EP0114015A1 - Light-metal girders with increased moment of inertia, and method for their production - Google Patents

Abstract

Light-metal girders with an "I" or "H" cross-section, used in construction work, especially for the shuttering of concrete on building and civil engineering sites. The single or multiple wood casing (1), serving to fasten panels on the girders and lining the upper flange is very securely fastened to the metal, by adhesive bonding and crimping, for example, thus influencing the inertia of the section and increasing the strength of the assembly. The lower metal flange, which is flat and horizontal, is bent into a "hook" shape at each lateral end of the section, forming two continuous slides (2). On these slides, slide detachable parts (3) for fixing the girders on the support flange, as profiled bars, by virtue of a conical opening. Connection fishplates for the girders (4) are locked behind these slides, only one central clamping element being required, to the exclusion of all bolt connections with drilling of the girders. <IMAGE>

Description

The present invention relates to light alloy beams used in construction, in particular for concrete formwork on building sites, engineering structures or civil engineering.

Concurrently with beams made of glued wood, light alloy beams already known often replace square timber (bastaings or planks) thanks to their significant weight gain with equal resistance and their greater longevity.

• - Horizontalement et soutenues par des étais, elles constituent un soli- vage provisoire supportant les coffrages qui reçoivent le béton des planchers ou des dalles en élévation (fig.I).
• - Verticalement, elles servent de raidisseurs verticaux aux deux coffrages opposés entre lesquels est coulé le béton des murs (fig.2).

In concrete formwork, they are mainly used in two ways:

• - Horizontally and supported by props, they constitute a temporary joist supporting the formwork which receives the concrete from the floors or slabs in elevation (fig.I).
• - Vertically, they serve as vertical stiffeners for the two opposite forms between which the concrete for the walls is poured (fig. 2).

• - En "I" comportant une seule âme verticale.
• - En "H", caissonnée, comportant deux âmes parallèles.

The various existing light alloy beams can be reduced to two types of section (fig. 3)

• - In "I" comprising a single vertical core.
• - In "H", boxed, comprising two parallel cores.

• - A leur partie supérieure, dans une gorge, une fourrure en bois (1) servant au vissage des panneaux en structure définitive, ou au clouage provisoire et répétitif des coffrages,
• - A leur partie inférieure, au milieu de la membrure, une rainure en forme de "C" (2) destinée à recevoir une tête de boulon pour la fixation par crapauds des poutrelles sur les fers profilés leur servant de support.

For both types, the beams generally have (fig. 3)

• - At their upper part, in a groove, a wooden furring (1) used for screwing the panels into final structure, or for provisional and repetitive nailing of the formwork,
• - At their lower part, in the middle of the frame, a "C" shaped groove (2) intended to receive a bolt head for the clamping of the beams on the profiled bars serving as their support.

• - Déformations importantes en flexion du fait de la forte élasticité de l'aluminium, ce qui conduit le plus souvent à limiter la charge ou la portée libre des poutrelles en fonction de leur flèche et non de leur résistance.
• - Fixation sur les supports par boulonnage, procédé lent et dispendieux dans l'emploi en coffrage ou les montages et les déposes sont fréquents, avec l'inconvénient d'un boulonnage par dessous.
• - Prix élevé au mètre linéaire dû au coût des alliages légers et à l'adjonction de la fourrure bois, fixée artisanalement et destinée au clouage des panneaux sur les poutrelles utilisées comme solives (la rentabilité des poutrelles étant par ailleurs réduite du fait de la limitation des charges en fonction des tolérances de déformation).

These types of beams have the following main drawbacks:

• - Significant bending deformations due to the high elasticity of aluminum, which most often leads to limiting the load or the free span of the beams according to their deflection and not their resistance.
• - Fixing on supports by bolting, slow and expensive process in the use in formwork or assemblies and removals are frequent, with the disadvantage of bolting from below.
• - High price per linear meter due to the cost of light alloys and the addition of wood furring, handcrafted and intended for nailing panels on beams used as joists (the profitability of beams is also reduced due to the limitation charges depending on the deformation tolerances).

The beams according to the invention make it possible to avoid these drawbacks.

They have a section in the shape of an "I" (fig.4), with a full and continuous vertical core, single or double, an upper chord and a lower chord.

The upper chord of section in the form of a fork with two or more branches (1), receives between the branches one or more wooden furs (2) strongly fixed on the metal, for example by gluing on the entire surface of contact with the metal.

The lower chord (3) is constituted by a flat and horizontal sole having at each of its lateral ends a return (4) forming an acute angle with the horizontal part. These "hook" returns are continuous over the length of the beam. - For the upper chord, the peculiarity of the invention consists in involving the single or multiple wood furring in the resistance of the beam.

