STRUCTURAL ELEMENT PARTICULARLY FOR OBTAINING ELECTRIC LINE SUPPORT GIRDERS

Abstract: A structural element for metal structural work is form­ ed, in the manner of a tube, by a pair of half-shell fellow sections, arranged with their concavities opposed and con­ nected together in a discrete manner along their long sides, such as to guarantee a much higher torsional rigidity than that provided by corresponding open sections. The structures which can be obtained with structural elements of this type include flat and three-dimensional girders, particularly in the form of supports for electric lines, of which the stringers are formed with said elements in order to provide high torsional rigidity.

Description: This invention relates to improved bidimensional truss structures to be used in particular as supports for overhead electric power transmission lines, the stringers of which are constructed in a particularly advantageous manner. For the construction of supports for overhead electric power transmission lines, structural elements are currently used consisting essentially of open sections (usually angle irons), which are favoured for their low production costs, easiness of connection, easy protection treatments (galvanising) and reduced transportation bulk. However these elements, which are well known and widely spread, give rise to local or torsional instability problems when used as bars subjected to combined compressive and bending stresses, such problems being solved by using sections which are thicker and heavier than desirable. Moreover, flat or slender structures constructed with these conventional elements have very low critical out-of-plane twisting loads, a consequence of the torsional instability of the component parts, and this can be a serious limitation in planning certain advanced types of supports for electric lines. All these drawbacks could easily be eliminated by replacing the structural elements in the form of open sections by tubular metal elements. However these latter, though having properties which have long been known and appreciated, have had little application in practise because of the high production costs of the tubes, the difficulty of making the connections and the consequent high costs of these latter, and the considerable transportation bulk thereof. The object of the present invention is to provide bidimensional truss structures comprising stringers formed with structural elements which combine the advantageous properties of the aforesaid known struc tural elements, without possessing their defects, thus allowing to plan and construct bidimensional supports for overhead electric power transmission lines, or any other type of bidimensional truss structure, with considerable advantages over the known art. The LU-A-60543 already discloses structural elements for metal structural work formed by a pair of half-shell sections, arranged with their concavities opposed and connected together in a discrete manner along their long sides, such as to guarantee a much higher torsional rigidity than that provided by corresponding open sections. Nevertheless, in these structural elements, the long sides of connection of the two half-shell sections forming them are in mutual contact. The invention now supplies a bidimensional truss structure comprising stringers constituted by structural elements formed as a tube by a pair of half-shell sections, arranged with their concavities opposed and connected together in a discrete manner, along flanges of their long sides, by means of bolts applied at spaced locations along said flanges, characterized in that, the section flanges are kept spaced apart and parallel by inserting cross stiffening brackets in correspondence with the connection bolts, such that slots are provided between the flanges. The invention especially concerns a particularly slender bidimensional truss structure, in the form of a self-braced trestle support for overhead electric power transmission lines, wherein said structural elements forming the stringers are connected together in such a manner as to prevent any relative rotation of the sections of the two stringers, so that the torsional rigidity of said stringers opposes any lateral deflections thereof. Some embodiments of the invention are described hereinafter in greater detail with reference to the accompanying drawings, in which: Fig. 1 is an interrupted perspective view of a first embodiment of the structural element used to form the stringers of bidimensional truss structures according to the invention; Fig. 1bis shows, on an enlarged scale, a construction detail of said structural element; Figs. 2 and 3 are interrupted perspective views of two other embodiments of said structural element; Fig. 4 shows the transport packaging system for the half-shell sections used to form the structural elements of figs. 1 to 3; Fig. 5 is a diagrammatic illustration of a particularly slender bidimensional self-braced trestle support for overhead electric power transmission lines, constructed using structural elements of the type shown in figs. 1 to 3 to form its stringers; Figs. 6 and 7 are detailed views of some construction details of the support of fig. 5; Fig. 8 shows a lattice support or anchor tower for overhead electric power transmission lines, constructed in the form of a three-dimensional girder, using structural elements of the type shown in fig. 3 to form its stringers; and Figs. 9 and 10 are detailed views of some construction details of the support of fig. 8. With reference to the drawings, it can be seen from figures 1 to 3 that the structural element used to form the stringers of the bidimensional truss structure according to the invention consists of a pair of open half-shell fellow sections 1, arranged with their concavities opposed and connected together in a discrete manner along their long sides. In the embodiments shown, the sections 1 are channel sections with a very wide base 1A and with outwardly inclined sides 1B, terminating with flanges 2 parallel to the base 1A. The discrete or discontinuous connection of the two sections 1 is obtained, in the illustrated embodiments, by means of bolts 3 applied at spaced locations, either singly or in pairs, along the flanges 2 of said sections 1. According to the invention, the sections 1 and their flanges 2 are kept spaced apart in order to form slots 4 in the above structural element, apt to prevent extended contact between the flanges which could give rise to corrosion phenomena. These slots are also useful for inserting hooking members to facilitate climbing the structures formed therewith, and for introducing means to spray-paint the interior of said structural elements. For this purpose, cross stiffening brackets 5, disposed at a certain distance apart, are inserted between the flanges 2 in the zones of application of the bolts 3. One method for