AR-461: BUILDING SCIENCE
By:
RAVINDAR KUMAR
Assistant Professor
Department of Architecture and Planning
NED University of Engineering and Technology
Karachi
LECTURE NO. 13
TOPIC: MECHANICAL CIRCULATION SYSTEM: STUDY OF ELEVATORS, ESCALATORS, ETC. (PART–02)
INTRODUCTION:
In the field of architecture, circulation refers to the way people move through and interact with a building.[1] In public buildings, circulation is of high importance; for example, in buildings such as museums, it is key to have a floor plan that allows continuous movement while minimizing the necessity to retrace one's steps, allowing a visitor to see each work in a sequential, natural fashion. Structures such as elevators, escalators, and staircases are often referred to as circulation elements, as they are positioned and designed to optimize the flow of people through a building.[2] The current discussion is about mechanical circulation system in a building. In this respect the study about elevators and escalators is outlined below:
ESCALATOR:[3]
An escalator is a moving staircase – a conveyor transport device for carrying people between floors of a building. The device consists of a motor-driven chain of individual, linked steps that move up or down on tracks, allowing the step treads to remain horizontal. Escalators are used around the world to move pedestrian traffic in places where elevators would be impractical. Principal areas of usage include department stores, shopping malls, airports, transit systems, convention centers, hotels, and public buildings. The benefits of escalators are many. They have the capacity to move large numbers of people, and they can be placed in the same physical space as one might install a staircase. They have no waiting interval (except during very heavy traffic), they can be used to guide people toward main exits or special exhibits, and they may be weatherproofed for outdoor use.
DESIGN, COMPONENTS, AND OPERATION OF ESCALATORS:
Operation and layout
Escalators, like moving walkways, are powered by constant-speed alternating current motors and move at approximately 1–2 feet (0.30–0.61 m) per second. The typical angle of inclination of an escalator to the horizontal floor level is 30 degrees with a standard rise up to about 60 feet (18 m). Modern escalators have single-piece aluminum or steel steps that move on a system of tracks in a continuous loop.
Escalators have three typical configuration options:
parallel (up and down escalators "side by side or separated by a distance", seen often in metro stations and multilevel motion picture theaters), crisscross (minimizes structural space requirements by "stacking" escalators that go in one direction, frequently used in department stores or shopping centers), and multiple parallel (two or more escalators together that travel in one direction next to one or two escalators in the same bank that travel in the other direction).[4] Escalators are required to have moving handrails that keep pace with the movement of the steps. The direction of movement (up or down) can be permanently the same, or be controlled by personnel according to the time of day, or automatically be controlled by whoever arrives first, whether at the bottom or at the top (the system is programmed so that the direction is not reversed while a passenger is on the escalator).
DESIGN AND LAYOUT CONSIDERATIONS OF ESCALATORS:
A number of factors affect escalator design, including physical requirements, location, traffic patterns, safety considerations, and aesthetic preferences. Foremost, physical factors like the vertical and horizontal distance to be spanned must be considered. These factors will determine the pitch of the escalator and its actual length. The ability of the building infrastructure to support the heavy components is also a critical physical concern. Location is important because escalators should be situated where they can be easily seen by the general public. In department stores, customers should be able to view the merchandise easily. Furthermore, up and down escalator traffic should be physically separated and should not lead into confined spaces. Traffic patterns must also be anticipated in escalator design. In some buildings, the objective is simply to move people from one floor to another, but in others there may be a more specific requirement, such as funneling visitors towards a main exit or exhibit. The number of passengers is important because escalators are designed to carry a certain maximum number of people.
For example, a single-width escalator traveling at about 1.5 feet (0.46 m) per second can move an estimated 170 persons per five-minute period. The carrying capacity of an escalator system must match the expected peak traffic demand, presuming that passengers ride single file. This is crucial for applications in which there are sudden increases in the number of riders. For example, escalators at stations must be designed to cater for the peak traffic flow discharged from a train, without causing excessive bunching at the escalator entrance.
In this regard, escalators help in controlling traffic flow of people. For example, an escalator to an exit effectively discourages most people from using it as an entrance, and may reduce security concerns. Similarly, escalators often are used as the exit of airport security checkpoints. Such an egress point would generally be staffed to prevent its use as an entrance, as well. It is preferred that staircases be located adjacent to the escalator if the escalator is the primary means of transport between floors. It may also be necessary to provide an elevator lift adjacent to an escalator for wheelchairs and disabled persons. Finally, consideration should be given to the aesthetics of the escalator. The architects and designers can choose from a wide range of styles and colors for the handrails and balustrades.
