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Bridges B-0071, and B-0171 in Hamilton County, Ohio have been in service for about fifty years. They are short span bridges with prestressed concrete girders. Until late 2001, they had conventional reinforced concrete decks. On November third of that year the ribbon was cut to reopen the bridges, now with Fiber Reinforced Polymer Decks. One of the bridges also had the girders replaced. These are the only bridges in existence that have FRP decking on concrete girders. The Hamilton County Engineers Office contracted with the Civil Engineering Department at the University of Cincinnati to perform research on these bridges. Information gained from this research will seek to confirm the safety of the new technology, approve construction and design techniques with reference to the FRP deck, and determine overall performance of the bridge to provided understanding of the system. The 50-year-old prestressed concrete girders were subjected to destructive load testing. The girders showed little loss of strength or stiffness from aging. The information on the performance of the girders was used in the analysis of the bridge system. Two of the bridges were subjected to nondestructive load testing. A three-dimensional finite element model was then created to replicate the performance of the bridges. Data from the bridge tests provided enough information to create an accurate model of the bridge girders, but not the deck. Using the finite element model, a Load Rating was performed. The bridges were found to be sufficiently strong to resist the loads that may be applied to them. The deck showed no signs of separation from the concrete girders as was previously suspected. The bridge system acted as a fixed end beam because of the semi-integral end abutments for the range of loads tested. The deck was not adding any strength tot the girders through composite action. The load transfer from one girder to another was not provided by the deck as was assumed in the design process, but by the concrete diaphragms used for lateral stability. Further testing will be needed to understand the deck performance better so that a full bridge analysis may be performed.
Bridges B-0071 and B-0171 in Hamilton County, Ohio have been in service for about fifty years. They are short span bridges with prestressed concrete girders. Until late 2001, they had conventional reinforced concrete decks, which have been replaced with fiber reinforced polymer (FRP) decks. Two girders in bridge B-0171 were replaced with new prestressed girders. These bridges are significant as there are few instances of FRP decks on concrete girders. The Hamilton County Engineers Office contracted with the Civil Engineering Department at the University of Cincinnati to perform load testing on the bridges. Information gained from this research will seek to confirm the safety of the new technology, evaluate construction and design techniques with reference to the FRP deck, and determine overall performance of the bridge to provide understanding of the system. The two short span prestressed concrete bridges with fiber reinforced polymer decks were subjected to four sets of nondestructive truckload testing. Strain gauges were placed along the height of the girder cross-section, and longitudinally and transversely across the bottom of the deck. Displacement transducers were placed to measure overall girder displacement, relative deck displacement, deck panel separation, and deck-girder connection separation. A three-dimensional finite element analysis model was created to replicate the performance of each bridge. The two new prestressed girders in bridge B-0171 strengthened the bridge considerably and increased its load carrying capacity. But the old prestressed girders in bridge B-0071 and bridge B-0171 did not show any sign of deterioration. The four sets of test data collected over a two-year period show that the age effect on structural behavior is very small for both the bridges. The deck had very little influence on the distribution of loads in the structure for these bridges. Due to low deck stiffness and incomplete connectivity, the FRP deck did little to strengthen the girders. The long term monitoring of the deck result complied with the short term testing as reported by Eder8. The finite element model closely matched with the structural components of the original bridge. The new improved model is a better representation as it was calibrated with four sets of field data collected over a period of two years. The field test data from both tests shows that the girders are simply supported on the abutment. But the girders in the model are designed as fixed end beams to have a reasonable value for the modulus of concrete used in the model. In reality it can be assumed that the support condition is between fixed and simply supported. It was also demonstrated that the deck had very little influence on the distribution of loads in the structure for these bridges. The majority of the load transfer between girders was most likely due to the diaphragms. The Impact Factor based on one set of experimental results was 1.217. However, for analysis the LRFD value of 1.33 was used. The Load Rating Factor for bridge B-0071 was 1.66 and for bridge B-0171 was 2.48 with the governing truck loading being the Design load Type Tandem. These rating factors were based on girder performance only due to insufficient deck information.
