A structure providing a polygonal visual control room for an airport is enclosed along at least a major portion of its periphery by transparent panels, the roof of the room being supported by mullions disposed only in a minor portion or the remaining minor portion of the periphery of the room. The upper ends of the transparent panels are mounted for sealed vertical sliding movement relative to the roof.

BACKGROUND OF THE INVENTION 
     This invention relates to structures and has a particularly useful application in buildings such as airport visual control rooms where an angle of at least 180° of uninterrupted vision is desirable. To minimize visual distortion effects in airport visual control rooms, flat glass panels are employed which are inclined downward at an angle of 15° to the vertical, and the control rooms may be of pentagonal, hexagonal, octagonal or other polygonal form. The glass panels are mounted in similarly inclined mullions which conventionally support also the roof of the control room. The mullions are therefore necessarily of strong construction and interrupt the field of view to a small but not negligible extent. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is disclosed a structure providing a polygonal visual control room enclosed along at least a major portion of its periphery by planar transparent panels and having a roof a major part of the area of which is supported in cantilever fashion from the upper ends of mullions disposed at the periphery of only a minor portion or the remaining minor portion of the periphery of the room. 
     In a preferred embodiment of the invention, the room is octagonal and the mullions are disposed at four neighboring corners of the room, the mullions at the outermost two of the four corners having their upper ends interconnected by a first structural element, and further structural elements extending from the upper ends of the mullions at the two corners intermediate the outermost two to the first structural element and thence in cantilever fashion to at least some of the remaining four corners of the room. 
     Preferably, the structural elements are in the form of trusses. 
     According to another preferred feature of the invention, the upper end of each of the transparent panels is mounted for sealed sliding vertical movement relative to the roof of the room. 
     The invention also provides a mounting arrangement for the upper edge of a transparent panel which is inclined to the vertical, comprising a member providing an elongate channel correspondingly inclined and adapted to receive the upper edge of the panel and having a vertically upwardly projecting portion, and a fixed elongate support element with which said upwardly projecting portion is in sealed vertically sliding engagement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the invention will now be described with reference to the accompanying drawings in which: 
     FIG. 1 shows diagrammatically, in perspective from above, the structure of an airport visual control room incorporating the invention; 
     FIG. 2 shows a form of sliding sealing mounting of the transparent panels of the room in its roof; and 
     FIGS. 3A and 3B are respectively front and side elevations of the completed control room installed on a tower. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 3A and 3B of the drawings, there is shown an airport visual control room 10 at the top of a tower 11. The room is octagonal and in the usual manner its glazing panels 12 are inclined downward at 15° to the vertical. In the illustrated room the room is glazed all around for 360° vision. The roof 13 is supported in cantilever fashion from mullions 14 at four adjacent corners of the room. 
     Referring now to FIG. 1 of the drawings, there is shown diagrammatically the skeleton of the structure by which the roof 13 is supported. As shown, mullions 14a, 14b, 14c, 14d are disposed at four neighboring corners of the room. The two outermost mullions 14a, 14d are interconnected at their upper ends by an upright planar truss 15 comprising a main horizontal member 16, spaced struts 17, a second horizontal member 18 interconnecting the upper ends of the struts 17, and inclined members 19 respectively extending from the upper ends of the struts 17 to opposite ends of the member 16. Two cantilever trusses 22 extend parallel to each other from the upper ends of the two inner mullions 14b, 14c to respective corners 23a, 23b of the room. Each of the trusses 22 comprises a horizontal member 24 connected intermediate its ends to the lower end of one of the struts 17 and two inclined members 25 connected to the upper ends of the associated strut and to opposite ends of the horizontal member 24. A horizontal member 26 and an inclined member 27 extend from the lower and upper ends of the two struts 17 to the remaining two corners 23c, 23 d of the room. Further horizontal perimeter members 28 extend along the periphery of the room interconnecting the outer ends of the trusses. 
     As shown in FIGS. 3A and 3B, each of the eight sides of the room is glazed by two panels of glass 12 arranged side edge to side edge and inclined downward at 15° to the vertical, and a silicon rubber or other suitable seal is disposed between these side edges. In addition, at the corners 23a to 23d a similar seal is disposed between the sheets. The omission of mullions at these corners results in a marked improvement in the field of view due to the reduction in the size of "blind spots", because the seals are relatively narrow. The consoles or desks for control room staff are usually disposed in the area indicated at C in FIG. 1 and the control room personnel thus have a substantially uninterrupted field of view over an angle well in excess of 180°. 
     It will be appreciated of course that the two panels of glass 12 in each side of the room could be replaced by a single panel or even three or more panels as desired. 
     Referring now to FIG. 2 of the drawings, a sliding sealing mounting for the upper ends of the glazing panels 12 in the roof structure 13 is shown. The top edge portion of the panel 12 is enveloped in an elastomeric or other suitable sealing material 29 and is clamped in a channel in an elongate member 30. One arm 31 of the channel is fixed, and the other arm 32 has one end pivotally engaged in a groove 33, and a setscrew 34 extends through a hole in the arm 32 and is received in a threaded socket 35 in the arm to clamp the edge of the panel adjustably and releasably. Along its upper edge the member 30 has two parallel arms 36 which are slidably engaged in a channel in a fixed upper horizontal member 38. One arm 39 of the channel is fixed and the other arm 40 has one end pivotally engaged in a groove 41, and a setscrew 42 extends through a hole in the arm 40 into a threaded socket 43 in the fixed arm enabling the width of the channel to be adjusted to provide the required degree of sealing. The inner surfaces of the arms 39, 40 have nylon bearing strips 44 secured to them to provide a smooth bearing surface for the arms 36 of member 30. The upper end of the member 38 is secured to a fixed hanger 46 attached to a horizontal member 16, 24 or 26. A ledge 47 on the outer side of the arm provides a support for ceiling tiles 48 and a similar ledge 49 on the arm is connected to the lower end of a fascia member 50 attached to a perimeter member 28. 
     The sliding of the arms 36 in the channel in member 38 allows the roof 13 of the room 10 to deflect to a degree as a result of external forces for example climatic forces such as wind or buildup of snow, thereby reducing any stress on the glazing panels. 
     It will also be appreciated that considerations such as the size of the structure may dictate that further cantilevers and other support means are provided in addition to those shown in the exemplary embodiment of FIG. 1. For example a further cantilever truss could be provided parallel to and between the trusses 22.