An experimental study was performed on fiber wrapping to strengthen RC columns with insufficient moment capacity and ductility. In pseudo-seismic test of four columns with a circular cross section, the test variable was fiber type: none, carbon fiber (CF), polyethylene terephthalate (PET), and combined use of CF+PET. PET has high tensile strength and ductility, but very low elastic modulus. While a large area of PET typically needs to be used, the amount of PET actually utilized was about 50% of CF in terms of fiber axial stiffness (E f A f). All columns wrapped by CF and/or PET showed significantly improved strengths over the control column (121~143% of control column) while ductility also significantly improved (2.3~3.1 times the control column). Performance of PET was comparable to that of CF in terms of strength and ductility improvement while no sign of fiber rupture was observed at ultimate stage due to excellent ductility intrinsic with PET.
Many studies have been performed to apply research results for the time-dependent behaviour of reinforced concrete (RC) framed structures to the design and construction of high-rise buildings. However, shoring, removal of forms, and backshoring at early ages have not been adequately reflected in most studies. Removal of forms and backshoring activities have been dealt with as one construction sequence and the deformation of columns that occurs at an early age before removal of shores was not considered. In this study, a two-dimensional frame analysis program was developed to predict time-dependent behaviour of RC structures. In the program, the actual construction sequence of installation of forms and shores, concrete placement, removal of forms and shores, backshoring, removal of backshores, and application of additional loads are considered to predict axial force variations in RC columns and shores due to the change of concrete member stiffness. In order to evaluate the validity of the developed program, a model RC-framed specimen was tested under the same construction sequence. It was noted that with increasing time the axial forces in columns and shores were increased and decreased, respectively. In addition, column deformations occurred before removal of shores and axial forces in shores were redistributed to columns. Finally, it was also observed that the program predicted experimental results well.
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