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1950-51 Theatre Catalog, 9th Edition, Page 110 (90)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 110
Page 110

1950-51 Theatre Catalog, 9th Edition, Page 110

FIG. 1. Left: (A) Common ioint. Right: (3) Special ioint.



The lamella roof is made up of comparatively short timbers of uniform length called itlamellas." These short pieces are bevelled and bored at the ends, and bolted together at an angle. They thus form a network of structural timbers. Standard lamella roofs use the common or eccentric joint (Fig. 1a), but special roofs and extremely large spans make use of special joint connector plates (Fig. 1b).

The network of lamellas forms an arch of mutually braced and stiffened timbers. In view of the fact that it is an arch, rather than a truss, the roof naturally exerts a horizontal reaction in addition to the vertical one. The net result of these .tWo reactions is the roof thrust distributed to thrust supports-tierods or buttresses, generally spaced from 12' to 20 feet-by timber, steel, or concrete sill beams between these supports. If a continuous wall support for the sillbeam is available, it is only necessary to design it for the horizontal reaction (Fig. 2).

Types of Roofs

First among the four types of lamella roofs is the tied segmental arch (Fig. 3a). Inasmuch as the thrust is taken up by tierods in this type, the method is used primarily in cases where buildings occupy a full lot area and where the type of building in question precludes the use of buttresses, or extended wall columnsdeveloped as cantilever beams-to take up the roof thrust.

The horizontal reaction taken up by the tierod is determined by the formula:

H.Dead + Live Load per sq. ft. X span2 X tierod spacing 8 X Roof rise

The tierod area required at the root of the threads is obtained by dividing H by the permissible tensile stress for steel. The roof rise varies between one-sixth and one-seventh of the roof span considered as a whole. A lamella roof is coma pletely selfusupporting when tied in this fashion, and it exerts only vertical pressure equal to the live and dead load upon the wall or column supports. It is important, of course, to anchor it properly to resist wind action.

In the case of the buttress segmental arch (Fig. 3b), the thrust, previously defined as the natural resultant of horizontal and vertical reactions, is taken up by buttresses, concrete or steel beam columns, timber or steel bents, or rigid frame bents. The roof rise variation falls between one-sixth and one-quarter of the roof span; the customary rise approximates one-fifth.

This particular type of roof is most desirable, from the economical point of view especially, in buildings where high clearance centers are required. Auditoriums, gymnasiums, field houses, indoor tennis and badminton courts, hangars, and exhibition buildings are a few typical examples. Buttresses are extremely advantageous in these applications, for they permit the use of low and light sidewalls.

The parabolic arch (Fig. 3c) is a type of lamella roof construction in which the roof generally starts from the floor line or atop a low foundation wall. This wall is reinforced to take up the relatively low horizontal thrust component, while

the floor construction acts as tie membrane.

The parabolic lamella roof has been found to be readily adaptable to small churches, indoor rifle ranges, and small motion picture theatres, for it combines wall and roof construction into one unit.

The gothic arch (Fig. 3d) type of lamella roof represents a three-hinged arch. It may be used with tierods to cover buildings which possess a trapezoid fioor plan. When used in church designs, it can be started above the side aisle

height to span the nave. Low, buttressed walls may mark its starting point in storage sheds with overhead conveyors.

Roof Plans

Three principal basic arrangements are possible for the lamella roof. These patterns may be varied and combined to provide sufficient leeway in design to meet any roof requirements.

(a) The continuous lamella roof carries the network from gable wall to gable wall and acts as a horizontal wind-truss between gable walls (Fig. 4a).

(b) The lamella roof with sloped and raftered end, or ends (Fig. 4b), stops with its network 15 to 20 feet from one or both ends. This space is covered by simple rafters supported by the lamella roof endarch and the end wall. These raftered ends provide a warped surface of varying slope.

(c) The lamella roof with broached ends (Fig. 5) is formed by intersection with lamella roofs of the same radius which spring from the end walls. These broached ends may be rectangular or multi-sided. Lamella roofs can also be made to intersect as occasion requires for L,T,U, or cross-shaped floor plans.


Since all units are precision-fabricated in accordance with specifications, erection of lamella roofs is a fairly rapid process. The units are generally erected from a movable scaffold equal in width to that of the roof and the depth of one bay (spacing of tierods). After the timber sills-or spacers in the case of steel or concrete beams-have been placed, the lamella network is woven from the sill up, from both sides, to meet and join in the center. Spacer boards set over the lamella joints assure uniform spacing

and obviate any chance of the network spreading laterally, while and after the scaffold is moved into the next bay for weaving another roof section.



Insulation or acoustical board may be Employed in the panels to augment the naturally good acoustical properties of lamella roofs themselves. The network as an entity breaks up and reflects the sound in numerous directions, and the

FIG. 2. Typical siII details. (A) Tilled timber sill. (B) Reiniorced concrete sill. (D) Flat timber sill.

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1950-51 Theatre Catalog, 9th Edition, Page 110