Patent Publication Number: US-2007116513-A1

Title: Road safety barrier

Description:
This application is a divisional of application Ser. No. 11/404,161, filed Apr. 13, 2006, which claims priority to an earlier filed Great Britain Patent Application No. 0507767.2, filed Apr. 18, 2005, entitled “Road Safety Barrier”, by inventor Steven Bowyer., all of which are incorporated herein by reference. 
    
    
      The invention relates to road safety barriers and in particular but not exclusively to road safety barriers of the ‘W’ profile ‘post and beam’ type.  
      One known road safety barrier comprises a series of ‘W’ profile beam sections that are joined together at overlapping ends. The beams are supported above the ground by posts positioned along the length of the barrier. The design criteria for a given length of safety barrier with respect to impact resistance and flexibility on impact are determined according to the road conditions. For example, the safety barrier of a central reservation between roads carrying vehicles travelling in opposite directions may be designed to offer a relatively high resistance with lower flexing on impact in order to ensure errant vehicles are deflected back into their direction of travel. On the other hand, a more flexible barrier may be desirable in other circumstances, not least because it may be simpler and less expensive to install.  
      The impact response, particularly with respect to flexibility, of a safety barrier of this type is governed to a significant extent by the length of beam sections and number of posts per section. Essentially, since the beam sections are manufactured in standard lengths, the more posts supporting each section, the more resistant the barrier is to flexing on impact. In these ‘post and beam’ prior art road safety barriers, the posts are invariably positioned at the same locations relative to each beam section. That is to say, for any given length of barrier, the posts are positioned at points which are the same distance from the position where beam sections overlap. In another configuration, representing a barrier more resistant to flexing on impact, two posts per section may be adopted, positioned at the same location relative to the section supported by them from one beam section to the next.  
      Installation of these ‘post and beam’ road safety barriers requires careful planning in order that the lengths of beam sections and number of posts carried to the site are appropriate to meet the impact design criteria for the section of safety fence under construction. This is limiting in cases where the crash characteristics of the barrier may be redesigned or varied during the installation programme. The fixed post-beam relationship for the length of the barrier also makes it difficult to construct a barrier that has an impact flexibility that varies along its length to provide for changing road conditions. For example, it may be necessary to construct a stretch of barrier alongside a bridge buttress having a different flexing characteristic from the sections of barrier farther away. In this case, different post positions will be required. A further limitation arises if the design criteria require a gradual or even a stepped change in barrier flexibility over a given stretch of road.  
      For example, a known barrier comprises a series of beam standard length sections of 3.2 m, with posts spaced either at intervals of 1.6 m or 3.2 m. In the first case, each post is positioned 0.8 m from the central point of overlap of sections or, for a less flexible barrier in the second case, an additional post is provided midway between the posts of the first case so that there are two posts supporting each section. The beam is provided with means for facilitating attachment of posts at each of these positions. The posts may be fixed to the beam section by means of bolts passing through slots or holes in the section. However, the problem is that as the slots or holes are formed during the manufacture of the beam section, the ability to add additional ones to a given beam section on site in order to provide a stiffer section of barrier is limited. It is therefore not possible to construct a barrier with flexibility characteristics that differ from either the 1.6 m-spacing barrier, or the 3.2 m spacing barrier.  
      It is an aim of the present invention to provide a road safety barrier that alleviates the aforementioned problems and limitations.  
      According to the present invention, there is provided a road safety barrier comprising a series of beam sections together forming a length of barrier and supported above the ground by way of posts, wherein the positions of successive posts along at least part of the length of the barrier shift relative to the centres of the beam sections.  
