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| United States Patent |
3,603,562 |
|
Glaesener
|
September 7, 1971
|
VEHICLE GUARD RAILS
Abstract
Vehicle guard-rail or barrier arrangement for the shoulders and median
strips of roads. These vehicle guard rails, the length of which may be
more than 20 meters, are constituted by a sheet-metal member (or a
plurality of such members arranged in superposed manner), with a thickness
less than 3 mm. and folded on themselves, so as to form a kind of closed
or open hollow-profiled casing or channel. The vehicle guard rails are
mounted on supporting sleeves or posts by means of fixing keys which match
the form of the internal hollow of the rail.
| Inventors: |
Glaesener; Ernest (Dudelange, Grand-Duchy, LU) |
| Assignee: |
Arbed, Acieries Reunies de Burbach-Eich-Dudelange
((Grand-Duchy de Luxembourg),
LU)
|
| Appl. No.:
|
04/814,054 |
| Filed:
|
April 7, 1969 |
Foreign Application Priority Data
| Current U.S. Class: |
256/13.1 |
| Current International Class: |
E01F 15/02 (20060101); E01F 15/04 (20060101); E01f 015/00 () |
| Field of Search: |
256/13.1,59 287/58
|
References Cited [Referenced By]
U.S. Patent Documents
Foreign Patent Documents
| | | | | |
|
| 649,274 | |
Sep., 1962 | |
CA |
|
| 1,207,418 | |
Dec., 1965 | |
DT |
|
|
Primary Examiner: Taylor; Dennis L.
Claims
I claim:
1. A vehicle barrier adapted to be positioned along the road, comprising an elongated vehicle guardrail having an external surface formed from sheet metal of a thickness of at most 3 mm. and of hollow profile configuration, said guardrail having a pair of downwardly extending flanks connected at a bight along the top of the guardrail with at least one of said flanks being formed with at least one outwardly facing trough and at least one
outwardly projecting bulge extending longitudinally along the guardrail whereby the cross section of the guardrail has an inwardly convex portion corresponding to said trough and an inwardly concave portion corresponding to said bulge, said flanks
defining a longitudinally extending slot between them along the lower edge of said guardrail communicating with the interior thereof and of a width less than the width of the inner space of the guardrail in the region of said bulge; and a plurality of
posts spaced along said guardrail for supporting same, each of said posts including a flat key of a thickness less than the width of said slot and of a profile complementary to the cross section of the interior of said guardrail whereby each key is
insertable into said guardrail while parallel to said slot and is rotatable through 90.degree. to lie transversely to said guardrail with its contours in substantially continuous contact with the interior of said guardrail.
2. The vehicular barrier defined in claim 1 wherein each of said keys has a blade portion of a profile complementary to said interior of said guardrail and a shank portion extending downwardly from said blade portion through said slot, each of
said posts comprising an upright member anchored in the ground and forming a socket receiving the respective shank.
3. The vehicular barrier defined in claim 2 further comprising cooperating catch means on each shank and the respective socket for retaining each shank therein.
4. The vehicular barrier defined in claim 2 wherein a plurality of said guardrails are joined in longitudinally contiguous relationship so that their adjoining edges are flush with one another, said barrier further comprising an insert of a
profile corresponding to the interior of each of said guardrails and received in the adjoining guardrails at their junction.
5. The vehicular barrier defined in claim 2 wherein said guardrail comprises geometrically similar inner and outer walls defining a space between them, said barrier further comprising an impact-damping filler received in said space.
6. The vehicular barrier defined in claim 2, further comprising an impact-damping filler received in said guardrail between said keys.
7. The vehicular barrier defined in claim 6, further comprising a closure of a contour corresponding to that of said guardrail and fitted thereon at an end of the guardrail to close the interior thereof.
Description
The present invention relates to barriers in the form of vehicle guardrail for the median strips or shoulders of highways and roads.
It is well known that the main function of a roadside vehicle barrier or guardrail is to provide mechanical protection for the vehicles travelling on a road, preventing any vehicle, which for any reason may have gotten out of its driver's
control, from crashing against a fixed obstacle, falling into a ravine or passing through the central or median strip separating the roadways of a highway or the like.
