Cyclic Response of Unbonded Posttensioned Precast Columns with Ductile Fiber-Reinforced Concrete

A precast segmental concrete bridge pier system is being investigated for use in seismic regions. The proposed system uses unbonded posttensioning (UBPT) to join the precast segments and has the option of using a ductile fiber-reinforced cement-based composite (DRFCC) in the precast segments at potential plastic hinging regions. The UBPT is expected to cause minimal residual displacements and a low amount of hysteretic energy dissipation. The DFRCC material is expected to add hysteretic energy dissipation and damage tolerance to the system. Small-scale experiments on cantilever columns using the proposed system were conducted. The two main variables were the material used in the plastic hinging region segment and the depth at which that segment was embedded in the column foundation. It was found that using DFRCC allowed the system to dissipate more hysteretic energy than traditional concrete up to drift levels of 3–6%. Furthermore, DFRCC maintained its integrity better than reinforced concrete under high cyclic tensile-compressive loads. The embedment depth of the bottom segment affected the extent of microcracking and hysteretic energy dissipation in the DFRCC. This research suggests that the proposed system may be promising for damage-tolerant structures in seismic regions.     

Seismic Performance of Concrete-Filled FRP Tube Columns for Bridge Substructure

A set of column-footing subassemblies were prepared to investigate construction feasibility and seismic performance of structural joints for concrete-filled fiber reinforced polymer (FRP) tubes (CFFT) as bridge substructure. Based on the common practices of the precast industry and previous research on CFFT, the test matrix included a control reinforced concrete (RC) column and three CFFT columns, all with similar RC footings. The three CFFT columns included a cast-in-place CFFT column with starter bars, a precast CFFT column with grouted starter bars, and a precast CFFT column with unbonded posttensioned rods. The columns were subjected to a constant axial load and a pseudostatic lateral load. All proposed joints proved feasible in construction and robust under extreme load conditions. FRP tube, when secured properly in the footing, showed great influence on the seismic performance of the column by providing both longitudinal reinforcement and hoop confinement to the core concrete. The CFFT columns exhibited significant improvement over traditional RC columns in both ultimate strength and ductility. The study also showed that practices of the precast concrete industry can be easily and effectively implemented for the CFFT column construction.     

Compound Shear-Flexural Capacity of Reinforced Concrete–Topped Precast Prestressed Bridge Decks

Modern concrete bridge decks commonly consist of stay-in-place (SIP) precast panels seated on precast concrete beams and topped with cast-in-place (CIP) reinforced concrete. Such composite bridge decks have been experimentally tested by various researchers to assess structural performance. However, a failure theory that describes the failure mechanism and accurately predicts the corresponding load has not been previously derived. When monotonically increasing patch loads are applied, delamination occurs between the CIP concrete and SIP panels, with a compound shear-flexure mechanism resulting. An additive model of flexural yield line failure in the lower SIP precast prestressed panels and punching shear in the upper CIP-reinforced concrete portion of the deck system is derived. Analyses are compared to full-scale experimental results of a tandem wheel load straddling adjacent SIP panels and a trailing wheel load on a single panel. Alone, both yield line and punching-shear theories gave poor predictions of the observed failure load; however, the proposed compound shear-flexure failure mechanism load capacities are within 2% accuracy of the experimentally observed loads. Better estimation using the proposed theory of composite SIP-CIP deck system capacities will aid in improving the design efficiency of these systems.     

