the underhang type of

stage is rigged, it is extremely difficult to make any inspection or to do any maintenance work, since the stage proper is full of drapes, lights, etc., and there is no chance to get ladders up to the


stage equipment. In building such a type of structure it should be remembered that a 40' ladder is about the extreme height at which men can work. If the beams are higher than 40', and in many cases they are, it is necessary to construct movable scaffolding called "boomerangsfl and the cost of such scaffolding is very high. Thus, from a practical standpoint, it would seem that the underhang type of gridiron should never be used when it can be avoided, since it has no flexibility, makes maintenance and inSpection next to impossible, and precludes the possibility of hanging additional sets or temporary lines that may be required from time to time.

During the past two or three years it has become quite common practice to erect this type of gridiron and then plaster over the beams. The installation cost really soars because the blocks all have to be specially built, and the plaster has to be chiseled away in order to get the clamps on the beams. Furthermore, the job, when completed, is not a good installation. It is diflicult to say Where this practice started, as it adds nothing to the strength of the structure; in fact, it adds an additional load. In the final analysis, there is no reason for plastering the ceiling of a stage house, and such practice should be discouraged.


While the ventilating system is not a part of the gridiron, it is, nevertheless, of considerable importance, and in many cases the designs of ventilators have not met requirements. The purpose of the ventilators in the roof is to carry off heat and gases generated by a fire on the stage and to prevent a pressure from building up suf'liciently to interfere with .the asbestos curtain descending to close the proscenium opening.

The area of the ventilators should be calculated in proportion to the size of the stage house and thus give ample release to these gases.

In many cases, fusible link systems operating the ventilators have been brought down only to the gridiron floor. This is not sufficient to give the type of protection necessary, and these fusible link systems should be brought down to within 6' of the stage floor. If a fire were to start close to the stage floor, these links would let go and open the ventilators, whereas if all fusible links are above the gridiron, the fire would get quite a start before the ventilators opened up. This system of fusible links is, of course, entirely independent from the asbestos curtain fusible link system.


For added helpful data on Theatre Stages, the reader is directed to iiDesign and Furnishing of the Small Stagell on I). 229 of the 1945 Edition of THEATRE CATALOG, and to

iiDesign and Equipment for Cinema Smgesll on P. 237 of the 1946-47 Edition of THEATRE CATALOG. In both, the same author analyzes other relating facts gained from his long experience.

1950-51 Theatre Catalog, 9th Edition, Page 118