GB2578686A

GB2578686A - Emergency bridge and method of deployment

Info

Publication number: GB2578686A
Application number: GB1913626.6A
Authority: GB
Inventors: Zhekova Siana; Haydu-Jones Trevor; Bull Paula
Original assignee: Individual
Current assignee: Individual
Priority date: 2018-09-21
Filing date: 2019-09-20
Publication date: 2020-05-20
Anticipated expiration: 2039-09-20
Also published as: GB201913626D0; GB2578686B; GB201815413D0; WO2020058515A1

Abstract

A temporary bridge comprises a deck 102, a first anchor 116 on one side of a space 120 and a second anchor 122 on the other and a pair of flexible supports 110, such as cables or wires, extending between the anchors and having first and second end portions 112, 114. A first abutment surface 106 is fixedly mounted to the first end portion, allowing the flexible supports to move relative to the first abutment surface. A second abutment surface 108 is fixed to the second end portion of the supports. A plurality of bridge elements 104 are mounted on the flexible supports between the abutment surfaces. In use, the tension (arrows 132) in the flexible supports is greater between the abutment surfaces than the tension (arrow 134) between the second abutment surface and the second anchor, imparting a compressive force between adjacent bridge elements and the abutment surfaces. A method of deploying a bridge may include the step of tensioning flexible supports using a winch, jack or turnbuckle. A kit of parts for a temporary bridge comprises flexible supports, bridge elements and first and second abutment surfaces.

Description

EMERGENCY BRIDGE AND METHOD OF DEPLOYMENT

FIELD OF THE INVENTION

The present invention relates to a temporary bridge. In particular, the present invention relates to a temporary bridge for rapid deployment across a space in an emergency, and a method of deploying said bridge.

BACKGROUND

Extreme weather events are becoming more and more evident in locations where previously such events were very rare, leading to floods and mud slides washing away bridges. Earthquakes and war have hitherto been the main causes that led to similar damage. Both impose consequences that small, often remote, communities in jeopardy particularly where the very young, those needing frequent medical intervention, the wholly or partly disabled, and the very old, are placed under stress and face the risk of medical deterioration if not quickly rescued.

In circumstances less dramatic, defence forces may find a light-weight simple bridge useful in their complement of equipment that enables a force to move forward in difficult terrain where only light armoured vehicles can be driven, such as across a wadi in desert deployments.

It is already known in that art that precast concrete sections can be used to form permanent bridges, the so-called ribbon bridge concept. These form a quasi-rigid deck-work by incorporating many units side-by-side laid permanently across vertical bridge pillars to form a river bridge with internal wires incorporated in enclosed septum chambers so that additional rigidity can be achieved for the deck. In such bridges, the intermediate bridge vertical pillars are an essential part, with the concrete sections laid onto them, the consequent rigidity avoiding the need for expensive and complex suspension cables and towers.

A stressed ribbon bridge is a tension structure in which suspension cables are embedded in the deck and which follows a catenary arc between vertical supports. The ribbon is stressed in traction, which adds to the stiffness of the structure. The stressed ribbon bridge deck typically consists of precast concrete blocks which are pre-tensioned with high-strength (e.g. steel) tendons to confer extra rigidity, stability and durability to the structure. The concrete sections are supported by pre-stressed suspension/support cables which span between vertical supports. Typically, the suspension cables are permanently attached to the concrete sections through curing with the concrete matrix. Post-tensioning of the concrete blocks produces the final bridge structure.

However, such bridges are permanent structures, and due to the heavy nature of the concrete units and the complicated tensioning mechanism, they are not suitable for deployment during an emergency.

Accordingly, there is a need for a rapidly deployable, modular and low cost bridge that is simple for a small team to deploy in order to establish a temporary link across a space, such as a ravine, river or canal.

SUMMARY OF THE INVENTION

The invention described herein, relates to a modular bridge, conceived as a kit of individually light-weight parts, which can be rapidly deployed using minimal equipment and personnel, to traverse a small ravine, watercourse or canal across which a pre-existing bridge has perhaps been destroyed, for example by excessive flood water or canal embankment collapse. It is intended to form a temporary relief bridge to allow any isolated people at risk to be rescued, and which can be easily dismantled for later re-use.

The present inventors have found that a pair of flexible supports can be projected across a space to be bridged, and themselves act as guide rails for a plurality of light-weight rigid bridge elements, which are slid across the flexible supports or rope-hauled into place. A rigid bridge deck is formed by tensioning the flexible supports against a second abutment surface (e.g. a retention locking collar), thus compressing the bridge elements and thereby rendering the initially flexible structure rigid enough to support the passage of pedestrians (or vehicles) safely from one side of the space to the other with minimum catenary central depression.

According to a first aspect of the present invention, there is provided a temporary bridge for rapid deployment across a space in an emergency. The term "space" as used herein refers to the area to be bridged, and includes a gulf, a river, a stream, a canal, a ravine, a gorge, or a crevasse. It can also simply refer to dangerous or untraversable terrain such as bogland or marshland.

The bridge according to the present invention comprises: a deck; a first anchor located on one side of the space and a second anchor located on the opposite side of the space; a pair of flexible supports having first and second end portions, the pair of flexible supports extending in parallel between said first and second anchors; a first abutment surface provided on and fixedly mounted relative to the first end portion of the pair of flexible supports; a second abutment surface provided on and fixed to the second end portion of the pair of flexible supports; and a plurality of rigid bridge elements, each bridge element mounted on the pair of flexible supports and the plurality of bridge elements provided between the abutment surfaces to form the deck of the bridge; wherein the pair of flexible supports is under tension such that the tension (Ti) between the first and second abutment surfaces is greater than the tension (T2) between the second abutment surface and the second anchor, thereby imparting a compressive force (Ci) between adjacent bridge elements and the abutment surfaces.

The term "flexible supports" refers to any means capable of supporting the rigid bridge elements that are also capable of being tensioned. Preferably, the flexible supports are selected from wires, cords, cables, or ropes.

