Jonathan Kim

Beginning from the last quarter of the 19th century, skyscrapers emerged as competition for space grew fiercer in New York City. With the limited area on the island and demand for more space for living and for business, people began to reach higher. In order to achieve more height, engineers needed better structural technologies so that the skyscrapers can withstand its own dead weight, resist lateral forces like wind, and, above all, be safe for the people living in upper stories from hazards such as fire.

Masonry is the oldest form of construction where individual blocks are piled up with a binding element like mortar. The most popular example is the use of cinder blocks or bricks, which we see in many of our homes today. Masonry has many advantages: it protect buildings from fires, is more resistant to debris from hurricanes or tornadoes, and lasts as much as 500 years compared to 30 to 100 for structures made of steel or reinforced concrete.

Up until around 1880 most building had a common defining feature: pure bearing-walls. Many buildings prior were built with thick walls that carried all the weight of the structure: the floors, the roof and the wall’s weight itself. This method required the base of the building to be comparably thick compared to upper walls, which are also considerably thick. This limited buildings’ heights because the higher the building, the heavier it meant and the walls needed to be very thick to support additional weight. Large structures like castles and cathedrals used this as an advantage. Castles with thick walls protected them from their enemies and cathedrals used its walls for design.

However, in cities with limited spaces like New York City and Chicago, the buildings need height without large width that many shear wall buildings had. The architects and engineers needed a better structural technology to support the weight of the high-rise buildings without wasting the space at the base.

In 1855 the Bessemer process made steel production more efficient. Cheap steel, which had high tensile and compressive strengths plus good ductility, were available, but wrought and cast iron continued to meet the demands for iron based building products because the quality of the steel was not the best at the time. In 1879 Sidney Thomas solved this problem and by the 1880s the high quality of steels being produced had become reasonably consistent.

In 1884 the 10 story Home Insurance building was built in Chicago and it is considered the first skyscraper to be built with a steel structure. Steel skeleton is basically a large vertical steel box with many smaller boxes inside it. With this method, the main loads of the building are supported by the steel frame and the walls can be replaced by glass that keeps away weather and let light in.

Many of the skyscrapers built from the end of 19th century used the steel skeleton. In 1896, the 20 story American Surety Building was built with a high-steel frame and finally broke Chicago’s record.

HIB

ASB

As buildings reached 10 to 20 stories, most people found stairs not useful in climbing to higher floors. Many people only used the stairs for either second or third floor and found it inconvenient to use stairs beyond that. Many buildings in second half of 19th century did have primitive elevators, but they were not considered safe for people; if the cable broke, they would plummet to the bottom of the elevator shaft. Then in 1853, Elisha Otis developed a safety device that kept the elevators from falling if a cable were to break. The elevators revolutionized the skyscrapers, literally turning them upside down; upper floors became most valuable rental property with the best view of a skyline.

In 1902, an inventor, Ransome developed a system of precast concrete walls that made the construction quicker by eliminating the time required to cure at the construction site. He also created the reinforced concrete that took advantage of the tensile and ductile strength of steel with cheaper, fire proof, and damping concrete. Reinforced concrete is made by pouring concrete into a steel mesh and allowing it to set with steel skeleton within it. With the advent of reinforced concrete near the end of 19th century, the concrete became one of the most versatile building materials from being a very limited material.

In 1913, Woolworth building was constructed and was the first that combined all the components of a true skyscraper. Its steel skeleton rose from a foundation supported on concrete pillars that extended down to bedrock. Its frame was braced to resist the wind and its elevators provided both local and express services to all of its floors.

Many modern buildings now place the reinforced concrete in the center providing the building with most lateral strength. The One World Trade Center was built with a solid concrete core as its backbone. The concrete core is one meter thick and contains pressurized stairs that keeps away smoke. The steel frame is structured around the core to support the weight of each floor and the glass walls.