Hai Nguyen | Marshall University (original) (raw)

Papers by Hai Nguyen

Research paper thumbnail of Ultrasonic pitch and catch technique for non-destructive testing of reinforced concrete slabs

Journal of Infrastructure Preservation and Resilience

This study aims at evaluating reinforced concrete (RC) bridge elements using ultrasonic pitch and... more This study aims at evaluating reinforced concrete (RC) bridge elements using ultrasonic pitch and catch (UPC) non-destructive testing (NDT) technique. A validation reinforced concrete slab with two embedded layers of rebars and artificial defects (voids, honeycombs, and debondings) was designed and tested. A commercial UPC NDT device (hereafter called “UPC device”), which is based on the ultrasonic shear-wave test method using dry-point-contact transmitting and receiving transducers in a “pitch-catch” configuration, was used to map internal defects of the validation RC slab. The recorded data from the UPC device was analyzed using a modified synthetic aperture focusing technique (SAFT). A software was developed to reconstruct 2-D images of the RC slab cross-sections using novel signal filtering and processing techniques. The results revealed that the 2-D image reconstructed from the developed software accurately exhibited locations and horizontal dimensions of the steel rebars, void...

Research paper thumbnail of Tensile Behavior of Pultruded Fiber-Reinforced Polymer Laminates with Bonded and Bolted Splice Joints

Transportation Research Record: Journal of the Transportation Research Board, 2017

This paper presents an experimental investigation on double-lap joints of grit-blasted surface fi... more This paper presents an experimental investigation on double-lap joints of grit-blasted surface finish fiber-reinforced polymer (FRP) splice plates bonded and bolted to FRP laminates. Eighteen coupon joint specimens were tested under tensile loading with varying types of FRP splice plates and FRP laminates. Four types of bolts were evaluated: FRP bolts, high corrosion-resistant steel (HCRS) bolts, stainless steel (SS) bolts, and SS bolts wrapped with glass FRP (GFRP) (referred to as “SF” bolts). The test results indicated that double-lap splice joints, which incorporated HCRS bolts, epoxy adhesive, and grit-blasted surface finish FRP splice plates, provided strong bonds with FRP laminates. The grit-blasted surface finish of the FRP splice plates and the epoxy adhesive contributed to improving joint stiffness and strength. The specimens with FRP bolts showed brittle behavior and failed at relatively low ultimate load. The failures of those specimens were debonding of epoxy layers followed by shearing of the FRP bolts. The specimens with steel bolts (i.e., HCRS, SS, and SF bolts), however, exhibited ductile behavior and failed at a much higher ultimate load than did the FRP bolt specimens. Typical failure modes of the steel bolt specimens were fracturing of the FRP laminate (resulting from fiber rupture or kink, shear-out, and delamination failure of the GFRP plies and bearing failure of FRP materials near the edge of bolt holes in the load direction), bearing failure of the FRP splice plates, epoxy debonding, and yielding of bolts. Although FRP wraps may enhance the durability of the SS bolts, the use of SF bolts may significantly affect the failure mode of the splice joints.

Research paper thumbnail of Structural behavior of hybrid FRP composite I-beam

Construction and Building Materials, 2010

This paper presents the structural behavior of an innovative hybrid Fiber Reinforced Polymers (FR... more This paper presents the structural behavior of an innovative hybrid Fiber Reinforced Polymers (FRP) beam consisting of carbon/glass fibers and vinyl-ester resin. The advanced feature of this hybridization is the optimum use of carbon and glass fibers in the flanges to maximize structural performance while reducing the overall cost by using only glass fibers in the web section. A series of beam tests were conducted under four-point bending varying ratio of flange to web width (b f /b w) and volume content of carbon and glass fiber in the flanges. Experimental investigations revealed that the ratio of flange to web width of hybrid FRP I-shaped beams plays an important role in their structural behavior. Small flange beams (b f /b w = 0.43) showed stable and linear behavior under bending moment and failed in a brittle manner by delamination of the compressive flange at the interfacial layers while wide flange beams (b f /b w = 1.13) exhibited unstable and nonlinear behavior in the buckling and post-buckling region leading to delamination failure of the compressive flange. The experimental and analytical results discussed in this paper emphasize on the best composition of carbon and glass fibers for the optimum design of such hybrid beams. It is found that the maximum strength of hybrid FRP beams can be obtained with the volume content of carbon fiber to be 25-33%. Furthermore, the results of this study show the potential of applying hybrid FRP beams for bridge components.

