Developments in heavy lift technology are enabling increased use of Accelerated Bridge Construction (ABC) in areas normally reserved for conventional construction techniques. The recent installation of the Fore River Bridge in the Boston Metropolitan area, US, is a case in point. It showed how the combination of jack-up lift system and self-propelled modular transporter (SMTP) is a powerful addition to the range of lifting options for ABC contractors.
Fore River Bridge
No one would call the temporary bridge that was constructed in 2002 over the Fore River between Quincy and Weymouth, Mass., a work of art. The bridge replaced a 1936 Art Deco gem when it could no longer safely carry the 32,000 cars that cross the river each weekday.
Despite being safe, the temporary “Erector set” bridge seemed a bit rickety to some local residents. The bridge has been replaced with a $272 million steel vertical lift bridge that will smooth traffic flow, and reduce waiting times by opening and closing in half-the-time compared to the temporary bridge during good weather.
The design/build team White-Skanska-Koch was selected to build the new, permanent, Fore River Bridge. The 1,500 ton bridge features a structural steel lift span with a length of approximately 324 feet with supporting towers of approximately 250 feet in height. The towers are situated over a cast-in-place concrete plinth approximately 50 feet in height and supported by two individual pile caps on each side supported by over-drilled shafts. In addition to the lift bridge, the project also includes a 3 span approach structure on each side of the bridge. The expected life of the new bridge is 75 years.
Due to the bridge’s higher horizontal channel clearance from 175 feet to 250 feet when raised, larger ships will now be able to pass beneath the new bridge, providing better access to the Fore River’s Designated Port Area. The Commonwealth of Massachusetts has established Designated Port Areas to promote and protect water-dependent industrial uses such as commercial fishing, shipping, and other vessel-related marine commercial activities.
Moreover, at 60 feet clearance in its lower position, most sailboats can also sail underneath the bridge without the need for raising the lift span, simultaneously improving both vehicle and boat traffic flow.
Accelerated Bridge Building
The Fore River Bridge is being replaced through the Commonwealth’s historic, $3 billion Accelerated Bridge Program (ABP). Concluded at the end of 2016, this program has reduced the number of structurally deficient bridges across Massachusetts and prevented others from falling into this classification. Replacement of the Fore River Bridge is one of the most significant projects undertaken through this program. Construction of the Fore River Bridge will continue past the sunset of the ABP, the project is paid for and will continue through to completion.
Accelerated bridge construction moves construction away from traffic and builds as much of the new bridge as possible nearby the existing bridge. This enables a faster construction schedule for the fabrication and erection of replacement bridge systems. The primary benefit of ABC is to minimise traffic delays. ABC principles rely on three main methods of bridge construction: building pre-fabricated components off-site and quickly installing them once on-site; building the entire structure off-site and moving it in place using a self-propelled modular transporter; and building the bridge off-line/adjacent to the existing bridge and sliding it into place.
Heavy Lift Challenge
In addition to building a bridge that would function well in cold and/or windy weather with minimal maintenance upon completion, the Fore River project had to ensure minimal disruption to vehicle and boat traffic during construction. Safety, as always, was a primary concern, particularly while lifting very heavy loads into place from barges beneath the bridge.
Burkhalter Rigging Inc., of Columbus, Miss., was selected to lift the 1,500-ton lift span into place. Using ABC principles, the entire bridge was built off-site and moved in place using a self-propelled modular transporter.
Burkhalter worked with Enerpac in selecting the best heavy lift technology needed to perform the lift safely and correctly. “Both companies work well together to find the best solutions with the customer’s goals in mind,” said Mike Beres, Americas Sales Leader for Integrated Solutions, Enerpac. “When they determine what they need, they’ll ask us, ‘Can you do something like this?’ In this instance, they needed to build jack-up towers next to the existing towers, then lift the towers 20 meters into place from a barge under the bridge.”
Enerpac’s JS-Series jack-up system is a custom-developed multi-point lifting system. A typical system includes four jack-up towers positioned under each corner of a load. The four-tower setup has a lifting capacity of 2,000 metric tons (500 metric tons per tower). The lifting frame of each jack-up tower contains four hydraulic cylinders in each corner, which lift and stack steel boxes. The load is lifted in increments as boxes are inserted via an automated system, lifted, and stacked, forming the lifting towers. A JS-750 jack-up system was used for the Fore River bridge lift with boxes measuring 1 meter high x 2.3m x 2.3m.
When it was time to set up the Jack-up system, an Enerpac support crew and an electrical engineer were on site to ensure the lift went smoothly and stayed on schedule. The fully raised jack-up system was used during bridge construction off-site. It was then lowered, while the bridge was transported by SPMT onto a waiting barge. Once on the barge, the jack-up was raised to its full height for the bridge installation. The barge then made its way three quarters of a mile down river shepherded by tugboats. On nearing the bridge, the barge was rotated and held in position under the bridge between the two towers until the outgoing tide lowered it into place. The Jack-up system provided precision control allowing the bridge to be positioned and held in place while being secured to the towers.
Despite challenges including potential storms, general bad weather and working on moving water affected by two high tides and two low tides every 24 hours, the lift went off without a hitch. Using the jack-up system, Burkhalter was able to raise the lift span 20 meters from the barge and float it into place at almost exactly the correct height.
“Timing was critical as the Coast Guard indicated the lift time frame, because the river was closed to shipping during the lift window,” said Beres. “Everything went perfectly with the lift, allowing river traffic to return on time and minimising disruption.”
Officials from the Massachusetts Department of Transportation appreciated how Burkhalter safely and efficiently raised and moved the lift span into position – exactly how it was planned. Burkhalter’s professionalism and attention to detail, with assistance from the Enerpac jack-up system, allowed them to make this engineering feat look relatively easy.
For more information on Enerpac visit www.enerpac.com.
Current stage of the project:
According to the Fore river project overview: Finish placement of roadway decks on the approach and lifting spans – April, 2017.
Reduced capacity on Route 3A associated with transitioning from the temporary bridge to the new structure – May, 2017.
Click to enlarge photo.