Designing and Testing of Concrete Bridge Decks Reinforced with Glass FRP Bars

In addition to their high strength and light weight, fiber-reinforced polymer (FRP) composite reinforcing bars offer corrosion resistance, making them a promising alternative to traditional steel reinforcing bars in concrete bridge decks. FRP reinforcement has been used in several bridge decks recently constructed in North America. The Morristown Bridge, which is located in Vermont, United States, is a single span steel girder bridge with integral abutments spanning 43.90 m. The deck is a 230 mm thick concrete continuous slab over girders spaced at 2.36 m. The entire concrete deck slab was reinforced with glass FRP (GFRP) bars in two identical layers at the top and the bottom. The bridge is well instrumented at critical locations for internal temperature and strain data collection with fiber-optic sensors. The bridge was tested for service performance using standard truck loads. The construction procedure and field test results under actual service conditions revealed that GFRP rebar provides very good and promising performance.     

Field Investigation on the First Bridge Deck Slab Reinforced with Glass FRP Bars Constructed in Canada

Recently, there has been a rapid increase in using noncorrosive fiber-reinforced polymers (FRP) reinforcing bars as alternative reinforcement for bridge deck slabs, especially those in harsh environments. A new two-span girder type bridge, Cookshire-Eaton Bridge (located in the municipality of Cookshire, Quebec, Canada), was constructed with a total length of 52.08 m over two equal spans. The deck was a 200-mm-thick concrete slab continuous over four spans of 2.70 m between girders with an overhang of 1.40 m on each side. One full span of the bridge was totally reinforced using glass fiber-reinforced polymer (GFRP) bars, while the other span was reinforced with galvanized steel bars. The bridge deck was well instrumented at critical locations for internal temperature and strain data collection using fiber optic sensors. The bridge was tested for service performance using calibrated truckloads as specified by the Canadian Highway Bridge Design Code. The construction procedure and field test results under actual service conditions revealed that GFRP rebar provides very competitive performance in comparison to steel.     

Influence of Reinforcement on the Behavior of Concrete Bridge Deck Slabs Reinforced with FRP Bars

This paper presents the results of an experimental study to investigate the role of each layer of reinforcement on the behavior of concrete bridge deck slabs reinforced with fiber-reinforced polymer (FRP) bars. Four full-scale concrete deck slabs of 3,000?mm length by 2,500?mm width and 200?mm depth were constructed and tested in the laboratory. One deck slab was reinforced with top and bottom mats of glass FRP bars. Two deck slabs had only a bottom reinforcement mat with different reinforcement ratios in the longitudinal direction, while the remaining deck slab was constructed with plain concrete without any reinforcement. The deck slabs were supported on two steel girders spaced at 2,000?mm center to center and were tested to failure under a central concentrated load. The three reinforced concrete slabs had very similar behavior and failed in punching shear mode at relatively high load levels, whereas the unreinforced slab behaved differently and failed at a very low load level. The experimental punching capacities of the reinforced slabs were compared to the theoretical predictions provided by ACI 318-05, ACI 440.1R-06, and a model proposed by the writers. The tests on the four deck slabs showed that the bottom transverse reinforcement layer has the major influence on the behavior and capacity of the tested slabs. In addition, the ACI 318-05 design method slightly overestimated the punching shear strength of the tested slabs. The ACI 440.1R-06 design method yielded very conservative predictions whereas the proposed method provided reasonable yet conservative predictions.     

Fatigue Behavior of Carbon Fiber Reinforced Polymer-Strengthened Reinforced Concrete Bridge Girders

This study examines the effects of one-dimensional fiber-reinforced polymer (FRP) composite rehabilitation systems on the flexural fatigue performance of reinforced concrete bridge girders. Eight 508?mm deep and 5.6?m long reinforced concrete T-beams, with and without bonded FRP reinforcement on their tensile surfaces, were tested with a concentrated load at midspan under constant amplitude cyclic loading. The objective of this investigation is to establish the effect that these repair systems have on the fatigue behavior and remaining life of the girders. Results indicate that the fatigue behavior of such retrofit beams is controlled by the fatigue behavior of the reinforcing steel. The fatigue life of a reinforced concrete beam can be increased by the application of an FRP retrofit, which relieves some of the stress carried by the steel. The observed increase in fatigue life, however, is limited by the quality of the bond between the carbon FRP and concrete substrate. Debonding, initiating at midspan and progressing to a support, is common and is driven partially by the crack distribution and shear deformations of the beam.     

