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Introduction to Architecture-M. Yamasaki

Posted 24 Aug 2011 at 23:50 PM by clive

A first hand account from the architect of the WTC:-

From: Minoru Yamasaki, A Life in Architecture, New York, 1979, pp. 112-128

15 World Trade Center New York, New York Commissioned, 1962; completed, 1976

Over the years it has become apparent to me that the purpose of the World Trade Center is so basic and so obvious that it is too conveniently overlooked by its critics. One of the fundamental responsibilities of the Port Authority of New York and New Jersey from its inception has been the promotion of international commerce in the Port of New York as a means of enhancing the economic well-being of the entire northern New Jersey and New York metropolitan region. For this reason, the legislatures of the two states directed the Port Authority to construct the World Trade Center, to bring together the activities of private firms and public agencies engaged in world trade in one central location, thus facilitating international business contacts among the members of the foreign trade community of this country's major port. The center's intent is to provide communication, information, proximity, and face-to-face convenience for exporters, importers, freight forwarders, customs brokers, international banks, and the many other enterprises involved in world trade.

As I learned to understand the purpose of the project, it became clear that the Trade Center, with its location facing the entry to New York harbor, could symbolize the importance of world trade to this country and its major metropolis and become a physical expression of the universal effort of men to seek and achieve world peace.

New York is unique among the large cities of the world; Manhattan itself is an ever-changing landscape of buildings, high and low, a unique island with a very high density of population, both permanent and commuting. A few of the buildings are very handsome, most are mediocre; in certain lights, the silhouette of the skyline is very beautiful, and even poorly designed buildings become merged into the texture of this fascinating conglomeration of structures surrounded by water. Although an unplanned effect, at particular times of the day this results in one of the most beautiful man-made landscapes that can be seen.

It is my opinion that in metropolises like New York with a high population density, it is important that the city be so planned that high buildings are separated by lower ones. There should be sufficient ground space, not full of automobiles, so that the great numbers of people who work and live in the city can enjoy moments of pleasure outdoors on the many beautiful days that New York experiences throughout the year, just as in many European cities, where people can enjoy squares, plazas, and gardens on working days as well as holidays
The opposite is dramatically evidenced in many of our Eastern and Midwestern cities, where developers long ago crowded the land with low buildings, leaving no room for playgrounds or gardens. Ground space available to the public and enhanced by the lovely greenery, possible even in our not-so-pure air, is vitally important to the daily life of the ever-increasing urban population of both our country and other industrialized nations. No matter how clever the urban planner, unless he brings openness and greenery as a measure of enjoyable relief, the result is a city built totally of unrelieved masonry -- hard, cold, and uninspiring for either work or play. Moreover, as a result of the heavy traffic brought on by the increased use of the automobile, most of the lovely trees that once gave green to our cities were eliminated by the widening of our major streets. Since so many of us spend so much of our time in cities, they should be made as pleasurable as possible, and this must be the first objective in the rehabilitation of our older urban areas or in the planning and building of new developments.

In designing the World Trade Center, the first step was to become completely acquainted with the project site, which extends from Vesey Street south to Liberty Street, and from Church Street to West Street, an area of more than seventeen acres just slightly north and west of Wall Street. Originally this section was cut up into fourteen tiny, irregular blocks. During many, many walks through and around the area, I thought it very fortunate that there was not a single building worth saving in the fourteen-block site. It was quite a blighted section, with radio and electronic shops in old structures, clothing stores, bars, and many other businesses that could be relocated without much anguish. The contention that the Port Authority tore down several blocks of historical old New York houses is completely mistaken. If this were true, there would have been an uproar much greater than occurred when the Savoy Plaza was demolished to make room for the General Motors Building. There were only two large buildings on the site, dilapidated and no architectural gems. These served as the terminals for the Hudson and Manhattan Railway, which tunneled under the Hudson River to New Jersey. This line, now called PATH (Port Authority Trans Hudson), is owned and operated by the Port Authority.

