by James W. Fortune As we turn the corner into the next millennium, a number of large engineering and development firms have already announced plans to construct mega high-rise towers - buildings with 100+ stories and heights in excess of 450 m - some with heights of 600 m, 1,000 m, 2,001 m, and even 4,000 m envisioned. These 150- to 1,000-story, multi-use behemoths (averaging 4.0 m per story) are to be mega cities with self-contained habitats.
Just as the mile-high, 1,600-m, 528-story Illinois Office Tower - designed by Architect Frank Lloyd Wright in 1956 - was conceptual in nature many of these designs are "pie-in-the-sky"dreams that could not be practically or economically built with today's technologies. However, with the development of new materials and building designs, operations and systems, such towers may become commonplace in the future. It is interesting to speculate how mega high-rise buildings would be elevatored, with the purpose of this paper being to explore practical methods, while not exceeding the physiological body limits and psychological wait-tolerance limits of the typical elevator rider.
The key to efficient, mega high-rise elevator design is to stack local
zones served by their own local elevators on top of one another. These local zones are then served by very high-speed, sky-lobby shuttle elevators, serving express between the ground terminal floor(s) and the sky lobby(ies). Each sky lobby floor(s) is then served by its own express-shuttle elevator group (Figure 1), or a single group of sky-lobby shuttles (sky train), serving between the ground terminal floor and all the upper lobbies (Figure 2). The latter concept is similar to the utilization of municipal local and express commuter trains to handle outlying suburbs, or a modern airport terminal using connecting shuttle trains to handle traffic between the land-side terminal and the air-side concourses (Figure 3). In order to meet the psychological waiting-time limits and acceptable headways for these high-speed, sky-lobby shuttle lifts, very high-speed, express shuttle speeds (12-25 mps) will be required.
Mitsubishi Elevator Co., in a recent article "Elevators for Skyscrapers,"identified seven technical problems elevator equipment designers must consider when planning elevator equipment required for mega high-rise, high-speed, express-shuttle elevators in the 21st century.
Items one through four reflect the elevator passenger's comfort and
health. Except for the ear-discomfort problem caused by cab noise, rope oscillation and cab-sway problems have substantially been solved for mega high-rise shuttle cars. The car-safety and buffer-length problems can be overcome through application of new materials and control features. The remaining hoist cable-length problem opens up some interesting possibilities - particularly if the linear induction motor, ropeless elevator can be fully developed. The ropeless, self-powered elevator would permit more than one elevator car (lifting pod) within a dedicated hoistway. Peak handling capacity could be increased during intense usage periods by bringing more lifting pods on line. This would be similar to adding more trains or individual cars to a train as passenger demand increases. In order to keep the elevator lifting pods from blocking a single load/discharge portal, particularly if the equipment fails, it would probably be necessary to load and unload the pods outboard of the dedicated express lift shafts.
Anytime a high-rise office tower exceeds about 60 stories in height (80 stories for pure double-deck lifts), it probably contains in excess of 93,000 m2 of space, and is usually serviced by four single-deck lifts - up to eight elevators each. The dilemma of how to best serve additional building floors then arises. If we continue attempting to service more upper floors with conventional zones of single-deck or pure double-deck elevatoring solutions, the bottom floor areas are quickly reduced -containing little to nothing but elevator shafts - rendering the project uneconomical. There are at least four viable elevatoring solutions that can be employed to overcome this loss of rentable area and shaft encroachment dilemma:
1) Create upper sky lobby(ies) so building tenants can travel express from the ground to the sky lobby, and then transfer to "local" lift zones. The sky-lobby/local solution partially overcomes the problem of increased shafts in the lower portions of the project because all elevators do not have to serve the entry level. The upper local zones are stacked on top of one another, so the lift shafts, generally, occupy the same "footprint" as the local zones below. Unless the building tapers or steps back - the same number, arrangement, size and speeds of the local lifts are again duplicated in each stacked zone.
Sky-lobby shuttles can be either: top-up - the local lifts are dispatched up from the sky lobby (Figure 1); or top-down - the local lifts are loaded at the sky lobby(ies) and then travel up and down from this floor (Figure 2).
Sky-lobby shuttles can be single-deck, 1,600-kg to 4,500-kg units,
double-deck lifts or car-car counterbalance lifts, and can have front and rear openings for ease in loading or unloading.