Research paper thumbnail of Structural behavior of double-lap joints of steel splice plates bolted/bonded to pultruded hybrid CFRP/GFRP laminates

Construction and Building Materials, 2012

This paper presents results from experimental and numerical studies on the structural behavior of... more This paper presents results from experimental and numerical studies on the structural behavior of double-lap joints of steel splice plates bolted/bonded to pultruded hybrid CFRP/GFRP laminates. A total of 45 tensile coupon specimens with double-lap bolted/bonded joints and six large-scale flexural beam specimens with/without butt joints in the mid-span section were conducted. Two types of double-lap joints were investigated including bolted joints and hybrid joints (bonded-and-bolted). The results indicate that the double-lap hybrid joint which combined of stainless steel bolts, adhesive bonding, and V-notched splice plates is an effective method of joining the hybrid FRP laminate. The rough surface of the V-notched splice plates and the adhesive bonding contribute to improve the joint stiffness. Numerical analysis was carried out to predict load-displacement curve of the hybrid joints and the results showed a good correlation with the experiments. A design idea for use in the practical design of joints was proposed.

Research paper thumbnail of Recent technology of prestressed concrete bridges in Japan

IABSE-JSCE Joint Conference on Advances in Bridge Engineering-II, 2010

Prestressed concrete (PC) technology is being used all over the world in the construction of a wi... more Prestressed concrete (PC) technology is being used all over the world in the construction of a
wide range of bridge structures. However, many PC bridges have been deteriorating even before the end of
their design service-life due to corrosion and other environmental effects. In view of this, a number of innovative
technologies have been developed in Japan to increase not only the structural performance of PC bridges,
but also their long-term durability. These include the development of novel structural systems and the advancement
in construction materials. This paper presents an overview of such innovative technologies on PC
bridges on their development and applications in actual construction projects. Some noteworthy structures,
which represent the state-of-the-art technologies in the construction of PC bridges in Japan, are also presented.

Research paper thumbnail of Push-out tests for shear connections between UHPFRC slabs and FRP girder

Composite Structures, 2014

This paper presents an experimental investigation on the shear connections between carbon/glass F... more This paper presents an experimental investigation on the shear connections between carbon/glass Fiber-Reinforced Polymer I-girder and Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) slabs. Effects of straight/inclined bolt shear connectors and effective embedment depth-to-bolt diameter (h ef / d) ratios were investigated. Fourteen push-out tests were conducted to evaluate the load-slip behavior and the ultimate resistance of the bolt shear connectors. With the use of the UHPFRC, the h ef /d ratio needed for obtaining a shear connector failure mode was 2.7 times lower than that obtained from 43 push-out tests in the literature for normal weight and lightweight concrete slabs. The inclined bolt shear connectors showed a more ductile behavior than the straight bolt shear connectors. The experimentally obtained ultimate resistance of the bolt shear connectors was compared against the equations provided by ACI 318-11, AISC 2011, AASHTO LRFD 2010, PCI 2004, and EC-4 2004. An empirical equation to predict the ultimate shear connector resistance was proposed and validated by the experimental data. Idealized load-slip models and equations to predict the load versus slip relationship for all push-out tested specimens were proposed. Curve fitting was performed to find fitting parameters for all tested specimens and the results showed a very good correlation with the experiments.

Research paper thumbnail of Influence of grouting conditions on deterioration of post-tensioned prestressed concrete beams

Japan Concrete Institute, 2006

Chloride-induced corrosions of a sheath and a prestressing tendon in post-tensioned prestressed c... more Chloride-induced corrosions of a sheath and a prestressing tendon in post-tensioned prestressed concrete (PC) beams are investigated under different grouting conditions. Two series PC beams were tested by the electrically accelerated corrosion. The first series of accelerated corrosion tests were performed to determine the influence of grouted ratios in a curved sheath on the corrosion of the sheath and the prestressing tendon. In the second series of tests, the relationship between corrosion crack and expansive pressure surrounding the sheath and tendon during the corrosion process was clarified.

Research paper thumbnail of Hybrid FRP-UHPFRC composite girders: Part 2 -Analytical approach

Composite Structures, 2015

A companion paper shows the experimental testing and numerical analysis of composite girders cons... more A companion paper shows the experimental testing and numerical analysis of composite girders consisting of hybrid carbon/glass fiber-reinforced polymer (HFRP) I-girders topped with precast ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs. This paper presents derivations of analytical equations to examine the composite behavior of the HFRP-UHPFRC girders with varying levels of interaction at the slab/girder interface. The derived equations to predict interfacial slip strain, curvature, and deflection of the composite girders were validated by the experimental data. An equation to determine the effective moment of inertia of the HFRP-UHPFRC composite girders with partial interaction is proposed and compared against the experiment. A fairly good agreement between the experimental and analytical results was found. The derived/proposed equations can simply and reliably evaluate the composite behavior between the HFRP I-girder and the UHPFRC slab.

