Micro Steel Fiber Reinforced Concrete Gradient Composites And Their Structural Cracking Properties

Based on the concept of gradient material,this paper presents a local high-content micro steel fiber concrete gradient composite(Micro Steel Fiber Reinforced Concrete,referred to as MSFRC),and carries out material design and performance test research.Combining the material structure design idea,the concept of locally high-volume microsteel fiber reinforced concrete controlled-fracture gradient composite beam was put forward,and the gradient beam crack characteristics were studied to form a gradient beam design method based on crack control.The numerical analysis is used to simulate and verify the bending performance and crack characteristics of the gradient beams.The main work of the thesis is as follows:(1)The basic mechanical properties of micro steel fiber reinforced concrete materials were tested,and the effects of adding Class I ash and ultra-fine ash to ordinary concrete and micro steel fiber reinforced concrete were compared.(2)According to the concept of gradient composites and local reinforcement design,the mechanical properties of micro steel fiber reinforced concrete gradient composites with different MSFRC gradient layer thicknesses were experimentally studied.The results show that the arrangement of high-content steel fiber reinforced concrete gradient composites within the 1/5 section height of the beam can achieve a comparable reinforcing effect with full-section steel fiber reinforced concrete.The use of local gradient design improves the mechanical properties and further optimizes the gradient composite structure to solve the economic problems caused by the high volume rate.(3)The bondability between steel fiber reinforced concrete and high-strength steel bars was experimentally studied and finite element analysis was performed.Compared with ordinary concrete,the bonding performance between steel fiber reinforced concrete and high-strength steel rebar is significantly improved,and the ultimate bond strength is increased by more than 125.5%.(4)According to the theory of strength and fracture mechanics,the design method of steel fiber reinforced concrete gradient composite structure is analyzed,and the corresponding structure of controlled bending gradient bending beam is proposed.Based on the strength theory,the gradient of MSFRC gradient layer thickness is 1/3 section height is designed.The composite beam(MSFRC85),based on the principle of fracture mechanics,designed a gradient composite beam(MSFRC50)with an MSFRC gradient layer thickness of 50 mm.(5)Comparing with ordinary concrete beams,two kinds of steel fiber reinforced concrete gradient composite beams are designed and tested for bending performance.The bearing capacity of different experimental beams and the stress state of steel bars are analyzed.The crack characteristics of different test beams under load were studied,including crack distribution in each loading zone,crack development stage analysis,and comparative analysis of crack development height,width,and spacing.Finite element analysis method was used to verify the stress characteristics and crack distribution of the test beam.The thesis analyzes the crack characteristics of steel fiber reinforced concrete gradient composite structure based on gradient composite design theory through theoretical analysis,experimental research and finite element verification,and provides a reference for the research and application of high-volume-rate steel fiber reinforced concrete gradient composite structure.