The largest top-up,
single-deck sky-lobby shuttles are the 46 4500-kg, 8.0 mps units installed in the twin, 110-story New York World Trade Center Towers. The largest double-deck shuttles are the 14 2,250/2,250-kg at 7.0 mps and 8.0 mps elevators installed in the 110-story Chicago Sears Tower project. The Eiffel Tower and the Place de La Defense projects in Paris, France both employ sky-lobby, car-car counterbalance lifts (Figure 4), used for shuttling visitors to and from the upper-level observation decks. This same technology could be utilized for mega high-rise, sky-lobby shuttle transport, probably utilizing dual, double-deck lifts (Figure 5) in order to minimize the required shaft sizes.
2) Provide more than one elevator car per shaft, thus reducing the number of hoistways required in a given project. Two methods exist for accomplishing this scheme. In 1931, dual, independently operated elevators were installed in a 20-story Pittsburgh building. Each elevator was assigned a certain number of floors, with the local unit assigned to the lower 10 floors, while the upper express unit served the top 10 levels. The average round-trip times were balanced so the lower elevator would return to the lower terminal just ahead of the upper unit. The attendant-operated units were equipped with blocking signals, much like a train system, electrically interlocked so the cars could only run on the same direction. Since the delay or failure of one car can adversely impact the other car even if the dispatching were coupled with the latest microprocessor controls, it is doubtful that this scheme has a future application. In 1932, the first double-deck lifts - two tandem cars stacked one above the other and fixed in the same frame - were installed in the New York City Subway Terminal Building. This "pure" double-deck scheme was an attempt to increase group-handling capacity of the zone lifts by having each car only stop at alternate levels during peak-traffic periods. Then, the cars simultaneously loaded and unloaded while serving two floors at each stop. In this way, it is expected that each double-deck lift could provide service to more zone floors while reducing the required number of lifts (and shafts) compared to conventional, single-deck elevatoring required to provide similar service in a given-size building.
To date, about 30 large office buildings have been constructed throughout the world utilizing this solution, and they work quite well. The double-deck to single-deck ratio works out to about 70%, or a 30% savings in the number of hoistways required.
The St. Louis Gateway Arch actually employs two trains of multiple cars installed in each leg for transporting visitors from the ground to the top observation platform, which is 190 m above the surrounding park. Each "train" is powered by a geared elevator hoist machine, contains eight lifting pods (they look like enclosed ferris-wheel cages) that can accommodate five seated passengers each and operates at a speed of 1.75 mps. The whole "train" is constructed of aluminum parts and weighs about 4,000 kg.
The Frank Lloyd Wright lift design for the Illinois Office Tower - utilizing a "pure" quintuple-deck lift strategy - was a similar attempt to pack more than one lift per shaft, thus reducing the number of shafts required.
With development of the ropeless elevator (Figure 6), it would be possible to service the upper sky lobbies with multiple-lifting pods that would dock laterally when loading and unloading, plus utilize dedicated vertical shafts (one up and one down) for express transport to and from sky lobbies. The transport vehicles may simply be shells that are loaded and unloaded, with mobile transport lounges containing the seated passengers, similar to Walt Disney World's MGM Studios "Tower of Terror" elevator ride (see ELEVATOR WORLD, December 1994).
3) Provide very large (or double-deck) shuttle lifts that stop at, perhaps, every 10th level, where the passengers discharge and then use side, local lifts or escalators to shuttle up and down between the five interconnection levels between skip stops. The 47-story Hong Kong Bank project employs 23 skip-stop lobby shuttles - serving five subzone sky lobbies - with 60 escalators interconnecting the levels in between.
4) The ability to stack 50- or 60-story office-building segments, each containing their own four to five groups of local lift systems, and set them on top of one another is the key to designing mega high-rise office structures. Each connection-point sky lobby located between the "stacked" structures can be serviced by its own set of dedicated shuttles; by a sky-lobby shuttle train serving all sky lobbies; or the sky lobbies can be connected to each other by "feeder shuttles" so that multiple sky lobby transfers can be required to get to and from the upper building sections (Figure 3).
