This paper presents the results of an experimental study that was conducted to investigate the postfire seismic behavior of reinforced concrete columns. Five full-scale, flexure-critical code-complying (e.g., ACI 318-14) cast-in-place reinforced concrete columns were tested to failure under a constant axial load and reversed cyclic lateral displacements after being exposed to an ISO-834 standard fire for 30, 60, and 90 min. Other than the effects of the duration of the fire exposure, the effects of the thickness of the concrete cover (25 and 40 mm) on the structural performance was also investigated for the short fire exposure duration (30 min). The responses of the columns were analyzed in terms of lateral load-displacement relationships, ductility, stiffness, energy dissipation capacities, and residual displacements. The test results indicated that the fire exposure reduced the lateral load capacity of the columns, whereas the deformability capabilities were found to be satisfactory in terms of a structural response. It was also observed that the thickness of the concrete cover had only a slight influence on the postfire seismic behavior of the columns. Furthermore, a numerical study was conducted to predict the load-displacement response of the fire exposed columns. The comparison of the experimentally and numerically obtained load-displacement relationships indicated that the principles of structural mechanics usually applied to conventional columns are also valid for the columns exposed to fire.

As the first study reported in the literature on the axial behavior of noncircular high-performance fiber-reinforced cementitious composite (HPFRCC) members externally jacketed by fiber-reinforced polymer (FRP) sheets, the aim of this paper is to experimentally identify the axial behavior characteristics of these members under compression. The test results of 21 specimens showed that the axial and lateral deformation characteristics of FRP-jacketed HPFRCC members are significantly different from those of FRP-confined conventional concrete members. Small voids in HPFRCCs due to the presence of fine aggregates and reduced crack widths due to the contribution of steel fibers limit the transverse deformations remarkably until the axial strain value is approximately 0.0035. The test results show that the dilation ratio increases after the axial strain reaches this value. Then, the external FRP jacket begins to noticeably affect the behavior, resulting in a significant improvement in the axial strength and deformation capacity. However, since the external FRP jacket is activated after relatively large axial strains, significant strength degradations can occur before the FRP jacket provides an effective contribution. As the stiffness of the FRP jacket increases, the strength degradation experienced before the activation of the FRP jacket decreases. Furthermore, the predictions of five available models that were developed for modeling the axial behavior of FRP-confined concrete are examined through comparisons with test results.

In this study, four full-scale reinforced concrete columns were built replacing 50% of natural coarse aggregates in concrete mix by recycled aggregates. Three of the columns were exposed to standard ISO-834 fire for 30, 60 or 90 minutes, while the reference specimen was not exposed. Sixty days after fire exposure, the columns were tested under constant axial load and reversed cyclic lateral displacements simulating earthquakes. Test results are evaluated in terms of lateral load capacity, ductility, stiffness and energy dissipation. In addition, an analytical study was conducted to predict the lateral load-displacement response of fire-damaged columns built with recycled aggregates.