The protection which a vehicle guardrail has to offer is intended to return a skidding vehicle into a direction approximately parallel to the vehicle guardrail, with a deceleration acceptable to the occupants of the vehicle. Therefore, the
vehicle guardrail has a double function; it must be a mechanical guide and also a brake and shock absorber, intended to dissipate the kinetic energy of a vehicle tending to leave the road and cause a more or less speedy immobilization along the vehicle
guardrail without violently rejecting or rebounding the vehicle onto the traveled lanes.
This latter role particularly will be fulfilled more satisfactorily if on the one hand the vehicle guardrail is constituted by a continuous strip, that is to say a substantially uninterrupted and relatively rigid strip, which retains a certain
elasticity (i.e. a semielastic protective barrier) and if, on the other hand, the guardrails are connected to the supports by means of elements which can yield if necessary.
Of the large variety of section members already designed there are practically only two types of section member which have been adopted generally for vehicle guardrails. These steel vehicle guardrails are constituted by a single profiled sheet
metal member which is covered and has a uniform thickness of about 3 mm. and a relatively short length, normally about 4 meters. Greater thicknesses up to 6 mm. are not really desired, and likewise lengths of much more than 4 meters have not found
favor among users. Vehicle guardrails are fixed to supports, normally U-section members, by means of bolts. In most cases the vehicle guardrails overlap at their joints and at the place where they are supported; that is to say the sliding surface is
not absolutely plane but, on the contrary, is stepped.
These bolted vehicle guardrails must necessarily be perforated at many places which, besides promoting corrosion, requires considerable additional work at the time of assembly.
Experience has also shown that these vehicle guardrails absorb too suddenly from a skidding vehicle too large a proportion of the kinetic energy which has to be damped at an unexpected impact.
It is, therefore, the principal object of the present invention to provide an improved vehicle guardrail adapted to extend along the median strip of a highway or the shoulders thereof which avoids the aforementioned disadvantages.
Another object of my invention is the provision of a guardrail of the character described which has improved energy-dissipating qualities, has reduced tendency to rebound an impacting vehicle onto the roadway of the highway, possesses greater
structural strength and reduced tendency toward deterioration and corrosion, and is readily assembled and positioned along the road.
The present invention relates to a novel design of vehicle guardrails which makes it possible to obviate in a surprisingly effective manner most of the disadvantages encountered hitherto, while offering a solution which comes closer to the ideal
desired condition than has been attainable heretofore.
The vehicle guardrails according to the present invention are constituted essentially by strips of continuous thin sheet metal members of a thickness less than 3 mm., folded on themselves so as to form a closed or open profiled hollow casing or
channel. The vehicle guardrails may be constituted by a single thicker strip or by a plurality of thin superposed strips, the latter case permitting the construction of a laminated structure. The extreme ease of assembly of lengths which, according to
need, may far exceed 20 meters and are bent before assembly so as to match all bends in the road constitutes a considerable economic advantage which, associated with the improved mechanical protection, ensures that the semielastic vehicle guardrails of
the present invention are greatly superior to all systems constructed hitherto.
According to a specific feature of this invention, a vehicle barrier which may be positioned along a highway median strip or shoulder, comprises a substantially continuous guardrail of hollow profile with longitudinally extending corrugations
formed by one or more crests flanked by one or more troughs, and a plurality of support posts spaced along this guardrail. The guardrail of the present invention includes at least one continuous sheet, bent into an inverted U-section or channel at its
upper edge so that the upper edge of the rail forms the bight of the U and a pair of legs extend downwardly as substantially vertical flanks to define the sides of the barrier engageable by the vehicle. The interior of the channel-shaped member, which
has a generally flattened profile, may be empty (i.e. filled with air under ambient pressure) or filled with an energy-dissipating medium such as a resiliently compressible elastomeric material, an impact-absorbing crushable cellular synthetic resin or a
particulate or flowable filler which dissipates the kinetic energy of impact by displacement of the filler material. A suitable particulate filler of this character is sand.
