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Thu October 20, 2011 - Northeast Edition
For years now, the Rhode Island Department of Transportation has been aware of the deterioration of the Providence Viaduct, which carries I-95 over downtown Providence. The last full inspection took place in November 2009, revealing a slew of structural problems.
The bridge consists of two structures: one northbound and one southbound, each with four lanes. The structures are separated by a 12-in. (30.5 cm) gap.
The deck was constructed with reinforced concrete supported by steel “I” girders. The substructure consists of post-tensioned hammerhead concrete piers, and the foundation is made of steel “H”piles driven underground.
Bridge Structural Condition
The 2009 inspection revealed that the deck is badly deteriorated, shielded and shored in many locations.
“The bridge deck has reached its service life,” said Bob Pavia, Rhode Island Department of Transportation (RIDOT) principal civil engineer. “Potholes are forming monthly.”
“We’ve had problems with the design of the steel girders from the beginning,” continued Pavia. “In the 1980s, a bearing froze up and almost split a steel girder in half.”
The steel girders have numerous cracks in secondary members, as well as some cracks in main member welds. With emergency repairs made in 2009, the bridge does meet standards for load carrying capacity and does not require posting.
The post-tensioned piers have a concrete design strength of 5,000 PSI, but their as-tested strength only rates at 3,500 PSI. Additionally, the P/T anchorages are badly rusting.
Repair Versus Replace
The bridge is currently safe for operating conditions and receives bimonthly inspections as a safeguard. The concrete piers are structurally sound. The steel cracks are due to poor weld quality, not over-stress, and are currently being repaired. The bad deck section recently has been shored.
However, these interim repairs are not a long-term fix for this viaduct.
“It is much more cost-effective to replace the bridge than to do a complete rehabilitation,” said Pavia. The piers, in particular, are very difficult and expensive to repair.
“There is no scheme to repair the bridge that wouldn’t disrupt traffic for a number of years,” continued Pavia. Inspection and evaluation of the bridge concluded that replacement is required. The final design and permit process is scheduled to start immediately.
There are two major challenges for RIDOT to overcome. The first is how to replace the existing bridge while maintaining traffic volume of 160,000 vehicles per day. Closing I-95 would cause unacceptable traffic congestion on local streets within Providence, as traffic backups and delays already occur every day on the bridge.
RIDOT’s plan is to vanquish this obstacle by phasing the construction as follows:
• Constructing a new southbound structure west of existing southbound lanes;
• Shifting southbound traffic onto the new southbound structure;
• Shifting northbound traffic onto the old southbound structure;
• Demolish the old northbound structure and replace with a new structure;
• Shift northbound traffic back onto the new northbound structure; and
• Demolish the old southbound structure.
Once the old bridge is demolished, there will be two separate structures once again — this time the northbound and southbound bridges will be separated by a 50- to 60-ft. (15.2 to 18.3 m) gap.
The larger challenge is funding. The estimated cost of the new bridge is $140 million. Currently, only $24 million is programmed for the project, therefore RIDOT is seeking alternative funding sources, including a possible toll booth on I-95 at the Rhode Island/Connecticut border.
In March 2008, Gov. Donald Carcieri established a Blue Ribbon Panel to assess Rhode Island’s transportation needs and to identify options for potential funding sources.
Over the course of 10 months, the Panel met 12 times, and held four public meetings. According to the Blue Ribbon Report, for Rhode Island to maintain its highway system in a state of good operation and repair, it would need to spend approximately $640 million per year. The current state and federal funding provides approximately $354 million per year, leaving a gap of $285 million per year.
The state is looking for funding that is “sustainable and reliable and comes from a variety of sources, primarily based on user fees.”
The report notes that Rhode Island relies more heavily on federal funds than most states and should strive to contribute at least 50 percent of the overall amount. The state currently supports 27 percent of its transportation spending with state funds, compared with a national average of 63 percent.
The new funding scenarios mentioned in the report include an increase in gas tax, a new petroleum products gross receipts tax, and the aforementioned I-95 toll, among other sources.
“We’re hoping to let the project in early 2013, unless another funding source becomes available sooner,” said Pavia. The estimated project duration is six years; three years per bridge.
“Tolling is the most feasible option for additional funding,” added Dave Fish, RIDOT managing engineer. A Tolling Expression of Interest letter was drafted by the RIDOT Office of the Director on June 29, 2011, and presented to the Federal Highway Administration for review.
In addition to the Providence Viaduct, RIDOT is looking for the capital to build a new connector between I-95 and SR 4 at Quonset Point Davisville Industrial Park. The project is currently in the planning stage and is estimated to cost $75 million. CEG