EP0246560A2 - Manufacturing method of prestressed steel girder and achieved girders - Google Patents

Abstract

Separate longitudinal sections 1,2 are prepared for assembly to make up the desired beam and the sections are assembled by juxtaposition. The resulting assembly is subjected to bending so as to obtain a virtually made-up bent beam. Adjacent portions of the sections 1,2 are connected and the external bending forces are then removed. The prepared sections 1,2 can be identical or different with regard to geometrical shape and grade of steel, e.g. I-section or T-section. Connection of the beams can be by use of a portable welding device moving along a curved U-track. <IMAGE>

Description

The invention relates to prestressed steel beams. The main idea pursued in the design of prestressed beams is to increase the load capacity when the beam is stressed under bending.

Belgian patent no. 495.318 teaches to manufacture a prestressed reinforced concrete beam, by first subjecting the uncoated metal reinforcement to bending, then coating with concrete at least a fraction of the part of the reinforcement subjected to traction. as a result of bending, by maintaining flexed the concrete-coated reinforcement during the curing thereof and finally suppressing the bending force after curing of the concrete. The frame is constituted by a laminated steel beam. The bending is carried out either by the application of a force at a point of the reinforcement lying between the ends which are kept fixed, or by the application of forces at the ends of the beam of which an intermediate point is kept fixed. Pre-stressed beams are obtained in this way where the prestressing is carried out using a partial concrete coating. Such beams are known under the name PREFLEX in the fields of heavy construction, bridges or viaducts.

A first disadvantage inherent in such achievements is the excess weight attributable to concrete; a second disadvantage is due the fact that the coating concrete itself must be reinforced and that the steel reinforcements must be fixed by welding to the main reinforcement, i.e. to the steel beam, which involves a tedious work of fitting and welding and impossible to carry out automatically. Finally, a third disadvantage arises from the fact that the coating covers the steel, so that it is difficult to carry out drilling at these places in the beam and impossible to carry out welding work.

The object of the invention is to create prestressed beams, free from the disadvantages described.

One could imagine constituting a pre-stressed steel beam from two separate concrete-free sections, in which one would induce the pre-stress by acting on one of the two sections in order to give it temporary expansion in the length direction. , by bringing the two sections together and eliminating the cause of the said dilation.

Thus one could exert on one of the sections a tensile force, before joining it with the other section. One of the sections could also be heated to temporarily lengthen it. In both cases it is conceivable to constitute a prestressed beam, but it would be necessary to implement enormous means of traction, resp. heating, if you want to build large prestressed beams beyond the mini-sections.

• a) On prépare deux sections distinctes qui sont susceptibles d'être assemblées pour constituer la poutrelle désirée;
• b) On appose resp. superpose les deux sections, de manière à ce que la poutrelle soit virtuellement constituée;
• c) On soumet les deux sections, en un même temps, à une force de flexion, de manière à obtenir une poutrelle fléchie, vir­tuellement constituée;
• d) On réunit les deux sections par leurs aires adjacentes.

Thus the object of the invention is achieved by the method according to claim 1 and the devices according to claims 9 and 10. The method is characterized by the following measures:

• a) Two separate sections are prepared which are capable of being assembled to constitute the desired beam;
• b) We affix resp. superimpose the two sections, so that the beam is virtually constituted;
• c) The two sections are subjected, at the same time, to a bending force, so as to obtain a bent beam, virtually constituted;
• d) The two sections are united by their adjacent areas.

Other features of the invention are described in the dependent claims.

The two sections according to measure a) can for example be two T-shaped sections which, after assembly, give an I-shaped section. The two sections according to measure a) can also for example be two I-shaped sections The assembly in question is done according to measure b), by framing the two sections using several steel frames, as will be explained below.

Measure c) provides that a bending force is applied to the assembly comprising the two sections affixed to each other and framed. This can be achieved by applying two equal forces and in the same direction at the ends of one of the sections, while supports are provided at quarters or thirds of a span at the other section. It is essential that the frames are dimensioned so that the assembly constituted by the two T-shaped sections, affixed to form an I, is immobilized in the sense that when the bending forces are applied, the two sections behave as much as possible as a whole beam, i.e. that only the adjacent areas can move towards each other by sliding one over the other.

