Papers by Author: Yun Cheul Choi

Abstract: Generally because of the economic advantage and stable behavior in seismic loading, shearwalls combined with coupling slabs are widely used in high-rise apartment buildings. When analyzing such structures for lateral loads, however, the question of the actual stiffness and strength of the coupling slabs arises. For more accurate analysis approach, an experimental investigation was conducted with half-scale representations of the reinforced concrete shearwalls with the opening and coupled with slabs were subjected to cyclic loads. The test results of opening installed specimen, severe decrease of strength was observed. The decrease of strength of the shear walls by installation of openings shows a great deal of difference compared to previous researches. This is because flexural capacity of the slabs is working as coupling elements for the shear walls. The critical section of coupling slabs that works as coupling elements for shear walls was a little different from the results of previous researches.

Abstract: The use of glass-fiber-reinforced polymer (GFRP) bars to replace steel reinforcement in concrete structures is a relatively new technique. GFRP bars possess mechanical properties different from steel bars, including high tensile strength combined with low elastic modulus and elastic brittle stress–strain relationship. Therefore, design procedures should account for these properties. This paper presents the experimental moment deflection relations of GFRP reinforced beam which are spliced. Test variables were lab-spliced length of GFRP rebar. A total of 6 concrete beams reinforced with steel and GFRP rebar tested. Three concrete beams reinforced with spliced GFRP rebar and 1 reference beams reinforced with non-spliced GFRP rebar was tested. All the specimens had a span of 4000mm, provided with 12.7mm nominal diameter steel and GFRP rebar. All test specimens were tested under 2-point loads so that the spliced region is subject to constant moment. The experimental results show that the splice length of GFRP increased with the ultimate load increasing and decreased with stiffness.

Abstract: A series of five shear wall specimens were tested under constant axial stress and reversed lateral cyclic loading in order to evaluate the seismic retrofit methods that had been proposed for shear walls with new openings. The test results showed that the failed specimens had shear fractures and two different retrofit methods had different effects on the strengths of each specimen.

Abstract: A series of three shear wall specimens were tested under constant axial stress and reversed cyclical lateral loading in order to evaluate the seismic retrofit that had been proposed for the shear wall with the opening induced by remodeling. One of these specimens was tested in the as-built condition and the other two were retrofitted prior to testing. The retrofit involved the use of carbon fiber sheets and steel plates (a thickness of 3mm) over the entire face of the wall. The test results showed that the failed specimens had shear fractures and that two different types of retrofitting strategies had different effects on the strengths of each specimen.

Abstract: The characteristics relating to high tensile ductility, High Performance Fiber Reinforced Cementitious Composites (HPFRCC) are being so that studied it’ll be adopted in repair and retrofit of buildings. A series of three shear wall specimens were tested under constant axial stress and reversed cyclical lateral loading in order to evaluate the seismic retrofit that had been proposed for the shear wall with the opening. The retrofit involved the use of ECC and MDF, both of which are sprayed through the high pressure pump, over the entire face of the wall. The results indicate that two different types of retrofitting strategies cause the different effects on the strength and ductility of each specimen.