Abstract:
An expansion joint for a parking structure includes first and second rails for mounting on adjacent slabs at opposite sides of a gap therebetween and a cover plate that overlies the rails and covers the gap while permitting relative movement between the slabs. A series of turnbars are pivotally coupled to the underside of the cover plate using ball and socket joints so that lateral loads imposed on the cover plate are transmitted directly into the turnbars, minimizing the risk of shear failure between the cover plate and the turnbars. At the same time, the ball and socket joints allow the cover plate and turnbars to tip with respect to one another. The turnbars have spherical end portions that are received in complimentary channels in the respective rails so that the turnbars maintain the cover plate centered over the gap.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to expansion joints for structures that carry vehicular traffic. The invention has been devised primarily in the environment of parking structures but may find application in other similar structures, for example, bridges.  
         BACKGROUND OF THE INVENTION  
         [0002]    Parking structures typically are constructed using reinforced concrete slabs to provide a traffic surface. The individual slabs are sized and spaced from one another to allow for relative movement between the slabs, in particular to accommodate expansion and contraction due to temperature changes. In some geographic areas, it is also necessary to accommodate relative movement caused by seismic events.  
           [0003]    Expansion joints are used to cover the gaps between the slabs and prevent infiltration of moisture and debris. In a parking structure, the expansion joints must also be designed to withstand repeated cyclical movement caused by vehicles travelling over the joints. An expansion joint in a high-traffic area such as an entrance or exit ramp must be designed to withstand millions of cycles over its lifetime.  
           [0004]    Another criterion is the ability to withstand lateral shear forces as vehicles move over the joints, and in particular lateral forces imposed on the joints when vehicles brake and/or accelerate with their wheels on the expansion joint.  
           [0005]    In an effort to address these criteria, many different expansion joint designs have evolved, ranging from elastomeric seals that attempt to fill the gap, to cover plates that extend over and cover the gap. Typically, a cover plate is located in shallow recesses that are formed in the respective slabs on opposite sides of the gap so that the top surface of the cover plate is generally flush with the top surfaces of the slabs. The cover plate overlies a pair of rails that are bolted to the slabs in the respective recesses. A trough or water stop is provided in the gap below the cover plate to catch any moisture that might penetrate between the cover plate and the rails.  
           [0006]    The cover plate is self-centering with respect to the gap by virtue of a series of turnbars that are pivotally coupled to the underside of the plate and engaged at their ends in slots that extend longitudinally of the rails. As the slabs move with respect to one another, changing the width of the gap, the turnbars angle more or less acutely with respect to the walls of the gap, maintaining the cover plate centred.  
           [0007]    A drawback to this type of joint is that it is relatively vulnerable to lateral loadings, for example, when a vehicle brakes or accelerates with its wheels on the cover plate. Pivot pins or bolts coupling the turnbars to the cover plate may bend or even shear off.  
           [0008]    Another weakness of this type of expansion joint is vulnerability to water infiltration around the rails that are mounted on opposing faces of the slabs. Typically, each rail is an extrusion that is bolted in place in a recess in the relevant slab. The extrusion is then “back filled” with elastomeric concrete which bonds to the extrusion and to the slab and is intended to seal out moisture. A difficulty with some expansion joints is that the extrusions have profiles that include undercut areas or “pockets” that can be difficult to fill with elastomeric concrete. Concrete is a highly viscous liquid that is poured into place and allowed to set. The highly viscous nature of the material makes it difficult to ensure that undercut recesses in the extrusion are completely filled. If they are not, the elastomeric concrete may tend to shrink or pull away from the extrusion and/or slab, creating areas for water infiltration.  
         SUMMARY OF THE INVENTION  
         [0009]    An object of the present invention is to provide improvements in expansion joints intended to address at least some of these drawbacks.  
           [0010]    According to one aspect of the invention there is provided an expansion joint for installation across a gap between adjacent slabs of a structure intended to carry vehicular traffic. The joint includes first and second rails for mounting on the respective slabs at opposite sides of the gap and a cover plate dimensioned to overlie the respective rails and cover the gap while permitting relative movement between slabs. A plurality of turnbars are carried by the cover plate and coupled to the respective rails for maintaining the cover plate centered over the gap. Each turnbar has end portions that are coupled to the respective rails for sliding movement longitudinally of the rails in response to relative lateral movement of the slabs. Each turnbar also defines a pivot axis between its ends about which the turnbar turns with respect to the cover plate in response to lateral movement of the slabs. Each turnbar is connected to the cover plate by coupling means that includes socket on one of the turnbar and cover plate and the rotational coupling element on the other. The coupling element and socket are complimentarily shaped to allow turning of the turnbar with respect to the cover plate about the said axis while transferring lateral loads imposed on the cover plate in use directly to the turnbar and into the relevant slab via the rail mounted on the slab.  
