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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to glazed structures and more particularly to glazed structures using semi-rigid plastic panels as the glazing material.  
         [0003]     2. Description of the Prior Art  
         [0004]     Semi-rigid plastic panels, particularly of polycarbonate, are widely used as a glazing material in building structures such as roofs and walls. It is relatively lightweight and is quite versatile in that it is able to accommodate a degree of bending and can therefore be incorporated into a curved roof or curved wall. One common method of securing the panels is by screwing directly to underlying support structure usually by means of self-drilling screws which incorporate a sealing washer to prevent water penetration at the point of penetration of the screw through the panel. However systems which do not require penetration of the panel are to be preferred. One such system which avoids the need for penetration by individual self-drilling screws and which permits significantly faster installation, uses plastic panels with an upstanding lip extending along each of its two longitudinal edges. The adjacent lips of two adjacent panels are fastened together by a connector channel which is a snap-fit over the two lips. A system of this type which is now extensively used in Australia and many other countries is sold under the trade mark DANPALON of Dan-Pal, Upper Galilee, Israel. The DANPALON system principally uses multi-cell polycarbonate panels having a core formed by three or more layers of elongate cells running the length of the panel or alternatively the panel may be solid sheet of appropriate thickness, for example 4 mm.  
         [0005]     In the existing DANPALON system, the glazing panels are secured to underlying support structure, such as purlins, extending widthwise of the panels by brackets which are screwed to the structure and which interfit with the upstanding lips of adjacent panels. When the connector channel is applied to the two lips, the channel also retains the lips against the brackets to thereby ensure that the panels are securely fastened at that point to the underlying structure. Accordingly a very secure and watertight fastening can be achieved without penetration of the panels and without the use of applied sealants or adhesives.  
         [0006]     While the system described above is an effective system, when used on large roof spans for example (typically those in excess of 4 metres), a significant under-structure is required to provide adequate structural support. This not only adds to the expense of the structure but may also adversely affect its aesthetics.  
         [0007]     Moreover, although the fastening system using the connecting channels does facilitate installation while providing a watertight connection between the adjacent panels, nevertheless the brackets by which the panels are held to the underlying support structure are required to be individually attached to the structure by being screwed to the structure and this in itself can be a relatively time consuming exercise.  
       SUMMARY OF THE INVENTION  
       [0008]     According to the present invention there is provided a glazed structure comprising glazing panels arranged side-by-side with adjacent longitudinal edges of pairs of adjacent panels being supported by a bar common to both panels and extending lengthwise of the two edges, each of the adjacent edges having an upstanding lip and the bar including an integral T-section extension from a panel-support surface of the bar, with the upstanding lips of the two panels lying between the support surface and the transverse flange of the T-section extension at respective sides of the central flange of the T-section extension, and a connector applied over the projecting lips to hold the lips captive within the T-section extension and thereby to secure the longitudinal edges of the panels to the bar.  
         [0009]     Further according to the invention there is provided a glazed structure comprising semi-rigid glazing panels of plastic material arranged within the structure with longitudinal edges of pairs of adjacent panels in side-by-side relation and each longitudinal edge including an integral upstanding lip, each pair of adjacent panels within the structure being supported at their adjacent longitudinal edges by an outwardly facing surface of a longitudinally-extending support bar whereby the two adjacent edges of the two panels are supported by that bar along their entire length, the bar including a retaining flange parallel to the said surface of the bar but spaced outwardly therefrom with the two lips being located between the retaining flange and said surface, and a connector channel applied over the retaining flange and the outer sides of the two lips to retain the lips between the retaining flange and the said surface of the bar and thereby securing the edges of the two adjacent panels to the bar.  
         [0010]     Still further according to the invention there is provided a glazed structure comprising bars which provide structural support arranged in parallel relation, semi-rigid glazing panels arranged within the structure with longitudinal edges of pairs of adjacent panels being supported by a said bar which is common to both panels and which extends lengthwise of the two panels, each of the adjacent edges having an upstanding lip and the bar including an integral T-section extension from a panel-support surface of the bar, with the upstanding lips of the two panels lying between the support surface and the transverse flange of the T-section extension at respective sides of the central flange of the T-section extension, and a connector applied over the projecting lips to hold the lips captive within the T-section extension and thereby to secure the longitudinal edges of the panels to the bar.  
