Study On Impact Resistance Of Carbon Fiberreinforced Concrete Beams

As the most important building material,concrete is made into reinforced concrete and prestressed concrete together with steel reinforcing bars and prestressing steel strands.However,due to the brittle nature and poor fracture energy absorption capacity of concrete,although reinforced concrete and prestressed concrete can be widely used under static conditions,they can no longer withstand extreme loading conditions.In order to overcome these shortcomings of concrete under impact and explosion loads,fiber textiles,short fibers,and external fiber-reinforced polymer can be used to improve the impact resistance of concrete.Moreover,the carbon fiber-reinforced concrete（CFRC）,in which carbon fibers are dispersed uniformly,has excellent impact resistance and multifunction such as electrical conductivity,strain self-sensing behavior,etc.The main work of this paper is as follows:The flexural behavior of CFRC beams under impact loading was studied herein.A modified molding process was proposed for manufacturing CFRC beams to achieve the uniform dispersion of 20-mm long carbon fibers in the concrete matrix.Different fiber volume fractions and impact velocities were considered.Their effects on the tensile and compressive strain,distribution of vertical displacement,and acceleration,energy absorption,and dynamic increase factor（DIF）were analyzed to investigate the mechanical properties.The results indicated that the CFRC beams with 0.35%fiber content absorbed the highest energy（about2.3 times that of beams without fibers）.Based on the approximate linear distribution of inertial force along CFRC beams,an equation was deduced to calculate the generalized inertial force.The results indicated that the DIF increased with strain rate,and an empirical equation was proposed to describe the strain rate effect.Based on ABAQUS,a three-dimensional finite element analysis model of CFRC beam was established;and the damage and response of the beam under the impact loading were numerically simulated.The validity of the finite element model was verified by comparing the experimental results.Furthermore,the effects of different carbon fiber volume fractions and impact velocities on the bearing reaction,midspan-vertical displacement,fracture energy absorption capacity,and failure mode of CFRC beams under impact loading were analyzed.The results indicated that the three-dimensional finite element analysis model can more intuitively understand the deformation and damage of carbon fibers and concrete matrix in the process of impact.Under impact velocity of 3 m·s^–1,the energy absorption of CFRC beams increased gradually with the increase of carbon fiber volume fraction.Under the case with the0.80%carbon fiber volume fraction and 12 m·s^–1 impact velocity,the failure mode of CFRC beams changed from bending failure to shear failure;and the energy absorption of beams decreased.Drop-weight impact tests were carried out on plain concrete（PC）beams and CFRC,glass fiber-reinforced concrete（GFRC）and basalt fiber-reinforced concrete（BFRC）beams with the fiber length of 6–8 mm and volume fraction of 0.30%.The flexural behavior and fracture energy absorption of PC beam and fiber reinforced concrete beams were studied.The fracture process of each beam was recorded with a high-speed camera;and the tensile and compressive strain,vertical displacement,and acceleration were extracted and analyzed.The impact force and inertia force of tup were analyzed;the generalized bending load-displacement curves were obtained;and the fracture energy absorption of fiber reinforced concrete beams were calculated.The results indicated that the failure mode of each specimen was typical bending failure;and a vertical main crack was formed.The energy absorption of GFRC beam was the most,which was 88%higher than that of PC beam.The energy absorptions of CFRC and BFRC beam were 43%and 18%higher than that of PC beam,respectively.