FR2697857A1 - Precast concrete T beam for composite floor construction - has three main reinforcing bars two in flange fixed to bottom of zigzag bent stirrups third fixed to top as starter bars for finishing concrete - Google Patents

Abstract

The precast concrete T beam for supporting floors is inverted for use and has two main reinforcing bars in the flange (4), each fixed to a stirrup bent in zigzag fashion forming a lattice. The concrete is poured to form the flange with a groove on each side of the web. The web projects roughly the same height as the flange overall thickness, leaving roughly half the height of the stirrups projecting as starter bars fixed to a third main bar for the finishing lift of in situ concrete poured over and between floor blocks. USE/ADVANTAGES - Improved design, speeds up construction, no shutter props required for floor construction.

Description

The present invention designs the beams used as load-bearing elements of prefabricated floors.

These beams, structural components associated with various forms, and supplemented by concrete poured during implementation, are widely used in the field of current constructions. From the 1950s, two main types of these beams experienced considerable development in France and in Europe.

On the one hand, the massive beams with cross section in the shape of an inverted T, as shown in Figure I; Originally made of reinforced concrete, today, for the most part, they use prestress by adhesion.

On the other hand, the light metal beams with a base coated with concrete, as shown in Figure 2; they comprise a welded reinforcement of Warren type trellis, composed of an upper stiffener (I), of a trellis (2) generally with two plies, and of two base steel bars (3) wrapped by a heel (4) in precast concrete, generally rectangular section; these light beams, from 1 origin, use for their dimensioning the calculation of reinforced concrete.

Your present invention prioritizes these light beams with coated base, it aims at their improvement, by better use of their usual constituents, in order to improve their performance, and thereby their possibilities of use.

These light beams, as their name suggests, are easy to handle and easy to transport; their implementation requires no mechanical handling, an advantage appreciated in particular by the builders of individual houses; in return, they require a greater provisional shoring than that required by the use of inverted T-shaped beams, of a higher metric weight, but which on the other hand are endowed with greater longitudinal stiffness. It is therefore normal that we have sought to increase this longitudinal stiffness in light beams with coated lattice, the reduction, or even the elimination of the provisional shoring, being an argument of certain economic value. Several arrangements have therefore been devised and used for this purpose.
First, increase the inertia of the prefabricated base, by modifying its shape in a more or less elaborate way; Figures 3,4 and 5 show three known variants of this solution, simple and effective, but which all have the disadvantage of significantly increasing the beam, suppiinunt thus the important and original advantage of its maneuverability. In illustration of this, the most elaborate current variant, which is represented in FIG. 5, effectively makes it possible to obtain a longitudinal stiffness roughly equivalent to that of prestressed beams of the current type, but obviously for a metric weight of the same order.

Secondly, it is known and practiced to increase the stiffness of light beams, by increasing the cross section of their stiffener (I) and sometimes also that of their trellis (2) without any modification of their prefabricated heel (4).

This second solution, if it markedly increases the longitudinal stiffness of the beam thus reinforced, without significantly modifying its metric weight, is unfortunately very quickly limited in 2nd practical applications by the additional cost of steel which results therefrom.

The present invention proposes to solve this problem, currently without any real solution, by significantly improving the longitudinal stiffness of light truss beams, without thereby modifying their metric weight, while retaining an equivalent production cost.

The object of the invention is a light truss with pre-coated base, called "Light beam with improved stiffness".

This improvement is obtained according to the invention by means of a new and more effective combination of the usual constituents of a light truss, namely its frame and its prefabricated concrete base.

This new, more effective combination is the result of a very precise arrangement and a very elaborate conformation of these usual and known constituents; it has the new result of optimizing their mechanical collaboration, the armature being partly immobilized by a rigid concrete rod opposing its deformation and buckling, and the prefabricated base, of particular shape, being elegant, or relieved, of any material not essential to the sheathing of the reinforcement, as also to the resistance necessary for that same prefabricated base.

