Building a Skyscaper - The Skeleton

As part of our first task, we were to watch this video on the Caltrans building in Los Angeles.

Designed by Morphosis, a very well-known architecture firm, and built by Clark Construction Group, the Caltrans building does not meet the heights of some of the world's tallest skyscrapers, but it is a very unique and intricate building.  The design and sustainability aspects of this building and the San Francisco Federal Building (also designed by Morphosis) are quite interesting.  I could continue on with the architecture of this project, but focus should be put on the construction element.

It was interesting in the video that the skyscraper was regarded like a "testbed" and that it is a place where they like to "work out new technology, new ideas, and new construction methods" as they try to build "ever taller, faster, cheaper."  The video also highlighted the role of the general contractor and his team.  The construction process is under high pressure as the GC works "like a traffic cop" to coordinate all subcontractors, scheduling, and costs.  The contract contained a $25,000 penalty for everyday the construction goes beyond the scheduled completion date.  And besides what is stated in the contract, the GC is constantly responding to issues on site, such as injury or death, weather conditions, mistakes, and crime.  The construction site can become something other than intended, like a memorial site for the worker who died, or a media spectacle when the crane was hijacked. 

I enjoyed the historical components in the video as well (architectural history was my favorite subject in my undergraduate studies).  The invention of cast iron columns replaced the use of thick masonry exterior walls for structure.  This started a huge revolution in design and construction due to the fact that with "skeletal construction" the building can be supported from within which freed the facade to be independent and designed separately.  This innovation allowed for unlimited height of buildings to be constructed and the interior could then be designed to utilize maximum floor space (more square feet to be rented out). 

The structural engineering of this building, although always an important element, was vital in this project due to its location.  Because the building is located in an active seismic zone, careful consideration had to be given to the design of the framing in the project.  The video went further and described a skyscraper in Taiwan, a location where construction must consider seismic activity and typhoon winds.  Steel framing is used to handle any earthquake activity but it is so lightweight compared to the strong winds the building must face, so a braced core with outriggers was engineered.  I worked on a project for school in which I had to analyze the Jin Mao Tower in Shanghai, designed by SOM (the same firm who designed the John Hancock Center in Chicago which was mentioned in the video for its innovative structural design).

The building contains an octagon-shaped concrete shear wall core surrounded by 8 exterior composite supercolumns and 8 exterior steel columns. Three sets of 8 two-story high outrigger trusses connect the columns to the core at 6 of the floors to provide additional support. (The number 8 is associated with prosperity in the Chinese culture, which appears in other areas of the design, such as 88 floors. The design also draws on traditional Chinese architecture by utilizing the tiered pagoda form.) Additionally, the steel shafts have shear joints which act as shock absorbers for the lateral forces imposed by winds and earthquakes.  The drawing below is one I did as part of the above-mentioned project to illustrate a composition containing both the elevation and a section cut through the tower.  Mid-way through the drawing, one can also see a partial floor plan and some enlarged structural details.