Splicing of Precast Concrete-Filled FRP Tubes

This paper reports on a feasibility study of splicing techniques for precast concrete-filled fiber-reinforced polymer (FRP) tubes (CFFT). A total of four spliced beams were tested. Three were internally spliced using grouted steel bars, grouted FRP bars, or unbonded posttensioning bars, and the fourth was spliced with FRP socket, commonly used in the piping industry. A control CFFT beam with no internal reinforcement was also tested as a reference. The experiments showed the superior effect of FRP tube continuity on system performance. Although initially stiffer, none of the spliced beams tested in this program was as strong as the control specimen. This may be primarily attributed to the lack of continuity of the FRP tube, as well as the quality of the cement grout for dowel reinforcement. Posttensioning proved to be efficient in improving system performance. The system may benefit from FRP continuity through either a longer and more effective socket or a threaded coupler insert or sleeve. Internal reinforcement can further increase the stiffness and strength of the connection, if grouting quality is controlled. Splicing may be improved by combining the methods tested in this program. Further understanding of the implications of composite action between FRP and concrete was achieved. Finally, the behavior of spliced CFFT beams was closely described using a combination of beam theory and rigid body deformations; the extent of the latter depends on joint stiffness.     

Endurance of Deck-to-Deck Connections in Transverse Hardwood Glulam Decks

Dowel and stiffener beam deck-to-deck connections transfer shear and moment between hardwood glued-laminated (glulam) transverse deck panels in longitudinal timber bridges. The connections resist relative deflections between the deck panels and aid in the prevention of reflexive cracking of the bituminous wearing surface at panel joints. Cyclic loading can reduce the stiffness of some types of deck-to-deck connections resulting in shortened service life. The performance of dowel and stiffener beam deck-to-deck connections for hardwood glulam transverse panel bridge decks was evaluated during cyclic laoding. Five tests were conducted with steel dowel connected deck panels, and five tests were conducted with glulam stiffener beam connected deck panels. Each connection was subjected to 1,000,000 load cycles. Degradation of connector stiffness with increasing number of load cycles was determined. Stiffener beam connections had better cyclic load response than the steel dowel connections. Steel dowel connections experienced approximately 20% degradation of stiffness after 1,000,000 load cycles. Most stiffener beam connections experienced little to no stiffness degradation after 1,000,000 load cycles; the smaller stiffener beam experienced 14% degradation after 1,000,000 load cycles. All connections remained within the limits of deflection criteria established in the 1994 AASHTO LRFD Bridge Design Specifications.     

Development of Fiber-Reinforced Polymer Roof-to-Wall Connection

A significant proportion of damage to buildings in hurricanes occurs owing to weak roof-to-wall connections. The objective of this study was to develop an innovative, efficient, and nonintrusive roof-to-wall connection for wood-frame structures by using high-performance fiber reinforced polymer (FRP) composites. Several connection configurations were developed and tested at the component level under uplift loading. The most feasible configuration was selected and further tested at the component level under lateral loadings. The selected FRP tie system was then tested at a full-scale model designed to represent conventional wood-frame buildings. The objective was to assess the connection’s in situ performance under simulated uplift forces. The results of the full-scale tests were in close agreement with those obtained from the component-level tests. Control tests were also performed to evaluate the load capacity of a typical commercial metallic hurricane clip to facilitate comparison of its results with that of the newly developed FRP tie. The FRP tie system described in this study offers an easy-to-apply, nonintrusive, and viable alternative to existing metal hurricane clips for both new construction and existing structures.     

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.     

Experimental Performance of Full-Depth Precast, Prestressed Concrete Overhang, Bridge Deck Panels

The performance of a new full-depth precast overhang panel system for concrete bridge decks is investigated experimentally. In contrast to conventional cast-in-place deck overhangs, the proposed full-depth precast overhang system has the potential to speed up construction, reduce costs, and improve safety. Load-deformation behavior up to factored design load limits is first investigated. The panel is then loaded near its edge to examine the collapse capacity and the associated failure modes—particularly the influence of panel-to-panel connections that exist, transverse to the bridge deck axis. Comparative tests are also conducted with a conventional cast-in-place overhang system. When compared to the conventional cast-in-place overhang behavior, the experimental results show that the precast full-depth overhang introduces different behavior modes, largely due to the influence of the partial depth panel-to-panel connection, which reduces the capacity by some 13%.     