One of the great advantages of this location was that all three New York subways traveled through or adjacent to the site. This, plus the direct connection to New Jersey with PATH's new central station within the project, makes it quite simple for the commuter to reach the Trade Center. The confluence of these rail and subway facilities was the basis for the transportation and shopping concourse below the plaza. This level provides a protected, all-weather connection to all of the Trade Center buildings, the subways, PATH, and the underground pedestrian network leading to the Wall Street area. Arcop, the Canadian group of architects who designed Place Bonaventure in Montreal, have done a very fine series of schemes for this shopping area.

One of the most difficult problems of lower New York is that the area is cut up into such tiny little blocks, making it is almost impossible to walk or drive comfortably along the streets; the tremendous number of intersections make for a chaotic traffic situation. This area was planned for the horse and carriage days, and I am sure no one anticipated the high density of people that would one day accompany its being the financial center of our country. This density needs correction badly with a new plan, but this is difficult to achieve with the existing concentration of fine buildings, particularly east of Broadway. New Yorkers who work there have to fight their way through the impossible traffic morning, noon, and night. There are ground areas there that are barely touched by the sun because of the tall buildings and narrow streets. The intersections are so close together, each controlled by a stop light, that the traffic through these streets moves at a crawl.

For the Trade Center, the first task was to see if we could eliminate the interior streets and make a superblock of the total site in order to relieve this traffic chaos. After much insistence on my part, this was accomplished by such able Port Authority officials as Guy Tozzoli, head of the World Trade Department, and Malcolm Levy. These two men led the negotiations with the city. In exchange for the street closings, the Port Authority used the earth from the excavations for the Trade Center to make twenty-six acres of new land along West Street within the Hudson River bulkhead line. This landfill program has continued, and there will be much more such man-made acreage for new buildings. These sites along the lower-Manhattan Hudson-River front are intended to become a pleasant living area for families of varying income levels, and many will have the convenience of being able to walk to work. I am very hopeful that the landfill will be occupied by housing rather than by more offices.

Except for West Street, the streets surrounding the project were widened to at least three times their original dimensions in order to improve the flow of traffic. The sidewalks were also significantly broadened for easier pedestrian movement, and the facades of the lower buildings were articulated and recessed back and forth, making, the pedestrian experience more interesting than it is on the usual New York street, where the building line exactly parallels the absolutely straight sidewalk line.

What the Trade Center speaks to architecturally is the use of a unique opportunity to create a group of tall and low buildings, combined with a significant expanse of open space at ground level. It is self-evident that Manhattan is so overcrowded and the cost of land so expensive that a high density of structures is required in order to make any building project viable. I had long felt that it doesn't really matter in Manhattan how high you go up; what really counts to the people using buildings is their scale at or near the ground. The real opportunity at the Trade Center was to open up one area in our largest urban concentration and provide a great outdoor space, shielded from vehicular traffic, easily accessible to pedestrians, and a pleasure to the occupants, visitors, and people in and around the Trade Center site. The buildings went upwards in order to free the ground space for daily human enjoyment, the sidewalks and streets around the complex being widened for easier circulation in an area where one is too often fearful of being forced into the path of an automobile. At the same time, the monotony of ever-parallel, ever-too-close curbs and building walls was relieved. Had the site been filled with more numerous, relatively lower towers, the ground area would have been almost totally covered, with only a few small open spaces and narrow streets to relieve the concentration. This would have been merely a repetition of the Wall Street density.

Manhattan is, after all, a place of great scale that millions of New Yorkers and visitors over many generations have learned to enjoy. To convince myself that the concept of the high buildings was correct, I passed by, visited, and looked at the Empire State Building frequently over a period of time. That experience assured me that one becomes as comfortable standing next to a 100-story building as one forty stories high; the width of the streets in the city tends to limit the vision of the passerby, and it is only the first-time visitor who cranes his neck to see the tops of the higher buildings. I decided that in the design and detail of the buildings that we were about to undertake, a measure of openness and transparency was appropriate at their bases. When my associates expressed their concern that the structures might be too big, a couple of them went to stand next to and walk around the Empire State Building a few times, as I had. They came back convinced, as I was, that there was no diminution of the soul, no ant-like feelings in the face of such a large object. Man had made it and could comprehend it, and its parts could be understood to relate to its whole. There was a wish and a need to be able to stand back from it, to see and comprehend its height, and we tried to do that at the Trade Center.