Measure d) is advantageously carried out using a mobile and automated electric welding device.

• - la Fig. 1 montre une vue latérale de deux sections en forme de T, encadrées pour former une poutrelle virtuelle qui est sollicitée par des forces de flexion appliquées aux extrémités;
• - la Fig. 2 montre une coupe à travers l'ensemble comportant la pou­trelle virtuellement constituée et un cadre de fixation, à l'endroit d'application de la force de flexion;
• - la Fig. 3 montre une coup à travers l'ensemble comportant la pou­trelle virtuellement constituée et un cadre de fixation, à l'endroit de l'appui;
• - la Fig. 4 représente une coupe des deux sections destinées à for­mer la poutrelle, l'accent étant mis sur les aires adjacentes;
• - les Fig. 5 et 6 montrent l'exécution de chanfreins aux entré­mités des aires adjacentes, avant le soudage;
• - la Fig. 7 représente une coupe à travers une poutrelle, dont les deux sections qui la constituent sont réunies par collage;
• - les Fig. 8 et 9 représentent des coupes à travers des poutrelles constituées par des sections en forme de I;
• - la Fig. 10 représente une des applications possibles de poutrelles suivant l'invention.

The invention will be illustrated with the aid of schematic drawings which represent, without limitation, possible embodiments.

• - Fig. 1 shows a side view of two T-shaped sections, framed to form a virtual beam which is stressed by bending forces applied to the ends;
• - Fig. 2 shows a section through the assembly comprising the virtually constituted beam and a fixing frame, at the place of application of the bending force;
• - Fig. 3 shows a shot through the assembly comprising the virtually constituted beam and a fixing frame, at the location of the support;
• - Fig. 4 shows a section of the two sections intended to form the beam, the emphasis being on the adjacent areas;
• - Figs. 5 and 6 show the execution of chamfers at the ends of the adjacent areas, before welding;
• - Fig. 7 shows a section through a beam, the two sections which constitute it are joined by gluing;
• - Figs. 8 and 9 show sections through beams formed by I-shaped sections;
• - Fig. 10 shows one of the possible applications of beams according to the invention.

In Fig. 1 we distinguish the two T-shaped sections 1 and 2 which can for example be obtained by cutting an I-shaped beam. We can also prepare two different sections from the point of view of the geometric shape as well as the quality of the steel and this as a function of the direction of the bending to be operated and as a function of the mechanical characteristics targeted in the assembled beam. The sections are kept in position such that areas 11 resp. 21 are adjacent. In practice, these areas can be touched resp. be at a distance of the order of 2 to 5 mm from each other, to avoid difficulties during subsequent welding. The sections are maintained by executives; in the case of four frames for example, the two frames 3 and 4 are arranged at the ends of the sections, while the two frames 5 and 6 are arranged at quarter spans.

The lower section 2 is shorter than the upper section 1, to take account of the changes in length occurring during the bending; the appearance of the flexed assembly is indicated by the dotted lines.

As seen by way of example in FIG. 1 and in Fig. 2 resp. Fig. 3 , the bending forces F are applied to the frames 3 and 4; they are taken up at supports A by frames 5 and 6. Frames 3, 4, 5 and 6 are identical from the point of view of their construction, their arrangement however varies according to their role. Thus the frames 3 and 4 are arranged so that the opening is directed downward, while the frames 5 and 6 are arranged upside down; the application of the forces resp. reactions to pressing with arrows to illustrate where the frames are used.

Thanks to the frame concept, welding is easily carried out using an automatic welder. As seen in Fig. 2 and 3 the welder S moves on a U-shaped profile 7 which is supported at the location corresponding to FIG. 2 on the lower part of the frame and at the place corresponding to FIG. 3 on the sole of section 2, via a hatched bar which compensates for the difference in level.

