New Portsmouth Bridge design evokes history of predecessor
Old Memorial bridge main span floated out Feb. 8-9.

After three days of delays, a visit from the Federal Highway Administrator and spirited public input, demolition began Feb. 8-9 on a key crossing between New Hampshire and Maine.

During a 72-hour window authorized by the Coast Guard to interrupt shipping, a design-build team led by Archer-Western Constractors used barges to float out the 300-ft-long center span of the Memorial Bridge in Portsmouth, N.H. during high tide. Through March, the towers and 40-ton concrete counterweights of the lift bridge will be removed using a 500-ton crane.

The 88-year-old bridge was closed permanently to vehicular traffic on July 27 after New Hampshire Dept. of Transportation engineers discovered serious corrosion in gusset plates that support bridge girders and beams under the lift span. The $90-million project to replace the bridge got a boost from a $20-million Transportation Investment Generating Economic Recovery grant. The replacement bridge is to open to traffic this summer.

FHWA chief Victor Mendez visited the site the day before the float-out, which had originally been planned for Feb. 6 but was delayed due to a glitch with the hydraulic jack. He used the visit to tout President Obama's State Of The Union address.

"President Obama has called on us to construct bridges, roads, transit systems and airports that are built to last,"  Mendez said. "It's a great day for this region—work will start soon, which means jobs as well as a much needed new bridge."

Some 200 people took their last nostalgic walk over the historic World War I Memorial Bridge on Jan 8 as the New Hampshire Department of Transportation prepared for demolition to replace the bridge that links the cities of Portsmouth, N.H. and Kittery, Maine.

An estimated 11,000 vehicles cross the bridge daily and 1,500 pedestrians and cyclists, up from 1,000 since the bridge closed to vehicular traffic on July 27. The bridge span still lifts to allow for passage of ships. A majority of daily users work at the Portsmouth Naval Shipyard and are now relying on a shuttle that takes a 22-mile detour around the bridge, says Keith Cota, senior project manager with NHDOT.

“What’s important for us is replacing a bridge designed by a polymath of bridge engineers,” adds Ted Zoli, national bridge chief engineer at HNTB Corp., who designed the bridge.  He was referring to John Alexander Low Waddell, acknowledged dean of bridge engineers and father of the vertical lift bridge.

The bridge design is intended to be visually similar to the historic bridge while achieving mechanical skew control, Zoli says.  In the 1920s, it was very successful operationally and made international news, he says.  Improving the design of the trusses for safety is a primary focus, he says.

 The new bridge design eliminates gusset plates from the primary truss by making spliced connections rather than gusseted connections.  “My career has been influenced by events of 9/11 and the I-35W bridge collapse in Minneapolis which involved a problem with gusset plates,” he says.

But some Portsmouth community members argue that the bridge needs more architectural finesse to replicate the design of the original historic bridge. Lisa DeStephano, architect in Portsmouth has suggested adding cables to the design to echo the visual character of the old bridge design.

Zoli says he is not a fan of embellishments on structural systems, especially when building public works projects with taxpayer money. “I am sensitive to honoring the work of Waddell by approaching the mechanical and structural system as a work of innovation,” he says.

For instance, all of the bridge operating equipment was housed in the bridge span of the original structure. In the new design, machinery is tucked under both ends of the span near where the bridge lifts. “This will eliminate the “Chitty-Chitty-Bang-Bang gear system and provide more direct control,” Zoli says.