Our involvement with the Trade Center began in 1962, when I received a letter from Richard Sullivan of the Port Authority, who, along with Mr. Levy, had been assigned the task of selecting the architect for the project. He wrote to ask if we would be interested in the architectural development of the project; an estimated, cost of $280,000,000 was indicated. My first reaction was that an extra zero had been added and that the intended scope was actually only one-tenth the stated one. Otherwise the project would be much too large an undertaking for an office like ours, which then consisted of fifty-five people.

My associates insisted that I call Mr. Sullivan and ask about the additional zero; I did, and he replied that the amount he had stated originally was correct. I said it would be too much for us to tackle, but he insisted that I visit them for an interview. I did so, thinking that it would be a waste of time, since there were many architectural offices with staffs of several hundreds, and I presumed that competing firms would have the advantage of size. Nonetheless, I had an extremely interesting and informative meeting with Mr. Sullivan and Mr. Levy. The latter has been our "constant" client throughout the project, successively heading the entire design and construction effort for the Port Authority. I became very excited about the project when I realized that they were searching for a chief architect who, with their agreement, would put together a design group of the most qualified architects and engineers available in the country.

The executive director of the Port Authority was Austin Tobin, one of the most able and effective leaders I have ever met. He was great -- a court of last resort, always available throughout the design stages of the project—and I was personally very disappointed when he resigned several years ago. After the most thorough investigation (apparently more than forty architectural offices were considered), Mr. Tobin called to say that he intended to recommend our firm for the commission. You may be sure that we had a celebration in our office that was the best we ever had. We are very enthusiastic when we receive an especially important project to design, but we had never had as wonderfully happy a party as that one.

We employed additional people quite slowly and deliberately after receiving the Trade Center commission, pursuing my conviction that a professional firm should not be too large or have multiple offices. I believe that responsibility to one's clients and projects can be achieved only with a relatively small, close-knit group of able and experienced people who have worked together for a long period of time. During the early part of the Trade Center design period, we reached our present size of about eighty people, of whom fifty are architects, the rest being mechanical engineers, model makers, and staff. With that number, our firm was able to carry on our Trade Center responsibilities of concept, design, and detailing, and also take on a limited number of other interesting projects.

One source of criticism of the Trade Center has to do with its very bigness. I will admit to sharing a measure of fascination with the numbers and statistics that this and other large projects seem to generate, but I had realized long before it happened that it would only be a matter of time before another building would be announced as the "tallest in the world." I had never believed that the Trade Center towers would retain that distinction for very long in a society such as ours, which is one of large-scale and grand achievements, and I am very content to let the latest new champion, the Sears Building in Chicago, or its successors defend the title for the "tallest" or the "biggest."

I am happy I was able to design these very large buildings with the proper scale relationship so necessary to man; they are intended to give him a soaring feeling, imparting pride and a sense of nobility in his environment. The Trade Center towers are set well back from the Church Street entrance—the entrance from the city—to the project. Their changing quality as one approaches across the plaza is, to me, especially interesting. So many tall buildings say nothing at all when one is next to them; their great beams and columns may be gloomy and fearsome from directly below, as they sit so solidly and so close to the sidewalk and street.

Now that the plaza is completed, its intent as the true focus of the Trade Center should be evident. Like many other important plazas of the world, it is designed as an end in itself, to set off the buildings facing it and to create an environment made totally for pedestrians and away from automobiles—an oasis, a paved garden where people can spend a few moments to relieve the tensions and monotonies of the usual working day. The plaza offers variation in scale; its central area, with its great spherical bronze sculpture and ninety-foot-diameter fountain by Fritz Koenig of Munich, contrasts with the recesses and planted areas in the bordering niches and courts that lead to the lower structures. There are other sculptures on the plaza: a beautiful black granite grouping by Masayuki Nagare of Japan and a stainless steel composition by James Rosati of New York. There are rings of benches, a graceful arc of light standards, and a 130-foot circle off lower boxes, with changing bursts of color through the spring, summer, and autumn, and evergreens in the winter. I am very aware of the enthusiastic delight that New Yorkers find in the relatively new pocket parks or in the open spaces of Rockefeller Center or Lincoln Center, and the plaza is definitely the unexpected grand experience of the Trade Center. It will offer a great open space with sufficient containment and variety to permit its users to observe and relate the overall scale of the towers to the detail of their parts, making them comprehensible and accessible, not overwhelming and forbidding. Certainly on pleasant days many people will be drawn there to gain an expansive experience, in contrast to the traffic, tightness, and density of lower Manhattan.

