Lateral Behavior of Columns With High-Strength Steel Coiled Strip Confinement

This paper presents the experimental investigation of the behavior of square reinforced concrete columns with high-strength (100 ksi [690 MPa]) steel coiled strips as embedded confinement reinforcement under reversed-cyclic lateral loading and constant axial compression load. Six full-scale specimens (20 × 20 in. [508 × 508 mm] cross section) with the following vari¬ations were tested: confinement type (strip or reinforc¬ing bar), layout (hoops and ties, spirals), and reinforce-ment ratios. The strip-confined specimens had similar peak strengths as a specimen confined by reinforcing bar ties, and this strength exceeded analytical predic¬tions. The stiffness of the strip-confined specimens was greater than the reinforcing-bar-confined specimen. In accordance with the American Concrete Institute’s Acceptance Criteria for Moment Frames Based on Structural Testing (T1.1-01), all specimens met the cri¬terion that the lateral load at 3.5% drift was not below 75% of the peak. Strip-confined specimens demonstrat¬ed improved residual strength behavior relative to the reinforcing-bar-confined specimen. Overall, the study demonstrated the promise of steel strip confinement for reinforced concrete columns in seismic regions.