The tragic collapse of the precast concrete pedestrian bridge in Sweetwater, Florida, on March 15 has moved some to question the wisdom of using “novel” accelerated bridge construction (ABC) techniques.
Not new or unusual, these techniques have been used successfully in the United States. long before the phrase was coined a few years ago. In New England, hundreds of projects using one or more elements of ABC have been completed safely.
“The techniques used to build and install the Sweetwater bridge have also been used successfully to replace many bridges in Connecticut,” said Kevin Nursick, Spokesman for the Connecticut Department of Transportation (CTDOT).
“The specifications, materials and designs of the bridges are the same as those of conventional construction, but the project delivery method is different,” Nursick said.
“They’re not reducing the quality of the final product,” he added.
ABC techniques include using prefabricated bridge elements (PBEs) for superstructure, substructure and foundation components. Usually made of precast concrete, steel or composites of these, PBEs may be fabricated in a factory and transported to the jobsite, or fabricated adjacent to the bridge alignment but clear of live traffic.
While ABC techniques save time, they are usually pricier than conventional construction methods. But according to the Federal Highway Administration (FHWA), reducing project duration lessens exposure of construction workers to potential traffic accidents and eases the impact on the motoring public, which may yield offsetting financial benefits.
FHWA notes that because ABC often involves building part or all of a bridge away from live traffic, the end product is generally of higher quality, and worker productivity is often greater, than for conventional construction. Furthermore, elements may incorporate advanced materials such as high performance concrete, and are designed to meet or exceed industry safety standards and structural design specifications for similar elements cast in place. This helps the units withstand not only design dead and live loads, but also the stresses of being transported to job sites at highway speeds, offloaded from trucks and moved or hoisted into position.
There are many types of PBEs that may be combined on ABC projects for superstructure, substructure and even foundations. Among these PBEs are deck panels, deck beams, parapets, abutments, columns, pier bents, pile caps, footings and approach slabs.
Oftentimes an entire bridge is prefabricated near the final alignment and put in place using either slide-in bridge construction (SIBC), or giant, multi-axle self-propelled modular transporters (SPMT).
A few New England bridge projects built over the past 15 years demonstrate some of these ABC techniques:
Connecticut Uses SPMTs to Replace I-84 Bridges
The technique used to build and install the pedestrian bridge, which collapsed in Florida, has been used to replace many bridges in Connecticut, according to Nursick. He said the largest of these projects involved I-84 bridges in Southington.
On that project, construction workers built two, 1,000-ton bridge superstructures near the existing bridges and later moved them to the Interstate alignment using self-propelled modular transporters (SPMTs).
Marino/Barnhart, under subcontract to general contractor Northern Construction LLC of Palmer, Massachusetts, operated two Goldhofer SPMTs to transport and position the 2 million-pound structures. Northern Construction’s $6 million contract called for removing and replacing the deteriorated decks and superstructures of the two 50-year-old bridges.
Several months before replacing the old bridges, Northern Construction fabricated new spans in staging areas set up next to the Interstate, and made repairs to the existing substructures. Later, Marino/ Barnhart moved the new bridge superstructures into place on the reconditioned abutments using SPMTs. Each structure consisted of 10 pre-stressed concrete Northeast Bulb Tee (NEBT) girders topped by an 8-1/4-inch cast-in-place concrete slab. Manufactured by Northeast Prestressed Products, the 102-foot girders weighed about 87,000 pounds each.
The old I-84 bridges remained open during the entire prefabrication period, with only some temporary lane closures when the old bridge superstructures were removed and replaced with new ones.
SML Bridge Linking Maine and New Hampshire Opens
A $170 million railway/vehicle bridge over the Piscataqua River between New Hampshire and Maine was built using PBEs for the structure’s 200-foot-tall lift-span towers.
Opened on March 30, the Sarah Mildred Long (SML) Bridge was built to replace a 1940s span linking Portsmouth, New Hampshire, and Kittery, Maine. General contractor Cianbro constructed the bridge, which was designed by joint venture Hardesty & Hanoverand FIGG Engineering. The bridge is a joint venture of the Maine and New Hampshire DOTs, with Maine DOT serving as venture lead.
The bridge utilizes two pairs of 200-foot-tall precast post-tensioned towers to support a 300-foot-long steel lift-span that accommodates vehicle traffic at its highest setting and trains at the lowest.
Each of the towers consists of 22, 80-ton concrete PBE segments cast by Cianbro workers in a casting yard on land nearby. Unistress Corporation in Pittsfield, Massachusetts, provided roadway and railroad box girder segments, with the largest weighing about 100 tons. Segments were barged to the bridge site where they were raised and installed using several cranes ranging from medium-sized hydraulic and lattice-boom cranes to the largest rig, a Manitowoc Series 3 Ringer.
Seacoast Ready Mix supplied an estimated 18,000 cubic yards of ready mix concrete, which was pumped in place by Independent Concrete Pumping of Wakefield, Massachusetts.
Casco Bay Steel Structures, Inc. of South Portland manufactured the steel box girders for the bridge’s lift-span.
Fast 14: Accelerating Bridge Replacements in Massachusetts
The Massachusetts Department of Transportation (MassDOT) replaced 14 bridges on I-93 in Medford in just 10 weekends between June and August 2011. The I-93 Rapid Bridge Replacement slashed three years from a conventional schedule and greatly reduced impacts on drivers.
