Abstract

Multi-spiral transverse reinforcement has been shown to provide superior seismic performance than conventional rectilinear tie reinforcement. This research intends to investigate the flexural behavior of the five-spiral transverse reinforcement configuration for square concrete columns. Large-scale flexure-critical five-spiral columns and counterpart conventional tied columns were tested under low (0.1fca′Ag) and high (0.3fca′Ag) constant axial load and subjected to double-curvature lateral cyclic loading. Test results showed that with 16%–29% less transverse reinforcement, the five-spiral columns displayed superior flexural strength, higher ductility, and larger drift capacities than the counterpart conventional tied columns. The five-spiral columns also showed improvements in the seismic capacity of the column in terms of energy dissipation. Furthermore, it was determined that the nominal moment strength could conservatively compute the actual moment strength of five-spiral columns. However, the five-spiral columns showed a higher flexural overstrength from the nominal moment than the counterpart tied columns. From the existing code methods examined in calculating the expected maximum moment, the Caltrans SDC 2019 method provided the best prediction of the maximum flexural strength of the columns, followed by the AASHTO 2017 method, then the ACI318-19 method. All three methods, however, could not fully capture the superior confinement effect of the five-spiral reinforcement.

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