Ned's Lecture

Last night, I attended a lecture by N__B on the development of the skyscraper in the late 19th century. Ned mainly focused on the newspaper headquarters of Printing House Square in lower Manhattan. While he lamented the fact that he could have done better, the lecture was clear, informative, and entertaining... perfectly suited for laypersons as well as for individuals involved in the building trades.

Ned began his lecture with a discussion of the origin of the skyscraper. Besides height, he defined skyscrapers as being slender- the Manhattan Building of Chicago is a prime example of an early skyscraper, even though it's not very slender, and Ned noted with glee how a friend of his from the Windy City is a bit miffed that this Chicago landmark bears the name "Manhattan".

Ned defined characteristics of buildings- to paraphrase, they must resist the effects of gravity, they must resist the effects of lateral load (modern buildings must also resist the lateral effects of wind, and seismic activity as well), buildings must have interiors sheltered from external elements, buildings must have floor space, as an added characteristic, buildings should have some degree of fire resistance. Ned used the example of a tool shed as the simplest building- it resists gravity and lateral load, it has an interior sheltered from the elements, and it has a floor. Giving the example of the Statue of Liberty as a structure which is not a building, as Ned noted that it doesn't possess floors.

Until recently, most buildings had bearing walls- the masonry walls of the building provide the support for the structure. The walls are thicker at the base of the building and gradually thin as the building rises. Interior walls tend to be thick, as they also support the structure. Ned cited the Hotel Chelsea as a prime example of a building with masonry bearing walls, and quipped that the thick interior walls provided quiet rooms, which explains the popularity of the hotel with writers, musicians, or whatever Sid Vicious was. One problem with tall buildings with masonry bearing walls is that the thickness of the walls makes the interiors of the lower floors dark, as the windows tend to be tunnel-like. An advantage of masonry bearing walls is that additional stories can be stacked on the building- Ned used the example of the New York Tribune Building to illustrate this nicely.

Ned then went on to describe what he terms "Cage Frame" buildings, in which the masonry walls are reinforced by columns- originally, the columns would be adjacent to the masonry walls, but they came to be imbedded within the walls. As the masonry walls taper as the building gets taller, the columns in the upper stories tend to emerge from the walls, while they are completely imbedded in the lower floors. In these buildings, the walls do not have to bear the entire weight of the structure.

Finally, we have the development of the steel "skeleton" framed building, in which the structure is supported by, you got it, a steel skeleton, while the walls merely keep out the elements. As a fascinating aside, Ned noted that, originally, the walls were constructed from the bottom up, as bearing walls necessarily were, but that the wear and tear of construction often damaged the walls, necessitating replacement- relatively early in the development of curtain walls, builders came to begin construction of the walls at the second or third story, thus obviating the need for replacement of first story walls. One drawback to the steel skeleton building is that it is more difficult to increase the height of such buildings, unlike the bearing wall constructed buildings, on which additional stories can be stacked.

The greatest advantage of steel skeleton framed buildings is the cost of construction- most of the building components can be made off site. Masonry construction requires skilled on-site construction. While steel was initially expensive, it was less costly to build such a building than to have a crew of masons working on site constantly.

Of course, Ned illustrated his lecture with gorgeous old photographs of such gorgeous old buildings as the Singer Building, City Investment Building, and other stellar examples of early skyscrapers, such as can be found at his beautiful blog. While he posted a self-deprecatory entry on his blog today, don't believe him for one minute- he hit a home run with his presentation. My post does not really do Ned's lecture justice, so you'll just have to check out his blog on a regular basis, as he posts on the arcana and minutia of structural engineering.