Research paper thumbnail of Hybrid FRP-UHPFRC composite girders: Part 1 -Experimental and numerical approach

Composite Structures, 2015

This paper presents experimental testing and numerical analysis of durable composite girder syste... more This paper presents experimental testing and numerical analysis of durable composite girder systems consisting of hybrid carbon/glass fiber-reinforced polymer (HFRP) I-girders and precast ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs. Epoxy adhesive and/or bolt shear connectors (SCs) were used to transfer horizontal shear forces from the UHPFRC slabs to the HFRP I-girders. Push-out tests were performed to evaluate the shear interaction at the slab/girder interface. The results of the push-out tests were used to design five large-scale composite girders. The experimental variables included two types of bolt SCs (straight and inclined bolt SCs) and different slab geometries. The composite behavior between the HFRP I-girder and the UHPFRC slab was examined. The test results showed that the combined use of the bolt SCs and the epoxy adhesive was essential to achieve a full interaction between the HFRP I-girder and the UHPFRC slab. The use of the epoxy adhesive resulted in improving the strength and stiffness of the composite girders, reducing the stress concentration around the bolt-holes, and increasing the shear strength of the bolt SCs. The girders with the inclined bolt SCs showed a more ductile behavior than those with the straight headed bolt SCs. A three-dimensional finite element (FE) analysis of the HFRP-UHPFRC composite girder was carried out that considered slip effects at the slab/girder interface and the nonlinear behavior of the bolt SCs. Comparisons between the experimental results and the FE analysis were performed and a fairly good agreement was found. A companion paper shows derivations of analytical equations to predict composite behaviors of the HFRP-UHPFRC girders with varying levels of interaction at the slab/girder interface.

Research paper thumbnail of Hybrid Fiber-Reinforced Polymer Girders Topped with Segmental Precast Concrete Slabs for Accelerated Bridge Construction

Transportation Research Record: Journal of the Transportation Research Board, 2014

The behavior of composite girders made of hybrid fiber-reinforced polymer (HFRP) I-girders, toppe... more The behavior of composite girders made of hybrid fiber-reinforced polymer (HFRP) I-girders, topped with precast ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs is presented in this paper. HFRP I-girders were manufactured under the pultrusion process in which unidirectional carbon fibers and bidirectional fiberglass fabric or continuous strand mat were used. Four large-scale composite girders were tested under four-point flexural loading. In the first composite girder, the HFRP I-girder was topped with a full-length precast UHPFRC slab. Twelve precast UHPFRC segments were used in each slab of the other three composite girders. Either epoxy or mortar connections were used to connect the precast UHPFRC segments. The test results showed that the flexural stiffness of the composite girder with the epoxy-connected segmental precast slabs was similar to that of the full-length precast composite girder. The mortar-connected girder exhibited more ductile behavior than the epoxy-connected girder. All the composite girders exhibited significant improvements in strength and stiffness compared with the HFRP I-girder without the UHPFRC slab. The HFRP–UHPFRC composite girders were shown to provide a promising and sustainable solution for accelerated bridge construction.

Research paper thumbnail of Flexural Behavior of Pultruded Hybrid Fiber-Reinforced Polymer I-Beams with Bonded-and-Bolted Splice Joints

Transportation Research Record: Journal of the Transportation Research Board, 2016

This paper presents experimental results of double-lap joints of fiber-reinforced polymer (FRP) o... more This paper presents experimental results of double-lap joints of fiber-reinforced polymer (FRP) or steel splice plates bonded and bolted to flanges and web of pultruded hybrid I-beams with carbon FRP and glass FRP. Eight large-scale specimens with bonded-and-bolted splice joints and two control beams were tested under four-point static flexural loading. The test results indicated that the double-lap splice joints, which incorporated high corrosion-resistant steel bolts, epoxy adhesive, and FRP splice plates with a grit-blasted surface finish provided an effective solution for joining the hybrid FRP I-beams. The grit-blasted surface finish of the FRP splice plates and the epoxy adhesive contributed to improving the joint stiffness and strength. Before debonding occurred, the stiffness of the bonded-and-bolted splice joints was dependent mainly upon the strength of the epoxy adhesive and the bonding surface of the splice plates, while the ultimate load and failure mode of the joints was governed by the number and strength of bolts. The specimens with failures in the splice connections showed more ductile behavior than specimens with failures beyond the connections. This difference is attributed to the slippage of the splice connections.

