AU709875B2 - Suspension device for civil engineering construction and method of construction - Google Patents

Description

SUSPENSION DEVICE FOR CIVIL ENGINEERING CONSTRUCTION AND METHOD OF CONSTRUCTION The invention relates to civil engineering constructions comprising subassemblies suspended from suspension cables or stays themselves carried by piers or the like, each subassembly being suspended via hangers attached by clamps to said suspension cables or stays.

The invention is more specifically directed to the case where the cables consist of a lateral juxtaposition of identical multiple strands distributed in superposed layers, the word "strand" being adopted here for the purpose of simplification, but with no implied limitation, to denote either individual filaments or "strands" proper, or cables 15 or bundles of such strands or even bars.

More specifically still, the invention is directed to the suspension devices of the constructions of the sort in question as well as the methods of construction of these 0- devices.

S: 20 In the known ways of producing the said constructions, each strand has a cylindrical overall shape, and the mutual contacts between strands are made along narrow, or even linear, longitudinal regions of these strands.

The transverse load exerted on the cable by each 25 hanger, and more specifically by the clamp arranged at the top end of this hanger, is therefore transmitted to the cable from strand to strand along said regions with nonuniform distribution, especially if these regions are made of a relatively flexible material like that from which a sheath of a strand of the self-protected type is made.

The result of this is that said strands are not all stressed equally by said load: some of said strands are therefore relatively overloaded, which requires the cable to be oversized as a whole and increases the cost price of this cable and of the construction equipped with it.

In German Patent 759,490, it has been proposed to interpose a filler sheet between the portions, lying inside the clamp, of the superposed layers of strands. This filler sheet has the overall shape of an inverted T, the crossbar of which serves as a stop to prevent the clamp from moving down along the suspension cable. The vertical bar of this T has the width of the layers of strands between which it is inserted. Its function is to give an additional area for friction in order to strengthen the anchorage of the clamp on the suspension cable: the overall friction which provides this anchorage does not result only from the contact area between the internal face of the clamp and the periphery of the cable, but also from the additional areas thus created between the layers of strands and the filler sheets. As a consequence, this filler sheet is stressed in tension, and 15 plays no part in evening out the stresses exerted on the various strands inside the clamp.

One object of the present invention is to achieve a better distribution between strands of the loads exerted at the hanger clamps.

20 The invention thus proposes a suspension device for civil engineering construction, comprising a suspension cable itself consisting of a lateral juxtaposition of multiple strands distributed in superposed layers, and hangers attached to this cable by clamps and capable of transmitting the load of the construction to said cable, an interlayer sheet being interposed between the portions, situated inside each clamp, of at least two of the superposed layers of strands of the suspension cable, in which the interlayer sheet is ribbed alternately on its two faces with parallel spacer strips which have a curvedtriangular profile, these strips being capable of contiguously filling the gaps between said layers.

In preferred embodiments, recourse is further had to one/or other of the following provisions: in a construction for which each strand is surrounded by a sheath made of a flexible material, the 3 interlayer sheet is made of the same material as this sheath or of a material of similar hardness, the flexible material according to the previous paragraph is high-density polyethylene or a polyolefin, the thinned portions of the interlayer sheet which lie between its ribs are very thin, the thickness being of the order of 0.1 mm or even less.

As far as the method of manufacture of the interlayer sheet is concerned, this sheet is advantageously formed: either as a single piece by extrusion, or by forming by extrusion each of the strips which have a curved-triangular profile and by bonding these alternately on each side of a thin sheet or of a set of 15 parallel thin tapes.

As far as fitting the interlayer sheet on the cable is concerned, the procedure is advantageously as follows: before mounting a clamp on the portion of cable intended to receive it, the superposed layers of strands of which said 20 portion is made are successively parted in pairs, then a piece of sufficient surface-area of the spacer sheet is introduced horizontally into each of the spaces thus freed in succession between two layers, then said two layers are brought vertically back together, which makes the ribs of 25 the sheet fill in the gaps between these layers, and after all of the gaps between the layers have thus been filled in, the suspension clamp is mounted on the portion of cable thus equipped.

Embodiments of the invention will now be described by way of non-limiting examples, with reference to the drawing appended hereto.

Figure 1 of this drawing shows very diagrammatically a suspension bridge to which the invention is applicable.

Figure 2 shows a partial cross section through a suspension device in accordance with the invention, included in such a bridge.

Figure 3 shows a detail of this section on a larger scale.

Figures 4 and 5 show two alternative ways of forming a ribbed spacer sheet in accordance with the invention, equipping the above device.

