Rapid Strengthening of Short-Span Reinforced Concrete T-Beams with Unbonded Carbon Fiber–Reinforced Polymer Straps

The ability to rapidly strengthen reinforced concrete structures is critical for military and disaster response applications, where conventional strengthening techniques may be impractical due to time, logistical, or technical constraints. This study evaluates the effectiveness of unbonded carbon fiber–reinforced polymer (CFRP) straps installed with mechanical anchors as a rapid strengthening technique for simply supported short-span reinforced concrete bridges. An experimental program was conducted on six 6-m-long reinforced concrete T-beams, including two control specimens and four strengthened beams, incorporating single or double layers of CFRP straps and variations of a custom-designed mechanical anchorage system. The introduction of tensioners improved load sharing by promoting a more uniform strain distribution among the CFRP straps. Experimental results demonstrated that unbonded CFRP strap systems can significantly enhance flexural capacity, achieving strength increases of up to 22% for beams strengthened with a two-layer CFRP configuration. Serviceability was also improved, with reduced deflections at high load levels and visibly delayed crack formation and propagation. Although no intentional prestressing was applied, posttest analysis indicated that beam elongation induced significant additional tensile forces in the CFRP straps during loading. A numerical model was developed to predict the load–deflection response of the strengthened beams and showed reasonable agreement with the experimental results. Overall, the study confirms that unbonded CFRP straps combined with mechanical anchorage provide a viable and practical solution for the rapid strengthening of short-span simply supported concrete T-beams, offering a promising alternative to bonded CFRP systems in time-sensitive applications.