ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.

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This bridge replacement project will ultimately reduce traffic congestion in the infamous bottleneck area of US 101 north of San Francisco, Calif., known locally as the Marin Sonoma Narrows (MSN). In this area, US 101 narrows to a four-lane expressway with multiple access points from neighboring properties. The proposed MSN project will improve a 16.1-mile- long segment of this congested area w i t h i m p ro v e m e n t s t h a t i n c l u d e constructing high-occupancy vehicle (HOV) facilities, widening and realigning portions of the highway, constructing new interchanges, upgrading drainage systems, and constructing new frontage roads and bikeways. The Petaluma River Bridge Replacement project is one of the key high-profile projects in this segment. Bridge Setting The existing bridge consists of a nine- span, 886-ft-long twin structure that utilized a cast-in-place reinforced concrete box-girder bridge with a drop-in precast concrete girder span over the navigable Petaluma River. The existing twin structures were each 6 ft deep, 32 ft-4 1 ⁄2 in. wide, and were supported on single column bents. A former rock quarry lies south of the bridge, allowing the existing structure f o u n d a t i o n t o b e s u p p o r t e d o n spread footings. However, worsening soil conditions at the northern end o f t h e e x i s t i n g b r i d g e r e q u i r e d the use of driven concrete piles. All supports were on an approximately 36-degree skew. The existing bridge had a minimum vertical clearance of approximately 70 ft over the mean high-water level and a horizontal c l e a r a n c e re q u i re m e n t o f 1 0 0 f t from the United States Coast Guard (USCG). Seismicity for the site has an anticipated peak acceleration response spectrum of 1.4g from an earthquake with a magnitude of 7.1 and 0.6g peak rock acceleration. Bridge Type Selection One goal for the Petaluma River Bridge Replacement project was to replace the existing twin structures with one single structure that is 117 ft wide and 907 ft long. The replacement bridge accommodates three lanes of traffic in each direction plus standard-width shoulders. The number of spans is reduced to five with a bridge span layout of 113, 180, 212.5, 212.5, and 169 ft. Right-of-way restrictions on either side of the bridge, design speed requirements of the freeway, line of sight requirements for vehicles (limited height to raise the highway), and marine vessel vertical clearance requirements restricted the location of the replacement bridge to be in basically the same location as the existing bridge. Therefore, one of the main challenges of this project was determining how to stage the c o n s t r u c t i o n o f t h e n e w b r i d g e . During bridge-type selection, it was a n t i c i p a t e d t h a t t h re e s t a g e s o f construction would be needed, with the first stage of the replacement bridge (both superstructure and substructure) to be constructed between the existing twin structures. The existing northbound bridge could then be removed and construction of the new northbound side of the bridge (stage two—both s u p e r s t r u c t u re a n d s u b s t r u c t u re ) profile PETALUMA RIVER BRIDGE REPLACEMENT ON US 101 / PETALUMA, CALIFORNIA BRIDGE DESIGN ENGINEER: AECOM, Sacramento, Calif. PRIME CONTRACTOR: Ghilotti Bros. Inc., San Rafael, Calif. (prime contractor) and C. C. Myers Inc., Rancho Cordova, Calif. (bridge contractor)—a joint venture PRECASTER: Con-Fab California Corporation, Lathrop, Calif.—a PCI-certified producer POST-TENSIONING CONTRACTOR: DYWIDAG-Systems International, Long Beach, Calif. ERECTION CONTRACTOR: Bigge Crane & Rigging, Stockton, Calif. Completed northbound side of the Petaluma River Bridge. Photo: Caltrans. by Walt LaFranchi, AECOM Petaluma River Bridge Replacement on US 101 Project aims to lessen traffic congestion north of San Francisco, California 22 | ASPIRE Spring 2016 P R O J E C T

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