IE85561B1 - Parapet - Google Patents

Abstract

ABSTRACT In one aspect the invention relates to a parapet upright (14) of a fabricated metal construction, having a base plate (16) and an upstanding column (22) for supporting one or more rails (l l,l2,13) off a front face (15) of the column. The upright includes an L-shaped gusset (26) having a substantially horizontal arm (28) welded to the base plate and a substantially vertical arm (30) welded to the front face. The vertical arm of the gusset extends less than 100 mm above the base plate. In another aspect a parapet rail support system includes a clamp bar (54) and a cleat (56). The cleat is formed of a length of metal of uniform cross section including a front face (70a, 70b) provided with a recess (72) for receiving the clamp bar, and a back face (68). The metal cross section has a single web (74) of metal having a thickness between the back face and the recess. Fastener means (58) secure the cleat and clamp bar to the rail.

Description

PARAPET The present invention relates to a parapet. In particular, the present invention relates to a parapet upright of a fabricated metal construction and to a parapet rail support system.

Parapets are used, for example, on bridges as a safety barrier to prevent vehicles from crashing over the‘ edge. A parapet will normally include at least one, and usually two or more, horizontal rails supported by uprights ~ spaced at intervals along an edge of the bridge. The parapet uprights are fixed to the bridge using a suitable anchorage arrangement. The rails are supported off the uprightshusing a support system, details of which will be described in more detail hereafter. .

;In Europe, parapets are designed to meet European standards, which require crash testing. In the standard tests, a length of parapet is constructed on a ground base, and an unmanned vehicle is propelled towards and into-the parapet. The spacing of the uprights is such that when a large vehicle strikes the parapet, two or more uprights absorb the force of the impact. In the tests, the parapet has to be strong enough to prevent the large vehicle from breaking through. However, when a small vehicle strikes the parapet, it only impacts directly on one upright. Ifythe upright is too strong, the entire parapet will be too rigid, increasing the severity of the impact. This means that the uprights must be designed to break so as to allow flexing of the rails, but without the rails breaking.

It is a further requirement that the upright breaks, "rather than tearing out the anchorage, which would damage the fabric (e.g. concrete) of the bridge.

Therefore, the upright is designed to fracture at 2 position above the anchorage.

Even with systems that meet the European standards, there can be fiirtlier problems arising from the design of the uprights and rail support systems.

Firstly, to provide the required strength of the parapet support,‘ the upright has a substantial depth (i.e. front to back distance) at its base, but tapers H along its height above the base. However, in many cases this is not sufficient to provide the required strength of the upright. Increased strength is. . provided in a short parallel sectionextending upwards from the base below the tapered section. As well as increasing the amount, and therefore the weight, of metal used in the parapet upright, a further problem arises because ~ the upright tends to fracture at or above the parallel section. This means that after a vehicle has struck the parapet and broken an upright, there remains an upstanding section of metal, which may have a jagged or sharp edge where the upright has fractured. This upstanding section is a hazard because it may cause damage to the vehicle especially if it penetrates the vehicle body.

‘The second problem with known systems that meet-the standard occurs when the upright is not sufficiently rigid. If the fle'xing..,of the parapet, when struck. by a vehicle, is sufficient for one or two wheels of the vehicle to pass beyond the edge of the bridge, then the vehicle starts to roll; The rolling of the vehicle greatly increases the amount of damage -that it receives from the parapet structure. This problem is not apparent from the standard tests, which are performed with the parapet at ground level.

Another problem arises with known rail-support systems. In these systems, a clear arrangement is used to secure the rail to the upright. The cleat arrangement is relatively rigid, so that when a vehicle strikes the rails, a significant shear force is applied through the rail. This can cause the rails to fracture at the cleat position, thereby reducing the’ effectiveness of the parapet, and increasing the chances of a damaged rail penetrating the vehicle body. ' It is an object of the present invention to provide a parapet that substantially alleviates the aforementioned, problems.

According to the present invention there is provided a parapet upright of a fabricated metal construction, having a base plate and an upstanding column for supporting one or more rai-ls off a front face of the column, wherein the » upright includes an L-shaped gusset having a substantially horizontal arm welded to the base plate and a substantially vertical arm welded to the front face, and wherein the vertical arm of the gusset extends less than 100 mm above the base plate.

