Chris Martin, chief executive of Los Angeles architecture firm AC Martin Partners, faced a dilemma: How do you construct the tallest building in the West on a narrow lot in earthquake-prone Los Angeles? Such a towering and slender structure would need an extremely strong foundation to support the massive weight resting on such a small footprint.
The answer: Pour a world record amount of concrete at one time.
So on Feb. 15 and 16 more than 2,000 trucks will participate in the continuous pour. They will pump 21,200 cubic yards of concrete at the site of the reimagined $1 billion Wilshire Grand Hotel at 900 Wilshire Blvd. in downtown Los Angeles. That is more than 82 million pounds of concrete – or the weight of 250 blue whales. The pour will take about 20 hours.
Due to the scale of the project, surrounding streets will have to be shut down during the operation, which will be on a Saturday and Sunday. Rather than sheepishly apologize for the temporary inconvenience, Martin and his construction partners have decided to embrace the magnitude of the event and turn the pour into a party.
“We’re treating it as a celebration,” Martin said. “We’re bringing in the USC Trojan Marching Band to lead the parade of trucks. I think all Angelenos should take pride in this.”
Korean Air Lines Co. bought the 1950s-era Wilshire Grand Hotel in 1989. The hotel always did steady business, averaging occupancy rates above 80 percent. But five years ago, Korean Air Chief Executive Y.H. Cho announced plans to turn the property into something spectacular. His suggestion: Tear down the old hotel and replace it with the tallest building in the Western United States.
Once completed, the 73-story structure will be 1,100 feet tall. It will supplant downtown L.A.’s U.S. Bank Tower building, which has been the tallest building west of the Mississippi River since it opened in 1990. The bank tower also has 73 stories but is only 1,018 feet high.
The new Wilshire Grand will contain 900 hotel rooms, 400,000 square feet of Class A office space and an observation deck on the 70th floor.
The transformation brought several engineering challenges that required the architect to get creative in figuring out how to support it.
“The solution came down to, well, why don’t we just do a very large concrete mat?” Martin said. “When we were all done with the planning, somebody said, ‘Do you realize this pour may be one of the largest ever?’ ”
Martin and his team verified that the planned pour would indeed be the largest ever recorded and have embraced the world record as a point of pride for Los Angeles construction.
“I want L.A. to be able to boast about its achievements,” Martin said. “Why not let us boast about a very significant engineering feat as a precursor to topping out the tallest structure in the Western United States? It’s something to celebrate.”
Concrete available
Martin was able to propose the massive concrete mat because of the abundance of concrete mixing stations, commonly known as batch plants, and mixing trucks available in Los Angeles.
Scott Borland, an executive at New York firm Turner Construction Co., the general contractor on the Wilshire Grand project, said the mat will be more than 17 feet deep, compared with the 10 to 12 feet typical for tall buildings built on a solid concrete foundation.
Borland said such a thick slab was necessary because the slender design of the Wilshire Grand concentrates the weight of the building on a smaller surface area than a building of equivalent weight with a larger footprint.
Keeping the massive mat cool after the pour is another major challenge. As concrete sets, it releases heat. In order to keep the concrete of uniform consistency, the construction team will use two massive cooling units, called chillers, that will pump cold water through 19 miles of piping coiled around the concrete to keep the temperature at a constant 160 degrees. The cooling process is scheduled to last up to three weeks after the pour.
“I don’t know that we’ve ever done a project where we’ve had to do this kind of thermal engineering around a pour,” Martin said.
The Wilshire Grand’s height is not the only aspect of the building that sets it apart from the other skyscrapers of downtown Los Angeles. The developers obtained an exemption to a 1974 fire ordinance requiring all tall buildings in the city to have a rooftop helipad. The Wilshire Grand, on the other hand, will be topped with a curved, sail-shaped roof punctuated by a spire.
Martin believes that the building will become an iconic tower on the L.A. skyline.
“There are 18 million people who see this structure,” he said. “And they’re all going to say, ‘I want to go to the top of that building to the observation deck and have a glass of wine.’ And if they all do that, we’re phenomenally successful.”
