This thirteen-story LEED Platinum Certified building, with a performance mandate of immediate occupancy after a design basis earthquake (DBE), had had two previous lateral systems designed by other seismic consultants. The first was a base-isolation system; the second, value-engineered design was a structural-steel moment frame with supplementary viscous dampers. Despite the value engineering, estimated construction costs were still far too high. The contractor, Webcor, had learned about the team’s innovative post-tensioned lateral system that returns a building to plumb after a seismic event and challenged us to devise a third system for SFPUC. Led by David Mar, the team chose to redesign the building in concrete with our post-tensioned concrete cores, thus delivering immediate-occupancy performance at a much lower cost. The new structural design solution (1) added a thirteenth story owing to lowered floor-to-ceiling heights; (2) trimmed the construction schedule owing to our optimized link-beam design that, in conjunction with our PT lateral system, reduced steel reinforcement by 50 percent; (3) saved the project $10 million; and (4) decreased the project’s carbon footprint by 7 million pounds of carbon dioxide emissions.

Photo by Bruce Damonte