Research paper thumbnail of Flexural Behavior of Hybrid Composite Beams

Transportation Research Record - Journal of Transportation Research Board, 2013

This paper presents the development of composite beams, which consist of hybrid carbon and glass ... more This paper presents the development of composite beams, which consist of hybrid carbon and glass fiber-reinforced polymer (FRP) I-beams and precast, ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs. Hybrid FRPs (HFRPs) provide the advantage of high resistance to corrosion, while UHPFRC has great strength and durability. The combination of these two materials is expected to benefit structures subjected to severe environmental conditions and to respond to the need for accelerated bridge construction. Three full-scale composite beams with varied UHPFRC slab width were tested under four-point flexural loading. Bolt shear connectors with and without epoxy bonding were used in the tested beams. The bolt shear connectors and epoxy were used to resist the horizontal shear flow at the interface between the HFRP I-beam and the UHPFRC slab. The composite action between the HFRP I-beam and UHPFRC slab was investigated. The test results showed that all of the composite beams exhibited significant improvements in stiffness and strength properties, above those of single HFRP I-beams without a UHPFRC slab. A fiber model was developed to predict the strength and stiffness of the composite beam, and the model accuracy was verified. Good agreement was found between the experimental and analytical results. The high tensile strength of a carbon FRP in an HFRP tensile flange could be used effectively, and the delamination failure of an HFRP compressive flange could be prevented through the addition of a UHPFRC slab on the top flange of the HFRP I-beam. The study revealed that HFRP–UHPFRC beams were efficient and could provide a competitive, cost-effective, and sustainable solution to bridge structures.

Research paper thumbnail of Condition Assessment of Ground-Mount Cantilever Weathering-Steel Overhead Sign Structures

Journal of Infrastructure Systems, 2017

This paper is a part of an expansive research work aimed at assessing 82 weathering steel overhea... more This paper is a part of an expansive research work aimed at assessing 82 weathering steel overhead sign structures (WSOSSs) in the Charleston Interstate System in West Virginia. A total of 26 comprehensive inspection forms were developed to objectively evaluate the current condition of 11 general types of sign structures. This article focuses on analyzing 25 single-armed and double-armed ground-mount-cantilever WSOSSs (GMC-WSOSSs). A reliable ultrasonic testing technique was used to examine key components of the sign structures while the other components were inspected by visual inspection technique. A rating methodology was developed to evaluate the sign structures at both the element level and their overall condition. The element condition was rated based on the developed rating criteria and score. The overall condition of each sign structure was then evaluated by the ratio between the total score of each structure (S) and its maximum possible total score (Smax). As a result of this work, it is concluded that all the GMC-WSOSSs performed relatively well after more than 40 years of service and exposure to moist weather condition of Kanawha County (climate zone 4A). Specifically, as a result of the developed rating methodology, 52% of sign structures were found to be in fair condition and 48% were in good condition. The rating system is intended to assist the West Virginia Department of Transportation in making rational decisions about whether there is a need to repair or replace at-risk elements, connections, or structures.

Research paper thumbnail of Hybrid polymer composites for structural applications

Hybrid Polymer Composite Materials - Applications, 2017

Hybrid composites have unique features that can be used to meet specified design requirements in ... more Hybrid composites have unique features that can be used to meet specified design requirements in a more cost-effective way than nonhybrid composites. They offer many advantages over conventional composites including balanced strength and stiffness, enhanced bending and membrane mechanical properties, balanced thermal distortion stability, improved fatigue/impact resistance, improved fracture toughness and/or crack arresting properties, reduced weight and/or cost, and reduced notch sensitivity. “Synergistic” effect of hybrid composites (defined as the difference between the performance of a fiber in a hybrid composite and in a single fiber composite) has attracted the interest of researchers worldwide. This chapter reviews recent structural applications of hybrid composites for various sectors such as aerospace, automobile, civil engineering, energy, marine, sport, and telecommunication. The development and applications of innovative hybrid FRP–concrete composite structural system for civil infrastructure (e.g., highway bridge decks, girders, columns, and piles) are emphasized.

Research paper thumbnail of Mechanical properties of hybrid polymer composite

Hybrid Polymer Composite Materials - Properties and Characterisation, 2017

Hybrid composites have unique features that can be used to meet specified design requirements in ... more Hybrid composites have unique features that can be used to meet specified design requirements in a more cost-effective way than nonhybrid composites. They offer many advantages over conventional composites including balanced strength and stiffness, enhanced bending and membrane mechanical properties, balanced thermal distortion stability, improved fatigue/impact resistance, improved fracture toughness and/or crack arresting properties, reduced weight and/or cost, and reduced notch sensitivity. “Synergistic” effect of hybrid composites (defined as the difference between the performance of a fiber in a hybrid composite and in a single fiber composite) has gained interest of researchers worldwide. This chapter reviews recent research activities on natural fiber-based hybrid composites with the main focus on their mechanical properties.

