Thermodynamics-based Constitutive Model Of Concrete And Its Application To Seismic Analysis Of Concrete Dams

In the dissertation, a form of energy dissipation fuction in the plastic procedure of concrete is constructed, and thermodynamics-based elasto-plastic constitutive models of concrete are derived and generalized to rate-dependent consistent visco-plastic model. The models have strict theoretical basis and automatically satisfy the thermodynamic laws. The performance of models coincides with experiments. Finally nonlinear seismic responses of Koyna gravity dam and Dagangshan arch dam are analyzed, and the effects of models and strain rate are discussed.The fundamental theories and general procedure of establishing constitutive models based on thermodynamic laws are introduced. Proper energy dissipation function is studied and the yield function in dissipation stress space is deduced. The mechanism of recoverable plastic work is tried to be analyzed macroscopically and mesoscopically. The association and non-normality of plastic flow of concrete are proved. The flow rule in dissipation stress space is determined in terms of Ziegler orthogonality principle. The yield function and the flow rule in true stress space are deduced by the shift stress with the above procedures performed, a complete constitutive model is established.An incremental function of energy dissipation in principle stress is constructed to describe the non-circle loci of concrete yield function inπplane. The sensitivity to hydrostatic pressure and the unequal behavior of concrete subjected to tension and compression loading can be represented by the model. The non-normal plastic flow and the dilatancy of concrete under uniaxial compression are also well described. The stress-strain curves of concrete under uniaxial and biaxial tension and compression with parameters fitted are in good agreement with experiments.Based on the concept of consistent viscoplasticity constitutive model, consistent rate-dependent viscoplastic models are constructed with the effects of strain rate considered in the static models based on energy dissipation. Compared with experiments, the consistent rate-dependent viscoplastic models can well represent dynamic behavior of concrete specimens. The responses of concrete structures are calculated, the results show that the responses of concrete structures vary apparently with the effects of strain rate considered. Therefore, the influence of strain rate is inneglectable in the analysis of concrete structures. Seismic responses of Koyna gravity dam and Dagnagshan arch dam are analyzed with linear elastic model, rate-independent models and rate-dependent models presented respectvely, and the influence of different models and strain rate on seismic responses are discussed. It shows that tensile stress is the control stresses of seismic design of arch dam. With the influence of strain rate considered, the strength of concrete is enhanced, and the dam can sustain higher tensile stress, so the plastic strain decreases and the region of failure shrinks, and the plastic strain rate changes as well. Compared with tensile stress, compressive stress is not influenced much by strain rate. The calculations provide reference for seismic design and safety evaluation of Dagangshan arch dam.