Figure 6 shows a perspective view of a fragment of the first of these two sheets.

Figure 7 shows very diagrammatically one step in the method of manufacture in accordance with the invention for the above suspension device.

The bridge represented diagrammatically in Figure 1 comprises, on the one hand, a suspension cable 1 which rests on two piers 2 and which is stretched between two anchorages 3 and, on the other hand, a deck 4 which is suspended from 15 suspension cable 1 via hangers These hangers 5 are attached to the cable by clamps 6 and may extend either vertically, as visible in the lefthand portion of Figure 1, or at right angles to the cable, as visible in the right-hand portion of the Figure.

20 The cable 1 is composed of a plurality of individual strands 7 distributed in a plurality of vertically 0superposed layers, each layer comprising a varying number of horizontally juxtaposed strands, this number varying for example from three for the two outermost layers, to ten or 25 fifteen or even more for the middle layer: if the overall "0 section of the cable is circular, which is most often the case, the number of the layers is of the same order of magnitude as the number of strands of which the middle layer is composed.

When superposed naturally so that they are contiguous, the strands 7 automatically fall into a staggered configuration, as clearly visible in Figures 2 and 3, the base of each strand automatically lodging in the groove formed at the top between two horizontally juxtaposed strands of the layer immediately below.

The gap T thus formed between the three strands in question and more generally between any mutually contiguous three strands of the whole has the overall shape of a prism, the cross section of which is delimited by a curved triangle: more specifically, the triangular cross section is delimited by three arcs of circles of identical radius tangential to each other in pairs, and bulging towards the inside of the triangle.

Each strand 7 is advantageously of a self-protected type, that is to say consists of a plurality of twisted filaments 8 (Figure 3) housed inside a sheath 9 with the interposition of a protection product 10 such as an epoxy resin, a wax or a grease.

The sheath 9 generally consists of a product which is incompressible but has a certain degree of flexibility, 15 such as high-density polyethylene (HDPE) or a polyolefin.

S: The various strands 7 therefore are in contact with one another along very narrow, and even theoretically linear, regions P which extend longitudinally along the 0 strands.

Each gap T is therefore delimited by three portions of sheath 9 each extending transversely between two successive regions P.

In currently known embodiments, the gaps T are empty and the load C applied by the hangers 5 to the cable 1 by 25 means of the clamps 6 is transmitted to the various strands 7 of which the cable is made, only at the regions P.

Given the relative flexibility of the portions of sheath 9 delimiting regions P, the transmission in question may give rise to local and uncontrolled crushing, resulting in an uneven distribution of stresses in the various strands 7.

The invention makes it possible to overcome this drawback by filling in the gaps T in each portion of the cable 1 which is intended to be surrounded by a clamp 6.

This filling-in is achieved using filler elements the volume of which practically complements that of the gaps to be filled in However, these elements do not just consist of small rods corresponding in isolation to each gap: it would be too difficult to fit such small rods.

The element here consists of sheets 11 ribbed with parallel strips 12 projecting alternately from their two faces, each strip having the shape of one of the gaps T, that is to say that of a prism the base of which is delimited by a curved triangle.

The links 13 of each strip 11 which link together two successive ribs or strips 12 have a width which corresponds to the mutual separation of two gaps T in the cable 1.

Each link may be very thin, with a thickness for 15 example of the order of 0.1 mm or even less: experience shows that the tensile strength of plastic sheets as thin as .this is quite adequate to ensure the coherence required for such a sheet during handling thereof.

The sheets in question are advantageously made of S: 20 the same material as the sheaths 9, but this material could be different while at the same time of course being compatible with that of which the sheaths are made.

The sheets 11 may be produced in any desirable ways, for example: 25 as a single piece by extrusion (Figure 4), or by forming prismatic strips 12 beforehand and then fixing these strips alternately to the two faces of an independent sheet 11 (see Figure 5) which sheet may consist of a plurality of parallel thin tapes especially by bonding the strips onto these two faces, it being anticipated that these be selfadhesive.

The sheets obtained have the overall appearance of roller blinds or shutters with parallel strips (see Figure 6) and may, like these, come as rolls to be unfurled on site as required.

To simplify the manufacture of the strips 12 and to reinforce them, whether they be integral with the sheet 11 or affixed thereto, their tips A may be chopped off, which gives these tips a small thickness, for example of the order of 1 mm as visible at A' in Figure 5, although theoretically this thickness should be nil.