The first abutment surface is defined as being provided on and fixedly mounted relative to the first end portion of the pair of flexible supports. This means that the first abutment surface is mounted on the first end portion of the pair of flexible supports in such a way that allows the flexible supports to move relative to the first abutment surface. This is in contrast to the second abutment surface, which is fixed to the second end portion of the pair of flexible supports, i.e. the pair of flexible supports cannot move relative to the second abutment surface.

The bridge according to the present invention has the advantage that the section of the flexible supports between the second abutment surface and the second anchor (section (a)) merely takes the stress due to the weight of the bridge elements plus the weight of any personnel and/or vehicles traversing the bridge. The section of the flexible supports between the first and second abutment surfaces (section (b)) supports that stress plus the stress needed to impart compression to the bridge elements and thereby maintain adequate rigidity to prevent excessive depression or sag at the centre of the bridge.

The additional tension applied to the wires in section (b), and the resulting compression of the bridge elements converts a traditional catenary "rope" bridge into a rigid plank. It thus forms a beam of the class which is clamped at one end (Side A), freely supported at the other (Side B), has a static uniformly distributed load (the weight of the bridge elements), and a live moving load (i.e. a person or vehicle traversing the bridge).

The bridge may further comprise at least one anti-buckling clip or latch located between a pair of adjacent rigid bridge elements. Preferably the anti-buckling clip is self-locking and is mounted on the underside of one rigid bridge element and catches on the underside of a neighbouring bridge element. The anti-buckling clips prevent the bridge elements from detaching from the flexible supports ("break away") and reduce the risk of the bridge buckling or bending under a vertical load, for example a person or vehicle traversing the bridge. Preferably, the anti-buckling clips comprise stainless steel rod sections which are embedded into the tubular elements and sealed with epoxy resin. Alternatively, the anti-buckling clips are mounted the underside of the tubular elements. The anti-buckling clips may be made of any suitable material, including plastic, stainless steel, or an aluminium alloy. Preferably, the anti-buckling clips are fabricated by 3D printing in plastic or by sand-casting with an aluminum alloy.

The bridge may further comprise a handrail adapted to provide further tension (Ts) to the bridge. Preferably, the handrail comprises a pair of vertical stanchions mounted on each bridge element, wherein each vertical stanchion of each pair of vertical stanchions is mounted on opposite sides of each rigid bridge element. The handrail further comprises a pair of tensioned cords extending between the first and second abutment surfaces and mounted on and extending in parallel between the vertical stanchions of adjacent bridge elements.

The bridge may further comprise at least one spacer mounted on the pair of flexible supports. The spacer may be a single spacer spanning across the pair of flexible supports, but preferably, each spacer is mounted on a single flexible support. The role of the spacers is to take up any space between the first and second abutment surfaces once all bridge elements have been mounted on the supports. In a preferred embodiment, the at least one spacer is mounted between a final rigid bridge element and the first abutment surface.

The bridge may further comprise at least one damper mounted on the pair of flexible supports. The role of the damper(s) is to reduce vibration or oscillation triggered by pedestrians or vehicles traversing the bridge, or environmental factors such as wind. If the frequency of these oscillations matches the system's natural frequency of vibration (La its resonance frequency), the system will have a tendency to respond at an increased amplitude, which can ultimately lead to destruction of the bridge in a so-called "resonance collapse". The natural resonance frequency of the system depends on the level of compression as well as the bulk material properties of the bridge elements and the flexible supports. In order to counteract the tendency for oscillation, it is necessary to dampen the so-called quality factor or Q factor of the system. The quality factor is a parameter that describes the resonance behaviour of an underdamped harmonic oscillator. The dampers are preferably located between adjacent bridge elements. The thickness and resilience of the material of the dampers can be selected to avoid a set of resonance frequencies close to the resonance frequency of the system. Preferably, the at least one damper is a rubber damper. Alternatively, the at least one damper is a synthetic polymer sheet which can be attached to the bridge elements using glue or screws.

The first anchor and/or second anchor may comprise a single anchor, but, preferably, the first anchor and/or second anchor comprise a pair of anchors.

The first anchor may comprise any means suitable for anchoring the pair of flexible supports to one side of the space and the second anchor located may comprise any means suitable for anchoring the pair flexible supports to the opposite side of the space. For example, the flexible supports can be terminated in ground anchors known in the art, or have devices attached to them that can be secured to posts or stakes in the ground. Preferably, the first anchor comprises a winch. The winch frame may be fabricated from steel angle, hot dip galvanised after welding. Preferably, the second anchor comprises a retaining stake or a grappling hook.

The first abutment surface may be separate from the first anchor, but, preferably, the first abutment surface forms part of the first anchor.

Preferably the second abutment surface comprises a pair of retention locking collars, one located on each of the pair of flexible supports. The retention locking collars can be secured to the flexible supports by a clamping means. Alternatively, the retention locking collars can be secured to the flexible supports by a resin-bonded filling which entraps a loop or a knot, enclosed within a conical shell.

The rigid bridge elements may be any shape suitable for mounting on the pair of flexible supports. Preferably, each rigid bridge element comprises a pair of substantially parallel tubular elements connected by a deck panel or foot board. Each tubular element comprises a substantially downward facing and open ended radial slot extending longitudinally through said tubular element and adapted to receive one of the pair of flexible supports. Preferably the abutting surfaces of the rigid bridge elements are flat or are interlocking.

Preferably, the deck panel is fixedly connected to the pair of tubular elements. Alternatively, each tubular element may comprise a flange portion extending substantially perpendicular to the radial slot and configured to be moveably connected (e.g. by one or more pins) to the deck panel so as to enable rotational movement of the deck panel in the horizontal plane. This means that the deck panel can move relative to the pair of tubular elements.

