FR2885548A1 - Lifting and handling pin incorporating method for concrete hollow slab, involves introducing pins in each opening in slab and subjecting gripping ring of pin to rotation perpendicular to slab so that branches pass below reinforcement strand - Google Patents

Abstract

The method involves openings made in a concrete hallow slab using a shovel at four corners when the concrete is wet, and introducing a lifting and handling pin (6) in each opening, where the pin is constituted of a metal tie and comprises a middle bend defining gripping ring (7). The ring is subject to a rotation perpendicular to the slab so that positioning branches (81, 82) of the ring passes below a longitudinal reinforcement strand (2). The openings at the corners are trowel with freshly mixed concrete around the rings while filling contiguous zones of holes with the concrete. An independent claim is also included for concrete slab prestressed by iron or longitudinal reinforcement strand.

Description

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  The present invention relates to a method for incorporating lifting and handling pins in a prestressed concrete honeycomb slab by longitudinal iron or reinforcing strands placed between the cells at the bottom of this slab.

  The prestressed concrete hollow core slabs that appeared on the market in the 1950s are still highly appreciated by building professionals.

  Such slabs have the advantage of being cast not on sites but in factories before being transported and delivered as a rule trucks; consequently, their manufacture is not dependent on any bad weather.

  These slabs usually have a standard width of about 1.20 m and a variable length adapted to the range, up to 20 m, and have in their inner part 5 to 11 longitudinal cells.

  They are conventionally manufactured on pre-stress benches of great length (of the order of 150 m) and having a width corresponding to that of slabs, in particular by extrusion.

  During the manufacture of these slabs it is also advantageous to use a particular pouring device, said sliding formwork, which moves continuously along the prestressing bench.

  Such a device essentially comprises, in the direction of movement: son guides ensuring the maintenance of the strands, casting members of the lower layer dal-les, this layer being located below the cells and enclosing the reinforcing strands vibrating shoes, profiled cores movable longitudinally back and forth making it possible to obtain longitudinal cavities and cooperating with casting members of the concrete strips separating the cells, pads for vibrating these concrete strips, organs pouring of the upper layer of dal-les located above the cells, - a vibrating table.

  In order to manufacture the prestressed concrete hollow core slabs, the reinforcing strands are placed in parallel with each other, they are individually or generally tensioned with cylinders, and then the concrete is cast on heights varying between about 12 and 40 cm by means of the sliding form casting device which moves continuously along the prestressing bed, the dies are cut to the desired length, and after the setting of the concrete, the strands are cut so as to put the latter in prestressing.

  On site, these slabs are juxtaposed on beams or walls so as to form the floor of the floors of different buildings.

  When placed on the beams or walls, it is necessary to lift the slabs by means of cranes.

  For the purpose, two main lifting devices are currently used for this purpose.

  The first of these methods consists in suspending from hook 15 of the crane a large metal beam called rudder equipped at its ends with clamps for gripping a slab.

  Chains passing below the slab provide additional security.

  Such a process does not satisfy all 20 professionals.

  The second lifting method is to suspend from the crane hook a four-strand sling whose ends are respectively introduced into four through holes provided for this purpose at the four corners of the slabs.

  Two metal bars respectively strung at the ends of two associated strands, below the slabs, allow the hand-hold of these.

  Such a method has the disadvantage of requiring drilling on the slabs of four through holes to be then rebou-30.

  The object of the invention is to overcome the disadvantages of known lifting methods of hollow core slabs prestressed concrete.

  For this purpose, the idea behind the invention was to incorporate in these slabs lifting pins and handling to grasp them by means of a crane, directly downstream of the manufacture of these slabs by pouring concrete, when the concrete is still fresh.