To ensure good continuity between the interior face of each clamp 6 and the perimeter of the portion of cable 1 surrounded by this clamp, a sleeve 14, for example made of HDPE, is advantageously provided between this face and this portion, and a layer 15 made of a material which is more deformable than that of which the sleeve is made and offers good resistance to compression, such as neoprene, is advantageously provided against the interior face of this sleeve.

15 It is relatively easy to fit a spacer sheet of the S. sort described hereinabove between the strands of a cable.

For this, all that is required is for the portions of the layers of strands which are intended to be surrounded by this clamp, to be parted successively in pairs, before 20 each clamp 6 is fitted, for example using metal rods the ends of which are rounded to avoid any risk of damage to the sheaths 9.

A sufficiently large piece of ribbed spacer sheet 11 is then slipped transversely, in the direction of the arrow S 25 F of Figure 7, into each space E thus freed between two superposed layers of strands 7, taking care, at the end of this operation, to arrange the tips A of the strips 12 vertically facing the hollows they are intended to fill in.

The overhanging portion of the sheet 11 is then cut off at S.

The layers of strands thus filled are then brought vertically back together; the ribbed sheets thus immobilized between these layers fill the gaps T.

When all of the gaps T have been filled in, the clamp 6 is placed around the portion of cable thus filled and this clamp 6 is fastened to the corresponding hanger 8 because of the filling-in, the transverse stresses generated by the load C are therefore transferred excellently and very uniformly between the various strands 7.

As goes without saying, and as in any case already follows from the foregoing, the invention is not in any way limited to those of its applications and embodiments which have been more specifically envisaged; on the contrary, it encompasses all alternative forms thereof, especially those in which the suspension cables may consist of oblique stays.

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THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: i. Suspension device for civil engineering construction, comprising a suspension cable itself consisting of a lateral juxtaposition of multiple strands distributed in superposed layers, and hangers attached to said cable by clamps and capable of transmitting the load of the construction to said cable, an interlayer sheet (11) being interposed between the portions, situated inside each clamp of at least two of the superposed layers of strands of the suspension cable, characterized in that the interlayer sheet (11) is ribbed alternately on its two faces with parallel spacer strips (12) which have a curvedtriangular profile, these strips being capable of contiguously filling the gaps between said layers.

15 2. Suspension device according to Claim i, relating to a construction for which each strand is surrounded by a sheath made of a flexible material, characterized in that the interlayer sheet (11) is made of the same material as said sheath.

20 3. Suspension device according to Claim 2, characterized in that the flexible material is high-density S"polyethylene or a polyolefin.

4. Suspension device according to any one of the preceding claims, characterized in that the thinned portions 25 (13) of the interlayer sheet (11) which lie between its ribs (12) are very thin, the thickness being of the order of 0.1 mm or even less.

Ribbed spacer sheet (11) for a suspension device according to any one of the preceding claims, characterized in that it comprises alternately on its two faces parallel ribs or strips (12) which have the overall shape of prisms with a base delimited by a curved triangle, said strips being capable of filling in the gaps between the multiple juxtaposed strands of which the suspension cable of the device is made.

6. Method for manufacturing a ribbed spacer sheet

Claims (3)

1. 7. Method for manufacturing a ribbed spacer sheet according to Claim 5, characterized in that each of the strips (12) having a curved-triangular profile is formed by extrusion, and in that said strips are bonded alternately on each side of a thin sheet.
2. 8. Method for fitting a ribbed spacer sheet according to Claim 5, characterized by the series of the following operations: before mounting a clamp on the portion of cable intended to receive it, the superposed layers of strands of which said portion is made are successively parted in pairs, then a piece of sufficient surface-area of :i the spacer sheet (11) is introduced horizontally into each 15 of the spaces thus freed in succession between two layers, then said two layers are brought vertically back together, which makes the ribs (12) of the sheet fill in the gaps between these layers, and after all of the gaps between the layers have thus been filled in, the suspension 20 clamp is mounted on the portion of cable thus equipped.
3. 9. A Suspension device for civil engineering construction substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. Dated this 5th day of February 1997 FREYSSINET INTERNATIONAL (STUP) By their Patent Attorneys COLISOTTN F CO ABSTRACT The suspension device for civil engineering construction comprises a suspension cable itself consisting of a lateral juxtaposition of identical multiple strands (7) distributed in superposed layers, and hangers attached to this cable by clamps and capable of transmitting the load of the construction to said cable. This device comprises, interposed between the portions, lying inside each clamp, of at least two of their superposed layers of horizontally juxtaposed strands a sheet (11) ribbed alternately on its two faces with parallel spacer strips (12) which have a curved-triangular profile, these strips being capable of contiguously filling the gaps between said layers. 00 0 :o: o* oo