Escalator Speeds and Capacities
Escalators typically operate at 90 or 120 ft /min, as needed for peak traffic, and are reversible in direction. Slope of the stairs is standardized at 30 in the United States, although inclines of both 30 and 35 are used in other parts of the world.
Standard escalator widths are 32 and 48 in. Manufacturers rate their 90-ft /min units at corresponding capacities of 5000 and 8000 persons per hour, although observed capacities, even in heavy traffic, rarely exceed 2000 and 4000 persons per hour, respectively. Although 120-ft /min escalators will move about 30% more volume, they are rarely specified because of the potential for adverse litigation.
Planning for Escalators
The location of moving stairs should be selected only after a careful study of potential traffic flow within the planned project. They should be installed where most attractive to traffic and where convenient for passengers. The facility should be designed and signed in a manner that makes it apparent where the visitor will find the escalator. Since escalators are devices that will fail on occasion, the designer must provide alternative transportation (usually adjacent stairs) for times when the escalator is unavailable for passenger use. More importantly, where escalators will be operating at capacity as a result of specific programmatic considerations, the designer must plan alternative routing for times when one or more escalators is under repair. In retail applications, marketing needs generally motivate selection of escalator locations.
In design of a new building, adequate space should be allotted for escalators.
Generous areas should be provided at both loading and unloading areas. Special consideration should be given to the possibility of a disaster resulting at a constricted exit from an escalator when pedestrian traffic is restricted below the escalators capacity in the path of travel. Similarly, planning of landing areas should consider both queuing space and what happens when an escalator is stopped for some reason while pedestrian traffic continues. In addition, before stacked escalators are planned for an arena, stadium, or other facility having exit peaks, the potential for pedestrian traffic jams should be carefully weighed. If exiting traffic is very heavy in a stacked escalator system, upper levels can easily fill lower-level escalators, creating a jam at the escalator entries and leaving little space for lower-level pedestrians.
For an escalator installation in an existing building, careful study should be made to determine the necessary alterations to assure adequate space and supports.
Structural Considerations in Escalator Installation
Floor-to-floor height should be taken into account in determining loads on supporting members. Generally for floor-to-floor heights of less than 20 ft, the escalator truss need be supported only at top and bottom. Increased vertical rise can create the need for intermediate support points. A structural frame should be installed around the escalator well to carry the floor and wellway railing.
Inasmuch as an escalator is a mechanical device, careful consideration should be given to the potential for noise and vibration in design of the escalator structural supports. Where necessary, the escalator can be mounted on vibration-isolating devices to help reduce noise and vibration.
Escalator Installation
Design of escalators permits a vertical variation of 1â„2 in in the level of the supporting beams from the specified floor-to-floor height. The escalator is shimmed to bring it level. If variations in elevation exceed 1â„2 in, installation is difficult and much time will be lost. To allow for variations in overall escalator length, truss extensions can be provided.
Trusses generally are brought to the job in one section. There, they are raised into position with chain hoists, either through an elevator shaft or on the outside of the building. Typically, the escalator manufacturer does not furnish either the exterior truss cladding or the wellway railings and accessories. Because of the need for economy, escalator manufacturers design for minimal weight in the truss cladding.
Hence, care should be taken to coordinate carefully the desired design with the escalator manufacturer.
Escalators usually are installed in pairs one for carrying traffic up and the other for moving traffic down. The units may be placed parallel to each other in each story (Fig. 16.9), or crisscrossed (Fig. 16.10). Crisscrossed stairs generally are preferred because they are more compact, reducing walking distance between stairs at various floors to a minimum. The curved characteristic of the spiral escalator allows for several alternative arrangements (Fig. 16.11).
Fire Protection of Escalators
Escalators may be acceptable as required means of egress if they comply with the
applicable requirements for exit stairs (Art. 16.3.7). Such escalators must be enclosed
in the same manner as exit stairs. Escalators capable of reversing direction,
however, may not qualify as required means of egress.
An escalator not serving as a required exit should have its floor openings enclosed
or protected as required for other vertical openings. Acceptable protection,
as an alternative, is afforded in buildings completely protected by a standard supervised
sprinkler system by any of the following:
Sprinkler-vent method, a combination of automatic fire- or smoke-detection
system, automatic air-exhaust system, and an automatic water curtain.
Spray-nozzle method, a combination of an automatic fire or smoke detection
system and a system of high-velocity water-spray nozzles.
Rolling shutter method, in which an automatic, self-closing, rolling shutter is
used to enclose completely the top of each escalator.
Partial enclosure method, in which kiosks, with self-closing fire doors, provide
an effective barrier to spread of smoke between floors.
Escalator trusses and machine spaces should be enclosed with fire-resistant materials.
Ventilation should be provided for machine and control spaces.
