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Low-Cycle Flexural Fatigue Behavior of Concrete Beam Reinforced with Hybrid FRP-Steel Rebar
Choo, Jinkyo F.,Choi, Young-Cheol,Kwon, Seung-Jun,Park, Ki-Tae,Yoo, Sung-Won Hindawi Limited 2018 Advances in civil engineering Vol.2018 No.-
<P>Studies examined experimentally the flexural behavior of concrete beams reinforced with the hybrid FRP-steel rebar but very few among them evaluated their fatigue performance. In this study, the fatigue test has been performed, and an analytical model for simulating the flexural fatigue behavior of the concrete beam reinforced with the hybrid bar considering its postyielding behavior is developed. A formula relating the postyielding fatigue strain of the rebar to the number of the fatigue cycle is suggested and used in the proposed procedure. The method simulating the low-cycle behavior of the reinforced concrete beam is found to be satisfactory and can predict the number of cyclic loading to failure.</P>
Choo, Jinkyo F.,Ha, Dong-Ho,Lee, Chang Hyung,Jang, Won Seo Scitec Publications 2013 Advanced materials research Vol.811 No.-
<P> The bearings of a bridge are indispensable structural members, which support the superstructure, transfer the loads of the superstructure to the substructure and, accommodate the horizontal and vertical motions of the superstructure caused by all types of loads like traffic. Such traffic loads induce the bridge to vibrate but this energy is wasted. Therefore, a piezocomposite electricity generating element (PCGE) has been introduced in the bearing to exploit effectively this vibrational energy. The bridge bearing with built-in PCGE was seen to be effective for measuring the traffic loads and, detecting eventual overloaded or overspeeding vehicles. In a will to optimize the amount of energy generated by this bearing, this study compares experimentally the amount of electricity produced by the PCGE with respect to its position in the bridge bearing through a series of dynamic loading tests to find out the position of the PCGE providing the most efficient electricity generation. </P>
Yield Strength Prediction of UOE Pipes: From Forming to Flattening
Yi, Jiwoon,Kang, Soo-Chang,Koh, Hyun-Moo,Choo, Jinkyo F International Society of Offshore and Polar Engine 2018 International journal of offshore and polar engine Vol.28 No.2
<P>With the advent of higher steel grades for offshore pipelines and the reliance of the UOE forming process on trial and error, knowing the final yield strength of the pipe beforehand would be beneficial in terms of time and cost. However, predicting the yield strength of the UOE pipe constitutes a difficult task because of the alteration of the material properties throughout the forming process. Moreover, the yield strength is measured by tensile test executed on specimens obtained by flattening samples cut from the formed pipe, but this flattening process also alters the properties of the material. Accordingly, this study presents a 2-D finite element method (FEM) program considering both forming and flattening processes to predict the yield strength of the UOE pipe measured by tensile test. The results show that the simulation predicts the yield strength with good accuracy.</P>
Flexural and Shear Behaviors of Reinforced Alkali-Activated Slag Concrete Beams
Lee, Kwang-Myong,Choi, Sung,Choo, Jinkyo F.,Choi, Young-Cheol,Yoo, Sung-Won Hindawi Limited 2017 Advances in materials science and engineering Vol.2017 No.-
<P>The material properties of cement-zero concrete using alkali-activators have been studied extensively as the latest response to reduce the CO2 exhaust of the cement industry. However, it is also critical to evaluate the behavior of reinforced concrete beams made of alkali-activated slag (AAS) concrete in terms of flexure and shear to promote the applicability of AAS concrete as structural material. Accordingly, nine types of beam specimens with various ratios of tensile steel and stirrup were fabricated and subject to bending and shear tests. The results show that the flexural and shear behaviors of the reinforced AAS concrete members are practically similar to those made of normal concrete and indicate the applicability of the conventional design code given that the lower density of slag is considered. In addition, a framework using the elastic modulus and stress-strain relation from earlier research is adopted to carry out nonlinear finite element analysis reflecting the material properties of AAS concrete. The numerical results exhibit good agreement with the experimental results and demonstrate the validity of the analytical model.</P>
Dynamic Characteristics of a Multi-Functional Bridge Bearing with Builtin Piezocomposite Element
Ha, Dong-Ho,Choo, Jinkyo F.,Lee, Chang Hyung,Jang, Won Seo,Goo, Nam-seo Trans Tech Publications 2013 Applied mechanics and materials Vol.432 No.-
<P> A multi-functional bridge bearing with built-in piezocomposite electricity generating element (PCGE) is being developed by our research team to respond to the growing demand of self-powered sensing devices for the monitoring of bridges by harvesting the energy produced by the traffic-induced vibrations. For the intended application, a multilayered piezoelectric PCGE structure composed of layers of piezoceramic, glass/epoxy, and carbon/epoxy, has been developed to improve the durability, output voltage and power of the piezoceramic. The output voltage of this PCGE can be used for real-time traffic monitoring like in bridge-weigh-in-motion systems and can eventually be exploited to generate the electricity needed for the lighting and functioning of other embedded sensors. This paper presents the results of the dynamic loading tests conducted on a prototype of the proposed multi-functional bridge bearing to enhance its design details and verify the accuracy of the measurement. The results show that the bearing provides reliable measurement for traffic monitoring and enable to conceive details for the improvement of the output voltage of the PCGE. Since bridge bearings, as indispensable devices transferring the loads and movements from the deck to the substructure and foundations of the bridge, are continuously subjected to traffic loads, the proposed bridge bearing appears to be a natural and economic solution that can be applied to existing or newly built bridges without modification of the conventional design while providing additional and valuable functions for the maintenance of the structure. </P>
Jang Ho Park,조정래,Jinkyo F. Choo 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.2
Prestressed concrete (PSC) bridge resists to deflection and cracking by prestressing its concrete superstructure using steel strands. The initial prestress force introduced in the strands at the completion of the structure influences sensitively its long-term performance. Rating the health of the PSC bridge should thus start with the knowledge of this initial prestress. However, the measurements given by the hydraulic jack and load cell used during prestressing may not be absolute indicators of the effective stress introduced in the strands. Considering that the strain distribution in the anchor can be used to measure the prestress in the strands and that the anchor head is the most accessible part of the PSC member, this study presents a method using the deformation characteristics of the anchor head to evaluate the initial prestress of the strands. To that goal, experimental and numerical analyses were performed on an anchorage-strand system considering the coefficient of friction between the wedge and the anchor head. The results show that the variation of the hoop strain measured in the multi-strand anchor head can be used to evaluate effectively the initial prestress state of the strands with respect to the applied jacking force.