  In this context, the invention relates to a process for incorporating lifting and handling pins into a prestressed concrete honeycomb slab with longitudinal reinforcing bars or strands placed between the cells at the bottom of the slab. this slab according to which the slab is opened, in particular by means of a shovel near its four corners, and at the level of two lateral strands situated essentially symmetrically with respect to the longitudinal axis of the slab so as to clear these strands and the adjacent cells at this level and introduced a lifting pin and handling in each of the openings thus formed, on either side of the associated strand.

  According to the invention, these lifting and handling pins are each constituted by a metal rod bent symmetrically with respect to its center and comprising on the one hand a median bend defining an approximately planar gripping ring that can project from the upper part of the slab, and secondly, at the respective ends of the gripping ring, two lateral bends delimiting two essentially parallel positioning branches directed towards one another.

  These two positioning branches are separated by a distance slightly greater than the diameter of the associated strand so as to per-put their introduction on either side of this strand substantially parallel thereto.

  Given the spacing of the two positioning legs, the gripping ring is in fact not strictly flat but slightly left and has a shape that can be likened to that of an open trombone.

  According to the invention, after the introduction of the lifting pins into the openings, each of the gripping rings is subjected to a rotation of 90 perpendicularly to the slab so that its positioning branches pass below the associated strand and is rebouched. openings with fresh concrete around the gripping rings by filling the contiguous areas of the cells.

  The establishment of the lifting and handling pins can be performed manually very easily, with the help of a tool if necessary to drive them.

  At the end of the process, the slabs are equipped at their four corners with lifting pins and handling which the gripping ring can project from its upper end to the surface of the concrete.

  These slabs can be grasped by a lifting device comprising a four-legged sling suspended from the hook of a crane.

  The method according to the invention thus makes it possible to perfectly anchor the lifting and handling pins in the concrete so as to avoid any risk of breakage which could have dramatic consequences given the weight of the slabs which is of the order of 200 to 600 kg / m2 depending on their thickness.

  According to the invention, the lifting and handling pins are generally positioned on the two penultimate strands from the side edges of the slab.

  According to the invention, the gripping rings preferably have the shape of an isosceles triangle having a height of between 8 and 40 cm.

  The positioning legs can advantageously have a length of between 5 and 20 cm depending on the. geometry and the weight of the slab.

  The invention also relates to a hollow concrete slab prestressed by longitudinal iron or reinforcing strands placed between the cells at the bottom of the slab.

  Such a slab is characterized in that it is equipped at its four respective corners with a lifting pin and handling constituted by a metal rod bent symmetrically with respect to its center and having on the one hand a median bend defining an approximately planar gripping ring that can project from the upper part of the slab, and on the other hand at the respective ends of this gripping ring two lateral bends delimiting two essentially parallel positioning branches directed towards each other and extending beyond the grip ring.

  According to the invention, these two positioning branches are separated by a distance slightly greater than the diameter of the strands and are positioned below an associated strand, substantially perpendicular to this strand.

  The characteristics of the method as well as of the prestressed concrete hollow slab which are the subject of the invention will be described in more detail with reference to the accompanying nonlimiting drawings in which: FIG. 1 is a perspective view of a hollow slab of prestressed concrete; Figure 2 is a perspective view of a lifting and handling pin; - Figure 3 is a perspective view similar to Figure 2 but after 90 rotation of the lifting pin and handling.

  According to FIG. 1, the slab 1 is made of prestressed concrete with longitudinal reinforcing strands 2 which can project at its ends and is equipped with a series of longitudinal cells 3.

  The number of seven cells and six reinforcing wire selected by way of example is of course in no way limitative of the invention.

  The strands 2 are placed between the cells 3 at the lower part of the slab 1.

  It should be noted that each of the concrete strips 4 separating two cells 3 is not necessarily equipped with a strand 2.

  According to FIG. 1, slab 1 is equipped on its upper surface 5 and at its four corners with four lifting and handling pins 6 that can protrude from the surface of the concrete and whose function is to allow the slab 1 can be grasped by a not shown lifting device comprising a four-legged sling suspended from the hook of a crane.

