Monotonic and cyclic axial compressive properties and modeling of basalt FRP-retrofitted predamaged short columns

This study investigated the monotonic and cyclic axial compressive properties of predamaged concrete retrofitted using externally bonded basalt fiber-reinforced polymer (BFRP) sheets. Plain concrete cylindrical specimens were manufactured and predamaged under three axial compressive loading levels corresponding to peak strength, 10%, and 20% strength degradation after the peak strength of the plain concrete. Specimens for undamaged series were retrofitted with 2-, 4-, and 6-layer BFRP sheets, while the predamaged specimens were retrofitted with 2- and 4-layer BFRP and all the specimens for the cyclic loading series were retrofitted with 4-layer BFRP. Then these BFRP-retrofitted predamaged cylinders were retested under monotonic and cyclic compressive loadings to assess their compressive behavior. For BFRP-retrofitted specimens under monotonic compressive loading, the compressive strength and deformation capacities of the predamaged concrete cylinders were improved remarkably after the retrofitting. However, the initial elastic modulus and compressive strength of the BFRP-retrofitted predamaged cylinders decreased by 38%-55% and 7%-15%, respectively, compared to the retrofitted undamaged cylinders. Under cyclic compressive loading, the energy dissipation capacity of the BFRP-retrofitted concrete decreased gradually with an increase of the predamage level. Based on the test results and existing experimental data collected from the literature, peak strength, ultimate strain, and monotonic stress-strain relationship were newly defined for BFRP-retrofitted predamaged concrete considering the influence of the predamage level. Furthermore, based on the existing cyclic stress-strain model of FRP-retrofitted concrete, an equation for residual strain was introduced, and a modified cyclic compressive stress-strain model was established for BFRP-retrofitted damaged concrete.