Experimental Analysis of Crack Growth in GFRP Reinforced Concrete

For decades, bridge slabs have been troubled by the corrosion of steel reinforcement. The unique corrosion resistance of glass fiber-reinforced polymer (GFRP) bars makes them a promising alternative to steel bars. Experiments have been conducted to investigate the bond performance of GFRP reinforced concrete under constant amplitude cyclic fatigue loading. Each specimen was an identical length beam with a single GFRP bar at the bottom, intended to simulate a transverse strip of a typical bridge deck slab. The crack growth was monitored for specimens of different widths, simulating different transverse reinforcement spacings. Up to 2?million?cycles of cyclic loads were applied at 100% typical service load levels. No fatigue failure was encountered in the testing. The effects of moderate overloads were also investigated.     

Evaluation of Effective Width and Distribution Factors for GFRP Bridge Decks Supported on Steel Girders

Glass fiber-reinforced polymer (GFRP) bridge deck systems offer an attractive alternative to concrete decks, particularly for bridge rehabilitation projects. Current design practice treats GFRP deck systems in a manner similar to concrete decks, but the results of this study indicate that this approach may lead to nonconservative bridge girder designs. Results from a number of in situ load tests of three steel girder bridges having the same GFRP deck system are used to determine the degree of composite action that may be developed and the transverse distribution of wheel loads that may be assumed for such structures. Results from this work indicate that appropriately conservative design values may be found by assuming no composite action between a GFRP deck and steel girder and using the lever rule to determine transverse load distribution. Additionally, when used to replace an existing concrete deck, the lighter GFRP deck will likely result in lower total stresses in the supporting girders, although, due to the decreased effective width and increased distribution factors, the live-load-induced stress range is likely to be increased. Thus, existing fatigue-prone details may become a concern and require additional attention in design.     

Seismic Retrofit of State Street Bridge on Interstate 80

The State Street Bridge, in Salt Lake City, was designed and built in 1965 according to the 1961 AASHO specifications; the design did not include earthquake-induced forces or displacements since only wind loads were considered. The bridge consists of four reinforced concrete (RC) bents supporting composite welded steel girders; the bents are supported on cast-in-place concrete piles and pile caps. A vulnerability analysis of the bridge was conducted that determined deficiencies in (1) confinement of column lap splice regions, (2) anchorage of longitudinal column bars in the bent cap, (3) confinement of column plastic hinge zones, and (4) shear capacity of columns and bent cap–column joints. Seismic retrofit designs using carbon-fiber-reinforced-polymer (CFRP) composites and steel jackets were performed and compared for three design spectra, including the 10% probability of exceedance in 250 years earthquake. The CFRP composite design was selected for implementation and application of the composite was carried out in the summer of 2000 and 2001, while the bridge was in service. The paper describes the CFRP composite design, which, in addition to column jackets, implemented an “ankle wrap” for improving joint shear strength and a “U-strap” for improving anchorage of column bars in the bent cap; other retrofit measures were implemented, such as bumper brackets and a deck slab retrofit. A capacity versus demand evaluation of the as-built and retrofitted bents is presented.     