Research paper thumbnail of Ultrasonic pitch and catch technique for non-destructive testing of reinforced concrete slabs

Journal of Infrastructure Preservation and Resilience

This study aims at evaluating reinforced concrete (RC) bridge elements using ultrasonic pitch and... more This study aims at evaluating reinforced concrete (RC) bridge elements using ultrasonic pitch and catch (UPC) non-destructive testing (NDT) technique. A validation reinforced concrete slab with two embedded layers of rebars and artificial defects (voids, honeycombs, and debondings) was designed and tested. A commercial UPC NDT device (hereafter called “UPC device”), which is based on the ultrasonic shear-wave test method using dry-point-contact transmitting and receiving transducers in a “pitch-catch” configuration, was used to map internal defects of the validation RC slab. The recorded data from the UPC device was analyzed using a modified synthetic aperture focusing technique (SAFT). A software was developed to reconstruct 2-D images of the RC slab cross-sections using novel signal filtering and processing techniques. The results revealed that the 2-D image reconstructed from the developed software accurately exhibited locations and horizontal dimensions of the steel rebars, void...

Research paper thumbnail of Tensile Behavior of Pultruded Fiber-Reinforced Polymer Laminates with Bonded and Bolted Splice Joints

Transportation Research Record: Journal of the Transportation Research Board, 2017

This paper presents an experimental investigation on double-lap joints of grit-blasted surface fi... more This paper presents an experimental investigation on double-lap joints of grit-blasted surface finish fiber-reinforced polymer (FRP) splice plates bonded and bolted to FRP laminates. Eighteen coupon joint specimens were tested under tensile loading with varying types of FRP splice plates and FRP laminates. Four types of bolts were evaluated: FRP bolts, high corrosion-resistant steel (HCRS) bolts, stainless steel (SS) bolts, and SS bolts wrapped with glass FRP (GFRP) (referred to as “SF” bolts). The test results indicated that double-lap splice joints, which incorporated HCRS bolts, epoxy adhesive, and grit-blasted surface finish FRP splice plates, provided strong bonds with FRP laminates. The grit-blasted surface finish of the FRP splice plates and the epoxy adhesive contributed to improving joint stiffness and strength. The specimens with FRP bolts showed brittle behavior and failed at relatively low ultimate load. The failures of those specimens were debonding of epoxy layers followed by shearing of the FRP bolts. The specimens with steel bolts (i.e., HCRS, SS, and SF bolts), however, exhibited ductile behavior and failed at a much higher ultimate load than did the FRP bolt specimens. Typical failure modes of the steel bolt specimens were fracturing of the FRP laminate (resulting from fiber rupture or kink, shear-out, and delamination failure of the GFRP plies and bearing failure of FRP materials near the edge of bolt holes in the load direction), bearing failure of the FRP splice plates, epoxy debonding, and yielding of bolts. Although FRP wraps may enhance the durability of the SS bolts, the use of SF bolts may significantly affect the failure mode of the splice joints.

Research paper thumbnail of Structural behavior of hybrid FRP composite I-beam

Construction and Building Materials, 2010

This paper presents the structural behavior of an innovative hybrid Fiber Reinforced Polymers (FR... more This paper presents the structural behavior of an innovative hybrid Fiber Reinforced Polymers (FRP) beam consisting of carbon/glass fibers and vinyl-ester resin. The advanced feature of this hybridization is the optimum use of carbon and glass fibers in the flanges to maximize structural performance while reducing the overall cost by using only glass fibers in the web section. A series of beam tests were conducted under four-point bending varying ratio of flange to web width (b f /b w) and volume content of carbon and glass fiber in the flanges. Experimental investigations revealed that the ratio of flange to web width of hybrid FRP I-shaped beams plays an important role in their structural behavior. Small flange beams (b f /b w = 0.43) showed stable and linear behavior under bending moment and failed in a brittle manner by delamination of the compressive flange at the interfacial layers while wide flange beams (b f /b w = 1.13) exhibited unstable and nonlinear behavior in the buckling and post-buckling region leading to delamination failure of the compressive flange. The experimental and analytical results discussed in this paper emphasize on the best composition of carbon and glass fibers for the optimum design of such hybrid beams. It is found that the maximum strength of hybrid FRP beams can be obtained with the volume content of carbon fiber to be 25-33%. Furthermore, the results of this study show the potential of applying hybrid FRP beams for bridge components.

