US3707011A - Bracing apparatus for movement of a bridging work - Google Patents

Abstract

The unsupported end of a bridging structure being moved from a support to the next support is braced by cables extending from the unsupported end over a mast to the inshore end of the structure. Hydraulic means at the foot of the mast raise and lower the mast to provide compensating forces on the cables as the structure is moved.

Description

United States Patent Launay [4 Dec. 26, 1972 [54] BRACING APPARATUS FOR [56] References Cited MOVEMENT OF A BRIDGIlWG WORK UNITED STATES PATENTS [72] inventor: Hem versa'nes France 2,842,786 7/1958 Digby-Smith ..l4/6 [73] Assignee: Compagnie lndustrielle de Travaux, 3,299,191 1/1967 Mantscheff ..264/34 Paris France 3,490,605 1/1970 K088 212 3,571,835 3/1971 Buechler ..l4/l [22] Filed: March 1, 1971 Primary Examiner-Nile C. Byers, Jr. [21] Appl' "9,709 Attorney- Cameron, Kerkam 8c Sutton [30] Foreign Application Priority Data [57 ABSTRACT March 11,1970 France ..7008699 The unsupported end of a bridging structure being I moved from a support to the next support is braced by [52] US. Cl ..l4/l cables extending from the unsupported end over a [51] lnt.Cl. ..E0ld 1/00 mast to the inshore end of the structure. Hydraulic [58] Field of Search.....l4/i 6; 29/429; 212/1; 52/73 means'at the foot of the mast raise and lower the mast to provide compensating forces on the cables as the structure is moved.

3 Claims, 4 Drawing Figures BRACING APPARATUS FOR MOVEMENT OF A BRIDGING WORK BACKGROUND OF THE INVENTION The present invention relates to bracing apparatus for support of a bridging structure during movement more particularly, for example, support of a bridge during movement to bridging position by pushing the framework thereof away from a bank or support.

In usual methods of movement of a bridging structure and, in particular, by pushing the base of a prefabricated bridge or successive elements of such a bridge from one bank over the opening to be crossed, the base of the bridge is progressively moved toward its final position while resting on various piles or intermediate temporary abutments. During each movement of the bridging structure between adjacent supports, the outer end portion thereof is unsupported causing a distribution of stresses therein which are very different from those found in the bridge when in place and subjected to normal forces.

Several methods are now used to reduce to acceptable values the exceptional forces created during movement of the bridge structure. For example, a temporary light structure may be connected to the front of the bridging structure to support it on an adjacent pile or abutment before the bridging structure proper reaches such a support.

A bracing construction can also be provided for the front portion of the bridging structure to give it an inverse support for the forces that develop during movement of the bridge. It is evident that the value of the supplementary forces on the unsupported portion of the bridging structure increase progressively during movement of the bridging structure from one support to another and that these forces decrease abruptly when the free end of the bridging structure reaches the next support. Bracing cables for the bridging structure are therefore generally regulated to tensions such that excessive forces are not created in one direction while equalizing the opposed forces created during the unsupported movement of the bridging structure.

Improved techniques provide bridge constructions which are much lighter and thus can span greater distances but such bridge constructions have less re-' sistance to the forces created by the lack of support and these forces are increased by increase of the distances which can be spanned. As a result, difficulties arise in determining the correct bracing and these difficulties can be solved only by modifying, during movement of the bridging structure, the characteristics of the bracing to adapt it to the conditions met and measured during movement of the bridging structure. These modifications usually can be carried out only by acting on the anchor points of the cables which slows the movement of the bridging structure as it is necessary after each movement to proceed with a complex control of the forces actually measured.

SUMMARY OF THE INVENTION The present invention corrects these difficulties and provides for constant continuous variation of the forces provided by the bracing made up of a series of cables anchored at the outer extremity of the bridging structure and anchored at a second point inshore thereof, these cables resting on the upper part of a mast located substantially equidistant between the anchor points of the cables. The invention also provides for automatic variation of these forces.

In accordance with the invention, the base of the mast rests on an intermediate support including a continuously controlled lifting device, a dynamometer being disposed between the lifting device and the intermediate support which is mounted on the bridging structure.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail referring to a preferred embodiment .thereof by way of example as shown in the accompanying drawings.

In the accompanying drawings, in which like reference characters indicate like parts,

FIG. 1 is a schematic representation of the forward part of the base of a bridge during movement toward a bridging position provided with reinforcing bracing for this part;

FIG. 2 is a transverse view in larger scale on the line II--II of FIG. 1 showing in detail the mast for the bracing;

FIG. 3 is a detail of the foot of the mast; and

FIG. 4 is a diagram of the forces created at the foot of the mast for the bracing during movement of the bridging structure from one support to another.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a prefabricated bridging structure 1 is pushed by means not shown in the drawings and rests on the piles or supports 2 and 3 during movement toward the following pile or support 4. The extremityof bridging structure 1 is reinforced by bracing including a vertical mast 5 on the upper extremity of which a series of cables 6 are supported and extend between two anchoring points 7 and 8 on structure 1. At its outer extremity, structure 1' is provided with an advance shoe 9.

As better seen in FIG. 2,-cables 6 are divided into two groups, one on each side of bridging structure 1 and mast 5 has two vertical components spaced and supported by bracing 10. Each group of cables 6 is supported by the mast at the tops of the vertical components. The foot of each vertical component of the mast rests on a hydraulic cylinder device 12 and thus on bridging structure 1 as more clearly seen in FIG. 3.

