FR2862995A1 - Supple self-stressed beam for anti-seismic structure is made in sections held together by continuous cables passing round grooved rollers in straight and curved lines - Google Patents

Abstract

The beam is made from a series of adjoining sections (1) held together by continuous cables (3) passing round rollers (2) with grooved edges, positioned so that the cable lies in a straight line along the lower part of the beam and a curved line in the upper part. In a portal structure the beam is supported by uprights in sections (16) also held together by cables (18, 19) and grooved rollers (20).

Description

The present invention relates to beams, gantries and all

  structures used in civil or industrial engineering and building construction.

  Most often these structures are monolithic but, for the implementation of very large structures, it also realizes juxtaposed pieces beams prestressed. This is the case, for example of some bridges and motorway bridges built by successive corbels.

  Prestressing has allowed a considerable progress of achievements compared to traditional reinforced concrete. However, the prestressing may have, in the long run, disadvantages associated with fatigue phenomena of materials such as the relaxation of tensioned cables and the creep of compressed concrete, over time. In addition, it seems useless to maintain throughout the life of the structure a maximum prestress imposed definitively, while the overall stresses of the beam are most often variable and not always the maximum intensity. We will see later that the self-stressing according to the invention does not impose on the beam a constant and definitive stress.

  In addition to the distinction between monolithic beams and broken beams, it is also important to distinguish the quasi-deformable quasirigid elastic structures and the so-called flexible structures because they are more deformable.

  This class of flexible structures is very extensive since it can concern both large marine sails or the tent of a circus that beams in pieces held by cables that will be called flexible beams compared to the monolithic beams quasirigides traditional. These flexible beams consist of juxtaposed pieces separated by dry or elastic joints and joined by cables stretched by prestressing or self-stressing.

  The foregoing definition of the flexible beams is valid for the special beam claimed by the present invention with respect to its particular mode of self-stressing. Two mechanical self-stress embodiments based on the support rotation and the other on the boom have already been claimed. But these two methods are not simple and 2862995 -2- may present, due to unavoidable friction phenomena, insufficient mechanical efficiency to be effective.

  This is why the present invention proposes a new embodiment of self-stressing, this time much simpler, easily achievable and a much higher efficiency in efficiency thanks to the virtual disappearance of the negative effects of friction. Apart from this, the rolling friction of the rollers on their axis is practically negligible and ponderable by the possible use of ball bearings.

  To achieve the self-stressing according to the invention, it is a question of using the spacing, under loading, of the joints between adjacent pieces of the flexible beam, whereas the two processes already claimed used the boom and the bearing rotation. . The aforementioned three self-stressing means result, in fact, from the same cause which is the overall deformation of the beam by bending between supports under loading.

  The particularity of the present invention in relation to the methods already claimed and to any prior invention of the same order, lies in the use of a cable closed on itself to form a continuous belt, thanks to a looping device for connecting both ends of the cable and adjust its voltage. Unlike conventional prestressing cables which are discontinuous and anchored at both ends in the beam, this special self-stressing cable is closed on itself by the aforementioned looping device, which makes it a continuous belt in one piece.

  The flexible beam according to the invention is provided with a belt cable on each of its lateral faces. The specific form claimed for this cable is such that once closed, it constitutes a rectilinear belt, at rest, in the lower part and whose upper part is a broken line at the passage of each roller, so quasicurviligne if the pieces of the beam are numerous enough. Each belt cable passing over the rollers secures the pieces of the flexible beam and the tension of the cable is provided to ensure, by a suitable minimum prestressing, the horizontal and straight appearance of the beam under its own own weight at rest.

  The principle of operation of the self-stressing according to the invention is as follows: when the flexible beam is stressed by a load, it naturally tends to bend downwards between its two supports. This results in a spacing of the joints growing downwards. The sum of these spacings causes the elongation of the lower part of the beam which curves slightly. This elongation causes traction in the lower part of the cable of the belt. The belt being continuous in one piece, this traction causes, through the end rollers, equal traction in the upper part of the cable and tends to lift upward by straightening its original curvature. The straightening effect thus produced generates a vertically upward thrust that lifts the pieces and tends to thwart the downward effect of the natural gravity loading. Thus, the tension deformation of the waistband upwards achieves a compensating self-stress which attenuates the downward bending effect of the flexible beam under load, increasing its stiffness in conjunction with the applied load.

