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California Port Meets Sea Level, Seismic Challenges

A new wharf at the Port of Redwood City, in California, includes a 955 ft long sheet-pile seawall
A new wharf at the Port of Redwood City, in California, is the first wharf in the bay area designed with rising sea levels in mind. To protect the shoreline, the design team included a 955 ft long sheet-pile seawall that can be topped with a concrete cap, should that prove necessary. Jack Gerwick, Ben C. Gerwick, Inc.

This month marks the opening of a new, reconstructed wharf at the Port of Redwood City, California.

November 26, 2013—San Francisco Bay’s Port of Redwood City might not be as famous as the area’s Port of Oakland, but it now boasts an element that Oakland doesn’t have: a newly built wharf that is the first in the San Francisco Bay Area to be designed to accommodate an expected sea level rise of 18 in. within the next 50 years. This month marks the official completion and reopening of the wharf.

The Port of Redwood City is located in the Redwood Creek Channel on the San Francisco Bay. The original 900 ft long, 60 ft wide wharf at this location was built in the 1930s of treated timber piles topped with timber cap beams and decking, according to material provided by the Oakland, California-based marine structures’ engineering firm, Ben C. Gerwick, Inc., which oversaw the design/build project to reconstruct the wharf. After the port’s heyday during World War II, when it was used to support the nation’s Pacific fleet, the wharf was used for general cargo loading support and for the transfer of construction materials. Over the last decade, the timber wharf—which was located between a cement-handling terminal and a metal scrap terminal—fell into disrepair.

The project to reconstruct the wharf was the port’s first design/build project, according to Ted Trenkwalder, P.E., S.E., M.ASCE, the vice president of Gerwick and the project’s manager for the firm. Gerwick designed the project to the 35 percent stage before the request for proposals for the design/build project went out; a team comprising Manson Construction Company, which is headquartered in Seattle and has an office in Richmond, California, and the Oakland-based engineering firm Liftech Consultants, Inc., won the design/build contract.

Trenkwalder says the existing timber wharf had deteriorated, and reconstructing it would not only preserve it but also increase the port’s through-put and revenue.

The San Francisco Bay Conservation and Development Commission, known as the BCDC, mandated that the design take future increases in sea levels into consideration. “That is a fairly unique consideration for a marine terminal, and it’s the first project that was designed in the bay area to meet the adaptive climate change consideration and sea level rise criteria,” says Jack Gerwick, P.E., M.ASCE, the project engineer for Gerwick’s work on the port.

“Since this was the first project to consider adaptive climate change and mitigating measures, the port worked collaboratively with the BCDC to make sure that the project requirements and the adaptive measures met the intent of the regulations,” Gerwick says. “We took a practical approach in allowing for future sea level [increases] and designing our project to accommodate it.” The port’s design team took the project’s design life of 50 years, analyzed a number of sea level rise estimates issued by the California Climate Action Team in 2010, and established design criteria for existing and future conditions.

To accommodate this expected sea level rise, the elevation of the new wharf is 18 in. higher than would otherwise be required in the San Francisco Bay area, some 16 ft above the current mean lower low water (MLLW).

The rebuilt, reinforced concrete wharf is 426 ft in length averaging 60 ft wide, with access ramps located at either end. An 18 in. thick, cast-in-place concrete deck is supported by 108 octagonal precast, prestressed plumb piles that measure 24 in. in width, according to Erik Soderberg, P.E., S.E., M.ASCE, the engineer of record for the project, with Liftech, who wrote in response to written questions posed by Civil Engineering online. 

The wharf's deck is supported by 108 octagonal, precast, prestressed plumb piles that measure 24in. wide

The wharf’s deck is supported by 108 octagonal, precast,
prestressed plumb piles that measure 24 in. wide. The three
waterside rows of piles have moment connections between the
piles and deck to accommodate bending moments caused by
both earthquakes and berthing vessels. Piles in shallower water
are pinned into the deck. Mike Sedlak, DigitalSight

“The deck connection type is varied to equalize the bending stresses in the piles, limiting the amount of piling required for lateral support,” Soderberg said. “The three waterside rows of piles have moment connections with the deck forming a ductile moment frame, [while] the landside piles that are in shallower water are pinned into the deck.”

The thin deck is also designed to resist a crane outrigger load of 312,000 lb anywhere on the deck, resulting in heavy reinforcement along the edges and significant pile punching shear reinforcing, according to Soderberg. The design also incorporates a pile moment connection that transfers the large pile seismic bending moments into the thin deck.

The structure is relatively flexible compared to other pile-supported wharves, according to Soderberg, and is designed to respond well to earthquake forces while being strong enough to resist berthing loads up to 1.4 million lb from vessels, which can result in up to 5 in. of lateral displacement in the wharf.

The wharf is designed to remain functional after an estimated 6 in. lateral displacement caused by an “operating level earthquake,” which has 72-year return period and a 50 percent probability of occurring within 50 years, according to information provided by Liftech. After an estimated 16 in. lateral displacement caused by a “contingency level earthquake,” which has a 475-year return period and a 10 percent probability of occurring within the next 50 years, the wharf will be repairable.

Following a “design level earthquake,” determined according to the 2010 California Building Code and ASCE 7-05, Minimum Design Loads for Buildings and Other Structures (2006), the structure is designed to remain standing and support vertical dead loads, but will be heavily damaged, requiring extensive repairs or replacement, according to Liftech material. The design earthquake is estimated to cause 23 in. in lateral displacement and is 2/3 of a maximum creditable earthquake, which has a 2,500-year return period and a 2 percent chance of occurring within 50 years.

Additional provisions to accommodate sea level rise include taller fender panels along the wharf that can accommodate such low-draft vessels as barges as well as such high-draft vessels as bulk carriers transporting aggregate for concrete, for example. The fender panels are designed to continue to operate in both the near-term and long-term, adds Trenkwalder.

To protect the shoreline from rising waters, the design team included a 955 ft long, variable-height, sheet-pile seawall along the shoreline. The top wall elevation is level at 13 ft above MLLW, Trenkwalder notes. “There are provisions to increase the height of the seawall in the future, if needed, by casting a concrete cap on top of the seawall,” added Soderberg.

Newly added riprap protects the shoreline and seawall from scour.

The port originally proposed having a 500 ft long, 60 ft wide replacement wharf built, according to Trenkwalder. However, to save money, the port’s design team pared back the length of the wharf to omit unproductive space located alongside the bow of any berthing vessels. A walkway that extends to mooring dolphins that had been recently added to the existing timber wharf offers personnel access past the bow of berthing vessels as well as additional mooring options for far less cost than reconstructing a full-length wharf.

The project included a longshoreman building that houses a lunch room, changing rooms, two personnel offices, and space for seismic monitoring equipment, according to Trenkwalder.



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