Visitors and people who work in the Trade Center will find this grand five acre plaza a mecca, a great relief from the experience of the narrow streets and sidewalks of the surrounding Wall Street area. I remember when I worked on Forty-fourth Street in New York that I would walk to Rockefeller Center on almost every pleasant day and wander through the gardens, watching the activities in that relatively small plaza. At the Trade Center there is space for the many people who are in even more crowded conditions than in mid-town Manhattan. The towers are placed at the south and west corners of the plaza; their shadows, coupled with the natural breezes off the river, should make the plaza a very pleasant place on even the warmest of days. I have seen festivals in Europe and in Asia that are extremely delightful occasions; if periodically the foreign countries involved in the Trade Center were offered the opportunity to celebrate their most important holidays in the plaza, I am sure that such events would bring thousands of local people and tourists to the Trade Center at night, adding a dimension to New York that it presently does not have.

I've often felt that much of the criticism of the Trade Center has been underlaid with a form of antiurban bias, one that is not prone to appreciate the densities and diversities of Manhattan. In my mind, urban concentration and New York are very much here to stay, and our task is to enhance and to celebrate those facts, making the most of the urban condition and the urban opportunity.

During the long period from the great depression on into the early postwar years, there was little commercial high-rise construction in Manhattan. During that time, I am sure, individual perceptions of the silhouette of New York became fixed, and the general skyline of Manhattan came to be thought of as unchanging. As postwar development and prosperity ensued, Manhattan again became the site of renewed construction activity that first focused in the mid-town area and then shifted downtown. New techniques, organizations, and technologies manifested themselves in this intense construction activity, and the Manhattan skyline was no longer the same—the urban dynamic had reasserted itself and restated its exciting presence. Cities are not static entities; I am sure that, like the Trade Center, the Flatiron Building, the Woolworth Building, the Chrysler Building, and the Empire State Building were all criticized for breaking the then beautiful New York skyline, but as people became accustomed to them, they realized that it is the succession of new buildings that makes Manhattan the unique and fascinating urban center it is.

For the Trade Center's integrated superblock site, we developed more than one hundred schemes and made plans and block models of each. At about the fortieth one we felt that we were on the right track, but to test it we tried sixty or so other schemes. We then expanded this idea, with its central plaza and two 110-story buildings, into more detail and presented it to Mr. Tobin and the Port Authority Commissioners about fifteen months after we had begun the design.

The presentation was accepted with enthusiasm, and then we were faced with the enormous task of designing the buildings in detail. I must say that the most difficult part was to design the 110-story buildings with the human scale in which I believe, as well as with the use of the most advanced, yet proven, applications of modern technology.

One of our first technical problems was how to dig the necessary excavation, a very large area of about 500 feet by 1,000 feet, extending from the IRT Subway at Greenwich Street to West Street, and from Vesey to Liberty. The Port Authority engineers, who were to design the foundations, told us they planned to sheet pile the perimeter to a thirty-five-foot depth and then drive piles down to the rock for the tower foundations, solid rock being about seventy feet below grade. The site presented a serious dewatering problem, since the surface of West Street is only three feet above the Hudson River. A thirty-five-foot excavation would give a thirty-two-foot head of water, or a lateral pressure of more than 2,000 pounds per square foot at the bottom of the excavation. Since sheet piling tends to leak like a sieve, trying to pump the water out in order to excavate would be an immensely costly proposition, yet there would still be thirty-five feet to go to the solid granite that underlies that area of Manhattan.

