Dynamic evolution pattern of carbon‐fiber reinforced polymer strain in prestressed carbon‐fiber reinforced polymer constrained concrete cylinders under axial compression

Abstract Under axial loading, the strain of prestressed carbon fiber reinforced plastic (CFRP) varies as vertical load increases. To investigate the dynamic evolution of CFRP strain in prestressed CFRP‐constrained concrete cylinders, this study designs 12 columns, considering variables such as the number of CFRP layers, prestress levels, and unilateral versus symmetrical tensioning, and conducts axial compression tests to analyze CFRP strain behavior. Test results show that before loading, CFRP strain decreases from the anchorage's near end to the far end. Upon axial compression, the strain evolution reduces from the far end to the near end, transitioning from uneven to uniform strain and transforming the uneven confining pressure into uniform pressure along the column. Increasing CFRP thickness prolongs the effective action time of initial prestress and delays the critical transition point. Higher prestress levels lead to more gradual strain changes at various locations, extending the effective duration of initial prestress. With four layers of CFRP, the overall change is more gradual. Symmetrical tensioning produces a more uniform initial strain distribution than unilateral tensioning, shortening the transition time from uneven to uniform strain. Additionally, based on experimental results, the formula for calculating confining pressure stress in prestressed CFRP‐reinforced concrete columns was revised, and a new formula for calculating confining pressure stress under axial load was introduced. The developed calculation model aligns closely with experimental data, providing reliable information for analyzing and modeling prestressed CFRP‐constrained concrete cylinders under axial compression. Highlights The CFRP strain transitions from nonuniform to uniform under axial loading. More layers and prestress delay strain shifts. A new confining pressure formula is revised and proposed in this paper.