MODEL SIZES AND OTHER SPECIFICATIONS OF ESCALATORS:
Escalator Step Widths And Energy Usage | ||||
Size | Width (between balustrade panels) | Single-step capacity | Applications | Energy consumption |
Very small | 400 mm (16 in) | One passenger, with feet together | A rare historic design found mostly in older department stores | 3.7 kW (5.0 hp) |
Small | 600 mm (24 in) | One passenger | Low-volume sites, uppermost levels of department stores, when space is limited | 3.7 kW (5.0 hp) |
Medium | 800 mm (31 in) | One passenger + one package or one piece of luggage | Shopping malls, department stores, smaller airports | 7.5 kW (10.1 hp) |
Large | 1,000 mm (39 in) | Two passengers – one may walk past another | Mainstay of metro systems, larger airports, train stations, some retail usage | 7.5 kW (10.1 hp) |
COMPONENTS OF ESCALATORS:
LANDING PLATFORMS:
These two platforms house the curved sections of the tracks, as well as the gears and motors that drive the stairs. The top platform contains the motor assembly and the main drive gear, while the bottom holds the step return idler sprockets. These sections also anchor the ends of the escalator truss. In addition, the platforms contain a floor plate and a comb plate. The floor plate provides a place for the passengers to stand before they step onto the moving stairs. This plate is flush with the finished floor and is either hinged or removable to allow easy access to the machinery below. The comb plate is the piece between the stationary floor plate and the moving step. It is so named because its edge has a series of cleats that resemble the teeth of a comb. These teeth mesh with matching cleats on the edges of the steps. This design is necessary to minimize the gap between the stair and the landing, which helps prevent objects from getting caught in the gap.
TRUSS:
The truss is a hollow metal structure that bridges the lower and upper landings. It is composed of two side sections joined together with cross braces across the bottom and just below the top. The ends of the truss are attached to the top and bottom landing platforms via steel or concrete supports. The truss carries all the straight track sections connecting the upper and lower sections.
TRACKS:
The track system is built into the truss to guide the step chain, which continuously pulls the steps from the bottom platform and back to the top in an endless loop. There are actually two tracks: one for the front wheels of the steps (called the step-wheel track) and one for the back wheels of the steps (called the trailer-wheel track). The relative positions of these tracks cause the steps to form a staircase as they move out from under the comb plate. Along the straight section of the truss the tracks are at their maximum distance apart. This configuration forces the back of one step to be at a 90-degree angle relative to the step behind it. This right angle bends the steps into a shape resembling a staircase.
At the top and bottom of the escalator, the two tracks converge so that the front and back wheels of the steps are almost in a straight line. This causes the stairs to lay in a flat sheet like arrangement, one after another, so they can easily travel around the bend in the curved section of track. The tracks carry the steps down along the underside of the truss until they reach the bottom landing, where they pass through another curved section of track before exiting the bottom landing. At this point the tracks separate and the steps once again assume a staircase configuration. This cycle is repeated continually as the steps are pulled from bottom to top and back to the bottom again.
STEPS:
The steps themselves are solid, one piece, die-cast aluminum or steel. Yellow demarcation lines may be added to clearly indicate their edges. In most escalator models manufactured after 1950, both the riser and the tread of each step is cleated (given a ribbed appearance) with comb like protrusions that mesh with the comb plates on the top and bottom platforms and the succeeding steps in the chain. Seeberger- or "step-type" escalators (see below) featured flat treads and smooth risers; other escalator models have cleated treads and smooth risers. The steps are linked by a continuous metal chain that forms a closed loop. The front and back edges of the steps are each connected to two wheels. The rear wheels are set further apart to fit into the back track and the front wheels have shorter axles to fit into the narrower front track. As described above, the position of the tracks controls the orientation of the steps.
HANDRAIL:
The handrail provides a convenient handhold for passengers while they are riding the escalator. In an escalator, the handrail is pulled along its track by a chain that is connected to the main drive gear by a series of pulleys. It is constructed of four distinct sections. At the center of the handrail is a "slider", also known as a "glider ply", which is a layer of a cotton or synthetic textile. The purpose of the slider layer is to allow the handrail to move smoothly along its track. The next layer, known as the "tension member", consists of either steel cable or flat steel tape, and provides the handrail with tensile strength and flexibility. On top of tension member are the inner construction components, which are made of chemically treated rubber designed to prevent the layers from separating.
Finally, the outer layer—the only part that passengers actually see—are the cover, which is a blend of synthetic polymers and rubber. This cover is designed to resist degradation from environmental conditions, mechanical wear and tear, and human vandalism. In the factory, handrails are constructed by feeding rubber through a computer-controlled extrusion machine to produce layers of the required size and type in order to match specific orders.
The component layers of fabric, rubber, and steel are shaped by skilled workers before being fed into the presses, where they are fused together. In the mid-twentieth century, some handrail designs consisted of a rubber bellows, with rings of smooth metal cladding called "bracelets" placed between each coil. This gave the handrail a rigid yet flexible feel. Additionally, each bellows section was no more than a few feet long, so if part of the handrail was damaged, only the bad segment needed to be replaced. These forms of handrail have largely been replaced with conventional fabric-and-rubber railings.