I knew instinctively that there must be a better way, since the Port Authority engineers had much experience in building many tunnels for automobiles under the Hudson River and in sinking tremendous caissons for bridge abutments. Because of my opposition, the discussion continued over several months, and they agreed to seek a better system. The late Martin Kapp, one of the top structural engineers in the Port Authority, went on a worldwide search, and in Milan he saw a subway being built with a system called the slurry wall; this, he thought, would be the answer. It was, and instead of going down only the first thirty-five feet, it was decided to go all the way to rock.

The slurry wall was a very ingenious system, perfectly adaptable to a situation like ours. It used a "clam" to dig a slotted hole through the earth, in this case three feet by twenty-two feet, going seventy feet or more in depth, then into the rock to socket the final concrete wall. As these slots were dug, the material removed was replaced by the slurry material, a very heavy mixture of bentonite clay and water, of about the same specific gravity as the wet earth. The slurry maintained the shape of the slotted hole, holding back the earth and the high water pressure. Then a prefabricated steel reinforcing cage twenty feet plus by seventy feet deep was lowered into the excavation. A concrete tremie was lowered to the bottom, and, since concrete is heavier than slurry, the slurry rose to the surface, leaving a three-foot-thick reinforced concrete wall anchored into the rock. These twenty-two-foot-long sections were made and tied together in a continuing wall (except that when the demolition of a particular building was delayed it was skipped and the wall installed later), until the entire 500-foot-by-1,000-foot area was surrounded by the slurry wall. Thus the excavators were able to dig in the dry, which was vastly simpler; the concrete wall was tied back to the rock with steel cables so that as the excavation proceeded there was little danger of the wall being pushed into the hole by the external hydraulic pressures. I often said that on a summer day after a dry spell I could have taken a dipper and pail and removed all the surface water from this enormous excavation.
After digging was completed, the rock was cleaned off, and heavy steel base plates under each of the great steel columns that surround the tower buildings at ten-foot centers were grouted and bolted to the rock. As the basement floors were installed, the rock ties of the perimeter wall were released, and the completed slabs buttressed the slurry walls. I have been told by the Port Authority that the system saved at least $20,000,000, with three floors of 500,000 square feet each of badly needed basement thrown in for free. During the entire period, the trains to New Jersey were kept running through the excavation.

The frame of a skyscraper is a cantilever up from its foundations, and building this kind of cantilever sufficiently strong to resist the heaviest winds is the basic structural problem for tall buildings. Such winds occur in New York on those occasions when a Caribbean hurricane drives up the East Coast. We determined that the best application of present-day technology was to use the exterior wall as the basic cantilever structure. New York buildings have generally used X-bracing in their central cores to take the wind stress. This is inefficient and cumbersome, especially in higher buildings; there is no constancy in the core as elevator banks drop off and openings for stairs, elevators, and utility cabinets preclude a clean structural frame. Using the exterior wall meant employing the most efficient structural system available—the entire building perimeter—as a strong tube to act as the cantilever. In the Trade Center towers the exterior walls are constructed as Vierendeel trusses, consisting of vertical and horizontal members; such a truss may not be as efficient as the diagonally braced kinds used in recent high buildings in other areas, but it appears far lighter and less bulky and interferes minimally with the quality of the interior spaces.

An extensive program to develop wind-engineering criteria was undertaken, and two wind-tunnel facilities were used, one at Colorado State University, the other in London. As one part of the design to minimize the sway of the frame, the structural engineers came up with a most ingenious damping system that acts at the ends of the floor beams like the shock absorbers of an automobile. The mass of the stone exterior of a heavier structure such as the Empire State Building absorbs or damps a considerable amount of the energy of the wind. With a lighter building such as ours, that energy tends to move more directly into the frame. Thus the need for a shock-absorbing system. Also, the latter system uses much less structure and therefore makes for a tremendous saving on the expensive steel frame. The building moves about eight inches over ten seconds in a hundred-mile-an-hour wind, which is hardly any movement at all. There was an article some time ago stating that in high buildings of the sixty-story range in New York, the movement in a heavy wind was so great that the top stories had to be evacuated. This has never happened in the Trade Center towers, and I doubt if it ever will, despite the frequent gusts of strong winds at their upper elevations.

