EP0242238B1 - Steel and reinforced concrete structures, particularly for producing girders, in particular girders used as purlins or girders with a large span - Google Patents

Description

The invention relates to a reinforced concrete and steel beam, in particular for purlin use.

The present invention relates to a beam consisting of an upper reinforced concrete member of relatively small section compared to its length and of a lower steel member, the concrete member being at least locally placed above the steel member. , the steel frame being made up of a hull connected from place to place to the concrete frame by metal connectors disposed respectively to the right and to the left of the longitudinal vertical median plane of the beam, these connectors being welded to the hull and having their ends incorporated into the concrete frame.

A beam of this type is described in the publication GB-A 586 394.

The present invention relates to such a beam but in which the transmission of the compressive forces is essentially ensured by the concrete of the concrete member.

This is achieved, according to the invention, by the fact that the ends of the connectors which are incorporated in the concrete member are connected together, in this member, only by the concrete of the member.

In the aforementioned publication, on the contrary, these ends are fixed to longitudinal reinforcements which run in the concrete frame.

The present invention therefore relates to beams having the characteristic of using reinforced concrete in all the compressed parts and steel in the form of profiles in all the stretched parts.

Typically, a beam according to the invention is a rigid structure essentially consisting of reinforced concrete and steel intended to support in service compression forces and tension forces, where the parts intended to support compression forces are essentially constituted by a mass of concrete and the parts intended to resist tensile stresses are essentially constituted by an assembly of steel profiles substantially devoid of intrinsic rigidity, this assembly being mainly external to the concrete and being anchored in the concrete which provides lateral stiffness and buckling resistance.

In a typical embodiment, the steel part is constituted by an assembly of profiles of simple shape, for example rectangular plates or, better still, concrete bars.

Typical embodiments of beams in accordance with the invention will be described below, the most typical embodiment being a beam consisting of a concrete member of relatively small cross section relative to its length and of a steel member consisting of a hull which rises at its ends in the concrete frame and which is, on the other hand, connected from place to place to the concrete frame by couples arranged in transverse planes which are perpendicular to the concrete frame, the ends of these couples being embedded in the concrete frame.

The hull is preferably constituted by a single profile but can also be constituted by several profiles assembled end to end and / or by several metal profiles in parallel.

As a variant, the hull is constituted by a hollow tube which contains a prestressing cable, which in particular makes it possible to produce beams of great span.

The publication US-A-2 809 074 describes a steel-concrete beam comprising a hollow tube which contains a prestressing cable but this tube is part of a self-supporting metal frame and the concrete of the beam is a slab which does not coat the chassis and which has no effect on the resistance of the chassis.

• la figure 1 est une perspective d'une poutre réalisée selon la présente invention ;
• la figure 2 est une demi-coupe longitudinale de la poutre ;
• la figure 3 est une demi-coupe longitudinale d'une variante de réalisation de la poutre ;
• la figure 4 est une coupe schématique de la poutre par un plan vertical transversal passant dans la région d'un noeud de la membrure en acier de la poutre ;
• les figures 5 et 6 sont des vues agrandies de la figure 4 respectivement dans la région de la membrure en béton et dans la région de la membrure en acier ;
• la figure 7 est un schéma de la poutre dans sa position de moulage de la membrure en béton ;
• la figure 8 est une perspective de la poutre avant coulage de la membrure en béton ;
• la figure 9 est une coupe par un plan vertical transversal du moule de fabrication de la membrure en béton avant et après mise en forme du ferraillage de la membrure ;
• la figure 1O est une coupe, par un plan vertical longitudinal, des extrémités en regard de deux poutres sur un appui commun ;
• la figure 11 est une perspective d'une extrémité d'une poutre ;
• les figures 12, 14 et 16 représentent schématiquement, en vue longitudinale, des variantes d'exécution d'une poutre ;
• la figure 13 est une coupe de la poutre de la figure 12 par un plan vertical transversal ;
• la figure 15 est une coupe de la poutre de la figure 14 par un plan vertical transversal,
• les figures 17 à 19 représentent des exemples de réalisation de jonctions dans la membrure en acier,
• la figure 20 est un schéma en long d'une poutre selon une variante de l'invention, dans
  laquelle la carène formant la membrure en acier est constituée par un tube creux qui contient un câble de précontrainte,
• la figure 21 est une coupe schématique par le plan transversal aa de la figure 20,
• la figure 22 est un schéma en long d'une poutre plus complexe portée par deux poteaux,
• la figure 23 est une coupe schématique de la poutre de la figure 22 par le plan transversal aa de la figure 22,
• la figure 24 est une coupe schématique de la poutre de la figure 22 par le plan transversal bb de la figure 22,
• la figure 25 est une coupe schématique agrandie des extrémités voisines de deux membrures en béton contigües,
• la figure 26 est une perspective schématique de l'extrémité de l'une des membrures en béton de la figure 25,
• la figure 27 est une coupe transversale d'un tube de carène, et
• la figure 28 est un schéma en long d'une structure constituée de plusieurs travées avec continuité au droit des appuis.