ABC methods employed to speed up the $98 million project included design-build contracting, PBEs for the superstructure that were constructed off site and brought to the bridge location ready to install, and rapid-setting concrete.
Performed as part of the state’s Accelerated Bridge Program (ABP) adopted in 2008, MassDOT replaced the 60-year-old bridges' superstructures and repaired their substructures. For each replacement, the roadway was closed at 8 p.m. on a Friday and traffic directed to the other side of I-93, where the opposing lanes were separated by a moveable barrier. The existing superstructure was demolished and the new modular superstructure installed. Each module was composed of a concrete deck with two steel beams attached underneath. The segments were installed by crane and connected with rapid-setting concrete. At least one bridge was built each weekend.
By September 1, 2017, MassDOT had advertised and awarded about 200 ABP construction contracts with a combined construction budget valued at $2.44 billion.
New Hampshire DOT One of First to Build All Precast Concrete Bridge
The first New Hampshire bridge replacement using PBEs for all bridge components was the Mill Street Bridge in Epping. Built in 2004, this project replaced two short bridges over divided channels of the Lamprey River with a single bridge over both channels. JP Carrara & Sons Inc. of Middlebury, Vermont, manufactured all of the precast elements.
The New Hampshire Department of Transportation (NHDOT) used the project to demonstrate an ABC system for constructing state highway bridges in less than two weeks.
As described by FHWA, the NHDOT design used all precast concrete elements. The substructure is a simple cantilever abutment and cantilever wingwall system that is supported on reinforced concrete spread footings. Based on conventional reinforced concrete methods, typical component splicers were replaced by grouted reinforcing splice couplers. The superstructure consisted of precast pre-stressed adjacent box beams overlaid with a membrane waterproofing system and bituminous concrete pavement.
General contractor R.M. Piper Inc. was given two weeks to complete the bridge installation after the existing bridges were removed and excavation completed. Piper finished the bridge in eight days.
Accelerated Construction Used for Frenchtown Bridge
While the Rhode Island Department of Transportation (RIDOT) had made limited use of PBEs previously, in 2012 the agency replaced a deteriorated bridge in the Frenchtown neighborhood of East Greenwich using nearly all precast concrete PBEs.
Using ABC techniques, Aetna Bridge Company of Pawtucket, Rhode Island, installed the 150-foot precast concrete bridge over Frenchtown Brook as part of a $1.9 million contract while limiting road closure to about one month.
Concrete Systems Inc. (CSI) based in Hudson, New Hampshire, manufactured the ConSpan modular bridge system in 51 precast pieces weighing between 6,000 and 35,600 pounds each.
Twenty-five 6-foot-wide modular arches were snugged together on 12 precast Contech Express arch footings. Other PBEs were two headwalls, eight wingwall units, and four wingwall footings.
CSI used high-performance concrete (5,000-psi) to cast the arches, wall stems and headwalls; and 4,000-psi concrete to cast footings. The bridge is a 28-foot span, three-sided, arch-box culvert that was backfilled and paved over.
Testa Corporation demolished the old bridge, and Narragansett Improvement Company of Providence prepared the area for the new bridge. Aetna installed the precast units with a 265-ton Liebherr hydraulic crane provided by Bay Crane. A bridge of this size cast in place would have taken about six months, but was opened to traffic after having been closed for just 32 days.
Rhode Island is fixing more than 150 structurally deficient bridges and repairing another 500 bridges with revenue from a new toll program under RhodeWorks legislation passed in February 2016.
Vermont Flood-Damaged Bridges Get NEXT Beam Fix
Vermont’s Agency of Transportation (VTrans) implemented its Accelerated Bridge Program (ABP) in 2012 to rehabilitate bridges while reducing project costs through expedited project strategies including ABC techniques combined with road closures.
As an example, in 2015 VTrans employed these methods to replace four flood-damaged spans located on Route 73 in Rochester.
Two existing structures, Bridges 15 and 16, were cast-in-place reinforced concrete girder bridges built around 1930. Since they shared similar site characteristics, their replacements were designed as a single project to be constructed over the course of long weekend closures. Both structures used all precast components including NEXT Beams, beams integral with precast curtainwalls and approach slab seats, approach slabs, wingwalls, and concrete abutments on steel H-piles.
Designed by VTrans engineers together with consultants VHB, the bridge replacements were built by W.M. Schultz Construction Inc., based in Ballston Spa, New York, with all PBEs provided by J.P. Carrara & Sons Inc, of Middlebury, Vermont.
The non-proprietary NEXT Beam is a regional standard developed in 2012 by PCI Northeast Bridge Technical Committee, a consortium of state bridge engineers from the six New England states and New York, local fabricators, and members of PCI Northeast. PCINE Director Rita Seraderian, P.E. heads the committee. Joseph Carrara, P.E., President of J.P. Carrara & Sons, Inc., is a committee member.
According to Rob Young, P.E., Senior Project Manager of VTrans Structures Section, the Department has constructed or rehabilitated 79 projects using ABC methods since the ABP was launched in 2012 and has three projects currently underway and 17 in the planning stages.
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