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History of the Twin Towers,
This review is from: Twin Towers:: The Life of New York City's Trade Center (Paperback)
This book was written in 1999 as pressure was mounting for the Port Authority to turn the WTC over to a private agency. The book was reissued shortly after September 11 as the only scholarly history of the WTC. It's a fascinating study of political pressures and engineering feats.
It's impossible to discuss the World Trade Center Towers without first understanding the New York/New Jersey Port Authority. Conceptually, it was unique when it was created in 1921. Authorities - quasi-governmental agencies that were authorized to build projects and then levy user fees to pay for them - had a long and well-established history in England. What made this new authority unique in 1921, when it was created to build the Holland Tunnel, was that it was granted a charter to build facilities, i.e., multiple projects.
The idea for the WTC was conceived during a period of relentless optimism [Kenney] but "completed during a period of national gloom and retreat [Vietnam, 1970's, and Nixon's collapse.]" There were political aspects, aside from the desire to build the world's tallest building, and there was always the pressure from New Jersey to reduce bridge and tunnel tolls. A new project that would use these surplus funds would help to relieve that pressure. It was a project that was lauded by the critics at first, then reviled, only to be resurrected in the minds of New Yorkers, but never as an architectural triumph. It had the misfortune to fall between two architectural periods: International Style, with massive amounts of glass, and Postmodern, which represented a return to the more colorful and decorative building facades. Its Japanese architect, Minoru Yamasaki, used unique aluminum curtain walls that had been dyed to reflect light in unusual ways. The floor-to-ceiling windows were smaller, about the width of a large man, and set back from the curtain. This reduced heating and cooling expenses and eliminated the sense of vertigo that plagued other skyscrapers that had office space right up to the edge of the window, a more floor-efficient design. Yamasaki went through eighty iterations of the design, sometimes using three or four towers, but eventually settling on two. The spacing between them became critical because if placed too close together the winds sweeping down could create sympathetic vibrations in the buildings, destroying their integrity, i.e., a euphemism for causing them to fall down.
The engineering was incredible, and the building could not have been built without technologies developed in other countries. The "Kangaroo" cranes that hoisted themselves up the elevator shafts were developed in Australia. Nothing like them was available in the United States. They were needed to raise the very heavy steel columns that were the load- bearing walls, another unique design feature of the buildings, and the floors. It was initially thought that only U.S. Steel or Bethlehem Steel, the two largest steel companies in the United States, would be able to supply the enormous quantity of steel needed - the drawings for the steel construction weighed over 650 pounds - and Andrew Tobin, the Port Authority's director, thought that by involving them early in the design stage he would get a reasonable bid from them. Not so, and Tobin was so angry with their overbidding, which bore suspicions of collusion - a later investigation revealed no evidence of that - that he contracted portions of the steel to smaller companies, thereby saving over 30% of the anticipated costs. Going to different companies and subcontracting and bidding for smaller lots was to become the industry standard because of the cost savings.
Because the building was so close to the river and excavation for the huge buildings had to go deep down to hit bedrock (enough soil and material was excavated to create Battery Park, an eighteen-acre site that extended Manhattan Island an extra 700 feet into the river and creating additional real estate worth [$]), some method to keep the water out was needed that would not affect the adjacent structures. A slurry method imported from Italy permitted concrete and steel reinforcement for the huge "bathtub" that kept the water out. Slurry containing betonite clay was pumped in as the trenches were dug and then pumped out as concrete and rebar were placed to create the final walls.
The effect of sway on humans had to be tested. The buildings had to be flexible; any degree of stiffness could be built in, but it could not be changed after the building was complete. At its top the Empire State Building sways three inches in a one hundred-mile-per-hour wind. Swaying rooms were built to test people's reactions. Psychologists found that people would tolerate up to eleven inches of slow sway. That represented winds of 140 miles per hour, wind speeds that had never occurred in New York. The building was designed to withstand much higher gusts than that.
Wind can cause other problems. On a gusty day, the buildings twisted and moved so much that the freight elevators could not be used. They were the only elevators to go all the way to the top - all the others had shorter runs to assorted lobbies where commuters changed cars - and the 1350-foot cables would slap around too much. Everything had to be inspected daily. The elevators made 450,000 "movements" (one person on one trip) per day.
The Port Authority has its own police force, and forty-two officers were assigned to the WTC buildings. It is a unique force in that the officers have bi-state authority, the only police force in the country to have such authority. In fact, their jurisdiction lies in a circle with a twenty-five mile radius from the Statue of Liberty.
It's impossible to recount all the riveting (not a pun, since no rivets were used) details of the gargantuan buildings. It's a fascinating story of a building, and, aside from the enormous human tragedies of September 11, it was a great engineering loss as well.