GB2497811A - A connector for forming a movement joint between vehicle restraint or barrier members - Google Patents

Abstract

The connector comprises a spring 130 for applying a tensile force between ends of vehicle restraint or barrier members 90, 95 to com­pensate for thermal expansion and contraction of the members in use. The spring is connected to the members through a load sensitive coupling which in use is arranged to lock the connector, and thereby prevent movement between the adjacent members 90, 95, when the relative rate of movement between the adjacent members exceeds a pre-determined value such as in a crash or impact situation. The load sensitive coupling may be a hydraulic cylinder 10 and may further comprise a lock off valve which may be part of an external fluid transfer path 160 or may be provided as part of the piston.

Description

A CONNECTOR FOR FORMING A MOVEMENT JOINT BETWEEN VEHICLE

RESTRAINT MEMBERS, FORMING PART OF A VEHICLE RESTRAINT

SYSTEM

Field of the Invention

This invention relates to a connector for forming a movement joint be-tween vehicle restraint members, forming part of a vehicle restraint system.

Background to the Invention

Crash barriers (sometimes referred to as safety fences) are used by highways agencies and road authorities around the world to limit the travel of vehicles in a specified direction. The major component of a crash barrier is a series of vehicle restraint members, usually in the form of Corrugated Beams or Open Box Beams. Crash barriers are most commonly used to separate the car- riage ways of high speed roads having two or more lanes of traffic in each direc-tion, and to limit the risk of hazards in the verges such as lighting columns, sign poles, steep drops, and waterways.

Corrugated Beams, often referred to as ARMCO barriers, are elongated beams of a profiled or corrugated nature having a traffic facing side and a non-traffic facing side. Such beams are constructed from galvanised steel. For the purpose of this specification, the traffic facing side will be referred to as the front face and the non-traffic facing side will be referred to as the rear face.

The invention can be used in any safety fence consisting of steel vehicle restraint members acting together as components of the crash barrier.

As a particular example, the particular design of Corrugated Beam safety fencing, most prevalent in the UK, is Tensioned Corrugated Beam (TCB) safety fencing. In this design Individual vehicle restraint members are joined together to form a continuous barrier in maximum lengths of 70 metres.

Each of the 70 metre lengths is joined to the next by a pre-determined level of overlap between adjacent vehicle restraint members. A mechanical load is transferred between these connections by 24mm diameter steel bolts which are adjustable in length by means of steel brackets attached to the beams.

These connections are referred to as adjuster assemblies.

The primary purpose of these adjuster assemblies is to allow the slack in the individual components on first installation to be removed by the application of a tensile load to the adjuster bolts.

The secondary function intended by the original designers of the systems back in the 1960's was that the tension induced on first installation in each 70 metre length of beam would counteract the thermal movements caused by ex-pansion and contraction of the steel beams.

In use, this secondary function has proven not to be effective, and the tensioner bolts have to be checked and retightened bi-annually at least. This ensures that they are tight enough to prevent rotation by hand, thus ensuring that tensile loads caused on vehicle impact are transferred to the adjacent beam. The beams of the safety fence are designed to act as a tensile whole to ensure strike energies are dissipated longitudinally along the whole safety fence line. This would not occur if tensile loads generated from a vehicle impact were not transferred between individual members.

If there is slack at the tensioner assemblies, or if tension is insufficient to transfer the load immediately, the vehicle restraint members may effectively in- crease in length on vehicle impact. Such an increase in length permits the safe-ty fence to deflect to a greater degree than the design intended. A deflection beyond design specification may result in hazards being defended by the safety fence, which include the opposing carriageway and vehicles thereon, may not be defended from impact by the errant vehicle.

Too great a tension in the bolts may result in the connecting bolts be-coming fatigued, and the end terminal sections being placed under too great a lateral strain. In extreme load cases, vehicle restraint members flexing insuffi-ciently may result in a vehicle being badly damaged upon impact and potentially re-entering the traffic flow.

The potential range of movement at each joint is significant. It has been calculated that an increase in ambient temperature of 30 degrees Celsius, would cause a 27mm thermal expansion in a 70 metre run of vehicle restraint members. To counter this, at each adjuster location, a 76mm nominal overlap between adjuster beams is provided to account for thermal expansion and con-traction due to differences in the ambient temperature. The adjuster bolts must accommodate this movement.

