This study presents the flexural performances of hybrid beams where glass fibre reinforced plastic (GFRP) box profile, concrete, steel or GFRP bars were used together. By conducting flexural tests on beams of varying properties produced for this purpose, the minimum reinforcement effects in GFRP profile-concrete beams were experimentally presented. Beam series of two sizes, as 74-74-500 mm small beams and 100-100-1,500 mm large beams, and varying combinations were produced. In addition, some properties of GFRP box profiles were improved. Following the tests conducted on small beams, the number of large beam samples was reduced and while steel bars were used in some beams, GFRP bars were used in others. The hybrid beams were compared with reinforced concrete beams have the same dimensions in large beams. On the basis of the results obtained from the tests it was determined that the flexural performances of steel reinforced hybrid beams increased at a higher level. Flexural strength of the improved hybrid beams increased by about two times compared to the classical reinforced concrete beams. Fracture toughness of the hybrid beams improved 53%.

While Fibre-Reinforced Plastics are lightweight, show a high tensile strength, and have no issue with corrosion, they are unfortunately brittle and perform poorly against temperature. Therefore, it is important to know the time and magnitude of the temperature reaching the bars in the high-temperature effect of FRPs produced in the form of bar in reinforced concrete structural elements in concrete. This study set out to examine the time and temperature values of glass fiber reinforced polymer (GFRP) reinforced concrete under high-temperatures. The effects of concrete cover thickness and concrete strength on temperature transfer were researched experimentally. GFRP bars were placed in specimens prepared in three concrete strengths and three different concrete cover thicknesses (20-40-60 mm) exposed to temperature, and temperature-time graphs were created by measuring bar temperature, concrete surface temperature and ambient temperature. The critical time to a glass transition temperature, and optimum cover thickness of GFRPs according to concrete strength and concrete cover thickness were discussed. The study results appeared to indicate that the thickness of the concrete cover is very effective in protecting the bar against temperature in reinforced concrete structural elements, as concrete strength, itself, has only a limited effect.

There are serious concerns about the preference of Fiber Reinforced Polymer (FRP) bars, which are widely used in buildings, in reinforced concrete structures due to their sensitivity to high temperatures. Especially in cases where the glass transition temperature of FRPs exceeds, losses occur in the mechanical and physical properties of FRP bars. Fire insulation materials used in reinforced concrete structures are of great importance in protecting the building elements against high temperatures. Insulation materials protect concrete and rebars against high temperatures and prevent strength reductions. In this study, the effects of different fire insulation materials and concrete strength on temperature transitions in FRP reinforced concrete structural elements were determined by experimental studies. The protection performances of the concrete and the rebars in the concrete against the effects of temperature were investigated. The study was carried out in 500 oC environments that can reach the glass transition temperature (80-110 oC) of FRP bars. Ambient temperatures, concrete surface temperatures and reinforcement surface temperatures in the concrete were measured depending on time with the experimental setup created. As a result of the study, it was determined that fire insulation materials are more effective than concrete strengths. In the effect of ambient temperature on the concrete surface, while the rock wool allowed a temperature transition of 13%, this value was 22% in glass wool and 26% in red drywall.