Experimental Study on Prefabricated Concrete Bridge Girder-to-Girder Intermittent Bolted Connections System

This paper reports on a new bridge deck slab flange-to-flange connection system for precast deck bulb tee (DBT) girders. In prefabricated bridge system made of DBT girders, the concrete deck slab is cast with the prestressed girder in a controlled environment at the fabrication facility and then shipped to the bridge site. This system requires that the individual prefabricated girders be connected through their flanges to make it continuous for live load distribution. The objectives of this study are to develop an intermittent bolted connection for DBT bridge girders and to provide experimental data on the ultimate strength of the connection system. This includes identifying the crack formation and propagation, failure mode, and ultimate load carrying capacity. In this study, three different types of intermittent bolted connection were developed. Four actual-size bridge panels were fabricated and then tested to collapse. The effects of the size and the level of the fixity of the connecting steel plates, as well as the location of the wheel load were examined. The developed joint was considered successful if the experimental wheel load satisfied the requirements specified in North American bridge codes. It was concluded that location of the wheel load at the deck slab joint affected the ultimate load carrying capacity of the connections developed. Failure of the joint was observed to be due to either excessive deformation and yielding of the connecting steel plates or debonding of the embedded studs in concrete.     

Effect on Superstructure Stress of Replacing a Composite RC Bridge Deck with a GFRP Deck

Glass fiber-reinforced polymer (GFRP) composite bridge decks behave differently than comparable reinforced concrete (RC) decks. GFRP decks exhibit reduced composite behavior (when designed to behave in a composite manner) and transverse distribution of forces. Both of these effects are shown to counteract the beneficial effects of a lighter deck structure and result in increased internal stresses in the supporting girders. The objective of this paper is to demonstrate through an illustrative example the implications of RC-to-GFRP deck replacement on superstructure stresses. It is also shown that, regardless of superstructure stresses, substructure forces will be uniformly reduced due to the lighter resulting superstructure.     

Use of Glass-Fiber-Reinforced Polymer Tendons for Stress-Laminating Timber Bridge Decks

Researchers at the University of Maine led an effort in the mid-1990s to develop and use glass-fiber-reinforced polymer (GFRP) tendons, instead of the commonly used steel-threaded bars, for stress-laminating timber bridge decks. The GFRP tendons are 12.7 mm (0.5 in.) in diameter and consist of seven-wire strands similar in construction to steel prestressing strands. Because the modulus of elasticity of the GFRP tendons is approximately 1/9 that of steel, they are not as susceptible to loss of prestress as steel bars and may not have to be restressed during the life of deck. In 1997, researchers obtained funding to design, construct, and monitor a stress-laminated timber bridge located in Milbridge, Maine, utilizing the new GFRP tendons. The bridge was constructed from preservative treated No. 2 and better eastern hemlock laminations and is 4.88 m (16 ft) long, 7.75 m (25 ft, 6 in.) wide, and 350 mm (14 in.) deep. Based on 4.25 years of field monitoring the tendon forces and moisture content, the GFRP tendons have maintained an adequate prestress level without having to be restressed.     

Effect of Edge Stiffening and Diaphragms on the Reliability of Bridge Girders

Secondary elements such as barriers, sidewalks, and diaphragms may affect the distribution of live load to bridge girders. The objective of this study is to evaluate their effect on girder reliability if these elements are designed to be sufficiently attached to the bridge so as not to detach under traffic live loads. Simple-span, two-lane structures are considered, with composite steel girders supporting a reinforced concrete deck. Several representative structures are selected, with various configurations of barriers, sidewalks, and diaphragms. Bridge analysis is performed using a finite-element procedure. Load and resistance parameters are treated as random variables. Random variables considered are composite girder flexural strength, secondary element stiffness, load magnitude (dead load and truck traffic live load), and live load position. It was found that typical combinations of secondary elements have a varying influence on girder reliability, depending on secondary element stiffness and bridge geometry. Suggestions are presented that can account for secondary elements and that provide a uniform level of reliability to bridge girders.     

Development and Implementation of a Continuous Strain Monitoring System on a Multi-Girder Composite Steel Bridge

This paper describes the implementation and evaluation of a long-term strain monitoring system on a three-span, multisteel girder composite bridge located on the interstate system. The bridge is part of a network of bridges that are currently being monitored in Connecticut. The three steel girders are simply supported, whereas the concrete slab is continuous over the interior supports. The bridge has been analyzed using the standard AASHTO Specifications and the analytical predictions have been compared with the field monitoring results. The study has included determination of the location of the neutral axes and the evaluation of the load distributions to the different girders when large trucks cross the bridge. A finite-element analysis of the bridge has been carried out to further study the distribution of live load stresses in the steel girders and to study how continuity of the slabs at the interior joints would influence the overall behavior. The results of the continuous data collection are being used to evaluate the influence of truck traffic on the bridge and to establish a baseline for long-term monitoring.     

