Accelerated Bridge Construction with Time-Proven Technology

Detailed work is now under way for a new movable arch bridge that owes much of its world-first design to close cooperation between engineer and architect.

I St Bridge
Sacramento, CA (Article from Bridge Design & Engineering, Spring in Sacramento, June 12, 2020) – The need for a new bridge across the river that divides the cities of Sacramento and West Sacramento had been widely recognized for well over a decade. In 2011, the Sacramento River crossings alternatives study came to that same conclusion, identifying that the existing I Street Bridge needed replacement. The existing 100-plus-year-old structure features no cycle paths and its lanes are too narrow to serve buses or meet current pedestrian accessibility standards.

The I Street Bridge Replacement Project will provide a new connection across the Sacramento River between the Sacramento Railyards and a planned development in West Sacramento, serving vehicular, cycle, transit, and pedestrian users. The existing structure will be retained and the lower deck will continue to serve as a railroad crossing.

In 2018, a design competition was undertaken to engage a bridge architect for the design of the new bridge. There was much political and community support for the structure, along with a strong desire to make the bridge iconic. "They realized it was a once-in-a generation project. There hadn't been a new bridge over the river downtown in over 50 years, so there was a lot of energy to try and do something fresh," recalls Noel Shamble, lead bridge aesthetics designer at TY Lin International, which won the competition.

In common with other projects seeking iconic status, the structure's location, environment and local culture all had significant effects on the development of its design. Due to a slight bend in the river, the structure was required to be longer than others that cross the water, in order to accommodate the wide turning radius of US Coast Guard tug boats taking barges for the repair of levees. "It was tricky. The proportions were different to other lift spans, which are shorter and taller, while here it is longer with a lower lifting height," says Shamble.

The team also had to be sensitive to the existing I Street Bridge immediately to the south, as well as Tower Bridge less than 1km away: the latter is a gold-painted historical vertical lift truss bridge with a 64m-long central span that has connected the two cities for 85 years. "Tower Bridge is an icon that can be seen everywhere and people were concerned that the new bridge would overshadow the old. So we had to do something different that would preserve the historic structure and make a pathway for the new vision," says Shamble.

During 2019 nine concepts were presented and refined through a series of community workshops. Amongst the design ideas was a bridge featuring a movable span with trees, and this proposal advanced as far as working out soil type, drainage, weight changes and maintenance issues. Another initial concept featured a sculptured arch sweeping upwards from the top of the two lifting towers. "It was sort of a grand vision of metaphorically connecting the two cities without the lifting span breaking the line of the connection. The arch held up an array of solar panels that would harness enough solar power to lift the bridge up and down," Shamble recalls. Although this ambitious concept ignited much enthusiasm in the community, it had to be laid aside due to the prohibitive costs, even when taking into consideration generous pledges received from private donors for its realization.

Practicalities demanded that the final choice came down to two designs, a truss and an arch, each with two variants. "We were limited to crossings that had the structure above the deck, as there is a high flood level that is only 8ft [2.4m] under the deck. So that took out of the running the box girder systems and concrete systems that would have deeper structural sections. Then there was the aesthetic impact. Through-girders didn't make sense as you could not see out of the side. That is why we were coming to trusses or arches. The trusses evoke that historical nostalgia of bridges that people wanted to reserve for the historic bridge up the river. In contrast, the arch had the futuristic vision, framing transparent views through its cables and letting the beauty of the natural scenery shine," says Shamble, who notes that unlike most cities in California, which are surrounded by hills, the Sacramento skyline is clearly visible from many kilometers away, as would the new structure.

In January this year the winning design was revealed. Called the Spring, it comprises a 262m-long, 30.5m-wide bridge with a 100.6m-long, highly unusual basket-handle network tied-arch lifting span. The two parallel arches are connected to the movable span, which has a vertical lift height of 15m. The width of the deck is designed to be ample enough to accommodate a future light rail system without impacting on cycle and pedestrian lanes in either direction. Adding to the unusual nature of the structure, at either side of the lifting span are shaded observation areas that cantilever outwards by 3.6m. Furthermore, the four lifting towers not only feature extensive glazing, but they also stand at 90° from the standard position of lifting towers. This design owes much to the close co-operation between TY Lin and Modjeski & Masters, which enabled the arch span to be refined to a final iteration accepted by the community. In an earlier version, the significant weight of the lifting span called for a two-sheave pulley system in each of the four lifting towers. "And that meant the towers were massive and stocky, which was one of the main comments. The weight directly correlated with the aesthetics of the towers, so we tried to trim it down as much as possible whilst still providing the community spaces," says Shamble.

