Thursday 1 November 2012

Torre Latinoamericana

The “Latin-American Tower”, at 140 m tall (204 m if you include the antenna) was Mexico City’s tallest building from 1956 to 1984. Designing and constructing skyscrapers before modern computers were available was no small feat in itself, but that's not enough to make this building stand out from say all of the turn-of-the-century towers built in the U.S. But Torre Latinoamericana stands as a testament to the capabilities of engineers using rational design procedures. 

"Rational design = good engineering" - Torre Latinoamericana
The problem with building a skyscraper in Mexico City is two-fold. First, the soil of Mexico City is unstable. The city is located in an ancient valley lake-bed over a large aquifer that is being drawn down too quickly, so foundations frequently experience flooding, and parts of the city sink several inches every year. Second, Mexico is in a high seismic region. Making a tall building is one thing, but making it earthquake resistant is quite another. Remember, the design was carried out in the late 1940's, so analysis for earthquake loads would have been done by hand. And not "by hand" like we mean today, where we at least have an electronic scientific calculator to do computations for us. Calculations would've been performed either mentally or with a mechanical calculator (capable of only basic arithmetic), with the aid of pencil, paper, slide rule, and table of logarithms.

Imagine using this to multiply two numbers together. Every engineer's life before the 1970's.
The design began with soil investigations, which at the time was pretty rare. Today, soil investigations are common (often mandatory) in large construction projects. Having an accurate model of the local soil mechanics enabled the engineers to properly analyze the earthquake loads and design the deep pile foundation and steel structure accordingly. The building was first put to the test just a year after construction was completed, with a magnitude 7.9 earthquake in 1957. Many older and non-engineered buildings were severely damaged, but Torre Latinoamericana remained unharmed. The building has withstood several earthquakes since then, including the magnitude 8.0 earthquake of 1985 that caused several downtown buildings near Torre Latinoamericana to collapse. This has led to its reputation of being one of the safest buildings to be in during a Mexican earthquake.

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