نوع مقاله : پژوهشی
نویسندگان
دانشکدهی مهندسی عمران، دانشگاه فردوسی مشهد
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Concrete behavior in structural members is considerably affected by cracking due to tensile loads. The initiation of cracks is influenced by the properties of concrete under tensile stresses. The development of cracks plays a significant role in the nonlinear analysis of concrete structures. The cracking process in tension starts at a relatively low tensile strain, causing plain concrete to exhibit a gradual softening behavior. This softening behavior is magnified by the tension stiffening phenomenon in reinforced or strengthened concrete members. Very few studies can be found concerning the behavior of FRP (Fiber Reinforced Polymers)-strengthened reinforced concrete (RC) elements. Tension stiffening is an effective parameter in the behavior of externally bonded FRP sheets in tension. This parameter influences the crack width, spacing between cracks and the stiffness of the tensile members. In order to study the effect of tension stiffening of the FRP sheets, 16 concrete specimens were manufactured and tested. Each concrete specimen included 2 concrete prisms bonded together with adhesive, and 2 or 4 layers of either CFRP (Carbon Fiber Reinforced Polymers) or GFRP (Glass Fiber Reinforced Polymers) sheets. The dimensions of each concrete prism were 500$times$ 80 $times$ 40 mm. Two concrete mixtures with the compressive strengths of 25 MPa and 40 MPa were used for different specimens. The specimens were tested under tension through the application of tensile force on the FRP sheet ends. The stress-strain relationships of different specimens were compared with each other in order to evaluate the effect of tension stiffening of the strengthened members. The ratios of the effective modulus of elasticity of the strengthened concrete members, E$_{eff}$, over the modulus of elasticity of FRP sheets, $E_{frp}$ , were measured. Based on the test results, reduction of the FRP ratio in sections increased the effect of the tension stiffening of the members. The ratio of E$_{eff./}$E$_{frp}$ in the case of the GFRP sheet was larger than that of the CFRP sheet compared to the CFRP sheets. Also, the increase of concrete strength from 25 to 40 MPa increased the tension stiffening effect.
کلیدواژهها [English]
)