Patent GB-725345-A (GB)
Title: Improvements in and relating to rafter principals for use in roofs of large span
IPC: E04B1/344
Filed: 1953-03-17
Abstract: 725,345. Flexible rafters. PONT, H. M. March 17, 1953 [March 31, 1952], No. 7351/53. Classes 20(2) and 20 (4). The invention relates to a rafter principal for a roof of large span such as. the type described in Specification 649,729 in which flexible rafter principals, turned with their convex sides towards the outside, extend from supports provided at the corners of the roof to a common summit and are interconnected near the supports by means of cables or bundles of cables extending along the eaves and in which the rafter principals support flexible tightening means provided in the roofing planes and consisting of wires, bands or cables which are stretched between the principals and between the principals and the eaves-cables to support the roof covering. The rafter principal comprises a foot-member 1, Fig. 1, and a top member 2, the portion extending between them consisting of a plurality of resilient bars 8 which are short with respect to the length of the rafter principal and partly overlap each other in a plurality of layers the bars bearing with their outward and footward pointing ends on blocks 9 through cross bars 8a, Fig. 2, and with their inward and topward pointing ends on blocks 10, the blocks 9, 10 being hingedly connected by link rods 11  so that the bars 8 and link rods 11  enclose acute angles. The foot-member 1 bears through a universal joint on a foot 3 which bears with its spherical surface 4 on a corresponding surface 6 of a support 7 through balls 5 as in Specification 702,671. The link-rods 11 which are pivoted at their ends to the blocks 9 have their other ends passed through crossbeams 12 and fixed by nuts 13 threaded thereon, the beams 12 having semi-cylindrical surfaces 14 engaging corresponding recesses of the blocks 10. Braces 15 slidably connect the blocks 10 to a nearby layer of bars 8. Distance blocks 16 provided between the bars 8 are connected to the link rods 11 by braces 17. The blocks 9, 10 abut against each other or engage each other in the manner of hooks, when the rafter principal is at its minimum or maximum curvature respectively. Each row of blocks 9 may be connected to the blocks 10 by two or more rows of linkrods 11. In a modification, Fig. 4, blocks 18, 19 are provided on the outside and inside of the rafter principal respectively, each set of blocks engaging each other as hooks with such a clearance that during a minimum or a maximum bending of the rafter principal the blocks form a continuous outer layer or an uninterrupted inner layer respectively. Alternatively instead of using chain links as shown, the blocks may be interconnected by sliding parts or hook-shaped members engaging each other. The links 21 are hinged at 28 to the footward pointing ends of the bars 8 and have slots 29 engaging cross-rods 30 passed through the blocks 18. The links also have slots 23 to receive blades 20 which separate the bars 8 the supporting edges 22 of the blades 20 and the slots 23 being so shaped that the blades always contact the bars 8. The blades 20 may have rollers 24 for contacting an edge of the slots 23. Also guiding strips 25 are provided which are pivoted to pins 26 on links 21 and engage abutments 27 on the bars 8. In a further form, Fig. 6, each link is in two parts 21a, 21b which may be adjusted in the longitudinal direction of the link. The part 21a is similar to the links 21 of Fig. 4, the part 21b being adjustably attached to a fork-shaped end of part 21a by screw-rods 31 and nuts 32 and being pivoted at 33 to a bar 8. The parts 21b of the links carry cross-rods 34 which engage slots 35 of the blocks 19.