Kevin Johns, movable bridge business unit director at Modjeski & Masters, takes up the story. "The request was to put on our thinking caps and see what we could do to reduce tower size and make it more aesthetically pleasing," recalls Johns, "The only way to do that was to go from two sheaves in each tower to one. And the only way to do that was to significantly reduce the weight of the bridge. There wasn't much we could do with the structural framing, we had already come up with a fairly efficient arrangement there."

The team at Modjeski & Masters sought alternatives to steel and concrete for the deck, focusing on the potential use of an aluminium orthotropic deck. A lifting span made of reinforced concrete was estimated to weigh 3,400t, in comparison with around 2,200t if made in aluminium, with steel somewhere in between, estimates Johns. Among the benefits of using aluminum was a good expected lifespan and a comfortable experience for bridge users. Downsides were cost of the material, the need for insulation between the aluminium and the steel to avoid corrosion potential, and the requirement for an additional surface coating to provide traction in the wet. "Earlier versions of similar decks had been found to be somewhat fatigue prone," points out Johns. "But recent full scale lab testing for this particular version of the deck showed that it has the same fatigue resistance as a steel orthotropic deck."

Once satisfied that aluminium could be used for the lifting span, the towers were duly slimmed down. "The client was very excited that we were able to make that improvement to make the towers smaller," Shamble remembers. "Aluminium is more expensive, but then there are cost savings on the mechanical side, and the two offset each other in our estimates."

An aspect of the design that is unusual for a lifting bridge is the presence of two independent towers at each end, located perpendicularly to the roadway, rather than a single tower per end that traditionally houses the single counterweight and operating machinery.

With the traditional method, the main span's primary structural member, the lift sheave and the counterweight, line up, suspending the counterweight mass over the roadway. In a four-tower configuration where the sheaves and counterweights are aligned with the roadway, the tower and counterweight block are directly over the pedestrian path. This, explains Shamble, was not desirable for the I Street Bridge. "Doing this in our case, where the pedestrian path is wide and important, we would have needed to flare the path out around the tower to accommodate the tower being centered on the longitudinal line of the main span, and that would've required extra deck width all around – a look and cost we didn't prefer.

"Alternatively, the tower straddling the pedestrian path, with weight hovered above it, would require an extra tall tower - again, not preferred," says Shamble. The architectural concept for the Spring's basket-handle structure was to create a distinctive cathedral-like view that the presence of embedded towers would have compromised, he adds. "Moving them outboard of the deck entirely was possible by rotating them 90° and introducing a hidden structural member. Between each set of towers, nestled atop each pier wall, is a deep lift beam. This is the lifted member that is in line with the sheaves and weights as needed. Then the arch structure actually rests on the lift beam. This allows us to push the towers out from the deck a little on each side, giving the main span some breathing room, which in turn allows the sweeping arch form to blend into the approach deck edge unobstructed and continue out into the landscapes – a major theme of the design."

Very few vertical lift bridges are configured this way, explains Geoffrey Forest, senior mechanical engineer at Modjeski & Masters, with counterweight and sheaves perpendicular to the roadway, as well as the drum that hoists the span up and down. "This requires a right-angle turn in the driving machinery which can be difficult to fit in the narrow space of the pier. However, since the lift span and counterweights will be in line across the width of the roadway, we can take advantage of this arrangement and pull the lift span directly down to lower the bridge, and pull the counterweight directly down to raise the bridge. This eliminates small deflector sheaves at the tops of the towers. So a little bit of complexity also comes with the chance for some simplification."

Once completed, the bridge will be raised as needed by an operator housed on the eastern riverbank, on the outer part of the river's bend, in a two-storey building where the lower floor will be used for mechanical equipment. The roof is planned to become part of a path and will include a viewing area.

Shamble, Forest and Johns believe that the end result, on which construction work is expected to start next year, will be truly unique. "We think this may be the first vehicular network tied arch lifting bridge in the world," says Shamble.

Aluminum Bridge Decking Provides New Solution for Industrial Flooring

Ann Arbor, MI, March 2019 – AlumaBridge Aluminum Decking isn’t just for vehicular bridges. It’s the perfect replacement for deteriorating factory floors and new industrial applications that require very high load capacities. AlumaBridge Factory Floor Panels are lightweight, prefabricated, and modular for easy installation. Corrosion resistant aluminum reduces maintenance and is 100% recyclable. Skid resistant coatings are also available.

“We recognized the attributes of AlumaBridge decking also deliver an excellent flooring solution for factories, warehouses and other industrial applications,” says Greg Osberg, AlumaBridge President & CEO, “while providing a safe, sustainable and economical alternative to steel, concrete and wood.”

