In this study, a new precast concrete (PC) beam-column joint of moment resisting frame applicable for moderate seismic regions is proposed. A semi PC beam-column connection with U-shaped strands is developed in an attempt to improve workability and provide effective stress transfer mechanism at the joint. The structural system consists of PC beams with U-shaped strands, PC columns, PC slabs, and topping concrete. A series of three interior and three exterior semi PC joint specimens was tested to investigate the structural behavior of the system subjected to the lateral cyclic load. Key test variables are the number of strands placed in the PC beam and the presence or absence of the transverse reinforcements at the connection. The experiment and performance evaluation of the system were conducted in accordance with ACI T1.1–01 (2001). According to the test results, the proposed structural system with transverse reinforcements at the joint is sufficient to use in moderate seismic regions.
The use of carbon fibers (CF) and glass fibers (GF) were combined to strengthen concrete flexural members. In this study, data of tensile tests of 94 hybrid carbon-glass FRP sheets and 47 carbon and GF rovings or sheets were thoroughly investigated in terms of tensile behavior. Based on comparisons between the rule of mixtures and test data, positive hybrid effects were identified for various (GF/CF) ratios. Unlike the rule of mixtures, the hybrid sheets with relatively low (GF/CF) ratios also produced pseudo-ductility. From the calibrated results obtained from experiments, a new analytical model for the stress-strain relationship of hybrid FRP sheets was proposed. Finally, the hybrid effects were verified by structural tests of concrete members strengthened with hybrid FRP sheets and either carbon or glass FRP sheets.
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.
In high seismic regions, post-tensioned (PT) slab–column frames are commonly used to support gravity loads in conjunction with a lateral-force resisting system (LFRS) such as a core wall. The LFRS is designed to resist 100% of the design lateral forces as well as to limit lateral displacements to an acceptable level, whereas the slab–column frame must sustain the gravity loads under the expected (design) displacements. Given the relatively sparse data on the seismic performance of PT flat plate slab–column frames, cyclic tests of four interior PT slab–column connections were conducted. Primary test variables were the level of gravity shear at the slab–column connection and the slab tendon arrangement. Test results indicate that both the test variables strongly influence the cyclic behaviour of the PT connections, and that the use of slab bottom reinforcement at the slab–column connection was effective in resisting positive moment developed under lateral loading as well as improving the hysteretic energy dissipation capacity.
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