The elevator industry has developed the following physiological limits which standing elevator riders can tolerate without feeling discomfort: vertical acceleration/deceleration <= 1.0 - 1.5 m/sec2 jerk rates <= 2.5 m/sec3 sound <= 50 dBa horizontal sway 15-20 mg ear-pressure change <= 2000 Pa
All of the physiological elevator design parameters, except ear-pressure changes, can be regulated by proper equipment designs. Ear
comfort/pressure changes do not usually affect elevator riders, unless the descent speeds exceed 7.0 mps and the vertical travel exceeds 300 m. When Frank Lloyd Wright revealed his plans for the Illinois Office Tower to the Chicago Daily News (which subsequently published a story reviewing the proposed method of elevatoring the project), the paper immediately received comments from a number of airline pilots questioning the ability of the atomic-powered, 25 mps elevators to serve the project without causing eardrum discomfort in the riding public. Airline pilots are well aware of the problems associated with rapid changes in altitude. Apparently, the inner ear can react adversely to changes in pressure associated with rapid ascents and descents experienced as aircraft change altitude. The same condition can affect elevator riders when elevator speeds exceed about 7.0 mps, or the vertical travel distance exceeds about
300 m. Elderly persons, those with colds, flu or allergies, or those who
cannot rapidly clear their ear passages are more at risk. Obviously, if
25-mps, quintuple-deck elevators envisioned by Frank Lloyd Wright were to really rise and then descend about 1600 m above grade in just one minute, the riders would experience considerable pain if they did not sufficiently "clear" their ears en route, or if the cabin (cab) pressure was not controlled.
Think of the middle ear as a balloon that expands as exterior pressure
decreases during ascent, and contracts as exterior pressure increases
during descent. As the airline-cabin or elevator-cab pressure decreases during ascent, the expanding air in the middle ear pushes the normal Eustachian tube (Figure 7) open (at about 4,000 Pa), letting the increased pressure escape down into the nasal passages until the pressure in the inner ear and the cabin, cab or final ascent level is equalized. However, during rapid decent, the passenger must consciously open the Eustachian tube by swallowing, yawning or tensing muscles in the throat, or by closing the mouth, pinching the nose closed and attempting to blow through the nose (known as the Valsalva Maneuver) to equalize the pressure. If either the ascent or descent (particularly the descent) is too rapid and the pressure is not relieved, a painful condition called "ear block" can develop. Ear block can produce severe inner-ear pain and loss of hearing that can last from several hours to several days. If not treated, fluid can accumulate in the middle ear, which can become infected. In extreme
cases, eardrum rupture can occur.
Reportedly, the two 2,725-kg at 9.0 mps observation elevators that express 410 m from the ground to the 103rd observation deck in the Chicago Sears Tower building had to be slowed to 8.0 mps in order to minimize the problems and potential litigation associated with ear block (Figures 8 and9). Reportedly, one building visitor suffered a broken eardrum sometime after descending from the observation deck via the shuttles when they were running at the original contract speed. In order to better understand the problem and suggest some solutions that may assist in designing future, mega high-speed, high-travel shuttle lifts, it would be beneficial to review how airlines handle the problem. Most jet aircraft cruise at altitudes of 9,100-12,200 m above sea level, while the cabin is repressurized to a maximum of 2,450 m to protect the crew and passengers from discomfort. After takeoff, the cabin is repressurized at a nominal ascent rate of 1.75 mps, even though many jets climb at a rate of 15-20 mps. This combination of pressurization and ascent speeds apparently agree with the passengers, and little discomfort
is normally experienced. However, because of the difficulty some people have in clearing their inner ears' Eustachian tubes, the descent process is much more complicated. During descent, the cabin is repressurized at a nominal descent rate of 1.75 mps after the aircraft descends to 2,450 m, while the actual descent is accomplished at about 2.5 mps. At this rate, it would take about 23 minutes to increase cabin pressure to that at sea level. Notice that the salient points here are that ascent can be accomplished very rapidly with little discomfort, while descent must be carefully controlled. Have you ever noticed a baby crying on an airplane during descent? The baby cannot consciously clear its ears, so when the inner-ear pressure builds up, causing pain, the baby cries in response. Voila! The painful inner-ear pressure is naturally cleared!
