Study On Damage Of Concrete

Due to factors such as loading, temperature variation and so on , stress and strain are produced in concrete. Based on conceptions of damage mechanics, damage and damage accumulation appear in concrete at the same time, which lead to material deterioration and final failure. The aim of this paper is to build up the applied damage models for analyses of concrete and concrete structures. This paper consists of four parts as follows. 1. Modeling of uniaxial stress-strain relation of concrete by using multi-parallel-bars system, The mechanism of damage and softening of concrete under uniaxial compression is analyzed by the light of fracture mechanics; it is found that the bending and breaking due to the buckling of the cleaving crack surfaces are the major causes. A multi-parallel-bars model is developed to describe the above mechanism and a related damage index is initiated based on this model. The model parameters of plain and confined concrete of ordinary strength grades are determined. Comparison of bars distribution features and their causes are made among different kinds of concrete. 2.Three dimensional damage model of concrete based on Ottosen's constitutive relations, A new scheme is initiated through which one can derive the three dimensional damage model of concrete with an established constitutive model of concrete. When this model is applied, no new parameter demarcation tests are required, and damage can be calculated without the integration of damage evolution equations. A damage model is developed by using the Ottosen's constitutive model. Damage analyses are made on the whole process of typical proportional loading for different definitions of damage indexes and non-linearity indexes. Two different definitions of damage, based on stiffness decline and loss of residual deformation capacity respectively, show reciprocity in damage description. The non-linearity index of proportional increment is found simpler and more reasonable. Comparable calculation of classical Mazars damage model of concrete and this model is made. 3. Three dimensional damage model of concrete based on the revised Sargin equation, A three dimensional damage model of concrete based on the revised Sargin equation is given in order to remove the shortages of damage model based on Ottosen's constitutive model. Damage calculation is made on the whole process of typical proportional loading. After analyzing load-damage curve, damage index based on stiffness decline is found reasonable and available in any three dimensional cases. This damage model is an isotropic one, which is still useful for a single point though concrete damage is generally anisotropic. This damage model has better agreement with experiments and has wider applicability than the formal damage model based on Ottosen's constitutive model does. 4. Damage analysis of ordinary reinforced concrete beam. Appling damage model of concrete based on the revised Sargin equation, one dimensional damage calculation is performed on reinforced concrete simply supported beams under concentrated load and distributed load. Compared with existing experimental phenomenon, the theoretical results coincide well with the facts. Current model could provide a reference for complicated concrete structure analysis.