BACKGROUND OF THE INVENTION
The present invention is concerned with a method of anchoring wire ropes under prestressed conditions with a view to reduce the overall dimensions of the anchoring structure in comparison with known devices of this character.
It is known to anchor wire ropes under prestressed conditions by extruding a steel socket on a single- or multistrand wire rope, this anchoring, in the case of a multistrand wire rope, is facilitated by the interposition of a spring of very hard treated steel which embeds itself both in the socket material and in the strand during the extrusion process. However, in the case of particularly long structures this arrangement is conducive to anchor socket considerable and therefore cumbersome dimensions, since the length of the external threads formed on this socket depends on the wire rope elongation.
On the other hand, it has already been proposed to dispose the strands or wire ropes constituting the prestressed bracing assembly separately in side-by-side relationship in concentric recesses formed in the anchoring socket (cf. French Pat. No. 1,042,912); with this improved arrangement the friction forces are distributed among the elementary strands of the wire rope, thus permitting of reducing the length and overall dimensions of the anchoring sockets; the assembly is tensioned according to the conventional method by pulling the previously extruded socket by means of a suitable actuator until the desired tension is obtained in the bracing assembly. However, this method is objectionable because it still requires considerable overall dimensions for the anchoring socket and special means for gripping and pulling the anchoring head.
SUMMARY OF THE INVENTION
To avoid these inconveniences, this invention provides an anchoring socket consisting of a metal sleeve or cylinder preferably formed with external screw threads and with longitudinal, preferably parallel inner passages each adapted to receive a strand or wire rope extending through the relevant passage and emerging therefrom by a length sufficient to permit the gripping thereof by the anchoring head.
The anchoring of each strand or wire rope in the aforesaid longitudinal passages of the anchoring socket is improved by using a very hard spring penetrating into the socket and rope material during the extrusion operation. Thus, anchoring devices having particularly reduced dimensions, which project from the finished structure but by the minimum length, are obtained.
The wire rope system is tensioned by using an actuator, for example a cylinder-and-piston pulling unit, secured to an anchoring head in which the strands or wire ropes are engaged. The anchorage is locked in position by using a nut screwed on the socket; this nut bears against a metal abutment plate of the fixed structure. Then the strands utilized for tensioning the system are cut flush to the outer end of the socket, and the finished anchoring device thus obtained has relatively reduced overall dimensions.
However, these overall dimensions may be further reduced, especially in the longitudinal direction, by using a plain anchoring socket or sleeve comprising on the one hand longitudinal and preferably parallel through passages each adapted to anchor therein, separately, a strand constituting the reinforcing or bracing system, or a wire rope of the multirope system, which extends therethrough and emerges therefrom only by a quantity corresponding to the socket elongation resulting from the extrusion operation, and on the other hand an axial passage engaged by a steel rod of sufficient cross-sectional dimension which has its screw-threaded end screwed in the anchoring head.
As a consequence of the extrusion operation, the steel rod becomes practically an integral part of the socket either by becoming embedded in the central hole (in the case of a rod have both ends screw-threaded) or by indentation of a hard-steel spring interposed before the extrusion operation between this rod and the socket in said central passage of the socket.
As a consequence of the extrusion operation, on the one hand the strands or wire ropes constituting the bracing or reinforcing system, and on the other hand the rod, are rigidly connected to the socket, and the assembly can be tensioned by simply using an actuator secured to the free, screw-threaded portion of the rod which emerges from the socket.
Having thus tensioned the wire rope assembly, the prestressed anchorage is completed by locking a nut screwed on said central threaded rod and adapted to bear against a metal abutment plate. Then, if desired, the rod portion protruding from the nut may be cut off so that the projecting portion of the anchoring device corresponds simply to the thickness of this nut.
BRIEF DESCRIPTION OF THE DRAWING
A typical form of embodiment of the method of anchoring prestressed wire ropes, in the case of a multistrand wire rope, will now be described by way of example with reference to the accompanying drawing, in which:
FIG. 1 is an elevational, part-sectional view showing a conventional prestressed anchoring device in its finished condition;
FIG. 2 is a longitudinal sectional view of an anchoring device, showing the position of the parts before the final tension has actually been applied thereto;
FIG. 3 is a section taken along the line III-III of FIG. 2;
FIG. 4 is a view similar to FIG. 2 but showing the parts in the tensioned or stressed condition;
FIG. 5 is a view similar to FIG. 4 but showing the completed anchoring device;
FIGS. 6, 7 and 8 are views similar to FIGS. 2 and 4 but concerning a modified form of embodiment of the anchoring structure of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The conventional method of anchoring a multistrand wire rope system 1 or a multi rope system consists in engaging the wire rope or wire rope assembly through a socket 2 of a length corresponding substantially to the wire rope elongation under tension (FIG. 1). This extruded socket or sleeve 2 is gripped by the clamping member of a traction actuator (not shown) until it emerges from the outflared tubular member 3 and can be fastened to the abutment plate or flange 4 of the locking plug 9. In the case of bracing systems of considerable length, relatively bulky anchoring sockets are necessary and the tensioning operation is obviously delicate to perform.
According to his invention, barrel-shaped sockets or sleeves 2 are used, i.e. cylindrical sockets in which preferably rectilinear, parallel and concentric longitudinal through passages 5 are formed; the wire ropes or strands 1 are threaded through these passages and the length thereof which emerges from the opposite end of the socket is a least sufficient to permit the gripping or clamping thereof by means of a suitable device or anchoring head 6 rigid with an annular actuator 7 (FIGS. 2 and 3).
Having extruded the socket 2 on the wire rope core, preferably after inserting hard-steel springs 8 in the longitudinal passages 5, the assembly is tensioned in the conventional manner (FIG. 4) until the desired tension is obtained. The wire rope elongation is of course properly calculated beforehand, so that the screw-threaded socket 2 will be so positioned that it can be locked by means of the nut 9, whereafter the projecting free end of the wire rope can be cut off (FIG. 5).
Thus, an anchoring head of relatively reduced overall dimensions is obtained while facilitating the tensioning operation.
The barrel-shaped anchoring head may be formed with the desired number of longitudinal passages arranged in any suitable manner, the friction forces being exerted over the entire peripheral surface of each elementary strand or wire rope during its passage through the socket, so that the length and transverse dimension of this socket are reduced considerably.
In the modified form of embodiment of the anchoring method of this invention which is illustrated in FIGS. 6 to 8 of the drawing, the reinforcing, bracing or like wire rope assembly or structure 1, or each strand or rope, is anchored separately in one of the longitudinal parallel passages 5 of socket 2 so as to extend through it and emerge therefrom by a quantity corresponding only to the elongation l of the anchorage during the socket; this socket 2 further comprises an axial through passage 12 engaged by a rod 10 having at least one screw-threaded end, one end 11 of this rod being fastened to the head 6 of a traction actuator 7.
As a consequence of the extrusion operation, the socket 2 is rigidly assembled both with the strands or wire ropes 1 of the rope system or assembly and with the axial rod 10, suitable members such as hard-steel springs 8 being interposed if desired therebetween to increase the anchoring strength either between the strands and the passages 5 (FIG. 6) or between the axial passage 12 and the traction rod 10 which can be screw-threaded or plain (FIG. 8).
When the assembly has been properly tensioned the anchorage is locked by tightening a nut 9 engaging the abutment plate 4, and the projecting end 11 of this rod is eventually cut off.
Thus, a gain in the length of the wire ropes or strands projecting from the extrusion socket is obtained, and the tractive effort exerted on this socket for anchoring purposes is facilitated and more reliable.