The rigid bridge elements may comprise any material that has a low density and high compressive strength, for example, the rigid bridge elements may comprise a high compressive strength polymer. Preferably, the rigid bridge elements comprise at least one material selected from a low density syntactic foam, a polymethacrylimide (PMI) foam, balsa wood, Obeche, or a mixture of glass spheres and a thermosettable resin.

According to a second aspect of the present invention, there is provided method of deploying a temporary bridge having a deck across a space from a deployment side of the space to the opposite side in an emergency, said method comprising: providing a pair of flexible supports on the deployment side, the pair of flexible supports having first and second end portions, the first end portion being attached to a first anchor on the deployment side and having a first abutment surface provided thereon and fixedly mounted relative thereto, and the second end portion having a second abutment surface provided thereon and fixed thereto; transferring the second end portion of the pair of flexible supports from the deployment side of the space to the opposite side; anchoring the second end portion of the pair of flexible supports to the opposite side to form a second anchor such that the pair of flexible supports extend in parallel between the first and second anchors; and mounting in sequence a plurality of rigid bridge elements on the pair of flexible supports, each bridge element being moved towards the second end portion before a subsequent bridge element is mounted on the pair of flexible supports, until the space between the first and second abutment surfaces is at least substantially filled; wherein the pair of flexible supports are tensioned to form the deck until the tension (Ti) in the flexible supports between the first and second abutment surfaces is greater than the tension (T2) in the flexible supports between the second abutment surface and the second anchor, thereby imparting a compressive force (Ci) between adjacent bridge elements and the abutment surface and forming the deck.

According to the method of the present invention, rigidity in the bridge deck is achieved by using an additional applied tension in the flexible supports, and transferring that tension by means of the second abutment surface so as to compress the rigid bridge elements against the first abutment surface, thereby isolating that total tension in the flexible supports from the second anchor. The applied high tension in the flexible supports results in compression of the bridge elements, one against another, so as to render the structure rigid enough to support the passage of pedestrians and/or vehicles, safely from one side of the space to the other. The bridge deck may be fully suspended between the first and second anchors such that the bridge deck is not in contact with the bank on either side of the space. Alternatively, one or both end portions of the bridge deck may rest on the bank.

The method may further comprise mounting at least one spacer on the pair of flexible supports. Preferably, the at least one spacer is mounted between a final rigid bridge element and the first abutment surface.

Preferably, after a first bridge element is mounted on the pair of flexible supports, the pair of flexible supports is tensioned to a preliminary tension (To). This tension is sufficient to support the weight of the first bridge element.

In one embodiment, the pair of flexible supports are tensioned incrementally. For example, a small amount of tension can be applied to the pair of flexible supports after each bridge element is mounted in order to support the weight of the bridge element(s). Preferably, the tension in the pair of flexible supports is increased to achieve tension (T2) after a final rigid bridge element has been mounted on the pair of flexible supports.

Preferably, tension (Ti) is applied to the pair of flexible supports once the space between the first and second abutment surfaces is at least substantially filled, or once the at least one spacer has been mounted on the pair of flexible supports to fill any space between a final rigid bridge element and the first abutment surface.

The pair of flexible supports may be tensioned by any means capable of applying tension. Preferably, the pair of flexible supports are tensioned using at least one tensioning device selected from a winch, a hydraulic jack, or a turnbuckle.

Preferably, the second end portion of the pair of flexible supports is transferred ballistically from the deployment side of the space to the opposite side. Acceptable ballistic methods include the use of an air gun, catapult, cross-bow, mortar or line-throwing gun.

In one embodiment, the second end portion of the pair of flexible supports is anchored by attaching it to a fixed object, such as a tree or a post. In an alternative embodiment, the second end portion of the pair of flexible supports is anchored by a grappling hook. In a further alternative embodiment, the second end portion of the pair of flexible supports is anchored by a retaining stake.

Preferably, the plurality of rigid bridge elements is pulled towards the second end portion using a rope or a pulley.

The method may further comprise installing at least one anti-buckling clip between a pair of adjacent rigid bridge elements.

The method may further comprise installing a handrail to provide additional tension (T3) to the bridge.

According to a third aspect of the present invention, there is provided a kit of parts for a temporary bridge for rapid deployment across a space, the kit comprising: a pair of flexible supports; a plurality of rigid bridge elements adapted for mounting on the pair of flexible supports; a first abutment surface provided on and adapted to be fixedly mounted relative to a first end portion of the pair of flexible supports; and a second abutment surface provided on and adapted to be fixed to a second end portion of the pair of flexible supports.

The kit may further comprise one or more of the following features: a first and/or a second anchor; said second abutment surface comprises at least one retention locking collar; at least one tensioning device selected from a winch, a hydraulic jack, or a turnbuckle; a handrail; at least one spacer adapted for mounting on the pair of flexible supports; and/or at least one anti-buckling clip.

GENERAL DEFINTIONS

Throughout this application terms should be interpreted according to their standard meaning in the art unless specified otherwise. The following terms should be construed according to their standard meanings, as set out below.

As used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise. Thus for example, a reference to "a method" includes one or more methods, and/or steps of the type described herein and/or which will become apparent to those persons skilled in the art upon reading this disclosure and so forth.

The term "at least" when used in connection with a number has its standard meaning, i.e. means that number is the minimum value for the specified parameter/component. For example "at least one spacer" means there is one or more spacer and discloses the options of one spacer or more than one spacer being present.

The term "comprising" should be construed as meaning "including but not limited to".

Features which are described herein with reference only to a single aspect or embodiment of the invention apply equally to all other aspects and embodiments of the invention. Hence features from one aspect or embodiment may be combined with features from another aspect or embodiment.

In this specification, unless expressly otherwise indicated, the word 'or' is used in the sense of an operator that returns a true value when either or both of the stated conditions is met, as opposed to the operator 'exclusive or' which requires that only one of the conditions is met.

