Study On Material Damping Of Reinforced Concrete And Concrete-Filled Steel Tube

Damping is not only the parameter characterizing the energy dissipation in vibration of systems, but also an important factor affecting the dynamic and seismic response of structures. It is difficult to obtain the uniform understanding about damping to agree with reality until now for its comprehensive and complex mechanism.In real engineering, the damping values of structures are usually taken as constants according to composing material or Rayleigh damping. But these work only based on material property without considering dynamic system factors are not reasonable. Rayleigh damping is only set up for decoupling in computation without clear physical meaning. It is showed in plenty of research papers that under forced vibration, damping value is far more than that obtained in free vibration test and increases with the increase of stress or deformation. The increase of damping origines from the friction energy dissipation between joints and internal energy dissipation in material. Internal damping of engineering material, such as steel and Reinforced Concrete (RC), is tested as a constant and the experimental results are too scattered to obtain the material damping values and changing law in theory. As a new kind of composite material, the study for material damping of Concrete-Filled Steel Tube (CFST) is still in the initial stage and concerned document is too few to be seen. Therefore, the study for material damping of RC and CFST under forced vibration is urgent in theory and practice of seismic design and dynamic analysis of structures.Material damping value and influencing factors of RC and CFST under forced vibration are studied in this paper and it is included that:(1) Based on the study for relation between material damping and stress of Lazan, bilinear steel constitution model, confined and unconfined concrete constitution model and Karsan-Jirsa unloading-reloading law are utilized to compute energy dissipation of concrete components subjected to axial compression, RC components subjected to axial compression and RC components subjected to compression and bending by Open System of Earthquake Engineering Search. After the effect of a few parameters on energy dissipation is analyzed, the relation formulas of energy dissipation in material of concrete components subjected to axial compression, RC components subjected to axial compression and RC components subjected to compression and bending are set up by nonlinear regression with SPSS. It is the first time to establish formulas in theory for energy dissipation of concrete and RC.(2) Bilinear steel constitution model, confined concrete constitution model and unloading-reloading law are utilized to compute energy dissipation of CFST components subjected to axial compression and CFST components subjected to compression and bending. The relation formulas of energy dissipation in material with stress amplitude, concrete strength, reinforcement ratio and axial compression ratio of CFST components subjected to axial compression and CFST components subjected to compression and bending are originally set up by nonlinear regression with SPSS in theory.(3) The stress amplitude and distribution in components are calculated with the analytical method. With formulas of material energy dissipation, the material damping values of steel beams, RC beams and CFST arches are computed in theory and influencing law of parameters of material and dynamic system on material damping is analyzed quantitatively. The results show that not only does material damping change with material factors, but also geometric factors have great effect on material damping.(4) To avoid the defect of the analytical method only computing stress in the condition without damping, Finite Element Method is adopted to obtain the real material damping values and corresponding dynamic responses of steel and RC beams, steel and RC frames and CFST column-steel beam composite frame iteratively in dynamic system with hysteretic damping and the results are compared with dynamic responses by constant material damping.