EP0318450A1

EP0318450A1 - An element for the construction of lattice webs for girders and like structural members, and a method for manufacturing such an element

Info

Publication number: EP0318450A1
Application number: EP88850397A
Authority: EP
Inventors: Tage Carlsson
Original assignee: Skanska AB
Current assignee: Skanska AB
Priority date: 1987-11-25
Filing date: 1988-11-18
Publication date: 1989-05-31
Also published as: SE8704679D0; SE8704679L; SE461075B

Abstract

The element is comprised of a continuous length of bendable strip material which is bent to a sawtooth configuration, wherewith respective crests (3) which interjoin two adjacent diagonal struts (1, 2) of the strip material are flat, each crest (3) and adjoining struts (1,2) together forming one sawtooth in the sawtooth row. The outer surfaces of two adjacent struts (1,2) are unbroken continuations of the strip parts forming the crests (3) and lie in two parallel planes which are perpendicular to the plane of the flat crests (3) and lie on both sides of the crests (3).

The invention also relates to a method for manufacturing such a web element.

Description

The present invention relates to an element for use in the construction of lattice webs for girders and like structural members, and to a method for manufacturing said element.
Many demands are placed on web elements of this kind, in order that they are able to provide a satisfactory alternative to conventional girder webs, both economically and technically. In addition to being capable of manufacture without requiring large investments in production equipment, the web element shall also be capable of providing lattice web structures for girders and like structural elements of mutually different height dimensions and load bearing capacities.
The object of the invention is to provide precisely an element of this kind which will enable the lattice or open-work web of a girder construction to be adapted to different load bearing requirements and which can be produced by a method of manufacture which does not require the use of complicated machinery.
This object is achieved in accordance with the invention by means of a web element having the features set forth in Claim 1. Because the diagonal struts of the element lie in two separate parallel planes, a plurality of elements are able to co-act with one another to form a girder or like structural member of desired load bearing capacity, without increasing the total width of the lattice web. This enables the same flanges to be used for both single web elements and web-element assemblies, and will also enable the quantity of structural material in the web to be readily adapted to the transverse force diagram.
A method for the manufacture of the inventive web element is set forth in Claim 6.
So that the invention will be more readily understood, an exemplifying embodiment of an element for the construction of lattice webs for girders and like structural members will now be described in more detail with reference to the accompanying drawings, in which

Fig. 1 is a perspective view of part of an element constructed in accordance with the invention;
Fig. 2 illustrates the element of Fig. 1 from above;
Fig. 3 illustrates the element of Fig. 1 prior to roll shaping the element; and
Fig. 4 is a perspective view of two mutually co-acting elements according to the invention.

The inventive web element illustrated in Figs. 1 and 2 has a sawtooth configuration in the direction of its longitudinal axis and includes diagonal struts 1, 2 and flat crests 3. The struts have a hat-like cross-sectional shape, i.e. they are bent to form a central U-beam 4, the legs of which have outwardly bent flanges or brim 5 on the extremities thereof. As will be seen from Figs. 1 and 2, the inner surfaces of the struts face towards one another and in the case of the illustrated embodiment the depth of the central part 4 of respective struts is such that two of the flanges 5 of mutually adjacent struts will lie against one another at the crest part of each sawtooth. This enables the flanges of said parts to be readily connected together, e.g. by riveting or spot welding processes, thereby enabling satisfactory rigidity to be imparted to the element in a ready fashion.
The inventive element is produced from flat metal strip, which is coiled on a strip storage roll. The metal strip is fed from the roll and passed through a punch, in which recesses 6 having the configuration shown in Fig. 3 are punched in the strip. The distance between these recesses is a function of the desired height extension of the element, and will thus be contingent on the angle defined by two mutually adjacent struts of a manufactured element.
The punched strip is then passed through shaping rolls, in which the strip parts forming the diagonal struts are rolled to the aforesaid cross-sectional hat-like configuration. The bending lines 7, 8 along which the strip is bent are indicated in broken lines in Fig. 3.
Subsequent to thus shaping the strip, The strip is bent transversely through 90° along two mutually parallel bend lines 9 in the remaining portion of the recessed parts of the strip, these bend lines 9 being inclined at an angle to the longitudinal direction of the strip, as shown in Fig. 3, in which the bend lines are also shown in broken lines. In this case, the perpendicular distance between these latter bend lines will be equal to or greater than twice the depth a of the hat-like profile of respective diagonal struts. This last mentioned distance between the bend lines will preferably be 2 x a, partly so that adjacent flanges 5 of mutually adjacent struts within the crest of an element will abut one another, and partly so that mutually overlapping struts of mutually coacting web elements will abut one another.
The bend lines 9 in said remaining portion of the recessed parts of the strip are preferably angled at 45° to the longitudinal axis of the strip. This means that the diagonal struts will also slope at 45° to the longitudinal axis of the web element, which is beneficial from the aspect of load distribution.
It will also be seen from the Figures that the ends of those strut flanges 5 which do not lie beside adjacent struts in the crest region of the element are cut-off or bevelled, so as not to protrude above the flats of the crests.
Conceivably, the ends of the other two flanges may also be bevelled-off, as indicated by chain lines 10 in Fig. 3, so that the punch dies in the punch can be made reversible.
Fig. 4 illustrates part of a lattice or open-frame web comprised of two web elements which are constructed in accordance with Fig. 1 and which are inserted or threaded one within the other. The diagonal struts of the two elements are referenced 1₁, 2₁, and 1₂, 2₁ respectively. The buckle lengths of diagonal struts which are subjected to compressive loads, can be reduced, by joining together, e.g. by means of spot welds, the mutually overlapping parts of the flanges 5 of the struts 1₁, 2₁ and 1₁, 2₂ respectively, whereby those struts which are under tension will support struts which are under compression. In this case, the buckle lengths will be reduced by half, when the struts are displaced symmetrically in relation to one another. The reference 11 in Fig. 4 illustrates the attachment points between the two web elements.
It will also be understood that more than two web elements can be inserted one within the other, so as to decrease the buckle lengths still further. Thus, several web elements can be combined together within one and the same total section measurement required of a web element, by mutual displacement of said elements in the direction of their longitudinal axes. This enables a dense array of diagonal struts to be provided at certain parts of the girder web, without influencing the configuration of adjacent girder parts, such as flanges for instance.
By varying the number of mutually coacting web elements along the length of the lattice web, it is possible to adapt the web to the transverse load diagram of the girder or beam of which the element is to form part. This enables the material in such a girder web to be optimized quantitatively, solely with the aid of uniform web elements of mutually different lengths. Naturally, uniform web elements which have different plate thicknesses may also be used, provided that the hat-like profiles have mutually the same depth.
Because of the flat crests 3 and the outer surfaces of the struts 1 and 2, the inventive web element provides at its crest locations good attachment surfaces for the attachment of flanges which coact with the web.
In order to enable webs of mutually different height dimensions to be manufactured, the punch apparatus is preferably constructed so that the distance between the recesses in the strip can be adjusted. In this respect, the recess spacing adjustment means will conveniently be such as to enable said distance to be altered between mutually sequential punching operations. This will enable the web to be adapted for lattice saddle girders or other girders and like structural members in which the flanges in upper and lower edges are not parallel.
Thus, the invention provides a web element which enables the same basis construction unit to be used in the construction of a large variety of lattice web structures. At the same time, the element construction enables web element parameters, such as height and width dimensions, to be varied with the aid of relatively simple control equipment. Thus, it is possible to produce with the same production equipment mutually coacting web elements which can be adapted individually to a significant number of web loading circumstances.
It will be understood that many modifications can be made to the construction of the inventive web element within the scope of the invention, particularly with respect to the cross-sectional profile of the diagonal struts. The invention is therefore only restricted by the content of the following claims.

