EP3775389B1

EP3775389B1 - Road restraint system with improved ground constraint performance

Info

Publication number: EP3775389B1
Application number: EP19712587.5A
Authority: EP
Inventors: Mario Bruni; Claudio Angelo ARDEMAGNI; Davide BENETTON; Sergio Marco BASSI; Matteo BERNARDINI; Marco Anghileri
Original assignee: Crashtech Srl; Iniziative Nazionali Autostradali - SINA SpA Soc
Current assignee: Crashtech Srl; Iniziative Nazionali Autostradali - SINA SpA Soc
Priority date: 2018-03-26
Filing date: 2019-03-25
Publication date: 2024-01-03
Anticipated expiration: 2039-03-25
Also published as: WO2019185513A1; EP3775389A1; EP3775389C0; IT201800003913A1

Description

The present invention relates, in general, to the field of road restraint systems.
More particularly, the invention relates to a device for maintaining the performance of a road restraint system as the resistance of the ground in which the system is fixed is varied.
The invention also relates to a method for improving the performance of road restraint systems, both existing and newly installed.
By road restraint system, in this context, we mean any device suitable for the containment of vehicles and/or the reduction of stress to the occupants through mechanisms of energy absorption and/or redirection of the same in case of impact.
The restraint systems are therefore a valuable tool to keep and redirect vehicles safely.
Considering, by way of example and not exhaustively, the impact case between a vehicle and a safety barrier, the barrier must be deformed in order to mitigate the intensity of the impact, presenting to the vehicle a surface that remains regular and without roughness during deformation, dissipating impact energy and returning to the vehicle as little as possible.
Road safety barriers typically consist of one or more longitudinal elements (or beams, or blades) supported by a multiplicity of poles (or piers, or posts, as will be referred to hereafter). The posts are planted in the ground or fixed to the edge of a construction, such as a bridge, a retaining wall or the like.
In case of impact, the ribbons behave like beams on many supports, in which the supports are constituted by the posts. The latter are, therefore, the components of the barrier that absorb and dissipate the impact energy, discharging it to the ground, while the ribbons have the function of distributing the load on the posts, as well as of course providing the supporting surface for the bumping vehicle.
It follows that the performance of a road safety barrier highly depends on the behaviour of the posts, which in turn depends on the consistency of the ground in which the posts are fixed or the resistance of the connections and the edge of the structure to which the posts are constrained.
In its function of supporting a barrier subject to the impact of a vehicle, each post generally works mainly on bending, normally well beyond the elastic limits.
At present, road restraint systems, in order to be installed on the road, must follow a certification process that, according to the provisions of the EN 1317 standard, includes various experimental crash tests carried out at accredited test fields.
Certification tests on barriers whose posts are fixed in the ground are generally carried out on soils with good and uniform mechanical and performance characteristics. The subsequent road installations of restraint systems, however, take place on soils with a conformation and consistency different from those of certification tests, with a wide range of variability, thus making the behaviour of the restraint system different from that of crash certification tests.
This can create dangerous situations in the event of a collision of a vehicle against the restraint system, which may not perform the retention task for which it was designed.
EP 0845558 A2 discloses a cable safety barrier having means for disengagement of the cable from an anchor portion of the cable safety barrier when certain vehicle impact conditions are met. The means for disengaging the cable may involve allowing a cable end fitting to escape from an open ended slot, when the cable is deflected upwards, or causing the cable fitting to fail.
EP 1762660 A1 discloses a device having a crash barrier running along an edge of a road surface, where the barrier is turned towards the surface and includes a recess. A set of supports is attached at a side of the barrier turned away from the barrier, and is supported opposite to a base, where the supports are fastened to the base. A tie-rod is arranged in the recess of the barrier, where the barrier has a longitudinal groove in between upper and lower ring fences. The tie-rod is arranged in the groove and fixed in the recess.
GB 2458696 A discloses a road safety barrier comprising a plurality of posts spaced apart from one another other, at least one cable non-releasably engaged with and supported by the posts within the top 25% of the post height above the ground and at least one longitudinal element disposed along the posts and positioned within the lower 75% of the post height above the ground. The or each cable preferably follows a sinusoidal path around the posts.