In the figures:

• Figure 1 is a perspective of a beam made according to the present invention;
• Figure 2 is a longitudinal half-section of the beam;
• Figure 3 is a longitudinal half-section of an alternative embodiment of the beam;
• Figure 4 is a schematic section of the beam through a vertical transverse plane passing through the region of a node of the steel frame of the beam;
• Figures 5 and 6 are enlarged views of Figure 4 respectively in the region of the concrete member and in the region of the steel member;
• Figure 7 is a diagram of the beam in its molding position of the concrete member;
• Figure 8 is a perspective of the beam before pouring the concrete member;
• Figure 9 is a section through a vertical transverse plane of the mold for manufacturing the concrete member before and after shaping the reinforcement of the member;
• Figure 1O is a section through a longitudinal vertical plane of the opposite ends of two beams on a common support;
• Figure 11 is a perspective of one end of a beam;
• Figures 12, 14 and 16 schematically show, in longitudinal view, alternative embodiments of a beam;
• Figure 13 is a section of the beam of Figure 12 by a transverse vertical plane;
• FIG. 15 is a section of the beam of FIG. 14 by a transverse vertical plane,
• FIGS. 17 to 19 show exemplary embodiments of junctions in the steel frame,
• FIG. 20 is a longitudinal diagram of a beam according to a variant of the invention, in
  which the hull forming the steel frame is constituted by a hollow tube which contains a prestressing cable,
• FIG. 21 is a diagrammatic section through the transverse plane aa of FIG. 20,
• FIG. 22 is a longitudinal diagram of a more complex beam carried by two posts,
• FIG. 23 is a schematic section of the beam in FIG. 22 through the transverse plane aa of FIG. 22,
• FIG. 24 is a diagrammatic section of the beam in FIG. 22 through the transverse plane bb in FIG. 22,
• FIG. 25 is an enlarged schematic section of the neighboring ends of two contiguous concrete members,
• FIG. 26 is a schematic perspective of the end of one of the concrete members of FIG. 25,
• FIG. 27 is a cross section of a hull tube, and
• Figure 28 is a diagram along a structure consisting of several spans with continuity at the right of the supports.

The beams of the invention which are shown in Figures 1 to 19 consist of two superimposed members, one B of concrete and the other A of steel.

In the most common embodiments (Figures 1 to 3 and 14), the concrete member is systematically located above the steel member when the beam is in service.

However, it also falls within the scope of the invention to produce beams such that the concrete members can be locally below the steel member (as shown in Figures 12 and 16 by way of example) .

It will be understood that, in general, most of the concrete member remains above the steel member when the beam is in the service position.

The concrete frame B is generally constituted by an elongated rectilinear block of reinforced concrete and this block is preferably given a section which is easy to demold on a building site, such as for example a straight section of trapezoidal shape (FIGS. 7).

