One of the major challenges facing public-works departments across the northeast is an aging road and bridge infrastructure that is subject to harsh weather conditions with limited resources to replace it.
During my tenure as commissioner of public works for Erie County, N.Y., I became painfully aware of the ever-worsening conditions and the need to find innovative and cost-effective solutions.
Located in western New York, including the city of Buffalo, Erie County owns 289 bridges. Most of these bridges are over 50 years old and, located in an area that receives significant snowfall, have seen years of corrosion due to the heavy use of deicing salts. Over a third are single-span bridges with spans less than 40 ft. One of the innovative solutions Erie County was looking for was to use prefabricated elements as “big kids’ building blocks” in order to find an approach that could be quickly and cost-effectively duplicated in many locations, while providing long-term durable solutions. Prefabricated bridge elements offer bridge owners, designers and contractors significant advantages in terms of duration, cost, safety, environmental impacts, constructability and durability. Their manufacturing is done under shop-controlled conditions, which enables better quality control, while taking the fabrication time out of the project’s critical path.
Aussie hustle
In an effort to investigate innovative solutions, the Erie County Department of Public Works met with Wagners Composite Fibre Technologies Pty. Ltd. in 2003. Wagners is an Australian company that designs and manufactures composite bridge superstructures using a hybrid of reinforcement concrete and fiber-reinforced polymers (FRP), with an anticipated design life of 100 years. This was the first project in North America to use Wagners’ hybrid design and manufacturing, thus it served as a pilot to highlight new technology and rapid construction.
The New Oregon Road Bridge over the South Branch Eighteen Mile Creek in the town of North Collins was selected as the replacement bridge. The span was 28 ft with a width of 23.7 ft and a 3° skew, and there was 8 ft from the top of the deck to the top of the foundation rock. The location was on a low-volume rural road.
Erie County and Wagners retained TVGA consultants to perform the general engineering services. As this was Wagners’ first bridge in the U.S., certification required that the design be checked against AASHTO, New York State and local specifications. This was complicated by the fact that at the time there were no specifications adopted for the design of FRP or hybrid FRP superstructures.
In order to ensure the bridge was constructed in 2004, the design process had to be accelerated to ensure that there was sufficient lead time for advertisement, bidding and award, as well as fabrication of all bridge elements prior to road closure. The major concern was that the hybrid superstructure, following certification of design, had to be constructed and shipped from Australia to the U.S. The design process for the project, including the review of the hybrid superstructure design and testing and the preparation of contract documents, was completed in approximately three months in order to meet this schedule.
To further accelerate construction, it was determined that precast concrete blocks would be used for the abutments, wingwalls and bridge seat. Provisions were included in the contract documents, which allowed the contractor to choose the precast concrete system to be used based on cost, availability and speed of installation. No variance from the contract plans was permitted where critical dimensions or elevations were required for the substructure to fit together with the superstructure. To allow for the use of a variety of precast systems, variations such as the length of the wingwalls were specified with minimum and maximum dimensions. Any alternative was to be designed by the contractor, however it was subject to review by the engineer to ensure proper fit with the rest of the system.
To provide sufficient installation clearance and for the variation in the dimensions of the prefabricated elements, cast-in-place cheekwalls were incorporated into the design. These cheekwalls are located where the abutments, wingwalls and superstructure come together. Casting in place provided an allowance for the elements to be tied together, allowing for the variations in the dimensions. As with the footings, high early-strength concrete was used in these locations to minimize the time associated with the concrete curing.
Following design completion in June 2004 a total of nine contractors bid on the project, with award granted to UCC Constructors Inc. in July. Work could not commence until confirmation of the arrival of the superstructure in the U.S. This was done to ensure that the existing bridge was not demolished with time lost waiting for the superstructure, and allowing for lead time for the fabrication of the substructure elements.
A Sept. to remember
The precast concrete block system selected by UCC was manufactured by Rielfer Concrete Products. The units were approximately 4 ft 9 in. x 2 ft x 1 ft 1 in., stacked upon one another, with a geogrid anchorage into the backfill between selected layers. Two specialized half-bridge-width sloped blocks were placed on the standard blocks at each abutment to provide the cross slope for the bridge. Bars were installed from the bridge seat to the footing to ensure that the superstructure would remain in place during a flood, because the hybrid structure is buoyant.
Closure of the road took place on Sept. 7. Within two days, the existing bridge was demolished and the rock prepared for the installation of the abutment and wingwall footings. Concrete barrier cofferdams were installed on earth fill at each of the new abutment locations in an attempt to prevent stream waters from interfering with the footing placement.
The north abutment was the first formed and poured. On Sept. 13 the forms for the north footing were removed, and test cylinders indicated that the high early-strength concrete had reached the required strength for loading. As such, the precast concrete abutment and wingwall blocks were delivered to the project site for installation and placed. They were light enough that an excavator could easily lift the blocks and place them with a two-man crew for block installation and alignment.
Next, the wingwall course was installed. While the south footing was allowed to cure, the additional layers of precast blocks were being installed on the north side. Installation of the 41?2-ft design height north abutment and wingwalls took four days, while the south abutment and wingwalls took only two days. By Sept. 17, 10 days into the construction schedule, both abutments were ready for placement of the superstructure.
Two weeks after construction had begun, the superstructure arrived at the project site. To facilitate worldwide shipping, the superstructure was prefabricated as four full-length panels, each 7.15 ft wide. In order to avoid special permits for material delivery, the design dimensions and weight were limited and had the added benefit of allowing the contractor to lift and place the panels with two excavators, rather than requiring a crane.
On Sept. 22 the trucks carrying the panels arrived at the site and the interior panels were placed first to ensure proper alignment, because the cross slope on the bridge was obtained by using a sloped bridge seat. It took one hour to off-load and align these panels, which was followed by the installation of exterior panels. Then the specially designed and fabricated bridge railing connection brackets were installed on the fasciae of each exterior panel. Because the superstructure was new, there were no standard connections that could be used for the attachment of the typical NYSDOT bridge railing. These brackets also served as a connection point for a debris and ice barrier on the upstream side of the bridge to protect the FRP portion of the superstructure from impact damage due to waterborne debris.
Anchoring and grouting of the panels occurred on the following day, with an overnight cure. On Sept. 24 an aggregate-filled resin overlay was placed over the concrete deck and joints as an extra layer of protection for the concrete deck. The full installation of the superstructure and overlay took a total of three days to complete. To ensure the structure was performing as designed, the bridge was load tested and in all cases found to be performing within variances as predicted. The roadway was re-opened to traffic on Oct. 8, just 31 calendar days after the closure of the road with a relatively small crew on-site.
This project demonstrated how prefabricated elements, along with innovative design, can be used to accelerate construction for a typical bridge.