Aspects of the present invention include: #1. A temporary bridge for rapid deployment across a space in an emergency, said bridge comprising: a deck; a first anchor located on one side of the space and a second anchor located on the opposite side of the space; a pair of flexible supports having first and second end portions, the pair of flexible supports extending in parallel between said first and second anchors; a first abutment surface provided on and fixedly mounted relative to the first end portion of the pair of flexible supports; a second abutment surface provided on and fixed to the second end portion of the pair of flexible supports; and a plurality of rigid bridge elements, each bridge element mounted on the pair of flexible supports and the plurality of bridge elements provided between the abutment surfaces to form the deck of the bridge; wherein the pair of flexible supports is under tension such that the tension (T1) between the first and second abutment surfaces is greater than the tension (T2) between the second abutment surface and the second anchor, thereby imparting a compressive force (C1) between adjacent bridge elements and the abutment surfaces.

#2. A temporary bridge according to #1, said bridge further comprising at least one anti-buckling clip located between a pair of adjacent rigid bridge elements.

#3. A temporary bridge according to #2, wherein the at least one anti-buckling clip is self-locking.

#4. A temporary bridge according to any of the preceding aspects, said bridge further comprising a handrail adapted to provide further tension (T3) to the bridge.

#5. A temporary bridge according to #4, wherein the handrail comprises: a pair of vertical stanchions mounted on each bridge element, wherein each vertical stanchion of each pair of vertical stanchions is mounted on opposite sides of each rigid bridge element; and a pair of tensioned cords extending between the first and second abutment surface and mounted on and extending in parallel between the vertical stanchions of adjacent bridge elements.

#6. A temporary bridge according to any of the preceding aspects, said bridge further comprising at least one spacer mounted on the pair of flexible supports.

#7. A temporary bridge according to #6, wherein the at least one spacer comprises a pair of spacers.

#8 A temporary bridge according to #6 or #7, wherein the at least one spacer is mounted between a final rigid bridge element and the first abutment surface.

#9. A temporary bridge according to any of the preceding aspects, wherein the first anchor and/or the second anchor comprise a pair of anchors.

#10. A temporary bridge according to any of the preceding aspects, wherein the first anchor comprises a winch.

#11. A temporary bridge according to any of the preceding aspects, wherein the second anchor comprises a retaining stake or a grappling hook.

#12. A temporary bridge according to any of the preceding aspects, wherein the flexible supports are selected from wires, cords, cables, or ropes.

#13. A temporary bridge according to any of the preceding aspects, wherein the first abutment surface forms part of the first anchor.

#14. A temporary bridge according to any of the preceding aspects, wherein the second abutment surface comprises a pair of retention locking collars.

#15. A temporary bridge according to any of the preceding aspects, wherein each rigid bridge element comprises a pair of substantially parallel tubular elements connected by a deck panel, each tubular element comprising a substantially downward facing and open ended radial slot extending longitudinally through said tubular element and adapted to receive one of the pair of flexible supports.

#16. A temporary bridge according to any of the preceding aspects, wherein the abutting surfaces of the rigid bridge elements are flat or are interlocking.

#17. A temporary bridge according to any of the preceding aspects, wherein the rigid bridge elements comprise a high compressive strength polymer.

#18. A temporary bridge according to any one of #1 to #16, wherein the rigid bridge elements comprise at least one material selected from a low density syntactic foam, polymethacrylimide foam, balsa wood or Obeche.

#19. A temporary bridge according to any one of #1 to #16, wherein the rigid bridge elements comprise a mixture of glass spheres and a thermosetting resin.

#20. A method of deploying a temporary bridge having a deck across a space from a deployment side of the space to the opposite side in an emergency, said method comprising: providing a pair of flexible supports on the deployment side, the pair of flexible supports having first and second end portions, the first end portion being attached to a first anchor on the deployment side and having a first abutment surface provided thereon and fixedly mounted relative thereto, and the second end portion having a second abutment surface provided thereon and fixed thereto; transferring the second end portion of the pair of flexible supports from the deployment side of the space to the opposite side; anchoring the second end portion of the pair of flexible supports to the opposite side to form a second anchor such that the pair of flexible supports extend in parallel between the first and second anchors; and mounting in sequence a plurality of rigid bridge elements on the pair of flexible supports, each bridge element being moved towards the second end portion before a subsequent bridge element is mounted on the pair of flexible supports, until the space between the first and second abutment surfaces is at least substantially filled; wherein the pair of flexible supports are tensioned to form the deck until the tension (Ti) in the flexible supports between the first and second abutment surfaces is greater than the tension (T2) in the flexible supports between the second abutment surface and the second anchor, thereby imparting a compressive force (Ci) between adjacent bridge elements and the abutment surface and forming the deck.

#21. A method according to #20, the method further comprising mounting at least one spacer on the pair of flexible supports #22. A method according to #21, wherein the at least one spacer is mounted between a final rigid bridge element and the first abutment surface.

#23. A method according to any one of #20 to #22, wherein after a first bridge element is mounted on the pair of flexible supports, the pair of flexible supports are tensioned to a preliminary tension (To) sufficient to support the weight of the first bridge element.

#24. A method according to any one of #20 to #23, wherein the pair of flexible supports are tensioned incrementally.

#25. A method according to any one of #20 to #24, wherein the tension in the pair of flexible supports is increased to achieve tension (T2) after a final rigid bridge element has been mounted on the pair of flexible supports.

#26. A method according to any one of #20 to #25, wherein tension (Ti) is applied to the pair of flexible supports once the space between the first and second abutment surfaces is at least substantially filled or once the at least one spacer has been mounted on the pair of flexible supports to fill any space between the final rigid bridge element and the first abutment surface.

#27. A method according to any one of #20 to #26, wherein the pair of flexible supports are tensioned using at least one tensioning device selected from a winch, a hydraulic jack, and a turnbuckle.

#28. A method according to any one of #20 to #27, wherein the second end portion of the pair of flexible supports is transferred ballistically from the deployment side of the space to the opposite side.