The guardrail is, according to a further feature of this invention, attached to the posts alongside the rod via support keys of a profile complementary to the hollow of the guardrail and receivable therewithin. Thus the channel may have a
relatively narrow downwardly facing opening while the key may be flattened and has a thickness not exceeding the width of this opening so that the profiled portion of the key may be thrust through the opening into the interior of the channel while its
flattened portion lies in a longitudinal plane thereof. There upon, the key is rotated through 90.degree. so that its flattened portion stands transversely to the longitudinal plane of the channel and locks in the complementary hollow thereof. When
the shank of the key is provided with a thrust-type coupling with the sleeve of the post, the key may simply be inserted to engage the coupling member of the sleeve and thereby prevent withdrawal of the key. In an alternative arrangement, however, the
shank of the key fits the sleeve only after the key has been rotated through 90.degree. to lock it in the channel; this arrangement may be accomplished by using a square-section shank and a square-section sleeve. In yet another arrangement, a
bayonet-type coupling is employed whereby the twisting of the key to anchor it in the channel simultaneously locks its shank in the sleeve. The key can be dimensioned to prestress the guardrail outwardly.
According to yet another feature of this invention, successive lengths of guard rail are connected substantially contiguously and flush with one another so as to define a substantially nonstepped vehicle-contacting surface along the flanks of the
guardrail. In this system, a connecting tongue is inserted into the sockets formed by the confronting ends of a pair of contiguous guardrails such that these ends may be brought into substantially abutting relationship. Moreover, the present invention
advantageously provides that the gap between laminated guardrail sheets may be filled with an energy-dissipating substance, e.g. sand, as described above and that the inner and outer sheets in a laminated or double-sheet construction may have different
contours so that an outermost sheet initially deforms under the impact of the vehicle and only thereafter does the innermost sheet deform to dissipate the impact energy.
The above and other objects, features and advantages of the present
invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIGS. 1a, 1b and 1c of FIG. 1 are cross-sectional views of three vehicle guardrail structures according to the present invention;
FIGS. 2a, 2b and 2c of FIG. 2 are elevational views of fixing keys adapted to lock the guardrails of FIGS. 1a, 1b and 1c to respective support posts;
FIGS. 3a and 3b of FIG. 3 are elevational views showing sleeves adapted to accommodate such keys;
FIGS. 4a, 4b and 4c of FIG. 4 are elevational views partially in cross section showing the guardrail assembly according to the present invention;
FIG. 5 is a perspective view of an erected barrier according to another embodiment of this invention;
FIGS. 6, 7 and 8 are diagrammatic cross-sectional views illustrating additional embodiments of the invention;
FIG. 9 is a perspective view of still another guardrail arrangement of the invention;
FIG. 10 is a fragmentary elevational view showing another support arrangement for the guardrail; and
FIG. 11 is a sectional view through still another guardrail according to this invention.
The vehicle guardrails according to the present invention are produced from continuous metallic strips having a thickness less than 3 mm. and shaped
by means of a conventional profiling machine to form a channel with a longitudinal bight and two depending flanks receiving the support post between them. This procedure permits producing substantially greater lengths than has been customary hitherto
and than has been possible by conventional methods. However, if it is desired as in the past to construct only vehicle guardrails of a length of about 4 meters, it is also possible to bend the sheet-metal members by means of a press, although this
method is much less economical.
Some section members chosen from the large variety of possible section members are illustrated in FIGS. 1a, 1b and 1c. The section member 1b is suitable for all vehicle guardrails situated at road edges, whereas the double-face section 1c is
particularly suitable for vehicle guardrails arranged on the central or median strips of motorways, this latter use being illustrated in FIG. 5.
As will be apparent from FIG. 1a, the guardrail may have a semicylindrical bight 100a from which a pair of longitudinally extending smooth vertical flanks 101a and 102a depend. These flanks terminate in inwardly and downwardly extending lips
103a and 104a so that the internal hollow 105a of the profile is that of an inverted bottle. In the embodiment of FIG. 1b, the bight 100b is again located on the upper side of the downwardly open channel while the flank 101b confronting the travel lanes
of the highway is corrugated by the presence of a trough 101b' and a corrugation 101b" of trapezoidal configuration. The other flank 102b of the guardrail is flat and lies in a vertical plane and faces away from the travel lanes of the highway when the
guardrail 112 is positioned as a shoulder strip. Here again, lips 103b and 104b define the downwardly open slot-shaped mouth of the channel. The guardrail preferred for use in a median barrier between road lines of opposite travel direction is shown in
FIG. 1c. Here the bight 100c of the channel is formed as a flat (horizontal) web to which the flanks 101c and 102c are connected as part of a unitarily bent sheet. Troughs 101c' and 102c' of trapezoidal cross section define pairs of trapezoidal-section
corrugations 101c" , 101c' "; and 102c" and 102c '". The lips defining the mouth of the channel are represented at 103c and 104c.