The foot of each vertical component of mast 5 is formed as a cap 13. The branches 13' of the cap can be interconnected by means of axes 14 to supports 15 which rest intermediate concrete footings l6 and thus on bridging structure 1.

The body of the hydraulic device 12 is fixed at 17 within the cap and a dynamometer 18 is interposed between the head of the piston of device 12 and bridging structure 1.

It can thus be seen that by controlling hydraulic device 12 the forces exerted at 7 and 8 by cables 6 on the bridging structure 1 can be varied which also varies the forces exerted at the same time at the foot of mast 5. The forces at the foot of mast 5 are measured by dynamometer 18 and the known arrangement of cables 6 gives the value and direction of the forces exerted at 7 and 8.

Study of the variation of the forces created in the dangerous portions of the bridging structure during unsupported movement and study of the variation of the forces created in the same section by the simultaneous action of the bracing forces allows preparation, for each position of the bridging element during movement, of a graph of the bracing forces and particularly of the forces at the foot of the mast thus providing for adjustment of the forces within acceptable limits of tolerance. Beginning with the lower limit of the range of forces, the bracing forces would be insufficient to compensate for the stressesdue to unsupport of the bridging structure. At the upper limit, the bracing forces would create excessive counter forces. For a maximum given value of admissible counter forces in the bridging element, two curves can be prepared asa function of the displacement of the bridging element between which curves the forces at the foot of the mast should be maintained for each position of the bridging structure. Determination of these curves is obviously very complex but can be obtained by known computer procedures.

FIG. 4 generally shows such curves and 21 during displacement of bridging structure 1 from pile 3 toward pile 4. If the admissible counter forces are sufficiently high, the area defined by the two curves 20 and 21 is relatively large and the force P can be varied at the foot of the mast by successive increments by varying the pressure in the hydraulic devices 12 only after an elementary movement p, or, when the area is large, after several successive movements. Curve 23 gives the actual variation of the forces P thus obtained taking into consideration the controlled variations and the variations resulting from displacement of the bridging structure.

If on the other hand, only small counter forces can be utilized, the area defined by curves 20 and 21 then becomes very small and it then becomes necessary to continuously vary the force P on the foot of the mast by continuous control of the pressure in the hydraulic devices 12. These pressures can be varied automatically by a controlled program providing, for each position of the bridging structure, a comparison of the value P of the force measured by dynamometer 18 to the theoretical value given by a curve traced within the area between the curves 20 and 21. Such a control would not raise any technical difficulty to one skilled in the art.

It is to be understood that the present invention is not limited to the preferred embodiment above-described. Other constructions may be used for the bracing mast and the hydraulic devices may be replaced by screw jacks actuated by electrically controlled motors.

What I claim is:

l. Bracing apparatus for a bridging structure moved progressively from a bank toward a support comprising a plurality of cables anchored adjacent the outer end of the bridging structure and anchored at a second point inboard of the first anchorage, a substantially vertical mast equidistant between the two anchoring points of said cables supporting said cables, means for raising said mast disposed between the foot of said mast and the bridging structure, means for continuously controlling said raising device and a dynamometer disposed betwgen said control meaps and said bridging structure, sal continuous contro means being programmed according to the variation of the forces measured by said dynamometer. I

2. Bracing apparatus as described in claim 1, said raising means including at least one hydraulic jack supplied with fluid under pressure and controlled by said continuous control means.

3. Bracing apparatus for a bridging structure moved progressively from a bank toward a support comprising a plurality of cables anchored adjacent the outer end of the bridging structure and anchored at a second point inboard of the first anchorage, a substantially vertical mast equidistant between the two anchoring points of said cables supporting said cables, means for raising said mast disposed between the foot of said mast and the bridging structure, means for continuously controlling said raising device and a dynamometer disposed between said control means and said bridging structure, said continuous control means being programmed according to the variation of the forces measured by said dynamometer, said raising means including at least one hydraulic jack supplied with fluid under pressure and controlled by said continuous control means, said continuous control means for the pressure supplied to said hydraulic jacks being programmed according to the variation of the forces measured by said dynamometer as a function of the movement of said bridging structure.

i 4 1' III

Claims (3)

1. Bracing apparatus for a bridging structure moved progressively from a bank toward a support comprising a plurality of cables anchored adjacent the outer end of the bridging structure and anchored at a second point inboard of the first anchorage, a substantially vertical mast equidistant between the two anchoring points of said cables supporting said cables, means for raising said mast disposed between the foot of said mast and the bridging structure, means for continuously controlling said raising device and a dynamometer disposed between said control means and said bridging structure, said continuous control means being programmed according to the variation of the forces measured by said dynamometer.

2. Bracing apparatus as described in claim 1, said raising means including at least one hydraulic jack supplied with fluid under pressure and controlled by said continuous control means.

3. Bracing apparatus for a bridging structure moved progressively from a bank toward a support comprising a plurality of cables anchored adjacent the outer end of the bridging structure and anchored at a second point inboard of the first anchorage, a substantially vertical mast equidistant between the two anchoring points of said cables supporting said cables, means for raising said mast disposed between the foot of said mast and the bridging structure, means for continuously controlling said raising device and a dynamometer disposed between said control means and said bridging structure, said continuous control means being programmed according to the variation of the forces measured by said dynamometer, said raising means including at least one hydraulic jack supplied with fluid under pressure and controlled by said continuous control means, said continuous control means for the pressure supplied to said hydraulic jacks being programmed according to the variation of the forces measured by said dynamometer as a function of the movement of said bridging structure.

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