Want to Build a Skyscraper? An Article from the USA Says How.

When people are drawn to live in cities, a demand for high-rise buildings soon follows. America in the years after the Second World War is a case in hand, despite the fact that automobiles began their triumphal advance at the time, and single-family dwellings became the social guiding theme in housing.  In a 1969 Detail article, Mies van der Rohe’s grandson Dirk Lohan described how the situation was in the country back in those days: the American urban population had burgeoned 16-fold within a hundred years, the number of jobs in the service sector almost doubled between 1953 and 1968 alone, plus a square metre of real estate property in the downtown areas of Chicago and Manhattan cost the equivalent of DM 10,000. According to Lohan, use demands of office buildings in particular were subject to such swift changes that high-rises were designed for a life expectancy of 30 years. (As we know today, they have generally outlasted this life span quite considerably, albeit requiring high expenditure on refurbishment and renovation).
 
The towering buildings of the Chicago School had a structural framework built of steel even back in the late 19th century, and this held true of the skyscrapers of the post-war era. A significant innovation occurred in the late 1960s when Fazlur Khan developed the framed tube concept, with the result that a non-combustible core was no longer required to brace tall buildings and keep them upright. Rather, Khan assigned the constructional members another role, integrating an exoskeleton in the building skin and thus significantly contributing to lateral stiffening. As the article by Dirk Lohan shows, previously unknown building heights could now be achieved at great material efficiency. The John Hancock Center in Chicago designed by Skidmore Owings & Merrill and still undergoing construction in 1969, and the twin towers of the World Trade Center by Minoru Yamasaki in New York, also not yet complete, marked the zenith of this development.  
 
It was Mies himself who sparked off the second great U.S. tall building era of the 20th century. His apartment buildings completed at Lake Shore Drive in Chicago as of 1951 were also featured in Lohan’s article. The steel skeletal frame of the two 25-storey residential towers was systematically thought through to its end, plus the façade linings and stiffening non-combustible structural components of earlier eras were eliminated, with all vertical and horizontal loads now being carried by the flexurally strong steel skeleton. However, Mies had to abandon his wish to make the steel skeleton visible in the interior due to fire regulations – but not so regarding the facades, for which he developed one of architectural history’s most famous details:  the double-T beam mullions on all the buildings’ upper storeys. With regard to the newly-erected buildings, it was not for nothing that Walter Peterhans, Mies’ fellow professor at the Illinois Institute of Technology, remarked:  “These towers … are built out of the materials of steel and glass, and yet they seem to be harbingers of the age of steel and glass, as if steel and glass had never been seen before”.