The majority of experimental studies investigating the stress-strain behavior of square concrete columns confined with carbon fiber-reinforced polymer (CFRP) composites have focused largely on unreinforced columns of small size. Research on the influence of larger cross section, height, internal steel reinforcement, and initial damage on the axial strength and compressive behavior of CFRP-confined square reinforced concrete (RC) columns is, however, limited. To address such knowledge gaps, this paper presents the results of an experimental investigation on the axial stress-strain behavior of 34 larger-sized square-sectioned RC columns confined with CFRP composite wraps. The primary test variables were (1) cross-sectional dimensions, (2) volumetric ratio of internal hoop steel reinforcement, (3) number of layers of CFRP wrap, (4) nature of loading (i.e., monotonic and cyclic), and (5) damage level before CFRP wrapping. The experiments showed the CFRP wrap to considerably enhance the axial strain ca...

For the seismic design of fiber reinforcement polymer (FRP) confined reinforced concrete (RC) columns, the development of an accurate axial stress-strain model that considers cyclic compression is necessary. In light of such a demand, this paper presents a cyclic axial stress-strain model for FRP-confined RC square columns. The model is informed from physical observations and test measurements obtained from an experimental investigation reported in the companion paper, in which FRP-confined square unreinforced and reinforced concrete columns of larger size under varying cyclic axial compression patterns were tested. In the current paper, the proposed stress-strain model is presented and it consists of three main components, namely (1) a monotonic stress-strain model to describe the envelope curve, (2) a polynomial expression for the unloading path, and (3) a straight line for the reloading path. The influence of internal longitudinal and hoop steel reinforcement is also considered in the proposed ...

Numerous reinforced concrete frames have collapsed in major earthquakes because of severe local damage at the ends of columns. Many of these frames were designed and built according to out-of-date codes in which earthquake loads were either not taken into account or not sufficiently considered. To date, there are still a large number of such nonductile RC frames serving in the potential earthquake regions across the world. Thus, there is an urgent need for preearthquake retrofitting and strengthening of these RC frames to achieve desirable seismic performance. In this paper, a total of 11 large-scale cantilever square RC columns were constructed and nine of them were retrofitted with carbon fiber-reinforced polymers (CFRP) wraps at the column ends. These columns were then tested under combined constant axial compression and cyclic lateral displacement excursions. The variables in the tests included the axial compression ratio, the thickness of CFRP wraps, and the column size. The failure modes, hysteretic responses, energy dissipation, stiffness degradation, and equivalent viscous damping ratio of the tested columns were presented and interpreted. The test results showed that the ductility and energy dissipation capacities of nonductile RC columns can be significantly improved with the potential plastic hinge regions of the columns being retrofitted. The retrofitted columns were found to exhibit satisfactory seismic performance even when tested under an ultrahigh axial compression level (i.e., 0.75). Based on the test results, the degradation of the effective stiffness and the unloading stiffness of the columns was discussed and empirical equations were proposed through nonlinear regression analysis.

The majority of experimental and analytical investigations on the stress-strain behavior of rectangular concrete columns externally confined with carbon fiber–reinforced polymer (CFRP) composites have concentrated largely on unreinforced concrete columns of small size. However, research investigating the influence of larger cross-sectional size and internal steel reinforcement on the stress-strain behavior of CFRP-confined rectangular RC columns under axial compression loading has been limited. Therefore, the first part of this paper aims to present the results of experimental tests on 28 larger-sized rectangular plain and reinforced concrete (RC) columns confined with CFRP wraps. The primary test parameters were (1) cross-sectional size and aspect ratio; (2) number of CFRP composite layers; (3) volumetric ratio of hoop steel reinforcement; and (4) nature of loading (i.e., monotonic and cyclic). The experiments showed that the stress-strain curves of the monotonically loaded CFRP-confined columns exhibited a softening second branch followed by an ascending or almost flat third branch. All the confined columns experienced a significant enhancement in axial strain but only a slight enhancement in axial strength. An important finding of the study was that the internal longitudinal and hoop steel reinforcement influenced the shapes of the axial stress-strain envelope curves, the unloading and reloading paths, and the plastic strain values. A model was finally proposed for predicting the ultimate strength of CFRP-confined rectangular RC columns. The performance of the proposed model was validated against the results of current and existing experiments.

The energy dissipation bar has been proven to be an effective way to improve the lateral strength and the seismic capacity of the precast segmental bridge column. To date, however, investigations on how the main design parameters affect the residual drift of such bridge columns are quite limited. Focusing on this research gap, a novel numerical simulation method was proposed in this article to investigate the influencing factors of residual drift of precast segmental bridge columns with energy dissipation bars. First, the refined fiber element model was developed based on the OpenSees software package, considering the bond slip phenomenon at the column end and the boundary condition at the interface between the two adjacent segments. Then, the proposed numerical model was validated by comparing the simulated hysteretic behavior of the precast segmental bridge columns with available experimental data. After that, cyclic analyses were performed on 288 precast segmental bridge column models with different design parameters. Four important influencing factors were investigated, including the post-tensioning force, gravity load, energy dissipation bar ratio, and shear span ratio. According to the analysis results, some suggestions were provided for the practical design procedure of the energy dissipation bar reinforced precast segmental bridge columns.

In the present study, natural fiber (i.e., flax fiber) reinforced epoxy (FFRP) plates and tubes were prepared with a filament winding process. FFRP tubes with 150-mm diameter were filled with self-compacting concrete and tested in terms of static and cyclic compressive properties. Basalt fiber–reinforced epoxy (BFRP) plates and tubes were prepared and tested for comparison. The FFRP plate possesses a nominal tensile strength and modulus of 333 MPa and 48.5 GPa, respectively, and exhibits a nonlinear tensile strain-stress curve. Compared with the static tensile modulus of the FFRP plate, the strain modulus–controlled low-frequency cyclic test steadily decreases with the number of load-unload cycles as a result of cumulative damage, and the ultimate stress is also reduced by 36%. According to the static compression results, FFRP tubes exhibit a notable confinement effect on concrete cylinders. The confinement effectiveness coefficient determined by the static compression test ranges from 4 to 7 for ...