#29. A method according to #20 to #28, wherein the second end portion of the pair of flexible supports is anchored by attaching to a fixed object.

#30. A method according to any one of #20 to #28, wherein the second end portion of the pair of flexible supports is anchored by a grappling hook.

#31. A method according to any one of #20 to #28, wherein the second end portion of the pair of flexible supports is anchored by a retaining stake.

#32. A method according to any one of #20 to #31, wherein the plurality of rigid bridge elements is pulled towards the second end portion using a rope or a pulley.

#33. A method according to any one of #20 to #32, the method further comprising installing at least one anti-buckling clip between a pair of adjacent rigid bridge elements.

#34. A method according to any one of #20 to #33, the method further comprising installing a handrail to provide additional tension (T3) to the bridge.

#35. A kit of parts for a temporary bridge for rapid deployment across a space, the kit comprising: a pair of flexible supports; a plurality of rigid bridge elements adapted for mounting on the pair of flexible supports; a first abutment surface provided on and adapted to be fixedly mounted relative to a first end portion of the pair of flexible supports; and a second abutment surface provided on and adapted to be fixed to a second end portion of the pair of flexible supports.

#36. A kit according to #35, said kit further comprising a first anchor.

#37. A kit according to #35 or #36, said kit further comprising a second anchor.

#38. A kit according to any one of #35 to #37, wherein the second abutment surface comprises a retention locking collar.

#39. A kit according to any one of #35 to #38, said kit further comprising at least one tensioning device selected from a winch, a hydraulic jack, or a turnbuckle.

#40. A kit according to any one of #35 to #39, said kit further comprising a handrail.

#41. A kit according to any one of #35 to #40, said kit further comprising at least one spacer adapted for mounting on the pair of flexible supports.

#42. A kit according to any one of #35 to #41, said kit further comprising at least one anti-buckling clip.

DETAILED DESCRIPTION

The following is a description by way of example only and with reference to the accompanying drawings of presently preferred embodiments of the invention. In the drawings:-Figure 1 is a cross-sectional representation of a temporary bridge according to an embodiment of the present invention.

Figure 2 is a cross-sectional representation of a bridge element according to an embodiment of the present invention.

Figure 3 is cross-sectional view of a retention locking collar and adjacent bridge element according to an embodiment of the present invention.

Figure 4 is a cross-sectional view of a retention locking collar according to an embodiment of the present invention.

Figure 5 is an underside view of the tubular elements of two adjacent bridge elements and an anti-buckling clip according to an embodiment of the present invention.

Figure 6 is a side view of a first anchor according to an embodiment of the present invention.

Figure 7 is a graph illustrating the results of a stress simulation test for a bridge spanning 50 m.

Figure 8 is an underside view of the tubular elements of two adjacent bridge elements and an anti-buckling clip according to an embodiment of the present invention.

The Bridge Referring first to Figure 1, a bridge 100 comprises a deck 102 comprising a plurality of rigid bridge elements 104 provided between a first abutment surface 106 and a second abutment surface 108. Each rigid bridge element 104 is mounted on a pair of flexible supports 110, such as wires, cables or cords. The pair of flexible supports have a first end portion 112 and a second end portion 114 and extend in parallel between a first anchor 116 located on a first side 118 (Side A) of a space 120 and second anchor, retaining stake 122, located on the opposite side 124 (Side B) of the space 120. The first abutment surface 106 is provided on and fixedly mounted relative to the first end portion 112 of the pair of flexible supports 110. This means the pair of flexible supports 110 are able to move relative to the first abutment surface 106. The second abutment surface 108 is provided on and fixed to the second end portion 114 of the pair of flexible supports 110. Therefore, the flexible supports 110 are not moveable relative to the second abutment surface 108. The second abutment surface 108 forms part of pair of retention locking collars 126, secured to the pair of flexible supports 110 by clamps 128 (see also Figure 3). Alternatively, the retention locking collars 126 can be secured to the flexible supports 110 by a resin-bonded filling 125 which entraps a loop or a knot 127, enclosed within a conical shell (see Figure 4).

The pair of flexible supports 110 are under tension such that the tension (Ti) represented by arrows 132 between the first abutment surface 106 and the second abutment surface 108 is greater than the tension (T2) represented by arrows 134 between the second abutment surface and the second anchor 122, thereby imparting a compressive force (C1) represented by arrows 136 between adjacent bridge elements and the abutment surfaces. This is because the section 138 of the flexible supports 110 between the second abutment surface 108 and the second anchor 122 (section (a)) merely takes the stress due to the weight of the bridge elements plus the weight of any personnel and/or vehicles traversing the bridge. The section 140 of the flexible supports 110 between the first abutment surface 106 and the second abutment surface 108 (section (b)) supports that stress plus the stress needed to impart compression to the bridge elements and thereby maintain the adequate rigidity to prevent excessive depression or sag at the centre of the bridge.

Spacers 142 are mounted on the pair of flexible supports 110 between the final bridge element 144 and the first abutment surface 106. Anti-buckling clips 146 are located on the underside of the bridge elements 104 between adjacent bridge elements. Each anti-buckling clip 146 is mounted on the underside of one bridge element, and is clamped onto the underside of a neighbouring bridge element (see also Figures 4 and 8).

A handrail 148 provides further tension (T3) represented by arrows 150. The handrail comprises a plurality of pairs of vertical stanchions 152 and a pair of tensioned cords 154. Each rigid bridge element 104 has a pair of vertical stanchions 152 mounted on opposite sides of the rigid bridge element. The pair of tensioned cords 154 extends between the first abutment surface 106 and the second abutment surface 108 and is mounted on and extends in parallel between the vertical stanchions of adjacent bridge elements.

Referring to Figure 2, the bridge element (sponson) 104 comprises a pair of tubular elements 202 connected by a deck panel 204. Each tubular element 202 comprises a substantially downward facing and open ended radial slot 206, which extends longitudinally through the tubular element 202 and runs axially along the tubular element for its entire length. The radial slot 206 is adapted to receive one of the pair of flexible supports 110.