It is estimated that there are currently 29,895 kilometres of beams in the form of Corrugated Beams in use in the UK today. As an adjuster assembly is required at maximum intervals of 70 metres, it can be reasonably estimated that there are 427,000 adjuster assemblies currently in use. Due to the inherent na-ture of the adjuster assemblies, each one requires the torque applied to each of four bolts to be adjusted on at least a biannual basis. It is estimated that the an- nual cost of maintenance workers adjusting the torque for each adjuster as-sembly is at least £28 million.

It is further estimated that each year 1.4 million kilogrammes of CO2 is di-rectly or indirectly produced from maintenance teams adjusting the torque on adjuster assemblies around the country.

Further, there are also safety implications inherent with working adjacent to high speed carriageways. It is therefore not uncommon for roads, or certain lanes of them, to be closed while maintenance workers are working within the central reservation or the verges.

Summary of the Invention

The present invention provides a connector for forming a movement joint between vehicle restraint members, forming part of a vehicle restraint system, comprising a spring for applying a tensile force between the ends of the mem-bers to compensate for thermal expansion and contraction of the members, the spring being connected to the members through a load sensitive coupling ar- ranged to lock the connector, thereby preventing movement between the adja- cent members, when the relative rate of movement between the adjacent mem-bers exceeds a pre-determined value.

The present invention offers an improvement over current means of maintaining tension in adjuster assemblies provided between vehicle restraint members. Current means require the expenditure of large sums of money and considerable time in maintaining existing tension devices. The present invention provides a connector, which will provide a substantially constant tensile contact between adjacent vehicle restraint members without the need for regular maintenance.

Currently, vehicle restraint systems require a different torque to be ap- plied to the tension bolts depending on the ambient temperature during installa-tion. This has been found to dissipate over time to such an extent as to allow the adjuster bolts to become slack. The present invention requires that only a nominal torque is applied to the bolts as a tensile load will automatically be ap- plied by the connector according to the observed variations in ambient tempera-ture and corresponding relative movement of adjacent members.

The performance of vehicle restraint systems, in the event of an impact, depends on the nominal tension and direct tensile contact exhibited by the ad-justment bolts. If there is no direct tensile contact, the vehicle restraint members may flex too much to absorb the impact of a vehicle, causing the vehicle to penetrate the central reservation or perhaps even the opposite carriageway.

Too great a tension in the bolts may result in the vehicle restraint members flex-ing insufficiently and may result in a vehicle being badly damaged upon impact and potentially re-entering the traffic flow.

Upon impact of a vehicle into the vehicle restraint system, the present in-vention preferably allows for fluid in one chamber of a hydraulic cylinder to be accelerated through the small bore of an external pipe connected to each chamber. A lock off valve provided as part of the external pipe will lock in re- sponse to detection of fluid passing through the valve at a rate exceeding a pre-determined value. Prevention of fluid transfer from one chamber to the other effectively disengages the tensile load applied by the spring.

The way that the hydraulic cylinder operates, allows a coupling, connect-ed to one end of an internal rod, to engage the tension bolt thus applying the required tension in response to an amount of movement that may have oc-curred due to thermal expansion and contraction. The hydraulic coupling will cause the adjuster bolt, rod and plunger to act as a solid tensile connection.

Brief Description of the Drawings

Figure 1 shows an illustrative view of a device for maintaining the tension of adjuster bolts; Figure 2 shows an illustrative view of two tensioning connectors provided between adjacent vehicle restraint members.

Figure 3 shows an end view of a tensioning connector mounted on a Corrugated Beam.

Detailed Description of the Illustrated Embodiment

Referring to the drawings, Figures 1 to 3 identify an exemplary embodi-ment of the present invention.

According to Figure 1, a hydraulic cylinder 10 has first and second chambers 20, 30, separated by a plunger 40, movable longitudinally within the cylinder 10. A pre-determined quantity of fluid, preferably oil, is provided in each of said chambers 20, 30. The cylinder 10 has first and second ends 50, 60, the first end being mechanically connected to a load transfer member 70 which in turn acts against an adjuster bracket 80 provided as part of a first vehicle re-straint member 90.

