Seismically resilient

摘要

Seattle's Duwamish Waterway near King County, Wash., is the industrialized estuary of the Duwamish River valley, a seismically volatile region with a long history of being battered by earthquakes. The South Park Bridge, which spanned this estuary, had become structurally deficient after decades of seismic pummel-ing. After a planning initiative more than a decade in the making, the $167 million South Park Bascule Bridge Replacement project was completed and opened to traffic in June 2014. From its inception to completion, the project was an exercise in targeted design implementation. The new South Park Bridge is the first bascule bridge designed to meet post-seismic operational requirements of an AASHTO Seismic Zone 4 with 70- to 105-ft-deep soft soils. "Our goal was to design a movable bridge to remain open to traffic immediately after a 100-year return-period earthquake and closed to traffic for a matter of only hours or days after a 1,000-year return-period earthquake," Rich fohnson, HNTB's project manager on the South Park Bridge, told Roads & Bridges. "We achieved this by developing innovative design solutions, such as the sunken caisson foundations, isolated trunnion frames and a collapsible center joint on the bascule leaves."