Research paper thumbnail of Structural behavior of double-lap joints of steel splice plates bolted/bonded to pultruded hybrid CFRP/GFRP laminates

Construction and Building Materials, 2012

This paper presents results from experimental and numerical studies on the structural behavior of... more This paper presents results from experimental and numerical studies on the structural behavior of double-lap joints of steel splice plates bolted/bonded to pultruded hybrid CFRP/GFRP laminates. A total of 45 tensile coupon specimens with double-lap bolted/bonded joints and six large-scale flexural beam specimens with/without butt joints in the mid-span section were conducted. Two types of double-lap joints were investigated including bolted joints and hybrid joints (bonded-and-bolted). The results indicate that the double-lap hybrid joint which combined of stainless steel bolts, adhesive bonding, and V-notched splice plates is an effective method of joining the hybrid FRP laminate. The rough surface of the V-notched splice plates and the adhesive bonding contribute to improve the joint stiffness. Numerical analysis was carried out to predict load-displacement curve of the hybrid joints and the results showed a good correlation with the experiments. A design idea for use in the practical design of joints was proposed.

Research paper thumbnail of Recent technology of prestressed concrete bridges in Japan

IABSE-JSCE Joint Conference on Advances in Bridge Engineering-II, 2010

Prestressed concrete (PC) technology is being used all over the world in the construction of a wi... more Prestressed concrete (PC) technology is being used all over the world in the construction of a
wide range of bridge structures. However, many PC bridges have been deteriorating even before the end of
their design service-life due to corrosion and other environmental effects. In view of this, a number of innovative
technologies have been developed in Japan to increase not only the structural performance of PC bridges,
but also their long-term durability. These include the development of novel structural systems and the advancement
in construction materials. This paper presents an overview of such innovative technologies on PC
bridges on their development and applications in actual construction projects. Some noteworthy structures,
which represent the state-of-the-art technologies in the construction of PC bridges in Japan, are also presented.

Research paper thumbnail of Push-out tests for shear connections between UHPFRC slabs and FRP girder

Composite Structures, 2014

This paper presents an experimental investigation on the shear connections between carbon/glass F... more This paper presents an experimental investigation on the shear connections between carbon/glass Fiber-Reinforced Polymer I-girder and Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) slabs. Effects of straight/inclined bolt shear connectors and effective embedment depth-to-bolt diameter (h ef / d) ratios were investigated. Fourteen push-out tests were conducted to evaluate the load-slip behavior and the ultimate resistance of the bolt shear connectors. With the use of the UHPFRC, the h ef /d ratio needed for obtaining a shear connector failure mode was 2.7 times lower than that obtained from 43 push-out tests in the literature for normal weight and lightweight concrete slabs. The inclined bolt shear connectors showed a more ductile behavior than the straight bolt shear connectors. The experimentally obtained ultimate resistance of the bolt shear connectors was compared against the equations provided by ACI 318-11, AISC 2011, AASHTO LRFD 2010, PCI 2004, and EC-4 2004. An empirical equation to predict the ultimate shear connector resistance was proposed and validated by the experimental data. Idealized load-slip models and equations to predict the load versus slip relationship for all push-out tested specimens were proposed. Curve fitting was performed to find fitting parameters for all tested specimens and the results showed a very good correlation with the experiments.

Research paper thumbnail of Influence of grouting conditions on deterioration of post-tensioned prestressed concrete beams

Japan Concrete Institute, 2006

Chloride-induced corrosions of a sheath and a prestressing tendon in post-tensioned prestressed c... more Chloride-induced corrosions of a sheath and a prestressing tendon in post-tensioned prestressed concrete (PC) beams are investigated under different grouting conditions. Two series PC beams were tested by the electrically accelerated corrosion. The first series of accelerated corrosion tests were performed to determine the influence of grouted ratios in a curved sheath on the corrosion of the sheath and the prestressing tendon. In the second series of tests, the relationship between corrosion crack and expansive pressure surrounding the sheath and tendon during the corrosion process was clarified.

Research paper thumbnail of Hybrid FRP-UHPFRC composite girders: Part 2 -Analytical approach

Composite Structures, 2015

A companion paper shows the experimental testing and numerical analysis of composite girders cons... more A companion paper shows the experimental testing and numerical analysis of composite girders consisting of hybrid carbon/glass fiber-reinforced polymer (HFRP) I-girders topped with precast ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs. This paper presents derivations of analytical equations to examine the composite behavior of the HFRP-UHPFRC girders with varying levels of interaction at the slab/girder interface. The derived equations to predict interfacial slip strain, curvature, and deflection of the composite girders were validated by the experimental data. An equation to determine the effective moment of inertia of the HFRP-UHPFRC composite girders with partial interaction is proposed and compared against the experiment. A fairly good agreement between the experimental and analytical results was found. The derived/proposed equations can simply and reliably evaluate the composite behavior between the HFRP I-girder and the UHPFRC slab.