      In a preferred embodiment, the shift may be progressive but uniform along a section thereof so that the flexibility of the barrier is substantially constant. A change in the degree of shift from one post to the next can provide for a change in the flexibility of the barrier from one section thereof to another. The ability to shift the post positions along the length of the barrier allows the designer to tailor or vary the flexibility of the barrier along a predetermined length thereof using beam sections of substantially equal length. This allows greater flexibility in the use of standard length beam sections by simplifying installation time and costs. Furthermore, since the design criteria are determined by the performance classes of the relevant national or international standards (e.g. European Standard EN1317 Part 2), it is advantageous to have a system in which the flexibility/stiffness of the barrier can be altered according to the constraints of those official standards, whilst keeping the installation time and costs to a minimum. For example, a crash test scenario could involve use of a barrier having a post spacing that progressively changes along its length and so has a crash characteristic (i.e. stiffness) which progressively changes. This makes it easier to determine whether a given post spacing/barrier stiffness meets a performance class.  
      Fixing means are provided on the beam sections to facilitate fixing of the posts to the beam. In accordance with a preferred embodiment, these are provided at more than two but preferably more than five locations advantageously equi-spaced along the longitudinal axis of the beam. The provision of a greater number of fixing means permits shifting of posts from one to the next by smaller increments. This makes it easier to install a barrier which meets a given performance class using beam sections of the same length.  
      The advantage arising from the present invention is that by increasing the number of fixing means along the length of the beam section, the options for varying the positional relationship between adjacent posts increases. It is no longer necessary to position posts symmetrically with respect to the beam sections. Shifting the locations of the posts along the length of the barrier by an increasing or decreasing amount has the effect of increasing or decreasing the strength of the barrier so that different road conditions can be accommodated even though beam sections of constant length are used to construct the barrier. A stretch of barrier of constant strength along its length is established by locating the posts at an even spacing relative to one another, but the design options in terms of the absolute strength of the barrier for a given beam section length are increased.  
      According to the present invention, there is further provided a method of constructing a road safety barrier which at least in part comprises a series of beam sections of substantially equal length supported above the ground by posts, the method comprising shifting the locations of the posts relative to the centres of the beam sections from one beam section to the next.  
      This method is particularly advantageous as it allows the strength/flexibility of the barrier to be varied in accordance with the obstacles or features such as bridge buttresses that are situated along the length of the barrier as the barrier is constructed using a standard uniform length than necessary in the prior art method of construction.  
      Advantageously, the number of posts required that will allow the barrier to conform to the necessary safety criteria can be kept to a minimum, thereby minimising the cost of the barrier itself, and the associated installation and maintenance costs.  
      In some embodiments of the invention, the separation between adjacent posts may be such that some beam sections are not directly supported by posts, but are instead supported by the beams (and their supporting posts) to which they are joined at either end.  
      According to the present invention, there is further provided a method of testing a crash barrier system, the system comprising a series of beam sections together forming a length of barrier and supported above the ground by way of posts, wherein the positions of successive posts along at least part of the length of the barrier shift relative to the centres of the beam sections such that the stiffness of the barrier varies along the length, the method comprising conducting road crash tests at differing points along the length and determining whether the results of said crash tests satisfy predetermined criteria. 
    
