Wilshire Grand Week: From the Street to the Spire

The Wilshire Grand Center is the first Los Angeles High Rise not requiered to have a flat roof for helicopter landings.

DTLA - It could be said that the middle of the new Wilshire Grand Center is somewhat common. It’s huge to be sure, but the 889 hotel rooms and 400,000 square feet of office space are similar to other offerings in Downtown Los Angeles.What really makes the 73-story project stand out — in addition to being the tallest structure west of the Mississippi and a game-changer for the Downtown skyline — is what’s on top, and what’s on the bottom.
The Wilshire Grand is the first Los Angeles high-rise that doesn’t have a flat top for helicopter landings. At the base of the structure are seismic elements that would allow the building to withstand a magnitude 7.5 earthquake from one of the 29 active fault lines within 50 miles of the building.
The Wilshire Grand has an 18-foot-thick concrete foundation. That provides some of the greatest seismic support, according to Gerard Nieblas, president of Brandow & Johnston, one of the structural engineering firms that worked on the building.
The hotel rooms and office space are built around a concrete core (some elevators, staircases and other infrastructure are inside the core). That element provides stability for the tower’s outer walls.
Additionally, what are known as buckling restrained braced frames connect the outer beams of the building in three sections along the core for the entire height of the tower. The steel support structures are meant to absorb seismic energy and will help stabilize the slender edifice against wind and earthquakes. While the top of the tower can sway up to 17 inches, it won’t buckle.
Also running from the street to the top floor are stairways. Towers of this nature would normally have a pair of stairways, said Christopher C. Martin, chairman and CEO of AC Martin, which deigned the tower and managed its construction. He added that the Wilshire Grand has a third stairway to help with high occupancy on upper floors. The team also worked to make sure that first responders would have a clear path.
“On 9/11, there were issues with people running down and firemen coming up, so we put a firemen’s elevator in the concrete core,” Martin said. “It’s surrounded by two to four feet of concrete that’s almost impenetrable.”
Another set of braces are on floors 70-73. Martin said the design team opted to work that into the architecture.
“We left them as exposed steel. We buffed them until shiny and coated them in a toned lacquer,” he said. “It’s exciting and huge and right there at the bar.”
This is also why the Wilshire Grand has the curved top, rather than the usual flat roof designed for helipads. Flat roofs had been required in Los Angeles since 1974. Modern technology and new safety standards led the city to lift the restriction. The Wilshire Grand is the first building to take advantage of the change.
The loosening of the rules gave the design team more leeway, allowing them to build a curved glass crown that rises 107 feet above the rooftop pool.

http://www.ladowntownnews.com/development/wilshire-grand-week-from-the-street-to-the-spire/article_f692fa14-5515-11e7-a976-83ceb47fe756.html