Flexural Testing of Precast Bridge Deck Panel Connections

Precast deck panels are increasingly being utilized to reduce construction times and traffic delays as many departments of transportation (DOTs) emphasize accelerated bridge construction. Despite the short-term benefits, the connections between panels have a history of service failure. This research focused on the evaluation of the service and ultimate capacities of five precast deck panel connections. Full-scale tests were developed to determine the cracking and ultimate flexural strengths of two welded connections, a conventionally posttensioned connection, and two newly proposed, posttensioned, curved bolt connections. The conventionally posttensioned specimens were shown to perform well with the highest cracking loads and 0.42 times the theoretical capacity of a continuously reinforced concrete deck panel. The proposed curved bolt connections were shown to be a promising connection detail with approximately 0.5 times the theoretical capacity of a continuously reinforced panel. Data from the welded specimens showed that some welded connection types perform significantly better than others. The experimental results also compared closely with values calculated on the basis of finite-element modeling, which can be used for future analytical studies.     

CFRP Composite Connector for Concrete Members

Steel plate connections are frequently used in tilt-up and precast concrete building construction to tie adjacent wall panels together for shear and overturning effects, and to provide continuous diaphragm chord connections for wind and seismic loading. These welded connectors perform poorly in regions of high seismicity and are vulnerable to corrosion. Until now, retrofit and repair strategies for in-plane shear transfer strengthening were limited to attaching steel sections across panel edges. In the present paper, an experimental program is described that utilizes carbon fiber reinforced plastic (CFRP) composites to develop a viable retrofit scheme for precast concrete shear walls and diaphragms. Nine full-scale precast wall panel assemblies with CFRP composite connectors have been tested. The results show that the CFRP composite connection is an effective solution for the seismic retrofit and repair of precast concrete wall assemblies and other precast concrete elements, such as horizontal diaphragms, that require in-plane shear transfer strengthening.     

Case Study of Application of FRP Composites in Strengthening the Reinforced Concrete Headstock of a Bridge Structure

Worldwide interest is being generated in the use of fiber-reinforced polymer composites (FRP) in the rehabilitation of aged or damaged reinforced concrete structures. As a replacement for the traditional steel plates or external posttensioning in strengthening applications, various types of FRP plates, with their high strength-to-weight ratio and good resistance to corrosion, represent a class of ideal material in externally retrofitting. This paper describes a solution proposed to strengthen the damaged reinforced concrete headstock of the Tenthill Creeks Bridge, Queensland, Australia, using FRP composites. A decision was made to consider strengthening the headstock using bonded carbon FRP laminates to increase the load carrying capacity of the headstock in shear and bending. The relevant guidelines and design recommendations were compared and adopted in accordance with AS 3600 and Austroads bridge design code to estimate the shear and flexural capacity of a rectangular cracked FRP reinforced concrete section.     

Development and Evaluation of an Adhesively Bonded Panel-to-Panel Joint for a FRP Bridge Deck System

A fiber-reinforced polymer (FRP) composite cellular deck system was used to rehabilitate a historical cast iron thru-truss structure (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 a FRP deck. This bridge is designed to HL-93 load and has a 22.86?m clear span with a roadway width of 6.71?m. The panel-to-panel connections were accomplished using full width, adhesively (structural urethane adhesive) bonded tongue and groove splices with scarfed edges. To ensure proper construction, serviceability, and strength of the splice, a full-scale two-bay section of the bridge with three adhesively bonded panel-to-panel connections was constructed and tested in the Structures Laboratory at Virginia Tech. Test results showed that no crack initiated in the joints under service load and no significant change in stiffness or strength of the joint occurred after 3,000,000 cycles of fatigue loading. The proposed adhesive bonding technique was installed in the bridge in August 2006.     

