california construction

California To Get Almost Earthquake Free Building by 2017

The work is going on at the corner of Wilshire Boulevard and Figueroa Street, the making of Wilshire Grand will be the tallest structure built in a seismic hot zone when completed in 2017 is underway. Its design has undergone the most sophisticated earthquake modeling performed on a building in Southern California. But even that has its limits.

Leonard Joseph, renowned engineer said: Earthquake design is a fuzzy proposition. He worked in the firm Thornton Tomasetti. “You can’t ask an engineer to guarantee that a building will never collapse in an earthquake. That is not fair, and that is not the deal that society has made with the construction world,” he said. He also added, “You can ask that it will behave as well as possible, meeting at least the code requirements. Even that is a heavy responsibility.”

Journalist Thomas Curwen of Los Angeles Times recent article describes how evolution of building design happened. According to the him, there are many ways to hold up a tall building. Over the last 100 years, structural styles have come and gone, depending on the availability of materials and the building's needs. While Los Angeles may not be known for its high-rise culture, the city has a diversity of styles.

But steel-frame buildings lose their efficiency at about 60 stories. Above that, the columns have to become larger and more closely spaced, cutting into valuable real estate. In the 1970s, a new technique allowed buildings to shoot skyward. In place of the jungle gym, buildings were held aloft by perimeter columns, a technique known as a tube system. With its twin towers standing 110 stories, New York's World Trade Center was the nation's grandest example.

The perimeter columns had one drawback, however. They obstructed views. In the 1990s, advances in concrete technology — chemical additives that made the material stronger and easier to deliver hundreds of feet above the street — led to the conception of a high-rise as two interdependent structures: A concrete core, rising the height of the tower, serves as the central support for a skyscraper built around it. Exterior columns are still necessary, but they are much smaller.

High-rises with narrow concrete cores can be additionally supported with structural elements known as outriggers: braces that form giant triangles with horizontal and diagonal members extending from the core to the perimeter columns. Together, the outriggers and columns act like ski poles for the concrete core, helping to resist vertical and lateral forces.

The style met Martin's requirements for the New Wilshire Grand. Thirty outriggers, positioned between the 28th and 31st floors, the 53rd and 59th floors and the 70th and 73rd floors, extended from the core. But that didn't mean the tower could survive earthquakes.



Powered by Blogger.