attachment portion 121 each shelf support member 122 may be attached to a frame attachment portion 121 by inserting hooks 128 into corresponding slots 124 and moving the shelf support downwardly thereby hooking the hooks 128 into the slots 124 another exemplary embodiment of a shelf support is depicted in fig8 in this embodiment shelf 90 has projecting portion 92 confronting frame segments 42 threaded knob 95 extends through clamping portion 94 and threads into projecting portion 92 if threaded knob 95 is tightened frame segments 42 are trapped and frictionally secured between projecting portion 92 and clamping portion 94 thereby providing a support for shelf 90 shelf 90 may be positioned in any desired position along frame segments 42 by loosening threaded knob 95 sliding the shelf 90 along the frame segments 42 as depicted by the arrow until the desired position is reached and retightening threaded knob 95 referring to fig2 4 and 6 details of the horizontal trusses 26 are illustrated these trusses 26 may be linear in configuration as illustrated in fig4 and 1 or may be arcuate as illustrated in fig6 and 1 in either case the trusses have parallel frame segments 102 which may be joined by webbing members 104 proximate the ends or alternatively by conventional webbing 106 as depicted in fig4 as illustrated in fig6 the horizontal trusses 26 are utilized for connection of the graphic screen panels 108 which due to the positioning of the unshaped webbing 104 on the bottom of the bottom truss and the.