Study On The Forming Method Of Additional Ribs Of FRP Bars And The Effects On Anchorage Performance

The bond performance between FRP bars and concrete is the basis of the two kinds of materials working together,which affects the failure mode,bearing capacity,crack width and deformation capacity of FRP reinforced concrete members,and it is a critical factor to determine whether FRP bars can be a substitute for traditional steel bars in concrete structures.However,due to the anisotropy of the material,small elastic modulus and low shear strength,the bond strength of FRP bars is less than that of ordinary steel bars.A large number of research results show that,under the condition of short bond length,the bond failure between FRP bars and concrete is usually caused by the debonding of ribs of FRP bars,because the shear strength of FRP rib is generally lower than that of concrete.Aiming at the problem of poor anchoring performance of FRP bars,a new type of anchoring method-additional rib anchorage,was proposed in this paper,and a series of experiments were carried out to investigate the anchorage performance.The main content includes the following aspects:First,the interface shearing behavior between FRP bars and additional ribs with different forms were studied.The interface shear strength between FRP bars and additional ribs was obtained and compared with that of FRP bars and concrete.The effects of additional ribs on the ultimate tensile strength of FRP bars were tested.The results indicate that the shear strength between additional ribs and FRP bars is much higher than that of FRP bars and concrete,and additional ribs can be used to enhance the anchorage performance of FRP bars.Although the forming of additional ribs cause a certain degree of damage to the ultimate strength of FRP bars,the degree of damage is in an acceptable range,and with the optimization of forming process of additional ribs,the degree of damage can be further control.Then,the effects of the number of additional ribs on bond properties of BFRP bars and CFRP bars under different bond lengths were studied based on tests of 42 pull-out specimens.Studies showed that the anchorage performance of FRP bars was obviously improved with the existence of additional ribs,and the anchorage performance of CFRP bars with higher strength and elastic modulus is better than that of BFRP bars.Next,the influence of different distribution and arrangement of additional ribs on anchorage performance of FRP bars was studied based on two kinds of bond length using 20 CFRP bars.The results show that the anchorage performance of FRP bars is better when additional ribs are located at the back in anchorage length,and smaller spacing is more conducive to the enhancement of additional ribs on anchorage performance.Finally,the relationship between average bond strength and bond length was obtained based on data simulation of experimental results.The basic anchorage length of CFRP bars used in the experiment was calculated,and compared with that of CFRP bars anchored with additional ribs.The results show that additional ribs have a significant effect on the anchorage performance of FRP bars,and the basic anchorage length of FRP bars was obviously reduced by additional ribs.