EP0177634A1

EP0177634A1 - Structural element particularly for obtaining electric line support girders

Info

Publication number: EP0177634A1
Application number: EP84112273A
Authority: EP
Inventors: Luigi Paris
Original assignee: SAE Sadelmi SpA
Current assignee: SAE Sadelmi SpA
Priority date: 1984-10-12
Filing date: 1984-10-12
Publication date: 1986-04-16
Anticipated expiration: 2004-10-12
Also published as: ATE62519T1; DE3484441D1; EP0177634B1

Abstract

A structural element for metal structural work is formed, in the manner of a tube, by a pair of half-shell fellow 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.

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 structural elements for metal structural work, which have the advantages both of tubular elements (mainly, shape stability and torsional rigidity) and of open sections (mainly, low production costs, easiness of connection, convenience in transportation).
The present invention also relates to structures, generally flat and three-dimensional girders, and in particular supports for overhead electric power transmission lines, which can be constructed in particularly advantageous manner with said improved structural elements.
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 favored 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 of 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 a strutural element for metal structural work, which combines the advantageous properties of the aforesaid known structural elements without possessing their defects, thus allowing to plan and construct supports for overhead electric power transmission lines, or any other type of truss or structure, with considerable advantages over the known art.
Essentially, the structural element for metal structural work according to the invention is characterized in that it is formed of a pair of half-shell fellow 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.
In this structural elements the connection between said half-shell section is obtained by means of bolts applied at a certain mutual distance between flanges of said sections, said flanges being preferably kept spaced-apart and parallel by inserting cross stiffening brackets in correspondence of the connection. bolts, or by interposing sections or bent plates.
The structures which can be constructed using structural elements of the aforesaid type specifically include, in the present invention, a particularly slender flat girder, obtained by forming its stringers with structural elements of the aforespecified type, 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 deviations (outside the girder plane) of the compressed stringer.
Many other structures for metal structural work can also be obtained, and in particular three-dimensional girders in the form of lattice supports.
The invention is 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 according to the invention;
Fig. 1 bis shows, on an enlarged scale, a construction detail of said structural element;
Figs. 2, 3 and 4 are interrupted perspective views of three other embodiments of the structural element according to the invention;
Fig. 5 shows the transport packaging system for the half-shell sections used to form the structural elements of figures 1 to 4;
Fig. 6 is a diagrammatic illustration of a bidimensional self-braced trestle support for overhead electric power transmission lines, constructed as a particularly slender flat girder, using structural elements of the type show in figures 1 to 3 according to the invention to form its stringers;
Figs. 7 and 8 are detailed views of some construction details of the support of figure 6;
Fig. 9 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 figure 4 according to the invention to form its stringers; and
Figs. 10 and 11 are detailed views of some construction details of the support of figure 9.