Object of the invention

The object of the invention is to eliminate, or at least to make irrelevant, the drawbacks of the restrain systems of the prior art.
In particular, an object of the invention is to ensure the correct operation of the road restraint systems (according to EN 1317), namely safety barriers, crash cushions, terminals, transitions and movable barriers, also in the case of driving terrain different (in particular more yielding) compared to the conditions of TT (Type Testing, definition of "CPR-Construction Products Regulation"), i.e. conditions different from those present in the test field.
An important aspect of the present invention is that of constituting a system for improving the performance of the fixed constraints which can also be installed a posteriori, since the invention can be mounted directly and with minimum effort on the restraint systems already present on the road (retrofit) without the need of interventions that could change the original structure of the road restraint systems themselves.
Another object of the invention is to provide such a road restraint system which allows to obtain the prefixed results in a simple and economical way.
These and other objects of the invention are achieved by the road restraint system and by the method for improving the performance of a road restraint system which have the characteristics indicated respectively in the annexed independent claims 1 and 9.
Advantageous embodiments of the invention appear from the dependent claims.
Substantially, the road restraint system according to the invention comprises a plurality of posts fixed in the ground joined together by at least one current, and longitudinal connecting elements arranged at the base of the posts, such that in case of impact of a vehicle against the restraint system, said longitudinal connecting elements allow the transfer of the load to the base of the adjacent posts thus increasing the capacity of the system to effectively discharge the loads to the ground.
Said longitudinal connecting elements therefore favor the formation of a plastic hinge at the base of the uprights involved in the impact, close to the ground.
Conveniently, said longitudinal connecting elements are arranged in contact with the ground, or near the ground, above or below it.
Said longitudinal connecting elements are arranged so as to pass alternately in front of and behind said uprights.
The method for improving the performance of a road restraint system (10) comprising a plurality of posts fixed in the ground joined by at least one current, consists in disposing longitudinal connecting elements at the base of said posts, such that in case of impact of a vehicle against the restraint system, said longitudinal connecting elements allow the transfer of the load to the base of the adjacent posts thus increasing the capacity of the system to effectively discharge the loads to ground.

Brief description of the drawings

Further characteristics of the invention will be made clearer by the detailed description that follows, referring to purely exemplary and non-limiting embodiments thereof, illustrated in the appended drawings, in which:

- Figures 1 and 2 are schematic perspective views, respectively from the rear and front of a road restraint system, in particular a safety barrier, provided with the device according to the invention, constituted in this case of cables connecting barrier posts;
- Figure 3 is a view like that of Figure 1 of an alternative embodiment, in which elements are provided for spacing apart the cables from the posts;
- Figures 4 and 5 are two enlarged views taken from different angles showing a possible exemplary but not exhaustive typology of one of the spacers of Figure 3 acting as a terminal for constraining the ends of the cables;
- Figures 6, 7 and 8 show, in a simulation with finite element models, the behaviour of a post, of a road restraint system according to the prior art, hit by a vehicle;
- Figures 9, 10 and 11 show the same simulation with finite element models with a restraint system according to the invention.

