By Bridget McCrea
In November 2014, Mother Nature took a nasty swipe at Des Moines, Wash., whipping up a powerful storm that inflicted wide-ranging damage along the city’s coastline. The community of Redondo was hit particularly hard. There, the storm destroyed a much-loved wooden boardwalk, forcing officials to close it for nearly two years.
This year, the community will once again be able to enjoy the waterfront walking and biking trail thanks to a $4.7 million investment from city, state and federal sources. The rebuilt structure includes a precast concrete deck with a wood-stamp finish, stainless steel cable railing and low-level deck surface illumination, all positioned on top of the previous structure’s pile encapsulation.
Wanted: Better longevity and resiliency
Andrew Merges, the city’s transportation engineer, says the city worked with a design consultant that proposed an all-precast structure to replace the wooden structure. Working with EnCon Washington LLC, the city came up with a design that would fit its budget and aesthetic requirements.
“The project morphed from a wooden boardwalk into a concrete structure that would offer more longevity and resiliency against future storm events,” Merges said.
In an effort to replicate the existing structure’s wooden finish, Merges said EnCon proposed a few different precast samples in a variety of patterns.
“Both politically speaking and from a community perspective, EnCon sold the vision of creating a concrete product that possessed the aesthetics of real wood,” he said. “After seeing that, we were sold on the idea of using precast.”
Kirk Buhne, director of business development for EnCon, said his firm got involved with the project when the city’s design engineers called for help. The engineers wanted a structure that would stand up to “wave action” while also providing the same level of aesthetics of the previous structure.
“They talked to me about the boardwalk’s legacy and how people didn’t really want it to change or go away,” said Buhne, who helped quell the aesthetic concerns. “So we produced some samples with formliners and various stains to come up with a look that went over well.”
Precast takes center stage
During the material selection phase, Merges said his team also realized that construction sequencing would be difficult to achieve with cast-in-place concrete because of the tidal influences at the project site.
“One of the main reasons why we went to precast was because we needed a product that could be installed easily to accommodate the incoming and outgoing tides,” he explained. “We didn’t want any water intrusion into the product.”
From a structural standpoint, Buhne said precast exceeded the city’s needs for a product with a longer life cycle than had been used on the previous structure.
“This is a pretty important project for the area and surrounding communities,” said Buhne, who is particularly enthused by the high visibility of the EnCon project. “Our employees don’t always get to see and enjoy the fruits of their labors, but in this case all of their hard work is right there in front of their eyes. That’s pretty neat.”
600 pedestrians per hour
Roughly 1/2-mile long, the boardwalk – built by Stellar J. Corp. – incorporates 153 precast crossbeams that are approximately 8 feet long and 2 1/2 feet wide. The structure also includes 162 precast deck panels, which rest on the crossbeams, that are approximately 8 feet long and 15 feet wide. To install the precast crossbeams and panels, the contractor used anchor rods placed into the existing seawall and piles.
According to Merges, the new boardwalk was completed without any major challenges. It opened to the public in October and will once again host roughly 600 pedestrians per hour (average usage during “peak” hours).
“It’s a focal point that draws a lot of people from the surrounding areas and is a very important part of the area infrastructure,” he said. “And thanks to this contract, the project also provided quite a few jobs this past construction season, so it’s a real win-win for our area.”
Bridget McCrea is a freelance writer who covers manufacturing, industry and technology. She is a winner of the Florida Magazine Association’s Gold Award for best trade-technical feature statewide.