  The self-stress is simultaneous with the application of the load and is proportional to the intensity of loading applied. On the contrary, the prestressing is by definition imposed on the beam before commissioning and intensity fixed in advance by a final tension of the prestressing cables. This differentiates fundamentally prestressing and self-restraint both in the operating principle and the means of realization.

  According to another embodiment of flexible structure, the present invention also provides a flexible gantry consisting of a cross member made of self-stressed flexible beams and amounts which are divided posts in superimposed sections connected, as for the flexible beam, by cables passing on rollers groove axis attached to each section. These cables elastically secure each section with all other sections of the post so as to achieve a sufficiently deformable amount in the general plan of the gantry, while retaining the rigidity necessary for normal support of vertical loads.

  In addition, a joint is provided at mid-height of the posts to add to the flexibility of deformation of the gantry in its plane. To achieve the flexibility of a structure in all directions a grid of orthogonal flexible gantries is necessary to absorb the components of the forces in two perpendicular directions. In this case, the posts are armed with cables and rollers on the four sides of the sections.

  At the top of the columns, the assembly nodes of the beams and columns can be made of traditional reinforced concrete cast in situ, but also according to other embodiments of the invention such as: - The assembly node can be made by cables replacing conventional concrete reinforcements.

  - The assembly node can also be achieved by bolted plates and sealed in the pieces of beams and in the sections of the posts. Option that avoids any cast-in-place reinforced concrete and allows the assembly of strictly prefabricated elements.

  These flexible structures could be used to carry out earthquake-resistant constructions and to avoid or limit the drama inherent in earthquakes. The Boumerdès earthquake in Algeria in 2003 is a tragic and recent example of the loss of life, the disarray of the surviving populations and the problems of reconstruction.

  Earthquakes subject the constructions to sudden oscillations which are more like the effects of dynamic shocks by the level of energy developed instantaneously creating accelerations and therefore applied forces much higher than the quasistatic forces imposed in normal times on the structure. The consequences of earthquakes are therefore out of all proportion to the usual stresses, even limits, imposed on buildings.

  In non-earthquake earthquake-resistant structures, poles are sheared by earthquake tremor foundations, superimposed floors of tiered buildings collapse and pile up on each other creating the so-called thousand-sheet effect known specialists and feared by locals, prevention services, builders and public services.

  Therefore, by means of preliminary experimental tests, flexible gantries, according to the invention, should be able to absorb enough energy while maintaining adequate elastic and even plastic resistance to avoid the aforementioned collapse, allowing in cases the less unfavorable, reuse after repair. In the most critical cases, the most important thing is to save the maximum number of lives, at the moment of the earthquake, as at the time of the relief operations.

  The accompanying drawings illustrate the invention: FIG. 1 shows in elevation the assembly of a flexible beam and the closed cable in the form of a continuous belt according to the invention.

  Figure 2 shows a section on the beam of Figure 1 showing that the beam is provided with a belt cable on each of its two side faces and that the axes of the rollers are through.

  Figure 3 shows the closure device and closure of the belt cable.

  Figure 4 shows, on a larger scale than in Figure 1, the detail of a grooved roller of the flexible beam.

  Figure 5 shows, in elevation, the overall view of a span of a flexible gantry according to the invention.

  Figure 6 shows, in elevation, the support of an upper rail on one of the intermediate columns of a continuous multiple gantry. A detail on a larger scale shows a pebble and its against throat roller.

  Figure 7 shows a bank support flexible gantry.

  Figure 8 shows in section, on a larger scale, the connecting device of the end of the crossbar with a flexible gantry edge post. The part drawn in thicker lines is poured in place to ensure a monolithic connection between the edge piece of the crossbar and the head section of the support post.

  Figure 9 shows in section, on a larger scale, the connecting device of two beams of the cross with an intermediate pole of the flexible gantry. The part drawn in thicker line is cast on site to make a monolithic connection between the adjacent pieces of two successive bays and the head section of the support pole.

  Figure 10 shows a section of the flexible pole on a larger scale than in Figure 6, with a detail showing the arrangement of the cables crossing on the central roller.

