In an article about earthquakes published by Scientific American, they explain that, “Lateral shaking is the force that can cause the most damage to a building during an earthquake.” Since the force usually occurs in a direction parallel to the ground, skyscrapers in earthquake prone areas need to have lateral resistance to prevent quake damage and to protect against other lateral forces such as wind.
The Conco Companies are providing concrete services on the new Wilshire Grand Center in downtown Los Angeles, which when finished, will be the tallest structure built in a “seismic hot zone.” For this reason, the building’s design has been put through some of the most advanced and sophisticated earthquake modeling available.
The skyscraper’s earthquake resistance is further complicated by the fact that architect, David Martin, designed the building with large windows on every floor that required the construction of a concrete core. Since the core is 33 feet wide along its narrowest side for a building that will be 1,100 feet tall, the geotechnical firm, AMEC, was hired to ensure the building’s resistant to damage from a quake. Their job was to create simulated earthquakes to test the tower design and to evaluate “the maximum acceleration — the greatest jolt — that the building could experience.”
After a series of numerous tests and studying damage from past earthquakes in Southern California, the engineers refined the size and depth of the foundation to resist as much as “13.2 million pounds of force pulling up and 25 million pounds of force pushing down on each of the 20 perimeter columns as the tower swayed during an earthquake.” However the test still simulated some buckling so rather than increase the amount of concrete, AMEC’s solution was to add devices called buckling-restrained braces. The devices are long steel bars encased in a steel box filled with grout that allows the bars to compress or stretch when the building moves. The redesign of the Wilshire Grand will now include 170 of these devices.
The Conco Companies are a leading supplier of concrete services for the Western United States. We have built our reputation with superior concrete formwork, reinforcing, place and finish, shotcrete and other ancillary services that benefit from our vast experience. With four regional offices, we serve California, Oregon, Washington, Nevada and Colorado.
graphics.latimes.com/wilshire-grand-earthquakes/ – Sources: Leonard Joseph, Thornton Tomasetti; Tammy Jow, Joseph Varholick, Carey McLeod and Noel Moreno, A.C. Martin; Steve Carroll, Schuff Steel; Ian Aiken, SIE Inc.; Nippon Steel Engineering USA; G.G. Schierle, USC School of Architecture; Dave Eichten, Pankow.