 These means and arrangements are obtained according to the invention, a light beam with improved stiffness requiring less temporary props, and whose weight per meter is practically the same as that of a truss of common type, such as described on page I of this patent, and according to Figure 2 of the same.

The light beam with improved stiffness has, by virtue of its conformation according to the present invention, a good ability to restore monolithism within the finished floor, of which it is the resistant and load-bearing element; at the same time it achieves an effective structural connection.

These advantageous characteristics result directly from the arrangement and the conformation of the beam object of the invention, the structural connection there being ensured by the trellis (2), anchored in the heel (4) and whose upper part lower, welded to the stiffener (I) emerges awaiting the complementary concrete (8), and the restoration of the monolithism of the finished floor being favored by the shape given according to the invention to the prefabricated base, also designed for this purpose.

These useful characteristics, attached to the beam with improved stiffness, go in the direction of the regulatory requirements relating to prefabricated structures, which as we know, are particularly high in regions where there is a major seismic risk.

Figure 6 shows, in a preferred embodiment, in cross section and in perspective, the beam according to the invention with its frame and its prefabricated concrete base consisting of a heel (4) of preferably trapezoidal cross section, associated to a central rib (5) of reduced width.

On either side of this central rib (5) the heel (4) is hollowed out with a trapezoidal groove (6), preferably continuous, and on the quasi-vertical sides of the same central rib (5) it is made a notch (7) of shallow depth, preferably multiple, horizontal and continuous.

 The trapezoid grooves (6) have the utility of making the heel (4) particle at the recovery, or connection between the prefabricated base and the complementary concrete (8), and at the same time reducing the metric weight of this prefabricated base.

The notch (7) has the utility of improving the seal of the central rib (5), in the complementary concrete (8) of the finished floor, FIG. 7 represents, in cross section and in the embodiment described, the stiffness beam improved in place in a prefabricated floor with formwork interjoists (9); it makes it possible to see how the complementary concrete (8) fills and fills, by gravity, the trapezoidal grooves (6) dug in the heel (4), at the same time that it encloses the central rib (5) bi-laterally, the saddle is improved by the notching (7) of the sides of this central rib 15).

Figure 7 also shows how the formwork interjoists (9) rest, through their support spoilers (IO), on the upper part of the heel (4), and this as usual.

the particular shape given, according to the present invention, at the prefabricated base of the light beam with improved stiffness gives it, in the vertical axis, an inertia much greater than that of a rectangular heel of equal mass, as represented by Figure 2. Thus, the prefabricated base, composed according to the invention of the heel (4) associated with the central rib (5) offers increased resistance to the forces acting in the vertical plane, which is useful especially during implementation. from the floor.

In known processes intended to increase the longitudinal stiffness of the lattice girders, some, represented by FIGS. 4 and 5, provide an extension on the prefabricated heel whose width is practically equal to that of the final rib of the finished floor. , in its narrowest part.

Therefore, the connection between this central and vertical riser, and the complementary concrete (8) of the floor operates almost only in the horizontal plane, crossed vertically by the reinforcement or connection reinforcements; in the best case, the complementary concrete (8) cannot descend, for lack of sufficient space, lower than at the upper level of the support spoilers (IO) of the formwork interjoists (9). Unlike these known processes, the connection of the cemented concrete (8) with the prefabricated base of the beam object of the present invention takes place and takes place both in the horizontal recovery plane crossed by the trellis ( 2), but also, and in a new way, in the vertical recovery plane, in the sense that, thanks to the reduced width of the central rib (5) the complementary concrete (8) can freely penetrate on either side of that - by simple gravity, and fill the trapezoid grooves (6) of the heel (4), at the same time as it bi-laterally encloses the notch (7) of this same central rib (5).

By these arrangements according to the present invention, the light beam with improved stiffness has, in a new way, a wider recovery or connection area than that of the existing processes, and of interest both the central rib (5) and the heel ( 4) associated with it, thus achieving an almost total nesting of these prefabricated components in the complementary concrete (8).

