CPM Constructors Utilizes Accelerated Bridge Construction on East Kingston Span
Red-Listed Bridge Repair Nets ASCE Award: CPM Constructors Uses Accelerated Bridge Construction Methods and Innovative Materials for 25-Day Fix of New Hampshire DOT’s East Kingston Span
The New Hampshire Section of the American Society of Civil Engineers has recognized a structurally deficient New Hampshire highway bridge that was rehabilitated in less than a month with an entirely new superstructure for its innovative construction techniques, accelerated timeframe, and early completion under budget.
ASCE’s Outstanding Civil Engineering Achievement award was presented for New Hampshire Department of Transportation’s (NHDOT) East Kingston 107A Bridge Rehabilitation Project at the professional group’s annual dinner in Manchester, New Hampshire. The award is given annually for an engineering project "that demonstrates excellence in engineering skills and represents a significant contribution to mankind and engineering progress."
Using accelerated bridge construction techniques and innovative materials, the $1.6 million rehabilitation of the bridge was completed in under 28 days by general contractor CPM Constructors, Inc. of Freeport, Maine. Designed by consultants McFarland Johnson of Concord, New Hampshire, the project involved replacing the superstructure, paving approaches, installing new bridge rail and making needed repairs to the piers and abutments. It also required asbestos abatement, and sand blasting and painting existing piers to remove lead paint.
The NHDOT utilized two methods of construction new to the department on this project – Prefabricated Bridge Units (PBU), and the use of Ultra High Performance Concrete (UHPC) with steel fiber reinforcement.
Declining Yet Fixable
The East Kingston bridge is located on Route 107A, a 6-mile stretch of highway running from the Massachusetts border in Amesbury through South Hampton and East Kingston, ending near the intersections of routes 107, 125, and 111. Originally built as a grade separation, the steel stringer bridge carries about 2,200 vehicles per day. It was designed with three 40-foot simple spans, with the railroad occupying the center span. Amtrak’s Downeaster passenger train runs daily, while a number of unscheduled freight trains also use the tracks, which are owned by Pan Am Railway.
Built in 1937, the 120-foot-long bridge had an out-to-out width of about 32 feet, with an under-clearance of 18 feet, 6 inches between the bottom flange of bridge beams and the top of the track rail. This bridge underwent major rehabilitation in 1969, when crews replaced the concrete deck and bridge railing, but since then the structure’s condition has been in steady decline.
NHDOT bridge inspectors most recently noted the concrete deck was in serious condition, with timber blocking put in place to prevent concrete from falling on the tracks below. They rated the structural steel paint as fair with some rusting apparent, while the substructure was in satisfactory condition. Moreover, the concrete abutments and the steel piers’ concrete foundations showed spalling and cracking, but inspectors did note these flaws could be repaired.
State’s Red List Bridge Program
The Route 107A span is listed among half of the state’s bridges built before 1960. These structures weren’t designed to carry today’s vehicle loads or traffic volumes, and many of them are now approaching the end of their service life. Some, after inspection by NHDOT, were found to be structurally deficient and have been placed on the state’s Red List. Based on bridge inspections through December 31, 2017, there are 2,161 state owned bridges and 1,688 municipally owned bridges. Of these, there are 133 bridges on the State Red List and 252 bridges on the Municipal Red List, for a total of 385 bridges that have at least one major structural element such as deck, superstructure, substructure, or culvert in “poor” condition.
The Department has aggressively addressed the Red List problem, having removed 112 bridges from the State Red List between 2012 and 2017 through rehabilitation, replacement, or even closure. As part of this program, all publically owned bridges associated with highway traffic and recorded in the State Bridge Inventory are inspected every two years. State Red List (deficient) bridges are inspected every six months, while Municipal Red List (deficient) bridges are inspected every 12 months.
In line with this policy, East Kingston’s Route 107A bridge was placed on the State’s Red List in 2010.
Same Size But Stronger and Safer
State officials evaluated several alternatives for addressing the deficient bridge and decided that rehabilitating the span would be more cost-effective than replacing the entire bridge. This would involve replacing superstructure, i.e., the concrete deck and steel stringers, while maintaining the existing roadway grade, the 18-foot, 6-inch under-clearance, and staying within the state-owned right-of-way. It also kept the original out-to-out width of the bridge and accomplishes necessary safety improvements by replacing existing substandard aluminum bridge rail and approach rail with modern T2 steel rail and snow screening. The two existing bridge piers – composed of structural steel bents supported by concrete foundations, and the concrete abutments, were to be repaired. Furthermore, this alternative required no town funding – federal and state funds would pay for the project.
ABC Method With PBU
The 82-year-old bridge was selected as a candidate for accelerated construction because of its size, low traffic volume, and location over a fairly active railroad track that experiences about 18 trains daily. In addition, its location provided a short, convenient detour option for motorists via Routes 107 and 108.
Accelerated Bridge Construction (ABC) techniques include using prefabricated bridge elements (PBE) for superstructure, substructure and foundation components. Usually made of precast concrete, steel or composites of these, PBE are often fabricated in a factory and transported to the jobsite, or sometimes fabricated in large outdoor casting yards that may be remote from, or adjacent to, the construction site but clear of live traffic. PBE include innovations in design and high-performance materials and can be combined with the use of “fast track contracting” methods.
There are many types of PBE that may be combined on ABC projects for superstructure, substructure, and even foundations. Among these PBE are deck panels, deck beams, parapets, abutments, columns, pier bents, pile caps, footings, and approach slabs. Deck beam elements eliminate conventional onsite deck forming activities and are typically placed in an abutting manner. Often, a number of different PBE may be combined in a composite system or unit (PBES, or PBU). For the East Kingston bridge, CPM Constructors prefabricated 12 “modular beam with deck” PBU at its own casting yard in Freeport and shipped the completed units to the East Kingston site. These composites consisted of 8-1/2-inch thick concrete deck panels cast over 20-inch-deep welded plate girders. Each panel measured 7 feet, 6 inches wide by approximately 40 feet long. CPM employed two cranes for offloading and hoisting panels and assisting bridge demolition – a 275-ton Grove hydraulic crane, and a 100-ton lattice boom Link-Belt crawler crane.
Innovative Ultra High Performance Concrete
Another innovation employed on this project was the use of Ultra High Performance Concrete (UHPC), a cementitious composite material composed of an optimized gradation of granular constituents, a water-to-cement ratio less than 0.25, and a high percentage of discontinuous internal steel fiber reinforcement. UHPC has remarkable structural attributes including compressive strength close to 22,000 pounds per square inch, three times higher dynamic tensile strength and 29 times higher fracture energy than conventional concrete. UHPC was used for the important closure connections between the PBU deck panels.
Planning Pays Off
CPM Constructors won the East Kingston bridge project with a bid of $1.6 million. The project was scheduled to begin in mid-June 2018, with a 28-day shutdown period allowed to remove the old concrete deck and steel stringers and install the PBU. The contract included a $2,000 per day incentive/disincentive clause that added urgency to the project. The work had to be finished in fewer than 28 days so as not to affect the local school schedule, emergency vehicles, and daily train traffic. Trains continued running throughout the closure period, and since freight trains are not scheduled, a railroad flagger had to be on duty during construction.
Extensive planning was needed in order to limit the bridge closure to four weeks and thus avoid conflicts. Such planning in conjunction with accelerated bridge construction techniques were key to the project being completed early and under budget. The bridge was completed in 25 days – three earlier than allowed. This included placing all 12 PBU in a single day.