It is an advantage that the L-shaped gusset intzwases the strength of the upright, but that after the upright has fractured, the portionthat remains attached to the rails is rigid enough to prevent the parapet from flexing too far (but not-so rigid that the parapet does not flex far enough). The flexing of the parapet is related to time. The weaker the upright, the quicker it A breaks and more deflection of the parapet occurs because there has not been enough time for the direction of travel of the vehicle to be re-directed, and for energy to be transmitted through the parapet into the bridge. The stronger the upright, the slower it breaks, and less deflection occurs. The vehicle is redirected quicker due to a stiffer parapet and more energy is transmitted into the bridge. There is a balance to be found in obtaining the correct strength to accommodate flexibility for a light vehicle and rigidity for re-directing a heavy vehicle. - Embodiments of the present invention have the advantage of providing the balance between flexibility on the one hand, and rigidity on the other. This means that in an impact, the vehicle’s wheels will not pass beyond the edge of the bridge", reducing the likelihood of the vehicle rolling as it strikes the parapet. Furthermore, although the gusset significantly increases the ' strength of the parapet upright, the upright will fracture at a position close to the base. The fractured metal remaining fixed to the bridge does not stand up far above the ground, and so presents less_of a danger to a vehicle or its occupants, than other known uprights.

It will be appreciated that the exact dimensions of the gusset, in particular the lengths of the vertical and horizontal arms, are a matter for design optimisation. All four of the gusset dimensions: height of the vertical arm, length of the horizontal arm, thickness of metal, and width have an effect on strength of the upright. Nevertheless, in a preferred embodiment, the gusset has a vertical arm that extends less than 80 mm, but morethan 40 mm above the base. Preferably, the gusset has a hor'izontal-sarmathat is less than 50 long. The thickness of the metal is preferably in the range 8mm to 12mm. In an exemplary embodiment, the thickness of the gusset metal is 10mm, the vertical arm is co m long and the horizontal arm is 30. mm long.

Fr-fierably, the gusset has a wifth that is slightly less than a width ofthe front face of tha; column.

. Preferably, the vertical and horizontal arms of the gusset meet at a corner, which is provided with a chamfered edge to allow for a weld fillet between the column and the base to pass underneath the gusset. in a preferred’ embodiment, the base plate and column are welded to each other along a weld line. Preferably, the upright is tapered‘ from a point above and adjacent the weld line towards the top of the column. More . preferably, thetapered column has an inclined back face and a substantially vertical front face.

Preferably, the taper starts at a distance above the base plate that allows for a weld fillet between the column and the base plate. Typically, the short- distance is about 30 mm.

Embodiments of the invention may include a parapet rail support clear formed of a length of metal of uniform cross section including a front face provided with arecess for receiving a clamp bar, and a back face, wherein the metal cross section comprises a single web of metal having a thickness between -the back face and the recess, and wherein one or more holes is provided through the web for fasteners to secure the chest to the rail and to an upright. , It is an advantage that the cleat may be manufactured from a length of extruded metal section, and, because the cleat cross section has only a single - the fastener holes may be formed in a single punching operation Embodiments of the invention may include features of a parapet rail support system comprising a clamp bar and a cleat, wherein the cleat is formed of a length of metal of uniform cross section including a front face provided with a recess for receiving the clamp bar, and a back face, the metal cross section comprising a single web ofmetai having a thickness between the back face and the recess, and fastener means for securing the cleat and clamp bar to the rail, wherein the cleat extends along the rail a first distance from the , upright.

Preferably, the cleat is welded to the upright. Alternatively, the cleat may be secured to the upright with a fastening’ means. The fastening means may be one or more bolts.

The clamp bar may extend along the -rail a second distance from the upright.

The second distance may be greater than the tits! distance.

It is an advantage that, because the cleats are formed of a metal cross section having a single thickness web, the cleat is able to bend when the rail is subjected to an impact. The bending of the cleat reduces the shear force on . the rail and reduces the likelihood of a rail fracture. Similarly, because the ends of the cleat and the clamp bar are at different distances from the upright, the shear forces ‘through the rail caused by an impact occur at two different positions, further reducing the likelihood of a rail fracture.