  Figures 11 and 12 show schematically the deformations of a single gantry under the effect of a seismic shock. To simplify as much as possible, only the ground floor of a building is represented, and only the static and non-dynamic effects of the shaking are taken into account. While in reality, the earthquake is transmitted almost instantly to all floors and accelerations inherent in the brutality of the shaking involving dynamic effects, release a very important energy that amplifies the static effects and therefore the movements of the gantry , to cause the ruin of the structure for earthquakes of very high amplitude.

  FIG. 11 very schematically shows the cumulative static effects of the displacement of the foundation, assumed to be indeformable, and of the displacement of the upper cross member, adding up the deformations of the gantry due to these two displacements. In reality, all these movements being almost instantaneous and therefore quasi-simultaneous interfere with each other with the risk of reaching the natural frequency of the structure and causing resonance. In addition, it should be noted that the forces developed by the earthquakes are, most often, multidirectional and as they are quasi-combined their mechanical effects on a structure interfere with each other and also with the forces of inertia developed by the reactions of the structure. This makes the analysis of the overall specific effect of an earthquake more complex than a simple static solicitation acting in a single plane.

  Figure 12 shows the opposite effects of the shock due to the quasisimultaneous change in the meaning of the forces involved. Here only the horizontal components are taken into account, to simplify to the extreme, when in fact non-negligible vertical components also intervene in the shaking.

  Figure 13 is a plan view of a system of multiple orthogonal gantries constituting a resistant grid supporting the floors of a multi-storey building.

  Figure 14 is an elevational sectional view showing the various floors of the building as seen in Figure 13.

  Figure 15 shows in section the support node of the four beams arriving on an intermediate post flexible gantries according to the invention. The part drawn in thicker line indicates a zone of keying which will be cast on site, after installation of the four prefabricated beams, to ensure the connection and the continuity of the beams and the poles.

  Figure 16 shows in elevation section the head section of the post supporting the four beams shown in Figure 15 and its connection with these beams.

  Figure 17 is a section, reduced by half compared to Figure 16, the head section of the intermediate post of flexible gantries. A detail, on a larger scale, shows the arrangement of the cables solidarisant the various sections of the pole and which intersect on the two intermediate rollers.

  Figures 18 and 19 show in elevation sectional a variant of the gantry according to the invention to replace the cast-in-place reinforced concrete node of Figures 15 and 16 by an assembly device cables and angles. In Figure 19 the part shown in thicker line can be filled with concrete poured on site or left empty. In the latter case, an anticorrosive coating must enclose the cables enclosed therein and the support length of the beams must be calculated to take up all the loads of the upper post.

  Fig. 20 is a plan view of the connecting device 30 depicted in Figs. 18 and 19 with marking of the sections drawn in Figs. 18 and 19.

  Figures 21 and 22 show the large scale details of the connecting members shown in Figures 18 to 20.

  Figure 23 shows in elevation a variant of the assembly device shown in Figures 18 to 22.

  Figure 24 shows in elevation-section a new variant of the gantry according to the invention to replace the cast-in-place reinforced concrete node of Figures 15 and 16 by a bolted plate assembly and fully prefabricated device.

  With reference to these drawings, the flexible beam comprises, on its two lateral faces, a cable (3) which connects the various pieces (1) of the beam by means of grooved rollers (2) whose axis (8 ) is fixed in each piece (1) through which it passes.

  The cable (3) according to the invention is in the form of continuous belt in one piece. At rest of the unloaded beam, this belt is rectilinear in the lower part and becomes, in the upper part, a broken line passing through each roller (2). The belt is made by closing the cable (3) on itself by a device (4) for belt buckling which connects the two threaded ends of the belt cable (3). The looping device (4) comprises nuts (7) or any other means of closing and clamping for adjusting the tension of the belt cable (3).

  The flexible beam is supported at both ends by its edge pieces (1) on a knife rest (5) on one side allowing the support rotation and on the other side on a carriage rest (6). allowing the longitudinal displacement of the flexed beam in addition to its support rotation.

  The counter - roller (9) is hung under the roller (2) by means of a stirrup (10) of bent flat metal. Four connecting cables (12) connect the eight mooring rollers (11) of the two contiguous edge pieces (1) of the two contiguous flexible beams to the intermediate post. On the connection detail according to AA section 9 it is seen that the rollers (11) are twinned with the common axis (8) common edge rollers (2).