Claims

1. An element for the construction of lattice webs for girders and like structural members, which element comprises a continuous length of bendable strip material which is bent to a sawtooth configuration such that respective crests (3) which join two mutually adjacent diagonal struts (1, 2) of said material strip and which together with said struts form one sawtooth in the row of sawteeth are flat, and such that the outer surfaces of two adjacent struts lie in two parallel planes which are perpendicular to the plane of the flat crests and lie on both sides of said crests, said outer surfaces being an unbroken continuation of the strip parts forming the crests, characterized in that the diagonal struts have a hat-like cross-sectional shape, i.e. a U-shaped central part (4) whose legs have outwardly extending flanges or brim (5) extending from the extremities thereof; and in that the legs have a length or depth dimension such that the mutually facing surfaces of the flanges (5) contact a plane which lies midway between the two parallel planes in which the outer surfaces of the struts extend.

2. An element according to Claim 1, characterized in that the flat strip parts (3) which form the crests of the element are inclined relative to the longitudinal axis of the element, the acute angle (α) defined between the longitudinal axis of thre strip parts (3) and the longitudinal axis of the element being equal to the acute angle formed between the longitudinal axes of the struts (1, 2) and the plane of the crests.

3. An element according to Claim 2, characterized in that said acute angle (α) is 45°.

5. A method for manufacturing a web element according to Claims 1-3, characterized by the following steps:
- taking strip material from a strip storage reel and passing the strip through a punching apparatus and punching in said strip recesses in given spaced relationship such as to leave a central parallelogrammic strip part in the strip in respective recessed regions;
- passing the recessed strip through a shaping roll arrangement in which those parts of the strip located between the recesses are bent to a hat-like cross-sectional shape; and
- passing the thus shaped strip through a transverse bending device, in which the strip is bent through 90° along two mutually parallel bend lines on the central strip parts, said bend lines being inclined to the movement direction of the strip.

5. A method according to Claim 4, characterized in that the distances between said recesses are varied between mutually sequential punching operations, such as to obtain a web element with a varying height dimension along its longitudinal axis.

6. A girder web, characterized in that it is constructed from two or more web elements according to Claim 1, each of which comprises a continuous length of bendable strip material which is bent to a sawtooth configuration such that respective crests which join together two adjacent diagonal struts of the strip material are flat, which respective crest forms together with adjoining struts one sawtooth in the sawtooth row; such that the outer surfaces of two adjacent diagonal struts, said outer surfaces being a constant continuation of the crest strip parts, lie in two parallel planes which are perpendicular to the plane of the flat crests and lie on both sides of the crests; and such that the diagonal struts have a hat-like cross-sectional shape, i.e. have a U-shaped central part with outwardly extending flanges or a brim at the ends of the legs of the U; and in that the legs have a length dimension such that the mutually facing surfaces of the flanges contact a plane which lies midway between the two parallel planes in which the outer surfaces of the diagonal struts extend, said web elements being threaded one within the other and mutually displaced in the direction of their longitudinal axes, and mutually abutting parts of said elements being joined together.