Stiffness and Strength of Metal Bridge Deck Forms

Light gauge metal sheeting is often utilized in the building and bridge industries for concrete formwork. Although the in-plane stiffness and strength of the metal forms are commonly relied upon for stability bracing in buildings, the forms are generally not considered for bracing in steel bridge construction. The primary difference between the forming systems in the two industries is the method of connection between the forms and girders. In bridge construction, an eccentric support angle is incorporated into the connection details to achieve a uniform slab thickness along the girder length. While the eccentric connection is a benefit for slab construction, the flexible connection limits the amount of bracing provided by the forms. This paper presents results from the first phase of a research study investigating the bracing behavior of metal bridge deck forms. Shear diaphragm tests were conducted to determine the shear stiffness and strength of bridge deck forms, and modified connection details were developed that substantially improve the bracing behavior of the forms. The measured stiffness and strength of diaphragms with the modified connection often met or exceeded the values of diaphragms with conventional noneccentric connections. The experimental results for the diaphragms with the modified connection details dramatically improve the potential for bracing of steel bridge girders by metal deck forms.     

Effect of Transverse Reinforcement on the Flexural Behavior of Continuous Concrete Beams Reinforced with FRP

Continuous concrete beams are structural elements commonly used in structures that might be exposed to extreme weather conditions and the application of deicing salts, such as bridge overpasses and parking garages. In such structures, reinforcing continuous concrete beams with the noncorrodible fiber-reinforced polymer (FRP) bars is beneficial to avoid steel corrosion. However, the linear-elastic behavior of FRP materials makes the ability of continuous beams to redistribute loads and moments questionable. A total of seven full-scale continuous concrete beams were tested to failure. Six beams were reinforced with glass fiber-reinforced polymer (GFRP) longitudinal bars, whereas one was reinforced with steel as control. The specimens have rectangular cross section of 200×300??mm and are continuous over two spans of 2,800?mm each. Both steel and GFRP stirrups were used as transverse reinforcement. The material, spacing, and amount of transverse reinforcement were the primary investigated parameters in this study. In addition, the experimental results were compared with the code equations to calculate the ultimate capacity. The experimental results showed that moment redistribution in FRP-reinforced continuous concrete beams is possible and is improved by increasing the amount of transverse reinforcement. Also, beams reinforced with GFRP stirrups illustrated similar performance compared with their steel-reinforced counterparts.     

Demonstration of Use of High-Performance Lightweight Concrete in Bridge Superstructure in Virginia

The general objective of this research was the construction and evaluation of a bridge using high-performance lightweight concrete (HPLWC). The resulting bridge over the Chickahominy River near Richmond, Va., consists of 15 prestressed American Association of State Highway and Transportation Officials (AASHTO) Type IV girders made of HPLWC with a density of 1,920?kg/m3 and a minimum required 28-day compressive strength of 55?MPa. The bridge also has a lightweight concrete (LWC) deck with a density of 1,850?kg/m3 and a minimum required 28-day compressive strength of 30?MPa. This research study is chiefly concerned with investigating the effects of using lightweight concrete in prestressed girders on transfer length, development length, flexural strength, girder live-load distribution factor, and dynamic load allowance. Transfer length was determined to be 432?mm, or 33?db, for several girders at the time of prestress transfer. The development length was determined to be between 1,830 and 2,440?mm, while the flexural strength ranged from 11 to 30% higher than the AASHTO flexural capacity. The measured distribution factors and dynamic load allowance were smaller than the AASHTO standard and LRFD values.     