State of Practice for Positive Moment Connections in Prestressed Concrete Girders Made Continuous

Precast bridges are often constructed as single span for dead load, but continuous for live load. A diaphragm connection is provided for negative moment continuity. However, the connection may also be subjected to positive moments due to time-dependent effects. Because these moments may be large enough to damage the diaphragm or even the girders, a positive moment connection is often provided. This paper reports on a study to determine the types of positive moment connections used across the country and to identify potential problems with these types of connections. A questionnaire survey was conducted to assess the state of practice for precast prestressed concrete bridges made continuous. The survey provides valuable information on this type of bridge and updates a previous survey on this subject.     

Large-Bar Connection for Precast Bridge Bents in Seismic Regions

A new beam-to-column connection has been developed for assembling precast concrete bridge bents in regions of high seismicity. The connection is made with a small number of large column bars, which are grouted into large corrugated-metal ducts embedded in the cap beam. Bents built with these connections can be erected quickly and permit generous construction tolerances. To evaluate the seismic performance of the proposed connection, lateral-load tests were performed on three manifestations of the connection, as well as on a comparable cast-in-place connection. The tests demonstrated that the force-displacement response and damage progression in the precast connection are similar to those of typical cast-in-place concrete connections. Deliberate partial debonding of the longitudinal reinforcement only slightly affected the force-displacement response and observed damage.     

Seismic Behavior of High-Strength Concrete Columns Confined by Fiber-Reinforced Polymer Tubes

The use of high-strength concrete (HSC) in seismically active regions poses a major concern because of the brittle nature of material. The confinement requirements for HSC columns may be prohibitively stringent when ordinary grade transverse steel reinforcement is used. An alternative to conventional confinement reinforcement is the use of fiber-reinforced polymer (FRP) tubes in the form of stay-in-place formwork which can fulfill multiple functions of: (1) formwork; (2) confinement reinforcement; and (3) protective shell against corrosion, weathering and chemical attacks. The use of stay-in-place FRP formwork is investigated as concrete confinement reinforcement for HSC and normal strength concrete (NSC) columns with circular cross sections. Large-scale specimens with 270?mm circular cross-sections and different concrete strengths were tested under constant axial compression and incrementally increasing lateral deformation reversals. FRP tubes were manufactured from carbon fiber sheets and epoxy resin. The results indicate that inelastic deformability of HSC and NSC columns can be improved significantly by using FRP tubes, beyond the performance level usually expected of comparable columns confined with conventional steel reinforcement.     

Fatigue Behavior of Concrete-Filled Fiber-Reinforced Polymer Tubes

To date, research on concrete-filled fiber-reinforced polymer (FRP) tubes (CFFT) has focused on the effect of static loads, simulated seismic loads, and long-term sustained loads. Dynamic fatigue behavior of CFFTs, on the other hand, has received little or no attention. This paper reports on an experimental study to evaluate damage accumulation, stiffness degradation, fatigue life, and residual bending strength of CFFT beams. A total of eight CFFT beams with four different types of FRP tube were tested under four point bending. Test parameters included reinforcement index, fiber architecture, load range, and end restraints. Fatigue performance of CFFT beams is clearly governed by characteristics of the FRP tube and its three phases of damage growth: matrix cracking, matrix delamination, and fiber rupture. Lower reinforcement index increases stiffness degradation and damage growth, and shortens fatigue life. End restraints, e.g., embedment of FRP tube in adjacent members, promote composite action, arrest slippage of concrete core, and enhance fatigue life of CFFT beams. It is suggested that a maximum load level of 25% of the static capacity be imposed for fatigue design of CFFTs. With proper design, CFFTs may withstand repeated traffic loading necessary for bridge girders.     