Figures 8 and 9 demonstrate, by the cross section of a finished floor, this difference in constitution of a new character between the light beam with improved stiffness of Figure 8, and the existing and known solution shown in Figure 9. Without leaving within the framework of the invention, provision is made for the possibility of using to make the heel (4) and the central rib (5) a concrete with a density lower than that of ordinary precast concrete.

This arrangement according to the invention lightens the prefabricated base, while retaining a mechanical strength compatible with its functions; it conforms to one of the objectives of the invention, which is to keep the beam, object of the invention, a metric weight close to, or even slightly less than, that of the existing truss beams; it can be used alone or combined with any other arrangement aimed at the same result. The new, more efficient combination of con nnnited components, reinforced in and by the light beam with improved stiffness requires, in order to reach its maximum efficiency, very specialized production equipment, as well as permanent control of the internal quality and external profile of the products In the preferred, non-limiting embodiment described on page 2 and on page 3, this manufacturing can be carried out by unit molding, or by semi-spun on the ground continuous, with or without precast concrete extrusion.

Still without departing from the scope of the invention, provision is made for the use, in addition to the trellis reinforcements of the current type, of truss reinforcements whose stiffener (I) and (or) the trellis (2) have their section increased steel; it is also planned to carry out a possible reinforcement by superimposing on contact these reinforcements of current type or of reinforced type; ; Figure 10 shows schematically that in such a case, two reinforcements of unequal height and length are superimposed preferably the beam object of the present invention can also use, as main or complementary reinforcement, any reinforcement for reinforced concrete, welded or not welded, or even a prestressed reinforcement, when the geometrical and mechanical characters of these various reinforcements make this use possible,

Claims (4)

REVEXDICATIOIsS I) - light truss with pre-coated concrete base, with improved stiffness, characterized in that it achieves, by the arrangement and the conformation of its usual and known components, which are a metal frame and a prefabricated base in concrete, a more effective combination of these same known components, optimizing their mechanical collaboration, and improving their bending behavior by means of a concrete sheathing stiffening part of the trellis (2), and this without increasing their metric weight, which, thanks to arrangements made to elegant or lighten the heel (4) and to the narrowness of the central rib (5), remains close to that of a light lattice truss with a pre-coated base of known type 2) - light beam according to the first claim, characterized in that the mesh (2) partially sheathed by the concrete of the central rib (5), emerges therefrom sufficiently to ensure a solid anchoring in the complete concrete element (8) of the finished floor, and that the intentionally reduced width of the central rib (5) allows this same additional concrete (8) to flow freely by gravity on each side thereof, to fill and fill the grooves trapezoidal (6) practiced in the heel (4) and to bi-laterally enclose the notch (7) existing on the same central rib (5), thus achieving the nesting and sealing of the heel (4) and said central rib (5) in the complementary concrete (8) of the finished or final structure. 3) - light beam according to the preceding claims, characterized in that the concreting recovery area is very large and is of interest to the fcis the central rib (5) and the heel (4), and that the particular and elaborate conformation of these two elements, the primary purpose of which is their weight reduction, significantly improves their overall mechanical strength, in the vertical plane, and thus eliminates the risk of transverse cracking of the heel (4), which is subjected to high stresses related to the transport, installation and pouring of a floor. 4) - light beam according to claims I and 3, characterized in that there is provided the making of the heel (4) and the central rib (5) with a concrete density lower than that of common precast concrete. 5) - light beam according to the first two claims, characterized in that one uses for its reinforcement a metal truss of common type, or of reinforced type by increasing the cross section of the stiffener (I) and (or) of the lattice ( 2), and that its reinforcement by superposition of reinforcements is provided if necessary. 6) - light beam according to claims I, 2 and 5, characterized in that it is planned to also use, to ensure all or part of its function of supporting element of a prefabricated floor, a traditional reinforcement for concrete reinforced, or in addition to steelworkers prestressed, when the mechanical characters and the shape of these various reinforcements allow it.