Durability Design And Assessment For RC Structures Based On Probability Theory

The reinforced concrete is the material widespread used in the field of civil engineering.In recent years,the durability failure of reinforced concrete structures has puzzled the experts and become a worldwide question.As the same with foreign countries of the world,the reliability theory is taken as the foundation of design methods of structures in China.This method is an advanced design method at present and is most widely accepted by the experts.Therefore,in durability design of concrete structures,design rules based on the probability theory should be consistent in the method with the traditional structural design method.This method not only has the solid rationale,moreover,it can maintain consistent with the present structure reliability design method.It can be accepted by the designers easily,and the different reliability request can be considered reasonably.The paper research is on the base of the current structure durability research. Through probability analysis,the design methods of structural durability based on the probability limit states are established.Moreover,Rules of thumb for the durability assessment are studied.The paper mainly includes the following contents:(1) According to the research results,misunderstandings with respect to the concept of structure durability are eliminated through the discussing on time-depended reliability of structures,and the restrict definition of structure durability are provided by discussing its core objective and contents.The paper points out that structure durability is the special problem relating to the deterioration of material performance in the structure reliability research.Hence,the measurement methods of structure reliability should be the key for the durability of structures.So the probability methods are the way for the durability of structures,and the partial factors are used to describe the design expression.The methods can be consistent to the traditional structure design methods.This is the basic idea for the whole paper.(2) The target reliability indexes are the foundation of the design methods for the durability design based on the probability theory.In the design course of durability,the durability problem should be limited in the scope of serviceability limit states,and the three limit states of durability should be provided by the significance events under the common atmosphere condition for the concrete structures.The initiation of corrosion, appearance of cracking of protective cover,and concrete spalling are considered as the failure events with respect to durability.Each limit state should have the relative target reliability index.Finally the target reliability indexes with respect to durability of concrete structures are provided.The research results provide the basis for the durability design,assessment,and life forecast based on the method of probability limit states.(3) The limit states functions based on the three life criterion are established.From carbonation corrosion to spalling of concrete cover,the deterioration process of concrete structures under common atmosphere condition mainly includes 3 significant events. According to the models describing processes of reinforcement depassivation caused by carbonation,appearance of cracking,and limit crack width,the protective cover thickness and cubic compressive strength of concrete are considered as the durability parameters.The reliability indexes under the three different limit states are studied under various cover thickness and concrete strength.The durability design and life forecast methods are established which can satisfy the target reliability indexes.The design expressions and partial factors are provided.The design courses are illustrated by some examples,and the partial factors are verified through the frequency histogram of structural life that they can achieve the target reliability indexes.The research results of design methods for concrete durability fill a domestic gap in this field in China.The proposed methods are consistent with the current structural design codes of China.(4) With respect to the durability assessment of concrete structures,a practical method for durability assessment for existing structures is provided by the frontal design rules of durability methods.This method can be more accurate than using design method because it considers the actual information of the evaluation objects.Hence,this practical method can be more accurate than the design methods for the durability with respect to the assessment of residual service life of the buildings.