         [0011]     Still further according to the invention, there is provided a bar intended for use in a glazing system as defined above, the bar having a portion of hollow section with an outer surface providing a panel-support surface of the bar and a T-section extension projecting from the surface to act in conjunction with a connector to retain the lips of the panels, the portion of hollow section and the extension being integrally formed as an extrusion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which:  
         [0013]      FIG. 1  is a fragmentary exploded view showing the junction between two glazing panels and a structural support bar of a glazing system of a preferred embodiment of the invention;  
         [0014]      FIG. 2  is a cross-section showing the junction in its assembled condition;  
         [0015]      FIG. 3  is illustrative of a typical curved arched roof structure which can be formed using the system of the invention and showing as detail “A” the junction between two adjacent panels of the structure; and  
         [0016]      FIG. 4  is a section similar to  FIG. 2  and illustrating how the system can be adapted for use with a different type of glazing panel to that illustrated in FIGS.  1  to  3 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     The system of the preferred embodiment of the invention is based on the DANPALON system and, indeed, is able to use the panels and connector channels of the DANPALON system but uses a different form of underlying support which both enables larger spans to be achieved without the need for additional underlying support structure and also avoids the need for individual brackets for securing the panels. It is however to be understood that the invention is not confined in scope to the use of DANPALON panels and connectors. Accordingly the invention is suitable for use with other glazing panels having upstanding lips along their longitudinal edges for co-operation with connectors which fit over the two adjacent lips of two adjacent panels.  
         [0018]      FIG. 1  is a fragmentary exploded view showing the outer longitudinal edges of two adjacent glazing panels  2  of multi-cell form with integral upstanding lips  4  having one or more locking ribs  4   a  extending along their internal face. The panels  2  with the integral lips  4  along their opposed longitudinal edges are formed in standard widths by an extrusion process as will be well understood by those skilled in this art, to be subsequently cut to required length. The panels are preferably of polycarbonate. Also shown in this Figure, is the connector channel  6  having, along the inner surface of its two sides, ribs  6   a  which lockingly inter-engage with the ribs  4   a  of the upstanding panel lips  4  when the connector channel  6  is applied over those edges (see  FIG. 2 ). Depending on requirements, the connector channel  6  can be of extruded plastic or of extruded alloy or metal.  
         [0019]     In the system of the invention, each pair of adjacent panels  2  is supported along the entire length of their adjacent longitudinal edges by a support bar  10  which extends longitudinally of the panels  2 . The bar  10  is profiled to enable it to traverse a large span without the need for underlying support structure along its length. This is achieved by forming the main structure of the bar as a hollow section  12  reinforced along its outer side (the side to which the glazing panels  2  are applied) by an integral extension  14  of T-section. It will be understood that this T-section extension  14  acts in conjunction with the outer side of the hollow section  12  substantially in the manner of an I-beam to provide substantial reinforcement against bending deflection of the bar  10  under the applied loading of the glazing panels. In the particular form shown, the hollow section  12  of the bar  10  is tubular, specifically rectangular, although other sections which provide the required strength against deflection and which have a substantially planar outer surface against which the edges of the two panels  2  will rest, can be used. The bar  10  can readily be formed by extrusion, for example in aluminium or other suitable alloy or metal and the extruded bar can be roll-formed to a required curvature if it is to be used within a curved arched roof structure as illustrated by way of example in  FIG. 3 .  FIG. 3  illustrates the curved bars  10  in parallel relation and supported only at their two ends, with a continuous glazing panel  2  extending between each pair of bars and supported at its longitudinal edges by those bars.  
         [0020]     The T-section extension  14  in addition to strengthening the bar  10  to provide a greater span length, also acts as the means for securing the panels  2  to the bar without the need for additional brackets. For this purpose, the spacing between the outer transverse flange  14   a  of the extension  14  and the outer face of the hollow section  12  corresponds to the depth of the upstanding lip  4  along the longitudinal edge of the panel so that the lip  4  can fit beneath, and be held captive by, the underside of the flange  14   a . It is however to be noted that the upstanding lip  4  is not a tight fit under the flange  14   a  but instead a small gap is left, possibly of the order of 1 to 2 mm, to allow for thermal expansion of the plastic panel under elevated temperatures. The lateral projection of the transverse flange  14   a  to each side of the central flange  14   b  of the extension  14  also corresponds approximately to the width of the lip  4 .  