In preferred embodiments, any or all of the upright, the rails, the cleat and the clamp bar is aluminium.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 14 is a vertical _cross—section through a parapet; Figure 2 is a horizontal section through an upright of the parapet of Figure 1; Figure 3 is adetailed view of part of the parapet of Figure 1; Figure 4a depicts a known parapet upright design, showing a typical fracture location; Figure 4b depicts the parapet upright of Figure 1, showing a typical fracture location; Figure 5 is a- plan view of a parapet rail support system; Figure 6 is a view oi‘ the rail support system of Figure 5, from beitiud an upright; and Figure’? is sectional view through the parapet rail in the direction of arrows B-B of Figure'6. of Figure 4.

Referring to Figures 1 and 2, three rails 11, 12, 13 of a parapet are _supported by an upright 14. off a front face 15. Each of the rails 11, 12, 13 extend from the front face 15 of the upright to _a respective traffic face 11a, 12a, 133, which would be the first point of contact with a vehicle impacting the parapet.

The upright l4'has a base plate 16, which is anchored by an anchorage system 18 to a concrete beam 20 that forms an edge of a bridge, or raised roadway. The anchorage system 18 includes four anchor bolts 19a-19d. The upright 14 has a column 22 extending upwards from the base plate 16. The base plate 1.6 and the column 22 are welded to each other along a weld line « 24. As shown in Figure 2, the column 22 is a hollow box section. The column 22 is tapered along its height from a point 23 just above the weld line 24. The point 23 is’ typically about 20mm, and preferably no more than mm above the base plate 16.

The upright 14 also includes an L-shaped gusset 26, which is welded to both the base plate 16 and the column 22 at a lower end of the front face 15.

Referring to Figure 3, the gusset 26 has a horizontal arm 28 and a vertical arm 30. ‘The gusset 26 also has a chamferred corner so that it can be positioned between the base plate 16 and the column 22 without interference from the weld line 24. As shown in Figure 2, the gusset 26 is slightly narrower than the width of the front face 15 of the column 22.

The dimensions of the gusset 26 are selected to provide a required strength of the upright 14. In known designs various attempts have been made to provide an upright having the required strength to resist an impact, but which. once fractured, allows the right amount of flexibility- in the parapet.

In many cases, the strengthening of tfoeupright results in too much rigidity in the parapet so that the parapet will not meet the crash test standards for flexibility. In other cases, after fracture of the upright, the parapet flexes so far that the wheels of the vehicle will pass over the edge of the bridge, causing the aforenientioned problems of rolling. It has been found that, by selecting the correct dimensions of the gusset 26, the upright will be strong enough to meet the "crash test standards; after fracture, the parapet will flex far enough to -meet the standards, but not so far that the vehicle will cross the edge of the bridge._' Another problem with known upright" designs is shown with reference to‘ Figure 4a. A known upright 40, is strengthened near its base by providing a short‘ parallel section 42 below a tapered section 44. Although this may provide the required strength and flexibility for the parapet to meet the standards, the upright fractures above the parallel section 42, as shown by the _ broken line 46. The result is that; after fracture. a substantial portion of the upright 40 below the broken line 46 remains anchored. to the bridge. .

Moreover, the upright will not usually fracture with a clean break, but will leave a sharp, jagged edge that could cause further damage to the vehicle, or even penetrate the vehicle body.

In contrast, the upright 14 of the present invention is shown in Figure 4b.

The provision of the gusset 26 not only provides the required strengthening and flexibility of the upright 14, but ensures that, when the upright fractures, it does so much closer to the base plate 16. In fact, it has been found that the upright tends to fracture at just above or along the weld line 24, as shown by the broken line 48. This means that, after fracture, the .h.igi~est point of the upright that remains anchored to the bridge is the top of the vertical arm 30 of the gusset 26.

As stated above, the dimensions of the gusset 26 depend on the particular strength requiretnents for the upright. However, it has been found that a gusset having a metal section thickness of 10mm, a 30mm long horizontal arm and a 60mm long vertical arm, is suitable to meet the standards for many vehicle bridge parapet designs. It is clearly desirable for the vertical arm to be as low as possible so that the upright will fracture at a low position. For - this reason it is not envisaged that the gusset height would exceed 100mm.

