// CORE OBJECTIVE:With regard to the expansion of the use of carbon fiber reinforced polymer (CFRP) in strengthening civil engineering structures due to its high positive points (like high tensile strength and low thickness) as well as its weaknesses in high temperatures especially in buildings and weak points of existing thermal insulators, the experiments mentioned in this article have been carried out to investigate the post-fire conditions of CFRP retrofitting systems using the externally bonded reinforcement technique which resulted from the need to use insulation for this type of reinforcement system to improve its heat performance, as well as the weak points of common insulations. In the first phase, 12 samples of reinforced concrete (RC) beams strengthened with externally bonded carbon fiber reinforced polymer (UD200) were heated at 400 °C, 500 °C, 600 °C, and 800 °C and loaded after cooling, then they were compared with the results of the second phase of the tests which have been explained completely, consisting of 11 RC beams strengthened with CFRP having exactly the same properties as those in the first phase. They were also thermally insulated with intumescent paint that had some advantages like low thickness (1.1 mm) and the speed and ease of implementation and restoration. These results have clearly shown that the new insulating layer not only can maintain the positive feature of common insulations, but also unlike other common insulators, does not add to the thickness of the specimens. Moreover, the application of the intumescent paint both increased the performance of the specimens at high temperatures and covered the weaknesses of CFRP reinforcement system against heat so that the CFRP sheets unlike the ones on the non-insulated specimens did not completely disappear at the highest temperature.

// CORE OBJECTIVE:Inclusion of fibers can mostly enhance the mechanical properties of concrete; however, the role of those in reinforced concrete beams wherein the interaction between concrete, steel reinforcement, and fibers is crucial can be different. This paper provides an experimental study to evaluate the residual behavior of macro fiber-RC beams exposed to high temperatures. Thirty-six scaled reinforced concrete beams were designed and fabricated according to the ACI 318 criteria and requirements, subjected to high temperatures up to 800 °C. In this investigation, mechanical and deformation properties of heated RC beams, failure patterns, and confinement role of fibers were examined, discussed, and compared with non-heated specimens. This investigation indicated, adding steel fibers noticeably improved the residual bearing capacity and bond interaction between steel bars with concrete at high temperatures. Hence, this value for RC beams reinforced with steel and hybrid-synthetic fibers at 800 °C was 65% and 48% of their initial capacity, respectively; however, for plain concrete was about 40%. Moreover, the transformation of failure patterns depended on the type of used fibers and experienced temperatures.