For this heterogeneous section to be equivalent in resistance to a fictitious homogeneous section, as in the case of a reinforced concrete section for example, it is necessary and sufficient that under the shearing forces the wooden furring cannot slip in its metal sheath, so that the fixing (bonding for example) resists the molecular work of sliding.

By analogy with reinforced concrete, one must consider a coefficient of equivalence between metal and wood, coefficient equal to the ratio between the respective longitudinal moduli of elasticity of metal and wood.

We can then take into account a fictitious homogeneous section of metal where the section of the wood will be divided by the equivalence coefficient as defined. In the stress calculation, the stresses in the wood will be those of the metal divided by the equivalence coefficient.

In practice, it is advisable to choose components, light alloy and wood, whose equivalence coefficient is such that the maximum stresses calculated for the two materials are as close as possible to the maximum admissible stresses.

Thus the wooden fur required by the fixing of the panels and hitherto unused in resistance, becomes active, that is to say that it appreciably increases the moment of inertia of the beam, therefore its performance, for an increase. minimal cost.

• - For the lower chord, the particularity of the invention is constituted by the two lateral returns or "hooks" which make it possible:
• - rapid fixing of the beams on a profiled iron support (or on another beam serving as a support plate and placed "upside down") by removable staples / sliding along each hook, comprising a conical light ( 2), and forced with a hammer (fig. 5).
• - the joining of the beams with double "U" section fishplates sliding along the core without the possibility of lateral dumping (fig. 6). The fishplates can be clamped to each other in their middle, between the two beams joined by a conical key pin or by eyelet bolt, without the need for drilling the beams.
• - good stiffening of the edge of the lower member, which, when flat, is particularly sensitive to shocks and easily deformable.

The beams according to the invention can be produced in different substantially homothetic sections, according to the uses and the resistances to be obtained, depending on the loads and the free spans. In the use as joists and sand pits supporting horizontal or vertical formwork, a section height of the order of 20 cms seems well suited. Figure 7 shows an example of a beam 20 cm high.

For the manufacture of beams according to the invention, the light alloy profile is produced in a conventional manner by extrusion. The wooden fur is continuous along the length of the beam, with or without butt jointing using mini-cuts made according to the rules of the art.

Another feature of the invention resides in the method of fixing the single or multiple wooden furring, by gluing and crimping inside the groove (or grooves) that the frame of the metal profile has. To be effective, bonding must be carried out under pressure by clamping effect. In the present case, the pressure on the bonding planes is produced by self-tightening. For this purpose, the profile emerging from the hot spinning in the form indicated (fig. 8), fork legs separated.

• - soit à la presse de manière analogue à la réalisation des profils à froid en acier
• - soit par "laminage" à froid, la poutrelle cheminant entre des rouleaux à pression qui rabattent et resserrent les branches verticales de la fourche sur la fourrure, un autre rouleau comprimant la fourrure contre la paroi horizontale de la gorge (fig.9). Un dernier rouleau peut éventuellement, dans le cas d'une gorge en "C" (fig.10) rabattre et comprimer sur la fourrure les deux branches horizontales du C.

After gluing and placing the wooden furs, the fork legs are brought together cold by permanent deformation,

• - either with the press in a similar way to the production of cold steel profiles
• - either by cold "rolling", the beam running between pressure rollers which fold and tighten the vertical branches of the fork on the fur, another roller compressing the fur against the horizontal wall of the groove (fig. 9). A last roller can possibly, in the case of a groove in "C" (fig.10) fold and compress on the fur the two horizontal branches of C.

Claims (4)

1 Light alloy beams, cross section in "I", characterized by a fork-shaped upper frame enclosing one or more wooden furs strongly fixed on the metal, by gluing and crimping for example, so that this fixing resists to the sliding stresses due to cutting forces when the beam is loaded. Thus the wooden fur contains with the metallic part a heterogeneous section which can be calculated as a fictitious homogeneous section, taking into account a metal-wood equivalence coefficient. The wooden fur is no longer used only for the final or temporary fixing of panels on the beams by screwing or nailing, but it participates in the inertia of the beam, therefore in its resistance to bending and deformations, by increasing it notably. . 2 light alloy beams according to claim 1, characterized by a lower moldwork whose section is presented as a horizontal flat turned up "in hook" at its two lateral ends, these continuous returns being directed towards the core and making an acute angle with the horizontal central part. 3 light alloy beams, according to claims 1 and 2, characterized by removable slides for fixing the beams on the frame of a support iron profile, the upper part of the slide forming a groove enveloping the hook of the lower frame the beam and sliding thereon, the lower part having a conical light which encloses the frame of the profiled support iron. 4 A method of manufacturing beams according to one of the preceding claims, characterized by fixing the single or multiple wood furring on the metal profile by bonding and crimping, with self-tightening of the bonding planes, the metal parts surrounding the outgoing furs extrusion more apart than in their final position, and being subsequently brought together cold by permanent deformation after gluing and placing of the furs.

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