Referring to Figure 5. 6 and 7 , an arrangement for supporting and securing a rail 50 to an upright 52_includes a clamp bar 54, a cleat 56 and four bolts 58a-cl, secured with associated nuts 6_0a-cl. As can be seen in Figure 7, the rail 50 is formed of an extruded metal section, which includes opposing channel portions 60a, 60b. The charmel portions 60a, 60b are proportioned to siide over upper and lower flange portions 62a, 62b on the clamp bar 54.

The clamp bar 54 has a central portion 64 between the upper and lower flange portions. Four holes 66a-d at spaced apart locations through the clamp bar 54 receive the bolts 58a-d.

Also shown in Figure 7, the cleat 56 has a cross-section with a flat rear face 68 and upper and lower front faces 70a, 70b. ’A recess 72 between the upper and lower front faces 70a, 70b receives the central portion 64 of the clamp bar. The cross-section of the cieat is ‘such that there is a single web 74 of metal between the back face 68 and the recess 72. Four slot-holes 76a—d are rm-vided through the web 74. spaced. for alignment with the holes S6a—tl in the clamp bar. The four slot-holes 7_6a-d receive the bolts 58a~d for securing the clamp bar 54 to the clear 56, but allowing for slight variations in vertical alignment where the parapet is on a slope. The clear 56 is shown welded to _ the upright 52 along. a weld-line 78 on the rear face 68. However. in some cases the clear 56 may be secured to the upright 52 using bolts or other suitable fasteners.

As can be seen in Figures 5 and 6, the cleat 56 extends a first -distance on either side of the upright_52. The clamp ‘bar 54 extends a further, second distance beyond the ends of the clear 56.

There are two reasons for this configuration of the cleat 56. Firstly, the provision of a single web 74 means that the-manufacturing operation is greatly simplified when compared with other lcnown cleats. In particular the holes 76a-d can be formed in a single punching operation. Other known ‘ cleats have a more complex cross-section which. involves punching or drilling holes through more than one thickness of metal. Secondly, the single weh section 74 is not as stiff as other known clear sections. This, together with the different lengths of the cleat $4 and clamp bar 56, greatly reduces the likelihood of a rail 50 fracturing during an impact. The different lengths mean that there are two different locations at which shear forces resulting from the impact are transmitted through the rail 50. The lower stiffness means that the cleat 56 may bend under the impact loading, thereby i absorbing more of the impact force and reducing the shear force through the rail 50.

Claims (14)

Claims

1. A parapet upright of a fabricated metal construction, having a base plate and an upstanding column for supporting one or more rails off a front face of the column. wherein the upright includes an L’-shaped gusset having a substantially horizontal arm welded to the base plate and a substantially vertical arm welded to the front face, and wherein the vertical arm of the gusset extends less than 100 mm above the base plate. '

2. A parapet upright “according to claim 1. wherein the gusset has a vertical arm that extends less than 80 mm. but more than 40 mm above the base.

3. A parapet upright according to claim 2, wherein the gusset has a horizontal arm that is less than 50 mm long.

4. A parapet upright according to any preceding‘ claim, wherein the thickness of the metal is in the range Bmrn to izmm.

5. A parapetlupright accordingto‘ any preceding claim, wherein the gusset has a width that is slightly less than a width of the front face of the column.

6. A parapet upright according to any preceding claim, wherein the vertical and horizontal arms of the gusset meet at a corner, which is provided with a chamfered edge to allow fora weld fillet between the column and the base to pass underneath the gusset.

7. A parapet upright according to any preceding claim wherein the base plate and column are welded to each other along a weld line. 13

8. A parapet upright according to claim 7, wherein the upright is tapered from a point above and adjacent the weld line towards the top of the column.

9. A parapet upright according to claim 7. wherein the tapered upright has an inclined back face and a substantially vertical front face.

10. A parapet upright according to claim 8 or claim 9. wherein the taper ’ starts at a distance above the base plate that allows for a weld fillet between the column and the "base plate.

11. A parapet upright according to claim 9. wherein the distance is about 30 mm.

12. A parapet comprising a pluralltyof uprightsaccordingi to any one of the preceding claims and one or more rails supported from the uprights.

~ 13. A parapet upright according to any of claims 1 to 11, or a parapet ‘according to claim 12, wherein any or -all of the upright and rails is formed of aluminium.

14. A parapet upright or a parapet substantially as hereinbefore described with reference to the accompanying drawings in