|<< Previous||Contents||Next >>|
Prefabricated Bridge Elements and Systems Cost Study: Accelerated Bridge Construction Success Stories
The New York City Department of Transportation's Belt Parkway Bridge over Ocean Parkway in south Brooklyn was deteriorated and required complete replacement. The entire design-build project included replacing the existing bridge with a longer and wider bridge, reconfiguring the existing outdated cloverleaf interchange into a modified tight diamond interchange, and other rehabilitation and upgrade work to the Parkways.
The selected design-build team of Granite Halmar/Gannett Fleming specified extensive use of prefabricated bridge components to achieve an accelerated onsite construction timeline. The rapid construction was required to minimize disruption to the 166,000 average daily traffic volume that used the Belt Parkway, a major artery through Brooklyn that also had a large hospital and two schools fronting on the project limits.
Onsite installation of each half of the new bridge took only a few nights in each of two weeks. The entire design-build project was completed in 14 months, including a 3-month winter shutdown. Construction would have taken 3 to 4 years using conventional methods.
The old 2-span 149-ft long, 78-ft wide Belt Parkway Bridge was lengthened and widened to a 3-span 221-ft long, 134-ft wide bridge with span configuration of 49 ft - 107 ft - 65 ft. The width was increased to add shoulders and acceleration/deceleration lanes at the entrance and exit points, in addition to the existing 3 lanes in each direction.
Throughout the project, six lanes of traffic remained open during rush hour, with limited lane closures as needed during off-peak hours. A temporary bridge was erected adjacent to the south side of the existing bridge to maintain the existing number of lanes on Belt Parkway during the bridge reconstruction. Traffic was diverted onto the temporary bridge and the south portion of the existing bridge while the north portion of the existing bridge was demolished and reconstructed. Traffic was then rerouted to the six lanes, three in each direction, on the new north portion of the bridge which was overbuilt to accommodate the six lanes. The south portion of the existing bridge was then demolished and reconstructed.
To minimize traffic disruption, prefabricated components were used extensively. Prefabricated components included concrete-filled steel pipe piles, precast T-walls, precast post-tensioned cap beams, prefabricated superstructure segments, precast bridge parapets, median barriers, and approach slabs. High performance concrete with 4000 psi compressive strength was specified for all precast components. Stainless steel reinforcement was specified for the precast decks, parapets, and median barriers. While the stainless steel reinforcement increased the cost of the bridge by approximately one percent, the bridge is anticipated to last twice as long as the 45-year-old bridge it replaced.
The 51 span-length prefabricated superstructure segments, as well as the other precast concrete components, were fabricated at the Fort Miller plant in upstate New York and shipped 200 miles to the jobsite. Each (Inverset) superstructure segment consisted of two steel girders and a composite deck.
Various processes were adjusted to maximize onsite construction speed. For example, the mini-piles were installed with limited headroom while the existing bridge remained in use. Another example is pre-erection of the superstructure segments in the plant to ensure adequate tolerances for field erection.
The bridge is expected to see a 75-100 year service life due to the quality of its prefabricated components and the attention given to connection details, including the loop-on-loop closure joints connecting the deck segments.
The NYCDOT utilized a modified "A" + "B" bidding method, where "A" equals the bid items and "B" equals a "Critical Duration" (number of days specified by the contractor) times $85,000 to translate the duration into a delay-related user cost. "Critical Duration" was defined as the period of time from when the design-build team permanently impacted the roadways for construction until the time that all new roadways were in their final completed configuration.
Incentive/disincentive and liquidated damages clauses were included in the contract to help ensure early completion of critical activities to minimize traffic disruption. The contract specified an incentive of $85,000 per day for completion before the "Critical Duration," with a cap of $2M. Also specified was a disincentive of $85,000 per day for completion after the "Critical Duration," with no dollar limit.
The engineer's estimate for this project was $ 60.0M. The awarded bid of $55.5M from Granite Halmar Construction Co., Inc., was 8% or $4.5M less than the engineer's estimate. There were 5 bidders on this project. The awarded bid proposed a "Critical Duration" of only 285 days, which was 300 "Critical Duration" days shorter than the low bid. Therefore, at $85,000 per day, the awarded bid was the best value, with a delay-related user cost that was $25M lower than the low bid.
The 14-month construction schedule began September 2003 and included a 3- month winter shutdown. "Critical Duration" work began in March 2004 and was completed in November 2004, in one construction season. The bridge was completed 29 days ahead of the "Critical Duration" of 285 consecutive calendar days that was bid in the contract. The actual number of "Critical Duration" days was just 256 days, with no lane closures during peak traffic hours. The contractor received the maximum $2M incentive.
The bridge work on this design-build project was approximately a third of the total project cost. The project replaced the existing high-traffic-volume bridge with a longer and wider bridge, reconfigured the interchange, and completed other rehabilitation and upgrade work in significantly less time than conventional construction, and it was completed under budget.
|<< Previous||Contents||Next >>|