A bridge is like a living organism. It requires frequent health check-ups and maintenance, and its lifespan is 50 years on the average. With limited resources and an ageing bridge population, bridge owners need reliable information on bridge health in order to manage their bridge inventory efficiently and economically. Although the tragic bridge collapse in Minneapolis in the summer of 2007 was not attributed to poor maintenance, everyone was reminded of how crucial understanding bridge health and performance is to the safety of the motoring public.
The Federal Highway Administration (FHWA) has awarded a $25.5 million contract to establish a Long-Term Bridge Performance Program (LTBPP). The contract was awarded to the Rutgers Centre for Advanced Infrastructure and Transportation. The initial contract is for five years, but it is envisioned as a 20 year research study to improve the quality and quantity of information on bridge health to enable highway managers to make better decisions about bridge maintenance and repair.
Virginia Tech and the Virginia Transportation Research Council (VTRC) are subcontractors to Rutgers on this project. They are responsible for the instrumentation and monitoring of 10 bridges in the eastern part of the United States. They are working closely with researchers from Utah State University, who are responsible for similar work in the Western US.
Virginia Tech Civil and Environmental Engineering (CEE) faculty members Carin Roberts-Wollmann, Tommy Cousins, and Elisa Sotelino are the principal investigators for the project. They have considerable experience in the instrumentation, testing, monitoring and modeling of bridges. Together they comprise a formidable team.
Roberts-Wollmann, associate professor of CEE, has over 20 years of experience in the areas of design and construction of prestressed concrete bridges and laboratory and analytical research into the behaviour of concrete bridges. She also has considerable experience with field investigations of bridges. For her Ph.D. research, Roberts-Wollmann installed instrumentation in four spans of the San Antonio 'Y' project, an urban viaduct constructed with post-tensioned segmental box girders. She monitored the instrumentation through the construction process and for two years following.
'A project of interest involved the instrumentation, monitoring and live load testing of a bridge in Franklin County, which had Glass Fibre Reinforced Polymer (GFRP) bars as the top mat of reinforcement in the deck. GFRP bars have the benefit of not corroding due to de-icing chemicals used on the bridge. The embedded instrumentation systems were monitored for several years, and the material proved to be as reliable as more conventional mild steel reinforcement. The final outcome of the project was a set of guidelines for the future use of FRP in the Virginia Department of Transportation bridge decks,' Roberts-Wollmann said.
The second PI on the project, Cousins, CEE professor, focuses his research on evaluating and implementing high performance materials and innovative construction techniques in bridge structures. Materials he has investigated in the past include: high performance and ultra high performance concretes, lightweight concrete, fibre reinforced polymer composites, aluminium, and high performance steels.
In one recent project, Cousins gave an ageing Virginia bridge a face lift. 'We used a fibre reinforced polymer (FRP) composite cellular deck system to rehabilitate a historical cast iron thru-truss structure, namely the Hawthorne St. Bridge in Covington, Va. The most important characteristic of this application is reduction in self-weight, which raises the live load-carrying capacity of the bridge by replacing the existing concrete deck with an FRP deck,' said Cousins.
Cousins has worked with Tom Murray, CEE professor emeritus, and Sotelino on implementing the Sandwich Plate System (SPS), an innovative bridge deck system, in a Virginia bridge and also in a number of bridge applications throughout the United States as part of the Innovative Bridge Research and Construction (IBRC) program. Other projects Cousins has worked on include field-testing to determine the live load distribution factors and dynamic load allowance for a U. S. Army truck versus a civilian dump truck on reinforced concrete bridges, and measuring the distortion induced fatigue cracking at diaphragm-girder connections in bridges in Birmingham, Ala.
Recent projects in Virginia that Cousins and Roberts-Wollmann have collaborated on include the evaluation of the performance of the bridge deck panels on the Woodrow Wilson bridge, whose components were shown to be performing well after 20 years of service. They also were responsible for the implementation of full depth precast bridge deck panels, which will be used on a bridge deck replacement project in the Bristol district, scheduled to be completed in the summer of 2009.
The third PI on the project, Sotelino, CEE professor, brings the team considerable expertise in modelling and analysing highway bridges. Sotelino has worked on numerous bridge related projects including the development of a simplified equation for the determination of the load distribution factor to replace the current American Association of State Highway and Transportation Officials Load and Resistance Factor Design equation. 'The research involved the finite element modelling of hundreds of bridges and was supported by the Joint Transportation Research Program (JTRP), a consortium between Purdue University and the Indiana Department of Transportation,' said Sotelino.
On other projects funded by JTRP, Sotelino led the investigation of the use of FRP composites in highway bridges. These projects ranged from the use of FRP as retrofit to the adoption of FRP decks to rehabilitate deteriorated bridges. 'The first project involved the monitoring of bridge columns that had been retrofitted with composite jackets. With the combination of finite element modelling and laboratory testing, accurate predictions of the long term behaviour of these retrofits were realised. Two field applications were then developed and instrumented, which have been continuously monitored by the Indiana Department of Transportation and have confirmed the original predictions,' Sotelino said.
Since her arrival at Virginia Tech in January 2005, Sotelino has worked closely with Roberts-Wollmann and Cousins on several bridge related projects with the primary responsibility for the analytical portion of the research. On the LTBP project, Sotelino will create finite element models of all of the bridges to be instrumented and monitored. This will enable the team to develop optimum instrumentation and testing schemes, since they will have a solid understanding of the bridges' behaviour based on the models.
The three are looking forward to the challenges of the new LTBP project. They have an excellent working relationship with the researchers at VTRC, which include Jose Gomez and Michael Brown, who received his Ph.D. at Virginia Tech. 'We have an incredibly strong and well qualified team,' said Cousins. 'We have a lot of hard work ahead of us, but the resulting improvements in bridge health monitoring will be of great value to VDOT and the nation's highway infrastructure as a whole.'