The arrow of the elevation of the arches shall not be less than 1/7 span. However, the slope of the frame transom depends on the type of covering used, which is most often cardboard or sheet metal. Arches can have a rectangular or I-section, constant or variable in length. The height of the cross-section in arcs is assumed 1/40-1/60 span, while the height of the bolt 1/8-1/16 span. In frames with a larger span, variable sections of both rafters are assumed, and poles.
Due to the industrial production of structural elements, nailed or glued rectangular sections are more often used, less often I-sections. Also for reasons of ease of manufacture and transport, arches and three-hinged frames are mainly used.
The shelves of the frames can be made of one element (rys.a) with a curved corner, or from two elements joined at the corner with mechanical connectors.
Three-hinged frame made of glued wood: a) view, b) transom cross-section, c) detail of the support on the foundation; 1 — rama, 2 - skylight structure, 3 - external wall, 4 - rafters, 5 - purlin, 6 - lacing.
The figure shows the cross-section of a hall with a span 25,0 m. The load-bearing structure consists of three-hinged glued-laminated timber frames with curved corners. The cross-section of the transoms and mullions is rectangular, double-walled, connected with spacers by means of rings. Planks with a cross-section of 1.2 were used to make the half-frames×18 cm, the height of the frame transom in the ridge is 38 cm, a w narożu 94 cm. The frames are stiffened in the longitudinal direction of the hall by spaced vertical braces 4,5 m that also serves as a purlin. The tie in the floor level is made of wood with a cross-section 2 x 10×20 cm.