Performance of axially loaded square RC columns with single/double confinement layer(s) and strengthened with C-FRP wrapping under close-in blast

Abstract

Very recently a new variant of reinforced concrete (RC) columns confined with a double layer of transverse steel has been introduced by researchers and investigated its performance under axial compression and seismic loading. Analysis of blast performance of such columns is of considerable interest. Most of the columns in a building structure are found to be of square or rectangular cross-section. Being axisymmetric, the circular columns perform better than square/rectangular ones under impulsive loadings. The stability of a structure supported mainly on columns subjected to such loadings depends upon the performance of the columns. Therefore, it is important to enhance the response of supporting RC compression members of square or rectangular cross-sections of a structure subjected to high intense loadings. In this research work, one 3000 mm long, 300 mm × 300 mm square RC column with conventional transverse steel carrying an axial working load of 950kN subjected to 82 kg-TNT-equivalent close-in blast loading at scaled distance 1.0 m/kg1/3 tested experimentally has been first analyzed using the high-fidelity dynamic computer code, ABAQUS/Explicit-v6.15. For comparison, another singly confined concrete column with seismic reinforcement over its entire length is also analyzed. By comparing the numerical results with the experimental results in the open literature, the accuracy of the numerical model is verified. To improve the response, doubly confined RC columns having outer transverse confining steel stirrups of square and inner ones’ diamond/circular geometry with different combinations of stirrup spacing have been considered and investigated. The columns are of the same area of compression steel and carry the same axial load (950kN). Carbon-fiber-reinforced-polymer (C-FRP) wrapping of 2 mm thickness is also considered and modeled using Hashin’s damage initiation criteria and energy-based damage evolution to investigate the blast resistance of the columns. Blast performance in terms of displacement, damage dissipation energy, concrete crushing, and cracking are compared and discussed.