The Probability Method For Evaluating The Durability Of Existing Reinforced Concrete Structures

The degradation of concrete structure durability is a severe problem in engineering construction field in China at present,and it greatly damages the reliability and safety performances of structure, which should be paid high attention to.The paper evaluates durability grades of general concrete structure in three limit states i.e.carbonization depth limit state,rust expansion crack limit state and crack width limit state under the general atmospere.Based on probability design method for concrete structure durability and systemic dependability analysis,the paper sets up practical probability limit state method for evaluating reinforced concrete structure durability.In the process of evaluating structure durability,it should be limited to normal usage in limit states.With the references of both the durability design expression in different limit states and the form of "effect ratio of resistance-load",the paper sets up evaluation indices for concrete components durability,based on which the basic method for establishing grading standard is put forward.With the basis of target reliability index of durability design for reinforced concrete structure,the paper,by further analysis,expounds probability standard for durability evaluation, and presents three preliminary schemes for dividing durability grade according to reliability index.Based on the three durability design expressions under limit states:concrete carbonization, rust expansion crack and crack width,the paper proposes specific standard for dividing durability grade with the basis of evaluation indices.By means of a great number of probability analysis,the paper applies "JC"method to determine the value of each partial coefficient for different limit state and different reliability index.In accordance with the three preliminary schemes and the comparative analysis among them,it establishes the specific methods for durability evaluation in three limit states.The evaluation method in limit states with the basis of probability theory has solid theoretical foundation.Compared with the current evaluation method,it can reflect the standard of reinforced concrete structure's durability in a more objective and accurate way.The method not only considers the impact of various random factors,but also gives full consideration to existing structure of the current state.It organically integrates the effective information currently supplied by existing structure into evaluation formula,and offers reference for durability evaluation of existing structure under general atmosphere.