A rod 100 is provided, passing longitudinally through the centre of the cylinder 10 and protruding from each end 50, 60 of said cylinder. The portion of the rod 100 protruding from the first end 50 of the cylinder 10 has a coupler 110, in mechanical contact with a bolt 120.

The portion of the rod 100, protruding from the second end 60 of the cyl-inder 10, is provided with a spring 130. During normal thermal expansion and contraction of the vehicle restraint members, the length of a seventy metre run of said members can alter by as much as 27mm within the temperature range of -5°C to 25°C. Provision of the spring 130 enables the cylinder 10 to take up any slack in the bolt 120 resulting from an increase in temperature and subsequent expansion of the length of adjacent vehicle restraint members 90, 95.

Upon a variation in temperature, the spring 130 will compress or relax accordingly and act through the rod 100 and against the bolt 120, ensuring that a substantially constant level of tension is maintained.

Connectors are required to be positioned at intervals of seventy metres within each vehicle restraint system. It is not necessary to install a connector at every joint between vehicle restraint members 90, 95. As the cylinder 10 allows for 200mm of travel, and this could if required be provided at any length, it is expected that this connector would be suitable for use at intervals up to 21 Om or even greater lengths although current regulations for the Highways Agency TCB safety fence, stipulate that tension adjustment means must be situated at max-imum intervals of seventy metres.

It is important to note that whilst the Highways Agency TCB safety fence design is being used by way of a detailed example, the invention could equally well be applied to other designs of tensioned and untensioned safety fences to provide them with the ability to accommodate thermal expansion and contrac- tion whilst still allowing the vehicle restraint system to act as a tensile whole up-on a vehicle impact.

During installation, the bolt 120 is tightened to a nominal torque regard-less of the ambient temperature during installation. Subsequent variations in temperature will cause thermal expansion and contraction of the vehicle re-straint members 90, 95. As the vehicle restraint members 90, 96 increase in length, the fluid within the cylinder 10 will flow into the first chamber 20 from the second chamber 30, causing the coupler to slacken the bolt. Conversely, as the vehicle restraint members 90, 95 decrease in length, the fluid within the cylinder will flow into the second chamber 30 from the first chamber 20, causing the coupler 110 to act against the bolt 120 thus applying a tensile load.

The fluid is permitted to flow between chambers 20, 30 via a pipe 150 connected externally to each of said chambers 20, 30. As the vehicle restraint members 90, 95 thermally expand and contract, the plunger 40 slowly moves longitudinally within the cylinder 10. Movement of the plunger 40 results in fluid within the chambers 20, 30 being forced through the external pipe 150 from one chamber 20, 30 to the other.

The spring load applied to the connector causes the inner rod 100 and bolt 120 to remain under tension at all times. The load path transfers the spring load via the cylinder body 10 and load transfer tube 70 to the adjuster bracket forming part of the first vehicle restraint member 90. Such a configuration ensures that adjuster brackets 80, 85 on adjacent vehicle restraint members remain in constant mechanical contact with each other and the tensile load ap-plied by the spring 130.

The bolt 120 is contained within the load transfer tube 70. The adjust- ment brackets provided as part of the first and second vehicle restraint mem- bers have apertures of sufficient size to allow passage through of the bolt unim-peded. One or more nuts 160 are provided to mechanically connect the bolt to the adjustment bracket provided as part of the second vehicle restraint member, and to allow the exact required length of adjuster bolt 120 between adjuster brackets 80, 85. Sufficient thread length is provided at the end of adjuster bolt to allow this adjustment.

Referring to Figures 2 and 3, two connectors are provided at each ad-justment location. A connector is mounted on the rear face of each corrugated part of the first vehicle restraint member 90.

In the event of a vehicle impacting the crash barrier, any connector lo-cated within the deflection and tensile beam load zone caused by the impact will lock. A lock off valve 160 provided as part of the external pipe 150 will close up-on detection of a fluid flow rate exceeding a pre-determined value. The small bore of the external pipe 150 accelerates the flow rate of the fluid forced through it by rapid movement of the plunger 40, ensuring fast lock off.

