WooSeok Kim

Polyamide Fiber Reinforced Shotcrete for Tunnel Application

This study intends to establish the mechanical properties of polyamide fiber reinforced shotcrete (PAFRS) in terms of compressive and flexural strengths, in accordance with ASTM C1609/C1609M-12. The mechanical properties identified the influence of polyamide fiber content on the PAFRS strength. This study evaluated the toughness of PAFRS and proposed additional toughness level criteria to better represent organic fiber performance. In addition, the fiber rebounding rate and PAFRS performance in tunneling application were evaluated based on a tunnel application in Korea. PAFRS with 0.6%~0.8% volume content in tunneling shotcrete could significantly improve flexural ductility, toughness, and ultimate load capacity. Fiber rebounding tests exhibited a low rebounding rate (8.5%) and low fiber drop (63.5%). Therefore, PAFRS applied to a tunnel exhibited stability and constructability.

Modeling and Measurement of Sustained Loading and Temperature-Dependent Deformation of Carbon Fiber-Reinforced Polymer Bonded to Concrete

This paper aims at presenting the effects of short-term sustained load and temperature on time-dependent deformation of carbon fiber-reinforced polymer (CFRP) bonded to concrete and pull-off strength at room temperature after the sustained loading period. The approach involves experimental and numerical analysis. Single-lap shear specimens were used to evaluate temperature and short-term sustained loading effects on time-dependent behavior under sustained loading and debonding behavior under pull-off loading after a sustained loading period. The numerical model was parameterized with experiments on the concrete, FRP, and epoxy. Good correlation was seen between the numerical results and single-lap shear experiments. Sensitivity studies shed light on the influence of temperature, epoxy modulus, and epoxy thickness on the redistribution of interfacial shear stress during sustained loading. This investigation confirms the hypothesis that interfacial stress redistribution can occur due to sustained load and elevated temperature and its effect can be significant.

Processing and Mechanical Properties of Macro Polyamide Fiber Reinforced Concrete

This study developed a macro-sized polyamide (PA) fiber for concrete reinforcement and investigated the influence of the PA fiber on flexural responses in accordance with ASTM standards. PA fibers are advantageous compared to steel fibers that are corrosive and gravitated. The macro-sized PA fiber significantly improved concrete ductility and toughness. Unlike steel fibers, the PA fibers produced two peak bending strengths. The first-peaks occurred near 0.005 mm of deflection and decreased up to 0.5 mm of deflection. Then the bending strength increased up to second-peaks until the deflections reached between 1.0 and 1.5 mm. The averaged flexural responses revealed that PA fiber content did not significantly influence flexural responses before L/600, but had significant influence thereafter. Toughness performance levels were also determined, and the results indicated more than Level II at L/600 and Level IV at others.

Thermal-Structure Interaction Parallel Fire Analysis for Steel-Concrete Composite Structures under Bridge Exposed to Fire Loading

The objective of this research is to evaluate of global and local damage for steel-concrete composite structures under highway bridge exposed to fire loading. To enhance the accuracy and efficiency of the numerical analysis, the proposed transient nonlinear thermal structure interaction(TSI) parallel fire analysis method is implemented in ANSYS. To validate the TSI parallel fire analysis method, a comparison is made with the standard fire test results. The proposed TSI parallel fire analysis method is applied to fire damage analysis and performance evaluation for Buchen highway bridge. The result of analysis, temperature of low flange and web are exceed the critical temperature. The deflection and deformation state show good agreement with the fire accident of buchen highway bridge.

Bridge inspection practices and bridge management programs in China, Japan, Korea, and U.S.

Abstract The present study reviews bridge inspection practices and bridge management programs in China, Japan, Korea, and U.S. Bridges play an essential role in transportation systems and in the economic production process. Transportation agencies should maintain bridges in acceptable conditions to provide a desirable level of service to the public within limited budgets. In addition, a number of bridges are aging rapidly in these four countries. Fortunately, since several countries have experienced deteriorated bridges due to aging, the countries considered in this study have already developed comprehensive bridge management system (BMS) and bridge inspection practices. Therefore, the goal of this paper is to search for and synthesize useful knowledge on BMSs and bridge inspection practices of the four countries. Finally, recommendations that will serve as guidance to transportation agencies for potential enhancements to BMS and bridge inspections are presented.

Fire Risk Assessment for Highway Bridges in South Korea

The study presented in this paper developed a sequential and universal bridge fire risk assessment procedure for constructed bridges, as well as countermeasures to reduce the risk level. Of interest were concrete and steel bridges on highways, except for certain special types of bridges. The fire risk assessment procedure consisted of three steps: (a) preliminary risk analysis (PRA), which was a screening step to determine the likelihood of bridge fire events; (b) simplified risk analysis (SRA), which was performed with the use of bridge inventory databases and checklists; and (c) detailed risk analysis (DRA), which made use of computer simulation and collected data. A PRA determines whether a bridge requires an SRA on the basis of bridge clearance height and roadway conditions under the bridge. An SRA has three parts: analysis of fire occurrence, vulnerability to fire, and bridge importance. Itemized details were developed to evaluate the three parts and determine risk scoring. The SRA procedure identified which parts contributed to the resultant risk level. Reliability indexes concurrent with the latest ISO DP 10252 design code were used to determine the score of a given bridge and to perform an analysis to determine the risk level of 8,267 bridges in South Korea. The DRA was the final step, a detailed analysis of occurrence and vulnerability of a bridge mainly on the basis of computer simulation. This study provided guidelines to determine the DRA levels. Countermeasures also were developed for each of three risk levels (i.e., occurrence, vulnerability, and importance); the application of the countermeasures depended on the factors causing the risk.