• Students will be able to identify several different structural engineering principles relating to skyscrapers.
• Students will be able to match a design principle with famous skyscrapers.
• Students will be able to appreciate the difficulties in building tall structures.

After the newspaper tower activity, use the following history of skyscrapers, and the pictures found in later parts of this lesson.

Skyscraper Presentation

The San Gimignano Towers

For the beginning of the presentation, read the "Skyscraper Basics" portion of PBS's Building Big website. The information about the San Gimignano Towers, gothic cathedrals, steel and iron, and elevators provide a brief but informative early history of skyscrapers.

Another important concept to point out to students is the design element of foundations that allow skyscrapers to stand on the ground beneath them. Skyscrapers themselves would exert too great a force over too small an area for the soil to support them. Therefore, skyscrapers need a foundation to help spread that force over a larger area. If the soil is still too soft even with a large foundation, sometimes geotechnical engineers will dig down to reach bed rock to better support a building. However, sometimes, like in San Francisco, and many other coastal areas, the bed rock lies deep under ground. In those cases, MANY concrete piles (long rods of concrete) are driven into the ground with a large diesel hammer until they hit the bedrock. Then, the foundation and skyscraper sits on those piles.

The Home Insurance Building

The Empire State Building was completed in 1931 in New York City. It remained the tallest structure in the world for over 40 years! PBS's Building Big website provides background information and interesting facts about the Empire State Building Empire State Building.

Important concepts to point out to the students include the 3-D grid of columns evenly spaced throughout the entire structure disallowing large open spaces, its fast construction, and how the more-than-necessary amount of columns (redundancy) allowed the building to withstand the impact of a B-25 bomber.

The Empire State Building was the tallest building in the world from 1931-1972.

The Citicorp Center, shown at the top of the lesson, is a very interesting engineering design problem to point out to students. Although it was never the tallest building in the world, it still is a very impressive Civil Engineering feat. PBS's Building Big website provides information and interesting facts about the Citicorp Building and obstacles its designers had to overcome.

Important design aspects to point out to students include its cantilevered structure that allowed the church to remain in place. Also, an interesting fact is that when Hurricane Ella was approaching the city and the Citicorp Center, the city was only hours away from evacuating the area, concerned that the tower would not withstand the gale wind forces. The tuned-mass-damper is also a very interesting and advanced engineering accomplishment that would be good to discuss at least briefly.

The Sears Tower

The Sears Tower is still the tallest building in the United States since its completion in 1973. Since it was being built in the very windy city of Chicago, the building was designed to withstand the large lateral wind forces that it would experience during its lifetime. PBS's Building Big website provides more information about how the Sears Tower resists the wind.

Point out to the students the bundled tube structure of the Sears Tower and how it works to withstand both lateral and vertical loads. In addition, definitely point out how this tower sits on a large number of piles driven down to the bedrock.

The Petronas Towers, Kuala Lumpur, Malaysia

The Petronas Towers, featured in the movie Entrapment, which may be familiar to students, were until 2004 the tallest building in the world, and the first tallest structures not located in the United States. PBS's Building Big website provides Information and interesting facts about the Petronas Towers.

Point out to students the near-cylindrical design of the towers and how this design allows the towers to experience a lower wind force than if the towers were rectangular in nature. Also, the double-decker elevators are a fairly new-development and allow more stories and higher towers to be built, so they should be discussed.

The Taipei 101 in Taipei, Taiwan, is the newest tallest structure in the world standing 509 m high (1671 ft). An important point to discuss is how it was built in a highly active earthquake zone and therefore how it features a tuned mass damper system to increase the ability to withstand tremors. This tower also has double-decker elevators similar elevators to the Petronas Towers.

• Ask the students to explain why they built their towers the way they did. Encourage them to use the concepts and terms they learned in the history of skyscrapers presentation.
• Ask the students explain how their towers resisted the wind load (i.e. which parts of the towers supported the bulk of the load, or if their towers are really slender so that the wind has less area to act on, etc.)