This research is intended to investigate the fatigue performance of pre-cracked prestressed concrete T-beams for a specific strand stress range and its relationship to the level of strengthening gained. Controlling the strand stress range is accomplished by iterative cycles of nonlinear analysis to determine the amount of external carbon Fiber Reinforced Polymers (FRP) reinforcement needed for that purpose. Five pre-tensioned prestressed concrete T-beams were cast at a prestressed concrete plant in Newton, Kansas. Beam 1 was tested under static loading up to failure as a control specimen. Beams 2 and 3 were strengthened with Carbon Fiber Reinforced Polymers (CFRP) to have a design stress range of 18 ksi under service load condition. Beams 4 and 5 were also strengthened to have a higher stress range of 36 ksi. Beams 2 and 4 were loaded monotonically to failure while Beams 3 and 5 were cycled over a million times before they were brought to failure. The design yielded one layer of flexural CFRP wrapped around the web sides up to 2.25 in. from the bottom for the 18 ksi stress range design. It also resulted in two layers of longitudinal CFRP for the 36 ksi stress range design, the inner layer wrapped around the web sides up to 0.5 in. and the outer layer went up 3 in. on the web sides. External CFRP stirrups were used to prevent the longitudinal CFRP from premature separation. Beams 2 and 4 successfully reached their target strengthening design levels and Beams 3 and 5 performed very well in fatigue.
Accelerated Bridge Construction (ABC) has gained substantial popularity in new bridge construction and bridge deck replacement because it offers innovative construction techniques that result in time and cost savings when compared to traditional bridge construction practice. One technology commonly implemented in ABC to effectively execute its projects is the use of prefabricated bridge components (precast/prestressed bridge components). Precast/prestressed bridge components are fabricated offsite or near the site and then connected on-site using small volume closure pour connections. Diaphragms are also commonly used to strengthen the connection between certain prefabricated components used in ABC, such as beam elements. Bridges containing closure pour connections and diaphragms can be designed using AASHTO LRFD live-load distribution factor formulas under the condition that the bridge must be sufficiently connected. However, these formulas were developed using analytical models that did not account for the effects of closure pours and diaphragms on live-load distribution. This research study investigates live-load distribution characteristics of precast/prestressed concrete bridges with closure pour connections and diaphragms. The investigation was conducted using finite element bridge models with closure pour joints that were calibrated using experimental data and different configuration of diaphragms. The concrete material used for the closure pour connections was developed as part of a larger project intended to develop high early-strength concrete mixtures that specifically reach strength in only 12 hours, a critical requirement for ABC projects.
Throughout the United States including New York, many reinforced concrete bridges on county and state highway systems have deteriorated to the certain degree that structural strengthening is necessary to extend their service life. Fiber reinforced polymer (FRP) composite systems appeared to be one of the options to address the issues of cost-effective load-rating improvement. Recently, an FRP deck has been installed on a state highway, located in New York State, as an experimental project. This paper describes multi-step linear static analyses that were conducted using the finite element method to study the possible failure mechanisms of the deck-superstructure system. Finite element model was verified using the load tests of the bridge deck. Furthermore, the thermal behavior of the FRP deck was investigated and presented in this paper. Analytical results reveal several potential failure mechanisms for the FRP deck and truss bridge system.
The focus of this book is the study of the physical and mechanicalmetallurgy of aluminum alloys produced by processing methods. Itaddresses progress in research, development, testing andapplication of aluminum sheet, plate, extrusions, forgings, andother products in end uses. Those applications includetransportation, such as automotive, aerospace and marine, packagingand other key areas. A collection of papers from the ahref="http://www.tms.org/Meetings/Annual-07/AnnMtg07Home.html"target="_blank"2007 TMS Annual Meeting & Exhibition/a heldin Orlando, Florida, February 25 -- March 1, 2007.