It remains to be noted that the plates 8 resp. 9, between the frames and the cylinders not shown resp. between the frames and the supports, to avoid damage.

To condition the areas intended to be joined by welding (see Fig. 4 ), chamfers are provided, preferably at the end of the upper section. In Fig. 5 there is shown a suitable chamfer in the case of beams with thick webs. In the case of beams with thin webs, the chamfer shown in fig. 6 .

Instead of joining the sections making up the beam, by welding, the sections can also be joined by gluing (see F ig. 7 ). In the case shown, use is advantageously made of steel plates 73 bonded to the cores of sections 71 and 72 and this over their entire length.

Although the process has been explained by describing the use of T-shaped sections, it is obvious that it is possible, with adequate modification of frames 3, 4, 5, and 6, to make beams using mixed sections, hollow profiles and their combination. One can in particular use at the start two I-shaped sections and join them by their wings, either by welding, or by bolting or by any other suitable means. These sections can have comparable dimensions (see references 80 and 81 in Fig. 8 ) or clearly different dimensions (see references 90 and 91 in Fig. 9 ). In particular, it would be advantageous to use two I-shaped sections, one of the two wings of which has reduced dimensions and to join them together via these wings.

At the end of manufacture, a prestressed steel beam is obtained, part of which is in tension and the other in compression. Such a beam can support a higher maximum load than a laminated beam of the same dimension, since the part of the beam in tension supports the compressive forces and the part in compression supports the tension forces.

One of the possible applications is shown in Fig.10 where there is a prestressed and welded beam 100 supporting a slab 101 in reinforced concrete. The slab-beam connection is made using bolts 102. The T-sections used to form the beam have different transverse dimensions, the smallest section being in contact with the slab.

Claims (10)

1. A method of manufacturing prestressed steel beams, characterized in that two sections (1,2,80,81,90,91) are prepared, capable of being assembled to constitute the desired beam, which one assemble these sections by affixing them to each other, which is subjected to the assembly thus constituted at the same time to a bending, so as to obtain a bent beam, virtually constituted, which is joined together sections by their adjacent areas and that the external bending forces are eliminated at the end of the joining operation. 2. Method according to claim 1, characterized in that two sections (90, 91) of different geometric shape are prepared. 3. Method according to one of claims 1 or 2, characterized in that two T-shaped sections (1,2) are prepared by cutting I-shaped beams. 4. Method according to one of claims 1 or 2, characterized in that one prepares two sections (80,81,90,91) in the form of I. 5. Method according to one of claims 1 to 4, characterized in that two sections with different properties are prepared and these sections are affixed as a function of the direction of bending to be operated and as a function of the mechanical characteristics referred to in the assembled beam. 6. Method according to one of claims 1 to 5, characterized in that one fixes the position of the two sections (1,2,80,81,90,91) opposite to each other by the intermediate of frames (3,4,5,6) which have substantially the shape of a rectangle, one of the sides having a central opening for receiving and guiding the core of one of the sections (1,80,90) , its wing resting on the outside of the frame, while the opposite side of the frame, intended to support the wing of the second section (2,81,91), has an interior length substantially equal to the width of the 'wing of this section, the two remaining sides of the frame having lengths such that once the sections (1,2,80, 81,90,91) in place, the parts to be joined are spaced a few millimeters apart. 7. Method according to claim 6, characterized in that the bending forces (F) are applied to at least two frames (3,4) arranged at the ends of the sections (1,2,80,81,90,91 ) and that the reactions to the supports (A) are resumed via at least one frame (5,6) situated between said frames (3,4) arranged at the ends of the sections. 8. Method according to one of claims 1 to 7, characterized in that the two sections are joined by welding, bolting or gluing. 9. Prestressed steel beam, the wings of which are bent, characterized in that it is constituted by two T-shaped sections having their souls in the same plane and the sides of the core which are not connected to the wings, reunited. 10. Prestressed steel beam, whose wings are bent, characterized in that it is constituted by two I-shaped sections having their souls in the same plane and joined by the wings in contact.

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