  The cables (12), closed by a looping device (4), contribute, like the caps (13), to ensure the continuity of the two beams on the pole. The concrete reinforcements (14) and their pins (15) ensure the continuity of the ground floor post with the two flexible beams and also with the first floor post by the steels (14) provided for this purpose.

  The reinforcements (13) to (15) above, embedded in cast-in-place concrete, provide a monolithic knot assembling the sections (16) of the posts with the edge pieces (1) of the two beams joined to the cross member. The frames (17) frieze the vertical frames (14). The steels (22) to (24) connect the piece of edge (1) of the beam with the section (28) of the head of the bank post.

  At each floor level the base section (27) of all the posts will not be prefabricated, like the other sections (16), but cast on site to serve as a basis for the rest of the post consisting of prefabricated section (16). The waiting steel (21) fretted by the frames (17) constitute the armature of the section (27). Reinforcements (13) to (15) and (21) to (24) embedded in cast-in-place concrete are common binding methods commonly used in reinforced concrete.

  We have so far assumed that the above mentioned pieces and sections were of reinforced concrete. Their specific internal reinforcements have not been specified, because we will see later that these pieces (1) are not necessarily in reinforced concrete, as well as the sections (16) (27) and (28) which could be metallic , of wood or masonry, or other rigid and resistant materials.

  The cables (18) and (19), comprising a closing device (4), connect, on two opposite faces, the various sections (16) of the post by means of the grooved rollers (20) integral with the sections (16). ) by their axis which is drowned. The cable (25) secures, on two opposite faces, the sections (28) of the edge post.

  The sections (16) (27) and (28) of the columns are separated by thin sliding joints (29) and at the mid-height of all the columns there is a thick joint joint (30) with a cylindrical axis (31) perpendicular to the general plane of the flexible gantry. The angles (26) placed at the edges of the sections (16) (27) and (28) prevent the weaving of these edges in case of possible relative rotations of the sections of the posts.

  In the simplified representation of the deformations of a gantry siege of an earthquake the deformed (32) schematizes the gait of the average line of the gantry under the effect of the displacement of the foundation. The deformation (33) results from the displacement of the cross member.

  The deformed (34) is the sum of the deformities (32) and (33). Deformities (35) and (36) of strictly opposite and opposing meanings illustrate what can produce a sudden inversion of the direction of the seismic thrust, as an acceleration that can release a considerable destructive energy.

  The grid (41) of the seismic flexible gantries is represented according to sectional plane AA, FIG. 13. The armatures in caps (38) provide the connection and the continuity of the four flexible beams arranged in a cross on the upper section (16) constituting the head of the intermediate posts of one of the flexible gantry grid squares (41). The reinforcements (37) provide the connection of the four aforementioned beams with the lower and upper columns.

  The beam and column connecting device shown in the drawings by the reinforcements (37) and (38) embedded in the cast-in-place concrete is a traditional method of conventional reinforced concrete technique. But this method can be replaced, partially or entirely by other devices to ensure the same connection and such, for example, as those described later.

  The cables (39) and (40) disposed on the four faces of the posts, intersect on the two rollers (20) intermediate to secure the sections (16) of the pole. Only the reinforcements concerning the embodiment of the invention have been represented.

  In the case of a grid of gantries (41), the sections (16) of the columns are separated by thin sliding joints (29), as shown in FIG. 6. However, on the other hand, the thick joint (30) of articulation shown in this figure is provided, in the case of poles of a grid of beams (41), a spherical ball (31) replacing the axis of cylindrical articulation (31) shown in Figure 6.

  The appearance of the drawing, in these two cases remaining the same, the same number (31) was assigned to them. The spherical ball (31) allows the articulation of the pole in any direction. Direction most often unpredictable and possibly variable almost instantly.