Recently, AlumaBridge supplied panels to a large manufacturer that needed an elevated floor capable of supporting forklifts with each tire exerting a load of 35 kips. The existing floor was positioned above a number of levels consisting of mezzanines, walkways and mechanicals that support manufacturing. Welded steel plates served as the riding surface for forklift traffic. Forklift loads caused some welded plates to crack and buckle, requiring repair of the floor surface as well as repair to damaged forklift tires and undercarriages. AlumaBridge Factory Flooring panels can solve these types of problems with a minimum of downtime and loss of productivity. Moving forward, the AlumaBridge solution provides a smooth safe riding surface that will not crack or buckle, thus reducing future maintenance.

AlumaBridge has also supplied prefabricated panels for a nuclear power plant application where load capacity is also key. In this case, large panel assemblies must be periodically removed to perform maintenance on critical systems below. To improve this process, replacement of heavier decking with lightweight AlumaBridge decking will make handling more efficient, thereby reducing downtime and improving productivity for every future cycle of maintenance.

Factory Flooring

Moffat County, CO
– AlumaBridge Aluminum Decking and support beams have been installed on the Browns Park Bridge. The project presented unique challenges in that the bridge is a swinging bridge spanning a lengthy 320 feet. As with most bridge rehabilitations, deck weight is critical. AlumaBridge lightweight decking was ideal for this bridge application. Compared to the original timber decking, the AlumaBridge deck system also offers a solid skid-resistant riding surface.

Reconstruction of this historic bridge with an all-aluminum superstructure has provided vast performance improvements. Structural capacity more than quadrupled, from a 3-ton limit to 14 tons, which improved access across the bridge for firefighters, sportsmen, farmers, and other private business entities previously unable to use the swinging bridge.

Lightweight modular components also greatly facilitated construction over the Green River. The contractor was able to implement cost effective delivery methods to efficiently install the components. The erection equipment consisted of hand operated trolleys and a simple overhead crane rail. Overall, the consistency and predictability of deck panel dimensions exceed the Owners’ expectations.

AFTER – New AlumaBridge deck system spanning 320 ft over the Green River
AFTER – New AlumaBridge deck system spanning 320 ft over the Green River.

AlumaBridge deck system with skid-resistant riding surface. AlumaBridge deck system with skid-resistant riding surface.
AlumaBridge deck system with skid-resistant riding surface. AlumaBridge deck system with skid-resistant riding surface. Installation of new decking using overhead trolley system.

The Florida DOT has successfully completed testing of AlumaBridge Aluminum Decking. The evaluation included detailed inspection, structural testing, heavy vehicle simulation, and wearing surface tests. Lightweight aluminum deck panels were subjected to 600,000 passes using the heavy vehicle simulator at the FDOT State Materials Office. According to the final report, the weld detail for the test specimen can be considered to be within the infinite fatigue life stress limit.

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AluminaBridge Completes Fabrication of Aluminum Bridge Deck Ministry of Transportantion - Quebec

Ann Arbor, MI - AlumaBridge, LLC of Ann Arbor, MI has completed the successful fabrication of an aluminum bridge deck for the St. Ambroise River Bridge in Quebec, Canada. Two large panels, each measuring 32.9’ (10040 mm) x 12.3’ (3750 mm) x 8.0” (203.2 mm) deep, were required. The deck was shipped on December 10, 2014. The panels have been received, inspected and approved by the bridge owner, Ministry of Transportation – Quebec.

The project resulted in a number of fabrication advancements due to a unique set of specifications that had to be met. For example, AlumaBridge devised a way to attach the panels to galvanized steel girders without bolting the deck to the beams. This was accomplished by steel clamps (angles) that will be attached to the underside of the deck, but wedge on either side of the girder’s top flanges.

During preliminary design, AlumaBridge had to work with the existing girder spacing. This meant bridge engineers had to design unique aluminum extrusions to achieve the proper deck width. The design process also needed to consider clearances for fasteners between structural web members within the extruded aluminum profile. In addition, the curb sides of the deck had to provide a closure and structural support for the deck-mounted crash barrier. Therefore, the deck could not be trimmed to meet the required bridge width. To solve this problem, AlumaBridge designed a structural end extrusion that can be trimmed to provide deck panel width adjustability. The end extrusion was also designed to accommodate a deck-mounted crash barrier as well as a closure needed along the edges of the deck. Additionally, a special extrusion was introduced that is half the width of the base extrusion profile of 12.0” (304.8 mm). This extrusion made it possible to build the panel to the required width.

A design breakthrough was achieved with a splice joint that accelerates bridge construction and reduces the number of fasteners required. It was also important to create a positive connection at the bottom of the splice joint between panels where it rests on top of the girder. As noted above, the deck panels cannot be bolted to the beams, but each panel must be fastened together. The top flanges of the splice nest together with an overlapping flange and recess. The splice joint is fastened together by a single row of blind fasteners that are flush with the deck surface and utilize countersunk holes along the length of the splice. This splice joint design cuts the typical number of bolts in half and accelerates installation. At the bottom of the splice joint, a tongue and groove is incorporated into the extrusion profile for a positive connection.