Vertical stanchions 152 are mounted on the upper side of each tubular element 202 and a pair of tensioned cords 154 extend in parallel between the vertical stanchions of adjacent bridge elements. Anti-buckling clips 146 are located on the underside of the bridge elements between adjacent bridge elements.

Figure 7 shows a preferred anti-buckling clip 300 according to the present invention. The anti-buckling clip 300 comprises a base-plate 302 attached to the underside of first end portion of a first bridge element and a pivot pin 304 by which a hook 306 is pivotally mounted on the base plate. The hook is spring biased by a spring 308 and engageable with a pillar 310 located on the underside of a first end portion of an adjacent bridge element. When the bridge elements are pushed or hauled together, the hook 306 impacts pillar 310 causing the hook 306 to deflect to one side as indicated by arrows 312. The return action of the spring 308 causes the hook to engage with the pillar thereby latching the two bridge elements together. The anti-buckling clip can be opened by releasing tension in the spring thereby causing the hook to disengage with the pillar. This can be done manually, or by using a suitable instrument such as pliers.

Referring to Figure 6, a first anchor 116 includes a first abutment surface 106 which forms part of winch frame 302. The winch frame 302 is secured to the ground by four anchors 304 (only two shown). The first abutment surface 106 is provided on and fixedly mounted relative to the first end portion 112 of the pair of flexible supports 110, and the pair of flexible supports 110 is secured to a pair of winches 306 (only one shown).

Method of Deployment In a preferred embodiment, a pair of flexible supports 110, for example wires, cables or cords, having a small weight at one end, are projected by a known means (such as a compressed air gun, Lyle Gun, catapult or cross-bow) from a first side 118 (Side A) of a space 120 to be bridged, by a small team of rescuers to the opposite side 124 (Side B). The choice of projectile means will depend on size of the space to be bridged. A Lyle Gun can fire a light weight at least 500 metres whereas a simple hand operated catapult can fire a hauling line approximately 100 metres.

Also projected across is a pair of devices for clamping a locking plate to each flexible support, referred to herein as retention locking collars 126. These retention locking collars can be firmly secured to the flexible supports by a variety of methods, for example by a clamping means 128. Alternatively, the retention locking collars 126 can be secured to the flexible supports 110 by a resin-bonded filling 125 which entraps a loop or a knot 127, enclosed within a conical shell (see Figure 4).

A person on Side B drives a pair of retaining stakes 122 into the ground spaced apart by the width of the bridge. The flexible supports 110 are secured to the retaining stakes 122, for example, by passing loops in the flexible supports over the retaining stakes. Alternatively the flexible supports 110 can be secured to an existing object such as a tree or post. In an alternative embodiment, a ground anchor such as a grappling hook of known art can be attached to the pair of flexible supports 110 and can be fired across the gulf and embedded in the bank at Side B by anyone able to do this.

Members of the rescue team on Side A pass each flexible support 110 through the radial slots 206 extending longitudinally through the tubular elements 202 of a first bridge element so that the bridge element straddles the pair of flexible supports 110. A first end portion 112 of the pair of flexible supports 110 is attached to a first anchor 116. In a preferred embodiment, the first anchor comprises a winch drum, or other means for tensioning the flexible supports. A hauling rope is similarly catapulted across from Side A to Side B to act as a means of hauling the first bridge element across from Side A to Side B. A limited amount of tension is applied to the flexible supports, adequate to support the weight of the bridge element(s).

As a person on Side B hauls the first bridge element across and, if present, anti-buckling or snap-clips 146 are clipped by someone on Side A to a succeeding bridge element, and a train of coupled bridge elements is formed. Each succeeding bridge element is set onto the pair of flexible supports 110 using radial slots 206 until the space between the first and the second abutments surfaces has been substantially filled, i.e. until there is not enough space for a further bridge element to be installed. Any space between the final bridge element 144 and the first abutment surface 106 can be filled by installing one or more spacers 142 on the pair of flexible supports.

Once all of the bridge elements (and spacers if present) have been hauled across from Side A to Side B, the leading bridge element will butt against the second abutment surface 108 in the form of a retention locking collar 126. The final bridge element 144 (or spacer if present) will butt against the first abutment surface 106.

By applying further (secondary) tension to the flexible supports 110 using the winch and optionally accessory devices such as turn-buckles, sufficient tension in section (b) of the flexible supports results, and by compression of the bridge elements, this gives rigidity in the assembly so that central sag is minimized.

Referring to Figure 7, there is a graph illustrating the results of a stress simulation test for a bridge spanning 50 cm in which measurements of central depression (sag) were made for different compressive forces (compression loads), with a central load of 0.25 kg. The bridge used in this simulation included 8 bridge elements of 7 cm length with wooden tubular elements having a diameter of 3.75 cm. The bridge was clamped at one side and supported by a steel pin at the other side. The graph shows the decreasing centre depression (sag), and hence increasing rigidity as the compression load is increased. The curve to the left shows the results with no point load.

Theoretical Classical Structural Analysis For a structure bridging a span of length L, with a uniformly distributed structure weight Wi, and carrying a central point load (a person at the mid-point) of weight W2, the members having an identical vertical plane depth of D, the maximum bending moment M is found at the centre of the structure, that is, 0.5*L from either side.

The standard formula for this moment M at any point along the beam is given by the formula N -g kk a a^2 041 W2 a = 2 Here using MKS units, g = acceleration due to gravity (9.81 m/s), a is the distance from one end, b the distance from the other (so / = a +b), W1 is the bridge weight in kg, and W2 is the weight of a point load at a.

The maximum bending moment occurs at the centre where a = b = I /2 Mmax is given therefore by substituting these values, and gives = * 5 ) The expression above applies strictly to a uniform consolidated material such as a cable or plank of wood. The bending moment is resisted by the strength of the material fibres from which the cable or plank is made.

