Superstructure Replacement, 1980s
After the failure of the Mianus River Bridge at Greenwich, Connecticut in 1983, the Harvard Bridge was shut down and inspected because it contained similar elements, specifically the suspended spans. Traffic was restricted to the inner two lanes due to the discovery of two failed hangers on span 14. A few days later, all trucks and buses were banned from the bridge.
In 1986, a report was published containing the plan to replace the superstructure on the existing supports. Alternatives considered were very similar to the 1972 report, and were similarly decided. Structural modifications included an upgrade from four longitudinal girders to six of the same shape, elimination of ramp "B", and replacement of a stairway with a handicapped pedestrian ramp on the Boston end of the bridge.
The historic value of the bridge was considered significant, so the plan was to make the replacement superstructure appear similar, with similar railing and lighting. In order to document the pre-existing structure, a Historic American Engineering Record (HAER) would be prepared.
Ramp "B", from southbound (Boston bound) bridge lanes to eastbound Storrow Drive, caused traffic to merge onto Storrow Drive from the left (high speed) lanes using a short acceleration lane, causing safety issues. The MDC requested elimination of this ramp. Compared to overall bridge traffic of 30,000 vehicles per day, traffic on ramp B was found to be low, approximately 1,500 vehicles per day with a peak of 120 vehicles per hour.
Pier 12 was exhibiting inappropriate movement and was scheduled for reinforcement.
The work would be done in two phases. Phase 1 would reinforce the downstream side of the bridge to allow MBTA bus traffic, and was expected to take 5 months. Most of this effort would be spent on the underside of the bridge and would not affect existing traffic. Phase 2 would replace the entire superstructure and was expected to take three construction seasons to implement. Cost was estimated to be US$20M (US$42,000,000 with inflation). Phase 1 finished in 1987, and Phase 2 in 1990.
- Before-and-after images
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Bridge viewed from the upstream Cambridge side in 1985. Construction barrels restricting traffic from the outside lanes, and general wear and tear are visible (click on image to enlarge)
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Roughly the same view, in 2009. Superstructure is in much better shape only 20 years after completion, than the 1985 superstructure was roughly 40 years after its most recent major work.
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Underside of the bridge in 1985. Image shows how the bridge was originally built, and later modified, but before the superstructure was replaced.
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Underside of the bridge in 2009. Image shows how the replacement superstructure was built, with six longitudinal girders, different bracing, etc.
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