This frame is reinforced by a reinforcement F according to the rules of the art so that the frame mainly resists compressive forces. In addition, the member must have sufficient inertia to withstand buckling phenomena.

The steel frame A is constituted by a longitudinal section L which extends along the length of the concrete frame along a curve whose distance from the concrete frame is maximum in the middle of the beam and decreases progressively towards the ends of the beam, this longitudinal section penetrating into the concrete member in the region of the ends of this member and even emerging on the end edges of the concrete member, as seen in Figures 2, 3 and 1O.

The steel frame A comprises, on the other hand, steel connectors C which connect from place to place the profile L to the concrete frame. Preferably, these sections L and these connectors C have a part C₁ welded to the section L and a part C₂ anchored in the concrete member. In the examples shown, these connectors have a general V shape, the top of the V being flattened and welded along its length to the profile L while the ends of the wings of the V are also flattened and embedded in the concrete of the member B. Furthermore, in the embodiments shown, the connectors C are arranged in pairs respectively to the right and to the left of the longitudinal vertical median plane P of the beam, as best seen in Figures 5 and 6 which are sections (at two scales different) of the concrete frame (Figure 5) and the steel frame (Figure 6) by the transverse vertical median plane of the beam in Figure 3 (plane IV-IV) of Figure 3. We see in this figure that the longitudinal section L of the steel frame is constituted by a round of relatively large diameter concrete steel while the connecting connectors C, C 'of the steel frame A to the concrete frame B are constituted by ro concrete steel nds of smaller diameter and it can also be seen in FIG. 6 that the local connection between the concrete rounds of the couples C and C 'and the concrete round of the hull L are constituted by welds S.

As an indication, a concrete rod whose diameter is in the range 2O to 6O mm is used for the L profile while a concrete rod whose diameter is in the range 1O to 30 mm is used for the connectors, these ranges being given on a preferred but nonlimiting basis.

The longitudinal profile L is preferably formed by a single profile but it is not excluded to constitute it by several assembled profiles. FIG. 18 shows, by way of example, an assembly of two sections L₁, L₂ by means of an end-to-end assembly sleeve M in which the ends of the sections, previously shaped into truncated cones and threaded, are pressed in by screwing. It is not necessary to describe in detail this assembly means known per se. Profile L can, on the other hand, consist of several profiles arranged in parallel instead of being constituted by a single profile and FIG. 17 shows, by way of example, a mixed solution where profile L comprises a profile L₃ followed by two parallel profiles L₄, L₅, these various profiles being assembled by a plate p which is freely traversed by the profiles whose through ends are then welded to the plate. This type of assembly makes it easy to adjust the length of the L profile on request.

The number and shape of the connectors C is also chosen as a function of the performance requirements of the beam, knowing that the steel frame A essentially only has the role of supporting the tensile forces. On this subject, it will be noted that in the examples shown in FIGS. 1 to 3, the lower longitudinal section L of the steel frame follows the curve of the moments and supports a substantially constant tensile force over its entire length under symmetrical loading, while the upper concrete member B, which provides longitudinal rigidity, withstands a substantially constant compressive force under symmetrical loading.

The manufacture of a beam according to the invention can easily be done on site using a mold of simple design, a prototype of which has been shown in FIG. 8. The molding position is upside down from the service position in the sense that during molding the steel frame A is located above the mold Z, supported from place to place by suitable supports, as can be seen in FIG. 8. In the mold, the reinforcement F is arranged which is carried out according to the rules of art. By way of example, there is shown in FIG. 9 the cross section of a reinforcement, the parts in broken lines representing the reinforcement before shaping. The ends of the connectors C are introduced into the mold as well as the ends of the longitudinal profile L which pass through the reinforcement to come out at the longitudinal ends of the mold. At each of the longitudinal ends of the concrete member B, is fixed a metal part S in the shape of an L (FIGS. 10, 11) which is intended to ensure the fixing of the concrete member on a support by bolting. The fixing part S is incorporated into the concrete frame during molding.
This fastener S has a flat S₁₀ embedded in the end edge of the concrete frame and this flat has an opening T₁₀ for the passage of the end of the longitudinal section L of the steel frame, the protruding end being then welded to the flat, as best seen in Figures 1O and 11. On the other hand, the fixing part S has another flat S₂₀ intended to rest on the support of the beam, and this other flat S₂₀ has a light T₂₀ for the passage of a stud which will be used to fix the part S to the support of the beam. When two beams are brought into alignment on the same support, the plates S₂₀ and S'₂₀ of the fixing parts S and S 'are preferably superimposed, as can be seen in FIG. 1O, to be crossed by the same stud; alternatively, they could be independent of each other and crossed by respective studs.