The module size of three feet, four inches was deliberately chosen, with eighteen-inch-wide columns and twenty-two inches for windows plus sash, to minimize the acrophobia experienced in buildings with floor-to-ceiling glass. These windows are narrower than one's shoulders; I've often gone to a high floor and comfortably placed my nose against the glass to view the plaza below. I can't do this in a building with floor-to-ceiling glass and mullions say five feet apart because, as experienced as I am in high-rise buildings, I still have a strong feeling of acrophobia. Where we have used wider windows with floor-to-ceiling glass, I have insisted on a strong waist-high bar to give a sense of security to those who work in the building.
The standard small office used throughout the country is more or less ten feet wide; when a five-foot module is used, the offices have to be ten, fifteen, twenty feet, or larger. With the three-foot-four-inch module there is a ten-foot width for the basic office size, then thirteen feet, four inches; sixteen feet, eight inches; and twenty feet, giving a greater amount of flexibility in the layout of office areas and making the spaces more desirable for rental purposes.

The Trade Center is about thirty percent glass, whereas most all-glass buildings are about fifty percent. The columns are twelve inches deep from outer aluminum face to glass, which shades much of the glass of the narrow windows, particularly on the south and west facades, during most of the working hours. This saves a great deal of energy for air conditioning, and the low amount of glass saves heating in the winter, compared to the glassier buildings built in recent years.

I've heard much negative comment about the quality of the views from the windows. The purpose of buildings is to have comfortable working areas and not to be observatories where one stares out of the window at the view all day long. The windows are amply wide and sufficiently close together for both a dramatic outlook and little sense of claustrophobia. I have always been against high window sills simply because they prevent the people working at locations further away from the windows from seeing the city or the ground and water below.

Ninety-five percent of the total building frame is designed in standard steels. Steel is much stronger today, making it possible to have longer spans. Using these standard steels, the towers have freespan floors from core to exterior bearing walls, without the interference of the usual interior columns. In the Trade Center tower walls, where the interior faces are quite flush, the close spacing of the steel columns is part of the Vierendeel truss system. These columns also emphasize the fundamental verticality, which is properly characteristic in my mind of the architectural expression of a tall building.
As for the choice of the exterior wall material, any building of great height built now must logically have a light metal skin, since the great weight of stone walls, with their necessary heavy-masonry backing, imposes tremendous extraneous load on the structure at an unnecessary cost. When the World Trade Center was being designed, Fritz Close, then chairman of Alcoa, called me one day and said, "Yama, I understand you are going to use stainless steel for the curtain walls of the towers." I laughed and said I was thinking of it. He asked, "Why? Aluminum is significantly cheaper." So I told him I did not like the color of standard aluminum, since it was so cold-looking. He said he could change the composition of the alloy and provide exactly the warm color of aluminum I wanted, using new technologies to overcome problems of color consistency from panel to panel. I told him I did not want a coating, but a new alloy to give us the color throughout the panel. He agreed, so Alcoa's labs went to work and gave us several trials of pink, brown, and other shades. I said to him during this period of research, "You really aren't serious about making these two large buildings pink, are you?" He laughed. After a time, Alcoa did come up with a beautiful silver alloy, warm and sunny-colored, that was used on the Trade Center towers and has been since been adopted for several other high buildings.

In the curtain walls applied to other buildings, I had seen that many of the sealants used had failed to live up to their claims. Some sealants dry out in sunlight and crack and leak, letting water into the building. I could not envision the continuous maintenance of two million square feet of wall at the Trade Center or the need to reseal it periodically over the life of the towers. Consequently I asked the curtain-wall manufacturers to eliminate the use of sealants in their detailing for the walls, which they were to submit with their bids. Alcoa, which was the low bidder, took this concern very seriously, and its subcontractor, Cupples Products, was assigned the responsibility for development and manufacture of the curtain-wall. Cupples eventually produced a wall system for controlling the vertical movement that results from expansion and contraction of the wall, which in turn is caused by climatic changes in temperature. The ingenious system they devised uses aluminum sheets that have a considerable overlap. The pressure of the wind stops water from entering the building. Since the pressure in these cavities would equal the force of wind, this is called a pressure-equalization system, and it was developed in Canada. Thus the most economical, lightweight, maintenance free cladding wall possible was developed and used. The vertical joints between the aluminum column covers and the sash were continuously weather-welded. The column covers, which are U-shaped, act as accordions to take care of the horizontal expansion and contraction of the curtain wall. Since the curtain walls were built several years ago, no windows have blown out nor have the pressure-equalized walls admitted a single drop of water into the interiors of the towers.