connecting together the flanges 2 of the two half-shell sections 1 of said structural element, which is particularly advantageous for attaining the proposed objects, is shown in figure 1bis. As can be seen, the bores 2A for the bolts 3, made into the section flanges 2, are deep-drawn in order to cooperate with corresponding cavities 5A provided in the surfaces of the cross stiffening brackets 5. This arrangement prevents any possible relative sliding between the thus connected flanges 2 of the two sections forming the structural element, thereby also increasing the torsional rigidity of the structural element itself. Further solutions are shown in figure 2, wherein a zig-zag bent plate 6 is interposed between the flanges 2 of the half-shell sections 1, and in figure 3, which illustrates a structural element particularly suited to form the stringers of three-dimensional girders, for example for lattice supports of overhead electric power transmission lines. This element is formed by associating a half-shell section 1, of the type used for the structural elements of figures 1 and 2, to a simple angle iron 1C. The connection is again obtained using cross stiffening brackets 5 and bolts 3, applied between the flanges 2 of the section 1 and the edges of the long sides of the section 1C acting as flanges. Also in this case, slots 4 are formed between the two sections of the structural element, for the assembly of which the construction method of figure 1bis can be applied, with all the advantages deriving therefrom. In each case - as can be seen - a structural element is obtained, formed as a tube but the component parts of which are open sections. This element has all the advantages of open sections, with regard to production costs, easiness of connection (as illustrated hereinafter), easy galvanising, and reduced transportation bulk (as can easily be seen from figure 4 which shows the system for packaging the component half-shell sections). It also has the essential advantage of structural tube elements, namely to guarantee a much higher torsional rigidity than the corresponding open sections. However, this structural element has none of the basic drawbacks of tubes. By varying therein the assembly method of the component half-shell sections, it is also possible to vary the strength and flexural rigidity according to one axis. Thus, with the element of figure 2, in which a bent plate 6 is inserted between the flanges 2 of the sections 1, a greater spacing is obtained between the component half-shell sections, and thus increased strength and flexural rigidity than in the element of figure 1. The assembly can also be carried out in such a manner as to continuously vary the strength along the length of the structural element, by using cross stiffening brackets of different thickness, or plates of variable thickness, for spacing with slots of variable thickness the flanges of the opposed half-shell sections. A tapered structural element can thus be formed. It should also be noted that the component sections of the aforedescribed element can be manufactured using the same rolls for different sizes of their base 1A, leading to a further advantage in production costs. With this structural element, the invention proposes to construct the stringers of a bidimensional truss structure which allows, very advantageously, to form a particularly slender support for overhead electric power transmission lines wherein said stringers have such a high torsional rigidity as to prevent any lateral deviations - outside the support plane - of the compressed stringer. An example of a bidimensional self-braced trestle support for overhead electric power transmission lines of this type is shown in figure 5. To construct this support, use is made of two sets of structural elements 11 and 12 - for example of the type shown in figure 1 - arranged to form two stringers which are mutually inclined over the major length A of the height of the bidimensional truss structure forming the support, but which run parallel and close at the top B of said support. The stringers formed by the elements 11 and 12 are connected together in two zones C and D by similar transversal elements 13 and 14. Figures 6 and 7 show respectively a possible scheme for connecting together the elements 11 and 13 in zone C of the support, and for connecting together the elements 11 and 12 in the top part B of said support (this latter connection being obtained by applying simple channel sections 15). The simplicity, easiness and efficiency of the connections between the support components can be easily deduced from these figures. The advantages deriving from combining, in the stringers of the truss structures according to the invention, the merits of open sections and of tubes, but without their defects, also extend to the conventional three-dimensional girders, in particular three-dimensional lattice supports for overhead electric power transmission lines realized with similar stringers. Figure 9 is a diagrammatic view of one of these supports, in the form of a girder comprising four stringers 16, each constituted by structural elements of the type shown in figure 3. Figures 10 and 11 are a side view and, respectively, a horizontal section view of one of the stringers 16, at the connection point with the lattice members 17. It is apparant that, using the structural elements of figure 3, in a support of the type shown in figure 8, drastically reduces problems deriving from torsional and local instability, which are always present in these structures, whereby sections of very reduced thickness, and thus much lighter, can be used in said structures, with obvious considerable advantages.

Claims: Bidimensional truss structure comprising stringers constituted by structural elements formed as a tube by a pair of half-shell sections (1), arranged with their concavities opposed and connected together in a discrete manner, along flanges (2) of their long sides, by means of bolts (3) applied at spaced locations along said flanges (2), characterized in that, the section flanges are kept spaced apart and parallel by inserting cross stiffening brackets (5) in correspondence with the connection bolts (3), such that slots (4) are provided between the flanges. Bidimensional truss structure as in claim 1), being particularly slender and characterized in that said structural elements forming the stringers are connected together in such a manner as to prevent any relative rotation of the sections of the two stringers, so that the torsional rigidity of said stringers opposes any lateral deflections thereof. Bidimensional truss structure as in claim 1), in the form of a self-braced trestle support for overhead electric power transmission lines.

Inventors: PARIS, LUIGI
Applicants: SAE SADELMI S.P.A.
Application year: 1984
Main classification: E04C3
IPC codes: E04C3, E04H12