The support on which rests one end of the beam is any support in itself depending on the circumstances of use. It can be for example a wall, a post or a transverse beam. In the case where the beam according to the invention is intended to constitute a breakdown in a structural truss, the support will generally be a beam arranged as a crossbowman. In such an application, the concrete member provides lateral rigidity and works very slightly in bending under the loads of the material which constitutes the covering. The forces introduced by the local bending phenomena are second order compared to the main forces.

To make very long beams or for any other reason, it may be useful to give the concrete member B a special longitudinal profile other than straight and Figures 12, 14 and 16 illustrate exemplary embodiments where the concrete member has a long trapezoidal profile (Figures 12 and 14) or convex (Figure 16). In the case of FIG. 12, it is necessary to ensure continuity between the upper steel members of the two beams which follow one another on the same support.

The fixing of the profile L to the fixing piece S can also be obtained by mechanical means (bolting, etc.), for example by threading or machining the end of the profile L.

FIGS. 22 to 28 relate to a variant of the invention, more particularly with a view to the production of long-span beams.

• il n'existe pas, dans le commerce, de ronds à béton de très gros diamètre,
• les ronds à béton disponibles et transportables sont d'une longueur limitée.

When you want to make beams with large spans, you run into two problems:

• there are no commercially available concrete rods of very large diameter,
• the concrete bars available and transportable are of limited length.

Under these conditions, if we want to make beams of great span, we are led to assemble several sections end to end. This assembly is expensive and presents difficulties.

The present invention can in particular allow the production of long-span beams, in particular for making frames for industrial or sports roofs.

This is achieved, according to the present invention, by constituting the hull by a hollow steel tube capable of receiving a prestressing cable which will later be tensioned. In particular, the tube consists of a single tube section or of several tube sections fixed end to end by welds or by fixing pieces, for example by bolted plates.
More specifically, the structure shown in FIGS. 20 and 21 comprises a beam S consisting of a rectilinear concrete member B and a steel member A consisting on the one hand by a tube T of arcuate shape, the concavity of which is turned towards the top when the beam is in the service position and, on the other hand, by diagonals, for example concrete rods, arranged in pairs C, one end of which is welded to the tube and the other end of which is embedded in the concrete of the concrete member B.

These beams can be made according to the technique described above, where the beams are made with the steel frame disposed above the concrete frame.

A multi-strand prestressing cable F is threaded into the tube and tensioned according to the calculated force, by any means known per se and so as to bring into the tube compressive stresses always below the elastic limit. These means are shown diagrammatically in FIG. 20 by cones W. Subsequently, the tube is injected with mortar or other curable medium to block the prestressing cable and protect it from rust.

The prestressing is calculated so that under normal use load of the beam, the tube remains slightly compressed.

If the load is increased, the prestressing cable first lengthens by a few centimeters, then the tube begins to work in tension: at break, all the steel is tensioned.

This process has great advantages because it allows the prefabrication described above under normal conditions.

The tubular member is possibly made up of several sections, connected by bolted plates, or welded end to end. The welding of large diameter tubes is a known and simple operation.

After assembly, we benefit from the efficiency of the prestressing cable.

The invention thus uses prestressing cables which are delivered in great length while the tubular profiles are limited due to the transport difficulty.

