Title: Effect of Confinement Using Fiber-Reinforced Polymer or Fiber-Reinforced Concrete on Seismic Performance of Gravity Load-Designed Columns

Author(s): Mohamed H. Harajli and Ahmad A. Rteil

Publication: Structural Journal

Volume: 101

Issue: 1

Appears on pages(s): 47-56

Keywords: bond; column; ductility; fiber-reinforced concrete; seismic; slip; splitting; strength

DOI: 10.14359/12997

Date: 1/1/2004

Abstract:
This paper presents the results of an experimental investigation undertaken to evaluate the seismic performance of reinforced concrete (RC) columns designed for gravity load and confined externally with carbon fiber-reinforced polymer (CFRP) flexible sheets. Other types of confinement including the use of steel fiber reinforcement, or conventional transverse reinforcement to satisfy the minimum requirements of ACI 318-99 in areas of moderate seismic hazard, were also evaluated for comparison. The specimens consisted of 150 x 300 x 1000 mm-long columns projecting outside a stiff column stub. The main parameters included the reinforcement ratio in the columns, the area of CFRP sheets, and the volume fraction of steel fibers. To simulate gravity load design, the column reinforcement in all specimens was spliced at the column base with a splice length of 30db, where db is the bar diameter. All specimens experienced significant slip of the column reinforcement and widening of one single crack located at the column-stub interface. Consequently, most of the column lateral drift was attributed to the fixed end rotation at the column base. Without confinement, the RC columns suffered significant deterioration of bond resistance of the spliced reinforcement, accompanied with considerable reduction in strength and stiffness degradation in the initial few load cycles following yield. Confining the concrete with a relatively small area of CFRP sheets reduced the bond deterioration, considerably increased the energy absorption and dissipation capabilities of the columns, and resulted in effect in significant improvement in seismic performance. Internal confinement using steel fiber reinforcement in the critical region improved performance similar to external confinement with CFRP. While confinement with ordinary transverse steel enhanced the seismic behavior and increased the energy absorption capacities of the columns, it was not as effective as CFRP or steel fiber reinforcement.