  According to Figure 2 each of the lifting and handling pins 6 is constituted by a metal rod bent symmetrically with respect to its center C. This metal rod 6 has at its center C a median bend defining a gripping ring 7 shaped of isosceles triangles and at the respective ends of this gripping ring 7 two lateral bends Ci, C2 delimiting two positioning branches 8i, 82.

  The gripping ring 7 is approximately plane (in fact slightly left) and can project on the upper face 5 of the slab 1 as shown in FIG.

  The two positioning branches 8i, 82 extend in parallel parallel to one another at a distance e slightly greater than the diameter d of the associated strand 2.

  According to FIG. 2, the positioning pins 6 are introduced into unrepresented openings made in the concrete, when the latter is still fresh, on either side of the associated strand 2 so that the positioning branches 81, 82 are essentially parallel to this strand 2.

  From this position, shown in FIG. 2, and according to FIG. 3, each of the gripping rings 7 is then rotated 90 perpendicularly to the slab 1 so that its positioning branches 81, 82 pass below the associated strand 2.

  It is thus possible to anchor the lifting and handling pins in the concrete.

  All that remains is to re-seal the opening previously made in fresh concrete.

Claims (5)

  1) A method for incorporating lifting and handling pins (6) into a prestressed concrete honeycomb slab (1) with longitudinal reinforcing bars or strands (2) placed between the cells (3) at the lower part of this slab (1), directly downstream of the manufacture thereof by pouring concrete comprising the following steps: - when the concrete is still fresh, the slab (1) is opened by means of a shovel near its four corners and at two lateral strands (2) located substantially symmetrically with respect to the longitudinal axis of the slab (1) so as to release these strands (2) and the cells (3) contiguous to at this level, a lifting and handling pin (6) is introduced into each of the openings thus formed, on either side of the associated strand (2), these lifting and handling pins (6) being made, - one, by a symmetrically bent metal rod relative to its center and having on the one hand a median bend (6) defining an approximately planar gripping ring (7) which can project from the upper part of the slab (1), and on the other hand, at the ends respective of this gripping ring (7), two lateral bends (Ci, C2) delimiting two essentially parallel positioning branches (81, 82) directed towards one another, these two positioning branches (81, 82) being spaced apart by a distance (e) a little greater than the diameter (d) of the associated strand (2) so as to allow their introduction on either side of this strand (2), essentially parallel to it, is submitted each of the gripping rings (7) at a rotation of 90 perpendicularly to the slab (1) so that its positioning legs (81, 82) pass below the associated strand (2), and the openings are re-opened with fresh concrete around the gripping rings (7), filling the contiguous areas of the cells (3).   2) Method according to claim 1, characterized in that the lifting and handling pins (6) are positioned on the two foremost strands (2) from the side edges of the slab (1).   3) Method according to any one of claims 1 and 2, characterized in that the gripping rings (7) have the approximate shape of an isosceles triangle having a height of between 8 and 40 cm.   4) Method according to any one of claims 1 to 3, characterized in that the positioning legs (81, 82) have a length of between 5 and 20 cm.   5) Cellular slab (1) prestressed concrete by irons or reinforcing wire strands (2) placed between the longitudinal cells (3), at the bottom of the slab, obtained by the implementation of the method according to l any one of claims 1 to 4, characterized in that it is equipped at its respective four corners with a lifting and handling pin (6) consisting of a metal rod bent symmetrically with respect to its center and comprising on the one hand a median bend (c) defining an approximately planar gripping ring (7) projecting from the upper part of the slab (1), and on the other hand at the respective ends of this gripping ring (7). lateral bends (C1, C2) delimiting two substantially parallel positioning branches (81, 82) directed toward each other, these two positioning branches (81, 82) being spaced apart by a distance (e) a little greater than the diameter e (d) strands and being positioned below an associated strand (2), substantially perpendicular to this strand.