It should be noted that this technique does not penalize the quantity of metal used for the following reason: if one loads such a structure until rupture, the steels of the tube and prestressing work at the maximum of their capacity taking into account their possibilities relative elongation.

However, in the failure calculation, the authorized load represents a percentage of the breaking load.

The relationship between these two loads - working load and breaking load - represents what we usually call the "safety factor" of the frame concerned.

In addition, under normal use load, the tube remains compressed and thus the beam is clear of the risk constituted by a bad weld in the assembly of the tubes end to end; noting however that the resistance capacity of the tube was tested by the tensile force generated by the self-weight before tensioning of the cable.

In this embodiment, the prestressing is carried out after the beam has been placed in its service position. It is possible to use the beam supports to tension the prestressing cable. In a particular variant, the cable is tensioned before the beam is brought into the service position.

A beam as described above is suitable for spans from 20 to 50 meters, for example.

For larger spans, for example from 50 to 100 meters, it is preferable to use a more complex beam made up in fact of several beams arranged end to end and crossed by a common prestressing cable.

Figures 22 to 27 schematically show an embodiment of such a beam.

The structure shown in Figure 22 includes a central beam S₁ and two end beams S₂, S₃. The central beam S₁ consists of a concrete frame B₁, of arcuate shape, the concavity of which is turned downwards when the beam is in the service position, and a steel frame, formed on the one hand by a tube T₁ , of arcuate shape, the concavity of which is turned upwards when the beam is in the service position and, on the other hand, by diagonals, arranged in pairs C dont, one end of which is welded to the tube and the other of which end is embedded in the concrete of the concrete member B.

The end beams S₂ and S₃ have a similar structure but the curvatures of the members are less accentuated and the relative positions of the members are reversed.

To set up the beam on two supports or posts P, first place the two end beams S₂, S₃ which are each fixed to one of the posts P, so that the steel frame is at- above the concrete member, then the central beam S₁ is placed between these two beams after having turned it over (in relation to its manufacturing position) so that the steel member is below the concrete member and in so that the longitudinal tube T₁ of the central beam and the longitudinal tubes T₂, T₃ of the end beams S₂, S₃ are in continuity. These tubes are welded end to end, or connected by metal plates bolted together, while the concrete beams are secured by any suitable means, for example: welded or bolted metal plates.

Figures 25et26 illustrate an exemplary embodiment of the junction of the central beam S₁ and an end beam, for example the beam S₂. The concrete members of the two beams are provided at their ends with plates K₁, K₂ which are anchored in the members by rods (for example concrete rods) r₁, r₂ welded to the plates and embedded in the concrete. To assemble the two frames, the plates are applied one against the other and temporarily fixed by bolts. The two plates are then welded to each other.

The structure at this stage is stable under its own weight. Under the dead weight of the beam, the tube is stretched.

A multi-strand prestressing cable F is then threaded into the three tubes and into the posts P, from F₁ to F₂, and tensioned according to the calculated force, by any means known per se and so as to bring into the tube compression stresses always below the elastic limit. Later, the tube is injected with mortar or other curable medium to block the prestressing cable and protect it from rust.

FIG. 28 relates to a very long-span structure produced using the span technique the technique described in connection with FIG. 22, the prestressing cables being put in place by span, from F₁ to F₂, from F₂ to F₃, from F₃ to F₄, etc ...

It goes without saying that in a complex beam, the number of successive concrete members is generally two or three, but it can also be greater. It will also be understood that, depending on the case, the steel hull tube has its ends which are embedded in the concrete member or which pass through the concrete member.

The beams and structures of this variant of the invention (described with regard to FIGS. 20 to 28) are in particular intended to produce roof frames, the cover being located in the extension of the concrete frame, that is to say - say along the curved surface formed by straight and horizontal lines resting on the concrete members. It goes without saying, however, that the invention is not limited to this application: another important application of the invention is the production of bridges.