Design and Evaluation of Experimental Bridges in Tennessee

This paper describes the design and evaluates the adequacy of the moment connection of an experimental two-span highway bridge designed by the Tennessee Department of Transportation. The Massman Drive Bridge is an experimental design that unifies the construction economy of simple span bridges and the structural economy of continuous span bridges. The experimental connection, consisting of cover plates and kicker wedge plates, is used to connect the two adjoining girders over the center pier. As a result, the bridge is designed to function as a continuous bridge during the deck pour and behave compositely with the reinforced concrete deck under the live load. After completing a moment comparison analysis, it is concluded that the Massman Drive Bridge indeed acts as continuous over the pier as it was designed.     

Modified Yield Line Theory for Full-Depth Precast Concrete Bridge Deck Overhang Panels

Full-depth precast deck slab cantilevers also referred to as full-depth precast concrete bridge deck overhang panels are becoming increasingly popular in concrete bridge deck construction. To date, no simple theory is able to estimate the overhang capacity of full-depth concrete bridge deck slabs accurately. Observations suggest that interaction between flexure and shear is likely to occur as neither alone provides an accurate estimate of the load-carrying capacity. Therefore, modified yield line theory is presented in this paper, which accounts for the development length of the mild steel reinforcing to reach yield strength. Failure of the full-depth panels is influenced by the presence of the partial-depth transverse panel-to-panel seam. When applying a load on the edge of the seam, the loaded panel fails under flexure while the seam fails in shear. Through the use of the modified yield line theory coupled with a panel-to-panel shear interaction, analytical predictions are accurate within 1–6% of experimental results for critical cases.     

Response of Slab Bridges Before, During, and After Repair

Continuous reinforced concrete slab bridges rely on reinforcing steel bars near the top of the deck over the piers to carry negative moment. Transfer of forces in these bars may be jeopardized by deterioration and repair procedures that involve variable depth removal of deteriorated concrete around the bars. Partial or full loss of continuity could overstress the bottom reinforcement. Truckload testing of three bridges with various levels of damage was conducted before, during, and after repair in an attempt to quantify the level of loss of continuity and to examine the effectiveness of repair in terms of increasing the load transfer and enhancing the overall stiffness. Test results show loss of stiffness during repair but increased stiffness after completion of repair. The continuity was found to be lost during repair, and the slab dead load positive moments may be increased by as much as 50%. After repair, the continuity was restored, and the live-load distribution was essentially unaltered. For the test bridges, the redistribution of dead-load moment to the positive-moment zones did not appreciably affect the overall bridge rating factor. The amount of moment redistribution may be controlled through planning of repair steps.     

Carbon Fiber-Reinforced Polymer Strengthening and Monitoring of the Gr?ndals Bridge in Sweden

The Gr?ndal Bridge is a large freivorbau bridge (prestressed concrete box bridge), approximately 400?m in length with a free span of 120?m. It was opened to tram traffic in the year 2000. Just after opening cracks were noticed in the webs, these cracks have then increased, the size of the largest cracks exceeded 0.5?mm, and at the end of 2001 the bridge was temporarily strengthened. This was carried out with externally placed prestressed steel stays. The reason for the cracking is still debated and will be further discussed in this paper. Nevertheless, it was clear that the bridge needed to be strengthened. The strengthening methods used were CFRP plates at the serviceability limit state and prestressed dywidag stays at the ultimate limit state. The strengthening was carried out during 2002. At the same time monitoring of the bridge commenced, using LVDT crack gauges as well as optical fiber sensors.     

Experimental Characterization and Optimization of Hybrid FRP/RC Bridge Superstructure System

An experimental investigation was performed to assess the performance of a hybrid fiber-reinforced polymer/reinforced concrete bridge system. The full-scale laboratory specimen was representative of an 813?mm (32?in.) wide strip of a completed bridge in San Patricio County, Tex. The specimen was first subjected to static loading prior to casting the reinforced concrete deck. Displacement, strain, and acoustic emission were recorded. After completion of the nondestructive static loading a reinforced concrete deck was cast in the laboratory to represent one unit of the completed bridge. Load was statically applied with several increased load cycles until failure occurred at a load level exceeding 18 times the calculated design load. The results of the static testing indicated that the original design of the hybrid bridge was very conservative. An optimized design of the hybrid bridge was then derived. The static load testing program and the resulting optimized design are described.