Axial load behavior of reinforced concrete columns with high-strength steel coiled strips as confinement

This paper experimentally investigates the axial load behavior of square reinforced concrete columns confined using dual-phase high-strength (100 ksi [690 MPa] yield strength) steel coiled strips. Two phases of testing were conducted on reduced-scale specimens (8 × 8 in. and 10 × 10 in. [203 × 203 mm and 254 × 254 mm]). Varied parameters include con¬finement type (strip versus reinforcing bar), confine¬ment reinforcement ratio, confinement layout (hoops and ties, single spiral, two spirals), and strip anchor¬age. Although the reinforcing-bar-confined columns demonstrated better postpeak residual strength and ductility, important findings include the following: strip-confined columns had peak strengths exceeding the nominal axial strength predicted by code, strip-con¬fined columns were able to achieve similar normalized peak strengths and prepeak stiffness as columns with reinforcing bar hoop confinement, two strip spirals are necessary to achieve the desired postpeak residual strength and ductility for an eight-bar layout, and strip spirals and hoops may provide better restraint against buckling of corner bars compared with reinforcing bar hoops.