Wednesday, November 24, 2021

Maynard's Bridges Revisited

Florida Road bridge closed for replacement construction on November 23, 2021.

The Maynard Historical Society had in its collection a photograph of a wooden bridge across the Assabet River at Florida Road. The road was barely more than a cart path, and the caption with the photograph mentioned that wooden bridges at that site were repeatedly washed away by floods. A decision was made in 1914 to construct a rebar-reinforced concrete bridge, the first of its type in Maynard. The Town approved a budget of $6,500. The bridge was completed in 1915 for $6,011.  It is state bridge #M-10-006.

Even taking into account dollar inflation, that was a remarkable reasonable price. The current project to replace that bridge is budgeted at $3,362,437. Time-to-completion is estimated at two years, during which time the road will be closed to through traffic. As to why the bridge needs to be replaced, the Massachusetts Department of Transportation (MassDOT) has deemed it “Structurally Deficient” for years. Rebar-reinforced concrete was an extremely popular bridge construction material at the beginnings of the twentieth century. Concrete bridges have an expected safe lifespan of 50-70 years, depending on traffic burden and exposure to the elements (weather and road salt). This bridge is 106 years old. At the time the Florida Road bridge was constructed, there was no expectation for truck traffic, as immediately south, the road passed through a narrow, one-lane-wide underpass under the railroad. Hence, the bridge’s narrow lanes and poor sightlines were not considered unsafe, as bridge traffic speeds were expected to be slow and limited to horse-drawn vehicles and the automobiles of that era, but now make the bridge tagged as Functionally Obsolete in addition to Structurally Deficient.

Crumbling concrete an exposed rebar at base
of the 106-year-old Florida Road bridge
Florida Road is not the only bridge in the United States that is overdue for replacement. From a 2017 report, the U.S. has more then 600,000 bridges, of which 40 percent were more than 50 years old and 9.1 percent were Structurally Deficient (improved to 7.5 percent as of 2021). The estimated cost of remedying the nation’s backlog of bridge rehabilitation exceeds $100 billion.   

The MassDOT project to replace bridge #M-10-006 began in 2017 with a notice to proceed, traffic counts and confirmation of the state of deterioration. In places above and below the road surface, concrete had broken away, exposing steel rebar, which was rusting. Surveying was conducted in 2018. A preliminary design was presented to the town in February 2020. The existing bridge has 9-foot lanes, low curbs and 5.5-foot wide sidewalks; full width 30 feet. The new bridge will have a full width of 41 feet to accommodate 10-foot lanes, 4-foot paved shoulders to serve as bicycles lanes and 5.5-foot wide sidewalks. Much like the Waltham bridge replacement, this will be a concrete deck resting on steel beams. The additional width will all be on the downstream side. A recent walk through the site saw that about 40 trees on both sides marked for removal, some exceeding a foot in diameter, one-third of all the trees appearing to be dead.   

Sewer pipe under the existing Florida Road bridge (Click to enlarge)
One question of interest only to a few adventuresome people is the extent of vertical space under the bridge. With just the right river depth, it has been possible in the past to put kayaks and canoes into the river just downstream of the Ben Smith Dam, to pass through Maynard, crossing under six bridges. One of the proposal diagrams shows a 9-foot clearance between normal low water and the bottom of the steel beams. However, the diagram also shows water and sewer pipes suspended below the bridge, same as those exist at present. Successful passage would require water levels deep enough to float a boat, yet not so high as to make those pipes into head bangers.      

Foot-depth markers on wall
below John's Cleaners
Are any other of Maynard’s bridges deemed Structurally Deficient? Three reinforced concrete bridges date to 1922: Route 117/Great Road (also known as the Ben Smith bridge), Main Street and Walnut Street. These spans over the Assabet River were originally bridged in 1816, 1849 and 1865, respectively. The original bridge at Route 117 appears to have been a two-arch stone and mortar bridge that stood until the 1922 replacement. Main and Walnut were replaced by steel bridges in 1872 and then concrete fifty years later. Of the three bridges that are nearing their 100th anniversary, the Main Street bridge is officially Structurally Deficient, marking it as Maynard’s next bridge project. The other two still pass annual inspections. Maynard’s six other bridges range in age from 4 years (Rail Trail) to 84 years (Mill Street).    

Mark painted the foot-depth markers on the riverwall below John’s Cleaners.

  

No comments:

Post a Comment