The Sixth Street Viaduct Replacement Project consists of removing the existing Sixth Street Viaduct over the Los Angeles River and US Highway 101 and replacing it with a new viaduct approximately 3100 feet in total length and 100 feet in width. The new viaduct will carry two lanes of traffic in each direction over the Los Angeles River, 2 railroad corridors, US 101 and local City streets. It also provides walkways/bike paths at each side of the bridge. HNTB is the designer for the replacement viaduct.

The structural system of the new viaduct consists of mostly a series of continuous concrete tied arches with inclined arch ribs. The arch spans range from 240 ft. to 310 ft. are supported on concrete Y-Bents. The Y-Bents in turn sit on the base isolation bearings on top of the lower vertical column which is supported on a single 10-ft diameter CIDH pile.

Kwong Cheng of OPAC is appointed by the City of Los of Angeles as a member of both the Technical Advisory Committee and Seismic Safety Review Committee to advise them on issues related to the design and construction of the new viaduct as follows:

• Project-specific design criteria
• Analytical approaches, methodologies and tools
• Compliance with code requirements
• Design detail performance of design components

He also performed review and attended meetings for 35% Design, 65% Design and 90% Design.