FR2593536A1 - Structures made of reinforced concrete and steel, especially for making girders and, in particular, girders to be used as purlins - Google Patents

Abstract

The invention relates to structures made of reinforced concrete and steel. The structure is essentially made of concrete in all the parts in compression B and of steel in all the parts in tension A. The invention applies in particular to the manufacture of girders, particularly girders to be used as purlins.

Description

 The present invention relates to reinforced concrete and steel structures intended in particular to constitute beams and, in particular, beams for use of purlins.

For various types of construction and, in particular, for the roofing structures of industrial buildings, two principles of construction clash
- the reinforced concrete,
- the metal frame
To achieve economic structures, it is obviously necessary to use a minimum of material. This phenomenon is particularly sensitive for large spans because unnecessary material constitutes a parasitic overload.

 To consume a minimum of material in the realization of a structure, the ideal would be to saturate in all points the capacities of resistance of the material.

However, in the two main principles of construction cited above, we see
Reinforced concrete structures.
The steels entering the reinforced concrete structures are calculated to resist mainly the tensile stresses since the concrete material is considered as cracked in the tensed parts during the failure calculations.

Concrete material has several functions
- withstand compression and shear stresses in certain areas,
- in other areas, its main role is the coating of steels.

 In a conventional reinforced concrete beam, a significant amount of material is underused supporting insignificant stresses in the sense of the resistance of the materials.

The concrete material is heavy and the underused material leads to a double waste
- cost of the material,
- parasitic overload
Metallic structures.-
In a metal frame, the tensioned parts are calculated by making full use of the steel's resistance capacities.

 On the other hand, the compressed parts must have a certain inertia to resist the phenomenon of buckling and, under these conditions, the steel in the compressed zones is in a sense underused.

Metal profiles (angles,
U, profiles in I) have a cut section
- in order to present a certain inertia to resist buckling,
- in order to present shapes suitable for bolting or welding assemblies.

 In the first case, drilling the holes weakens the sections and, in the second case, a certain length of weld bead is necessary.

 The double problem of buckling and assembly therefore leads to complex shapes and overabundant sections for the profiles.

 On the other hand, a metal frame, during the assembly of large preassembled elements, must have a certain overall rigidity, often difficult to obtain with very resistant profiles but having in their conventional forms a low inertia. This leads to complementary triangulations and only intended to avoid overall buckling.

 The present invention relates to mixed structures having the characteristics of using reinforced concrete in all the compressed parts and steel in the form of profiles in all the tensioned parts.

 Typically, a structure in accordance with the invention is a rigid structure essentially consisting of reinforced concrete and steel intended to withstand compression and tension stresses in service, this structure being characterized in that the parts intended for supporting the compressive forces are essentially constituted by a mass of concrete and in that the parts intended to withstand the tensile forces 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 concrete which gives it lateral rigidity and resistance to buckling.

 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.

A structure according to the invention is significantly more economical than known structures, in particular for the following reasons
the mixed structure of the invention is lighter than a structure which would be made of reinforced concrete,
- The steel part of the structure of the invention can be much more economical than a wire mesh because the rigidity of the structure will be essentially due to the concrete part and not to the steel part.

In addition, when using concrete reinforcing steel as steel, which is never the case with a metal frame, we obtain mechanical resistance characteristics superior to those obtained with the profiles generally used in frame. metallic. In addition, compared to a conventional metal frame, the assemblies can be very simplified thanks to the invention since part of the assemblies is made by concrete and the rest of the assemblies can be made by simple welds,
- the concrete part can be produced in a simple way by molding on the site so that the structure of the invention is perfectly suitable for small sites where it is however desired to use structures of great lengths. application, we encounter serious difficulties due to the fact that the structures used are generally prestressed structures which are too expensive to produce on a site and which therefore have to be produced in the factory, which poses the problem of their transport and this problem is particularly difficult when the structures are very long.

 Typical embodiments of structures in accordance with the invention will be described below, the most typical embodiment being a beam made of a concrete frame of relatively small cross section relative to its length and of a steel frame made 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.

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 transverse vertical 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 transverse vertical plane of the mold for manufacturing the concrete member before and after shaping the reinforcement of the member
- Figure 10 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 in FIG. 14 by a vertical transverse plane, and
- Figures 17 to 19 show exemplary embodiments of junctions in the steel frame.

 The beams of the invention which are shown in the figures consist of two superimposed members, one B made of concrete and the other A made 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 audes under 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 lton preferably gives this block an easy-to-demold section on a site, such as for example a straight section of trapezoidal shape (Figures 4, 5 and 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 coming out on the end edges of the concrete member, as seen in Figures 2, 3 and 10.