Strength and Ductility of Concrete Beams Reinforced with Carbon Fiber-Reinforced Polymer Plates and Steel

Seven concrete beams reinforced internally with varying amounts of steel and externally with precured carbon fiber-reinforced polymer (FRP) plates applied after the concrete had cracked under service loads were tested under four-point bending. Strains measured along the beam depth allowed computation of the beam curvature in the constant moment region. Results show that FRP is very effective for flexural strengthening. As the amount of steel increases, the additional strength provided by the carbon FRP plates decreases. Compared to a beam reinforced heavily with steel only, beams reinforced with both steel and carbon have adequate deformation capacity, in spite of their brittle mode of failure. Clamping or wrapping of the ends of the precured FRP plate enhances the capacity of adhesively bonded FRP anchorage. Design equations for anchorage, allowable stress, ductility, and amount of reinforcement are discussed.     

Fatigue of Diagonally Cracked RC Girders Repaired with CFRP

Fiber-reinforced polymers (FRP) are becoming more widely used for repair and strengthening of conventionally reinforced concrete (RC) bridge members. Once repaired, the member may be exposed to millions of load cycles during its service life. The anticipated life of FRP repairs for shear strengthening of bridge members under repeated service loads is uncertain. Field and laboratory tests of FRP-repaired RC deck girders were performed to evaluate high-cycle fatigue behavior. An in-service 1950s vintage RC deck-girder bridge repaired with externally bonded carbon fiber laminates for shear strengthening was inspected and instrumented, and FRP strain data were collected under ambient traffic conditions. In addition, three full-size girder specimens repaired with bonded carbon fiber laminate for shear strengthening were tested in the laboratory under repeated loads and compared with two unfatigued specimens. Results indicated relatively small in situ FRP strains, laboratory fatigue loading produced localized debonding along the FRP termination locations at the stem-deck interface, and the fatigue loading did not significantly alter the ultimate shear capacity of the specimens.     

Fatigue Life Evaluation of Concrete Bridge Deck Slabs Reinforced with Glass FRP Composite Bars

Since bridge deck slabs directly sustain repeated moving wheel loads, they are one of the most bridge elements susceptible to fatigue failure. Recently, glass fiber-reinforced polymer (FRP) composites have been widely used as internal reinforcement for concrete bridge deck slabs as they are less expensive compared to the other kinds of FRPs (carbon and aramid). However, there is still a lack of information on the performance of FRP–reinforced concrete elements subjected to cyclic fatigue loading. This research is designed to investigate the fatigue behavior and fatigue life of concrete bridge deck slabs reinforced with glass FRP bars. A total of five full-scale deck slabs were constructed and tested under concentrated cyclic loading until failure. Different reinforcement types (steel and glass FRP), ratios, and configurations were used. Different schemes of cyclic loading (accelerated variable amplitude fatigue loading) were applied. Results are presented in terms of deflections, strains in concrete and FRP bars, and crack widths at different levels of cyclic loading. The results showed the superior fatigue performance and longer fatigue life of concrete bridge deck slabs reinforced with glass FRP composite bars.     

Critical Review of Deflection Formulas for FRP-RC Members

The design of fiber-reinforced polymer reinforced concrete (FRP-RC) is typically governed by serviceability limit state requirements rather than ultimate limit state requirements as conventional reinforced concrete is. Thus, a method is needed that can predict the expected service load deflections of fiber-reinforced polymer (FRP) reinforced members with a reasonably high degree of accuracy. Nine methods of deflection calculation, including methods used in ACI 440.1R-03, and a proposed new formula in the next issue of this design guide, CSA S806-02 and ISIS M03-01, are compared to the experimental deflection of 197 beams and slabs tested by other investigators. These members are reinforced with aramid FRP, glass FRP, or carbon FRP bars, have different reinforcement ratios, geometric and material properties. All members were tested under monotonically applied load in four point bending configuration. The objective of the analysis in this paper is to determine a method of deflection calculation for FRP RC members, which is the most suitable for serviceability criteria. The analysis revealed that both the modulus of elasticity of FRP and the relative reinforcement ratio play an important role in the accuracy of the formulas.