         [0021]     When the connector channel  6  is applied over the two adjacent lips  4  which abut against the opposite sides of the central flange  14   b , the ribs  6   a  along the sides of the connector channel  6  will snap-lock with the ribs  4   a  on the lips  4  to ensure that the lips  4  are anchored to the extension  14  and hence are positively locked to the bar  10 . This is the condition shown in  FIG. 2  and also in the detail A of  FIG. 3 . It will of course be understood that the junction between the two lips  4  and the extension  14  is enclosed within the interior of the connector channel  6  and therefore impervious to penetration of water, and the snap-lock between the channel  6  and the lips  4  will prevent accidental removal of the channel  6 .  
         [0022]     In a practical form of the preferred embodiment in which the bar  10  is designed for use with DANPALON multi-cell panels whereby the lateral projection of the transverse flange  14   a  corresponds to the width of the upstanding lips  4  on those panels, the bar  10  is also suitable for use with DANPALON panels of solid structure in which the lips are thinner than those of the multi-cell panels. This is achieved by the use of L-section insert strips  16  laid along the outer side of the bar  10 , as shown in  FIG. 4  prior to installation of the panels  2  or alternatively by the use of self-adhesive foam strips applied in a similar manner and this is the preferred method.  
         [0023]     Further components of the system are illustrated in  FIG. 1  as applied to a typical roof structure. This Figure shows a beam  20  extending along the length of the structure to locate and support the bars  10  at one end, with a similar beam being provided at the other ends of the bars  10 . However even when there is a substantial span between the two beams, the design of the bars enables that span to be traversed without the need for intermediate underlying structural support. As shown, a saddle bracket  22  screwed or welded to the beam  20  locates and secures the lower part of the main hollow section  12  of the bar  10 . An end sealing cap  24  of channel section is applied over the exposed end edges of the panels  2  and the connector channel  6 .  
         [0024]     The panels  2  with the integral upstanding lips  4  may be produced in a number of standard widths which are cut to required length for use. Although it is desirable to design the structure so that each section of the structure can accommodate a complete panel of standard width, in some situations an end section of the structure may be of a width less than a standard width. In that case the glazing panel for use in that section can be cut to the required width leaving a small excess portion which can be manually bent upwardly to form a projecting lip by partially cutting through the thickness of the panel to facilitate bending. That lip can then be secured to the extension  14  of the end-most bar  10  in the structure using the connector channel as previously described.  
         [0025]     As mention previously, although the preferred embodiment is particularly suitable for use with existing DANPALON panels, which are polycarbonate panels and connector channels, the embodiment is not confined specifically to use with those panels and the associated connector channels. Other glazing panels formed from polycarbonate sheeting or other suitable plastic sheeting and having upstanding lips along their longitudinal edges may alternatively be used; likewise other forms of connector which fit over the lips to secure the lips to the bar to provide a watertight seal can be used.  
         [0026]     It will be understood that the system in accordance with the invention in addition to permitting increased roof spans without the need for intermediate underlying support structure, also obviates the need for the incorporation of individual brackets to secure the panels to the structure as the function of the brackets is now fulfilled by the T-section extension which forms an integral part of each support bar. Accordingly installation time and costs are significantly reduced.  
         [0027]     Although the preferred embodiments have been described principally in relation to roof structures, it is to be understood the invention in its preferred embodiments is applicable to other structures such as wall structures. Although the structure can have curvature achieved by bending the support bars, the structure can be substantially planar in form.  
         [0028]     The embodiment has been described by way of example only and modifications are possible within the scope of the invention.

Summary:
A glazed structure has semi-rigid glazing panels of plastic material carried by support bars of hollow cross-section with an integral T-section extension. The extension reinforces the bar against bending and also co-operates with a system for coupling the panels to the bars in a weathertight manner.