With a 1000ft main-span, the Gerald Desmond Bridge replacement is set to become California’s first long-span cable-stayed bridge. Elegant mono-pole towers with a unique cross section, transforming from an octagon to a diamond, will form a distinctive landmark for the Port of Long Beach in Los Angeles, CA.
After nearly 45 years in operation, Los Angeles’s Gerald Desmond Bridge is approaching the end of its useful life. The existing bridge will be replaced with a six-lane, cable-stayed bridge. The replacement bridge will be two miles long, including over 6,000ft of elevated approach viaducts up to 200ft high, and a major freeway interchange providing 200ft of vertical clearance.
Arup is the design lead for this design-build project won with a technical proposal which scored highest among all competitors. The final design of this fast track project will be completed in 2014, with the opening of the bridge scheduled for 2019.
Challenging seismic design
While the span of the bridge is modest, the extreme seismic demands of the project mean that it is technically just as challenging. One of the key refinements of Arup’s design is the introduction of viscous dampers to seismically isolate the area between the deck and tower of this bridge.
The key seismic issue for the bridge is the ductile performance of its hollow 150ft tall columns. Our design team had to extend beyond the current California seismic code to develop acceptable ways of designing these hollow column sections.
Our design allows for relative movements at the deck-tower junction. By doing this, the forces in the tower are significantly reduced. Additionally, it allows for significant improvements to the cost, construction schedule, durability, aesthetics, and seismic performance of the tower compared to the reference design.
Although earthquake loads dominate, as for any long-span bridge, a thorough investigation of wind effects is considered in the final design of the bridge. The aerodynamic performance of the bridge has already been investigated through a programme of wind tunnel testing and numerical wind buffeting analysis to confirm high wind speed strength and stability, as well as, low wind speed serviceability against vortex shedding vibrations.