Research paper thumbnail of Hybrid FRP-UHPFRC composite girders: Part 1 -Experimental and numerical approach

Composite Structures, 2015

This paper presents experimental testing and numerical analysis of durable composite girder syste... more This paper presents experimental testing and numerical analysis of durable composite girder systems consisting of hybrid carbon/glass fiber-reinforced polymer (HFRP) I-girders and precast ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs. Epoxy adhesive and/or bolt shear connectors (SCs) were used to transfer horizontal shear forces from the UHPFRC slabs to the HFRP I-girders. Push-out tests were performed to evaluate the shear interaction at the slab/girder interface. The results of the push-out tests were used to design five large-scale composite girders. The experimental variables included two types of bolt SCs (straight and inclined bolt SCs) and different slab geometries. The composite behavior between the HFRP I-girder and the UHPFRC slab was examined. The test results showed that the combined use of the bolt SCs and the epoxy adhesive was essential to achieve a full interaction between the HFRP I-girder and the UHPFRC slab. The use of the epoxy adhesive resulted in improving the strength and stiffness of the composite girders, reducing the stress concentration around the bolt-holes, and increasing the shear strength of the bolt SCs. The girders with the inclined bolt SCs showed a more ductile behavior than those with the straight headed bolt SCs. A three-dimensional finite element (FE) analysis of the HFRP-UHPFRC composite girder was carried out that considered slip effects at the slab/girder interface and the nonlinear behavior of the bolt SCs. Comparisons between the experimental results and the FE analysis were performed and a fairly good agreement was found. A companion paper shows derivations of analytical equations to predict composite behaviors of the HFRP-UHPFRC girders with varying levels of interaction at the slab/girder interface.

Research paper thumbnail of Hybrid Fiber-Reinforced Polymer Girders Topped with Segmental Precast Concrete Slabs for Accelerated Bridge Construction

Transportation Research Record: Journal of the Transportation Research Board, 2014

The behavior of composite girders made of hybrid fiber-reinforced polymer (HFRP) I-girders, toppe... more The behavior of composite girders made of hybrid fiber-reinforced polymer (HFRP) I-girders, topped with precast ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs is presented in this paper. HFRP I-girders were manufactured under the pultrusion process in which unidirectional carbon fibers and bidirectional fiberglass fabric or continuous strand mat were used. Four large-scale composite girders were tested under four-point flexural loading. In the first composite girder, the HFRP I-girder was topped with a full-length precast UHPFRC slab. Twelve precast UHPFRC segments were used in each slab of the other three composite girders. Either epoxy or mortar connections were used to connect the precast UHPFRC segments. The test results showed that the flexural stiffness of the composite girder with the epoxy-connected segmental precast slabs was similar to that of the full-length precast composite girder. The mortar-connected girder exhibited more ductile behavior than the epoxy-connected girder. All the composite girders exhibited significant improvements in strength and stiffness compared with the HFRP I-girder without the UHPFRC slab. The HFRP–UHPFRC composite girders were shown to provide a promising and sustainable solution for accelerated bridge construction.

Research paper thumbnail of Flexural Behavior of Pultruded Hybrid Fiber-Reinforced Polymer I-Beams with Bonded-and-Bolted Splice Joints

Transportation Research Record: Journal of the Transportation Research Board, 2016

This paper presents experimental results of double-lap joints of fiber-reinforced polymer (FRP) o... more This paper presents experimental results of double-lap joints of fiber-reinforced polymer (FRP) or steel splice plates bonded and bolted to flanges and web of pultruded hybrid I-beams with carbon FRP and glass FRP. Eight large-scale specimens with bonded-and-bolted splice joints and two control beams were tested under four-point static flexural loading. The test results indicated that the double-lap splice joints, which incorporated high corrosion-resistant steel bolts, epoxy adhesive, and FRP splice plates with a grit-blasted surface finish provided an effective solution for joining the hybrid FRP I-beams. The grit-blasted surface finish of the FRP splice plates and the epoxy adhesive contributed to improving the joint stiffness and strength. Before debonding occurred, the stiffness of the bonded-and-bolted splice joints was dependent mainly upon the strength of the epoxy adhesive and the bonding surface of the splice plates, while the ultimate load and failure mode of the joints was governed by the number and strength of bolts. The specimens with failures in the splice connections showed more ductile behavior than specimens with failures beyond the connections. This difference is attributed to the slippage of the splice connections.