The keys adapted to be used to support the guardrails of FIGS. 1a, 1b and 1c are represented in elevation in FIGS. 2a, 2b and 2c, respectively. Each of the keys has a flat profiled blade portion 106a, 106b and 106c whose outlines correspond to
the cross section of the hollows 105a, 105b and 105c of the guardrails. The thickness of the blade is equal to or less than the width w of the opening to the channel defined between the lips 103a, 104a, etc. Thus the blade 106a is generally
bottle-shaped while the blade 106b has a rounded upper end 107b and a trapezoidal protuberance 106b" as well as a trapezoidal recess 106b' corresponding to the corrugation 101b" and the trough 101b' . Similarly, the blade 106c has recesses 106c' and
108c' as well as protuberances 106c" , 106c '"; and 108c" and 108c '", all of generally trapezoidal configuration.
From the blades 106a, 106b and 106c, shanks 109a, 109b and 109c of square cross section extend and terminate in cylindrical shank portions 110a, 110b and 110c having circumferential V-section recesses 111a, 111b and 111c close to their bottom
ends for engagement with projections 4 of the sleeve posts 3 when the shanks are thrust downwardly into the latter. The recesses 111a, 111b and 111c also serve to weaken the shank so that impact with a vehicle may brake the key loose from the post and
facilitate dissipation of the kinetic energy of impact. As indicated, the key may be first thrust into the post (see FIG. 5) and then enclosed by the guardrail which is placed upon the key while the latter is turned so that its blade lies parallel to
the longitudinal direction of the guardrail. The guardrail is anchored in place by rotating the key through 90.degree. until its blade lies transversely of the guard rail. Alternatively, the blade may be inserted in the guardrail and the key rotated
through 90.degree. whereupon the shank of the key can be inserted into the sleeve of the post until member 4 engages in the recess 111a, 111b and 111c. The assembled guardrail thus consists of the guardrail channel of FIG. 1a, 1b or 1c, the
corresponding key of FIG. 2a, 2b or 2c and a sleeve 3 of FIG. 3a or 3b with or without a cage 4. The assembled structure is shown in FIGS. 4a, 4b and 4c as well as in FIG. 5.
Owing to the continuity of long vehicle guardrails, it is no longer necessary to provide the guardrails at a large number of places with perforations for enabling them to be connected by means of bolts. Consequently the amount of kinetic energy
which the vehicle guardrails according to the invention are capable of absorbing progressively is considerably increased.
The butt connection of two consecutive vehicle guardrails is effected by means of a sleeve 5 having the same shape as the vehicle guardrail. This sleeve is incorporated half in one end of the vehicle guardrail already in position and fixed by
riveting. The adjacent vehicle guardrail is then fitted on the free end of the sleeve and riveted. In this way the sliding surface remains absolutely continuous (nonstepped) and smooth and consequently does not present any point which can engage the
wheels or body of a colliding vehicle. The ends formed when a plurality of lengths of vehicle guardrail are connected in the manner described are provided with caps or plugs 6 closing these ends. The vehicle guardrails thus constituted are, therefore,
free from all asperities and of the numerous perforations hitherto required.
As noted, according to the invention the connection of the vehicle guardrail to the support is advantageously effected by means of a part referred to as the fixing key 2, which is introduced on the one hand into the hollow of the vehicle
guardrail and on the other hand into the supporting tube 3. By rotation, this key will fit the internal shape of the vehicle guardrail. Fixing in the supporting tube is effected by means of the notch 111a etc. situated at the lower portion of the key
and by means of a catch 4 situated in the supporting tube and which may form for example a bayonet joint therewith (see also FIG. 9). Instead of closely fitting the internal shape of the vehicle guardrail, for economy reasons the fixing key may also be
constituted by a bar of square or rectangular cross section.
In FIG. 9, I have shown an arrangement in which the guardrail 200 (of 20 meters in length) extends about a curve and is supported on at least two tubular posts 201 and 202. It will be understood that other such posts may be spaced along the
barrier strip. The tubular post 201 which is driven into the ground 203 is formed with a pair of diametrically opposite vertical internal channels 204 (not shown) adapted to receive projections 205a and 205b of the cylindrical shank 206 of a key 207.