           [0011]    Preferably, the coupling between each turnbar and the cover plate is a ball and socket coupling so that the cover plate and turnbar can also tip to some extent with respect to one another. On the other hand, in applications in which tipping is unlikely to occur, the coupling element could, for example, be of cylindrical form. Most importantly, the coupling should provide a solid connection between the cover plate and turnbar so that lateral loads imposed on the cover plate are transferred directly to the turnbar and any propensity for the cover plate to move laterally with respect to the turnbars is minimized.  
           [0012]    Preferably, the end portions of each turnbar are provided by formations that are enlarged with respect to the main, elongate body of the bar that extends between the end portions. The formations preferably are in line with that main body of the bar so that forces imposed on the bar are transmitted directly to the enlarged end portions. The rails in turn preferably define undercut slots that are complimentary to the profile of the enlarged end portions of the bar and that relatively closely accommodate those formations so that there is minimum free play between the bar and the rails. Again, the objective should be to transfer directly to the rails and, from there to the slabs lateral forces that are imposed on the plates and transferred from there to the turnbars. There should be minimal free play between these components.  
           [0013]    Another aspect of the invention relates to the profile shape of the rail of the expansion joint. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]    In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which illustrate a particular preferred embodiment of the invention, and in which:  
         [0015]    [0015]FIG. 1 is a vertical sectional view through an expansion joint in accordance with a preferred embodiment of the invention;  
         [0016]    [0016]FIG. 2 is a vertical sectional view through the cover plate of the expansion joint; and,  
         [0017]    [0017]FIG. 3 is a perspective view of the expansion joint, partly broken away to show internal structure. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       [0018]    Referring first to FIG. 1, an expansion joint is shown generally at  20  installed across a gap “G” between adjacent reinforced concrete slabs “S” of a parking structure. The joint includes first and second rails  22 ,  24  that are mounted in respective recesses or rabbets  26 ,  28  in the two slabs adjacent respectively opposite sides of the gap. A cover plate  30  is dimensioned to overlie the respective rails  22  and  24  and cover the gap G while permitting relative movement between the slabs S. The slabs may move laterally with respect to one another (narrowing or widening the gap G or in the longitudinal direction of the gap) and vertically with respect to one another. Joint  20  must be capable of accommodating all of those movements, including simultaneous lateral and vertical movement.  
         [0019]    Each of the rails  22 ,  24  and the cover plate  30  is an aluminum extrusion of a length appropriate to the length of the gap to be covered. As shown in FIG. 1, the extrusions that define the rails  22 ,  24  are of different cross-sectional shapes. This is for illustrative purposes only; in practice, both rails would normally have the same cross-sectional shape. For reasons that will be explained later, rail  22  is the preferred shape; in FIG. 3 both rails are the same (rail  22 ).  
         [0020]    A plurality of turnbars are carried by the cover plate  30  and are coupled to the respective rails  22 ,  24  for maintaining the cover plate centred over the gap G. Only one of the turnbars is visible in FIG. 1 and is denoted by reference numeral  32 . In FIG. 3, part of the cover plate  30  is broken away to show three typical turnbars  32 . Two of those bars are shown extending partially outwardly from the rails  22 ,  24 , again for illustrative purposes only; the turnbars would never extend outwardly of the rails in normal use of the expansion joint.  
         [0021]    Reverting to FIG. 2, it will be seen that each turnbar has a main elongate body portion  34  with respective formations  36  at its ends, which are enlarged with respect to body  34 . These enlarged end portions are coupled to the respective rails  22 ,  24  for sliding movement longitudinally of the rails in response to lateral movement of the slabs S (to narrow or widen the gap G). Each turnbar also defines a pivot axis A-A between the enlarged end portions  36  about which the turnbar turns with respect to the cover plate  30  during such movement.  
         [0022]    In FIG. 3, the turnbars  32  are shown angled with respect to the rails  22 ,  24 . If the slabs move towards one another, the angular inclination of the turnbars  32  with respect to the rails  22 ,  24  will become more acute as the turnbars pivot about their respective axes A-A. Conversely, if the slabs move apart, the angular inclination of the turnbars will become less acute.  
         [0023]    Each of the turnbars  32  is coupled to the cover plate  30  by a ball and socket coupling  38  which in this case comprises a ball  40  on the turnbar and a socket  42  on the cover plate. As best seen in FIG. 3, the ball is a generally hemispherical formation and the main body  34  has a generally flat plate-like shape. The socket, on the other hand, is formed by respective ribs  44  at the underside of the cover plate that have arcuate surface portions  44   a  corresponding to the curvature of the ball  40 . Because the cover plate  30  is an extrusion, the socket  42  engages the ball  40  only at the sides, i.e. in directions transverse to the length of the gap G. Nevertheless, since the concern is to transfer lateral loads from the cover plate  30  to the turnbars, this form of socket accomplishes the desired objective; it is unnecessary to provide what might be called a “full” socket that encircles the ball (though this certainly could be done in other applications).  
