Research On The Active Crack Control Method Of Reinforced Concrete Beam And The Bending Properties Of Its Composite Structure

The paper based on active crack control method.The high performance cement-based composite micro steel fiber concrete(micro steel fiber reinforced concrete,referred to as MSFRC)arranged in high-strength reinforced concrete beam tension edge.An excellent crack resistance of functionally graded composite beam is developed.The traditional passive crack control is the normal use of the stage of the application of control.The formation and development of cracks have no effect on the performance of the structure.Active crack control is to delay the appearance and development of cracks in the structure,and even does not produce cracks,to meet the requirements of crack resistance performance.According to the idea and concept of functionally gradient materials(FGM),the MSFRC material with high tensile strength and good deformation resistance is arranged on the tensile edge of the reinforced concrete structure.The FGM active control of crack and delay the development of crack.The paper based on the strength theory and fracture mechanics were designed functionally graded composite beam fiber with different thickness of enhancement resistance cracking layer,and the composite beams for flexural test.According to the bending test of the fiber anti crack enhancement layer of crack initiation and crack and the control effect of the process of development,determine the optimum fiber layer thickness of the functionally graded beams,the composite structure has excellent anti crack performance at the same time taking into account the economy.In this paper,the following conclusions are obtained by the theoretical analysis,the basic mechanical properties test of the material,the flexural performance test and the numerical simulation of the functionally graded composite structure:(1)The mechanical properties of the cement composites were significantly improved by the micro fiber volume fraction of 6%.MSFRC compared with ordinary concrete,the compressive strength increased by 65.9%,axial compressive strength increased by 30.9%,the flexural strength improves the 227.6%,axial tensile strength increased by 25.6%,the splitting tensile strength increased 73.8%,and elastic modulus increase amplitude was 9.3%.Compared with the brittle failure of ordinary concrete,the failure process of MSFRC is typical of plastic failure,which significantly improves the failure mode of the cement materials.(2)According to the fracture mechanics,the stress factor of the internal eccentric crack is smaller than that of the edge crack,a functionally graded composite beam with MSFRC fiber layer thickness of 50mm(hf50)was designed;Based on the strength theory and the relationship between the MSFRC layer thickness and the cracking moment,a functionally graded composite beam with MSFRC fiber layer thickness of 83.3mm(hf83)was designed.Compared with ordinary reinforced concrete beams,the crack bending moment of functionally graded composite beams hf50 and hf83 are increased by 88.9% and 127.8% respectively,and the yield bending moment is increased by 19.5% and 34.1% respectively.The first crack in hf50 is an internal eccentric crack,and the crack is developed on both sides of the compression zone and the edge of the tension zone.The first crack in the common beam and the hf83 is the edge crack,and the crack develops with the load to the compression zone.In the early stage of crack growth,the crack width in the hf50 is more effective being control than the hf83,,because of the crack is the internal eccentric crack.When the crack width is 0.1mm,the bearing capacity of the composite beam hf50 is 136.1% higher than the ordinary beam,and is 28.8% higher the than the hf83.Late stage of crack development,the crack control effect of MSFRC crack resistance enhancement layer is remarkable.Under the yield load of PT beam,the width of 5 main cracks in pure bending section is more than 0.20 mm.The maximum principal crack width is 0.26 mm.The hf50 and hf83 only 1 to 2 main crack width is greater than 0.15 mm under the yield load.The maximum principal crack width of hf50 is 0.18 mm.The maximum principal crack width of hf83 is 0.19 mm.Fiber reinforced anti crack layer can effectively improve the stress state of the steel bar,and reduce the stress of the reinforced concrete structure after cracking.There is no significant difference in the effect of hf50 on the stress condition of the reinforcing bar in hf83.(3)In this paper,the ANSYS finite element software is used to simulate the composite beams,and the results show that the finite element analysis is consistent with the experimental results.The paper properties of the functionally graded composite structures are excellent,and it is a kind of new structure,which is worth exploring and studying.It has a certain application prospect in practical engineering.