Seismic behavior and design method of seawater sea-sand concrete reinforced with GFRP and five interlocking spirals

Seawater sea-sand concrete (SWSSC) columns reinforced with GFRP brings great benefit to island construction but its seismic behavior remains unclear. This paper provides an experimental study on the seismic behavior and design method of SWSSC columns reinforced with GFRP and five interlocking spirals. Seven columns with different stirrup configurations, spirals spacings, outer diameter of conner spirals, axial compression ratios and shear-span ratios were designed and tested under simulated seismic loading. Their failure modes, hysteretic responses, skeleton curves, stiffness degradations, ductility factor and energy dissipations were all attained and discussed in detail. The results show that the SWSSC column confined with interlocking multi spirals has better seismic resistance than that with composite rectangular stirrup. Moreover, the increase of shear-span ratio and outer diameter of conner spirals both improve the ductility and therefore enhance the seismic resistance. In contrast, the increase of axial compression ratio and spiral spacing have inverse impact on seismic resistance enhancement. Based on the testing results, a novel approaching method was also proposed to evaluate the shear bearing capacity of oblique section and the average prediction error was within 1.30% through verification with the test results.