  The cables (43), connecting two superposed posts, pass inside the tube (47) formed in the piece (1) for supporting the cross members on the post. These cables (43) are provided with the closing device (4) and replace the standing steel (37). Similarly, the cables (49) replace the continuity caps (38). These cables (49), connecting two successive beams, are moored to the beams by an anchoring arch (50) embedded in the concrete and surrounding the axis (8) of the rollers (2) according to detail Figure 22. This arch (50 ) can be made by a concrete iron or constituted by a cable. The cables (49) are fixed to the hoop (50) by bolts (51) for adjusting the tension of the cable (49). Angles (45) with sealing lugs (46) and anchor bolts (52) complete the assembly of the gantry node. The bolts (52) are screwed into threaded sleeves (42) prefabricated in the support pieces (1) of the beams. The axes (48) of the rollers (20) are fixed to their sealing tabs (44) by welding or bolting.

  The cables (56), homologous to the above-mentioned cables (49), connect two successive beams in a manner different from the cables (49): mooring rollers (53) and plates (54) with sealing lugs ( 55) replace the hoop (50) and the bolts (51). A loopback device (4) allows the closing and adjustment of the cable tension (56).

  The plate (57) is fixed on the lower post and the two beams of the crossbar by brackets (58) and bolts (61) sealed in the head section (16) of the lower post and in the beams of the cross. The plate (60), fastened to the base section (16) of the upper pole by sealing tabs (59), is connected to the two beams of the cross member by the bolts (61) sealed in the support pieces (1). of these beams. The plates {57) and (60), which replace the cast-in-place assembly reinforced concrete, are steel plates or other material of equivalent mechanical properties. These plates are square or rectangular and of sufficient thickness to transmit the loads and withstand the connecting forces and continuity under normal or even extreme stresses such as earthquakes or impact shocks.

  The process of implementing this last entirely prefabricated variant is done in three successive steps: first put the plate (57) on the head section (16) of the lower pole, then lay the four beams of the sleepers, then finally lay the base section (16) of the upper post on the four beams in place. Recall that this base section (16) is prefabricated integrally with the plate (60).

  According to a first variant not illustrated, the gantry can be single-span. In this case, Figure 7 shows that the edge pieces (1) of the cross member rest on the entire surface of the upper section (16) of the two posts and are connected to this section (16) by the frames (22). and (23) ensuring the continuity of the ends of the crossbar with the posts.

  According to a second variant not illustrated, the gantry can be two spans only. In this case, the cables (3) of the cross member may be running from one span to the other to form a single continuous belt raised in the upper part on the central pole and replace, thus, the traditional caps (13).

  According to a third variant not illustrated, the pieces (1) of the crossbar may be made using flexible bags filled with light powdery materials, or the earth, or a liquid or gaseous fluid. In this variant, the two pieces of edge (1) of each span would be made of rigid and resistant materials to ensure the good performance of the flexible beam. This variant would virtually eliminate the risks of the aforementioned thousand sheet effect, in the case of bags filled with light products since it is the rigidity and weight of the floors that are the cause of this phenomenon so deadly.

  The self-reinforcing flexible beam according to the invention is particularly intended to withstand very variable loadings or very high intensity relative to permanent loads, or heavy rolling loads, as for industrial or military bridges or railway viaducts.

  The grid of flexible gantries according to the invention would find, after successful test, an application in the earthquake resistant constructions of countries particularly victims of disasters inherent to earthquakes of great amplitude. Other applications could concern nuclear power plants and landfills of radioactive waste to be built in areas particularly exposed to earthquakes, or to provide for the case of an attack or accident by fallout from a jumbo jet on sensitive installations. chemical or nuclear activity.

  In addition to the problems of safety and prevention of major risks, the interest of piecewise flexible structures also lies in their ease of assembly, disassembly, transport and possible reuse. Hence an aptitude for use in mountain, expedition, military or police operation, or for rescues, and, more generally, whenever a rapid way of passage is to be considered. Moreover, the use of self-contained flexible beams can bring

  an answer to the problem of cracking of traditional reinforced concrete. Indeed, it is known that the concrete is cracking by traction, and in particular in the vicinity of tensile reinforcement of a traditional monolithic bent beam. The problem with cracking is that we do not know when and where, exactly, it will appear, how it will evolve, and therefore what will result from it as to the precise form of damage that the beam will subsequently undergo at the expense of its ability to resistance.

