22.214.171.124 Supporting Structure
(a) Slider-Bed Type. The carrying portion of the treadway shall be supported for its entire width and length, except where it passes from a support to a pulley. The surface of the slider bed shall be reasonably smooth. It shall be constructed so that it will not support combustion.
(b) Roller-Bed Type. Where the treadway is supported on a series of rollers, the combination of roller spacing, belt tension, and belt stiffness shall be such that the deflection of the treadway surface, midway between rollers, shall not exceed the quantity 0.25 mm (0.094 in.) plus 0.004 times the center-to-center distance of rollers in millimeters (inches) when measured as follows:
(1) The treadway surface shall be loaded midway between rollers with an 11.3 kg (25 lb) weight, concentrated on a cylindrical foot-piece 50 mm (2 in.) long by 25 mm (1 in.) in diameter, placed with its long axis across the belt. Deflection of this foot-piece from its unloaded position shall not exceed the figure obtained above.
(2) The rollers shall be concentric and true running within commercially acceptable tolerances.
(c) Edge-Supported Belt Type. When the treadway belt is transversely rigid and is supported by rollers along its edges, the following requirements shall apply:
(1) With the belt tensioned through the take-up system, the permissible slope of a straight line from the top of a treadway rib adjacent to the centerline of the treadway to the top of a treadway rib adjacent to the balustrade, in a plane perpendicular to the path of the treadway, shall not exceed 3% when the treadway is loaded with a 68 kg (150 lb) weight on a 150 mm × 250 mm (6 in. × 10 in.) plate, located on the centerline of the treadway with the 250 mm (10 in.) dimension in the direction of treadway travel.
(2) To support the treadway in case of localized overload, supports shall be supplied at intervals not exceeding 1830 mm (72 in.) along the centerline of the treadway. The supports shall be located at a level not more than 50 mm (2 in.) below the underside of the treadway when it is loaded under test conditions required by (1).
(d) Pallet Type. Pallet wheel tracks shall be designed and located to prevent more than 3 mm (0.125 in.) vertical displacement of the treadway should the pallet connection means break.