Research On Seismic Behaviors And Design Method Of Steel Reinforced High Strength And High Performance Concrete Frame Joints

As an optimized combination of high-tech concrete material and new-style structure, Steel reinforced high performance and high strength concrete structure (SRHSHPC structure for short) possesses excellent seismic behaviour and good endurance. The paper is devoted to studying on seismic behavoirs and design method of SRHSHPC frame joints. The main content is described as follows:1. To improve endurance of Steel reinforced concrete structure (SRC structure for short) and solve the bond-slip problem between steel and concrete, high strength and high performance concrete (HSHPC for short) applied to SRC structure is studied. The technical method to strengthen concrete and increase endurance is analyzed. Orthogonal test is done, and a multi-objective and nonlinear optimal mathematic model is established based on the bond-slip theory between steel shape and concrete, which takes the materials cost and bond strength as objective functions, and takes the other performance indexes of HSHPC as constraint conditions. Based on large amounts of experiments, the working mechanism of HSHPC is analyzed and stress-strain constitutive model of HSHPC is established based on the existed achievement.2. Cyclic loading tests were carried out on five half-scale interior joints to understand mechanical characteristics and seismic behaviors of SRHSHPC frame joints. The test parameters taken into account are concrete strength and axial column load. The study includes joints' mechanical character, stress distribution, crack development, failure mode, ductility and energy dissipation under cyclic load. A typical crack pattern is provided which can well reflect mechanical character and damage process of SRHSHPC frame joints. The influence of concrete strength and axial column load is analyzed. Though failure mode is panel shear failure, the joints' deformation and ductility factor can reach a high level, which indicates that SRHSHPC frame joints possess excellent seismic behaviors.3. According to seismic hysteresis curve and skeleton curve obtained from tests, restoring force characteristics of SRHSHPC frame joints including ductility, energy dissipation, and strength and rigidity degradation are analyzed. Based on the test results and numerical analysis, rigidity degradation rules and hysteretic rules are analyzed. A trilinear hysteretic model considering rigidity degradation is proposed for steel reinforced high strength and high performance concrete frame joints. The proposed restoring force model tallies with the test curves, which can be a good reference for seismic design of SRC structures. A seismic damage model applying to SRHSHPC frame joints is put forward, which takes deformation and cumulative damage into account. The damage performance of five tentative frame joints is compared and analyzed according to deformation and dissipated hysteretic energy under different loading levels, and the main influence factors on damage performance are established. The damage indexes of tentative frame joints are calculated, and the influence of strength of concrete and axial compression ratio on damage performance is discussed. The damage model presented can be a reference for seismic damage analysis of structure, prediction of earthquake damage in future, estimation of economic loss and repair after earthquake.4. Finite element analysis applying 3D solid elements and including material nonlinear and bond-slip between steel and concrete is presented. The bearing capacity and mechanical performance of joints under monotonic and cyclic loading is analyzed. The results of nonlinear finite element analysis can show the stresses distribution in the joints better, which provides the possibility to patch up the defects that couldn't be observed in experiments in detail. The results of finite element analysis are confirmed through contrasting with the test ones and the influences of axial compression ratio and concrete strength on the seismic behaviors of frame joints are discussed. Based on adjustment of model parameters in finite element analysis, the factor of brittle property of high strength concrete influencing on the shear capacity is analyzed.5. The resistant mechanism and failure pattern of SRHSHPC frame joints are analyzed based on experiment and finite element analysis. Horizontal resisting elements are determined, and contribution of each part at different loading stage is analyzed quantitatively. The factor of brittle property of high strength concrete influencing on the shear capacity is determined according to finite element analysis. The practical calculating formulas of crack resistance and shear bearing capacity of such joints were derived, in which the influence of concrete strength and axial column load are included.