SAFETY OF ESCALATORS:
Safety is also major concern in escalator design. In India where women wear saris, there are heavy chances of getting the pallu entangled in the escalator[5] special sari guard is inbuilt in most escalators.
There is a risk of feet injuries for children wearing footwear such as Crocs and flip-flops that might get caught in escalator mechanisms.[6] This was due to the softness of the shoe's material combined with the smaller size of children's feet.[7] Fire protection of an escalator floor opening may be provided by adding automatic sprinklers or fireproof shutters to the opening, or by installing the escalator in an enclosed fire-protected hall. To limit the danger of overheating, ventilation for the spaces that contain the motors and gears must be provided.
KEY SAFETY FEATURES DEVELOPED OVER TIME:
To enhance passenger safety, newer models of escalators are equipped with one or more of the following safety implementations:
- Antislide devices: Raised circular objects that often stud the escalator balustrade. Sometimes informally called "hockey pucks" due to their appearance, their purpose is to prevent objects (and people) from precipitously sliding down the otherwise smooth metallic surface.
- Combplate impact switches: Stop the escalator if a foreign object gets caught between the steps and the comb plate on either end.
- Deflector brush: A long continuous brush made of stiff bristles running up the sides of the escalator just above the step level. This helps deflect garments, shoes, and other items away from the gap between the moving steps and the skirt board.
- Emergency stop button: At each end of the escalator (in some models, also on the balustrade), a large red button can be pressed to stop the device in the event of an emergency. Typically, an alarmed transparent plastic guard plate covers the button; restarting requires turning a key.
- Extended balustrades: Allows riders to grasp the handrail before setting foot on an escalator, to ease customer comfort and stability/equilibrium. (The effect is similar to the flat steps described below.)
- Flat steps: Like a moving walkway, the first two or three steps at either end of the escalator are flat. This gives the passenger extra time to orient him/herself when boarding, and more time to maintain balance when exiting. Longer escalators often have four or more flat steps.
- Handrail inlet switches: . Sensors located at the bottom and top of the unit that guard the handrail termini. If something gets caught in these locations, a hard fault is generated in the controller, and the escalator shuts down automatically.
- Handrail speed sensors: These sensors are usually optical, and monitor how fast the handrail moves. If the sensor notices a speed difference between the handrail and the steps, it sounds an alarm, pauses, and then automatically stops the escalator. In these situations, the escalator must be serviced by authorized personnel before returning to an operable state.
- Missing step detectors: Depending on the manufacturer and model, this sensor is either optical or physical. When a missing step is detected, the escalator automatically shuts down.
- Raised step edges: In some models, a difference in tread height is utilized to keep passengers' feet from the skirt board.
- Safety instructions: A sign, typically posted on both escalator newels at the entrance landing platform. In some situations, safety precautions are posted on walls near the escalator, included on freestanding signs, or—as in some models—printed on the riser surface itself.
- Sensor switch: In automatic-start/stop escalators, this sensor automatically engages the escalator motion when a rider is detected on the first step of the entrance landing platform, and stops the escalator when there are no riders on the unit.
- Step demarcation lights: Either fluorescent or LED lights (traditionally green in color) located inside the truss. The illumination between the steps improves the passengers' awareness of the step divisions.
- Step demarcation lines: In order to clearly delineate the edges of each individual step, manufacturers offer steps trimmed in yellow, either painted or with plastic inserts.
REFERENCES:
[1] "Circulation (architecture)" in Britannica Online Encyclopedia; From: http://www.britannica.com/EBchecked/topic/118392/circulation (Retrieved April 6, 2011)
[2] Circulation; From: http://en.wikipedia.org/wiki/Circulation_(architecture) (Retrieved April 6, 2011)
[4] Strakosch, George R. Vertical Transportation, Elevators and Escalators, New York: John Wiley & Sons, 1983.
[5] Special devices in India; From: http://www.delhimetrorail.com/commuters/passenger_safety.html (Retrieved April 6, 2011)
[6] Snow, Kate (October 5, 2006). Crocs can pose a danger on escalators ABC News. From: http://abclocal.go.com/kgo/story?section=news/bizarre&id=4630653 (Retrieved April 6, 2011) AP (April 21, 2008). Kids Hurt While Wearing Crocs on Escalators. ABC Business News From: http://abcnews.go.com/Business/story?id=4694425&page=1 (Retrieved April 6, 2011).
[7] Experts recommend caution while wearing clogs WMC-TV Memphis Tennessee. September 21, 2006. From: http://www.wmctv.com/story/5441435/experts-recommend-caution-when-wearing-crocs?redirected=true (Retrieved April 6, 2011).
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