  However, we know for certain against the fact that the crack will reduce the stiffness of the beam and above all, the corrosion of strained bare steels, highly detrimental to the strength of the beam, with risk of failure in the long term. Now, it must be known that the pieces of the flexible beam are never stressed in tension. The problems of cracking are eliminated with regard to the flexible beam, the joints between pieces playing the role of artificial cracks without danger, provided by the manufacturer for bending without major problem.

  A last possible application, quite particular this one, remains to propose for flexible structures, it concerns the recycling of waste. Sludge from water treatment plants reaches exponential quantities that pose problems of storage, use or disposal. A biological process by microbial action has been considered, but is still too recent to be conclusive. In addition, the gases released can aggravate the prevailing pollution. Agricultural spreading also has its drawbacks and lacks opportunities for farmers who are reluctant to use them.

  Also, the flexible beams in pieces consisting of bags filled with mud might offer a possible outlet provided they are generalized to most buildings to build and all elements of the floors. It is also possible that these sludges have a sufficiently insulating power to build not only floors, but also insulating and carrying walls made of chipboard and mud.

  In this hypothesis, not necessarily utopian, the waste thus recycled could become not only ecological and useful, but perhaps necessary.

Claims (10)

  1-self-stressing flexible beam consisting of pieces (1) juxtaposed joined by grooved rollers (2) to tensioning cables (3) arranged on either side of the beam characterized in that each cable (3) forms a continuous belt of a single straight piece in the lower part, the upper part of this belt being a broken line of roller (2) roller (2), and a device (4) for looping the belt connecting the two ends cable (3) comprises means (7) for closing the cable (3) and adjusting its voltage.   2- flexible multi-portal portico consisting of flexible beams according to claim 1 characterized in that the supports (5) and (6) of these beams are poles divided into sections (16) (27) and (28) separated by joints thin (29) and connected by grooved rollers (20) to tension cables (18) (19) and (25) continuous and forming a belt closed by the looping device (4), these posts are hinged mid - Height by a thick seal (30) encasing a cylindrical axis articulation {31).   3- flexible gantries according to claim 2 characterized in that the flexible beams of the cross member are joined and secured by connecting cables (12) passing on mooring rollers (11) paired with the rollers (2) of the edge pieces ( 1) beams, the rollers (2) of the other pieces (1) being provided with counter-rollers (9) suspended under the rollers (2) by stirrups (10), an assembly device made of reinforced concrete irons ( 13) (14) (22) and (24) connects beams and columns.   4- flexible gantry according to claim 2 characterized in that it is a simple gantry single-span whose sections (28) of the columns are connected by the rollers (20) to tension cables (25), and that the edge pieces (1) of the cross member rest on the entire section (28) at the head of the posts.   5- flexible gantry according to claim 2 characterized in that it is a gantry with two continuous spans whose cables (3) are not interrupted on the central post, but are running from one span to another to form a single continuous belt raised in the upper part on the central post.   6. flexible gantry according to claims 2 characterized in that the pieces (1) of the cross are flexible bags containing light powdery materials, soil or a fluid with the exception of the pieces of edge (1) of the beams which are rigid and resistant, and that the sections (16) (27) and (28) of the posts are metallic or other rigid and resistant materials.   7- Grids gantry (41) formed of flexible gantries according to one of claims 2 or 6, characterized in that it consists of orthogonal multiple gantries optionally staggered whose amounts are divided columns armed with continuous cables (39) and (40) passing on grooved rollers (20) and arranged on the four faces of the sections (16) (27) and (28), these posts being articulated at mid-height around a spherical ball (31) drowned in a thick joint (30), that the flexible beams of the crosspieces are separated by a gap reserved for the assembly of the beams and columns by reinforced concrete of the irons (37) and (38), and that in span the rollers ( 2) comprise against-rollers (9).   8-gantry grid according to claim 7 characterized in that the connection of the beams and posts comprises cables (49) fixed by bolts (51) anchoring arches (50) surrounding the axis (8) of the rollers (2). ), and cables (43) shaped continuous belt closed by the looping device (4).   9- grid gantries according to claim 7 characterized in that the flexible beams of the cross members are connected by connecting cables (56) having the closure device (4) and mooring rollers (53).   10- grid gantries according to claim 7, characterized in that the connection of the beams and columns is achieved by plates {57) and (60) assembled to the beams and poles by bolts (61), angles (58) and sealing tabs (59).