Study On Unified Failure Model Of Evenly Distributed Reinforced Concrete Members

As a traditional composite material, the reinforced concrete has been used in structures for over one hundred and fifty years. The failures of reinforced concrete structures are mainly caused by different combinations of tension, compression, bending, shear and torsion. During the last one hundred years, many researchers have put forward many computational methods and failure theories. But, most of these models separate the actions of tension, compression, bending, shear and torsion. Only several models can describe different combination actions to some extent. A few can describe the full combination actions, because the computation process is very complex or even can not obtain analytical solutions when the deformation compatibility conditions are introduced. It needs to use computers to carry on a lot of iterations, which is less of intuitiveness. A mature theory should fully use the research contributions from plastic mechanics, fracture mechanics, compound material mechanics and should be expressed in simple way, which means that a perfect theory should be unified and expressed with simplicity. So, it can be concluded that the theory of reinforced concrete has not been mature yet. It is also recognized that any a little contribution to make the theory of reinforced concrete more mature is very difficult. In the present dissertation, based on existing material failure criteria, the failure mechanism of evenly distributed reinforced concrete members under generalized loading combination is analyzed fully and specifically. The following aspects are studied especially for the failure of evenly distributed reinforced concrete members:Firstly, according to the existing popular Nielsen failure model, the dowel action of reinforcement is considered by means of von Mises criterion and the Willam and Warnke five-parameter failure model is also introduced to adjust the original concrete failure model, which is so-called Mohr-Coulomb with tension cut-off. The original unified failure models of evenly distributed reinforced concrete members under combined actions of compression, tension, bending, shear and torsion are further improved, and the unified expression of evenly distributed reinforced concrete thin-walled members is derived under the generalized loading condition.Secondly, according to the features of evenly distributed reinforced concrete thin-walled members, the unified failure model on the box section members is derived. Then, the theoretical analysis results of both new model and Nielsen model will be compared with a large amount of experimental results so as to obtain the advantages and disadvantages of the new unified failure model. According to the comparing results, the limitations on application will be defined for the new unified failure model.Thirdly, on the basis of the unified failure model on box section, more research works have been extended, such as: (1) the unified failure model on annular sections, (2) the failure model of equivalent flat slab reinforced in arbitrary direction with different reinforcements, which can be considered into orthogonal reinforcement case, (3) the comparison and analysis of carrying capacity between uniaxial stress condition and uniaxial strain condition is conducted, which shows an important difference.In conclusion, the new unified failure model of evenly distributed reinforced concrete members under combination of axial force, shearing force, bending moment and torsion is more reasonable and meaningful for the application of unified failure theories in reinforced concrete structures.