Fluid passing through the lock off valve 160 at a speed and pressure ex-ceeding a pre-determined value causes the valve 160 to close, preventing fluid transferring between the chambers 30, 20. Effectively, the prevention of fluid transfer will disengage the tensile load applied by the spring 130.

Referring to Figure 3, the connector is mounted on the first vehicle re-straint member 90 by way of a plurality of bolts 170. Preferably, four bolts 170 will be provided to securely mount the connector on the top and bottom curved portions of the top or bottom corrugated parts of the first vehicle restraint mem-ber 90.

While a single, specific embodiment has been described by way of refer-ence to Figures 1 to 3, it will be appreciated that alternative methods could be used to accommodate the thermal expansion and contraction of vehicle re-straint members caused by variations in ambient temperature.

Specifically, a mechanical device having an inertial lock could be used to react to high speed actuation of a valve or snap action device in response to a high energy impact of a vehicle into the crash barrier. Under normal load caused by thermal expansion and contraction, a long throw screw cylinder would slowly rotate in response to the tensile load experienced by a bolt con-necting adjacent vehicle restraint members. Upon impact of a vehicle into the crash barrier, the long throw screw would lock thus preventing further rotation.

For such a configuration to be effective, either the long throw screw or a threaded retainer must be rotatable relative to the other. The threaded retainer must allow for rotation at an angulai velocity not exceeding a pre-determined value. If rotation occurs above a pie-determined angular velocity value, the threads will jam thus preventing rotation of one part relative to the other.

Various means could be utilised to provide further safeguards against ro-tation of the long throw screw, including but not limited to: a centrifugal clutch mechanism, lockable in response to a rate of rotation of the bolt in excess of a pre-determined value; a rotational damper, reducing rotation to almost nothing in response to a rate of rotation of the bolt exceeding a pre-determined value; a ratchet having an inertially actuated pawl, preventing rotation of the bolt from exceeding a pre-determined value; a support spring capable of compressing upon accelerated movement of the bolt thus preventing engagement of teeth on the screw body with corre-sponding teeth on an outer casing.

Claims (1)

1. <claim-text>CLAIMS1. A connector for forming a movement joint between vehicle re-straint members, forming part of a vehicle restraint system, comprising a spring for applying a tensile force between the ends of the members to compensate for thermal expansion and contraction of the members, the spring being connected to the members through a load sensitive coupling arranged to lock the connect-or, thereby preventing movement between the adjacent members, when the relative rate of movement between the adjacent members exceeds a pre-determined value.</claim-text> <claim-text>2. A connector according to Claim 1, wherein the load sensitive cou- pling comprises a hydraulic cylinder having two chambers, separated by a pis- ton adapted to move in the chamber in response to thermal expansion and con-traction of the vehicle restraint members, and a fluid transfer path between the chambers such that movement of the piston results in fluid from one chamber transferring to the other chamber, the fluid transfer path including a lock off valve arranged to close when the flow rate therethrough exceeds a predeter-mined value thereby preventing further transmission of movement to the spring.</claim-text> <claim-text>3. A connector according to Claim 2, wherein the lock off valve is provided as part of an external fluid transfer path between the chambers.</claim-text> <claim-text>4. A connector according to Claim 2, wherein the lock off valve is provided as part of the piston.</claim-text> <claim-text>5. A connector according to any preceding claim, wherein the cou- pling, when locked, is released as a result of the rate of movement between ad-jacent members falling below a pre-determined value.</claim-text> <claim-text>6. A connector according to any preceding claim, wherein the cou-pling is rigidly attached to at least one of the members.</claim-text> <claim-text>7. A connector according to Claim 2, wherein the piston is mounted on a piston rod passing through the cylinder and connected at one end to the spring such that a tensile force is applied to the piston rod, and at the other end to an end portion of a first of the vehicle restraint members, the spring bearing against the cylinder, which is in turn rigidly connected to the second of the re-straint members.</claim-text> <claim-text>8. A connector according to Claim 7, wherein a rigid tubular member extends between the cylinder and a mounting bracket attached to an end por-tion of the second restraint member.</claim-text>