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 frame. 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 frame 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 concrete frame (figure 5) and steel frame (figure 6) by the transverse vertical median plane of the beam in figure 3 (plane IV-IV) of figure 3. that the longitudinal section L of the steel frame is constituted by a round of relatively large concrete steel while the connecting connectors C, C ′ of the steel frame A to the concrete frame B are constituted by rounds made of concrete steel of diameter p read small and we also see 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 consist of S welds.

 As an indication, a concrete bar whose diameter is in the range 20 to 60 mm is used for the L profile while a concrete bar whose diameter is in the range 10 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. 17 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 profiles, 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.
L can, on the other hand, be made up of several sections arranged in parallel instead of being made up of a single section and FIG. 17 shows, by way of example, a mixed solution where the section L comprises a section L3 followed two parallel sections L4, L5, these various sections being assembled by a plate P which is freely traversed by the sections, the through ends of which 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. 9. 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 fastening part S has a flat S1 embedded in the end edge of the concrete member and this flat has an orifice T1 for the passage of the end of the longitudinal section L of the steel member, the protruding end being then welded to the flat, as best seen in Figures 10 and 11. On the other hand, the fixing part S has another flat S2 intended to rest on the support of the beam and this other flat S2 has a T2 light 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 in alignment on the same support, the plates S2 and S'2 of the fixing parts S and Are preferably superimposed, as seen in Figure 10, to be crossed by the same stud St alternatively, they could be independent of one another 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 examples of embodiment where the frame
concrete has a long trapezoidal profile (Figures 12 and
14) or convex (figure 16). In the case of Figure 12; continuity must be ensured between the upper steel members of the two beams which follow each other 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.

Claims (16)

1. Rigid concrete and steel structure, characterized in that it is essentially made of concrete in all the compressed parts (B) and in that it is mainly made of steel in all the tensioned parts (A). 2. Rigid structure essentially consisting of reinforced concrete and steel intended to withstand compression forces and tension forces in service, characterized in that the parts intended to support the compression forces are essentially constituted by a mass of concrete ( B) and in that the parts intended to resist tensile stresses are essentially constituted by an assembly (A) of steel profiles substantially devoid of intrinsic rigidity, this assembly being mainly external to the concrete and being anchored in the concrete which gives it lateral rigidity and buckling resistance. 3. Structure according to claim 1 or 2, characterized in that the steel assembly (A) of the structure consists essentially of concrete rods. 4. Beam made up of a concrete frame (B) of relatively small section compared to its length and a steel frame (A) made up of a hull (L) connected from place to place to the concrete frame by couples (C) arranged in transverse planes which are perpendicular or oblique with respect to the concrete member, the ends of these couples being embedded in the concrete member. 5. Beam according to claim 4, characterized in that the hull (L) and the couples (C) are constituted by concrete rods. 6. Beam according to claim 4 or 5, characterized in that the hull goes up at its ends in the concrete frame. 7. Beam according to one of claims 4 to 6, characterized in that the concrete member (B) has a trapezoidal cross section. 8. Beam according to one of claims 4 to 7, characterized in that the hull L is constituted by a longitudinal section which extends along the length of the concrete member according to a curve whose distance from the concrete member is maximum in the middle of the beam and gradually decreases towards the ends of the beam. 9. Beam according to claim 8, characterized in that the couples are connectors (C) which have a part C1 welded to the bottom L and a part C2 anchored in the concrete frame. 10. Beam according to claim 9, characterized in that the connectors have a general V shape, the top of the V being flattened and welded along its length to the hull while the ends of the wings of the V are also flattened and embedded in the concrete of the concrete member (B). 11. Beam according to claim 9 or 10, characterized in that 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. 12. Beam according to one of claims j to 11, characterized in that the hull follows the curve of the moments and supports a substantially constant tensile force both 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. 13. Beam according to one of claims 4 to 12, characterized in that at a longitudinal end of the concrete frame B is fixed a metal part S in the form of L which is intended to ensure the fixing of the concrete frame , on a support, by bolting. 14. Beam according to claim 13, characterized in that said fixing part S has a flat S embedded in the end edge of the concrete member, that this flat has an orifice T1 for the passage of the end of the hull (L) and that the protruding end of the hull is welded to the flat. 15. Beam according to claim 14, characterized in that the fixing part S has another plate S2 intended to rest on the support of the beam and this other plate S2 has a light T2 for the passage of a stud which will serve to fix the part S to the support of the beam, 16. Application of a beam according to one of claims 4 to 15 as a failure in a structural truss.