The channels 204 terminate at an annular internal recess 208 which forms with the radial projections 205a and 205b a bayonet coupling. To mount the guardrail assembly, the key 207 is thrust into the tubular post 201 with its projections 205a and 205b
guided in the channels 204 until the projections rest upon the bottom flank of the circumferential groove 208. Thereupon, the key may be rotated through 90.degree. about its axis to offset the projections 205a, 205b from the channels 204 and anchor the
key in the post at the same time that the blade 209 of the key lies transversely to the longitudinal channel of the guardrail.
The blade 209 conforms to the cross section of the interior chamber of hollow 210 of the guardrail 200 which, between the posts, is filled with a similarly shaped rubber cushion 211 and is closed by a weld seam 212 along the bottom of the
guardrail. The guardrail comprises an inner sheet-metal member 213 and is surrounded by an outer sheet-metal member 214 of geometrically similar configurations, the space 215 between these members being filled with sand 216 or other displaceable
shock-dissipating material. At 217, I show a key which has not yet been rotated through 90.degree. (arrow 218) and has a square shank 219 receivable in the square cavity 220 of the post 202 once rotation through 90.degree. has been completed. In this
case, no cage need be provided between the post 202 and the key.
According to the invention, the introduction of this fixing key makes possible a dynamic connection between the vehicle guardrail and the supporting tube. The lower end of the key being of adequate dimensions, it permits providing a connection
which can yield under the impact of a vehicle colliding with the vehicle guardrail.
According to the invention, fixing may also be effected by a sleeve surrounding the vehicle guardrail at least partly, and may at the same time act as a clip between two lengths of vehicle guardrail (see FIG. 10).
In FIG. 11, I have shown this modification of the means for supporting a pair of guardrails 301 which are brought together contiguously at 302 and form sockets fitting over a connecting tongue 303 shown in broken lines within the guardrail. The
support here comprises an upwardly open U-shaped clip 304 whose profiled grips to the profile of the corrugated guardrails and which is slipped over both of them to grip the guardrails resiliently. The clip is mounted upon a shank 305 which may be
received in a post as described in connection with the posts 3 and shanks 110a -110c, the post 301 and its shank 206 or the post 302 and the shank 219. Of course, this clip may be a sleeve which completely surrounds the guardrail and maybe replace the
rivets previously described as holding the guardrail onto the tongue or insert 303.
The nonprofiled lower portion of the fixing key may also be bent over in the manner of an angle bracket, thus moving the guardrail proper away from the foot of the supporting post. This precaution eliminates the risk of catching on the
supporting post and the danger of slewing which may result therefrom.
This arrangement is shown in FIG. 10 wherein the key 307 has an upright plate portion 309 connected to a shank 306 of angular configuration. The shank includes an upright lower portion 306' which is received within a sleeve such as that shown at
201 and has a bayonet coupling engaging the shank 306 (see FIG. 9). A horizontal portion 306" of the shank extends at right angles to the lower portion 306' and terminates in a short stretch 306"', extending upwardly and serving to support the blade
309.
Another modification according to the invention consists in using instead of keys which have to engage in the vehicle guardrail and instead of clips adapted to engage thereabout, the securing straps which are shown in FIG. 8 and with which the
supports may be provided. These straps are capable of carrying either a vehicle guardrail which is in the form of a single suitable profiled strip or a laminated vehicle guardrail which is in the form of a plurality of sheet metal members suitably
profiled and freely superposed. A vehicle guardrail of this kind may not comprise any perforation at all, so that only the straps are fixed to the supports. Therefore, the possibility of progressive reaction of free deformation forces inherent in the
vehicle guardrail according to the invention is completely guaranteed, when the guardrail has to damp the sudden shock resulting from a collision.
