Study On Durability Evaluation Methods For Existing R.C. Structures

Durability evaluation for existing R.C. structures is an important part of studies on durability of R.C. structures.Supported by the Natural Science Foundation of China, Science and Technology Foundation of Liaoning Province and some testing and evaluation projects for engineering structures, some studies on durability evaluation methods for existing R.C. structures are carried out. The main content are as follows.1. One method for reliability analysis of structures with resistance change with time considered is presented and compared to the methods given by the current building code and the equal resistance method.2. Poisson's distribution combined with Fick's diffusion law is used to describe invasion of chloride ions. Durability evaluation method of concrete structures subjected to invasion of chloride ions is presented.3. The influence of correlation of failure modes on structural reliability is considered. And structural reliability of R.C. structures subjected to several corrosive factors is analyzed using system reliability method.4. Based on attribute identification theory, the comprehensive evaluation model of variable weight for quality of existing R.C. structures is established to evaluate the durability of the structures. The weights are determined by the actual attribution of the evaluation factors and the subjectivity of artificial weights is overcome. The confidence criteria are adopted for comprehensive evaluation and the reclassifications can be made by calculating comprehensive scores among the same category. The evaluation is always based on the measured values and not or seldom affected by human factors.5. Combined with periodical and non-periodical testing results of existing R.C. structures, gray system theory is applied to predict remaining service life of existing R.C. structures. And the damage index representing the safety state of existing R.C. structures can be achieved by comprehensive evaluation method or reliability analysis presented above.6. Based on Faraday's law in electrochemistry, the control equations for accelerated electrochemical corrosion of rebar are derived. Accelerated corrosion tests for rebar in R.C. members are carried out. Then performance experiments of R.C. members under repeated loading are made. And the bearing capacity, rigidity, ductility and energy dissipation characteristics of specimens are analyzed. The results show that when corrosion rate (weight loss) of rebar is more than some extent (approximately 4% given by this experiment), corrosion of rebar has important influence on hysteretic characteristics of R.C. members. As corrosionAbstractrate of rebar increases, the bearing capacity, rigidity, ductility and energy dissipation capacity decreases rapidly and asymmetric characteristics of hysteretic curves are more obvious. A calculation method for skeleton curves of R.C. members with corroded rebar is presented.