Claims (18)

1. Beam consisting of an upper reinforced-concrete member (B) with a cross section which is relatively small compared with its length and a lower steel member (A), the concrete member being at least locally positioned above the steel member, the said steel member consisting of a casing (L) connected at intervals to the concrete member by connectors (C) disposed respectively to the right and left of the longitudinal vertical mid-plane of the beam, these connectors being welded to the casing (L) and having their ends incorporated in the concrete member (B), characterised in that, in the reinforced-concrete member, these ends are anchored in the concrete of the member so that in the concrete they are not connected to each other or to any other reinforcement in the concrete member.
2. Beam according to Claim 1, characterised in that the connectors (C) situated on one side of the said vertical mid-plane constitute, together with the connectors situated on the other side of this plane, ribs disposed in transverse planes perpendicular to the concrete member.
3. Beam according to one of Claims 1 and 2, characterised in that the connectors (C) are in the form of a V, the apex of the V being flattened and welded over its length to the casing, whilst the ends of the legs of the V are also flattened and embedded in the concrete of the concrete member (B).
4. Beam according to one of Claims 1 to 3, characterised in that the casing (L) goes up at its ends into the concrete member.
5. Beam according to one of Claims 1 to 4, characterised in that the concrete member (B) has a rectilinear, trapezoidal or convex cross section.
6. Beam according to one of Claims 1 to 5, characterized in that the casing (L) is formed by a longitudinal profiled section which lies along the length of the concrete member in a curve, the distance of which to the concrete member is at its maximum in the middle of the beam and decreases progressively towards the ends of the beam.
7. Beam according to one of Claims 1 to 6, characterized in that the casing (L) follows the moment curve and bears a substantially constant tensile force over its entire length under symmetrical loading, whilst the concrete member (B), which provides longitudinal stiffness, bears a substantially constant compression force under symmetrical loading.
8. Beam according to one of Claims 1 to 7, characterized in that an L-shaped metal piece (S), which is intended to fix the concrete member to a support by bolting, is fixed to one longitudinal end of the concrete member (B).
9. Beam according to Claim 8, characterised in that the said fixing piece (S) has a flat part (S₁₀) embedded in the end section of the concrete member, in that this flat part has an orifice (T₁₀) for the end of the casing (L) to pass through, and in that the protruding end of the casing is welded to the flat.
10. Beam according to Claim 9, characterised in that the fixing piece (S) has another flat part (S₂₀) intended to rest on the beam support, and this other flat part (S₂₀) has a slot (T₂₀) for a bolt to pass through, which will be used to fix the piece (S) to the beam support.
11. Beam according to one of Claims 1 to 10, characterised in that the casing (L) and connectors (C) are formed by reinforcement rods.
12. Beam according to one of Claims 1 to 10, characterized in that the steel casing is formed by a hollow tube (T) containing a prestressing cable (F).
13. Beam according to Claim 12, characterised in that the tube (T) of the casing is injected with mortar or other hardening medium to lock the prestressing cable in position after prestressing.
14. Beam according to Claim 12 or 13, characterized in that the concrete member (B) is substantially rectilinear.
15. Beam according to one of Claims 12 to 14, characterized in that the ends of the tube (T) pass into the concrete member (B).
16. Beam according to one of Claims 12 to 15, characterized in that the tube (T) is formed by several lengths of tube fixed end to end by welds or fixing pieces.
17. Beam according to Claim 12 or 13, characterized in that it comprises a central beam (S₁) between two end beams (S₂, S₃), the concrete member (B₁) of the central beam being placed above the steel member and being curved in shape with its concave part oriented downwards, and the steel member of the central beam consisting of a curved tube (T₁) with its concave part oriented upwards, the end beams having structures similar to that of the central beam but the curves of the members being less accentuated and the relative positions of the concrete and steel members being reversed, the concrete members of the three beams being disposed in continuity and connected together and the tubes of the three beams having a common prestressing cable passing through them.
18. Application of a beam according to one of Claims 1 to 17 as a purlin in a framework truss.

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