Building Design and Construction Handbook - Merritt - Ventech!

16.12 SECTION SIXTEEN
FIGURE 16.6 Details of a straight escalator. (Courtesy of Otis Elevator Co.)
(Fig. 16.6). The installation also includes a handrail on each side of the steps that
moves at the same speed as the steps; balustrades, or guards, that enclose the steps
on each side and support the handrails; brakes; control devices; and threshold plates
at the entrance to and the exit from the treadway. The purpose of the threshold
plates is to facilitate smooth passage of passengers between the treadway and landing.
The plates are equipped with a comb, or teeth, that mesh with and are set into
grooves in the treadway in the direction of travel, so as to provide firm footing and
to minimize the chance that items become trapped between treadway and the landing.
Each step is formed by a grooved tread portion connected to a curved and
grooved riser. The tread and riser assembly is either a single die-cast piece or is
assembled to a frame. Both are suspended on resilient rollers whose axles are
connected to the step chain that moves the steps. The step rollers ride on a set of
tracks attached to the trussed framework. The tracks are shaped to allow the step
tread to remain horizontal throughout its exposed travel.
16.4.2 Dimensions for Escalators
ANSI A17.1 sets the following limitations on escalator steps (Fig. 16.8):
Minimum depth of tread in direction of travel—15 3 ⁄4 in
Maximum rise between treads—8 1 ⁄2 in
Minimum width of tread—24 in
Maximum width of tread—40 in
Maximum clearance between tread and adjacent skirt panel— 3 ⁄8 in
Maximum distance between handrail centerlines—width between balustrades
plus 6 in with not more than 3 in on either side of the escalator (see Fig. 16.8b)