The easiest solution to major, high-rise, high-speed lift depressurization problems likely encountered in 100-story plus, sky-lobby shuttle elevators would be to ascend at about 10-15 mps, and to descend at no more than 2.5-4.0 mps. Another method would be to install sky-lobby breaks at every 75-100 stories. Passengers going to and from higher building floors and sky lobbies would transfer between the sky lobby by using interzone shuttles, getting a chance to depressurize and repressurize en route to their final destination. This system of "feeder" shuttles is the reason Ohbayashi Corp. indicated it would take approximately 15 minutes for a person to go from the ground to the top floor in their proposed 500-story, 2,000-m tall Aeropolis 2001 tower planned for Tokyo Bay. The most difficult problem would be designing a series of repressurization locks or
holding areas to be located at the top elevator sky-lobby terminal. There, the lift passengers would be reacclimated before boarding the shuttle lifts for the descent. Under this scenario, elevator hoistways or cabs would have to be enclosed and pressurized, along with the adjacent, preboard airlock. The advantage of this scheme is that the lift passengers could wait for the lifts in a prepressurization holding/waiting lock, and then board the lifts for a very rapid descent (speeds of 10-15 mps would not be uncommon) to the grade level. This scheme would also permit the lifts to express to heights in excess of 200 stories without having to transfer between intermittent sky-lobby shuttles (the feeder-lift scheme), or to travel down at very slow speeds. The mega height/speed scheme also dramatically reduces the time it takes to reach the top floors and total passenger transit times.
Over the years, the following design parameters and waiting-time standards have been developed for elevators in "Class A" office towers. The standards are for morning up-peak conditions (elevator ascents), and are designed to mollify the human expectations about what is an acceptable wait for an elevator:
* sky-lobby shuttles - average interval: <= 28-0 seconds; group-handling capacity: >=15-25% of combined local zone populations moved; transit-time to destination (calculated at 1/2 the average interval, plus the total time on the lift): <= 60-90 seconds - en route from main lobby to sky lobby; and * local lifts - vertical transportation - average interval: 25-0 seconds; group-handling capacity: >= 12-15% of zone population moved; average time to destination (calculated at 1/4 of the round-trip time, plus 1/2 or the average interval): <= 60 seconds - from sky lobby to local destination floor; and average waiting times: <= 20 seconds.
If mega high-rise, sky-lobby shuttle elevator travels and speeds must be slowed to comply with the maximum recommended ear-pressure changes, the waits for elevator descents at the sky lobby(ies) may increase from 30 seconds to two minutes. If these potential elevator riders must wait for service at the sky lobbies while the elevators are cycling - or must enter a predescent, pressurization air lock before boarding elevators - it will probably be desirable to provide audio-visual screens showing short subjects to minimize the boredom of the wait. Similarly, audio-visual screens may be installed in the shuttle elevators to accomplish the same purpose during slow descents to the ground from the sky lobbies.
It seems likely that a number of mega high-rise buildings will be
constructed (probably in Asia) in the near future. The local portions of
these stacked projects will likely be conventionally elevatored, with five zones of single- or double-deck lifts being dispatched from sky lobbies. An elegant approach to local service is to provide top/down groups serving ascent and descent from the upper sky lobbies so that the number of shuttle elevators is minimized. Initially, it seems likely that the sky lobbies will be served by their own single, dedicated sky-lobby shuttles, or interzone shuttles; then by sky trains serving between the ground and upper-floor sky lobbies; and finally by multiple, ropeless shuttle cars traveling in dedicated shafts.
The descending elevator ear-pressure-change problem can be alleviated by the use of interzone shuttles and multiple sky-lobby transfers (not likely), by keeping shuttle-elevator speeds and travels in the 7.0 mps and 300-m range, by limiting shuttles to speeds of no more than 2.5-4.0 mps or by prepressurization at the sky lobbies before boarding the lifts.
Publication: Elevator World
Issue: 07/01/95
References
Kendall, John. Ear Discomfort. Otis Internal Correspondence,1994.
Kendall, John. Pressure - Comfort Requirements. United Technologies
Research Center, 1994.
Wright, Frank Lloyd. A Testament. Bramhall House Publishers,1957.
James W. Fortune graduated from Pasadena City College with a degree in Architecture and from California State Polytechnic University with majors in Architecture and Industrial Technology. After a stint in the U.S. Navy, he served with Westinghouse Elevator Division in Los Angeles for three years, then joined Lerch, Bates & Associates - Denver Headquarters - in 1971 as a staff engineer. He later became project manager and regional vice president. In 1979, he relocated to Los Angeles as the consulting firm's vice president and West Coast zone manager, and in 1985, became the company's East Coast and West Coast vice president while relocating to the Denver Headquarters office. He obtained his MBA degree from the University
of Denver in 1989 and was elected president of Lerch, Bates & Associates, Inc. in 1994.