         [0024]    In the illustrated embodiment, the turnbar  32  is coupled to the cover plate  30  for turning about axis A-A (and located longitudinally with respect to the cover plate) by a pivot element in the form of a bolt  46  that extends down through the cover plate and is threaded into a complimentarily threaded bore in the turnbar. The bolt head is shown at  46   a  and is located within a recess in the top surface of the cover plate  30 . A washer  47  is used under the bolt head to allow head-to-cover plate movement. A rivet could be used as an alternative form of pivot element.  
         [0025]    The illustrated design has the advantage that the spacing between the turnbars can be set simply by drilling holes through the cover plate  30  at appropriate locations. For example, in high traffic areas, it might be appropriate to have turnbars that are very closely spaced, while wider spacings might be acceptable for less travelled locations. That advantage would be lost if the ball and socket arrangement were reversed and the ball provided on the cover plate and the socket on the turnbar, though that certainly is a possibility within the broad scope of the invention.  
         [0026]    The formations  36  that define the enlarged end portions of the turnbars preferably are spherical and are located generally in line with the centreline of the main body  34  of the turnbar, again so that lateral loads imposed on the turnbar are transferred directly to the formations  36 . The turnbars are one-piece metal (aluminum) castings, but could be made in more than one piece, of more than one material and not necessarily cast. For example, the formations  36  and ball  40  may be made of separate components and assembled to the main body  34  of the turnbar.  
         [0027]    Each of the rails  22 ,  24  shown in the drawings has a cross-sectional shape that includes a generally circular section undercut channel  48  that extends longitudinally of the inner face of the extrusion, i.e. so that the channels face one another. The channels  48  and formations  36  are sized relatively closely so as to minimize free movement therebetween. Above the “mouth” of each channel is a downwardly directed pointed formation  50  that provides a “drip” point for any moisture that may penetrate below the cover plate. The tip of each drip point  50  is positioned sufficiently inwardly of the inner edge of the respective slab so that any moisture drips into the gap and does not tend to migrate between the rail and the slab. Since the rails are extrusions, the drip edges  50  extend the full length of the gap.  
         [0028]    A water stop or trough  52  is installed in the gap G between opposing faces of the two slabs S. The water stop itself is essentially a conventional elastomeric moulding that is secured to the respective slabs by bolts  54  that are driven into the slabs. Behind the head of each bolt is a retainer element  56  that is continuous along the length of the gap and includes a lip  56   a  that laps over the corner of the slab adjacent the relevant rail.  
         [0029]    Outwardly of the respective channels  48 , the two rails  22 ,  24  have different profiles. Rail  24  has a lower limb  58  that lies on the bottom surface of the rabbet  28  and through which the extrusion is secured to the slab by concrete anchors  60 . An upper limb  62  of the extrusion is angled upwardly and away from channel  48  so that a cavity having a generally C-shaped inner wall  64  is defined above the concrete anchors. This cavity is filled with elastomeric concrete to complete installation of the expansion joint. While the C-shaped configuration of the inner wall of the cavity may be beneficial in that it allows the elastomeric concrete to “key” into the extrusion, there may also be a risk of air pockets developing as the elastomeric concrete is installed. Accordingly, the configuration of rail  22  may be preferred.  
         [0030]    Referring now to rail  22 , it will be seen that the extrusion defines outwardly of channel  48  what is essentially a closed cavity  66  (as seen in cross-section) from which extends outwardly a bottom limb  68  similar to limb  58  of extrusion  24 , and through which the rail  22  is secured to the slab by concrete anchors.  
         [0031]    A face  70  of the extrusion extends generally vertically upwardly from limb  68  adjacent the heads of the concrete anchors and includes grooves  72  that provide a key for the elastomeric concrete. Thus, face  70  defines with the rabbet  26 , a generally rectangular section cavity  74  that can be directly filled with elastomeric cement with virtually no risk of air pockets developing. As noted previously, air pockets can lead to poor bonding of the elastomeric cement to the extrusion and/or slab and consequent risk of water infiltration. Another advantage of this form of extrusion is that the cavity  66  essentially reduces the volume of cavity  74 , so that less elastomeric concrete is required.  
         [0032]    In summary, the expansion joint provided by the invention presents a number of advantages as compared with the prior art. A primary advantage is that lateral loads imposed on the cover plate  30  are transferred directly to the turnbars  34  and from there into the relevant rail  22  or  24  and into the slab on which the extrusion is mounted. The risk of shear failure between the cover plate and the turnbars is minimized. At the same time, extrusion  22  in particular provides for secure bonding of elastomeric cement to the rail  22  and slab, reducing the risk of water infiltration. The drip edges  50  ensure that any water that does infiltrate between the cover plate  30  and the rails  22 ,  24  will be directed into the water stop  22  where it can be controlled and directed appropriately.  
         [0033]    It is of course to be understood that the preceding description relates to a particular preferred embodiment of the invention only and that many modifications are possible within the broad scope of the invention. Some of these modifications have been mentioned previously and others will be evident to a person skilled in the art. It should be noted in particular that extrusions of either form shown in the drawings may be used as part of other expansion joints, for example joints that do not include the ball and socket couplings of the present invention.