For a bridge comprising multiple identical bridge elements segments, this moment will, in the absence of a compressive force, cause the segments to break away in the vertical plane by rotating about the upper edge so as to follow the catenary approximately as dictated by the central wire. If a string of spherical pearls is considered, strung along a wire, there is no turning point about which the bending structure will rotate, since each sphere has a single central point of contact with its neighbour. The wire "necklace" will follow the classical catenary curve, this curve becoming shallower as the tension in the wire increases. If that approach were to be used for a temporary rescue bridge, where minimum depression is desirable, that approach would impose an excessive strain on the anchors, which would then break out of the ground.

Applying a secondary tension in the flexible supports against a second abutment surface in the form of a retention locking collar at one end and a rigid buffer abutment (first abutment surface) at the other end, will confer axial compression, C, on the assembly of segments having a vertical dimension D and adjoining with plane faces on to another. However, in this case there is no additional stress in the anchor cables. This extra tension results in a countering moment against the catenary bending moment that otherwise tends to buckle the structure, the countering moment being: Mc = 0.5 C D Here Mc is the restraining moment countering the bending moment on the structure, C is the tension in part (b) of the wire that causes compression, and D is the diameter of the bridge element under compression.

By this means, as compression is increased, the structure behaves more and more like a rigid plank bridging the gap.

Provided this compression moment exceeds M by a safety factor SF, then buckling is prevented. The upper limit of C is determined by the breaking strength of the wire part (b) and the compressive strength of the bridge element segment material that is under compression.

Thus Mc = 0.5*C*D = SF*Mmax = SF * (5/16) * (Wi + W2) *9* (L/D) Here g = the acceleration due to gravitational spin, taking normally at the Earth's surface to be 9.81 m/s.

Where N bridge elements are employed to bridge a gap of length L, each having a length x, then the formula becomes C = 2 * SF * (5/16)* (V1/1+ W2)* 9.81* N * (x/D)* (1/D) To simplify the expression, SF might be taken as = 4, and it might be assumed (though it requires proof) that the optimum ratio (x/D) is the Golden Ratio 1.62.

Material Selection Bridge elements The criteria when choosing a material for the bridge elements should be to find a low density material but having high enough compressive strength. Suitable materials are Balsa wood, Obeche, polymethacrylimide (PMI) foam, low density syntactic foams comprising a mixture of glass spheres and thermosetting resin. The compressive strength and density of a number of suitable materials are listed below in Table 1.

Table 1

Material Compressive strength (MPa) Density (kg/m3) PMI Rigid Foam 0.883 52.1 Balsa Wood 7.0 130 Obeche Wood 29.3 380 Syntactic Foam A 2.1 150 Syntactic Foam B 3.4 250 Syntactic Foam C 4.14 460 The design of the bridge elements to span 30 m is shown in Table 2 below using Balsa wood blocks to form the tubular elements and pine-wood deck panels.

Table 2

Tubular elements Diameter (m) 0.4 Length (m) 0.7 Density (kg/m3) 130 Volume (m3) 0.088 Weight (kg) 11.44 Deck panel Width (m) 0.3 Section width (m) 0.15 Thickness (m) 0.05 Volume (m3) 0.00225 Weight (kg) 0.29 Assembly Total weight of bridge element (kg) 23.5 Span required (m) 30 Quantity of bridge elements required 44 Total weight (kg) 1034 Balsa wood is therefore particularly preferred as it gives a total weight of each bridge element of less than 25 kg. This means that the bridge elements could be easily lifted by two people and transferred onto the pair of flexible supports.

Balsa wood is available in moderate cross section dimensions, but can be exported from Central America in fabricated form. Preferably, a laminated construction is adopted, which also allows inserts to be included, such as the anti-buckling clips. Preferably the anti-buckling clips are manufactured from stainless steel bars.

The transverse deck panels are preferably made from a low density pine wood material according to the load to be carried. These should be secured to the tubular elements by means of a freely rotating pin to give lateral freedom of rotation and thus take up tolerances in the bridge element lengths and not impose any lateral distortion on the finished structure when fully stressed. Alternatively, the deck panels can be made from Balsa wood.

Flexible Supports The flexible supports can be considered in two sections. Section (a) is the portion of the flexible supports between the second anchor and the second abutment surface. Section (b) is the portion of the flexible supports between the first second abutment surface and the first anchor. Selection of the material for section (a) of the flexible supports is not critical, but section (b) of the flexible supports must be able to exert sufficient compressive force by virtue of the tension applied such that the sag at the centre under the applied load is for example less than 0.5% of the span length. Preferably, the flexible supports are made from stainless steel of the type used in ocean-going yachts. Optionally, the flexible supports comprise coupling eyes swaged to a high tensile quality.

