五螺箍筋柱反覆載重撓曲與偏心軸壓行為

Abstract

Multi-spiral transverse reinforced columns have been shown to outperform conventional rectilinear tie reinforced columns in seismic performance. This thesis intends to examine the flexural behavior of multi-spiral reinforced columns, particularly, the five-spiral transverse reinforcement for square columns. In the first phase, a method to determine the flexural capacity of five-spiral reinforced columns, which considers the confinement effect of the five-spirals, was introduced. Five small-scale columns were tested under increasing eccentric axial loading to validate the predicted axial-moment interaction of the five-spiral reinforced columns. In the second phase, large-scale flexure-critical five-spiral columns and equivalent conventional rectilinear tied columns were tested under low (0.1fca'Ag) and high (0.3fca'Ag) constant axial loads and subjected to double-curvature lateral cyclic loading. Test results showed that the five-spiral reinforced columns obtained higher flexural strength, superior ductility, larger drift capacity, and better equivalent damping ratios than counterpart conventional rectilinear tie reinforced columns, despite having 16% to 29% less transverse reinforcement. In addition, it was shown that code-based calculations of nominal moment strength can conservatively estimate the actual moment strength of five-spiral reinforced columns. On the other hand, among the existing code-based methods used in calculating the expected maximum moment of five-spiral columns, the Caltrans SDC 2019 method provided the most accurate prediction of the maximum flexural strength, followed by the AASHTO 2017 method, then the ACI 318-19 method. It was noted, however, that all three methods were not able to fully capture the superior confinement effect provided by the five-spiral reinforcement.

Multi-spiral transverse reinforced columns have been shown to outperform conventional rectilinear tie reinforced columns in seismic performance. This thesis intends to examine the flexural behavior of multi-spiral reinforced columns, particularly, the five-spiral transverse reinforcement for square columns. In the first phase, a method to determine the flexural capacity of five-spiral reinforced columns, which considers the confinement effect of the five-spirals, was introduced. Five small-scale columns were tested under increasing eccentric axial loading to validate the predicted axial-moment interaction of the five-spiral reinforced columns. In the second phase, large-scale flexure-critical five-spiral columns and equivalent conventional rectilinear tied columns were tested under low (0.1fca'Ag) and high (0.3fca'Ag) constant axial loads and subjected to double-curvature lateral cyclic loading. Test results showed that the five-spiral reinforced columns obtained higher flexural strength, superior ductility, larger drift capacity, and better equivalent damping ratios than counterpart conventional rectilinear tie reinforced columns, despite having 16% to 29% less transverse reinforcement. In addition, it was shown that code-based calculations of nominal moment strength can conservatively estimate the actual moment strength of five-spiral reinforced columns. On the other hand, among the existing code-based methods used in calculating the expected maximum moment of five-spiral columns, the Caltrans SDC 2019 method provided the most accurate prediction of the maximum flexural strength, followed by the AASHTO 2017 method, then the ACI 318-19 method. It was noted, however, that all three methods were not able to fully capture the superior confinement effect provided by the five-spiral reinforcement.