With reference to the drawings, it can be seen from figures 1 to 3 that the structural element according to the invention is formed 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 a certain mutual distance, either singly or in pairs, between the flanges 2 of said sections 1.
It is preferable to keep the sections 1 and their flanges 2 spaced apart in order to form slots 4 in the structural elements according to the invention, apt to prevent extended contact between the flanges which could give rise to corrosion phenomena. These slots are also useful for inserting hooking memebers to facilitate climbing the structures formed therewith, and for indroducing 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 a the structural element according to the invention, and which is particularly advantageous for attaining the proposed objects, is shown in figure 1 bis. As can 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 slinding 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 figures 2 and 3, wherein a zig-zag bent plate 6 and a channel section 7 are respectively interposed between the flanges 2 of the half-shell sections 1.
A solution representing a combination of those illustrated is also possible. This is obtained by connecting the flanges 2 to the plate 6 or section 7 - rather than in a discrete manner - with the interposition of cross stiffening brackets 5.
Figure 4 shows a structural element according to the invention, particularly suited to form the stringers of three-dimensional girders, for example for lattice supports for 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 to 3, to a simple angle section 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 1 bis can be applied with all the advantages deriving therefrom.
In each case - as can be seen - a structural element is obtained, formed likewise a tube but the component parts of which are open sections.
This element has all the advantages of open sections, with regard to productions costs, easiness of connection (as illustrated hereinafter), easy galvanising, and reduced transportation bulk (as can be easily seen from figure 5, 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, the structural element according to the invention has none of the basic drawbacks of tubes. In the element according to the invention, by varying 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 elements of figures 2 and 3, in which the bent plates 6 or channel sections 7 are 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, in which the component sections 1 are closer together as they are separated by the thinner cross stiffening brackets 5.
The assembly can also be carried out in such a manner as to continuously vary the strenth along the length of the structural element, by using cross stiffening brackets of different thickness, or plates or sections of variable thickness, for spacing 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 element according to the invention can be manufactured using the same rolls for different sizes of their base lA, leading to a further advantage in production costs.
With the structural elements according to the invention, it is possible to very advantageously obtain a particularly slender flat girder, with the two stringers formed from said elements, connected together in such a manner that the torsional rigidity of the stringers prevents any lateral deviations - outside the girder plane - of the compressed stringer.
An example of a girder of this type is the bidimensional self-braced trestle support for overhead electric power transmission lines shown in figure 6. To construct this support, two sets of structural elements 11 and 12 according to the invention are used, 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 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 7 and 8 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.
It should be noted that the support of figure 6 could advantageously be formed in its top part B as a single element shaped as a tube, by joining together the two structural elements which form its stringers through connection of their two outer half-shell sections with two inner channel sections (namely forming at the top B of the support a single structural element of the type shown in figure 3).
The structural elements according to the invention are suitable not only for constructing any appropriate type of metal structural work - with all the advantages deriving from combining the merits of open sections and of tubes, but without their defects - but also for forming ordinary three-dimensional girders, in particular three-dimensional supports for overhead electric power transmission lines.
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 according to the invention of the type shown in figure 4. Figures 10 and 11 are a side view and, respectively, a horizontal section view of one of the stringers 16, at the connection of the lattice members 17.
It is apparent that, using the structural elements of figure 4 according to the invention, in a support of the type shown in figure 9, drastically reduces problems deriving from torsional and local instability, which are always present in such structures, whereby sections of very reduced thickness, and thus much lighter, can be used in said structures, with obvious considerable advantages.
It is understood that only some embodiments of the structural element according to the invention and some examples of the structures which can be constructed therewith, have been described and illustrated. Other embodiments of the structural element, or modifications of those shown, obviously fall within the scope of the present invention, which also comprises any type of structure - even if quite different from those shown by way of example - using said structural element.

Claims

1) A structural element formed as a tube for metal structural work, characterized in that it comprises a pair- of half-shell fellow 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.

2) A structural element as in claim 1, wherein the connection between said half-shell sections is obtained by means of bolts applied at a certain mutual distance between flanges of said sections.

3) A structural element as in claim 2), wherein said flanges of the half-shell sections are kept spaced-apart and parallel by inserting cross stiffening brackets in correspondence of the connection bolts.

4) A structural element as in claim 3), wherein the cross stiffening brackets comprise cavities; designed to cooperate with deep-drawn portions of the bores for the bolts of the section flanges, in order to prevent mutual sliding between said flanges.

5) A structural element as in claim 1) and 2), wherein said flanges of the half-shell sections are kept spaced-apart and parallel by interposing sections or bent plates.

6) A structural element as in claims 1) and 2), wherein said flanges of the half-shell sections are kept spaced-apart and parallel by interposing sections or bent plates, together with cross stiffening brackets.

7) A structural element as in claims 1) to 6), formed with half-shell sections of such a shape as to allow them to be inserted into each other to form a pack.

8) A structural element as in claims 1) to 7) wherein at least one of the half-shell sections is a channel section with a very wide base and outwardly inclined sides.

9) A structural element as in claims 1) to 8), formed with two half-shell sections of the same shape.

10) A structural element as in claim 1) to 7), formed with a half-shell channel section having a very wide base and outwardly inclined sides, and with an angle section having the edges of its long sides acting as flanges.

11) A flat girder, characterized in that its stringers are constituted by structural elements as claimed in claims 1) to 10).

12) A particularly slender flat girder, characterized in that its stringers are formed by using structural elements as claimed in claims 1) to 10), 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 deviations of the compressed stringer.

13) A flat girder as in claim 12), in the form of a bidimensional self-braced trestle support for overhead electric power transmission lines.

14) A three-dimensional girder, characterized in that its stringers are constituted by structural elements as claimed in claims 1) to 8) and in claim 10).

15) A three-dimensional girder as in claims 1) to 8) and in claim 10), in the form of a lattice support for overhead electric power transmission lines, constructed in such a manner that the torsional rigidity of its stringers prevents instability thereof under combined compressive and bending stresses.