Early in the planning of the design, Mr. Levy recommended that an unmanned mechanical windowwasher be devised. Researchers at the Battelle Institute and AMF worked on the feasibility of the idea and developed design criteria. An unmanned window-washer is not only safer, but can run much faster day or night, thus being much more efficient than the manned washer.

Another basic advancement in technology came in the elevator systems and the introduction of sky lobbies. The biggest waste of space in high-rise buildings results from the many elevator shafts rising from the ground floor. To eliminate this, we divided each of the twin towers into three vertical zones. The lower third is served by a typical system of regular-sized, twenty-passenger, 3,500pound-capacity elevators. The upper thirds are served initially by the two groups of large express elevators called shuttles. These 10,000-pound-capacity shuttle cars carry fifty-five people to the upper sky-lobby floors, where passengers then transfer to conventional elevator banks. Thus they have only two stops at the ground floor and one at the sky lobby each group serves. It took some discussion before we could persuade Otis Elevator Company to undertake the motors for these large new cabs.

From the main lobby level, one group of eleven shuttle cabs goes nonstop to the forty-fourth floor; the cabs have doors at each end, so that the first passenger in is the first one out. Traveling at a speed of 1,600 feet per minute, it takes but a few seconds to arrive at this sky lobby and a few seconds more to walk to the local elevators serving the middle one-third of the tower. The shafts for these local elevators are stacked above the shafts of the local elevators below, thus saving space. Similarly, a group of twelve shuttle elevators reaches the seventy-eighth-floor sky lobby, which serves the upper one-third of the building. Selected shuttle elevators in each tower provide nonstop service to the facilities on the one-hundred-and-seventh floor, the restaurant in the North Tower, and the observation deck in the South.

This system greatly reduces the volume of floor area taken up by elevator shafts. Compared to conventional elevators, with all shafts beginning at the ground floor, the shuttle-sky-lobby system provides fifteen to seventeen percent more rentable floor space.

I have undertaken this lengthy description of the application of contemporary technology in the design of the World Trade Center to explain the rational means that were sought to achieve the fundamental composition of two very tall towers, with the great plaza and the lower buildings around them. These technological breakthroughs enabled the Port Authority to construct the towers at about the same cost as more conventionally designed fifty- or sixty-story buildings. I believe the Trade Center is a unique complex. The towers, relatively free of surrounding buildings, provide superior views. The project is an interesting mix of low and high structures around a great open space that constitutes almost one-third of the site.
Over the years, as I have revisited projects that we have done, I have found that their owners and occupants interact with the built environment, and special kinds of experiences become evident. A restaurant at the top of the North Tower was always intended, but the unique skills of restaurateur Joe Baum and architect Warren Platner have produced a truly marvelous experience in "Windows on the World," possibly one of the most exciting restaurants anywhere. In its special way, it is an example of the evolving process of personalization that is part of the living fabric of a large project.

For the delicacy of design at the Trade Center, which has been criticized as being "dainty," I often refer to the Emerson quotation cited earlier and its effect on my work. I was trained in the twenties and early thirties, when classic design was the theme of the day. Though the traditional historic architectures I was taught then are not appropriate to our present-day techniques of building, their graceful proportions are still vital to any structure. The ensuing peace and sense of permanency are essential parts of fine buildings, and the search for these qualities should never be forsaken.

I do think that the plan and the height of the Trade Center towers allow for outdoor space for people at ground level, and the advances in building technology I have described make for economic competition with lower buildings, giving us the opportunity to open up our urban centers with the spaces, be they green or paved, that are so important to life in the heart of our cities. I believe that the Trade Center will come to be seen and experienced as one of the really exciting places in New York, which I am confident will continue to be the most marvelous, stimulating contemporary city in the world.

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