21st Century Innovations
The bridge design and construction methods are filled with modern innovations, some being used the first time in the world. Here are just a few of these 21st century innovations that have been incorporated into the new Memorial Bridge:
The first of its kind in the world, a gussetless bridge
The new bridge design has eliminated the most vulnerable part of a truss – the gusset plate – that has historically been the cause of costly maintenance, repairs, and replacements. A gusset plate is a thick plate (sheet) of steel used to connect the various pieces of the bridge (or truss members) and kept in place with steel bolts. As the gusset plates corrode and weaken (and require costly retrofitting), as was the case with the 1922 Memorial Bridge, they compromise the strength of all the separate pieces.
The design team eliminated gusset plates entirely. Instead, the metal sections are all uniform in size so they fit together like puzzle pieces, through a process called splicing.
According to Ted Zoli, Innovative Designer for the new Memorial Bridge, “We are routinely involved in truss gusset retrofits that are often necessitated by corrosion. Our design approach for this bridge seeks to change this chronic weak link in trusses to provide a bridge that will substantially extend the service life of the structure. In our view, the only way to achieve a substantial enhancement to truss superstructure durability is to eliminate this weak link, and our truss eliminates the use of gusset plates.”
In addition to the long-term benefits of this gussetless design, significantly less bolting is required which results in faster construction and less costly maintenance long-term.
Use of a metalized coating
The steel portions of the new bridge will be finished with a metalized coating expected to last 40-50 years without requiring maintenance. The process utilizes an electric arc spray gun to apply molten zinc onto the surface of steel. Zinc provides the highest protection from corrosion and also keeps the look and feel of the new bridge in-line with the local U.S. Navy shipbuilding history.
Recently, at the Kittery Block Party, members of the community were able to see a sample of the steel with the zinc coating and voted on what to name the color of the new bridge. By popular vote the community selected the name of Piscataqua Mist!
Other names considered by the community were: Sea Foam, Portsmouth Pewter, Kittery Pewter, Sea Smoke, Sea Salt, Piscataqua Pewter, Sea Mist, Whipple Grey and many others. Regardless of the name chosen, the new bridge will be in-place before you know it and the long term maintenance costs have been significantly reduced just by this one innovation.
Consistent profile of three spans and cold bending of steel –another first of its kind
The three spans (or truss sections) have been designed with an uninterrupted consistent profile; therefore expediting fabrication and construction. The profile of the spans echoes the look and configuration of the 1922 bridge and meets a primary goal of returning the bridge to the community – fast.
To make those sections uniform, the design team created another innovation — cold-bent steel. In most truss bridges, individual steel beams are used; in Memorial Bridge, 65-foot curved sections are being fabricated.
During his interview with the Portsmouth Herald, Ted explained, “What we realized is, if we bent the plates to a fairly large radius, a fairly gentle bend, we can use cold bending.” The Memorial Bridge will be the first that incorporates cold-bent plates, he added. Cold-bending of steel was developed many years ago by the U.S. Navy in its construction of submarines. The design team honors this local tradition with the shipyard in plain view of the bridge.
These three spans, now the first of their kind in the world, are commonly referred to in the community as these:
- Portsmouth Span or South Span
- Center Span or Center Lift Span
- Kittery Span, or North Span
Reconstruction of the original 1922 granite piers
By using micropile technology to reconstruct the original 1922 granite piers for the new bridge virtually all in-water work has been eliminated and disturbance of the river bed will not occur. This technology protects aquatic habitats and the water quality of the river by eliminating the typical method of constructing cofferdams, which are in-water enclosures that would have been constructed around new piers into the river bed to create a dry work environment. In addition, the use of micropile technology expedites the overall project schedule.
Micropiles are deep foundations elements constructed using high-strength, small diameter steel casings (9.75 inch diameter). Reinforced steel rods (3.5 inch diameter) are inserted into the casings and then high strength grout is pumped (poured) into the casting.
The number of micropiles planned for each granite pier are 14 each for Piers 1 and 4 and 18 each for Piers 2 and 3. The approximate depth of drilling is 35 feet for Pier 1, 110 feet for Piers 2 and 3, and 25 feet for Pier 4.
Modern Control House
For maximum visibility for the bridge operators, the new modern control house will have windows providing a 360 degree view. Also, to improve visibility, and safety, an open walkway surrounds the control house and serves as an exterior viewing platform.
Sustainability & Cost Reductions
The project team has designed a bridge that meets the needs of the present without compromising the needs of future generations. The new bridge has been designed and constructed to demand as little as possible from natural resources.
The team has provided a bridge that greatly minimizes operating and life cycle costs. According to Keith Cota, “This is a pioneering design that will connect the generations of today to those in the future and will bridge the two communities for continued prosperous economic and social growth.”
According to Stephen DelGrosso of Archer Western Contractors, “Cost savings, both short-term and long-term, was the focus at each decision point during the design and construction plan development.” In addition, he adds, “Our primary means of reducing the cost of maintenance and repair was to create and build a structure that would simply not demand costly maintenance.” The goal of cost reduction has been achieved by the project team and we should all be proud of this accomplishment.
And, Archer Western also integrated sustainability into all aspects of the design and construction plan. The following strategies are just a few of the highlights on how this goal has been met:
- Maximize the use of recycled materials (with an emphasis on steel) and minimize materials with a significant carbon footprint.
- Minimize the weight of the center lift span and tower heights to reduce overall quantities of materials.
- Minimize the overall steel square footage which minimizes the volume of the metalized zinc coating.
- Reconstruct of the existing 1922 granite piers to avoid disturbance of the river bed and associated habitat and to protect the water quality of the Piscataqua River.
- Minimize life cycle costs by reducing future maintenance.
- Use of drilled shaft foundations for the new Scott Avenue Bridge (as opposed to pile foundations), to minimize subsurface vibrations near the historic buildings.
- Minimize power consumption by selecting motors with antifriction bearings which decreases horsepower requirement by at least 25 percent.
- Eliminate the traditional large machinery house normally required in favor of a smaller and more efficient machinery room that decreases power requirements for heating and ventilation alone by 50 percent.