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How Eight Mile Road Bridge in Hamilton County, Ohio, used a
bridge system prefabricated with integral beams and deck
incorporating the entire superstructure for a rapid installation.
Article contributed by Composite Advantage
Eight Mile Road Bridge, a short span concrete structure built in 1940, needed to be replaced in Hamilton County, near Cincinnati, Ohio.
In addition to replacing the bridge deck slab, the abutments required rehabilitation to extend the life of the structure. In 2000 and 2001, Hamilton County engineers chose to rehabilitate three bridges on Five Mile Road (Bridges B-0071, B-0087, and B-0171) with Fiber Reinforced Polymer (FRP) bridge decks on pre-cast, pre-stressed concrete beams.
An inspection conducted in July 2008 revealed only minor surface cracking in the decks. The decks were cleaned and sealed. Testing confirmed deck deflection was unaffected and corrosion nonexistent.
For Hamilton County engineers, the positive performance of the Five Mile Road composite bridge decks has established a track record for the technology’s capability to reduce maintenance and extend service life through the non-corrosive nature of the material. Innovative Bridge Research and Construction (IBRC) program funding supported the county’s request to use composite technology for Eight Mile Road. But county engineers had a more aggressive goal for the aging bridge.
The county’s bridge department wanted to eliminate the horizontal construction joints used in the previous composite deck designs. And, instead of a product that just provided a composite deck on reinforced concrete beams, engineers were looking for a total bridge superstructure application.
That’s where the integrated SuperFiberSPAN FRP bridge system came in. Unlike conventional FRP decks on steel beams, the bridge system is prefabricated with integral beams and deck incorporating the entire superstructure. Panels can be dropped in place for rapid installation.
“Eight Mile Road was the first site in the United States to receive this integrated composite superstructure” said Steve Mary, an engineer for Hamilton County, Ohio. “Typically, failure or structural issues occur where materials are joined together. This system eliminates the connection joints between deck and beams. Our office has always had a special interest in using innovative materials and products because our objective is to continually improve our infrastructure and extend service life. This integrated composite bridge system was a logical next step.”
Bridge parameters called for a 22 foot span and a width of 62 feet (1,364 square feet). Other specifications included the standard AASHTO HS 20 loading, an alternate military truck loading; L/800 deflection criteria; an integral concrete diaphragm; skew, cross-slope kick across the bridge to control asphalt thickness and an asphalt wearing surface. CA designed the FRP bridge superstructure, while LJB Engineering designed the concrete approaches leading up to the bridge’s entrance.
A unique infusion process was used to mold eight panels that covered the bridge’s full span length (22 feet) and were just less than 8 feet wide. Panel width was dictated by shipping size. A joint beam was bonded and bolted to join adjacent panels. The bridge skew was molded into the ends of net-shape panels. Beams and deck were integrally molded together. The deck facings, beam shear webs and beam caps consisted of multi-axial fiberglass fabrics.
In order to handle the high shear loads and crushing loads on the deck, a fiber reinforced internal core was used. The core has multiple shear webs in both longitudinal and transverse directions to minimize deck deflection. The entire lay-up of beams and deck were infused with a corrosion resistant vinyl ester resin with pigment and UV inhibitor. Eight panels were molded to cover the width of the bridge. A structural test program was conducted to validate the design.
Specimens and panels were tested in the following areas:
· Laminate (material properties)
· Deck (bending, shear)
· Integral deck/beam section static bending (full scale)
· Fatigue of the integral deck/beam section for 2M cycles
· Residual strength of the integral section
· Joint beam section static bending
Traffic volume for Eight Mile Bridge, located southeast of Cincinnati near the Ohio River, was considered low – about 2,000 vehicles a day.
“Eight Mile’s short span and low traffic volume made the bridge a good candidate for this new system,” Mary said. “Traffic downtime was close to 100 days with weather a partial contributor. But it only took one day to install the FRP bridge deck panels. Emergency vehicles and school buses made arrangements for alternate routing. The detour route was not lengthy. As a result costs were minimal.”
After the old bridge was removed, new abutments were poured. Bearing pads were located on the abutments at each FRP beam location. The panels were dropped in place starting with the east side of the bridge. To integrally tie the FRP bridge to the abutments, rebar was slid into pre-drilled holes through the FRP beams.
After the next FRP panel was fit-checked, adhesive was applied to the joints and the panels were bonded together. Bolts were used at the joint to clamp the mating surfaces together to ensure a consistent bond line and to provide a redundant shear connection between panels. All eight panels were installed in one day.
A poured concrete diaphragm was used to connect the FRP bridge to the abutment. The diaphragm was poured through holes cored through the deck to ensure even support under the deck, and the beams. An asphalt wear surfrace was applied to the bridge. Trend Construction Co. acted as the prime contractor. Rod-Techs tied the steel, Security Fence installed the guardrail, Bernard Concrete Sawing sawed the abutments and J.K. Meurer paved the roadway.
According to Mary, traditional construction methods and materials for the superstructure would have required more labor resulting in additional time and higher costs for construction. Since Composite Advantage prefabricated the bridge panels and preassembled them on their manufacturing shop floor, installation of the system in the field went quickly and smoothly.
“For this project in particular, the goal was to construct a total superstructure out of composites that could deliver a service life capable of exceeding 100 years,” Mary said. “In addition to a long life cycle, the non-corrosive nature of composites greatly reduces maintenance costs. The speed of construction combined with the ease of installing the light weight composite panels reduced the amount of time the road was closed and generated a savings to the traveling public.”
Andy Kloenne, vice president for Trend Construction, said working with the bridge system was convenient. “We did not need a large crane to position the panels, a piece of equipment that would have been expensive to use and taken more time,” he said. “The bridge was much easier to install using equipment already on site.”
Because the integrated system prefabricates more of a bridge’s components into one piece, the cost premium for using high performance composite material is reduced. The overall cost of the integrated system is less than a conventional FRP bridge deck and separate beams because fabrication and assembly of the panels takes place under one roof to minimize production costs.
“Choosing FRP for higher volume roads should reduce closure time and the costs of detour due to the fact the integrated bridge can be manufactured, delivered and placed quicker than traditional methods,” Mary said.
Hamilton County is also looking at applications for longer span bridges. The manufacturer of the bridge technology says it has integrated designs up to 60 feet. The integrated bridge system can be used for vehicle or pedestrian applications.
The SuperFiberSPAN bridge was installed in April 2008 and opened for public use in June 2008. Bridge performance has met expectations. Testing will be conducted on Eight Mile Bridge in 2010.
The Bridge Department expects that the service life of its bridge structures has increased through the use of FRP decks and that reducing maintenance costs will provide real cost savings in future.
All photos courtesy of Composite Advantage.