More specifically, I have shown in FIG. 8 an arrangement in which a post 310 is anchored in the ground 311 and carries a lower strap 312 which is bolted to the post 310 at 313. The flange 312' of the strap overhangs a vertical flange 314, 315 of
the guardrail 316 which is here shown to be composed of two sheet-metal members 317 and 318, respectively. As has been described in connection with FIGS. 1-5 and 9-11, the guardrail may be bent back on itself (dot-dash lines in FIG. 8) so that a similar
strap 312 may be provided on the opposite side of the post to hold the laminate guardrail in place. However, it is also possible to provide a further strap 319 at the upper end of each post to engage flanges 320 and 321 of a guiderail arrangement in
which the laminated or superimposed members lie only on one side of the post. As can be seen in solid lines in FIG. 8, the outermost sheet-metal member may be formed with longitudinally extending bulges of semicylindrical configuration with a radius of
curvature which is less than that of the registering bulges of the underlying sheet-metal member so that the bulges of the outmost member must first yield under the impact of the vehicle, thereby dissipating the kinetic energy of the latter, before the
bulges of the inner sheet-metal member are deformed. The assembly thus functions substantially as a laminated leaf-spring in taking up the shock of the vehicle.
In FIG. 7, I have shown an arrangement in which the hollow 325 of the guardrail is filled with a rubber cushion 326 while the chamber 327 between the members 328 and 329 is filled with air and is welded closed at the bottom via seams 330 and 331. In this case, the double-walled arrangement has the inner and outer members bonded together. In the modification of FIG. 6, the hollow 325 is empty but the chamber 327 is filled with sand. The guardrails of FIGS. 6- 8 may be supported with
correspondingly profiled keys as previously described and as preferred, or may receive simple bars such as that shown at 310 to mount the guardrails on respective posts.
The advantage of the new type of vehicle guardrail is not limited only to its new design, but also concerns its simple and rapid erection, which requires only a minimum of labor and working time at the site, and also the extremely easy and rapid
repair which is possible in the case of damage. Since the positioning of the supports is not strictly limited to the presence of perforations in the vehicle guardrail, the supports can be situated at any desired point on the vehicle guardrail.
Although, owing to the great length provided, the supports may be spaced further apart than is customary, without any disadvantage, it is also possible where necessary, for example at very dangerous places and at bends having a very small radius of
curvature, to increase the number of supports easily without any special prior arrangements having to be made.
The vehicle guardrails are normally constituted by a single strip of greater thickness, this thickness, however, being less than 3 mm.
Another possible constructional form of vehicle guardrail, according to the invention as already described, comprises two or more thin sheets superposed on one another. These sheets are constituted for example of covered-steel sheeting, or
sheets which are superposed without being in one piece. The object of this modification which gives a laminated structure being the substitution of a plurality of thin sheets for a single sheet, the total thickness of the vehicle guardrail can remain
substantially the same.
The vehicle guardrail in the form of a hollow casing may be downwardly opened (FIGS. 6 and 7); however, it will advantageously be closed (FIG. 9), since the closed structure has a lesser tendency to belly out in the event of a collision.
The material normally used for the production of vehicle guardrails according to the present invention is galvanized sheeting. It will be apparent from the foregoing that the vehicle guardrails are to be more or less elastic, since the encounter
of a vehicle with a rigid obstacle would compress the vehicle against the obstacle. The conditions for adequate elasticity are fulfilled by galvanized sheeting of a thickness less than 3 mm. However, in order to improve the aforesaid advantageous
effect still further, it may be found useful to produce the vehicle guardrails from strips made of low-alloy high-strength steel. The high elastic limit and the incomparable resistance of these steels to atmospheric corrosion make them an apt choice for
the use in question. Furthermore, the dark brown color of the patina which forms matches the countryside in a very harmonious manner, thus improving the aesthetic appearance of the vehicle guardrails, which is not satisfactory in the case of painted
galvanized sheets. High-strength steels notably reduce the danger of bellying and guarantee even greater safety. In fact, the formation of bellying in a vehicle guardrail between two supports when a collision occurs could cause the vehicle to be thrown
back towards the road rather than achieving a progressive dissipation of kinetic energy along the vehicle guardrail.
It is also known that vehicle guardrails placed in the immediate vicinity of the carriageway give the driver a guide as to changes of road direction. In order to enhance this effect, the central portion of the vehicle guardrails intended for a
winding section of road is provided when shaped on the profiling machine with regularly spaced projections 230 (FIG. 9). Before or after assembly, these projections are painted with a phosphorescent paint. In this way the vehicle guardrails, especially
those made of a steel capable of forming a patina, which are not painted and whose dark brown color merges easily with that of the natural surroundings, not only acts as mechanical protections but also fulfill the function of a visual guide.
* * * * *
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