The American Council of Engineering Companies (ACEC) of Washington has awarded its top honor — the Platinum Award — to Magnusson Klemencic Associates (MKA).
The award is for Structural, Seismic, and Wind Engineering on One Rincon Hill, a 60-story, 618-foot residential tower in San Francisco, located only eight miles from the San Andreas fault. With only a quarter of an acre allocated for the base of building, the tall, narrow structure can withstand seismic activity five times larger than the largest San Francisco earthquake ever recorded and uses a first-of-its-kind structural system.
Prominently located by the Bay Bridge, One Rincon Hill has become a highly visible landmark at the entry to San Francisco, showcasing progressive engineering, floor-to-ceiling views and opening the door to sustainable high-rise residential development in San Francisco and beyond.
Owner: Urban West Associates
Magnusson Klemencic Associates (MKA) developed precedent-setting engineering to solve the challenges of building a 60-story, 618-foot residential tower on a quarter-acre piece of land in one of the most seismically hazardous areas of the country.
Because the owner's requirements for floor-to-ceiling views and unit planning flexibility could not be met safely using traditional moment frames and dual system designs, MKA employed cutting-edge Performance-Based Seismic Design (PBSD) to create the optimum structure.
The team designed a concrete ductile core wall with four concrete outrigger columns connected by 16 buckling-restrained braces (BRBs) at Levels 28 to 32 and 51 to 55 to add stiffness and absorb energy in an earthquake. MKA selected the largest tested BRBs available to ensure maximum reliability and structural benefit and eliminate any possible performance concerns with this new technology. A system of embedded steel erection columns and plates connect the BRBs to their outboard columns.
To counteract building sway from high winds, MKA designed two 54,000-gallon tanks to be placed at the very top of the building. The system, known as a Tuned Liquid Mass Damper (TLMD), uses the oppositional movement of water 'sloshing' in a tank to counteract building movement, while 'baffles' (or screens) in the water modulate the flow.
The team invented a system to monitor weather conditions, ground motions, building sway and torsion, and water levels in the sloshing dampers that is viewable via the Internet 24 hours a day.
In working on the pieces that link the individual core wall sections into a complete structural 'tube,' MKA engineers developed alternative reinforcing bar detailing, modifying the method of reinforcing confinement, then organized laboratory testing at the University of California Los Angeles in partnership with the Charles Pankow Foundation and Webcor Concrete.
The testing proved that the alternative detailing performed as well as traditional detailing but can be constructed more easily and less expensively. The results of this research led to a modification of American Concrete Institute's Code 318-08.