Claims

CLAIMS1. A temporary bridge for rapid deployment across a space in an emergency, said bridge comprising: a deck; a first anchor located on one side of the space and a second anchor located on the opposite side of the space; a pair of flexible supports having first and second end portions, the pair of flexible supports extending in parallel between said first and second anchors; a first abutment surface provided on and fixedly mounted relative to the first end portion of the pair of flexible supports; a second abutment surface provided on and fixed to the second end portion of the pair of flexible supports; and a plurality of rigid bridge elements, each bridge element mounted on the pair of flexible supports and the plurality of bridge elements provided between the abutment surfaces to form the deck of the bridge; wherein the pair of flexible supports is under tension such that the tension (T1) between the first and second abutment surfaces is greater than the tension (T2) between the second abutment surface and the second anchor, thereby imparting a compressive force (C1) between adjacent bridge elements and the abutment surfaces.
2. A temporary bridge as claimed in claim 1, said bridge further comprising at least one anti-buckling clip located between a pair of adjacent rigid bridge elements; preferably wherein the at least one anti-buckling clip is self-locking.
3. A temporary bridge as claimed in any of the preceding claims, said bridge further comprising a handrail adapted to provide further tension (T3) to the bridge.
A temporary bridge as claimed in claim 3, wherein the handrail comprises: a pair of vertical stanchions mounted on each bridge element, wherein each vertical stanchion of each pair of vertical stanchions is mounted on opposite sides of each rigid bridge element; and a pair of tensioned cords extending between the first and second abutment surface and mounted on and extending in parallel between the vertical stanchions of adjacent bridge elements.
5. A temporary bridge as claimed in any of the preceding claims, said bridge further comprising at least one spacer mounted on the pair of flexible supports, wherein the at least one spacer preferably comprises a pair of spacers.
6. A temporary bridge as claimed in claim 5, wherein the at least one spacer is mounted between a final rigid bridge element and the first abutment surface.
7. A temporary bridge as claimed in any of the preceding claims, wherein the first anchor and/or the second anchor comprise a pair of anchors.
8. A temporary bridge as claimed in any of the preceding claims, wherein the first anchor comprises a winch; and/or wherein the second anchor comprises a retaining stake or a grappling hook.
9. A temporary bridge as claimed in any of the preceding claims, wherein the flexible supports are selected from wires, cords, cables, or ropes.
10. A temporary bridge as claimed in any of the preceding claims, wherein the first abutment surface forms part of the first anchor; and/or wherein the second abutment surface comprises a pair of retention locking collars.
11. A temporary bridge as claimed in any of the preceding claims, wherein each rigid bridge element comprises a pair of substantially parallel tubular elements connected by a deck panel, each tubular element comprising a substantially downward facing and open ended radial slot extending longitudinally through said tubular element and adapted to receive one of the pair of flexible supports.
12. A temporary bridge as claimed in any of the preceding claims, wherein the abutting surfaces of the rigid bridge elements are flat or are interlocking.
13. A temporary bridge as claimed in any of the preceding claims, wherein the rigid bridge elements comprise at least one material selected from a high compressive strength polymer, a low density syntactic foam, a polymethacrylimide foam, balsa wood, Obeche, or a mixture of glass spheres and a thermosetting resin.
14. A method of deploying a temporary bridge having a deck across a space from a deployment side of the space to the opposite side in an emergency, said method comprising: providing a pair of flexible supports on the deployment side, the pair of flexible supports having first and second end portions, the first end portion being attached to a first anchor on the deployment side and having a first abutment surface provided thereon and fixedly mounted relative thereto, and the second end portion having a second abutment surface provided thereon and fixed thereto; transferring the second end portion of the pair of flexible supports from the deployment side of the space to the opposite side; anchoring the second end portion of the pair of flexible supports to the opposite side to form a second anchor such that the pair of flexible supports extend in parallel between the first and second anchors; and mounting in sequence a plurality of rigid bridge elements on the pair of flexible supports, each bridge element being moved towards the second end portion before a subsequent bridge element is mounted on the pair of flexible supports, until the space between the first and second abutment surfaces is at least substantially filled; wherein the pair of flexible supports are tensioned to form the deck until the tension (Ti) in the flexible supports between the first and second abutment surfaces is greater than the tension (T2) in the flexible supports between the second abutment surface and the second anchor, thereby imparting a compressive force (Ci) between adjacent bridge elements and the abutment surface and forming the deck.
15. A method as claimed claim 14, the method further comprising mounting at least one spacer on the pair of flexible supports, wherein the at least one spacer is preferably mounted between a final rigid bridge element and the first abutment surface.
16. A method as claimed in claims 14 or 15, wherein after a first bridge element is mounted on the pair of flexible supports, the pair of flexible supports are tensioned to a preliminary tension (To) sufficient to support the weight of the first bridge element.
17. A method as claimed in any one of claims 14 to 16, wherein the pair of flexible supports are tensioned incrementally.
18. A method as claimed in any one of claims 14 to 17, wherein the tension in the pair of flexible supports is increased to achieve tension (T2) after a final rigid bridge element has been mounted on the pair of flexible supports.
19. A method as claimed in any one of claims 14 to 18, wherein tension (T1) is applied to the pair of flexible supports once the space between the first and second abutment surfaces is at least substantially filled or once the at least one spacer has been mounted on the pair of flexible supports to fill any space between the final rigid bridge element and the first abutment surface.
20. A method as claimed in any one of claims 14 to 19, wherein the pair of flexible supports are tensioned using at least one tensioning device selected from a winch, a hydraulic jack, and a turnbuckle.
21. A method as claimed in any one of claims 14 to 20, wherein the second end portion of the pair of flexible supports is transferred ballistically from the deployment side of the space to the opposite side.
22. A method as claimed in any one of claims 14 to 21, wherein the second end portion of the pair of flexible supports is anchored by attaching to a fixed object, by a grappling hook, or by a retaining stake.
23. A method as claimed in any one of claims 14 to 22, wherein the plurality of rigid bridge elements is pulled towards the second end portion using a rope or a pulley.
24. A method as claimed in any one of claims 14 to 23, the method further comprising: installing at least one anti-buckling clip between a pair of adjacent rigid bridge elements; and/or installing a handrail to provide additional tension (T3) to the bridge.
25. A kit of parts for a temporary bridge for rapid deployment across a space, the kit comprising: a pair of flexible supports; a plurality of rigid bridge elements adapted for mounting on the pair of flexible supports; a first abutment surface provided on and adapted to be fixedly mounted relative to a first end portion of the pair of flexible supports; and a second abutment surface provided on and adapted to be fixed to a second end portion of the pair of flexible supports.
26. A kit as claimed in claim 25, said kit further comprising a first anchor and/or a second anchor.
27. A kit as claimed in claims 25 or 26, wherein the second abutment surface comprises a retention locking collar.
28. A kit as claimed in any one of claims 25 to 27, said kit further comprising one or more of the following: at least one tensioning device selected from a winch, a hydraulic jack, or a turnbuckle; a handrail; at least one spacer adapted for mounting on the pair of flexible supports; and/or at least one anti-buckling clip.