Research On Punching Shear Behavior Of Steel Fiber Locally Reinforced Concrete Slabs With Reinforcement

Steel fiber reinforced concrete is developed rapidly and applied extensively in civil engineering as a new type composite material with superior physical and mechanical characteristics in recent years. Because of the excellent bonding behaviour between steel fiber and high-strength concrete, the superiorities of steel fiber reinforced concrete are effectively made use of with the raise of concrete strength, compensates the deficiencies of high-strength concrete including cracking susceptibility, high brittleness and poor ductility, improves mechanical and in-service performance of high-strength concrete. In order to popularize and apply steel fiber reinforced concrete, connected with experimental study and theory analysis, experimental research on punching shear behaviour of steel fiber locally reinforced concrete slabs with reinforcement have been carried out in this dissertation. The main contents of this dissertation are as follows:1. Joined with force behaviour of steel fiber reinforced high-strength concrete, the selection demand of raw material and design of mixture ratio are discussed in detail. On the basis of routine preparation methods, steel fiber reinforced high-strength concrete is provide with meeting the requirements for strength & working function, which is proved through the relevant test results.2. Through the compressive test, tensile test, rupture and elasticity modulus test, the effects of steel fiber volume fraction and concrete strength grade on the failure mode & the basic mechanical properties of high-strength concrete and steel fiber reinforced high-strength concrete. Based on the test results, the calculating formulas of compressive strength, tensile strength, rupture strength and elasticity modulus of steel fiber reinforced high-strength concrete are put forward in order to provide data and theory for the research on punching shear behaviour of steel fiber locally reinforced high-strength concrete slabs with reinforcement.3. The influences of steel fiber volume fraction, steel fiber additional range and concrete strength grade on punching shear force behavior, failure mode, crack occurrence and its development, cracking capacity and punching shear ultimate beating capacity, strain of steel bar and concrete, failure mechanism subjected to punching shear for steel fiber locally reinforced high-strength concrete slabs with reinforcement are studied through the experiment on the 13 two-way slabs with simply supported. And then, the steel fiber additional range of steel fiber locally reinforced high-strength concrete slabs which can reach the performance of steel fiber reinforced high-strength concrete slabs and the optimal steel fiber volume fraction which can attain the best effect on strength and ductility are discussed. The results show that steel fiber added in high-strength concrete improves effectively the punching shear performance of steel fiber locally reinforced high-strength concrete slabs with reinforcement. With the increases of steel fiber volume fraction or steel fiber additional range, the punching shear ultimate bearing capacity of steel fiber locally reinforced high-strength concrete slabs with reinforcement increases. It is observed that the punching shear ultimate bearing capacity hardly increases when additional range of steel fiber is improved more than two times of slab thickness. When steel fiber volume fraction is 2.0%, the effect on strength and ductility for steel fiber locally reinforced high-strength concrete slabs with reinforcement is the best.4. According to the test results and failure mode subjected to punching shear, the corresponding failure mechanism is proposed to deduce the plastic analytical formula for steel fiber reinforced high-strength concrete slabs with the method of the plastic limit analysis and three parameters criterion of unified strength theory. Combined the plastic limit analysis on punching shear ultimate beating capacity of this kind slab with the statistic analysis of the experimental data in this paper or collected in the literature, the unified calculating formulas of punching shear ultimate bearing capacity for high-strength concrete slabs with reinforcement, steel fiber locally reinforced high-strength concrete slabs with reinforcement and steel fiber reinforced high-strength concrete slabs with reinforcement are presented, considering the main factors and introducing influence coefficient of steel fiber additional range.5. According to the results of punching shear deformation of experimental slabs, the influence of steel fiber volume fraction, steel fiber additional range and concrete strength grade on punching shear deformation development and distributing of steel fiber locally reinforced high-strength concrete slabs with reinforcement is discussed. The calculating method of deflections of ascending branch of load-deflection curve for steel fiber locally reinforced high-strength concrete slabs with reinforcement is established with theory of thin plate small deflection. Based on experimental data, the ascending branch curves of load-deflection curves for experimental slabs are fitted and the fitted formula which is suitable for high-strength concrete slabs with reinforcement, steel fiber locally reinforced high-strength concrete slabs with reinforcement and steel fiber reinforced high-strength concrete slabs with reinforcement is put forward.6. Joined with the experimental results in the paper, the main influencing factors on the punching shear toughness of experimental slabs are analysed. The unified calculating formulas of punching shear toughness index for high-strength concrete slabs with bar, steel fiber locally reinforced high-strength concrete slabs with reinforcement and steel fiber reinforced high-strength concrete slabs with reinforcement are presented, and which coincided with the test data. It lays a foundation to quantitatively analyse punching shear toughness of slab.7. Nonlinear finite element analysis for punching shear performance of steel fiber locally reinforced high-strength concrete slabs with reinforcement is made by means with ANSYS program basis on the test in this dissertation. The crack patterns, crack position and development condition, concrete strain, punching shear ultimate bearing capacity., etal are simulated and which coincide with the test results.