NASHUA -- There have been several discussions in recent weeks about the facade of the future Broad Street Parkway, but less talk on exactly how the three bridges will be constructed.
This week, however, members of the Board of Public Works were presented with a recommendation to use steel beams to build all three bridges -- the new Nashua River Bridge and the two smaller bridges on Fairmount and Baldwin Streets.
While steel and concrete bridges are typical in New Hampshire, a local resident has urged city officials to explore the idea of using composite beams. Engineers on the project have determined that composite beams, which utilize fiber reinforced polymer technology, are not suitable or cost effective for the three bridges.
"In addition to cost, as a relatively new product, the New Hampshire Department of Transportation has concerns with several aspects of composite beam performance," says a letter from Fay, Spofford and Thorndike to John Vancor, the parkway's project manager.
Geoff Daly of Walden Pond Drive is a strong advocate for composite-built bridges, and has been in contact with an expert bridge designer out of Illinois about the feasibility of using composite beams for the $82 million road project.
"We can't afford not to investigate this option further," Daly said on Thursday, adding he was disappointed by the recommendation. "I will keep pursuing it."
Daly maintains the city could save up to 30 percent on the cost of the bridges if composite was utilized, adding it has a guaranteed lifespan of 50 years and a maximum lifespan of 100 years. Daly also said there may be federal funds available to further offset some of the costs.
John Stockton and Bill Moore of Fay, Spofford and Thorndike, acknowledge that composite beams are lightweight and have corrosion resistant benefits. Still, the engineers found that in the case of the Fairmount and Baldwin Street bridges, the cost for composite beams would be about 10 percent more, or an estimated $300,000 more than using traditional steel girders.
"Given its higher cost and only recent limited use in bridge applications, the composite beam is not a cost effective or appropriate alternative when compared to concrete or steel," they said in a letter distributed to the Board of Public Works this week.
According to the letter, a representative from the New Hampshire Department of Transportation, Mark Richardson, also has concerns about the long-term performance of composite beams, worrying about excessive deflection and possible flammability.
"I don't agree with that analysis," argued Daly, noting bridges in Maine that have used the composite beams successfully, in addition to three in New Hampshire.
Composite materials have been used on bridges since 2000, he said, adding some of the most high-tech aircraft and race car vehicles in the world are being constructed with composite materials.
With the city having to maintain the bridges once they are constructed, he said the composite bridges are easier to maintain because the salt doesn't attack the material.
Engineers admit that in years to come, as the composite material is proven and long-term characteristics are understood, costs for the materials may become more competitive with steel and concrete, according to the letter.
Meanwhile, city officials must decide whether to spend about $1.5 million on various bridge enhancements that could potentially be added to the three structures. Some of the options include decorative concrete rails, ornamental lighting, straight or haunched girders, concrete surface treatments with colored tints, pedestrian overlooks and arches or high focus treatments at the entrance and exits of the bridges.
The remaining cost to complete the Broad Street Parkway -- a nearly 2-mile roadway that will provide another crossing over the Nashua River -- is about $68 million, with $37.5 million being paid by the city and the rest through federal funds. Construction will begin this summer, with completion expected by the end of 2014.