Static structures (e.g. – buildings) – Openwork; e.g. – truss – trellis – grille – screen – frame – or... – Fabric or lattice; e.g. – indeterminate grating
Patent
1984-08-08
1985-10-01
Ridgill, Jr., James L.
Static structures (e.g., buildings)
Openwork; e.g., truss, trellis, grille, screen, frame, or...
Fabric or lattice; e.g., indeterminate grating
52693, 244131, 403195, 403201, E04B 124
Patent
active
045437629
DESCRIPTION:
BRIEF SUMMARY
The present invention generally relates to a flexible terminal point for lattice work constructions, and more particularly to such constructions subjected to dynamic forces.
Dynamic forces are usual when considering lattice work constructions of many different kinds, for example with buildings and parts of buildings such as floors and roofs and the like which are subjected to varying forces, with pillars, towers, masts, bridges other types of constructions which can be subjected to gravitational loads or side loads as a result of strong winds and the like. A special field where large dynamic forces arise are lattice work constructions which wholly or partially are in water and are there subjected to varying loads and high dynamic stresses resulting from wind and wave. Examples of such constructions are bridge foundations, breakwaters harbour piers docks or work platforms e.g. oil derricks.
The elements of a lattice work construction which are brought to a single terminal point always attempt to change the relative angles between the elements as the construction is subjected to normal loading. Unusual forces directly applied upon at the cross bars of the lattice work construction increase the need for flexibility of the terminal points. Conventionally, the design of lattice work terminal points are such that relative changes in the angles between the elements is restricted, creating concentrations of stress in an area where the material's fatigue strength is already reduced as a result of directional changes of the forces applied. The danger of fatigue failure is exaggerated further in cases where the inflicted loads change direction and cause stresses with changing sign in the terminal point's fittings.
To eliminate the named problems it has been suggested that the terminal points fitting should be made flexible, so that the lattice work element is allowed in some degree to be movable, reducing the risk for fatigue failure. Such flexibility of terminal points fittings is known through for example, the German Pat. Nos. 1 459 963 and 2 421 758. These terminal points fittings are formed as ball joints, where the ball and socket are fastened in the lattice work element and terminal plate or the like of the lattice work. These known types of joints are intended as simple methods of assembly and also allow for a certain movement between the different parts. These constructions are however, mainly suitable for lighter lattice work dimensions, and have the disadvantage that terminal point fittings can be subjected to both tension and compression stresses. Tension forces can cause the edges of the socket which partly encloses the ball to be drawn out, giving rise to play even to the extent that the ball can be pulled out of the socket. To make it possible for a de-mountable ball joint, or of the ball from its socket, the known constructions are made up of a large number of parts, of which many must be adjusted or tightened on assembly.
This invention endeavours to solve the problem of a simple and effective terminal point fitting, which allows a certain flexibility between the elements of the lattice work, which is simple to assemble and adjust, and which is well suited for large and heavy lattice work constructions.
A special aspect of this invention concerns the elimination of problems caused by dynamic forces of changing direction in terminal points fittings. Pre-tensioning of the terminal point causes the directional changes of dynamic loads to result in stresses of varying magnitude only, and the stress variations are reduced considerably in the pre-tensioned terminal point means by the transference of forces to the compressed parts of the fitting. This construction achieves much improved properties of strength in comparison with constructions which allow directional changes of stresses from tension to compression.
A development of the invention is that the terminal point fitting is formed with three different but co-acting elements, which are arranged to bring about the named pre-tension, and where one elemen
REFERENCES:
patent: 1500235 (1924-07-01), Clark
patent: 1545667 (1925-07-01), Kusterle
patent: 1846772 (1932-02-01), Wallis
patent: 1946408 (1934-02-01), Loudy
patent: 2391275 (1945-12-01), Shaw
Ridgill, Jr. James L.
Scanding Byggkonsult Aktiebolag
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