Seismic performance of large-scale rectangular reinforced concrete bridge columns with multi-spiral reinforcement

Multi-spiral rectangular column is composed of two central interlocking large spirals that are interlocked with four small spirals in the corners to match a rectangular cross-section. Compared to conventional tied column, the multi-spiral column can provide better confinement and its spiral cage can be automatically fabricated and pre-assembled in a factory. Two large-scale rectangular bridge columns were constructed and tested in this study to examine the constructability of multi-spiral reinforcement and the cyclic performance of columns subjected to strong-axis cyclic loading. The test program was also served as a pioneering demonstration of the new bridge column system to boost construction automation that was recently applied to a highway bridge construction project in Taiwan. Test results indicate that the multi-spiral column exhibits superior ductile behavior compared to the conventional tied column, even though the former has only 73% of the total weight of transverse reinforcement of the latter. The parameters of the smooth hysteresis model identified from the test results further indicate that the multi-spiral column can very closely imitate the hysteresis behavior of the conventional tied column despite its slightly greater stiffness degradation. In addition, incremental dynamic analysis of two idealized bridges with conventional tied column and multi-spiral column show that, when the former bridge reached damage index, DI = 1.0 (i.e. having 20% strength deterioration) at S_a(T_n) = 39.4 m/s² for far-field ground motions and at S_a(T_n) = 16.4 m/s² for near-fault ground motions, the corresponding DIs of the latter bridge are approximately 0.74 and 0.71, respectively, even without strength deterioration.