    
      An embodiment of the invention will now be described by way of example with reference to the following drawings, in which:  
       FIG. 1  depicts a length of road safety barrier constructed in accordance with the prior art;  
       FIG. 2   a  shows a beam section which may be used to form part of the barrier according to the invention;  
       FIG. 2   b  is a cross-sectional view of the beam section of  FIG. 2 ;  
       FIG. 3  is a cross-sectional view of a ‘Z’ section post which may be used to support the barrier according to the invention; and  
       FIGS. 4-7  are simplified representations of barriers according to exemplary embodiments of the invention. 
    
    
       FIG. 1  illustrates a prior art ‘post and beam’ type road safety barrier  1  constructed from beam sections  2   a  to  2   d  of length ‘L’ supported above the ground by a series of posts  3   a  to  3   g . The beam sections  2   a  to  2   d  are joined and secured together by bolts (not shown) passing through apertures  4   a  to  4   c  and/or  7   a  to  7   d  provided at overlapping ends of adjacent beam sections such that the distance between the centres of adjacent beam sections is ‘C’. Apertures  5   a  to  5   c  and  6   a  to  6   c  are provided along the longitudinal axis of each beam section to provide a fixing location for a supporting post. In this example, the posts  3   a  and  3   b  are fixed to apertures  5   a  and  5   b  respectively by bolts (not shown) and the same corresponding positions for the other beams along the length of the barrier  1 . The posts are spaced by a distance ‘d’ inwardly with respect to the centre of respective overlapping ends. It is apparent from  FIG. 1  that the prior art barrier is supported by posts that are in a fixed positional relationship with reference to the centres of the beam sections.  
       FIG. 2   a  shows a beam section  10  which may be used in accordance with one embodiment of the present invention. As illustrated in  FIG. 2   b , the beam section  10  has a ‘W’ profile. The section  10  is provided with a series of fixing means in the form of slots indicated in  FIG. 2   a  by ‘Slots A 1 , A 2 , A 3 ; Slots B 1 , B 2 , B 3 , B 4 ; and Slots C 1  and C 2 ’. Slots A 1 , A 2  and A 3  correspond to apertures  4   a ,  4   b  and  5   b  of  FIG. 1 , slots A 1  and A 3  providing for bolts to secure adjacent beam sections with an optional post. Slots C 1  and C 2  correspond to apertures  3   a  and  3   b  of  FIG. 1  and provide fixing locations for posts. However, in contrast to  FIG. 1 , the beam section  10  is provided with additional fixing means Slot B 1 , B 2 , B 3  and B 4  as shown substantially equi-spaced in relation to the others. These additional slots, although as would be apparent to the skilled man in the art that an alternative form of post fixing means may be adopted, provide fixing locations which allows the post locations to be shifted along the length of the barrier. Still further slots or fixing means may be provided in the beam section thereby allowing the posts to shift in relation to the beam sections by smaller increments along the length thereof.  
       FIG. 3  is an example of a ‘Z’ section post  3   a  which may be used in embodiments of the invention, showing additionally the orientation thereof in relation to the direction of traffic flow when installed.  
       FIG. 4  shows elevational and plan views of a longer section of road safety barrier  20  in order to illustrate the shift of posts relative to the centres of the beam sections as the barrier advances from one direction to the other. In this example, the barrier is constructed from beam sections  22   a ,  22   b ,  22   c  etc. which are of substantially equal length (3.2 m) and supported by posts  24   a ,  24   b ,  24   c  etc. which, although they are equally spaced apart (2 m), are staggered relative to the centres or ends of the beam sections. In other words, in this example, the spacing of the posts is such that although post  24   g  is fixed at the overlapping portions of adjacent beam sections  22   d  and  22   e  respectively, the next recurrence of coincidence between a post and beam section overlap occurs five beam section lengths away in either direction. The frequency of coincidence is therefore a function of the average number of posts supporting each beam section, i.e. 1.6 (8 posts divided by 5 beam sections) and so a function of the strength or flexibility of the barrier. Clearly, the closer the post spacing for a given beam section length, the stronger the barrier because, on average, each beam section is supported by more posts. However, from the constructional standpoint, it is clear that the flexibility or strength of the barrier can be simply varied by varying the post spacing in a progressive manner along the length thereof. Should it be desired to install a stronger section of barrier to shield a bridge buttress for example, the contractor simply has to bring the spacing of the posts closer together for that section. The advantage with the barrier embodying the present invention is that he may do so using standard beam sections. It is also possible for a designer/contractor to change the strength of a barrier after initial installation by shifting the posts without need to change the beam sections as well.  
       FIGS. 5-7  show three alternative embodiments. In  FIG. 5 , there are 4 posts supporting 3 beam sections—a ratio of 1.33 posts per section. In  FIG. 6 , the barrier is more flexible because there are fewer posts per beam section on average, namely 8 posts supporting 9 beam lengths. In  FIG. 7 , 4 posts support 5 beam sections so that every 5 beam lengths (or ‘repeat’), one beam is supported only by its adjacent beams.  
      Examples of the ratio, for a given length of barrier, of the distance between adjacent posts to the beam section length may include any one of: 0.5; 0.625; 0.75; 0.875; 1.0; 1.125; and 1.25 although the more flexibility there is for locating posts along a beam section, the more finely graded the shifting of the posts may be.  
      Although the aforementioned examples show equal post spacing, the degree of shift may increase or decrease along the length of the barrier to facilitate a graded change in flexibility.