Research paper thumbnail of Flexural Behavior of Hybrid Composite Beams

Transportation Research Record - Journal of Transportation Research Board, 2013

This paper presents the development of composite beams, which consist of hybrid carbon and glass ... more This paper presents the development of composite beams, which consist of hybrid carbon and glass fiber-reinforced polymer (FRP) I-beams and precast, ultra-high-performance, fiber-reinforced concrete (UHPFRC) slabs. Hybrid FRPs (HFRPs) provide the advantage of high resistance to corrosion, while UHPFRC has great strength and durability. The combination of these two materials is expected to benefit structures subjected to severe environmental conditions and to respond to the need for accelerated bridge construction. Three full-scale composite beams with varied UHPFRC slab width were tested under four-point flexural loading. Bolt shear connectors with and without epoxy bonding were used in the tested beams. The bolt shear connectors and epoxy were used to resist the horizontal shear flow at the interface between the HFRP I-beam and the UHPFRC slab. The composite action between the HFRP I-beam and UHPFRC slab was investigated. The test results showed that all of the composite beams exhibited significant improvements in stiffness and strength properties, above those of single HFRP I-beams without a UHPFRC slab. A fiber model was developed to predict the strength and stiffness of the composite beam, and the model accuracy was verified. Good agreement was found between the experimental and analytical results. The high tensile strength of a carbon FRP in an HFRP tensile flange could be used effectively, and the delamination failure of an HFRP compressive flange could be prevented through the addition of a UHPFRC slab on the top flange of the HFRP I-beam. The study revealed that HFRP–UHPFRC beams were efficient and could provide a competitive, cost-effective, and sustainable solution to bridge structures.

Research paper thumbnail of Condition Assessment of Ground-Mount Cantilever Weathering-Steel Overhead Sign Structures

Journal of Infrastructure Systems, 2017

This paper is a part of an expansive research work aimed at assessing 82 weathering steel overhea... more This paper is a part of an expansive research work aimed at assessing 82 weathering steel overhead sign structures (WSOSSs) in the Charleston Interstate System in West Virginia. A total of 26 comprehensive inspection forms were developed to objectively evaluate the current condition of 11 general types of sign structures. This article focuses on analyzing 25 single-armed and double-armed ground-mount-cantilever WSOSSs (GMC-WSOSSs). A reliable ultrasonic testing technique was used to examine key components of the sign structures while the other components were inspected by visual inspection technique. A rating methodology was developed to evaluate the sign structures at both the element level and their overall condition. The element condition was rated based on the developed rating criteria and score. The overall condition of each sign structure was then evaluated by the ratio between the total score of each structure (S) and its maximum possible total score (Smax). As a result of this work, it is concluded that all the GMC-WSOSSs performed relatively well after more than 40 years of service and exposure to moist weather condition of Kanawha County (climate zone 4A). Specifically, as a result of the developed rating methodology, 52% of sign structures were found to be in fair condition and 48% were in good condition. The rating system is intended to assist the West Virginia Department of Transportation in making rational decisions about whether there is a need to repair or replace at-risk elements, connections, or structures.

Research paper thumbnail of Hybrid polymer composites for structural applications

Hybrid Polymer Composite Materials - Applications, 2017

Hybrid composites have unique features that can be used to meet specified design requirements in ... more Hybrid composites have unique features that can be used to meet specified design requirements in a more cost-effective way than nonhybrid composites. They offer many advantages over conventional composites including balanced strength and stiffness, enhanced bending and membrane mechanical properties, balanced thermal distortion stability, improved fatigue/impact resistance, improved fracture toughness and/or crack arresting properties, reduced weight and/or cost, and reduced notch sensitivity. “Synergistic” effect of hybrid composites (defined as the difference between the performance of a fiber in a hybrid composite and in a single fiber composite) has attracted the interest of researchers worldwide. This chapter reviews recent structural applications of hybrid composites for various sectors such as aerospace, automobile, civil engineering, energy, marine, sport, and telecommunication. The development and applications of innovative hybrid FRP–concrete composite structural system for civil infrastructure (e.g., highway bridge decks, girders, columns, and piles) are emphasized.

Research paper thumbnail of Mechanical properties of hybrid polymer composite

Hybrid Polymer Composite Materials - Properties and Characterisation, 2017

Hybrid composites have unique features that can be used to meet specified design requirements in ... more Hybrid composites have unique features that can be used to meet specified design requirements in a more cost-effective way than nonhybrid composites. They offer many advantages over conventional composites including balanced strength and stiffness, enhanced bending and membrane mechanical properties, balanced thermal distortion stability, improved fatigue/impact resistance, improved fracture toughness and/or crack arresting properties, reduced weight and/or cost, and reduced notch sensitivity. “Synergistic” effect of hybrid composites (defined as the difference between the performance of a fiber in a hybrid composite and in a single fiber composite) has gained interest of researchers worldwide. This chapter reviews recent research activities on natural fiber-based hybrid composites with the main focus on their mechanical properties.