Jong-Sup Park

Flexural Behavior of Concrete Beam Strengthened by Near-Surface Mounted CFRP Reinforcement Using Equivalent Section Model

FRP (fiber reinforced polymer) has found wide applications as an alternative to steel rebar not only for the repair and strengthening of existing structures but also for the erection of new structures. Near-surface mounted (NSM) strengthening was introduced as an alternative of externally bonded reinforcement (EBR) but this method also experiences early bond failure, which stresses the importance of predicting accurately the bond failure behavior in order to evaluate precisely the performance of NSM reinforcement. This study proposes the equivalent section model assuming monolithic behavior of the filler and CFRP reinforcement. This equivalent section model enables establishing a bond failure model applicable independently of the sectional shape of the CFRP reinforcement. This so-derived bond failure model is then validated experimentally by means of beams flexure-strengthened by NSM CFRP reinforcements with various cross-sections. Finally, analytical analysis applying the bond failure model considering the equivalent section and defined failure criteria is performed. The results show the accuracy of the prediction of the failure mode as well as the accurate prediction of the experimental results regardless of the sectional shape of the CFRP reinforcement.

Flexural Behaviour of RC Beams Strengthened with Prestressed CFRP NSM Tendon Using New Prestressing System

CFRP has been used mainly for strengthening of existing structures in civil engineering area. Prestressed strengthening is being studied to solve the bond failure model featuring EBR and NSMR methods. The largest disadvantage of the prestressing system is that the system cannot be removed until the filler is cured. This problem lowers the turning rate of the equipment and makes it limited to experiment, which stresses the necessity of a new prestressing system. Therefore, the present study applies a new prestressing system which reliefs the need to wait until the curing of the filler after jacking to the prestressing of NSMR and examines the effect of the prestressing size and location of the anchorage on the strengthened behaviour. The experimental results show that the crack and yield loads increase with higher level of prestress, while the ductility tends to reduce, and the anchor plate should be installed within the effective depth to minimize the occurrence of shear-induced diagonal cracks. The comparison of the experimental results and results by section analysis shows that the section analysis could predict the maximum load of the specimens strengthened by prestressed NSMR within an error between 4% and 6%.

Condition Assessment of Corrosion-damaged Bridge Girders Strengthened with Post-tensioned Composite Strips

This paper presents the condition evaluation of bridge girders upgraded using post-tensioned near-surface-mounted (NSM) carbon fiber reinforced polymer (CFRP) strips subjected to corrosion damage. Computational models are developed to predict the behavior of the girders over a 100-year service period. Dynamic analysis exhibits that damage localization takes place, in conjunction with various mode shapes. As the extent of damage rises, the effectiveness of the NSM CFRP increases and the flexural stiffness of the girders decreases.

Evaluation of Shear Strength of Concrete Layers with Different Strength considering Interfacial Indentation

This study is a part of research to develop a steel-concrete hybrid girder using ultra high-performance concrete with a compressive strength of 80 MPa. To this end, the Eurocode design formula for the shear resistance developed in a concrete-to-concrete interface was examined for the interface between concrete layers of different strengths. To examine the effect of the surface roughness on the shear resistance, a push-out test was conducted on specimens while considering the parameters of the Eurocode design equation. The actual behavior was evaluated with respect to the compressive strength of the concrete, the reinforcement ratio of the shear rebar, and the interfacial surface condition. The specimen with a rough interface shows 20-50% higher shear strength than that estimated by the design equation. In the case of failure mode, abrupt failure tends to occur at the interface of the concrete layer for the specimen with a low reinforcement ratio. It is expected that the shear strength of the concrete layer will increase according to the strength differential in the concrete layers.

Effect of Corrosion Damage on Service Response of Bridge Girders Strengthened with Posttensioned NSM CFRP Strips

AbstractThis paper presents the effect of corrosion damage on the service response of prestressed concrete bridge girders strengthened with posttensioned near-surface-mounted (NSM) carbon fiber–reinforced polymer (CFRP) strips. Three-dimensional finite-element modeling, validated against experimental data, is conducted to deterministically study the static and dynamic behavior of the girders subjected to chloride-induced corrosion for a period of 100 years. With an increase in corrosion damage, the efficacy of the posttensioned NSM CFRP augments from a serviceability perspective. Modal analysis identifies critical regions along the girder where strain localization occurs at certain dynamic excitation frequencies. The unstrengthened girders are more reactive to dynamic responses than their strengthened counterparts; however, both exhibit similar ride quality. Corrosion damage significantly decreases the equivalent flexural rigidity of the decrepit girders up to 30% relative to that of the control girders. ...

Functional Performance of Bridge Girders Strengthened with Post-Tensioned Near-Surface-Mounted Carbon Fiber- Reinforced Polymer

This paper presents the performance reliability and functional complexity of prestressed concrete girders strengthened with an emerging rehabilitation method using post-tensioned near-surfacemounted (NSM) carbon fiber-reinforced polymer (CFRP) strips. The influence of corrosion damage on the flexural capacity of the girders is theoretically predicted based on a stochastic approach, including an emphasis on chloride diffusion and concentration. A total of 1,650,000 cases having various CFRP-post-tensioning levels from 0 to 60% of the strength of CFRP are simulated, and corresponding results are analyzed. Predictive results indicate that the effect of corrosion becomes distressful with a time gap of 13.7 years after the initiation of corrosion from a practical point of view. The efficacy of the post-tensioned NSM CFRP in terms of preserving flexural strength and reducing vulnerability to deterioration is more pronounced with an increase in service year, based on a robust stress redistribution mechanism. Functional complexity is also reduced after strengthening, which can better achieve the given functional requirements of constructed bridge girders. Performance-based design factors are proposed, depending on service categories that are a function of traffic volume.

Bond Behavior of CFRP Rod for Near Surface Mounted Strengthening Method Under Temperature Variation

Most of the tendons used in prestress concrete structures are made of steel which is vulnerable to corrosion in external environment. In order to solve strengthen efficiently the structure, active research has been widely conducted on the Near Surface Mounted (NSM) strengthening method using carbon fiber reinforced polymer (CFRP) tendon. This study is to investigate adhesive properties depending on the temperature variation(-15 o C~55 o C) of NSM method by filler. Total 18 cubic specimens were fabricated and pull-out tests were conducted. Bond behavior including bond strength under temperature variation and failure mode was analyzed and discussed.