At the abutments, the deck is sealed with a 0.79” (20 mm) one-piece closure plate that is mechanically fastened and runs the full width of the deck. Holes in the plate are predrilled at the factory as well as matching holes that are tapped in the deck for quick field installation.

Controlling weld shrinkage and holding tolerances on such large panels were critical. The top flange of each extruded aluminum profile is 0.850” (2.16 mm), while the lower flange is 0.350” (8.9 mm). Each panel incorporated four unique extrusion profiles – base, half, splice, and end extrusions. The range of extrusions required, together with two very different flange thicknesses, added to the complexity of friction stir welding utilized by AlumaBridge.

Previous aluminum bridge decks were fabricated with gas metal arc welding or earlier versions of friction stir welding. By contrast, AlumaBridge was able to deliver the St. Ambroise River Bridge deck with fully consolidated welds that achieve superior dimensional characteristics across the entire 32.9’ (10040 mm) x 24.6’ (7500 mm) deck assembly:
– Flatness Average: 0.37” (9.4 mm)
– Straightness: 0.21” (5.4 mm)
– Squareness: 0.167” (4.2 mm)
– Width: 0.125” (3.2 mm)

Satisfying the unique and challenging set of specifications from the Ministry of Transportation – Quebec made the fabrication of the St. Ambroise River Bridge a breakthrough achievement in the industry. AlumaBridge innovation met the specifications with a commitment to advancing and scaling aluminum bridge deck technology. AlumaBridge is providing new solutions for bridge owners to address accelerated bridge construction and rehabilitation.

The L. B. Foster Company is the North American distributor for AlumaBridge products. This NASDAQ company, founded in 1902, supplies fabricated bridge products and other infrastructure products worldwide.

AlumaBridge has fabricated and shipped 5" deep aluminum bridge decking to the Florida Department of Transportation.

The new 5" deep bridge deck system is designed to replace steel open grid. Corrosion resistant decking from AlumaBridge offers a solid riding surface and the preferred weight neutral solution to replace steel grid decks on moveable and fixed-span bridges.

FDOT aluminum bridge deck research will be presented by George Patton, PE of Hardesty & Hanover at the AASHTO Annual Bridge Meeting on April 20, 2015 in Saratoga Springs, NY.  The presentation is part of the T-8 Movable Bridges Technical Committee Meeting beginning at 8 a.m. in the Saratoga Hilton Hotel – Broadway Conference Rooms 1 & 2.

Aluminum Bridge Deck Design Solutions to Meet Current Challenges Faced by State DOT’s

Aluminum Bridge Deck Design Solutions
Sandisfield, MA — An aluminum bridge deck installed in 30 minutes recently in Massachusetts by AlumaBridge LLC may herald a solution for many of the country’s estimated 130,000 bridges in dire need of repair.

Using advanced technology to manufacture lightweight aluminum structures – that are then lifted into place by crane – transportation officials in Massachusetts replaced a 1950 bridge with a lighter and quicker-to-install substitute.

“The Accelerated Bridge Construction technology that is available today could signal a solution to the nation’s many aging bridges,” said Greg Osberg, president and CEO of AlumaBridge, LLC. “AlumaBridge aluminum bridge decking provides transportation officials with a rapid bridge rehabilitation tool that is more efficient and sustainable. Aluminum extrusion – which allows for large pieces of lightweight aluminum to be manufactured as prefabricated deck panels – offers a faster and more cost-effective solution.”

To replace the bridge in Sandisfield, MA, AlumaBridge created a lightweight aluminum deck that was pre-attached to the steel superstructure and lifted into place by crane in one piece. The use of prefabricated panels, which are one-fifth the weight of concrete, dramatically reduced the dead load, or overall weight of the structure, enabling the installation to be completed in record time.

A time-elapsed video capturing the installation process is available here.

A bridge is classified as “fracture critical” if it has at least one supporting element whose failure would result in the collapse of the bridge. More than 60,000 bridges in the U.S. are structurally deficient and another 70,000 are functionally obsolete, representing an urgent need for repairs on a massive scale.

AlumaBidge’s Aluminum Bridge DeckingAlumaBidge’s Aluminum Bridge Decking provides state DOT’s, toll authorities, counties and municipalities with a new solution to address structural deficiencies. Previously, the only alternative for many deficient bridges was total reconstruction.

Aluminum decking is about 75 percent more lightweight and sustainable than decking with steel and concrete. Unlike temporary bridges, once an aluminum deck is in place, it serves as a permanent structure. For older bridges, the use of aluminum decking permits roadways to be widened since the materials weigh less.

The Sandisfield bridge is an excellent example of the many benefits of aluminum bridge decking.