Skyscrapers: How much wind can they take?

Skyscrapers:
How much wind can they take?
By Ruth Flack
February, 2005
Skyscrapers: How much wind can they take?
The purpose of building skyscrapers (or tall buildings) has changed over the past one hundred and fifty
years. In the beginning skyscrapers were built for two different reasons; a) for god(s) or b) as a sign of wealth
and power (to intimidate lesser classes and gain more power). Today skyscrapers are built due to a lack of
space in major cities and as a status symbol.
Tall buildings have existed for centuries. Some of the earliest tall buildings included the Great Pyramid
of Giza, Egypt which was built by the ancient Egyptians, and thousands of years later the cathedrals in Europe
including the very famous Notre Dame Cathedral in Paris, France. Modern skyscapers include the Empire
State Building in New York City, the Sears Tower in Chicago, and the currently tallest building in the world, the
Taipei 101 located in Taipei, Taiwan and is 101 floors tall.
Advances in technology in the late 1800’s allowed the skyscraper as we see them today. Inventions
included pressurized toilets (force water up pipes great heights in order to make a flush to carry away waste
products), this was an extremly important one because without it people would only be willing to go upwards
a certain heght, (because as soon as you managed to climb all the stairs to the 5th floor, if you had to use the
bathroom you had to run down the stairs to get to the lowest floor, and then run outside to use the outhouse).
Another important invention is steel, without the lightweight material skyscrapers would never have been able
to be inexpensive, slighty artistic and as high up as they are today. (Steel is cheap to make, you can do lots of
stuff with it, because it’s light so now instead of having a huge thick wall as a base you can have the base walls
be as skinny as the upper walls. Steel is also very, very strong and gives (sways) from a few inches to several
feet if necessary, which means you can stack as much of it on top of it self as people are willing to climb. The
elevator was a huge achievment, it ties in with all of the above because with the elevator people didn’t have to
walk to the 57th floor, they could ride in a elevator.
Today architects and engineers are focused on designing and building ever higher and more
environmentally friendly skyscrapers. The current trend for people to want to live near where they work has
caused an increase in demand for high density living space. At the same time, according to the U.S. Department
of Energy, buildings consume 39% of all the energy in the United States and there is a growing demand for
environmentally friendly buildings.
I also did an experiment concerning Triangles vs. Squares for building structures as part of my
research. I conducted this experiment using GeoMags (a toy made of magnets.) At first I thought that
the squares would be stronger, because that’s what you see when you go into a skyscraper. I built two
separate skyscrapers out of GeoMags, one without beams acting as crossbraces, (Figure 1) and one with
(Figure 2). I noticed that the one without the beams was very shaky and didn’t hold its form, but the
one with beams was firm. Then I added a second story to the building, one with beams (Figure 3) and
another without (Figure 4.) With the second floors I observed that a slight nudge or push on the side
of the one without beams, and the whole structure would tumble, but from straight down on the top, it
was very strong. With the beams it didn’t collapse, no matter where it was pushed or nudged. I learned
that crossbraces or beams in the center turn squares into right triangles, which are stronger than squares
without any crossbraces, because the crossbraces distribute the weight so that it is spread out and make it
easier for the structure to support the load.
Hypothesis:
My hypothesis was that the building, which was reinforced with crossbraces, would be able to
withstand a much greater wind force than the building without. I thought this because based on past
research I knew that triangles are much stronger then squares because they are able to spread out the
weight load. What the crossbraces are doing, in a sense, is making the square sides of a skyscraper into
trianges. Triangles supposedly are able to withhold a greater amounts of weight because they don’t
collapse as easily as a square.
I choose to test my hypothesis by determining how much force can be applied to the side of a
structure (simulating wind force, see Figure 6) before it reached its breaking point. If the deflection
became dangerously high, that would be considered the breaking point alown with, joints loosening,
collapsing, and falling.
Materials:
The materials I used for my experiment were:
Bridge Street Toys set(s) of: (Bridge Street Toys toys are built HO scale (or 1/87 of real skyscraper)
•
Columns
•
Beams
•
Crossbraces
•
Base pieces
•
Hook
•
Basket (to hold the weight, small cardboard box works very well)
•
String
•
Weights (pennies, dimes, nickels and lots of quarters)
•
Pulley (1/4” diameter)
Methods:
My methods were as follows:
(Set Up)
1. Build a ten story building using the columns and beams. (the width and depth should only be one piece
deep.)
2. Attach to base. (if you didn’t build it on top of the base)
3. Attach string to hook, and then to the basket. (see figure 6)
4. Hang the basket off of one side of the rod.
5. Hook the hook to the side of the tower.
6. Make sure the basket isn’t touching the ground.
(Experiment)
1. Measure out the weight and record
2. Add weight slowly into the basket, make sure the weights don’t over-lap until they have to
3. Measure and record the amount of deflection
4. Repeat steps 1-3 until the building reaches it’s breaking point
5. Record how much weight it could take before collapsing
6. Rebuild the tower using the same method, except adding cross bracing
7. Repeat steps 1-5.
Results:
As I performed the experiment I noticed that with the crossbraces I had to add some weight to the base,
because the building was so stiff that we were movng the entire structure, not just bending the tower. Without
the bracing the structure swayed precariously before it gave way, thus giving lots of warning time, whereas
with the crossbracing the building just suddenly collapsed, not giving any signs of breaking unitl it reached the
breaking point.
With the crossbraces as soon as one support loosened the whole structure weakened and then collapsed.
Without the braces, the structure gradually fell off of the lower supports, and it took a swhile, such as first one
beam would ‘go’ on the third floor, then on the fith another would loosen and then finally one on the fourth
gave and the whole building collapsed. If people were inside of the building, they would have plenty of time
to escape, but if people were in the one with crossbraces it would mean almost certain death for many.
Bibliography
1. Cross Giblin, James. The Skyscraper Book. Toronto, Canada: Fitzhenry & Whiteside Limited, 1981.
2. Doherty, Craig A. and Doherty, Katherine M. The Empire State Building. Woodbridge, Connecticut:
Blackbirch Press, 1998.
3. Dupré, Judith. Skyscrapers. New York, New York: Black Dog & Leventhal Publishers Inc., 2001.
4. Estulin, Chaim and Jakes, Susan. “Going Up…and Up: When Height is All That Matters.” Time Magazine
3 January 2005: page 172-173.
5. Frangos, Alex. “Architecture: Greener and Higher.” The Wall Street Journal 31 January 2005, sec. R: 5.
6. Goodman, Susan E. Skyscrapers. New York: Random House Inc., 2004.
7. Lacayo, Richard. “Kissing The Sky.” Time Magazine 3 January 2005: page 170 – 178.
8. Searle, Bobbi. Inside A Skyscraper. Danbury, Connecticut: Grolier Educational, 2001.
9. Severance, John B. Skyscrapers. New York: Holiday House, 2000.
10. Skyscrapers. Dir. Joseph McMaster. 2000. DVD. WGBH Educational Foundation, 2000.
11. Stone, Lynn M. Skyscrapers. Florida: Rourke Publishing LLC, 2002.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Measuring Deflection