Description of preferred embodiments

Figures 1 and 2 schematically show a road restraint system, in particular a safety barrier, indicated as a whole with the reference number 10, constituted, in its essential elements, by poles or posts 11 (hereinafter called posts) fixed in the ground, and by a beam or blade 12 (hereinafter called beam) which joins the posts 11 and from which it is kept spaced by spacer elements and energy dissipators 13.
Although in this detailed description reference is made in particular to a safety barrier, the invention is extended to any road restraint system, such as crash cushions, terminals, transitions, movable barriers and other, comprising posts fixed in the ground joined by at least one longitudinal current.
According to the invention, longitudinal elements 20 are provided, such as, for example, but not exclusively, cables or ribbons, which connect the posts with the aim of restoring the energy containment and absorption performance of the system in case of impact.
In Figures 1 and 2 two cables 20 are provided, which intertwine or intersect with each other, so as to enclose the posts 11 between them, each cable 20 alternately passing in front and behind the succession of posts 11.
The cables 20 connect a certain number of posts 11, affecting a portion of the barrier 10, being joined together at their ends at the beginning/end of the section, as will be illustrated below by way of example.
Naturally, instead of the two cables 20, a single cable can be provided, which goes around an end post 11 and is clamped at the other end post.
The connecting cables 20 of the posts 11 are arranged at a lower height with respect to the beam or beams 12, preferably at or near the base of the posts. The optimal or nominal condition would be that shown in the figures, that is in contact with the ground, but the cables 20 can also be arranged above or below it, in this last case being covered by the ground. The ribbon 12 connects the posts 11 in order to transfer the load due to the impact, while the cables 20 interact with the posts 11 with the aim of increasing the capacity of the system to effectively discharge the loads to ground.
The embodiment of Figure 3 differs from the previous one by providing detachable fastening elements 30, for example saddles, fixed to the posts 11 which can be equipped, according to the specific needs, with components suitable for guiding and fixing the cables 11, as will be exemplified and schematically described below.
The saddles or spacers 30 serve in particular to increase the angle between the longitudinal axis of the barrier 10 and the direction of the corresponding cable 11 at the point where each saddle is arranged.
In the embodiment of Figure 3, the saddles 30 are arranged on the inner side, i.e. the one facing away from the road of each post 11. However, without departing from the scope of the invention, the saddles 30 may not necessarily be provided on all posts11 and/or saddles could also be provided on the outside of the posts 11.
The enlargements of Figures 4 and 5 show one of these saddles 30 mounted on a post 11 of the beginning or end of the section, it being understood that the same saddle is provided on intermediate posts of the section.
In the case in point, being shown, by way of an example, a post with an H section, the saddle 30 is fitted on a flange 15 of the post 11 and is fixed thereto by means of metal strips 31.
Of course, the indicated one is only one of the possible ways of fixing the saddle 30 to the post 11.
The cables 20 are guided on the saddle 30 passing under U-bolts 32 provided on the same.
Alternatively, grooves may be provided on the saddle 30 in which the cables 20 are housed.
At the ends of the cables 20 there are metal rings or lugs 21, for fixing the cables by means of one of the said U-bolts or brackets 32.
If only one cable is provided, which rotates around one of the end posts of the barrier section, the fixing system shown in Figures 4 and 5 is provided only in correspondence with the other end post of the section.
It is reiterated that what shown in Figures 4 and 5 is purely exemplary and does not constitute an essential feature of the invention, the cables 20 being able to alternately rotate ahead and behind the posts 11 in any other way.

Operation

From a general point of view, the behaviour of the road safety barrier with posts fixed in the ground, described above, or of any other restraint system, is linked to the fact that, by introducing a longitudinal connecting element, i.e. the cable 20 to the base of the posts 11 it is possible to involve a greater number of such posts during the impact with a vehicle; the participation of a greater number of posts to the phenomenon, with a redistribution of the impact load, favours the correct functioning of the restraint system.
During the impact of a vehicle against the barrier 10, the stress due to the crash is discharged to the ground through the posts 11. In the case of posts placed into the ground, the correct functioning of the system depends on the reaction and the behaviour of the ground itself. In the event that the soil does not have sufficient strength characteristics to allow it to adequately discharge the load coming from the posts of the restraint system, the post rotates without deforming correctly and without absorbing the impact energy.
With the introduction of the longitudinal connecting element 20, the problem is solved because, when an impact occurs and the deformation of the barrier is discharged onto a post, the presence of the inventive device allows to support the base of the post thanks to the state of tension created in the longitudinal connecting element; this tension state is generated because the longitudinal element subjected to traction by the displacement of the impacted post is supported by the adjacent posts, on which this stress state is discharged. The support provided at the base of the post allows to reestablish a condition equivalent to that of soil with adequate resistance characteristics and therefore serves to guarantee the correct functioning of the restraint system, favouring the formation of a plastic hinge at the base of the posts.
The system works therefore thanks to a state of tension that is generated inside the longitudinal connecting elements; for this reason, these elements alternately pass in front of and behind the posts of the road barrier, to ensure that the stress is transferred to all the posts around the one hit.
The proposed system is able to operate correctly either with the longitudinal elements not directly fixed to the posts or with a relative constraint between the two components, such as the removable saddles 30 of figures 3-5. The presence of fasteners can be used to implement, for example, sections breaker, cable tighteners or guides. As said previously, elements such as saddles 30 have the further advantage of increasing the angle between the longitudinal axis of the restraint system and the direction of the longitudinal elements 20; this aspect is advantageous because an increase in the relative angle causes an increase in the state of tension in the system with the same displacement of the post stressed by the impact, with a consequent increase in the effectiveness of the system.
The effectiveness of the system according to the invention has been verified through comparative simulations, carried out with finite element models able to correctly describe the real dynamics of vehicle, restraint system and terrain in case of impact.
The finite element model used for the comparison consists of one or more posts of a safety barrier fixed in a ground with poor resistance characteristics; during the simulation, a post is hit by a reference vehicle. The difference in behaviour of the system has been verified with and without the longitudinal connecting element between the posts. The following results were obtained:

Configuration without longitudinal connection element: the post impacted by the vehicle rotates rigidly in the ground, opposing a modest reaction force to the impact stress. The soil with poor characteristics is not able to support the post and therefore does not allow the load from the impact to be unloaded onto the ground (Figures 6, 7, 8).
Configuration with longitudinal connection element: the post impacted by the vehicle is deformed, forming a plastic hinge at the base, near the ground, where the longitudinal connecting elements are positioned, in the simulated case metal cables.

The introduction of connecting cables allowed the impact load to be transferred from the impacted post to adjacent ones (and subsequently to be discharged to the ground) by means of the tension state generated in the cables, allowing a behaviour to be achieved in accordance with what was desired also maintaining a terrain with poor characteristics (figures 9, 10, 11).
Through the finite element simulations carried out, therefore, the system's ability to restore the correct operation of the posts fixed in the ground, even if the performance characteristics of the ground are lower and less uniform than those present in the test field where the barrier has been certified, was verified.
Naturally, the invention is not limited to the particular embodiments previously described and illustrated in the accompanying drawings, but numerous detail modifications can be made to the reach of a person skilled in the art, without departing from the scope of the invention, as defined in the attached claims.

Claims

Road restraint system (10) comprising a plurality of posts (11) fixed in the ground joined together by at least one current (12), and longitudinal connecting elements (20) of the posts (11), characterized in that said longitudinal connecting elements (20) are arranged at the base of the posts, such that in case of impact of a vehicle against the restraint system, said longitudinal connecting elements (20) allow the transfer of the load to the base of the adjacent posts (11) thus increasing the capacity of the system to effectively discharge the loads to ground.
A restraint system according to claim 1, wherein said longitudinal connecting elements (20) are arranged in contact with the ground, or in proximity of the ground, above or below it.
A road restraint system according to claim 1 or 2, wherein said longitudinal connecting elements (20) are arranged so as to pass alternately in front of and behind said posts (11).
Road restraint system according to claim 3, wherein two longitudinal connecting elements (20) are provided which cross each other, so as to enclose the individual posts (11) therebetween.
Road restraint system (10) according to claim 4, wherein said two longitudinal connecting elements (20) are made so as to constitute a single longitudinal element (20) which turns around two terminal posts (11) of a section of the restraint system (10), and whose ends are joined together.
Road restraint system according to any one of the previous claims, wherein saddles (30) are arranged on at least some of said posts (11) to keep the longitudinal elements (20) spaced apart from the respective posts (11).
Road restraint system according to any one of the previous claims, wherein said longitudinal connecting elements (20) are cables, straps or the like.
A road restraint system (10) according to any one of the preceding claims, consisting of a safety barrier, or a crash cushion, or a terminal, or a transition, or a movable barrier or other, wherein said at least one current (12) is a beam or blade.
Method for improving the performance of a road restraint system (10) comprising a plurality of posts (11) fixed in the ground joined by at least one current (12), consisting in disposing longitudinal connecting elements (20) at the base of said posts (11), such that in case of impact of a vehicle against the restraint system, if said longitudinal connecting elements (20) allow the transfer of the load to the base of the adjacent posts (11) thus increasing the capacity of the system to effectively discharge the loads to ground.
Method according to claim 9, wherein said longitudinal connecting elements (20) are arranged in contact with the ground, or in proximity of the ground, above or below it, passing alternately in front of and behind said posts (11) of the road restraint system (10).