Experimental investigation on flexural response of post-tensioned concrete girders strengthened with near-surface mounted carbon fiber reinforced polymers

High-strength steel used in post-tensioned (PT) concrete structures significantly enhances serviceability and load-carrying capacity. However, without adequate protective measures, it is prone to corrosion, posing a critical risk to aging infrastructures. Combined with low residual prestress and heavy loading, this can precipitate premature failure. This study explores the effectiveness of Near Surface Mounted (NSM) Carbon Fiber-Reinforced Polymer (CFRP) systems for strengthening PT girders, leveraging their high strength-to-weight ratio and corrosion resistance. Experimental tests were conducted on four reduced-scale PT girders: two as-built (unstrengthened) specimens with different initial prestress levels and the others with equivalent prestress levels strengthened with NSM CFRP strips. Flexural behavior was evaluated at both global and local scales, analyzing force–displacement responses and load-induced strains in the CFRP strips under both monotonic and cyclic loading. Results reveal that NSM CFRP strips increased the load-carrying capacity by up to 44% compared to the as-built configuration. Analytical parametric analysis was conducted by varying the main mechanical properties of the strengthened girders. This research provides a robust framework for assessing and maintaining aging PT structures, highlighting the superior enhancement of flexural strength over ductility offered by NSM CFRP systems. • NSM CFRP system is investigated for strengthening PT concrete bridge girders. • The system increases flexural capacity by up to 44% with reduced ductility. • CFRP strips reached 57%–63% of their ultimate tensile strain with no debonding. • Analytical moment–curvature study supports experimental results (small model error). • Higher concrete strength increases ultimate bending moment while reducing ductility.