Durability Sturdy Of Concrete Structures On Inspection, Appraisal And Optimum Design

Reinforced Concrete (RC) structure is one of the most widely used structure types in civil engineering. Recently the durability failure of RC structure is becoming a world problem by which the field of civil engineering is greatly plagued. This paper studies on the durability of RC structure in two lines:in the first one,existing building is analyzed based on site inspection-load-carrying capability evaluation-reliability appraisal-residual service life prediction. In the other one,reliability-based optimum design for new concrete structure is discussed. The main contents are as follows:(1) Based on the investigation on the work performances of open-type piers on piles along the eastern coast of Zhejiang province,the damaging types,causes,characters of piers are analyzed. Then the measures to improve the durability of harbor structures are presented. The research provides some scientific evidence for future improved design,maintenance and reinforcement.(2) To take full advantage of the common concrete strength testing methods:drill and rebound,Fuzzy Neural Networks (FNN) was build up to evaluate concrete strength. FNN efficiently maps the complex non-linear relationship of training data for its automatic learning,generation and fuzzy logic inference. Through comparison calculations between FNN simulation and traditional method using exiting test data,the predicted result of FNN is more accurate than that of the latter.(3) Based on Pick's first and second laws,a simple and reliable method to predict the distribution of chloride concentration was presented. Linear chloride binding and time-dependent diffusivity are taken into account in this approach. Based on a chloride concentration test of field-exposed concrete specimens,a numerical example is given. The result shows that the chloride concentration increases with service time,decreases with diffusion depth,and the chloride diffusivity is a variable with time,depth and chloride concentration.(4) A nonlinear model including the loss of cross-sectional area of corroded rebar,the reduction of mechanical properties of corroded steel and the degradation of the bond strength between concrete and corroded rebar was presented. Finite element method (FEM) was employed to numerically analyze the load-bearing capability and failure mode of corroded RC beam. The result appears that the strength,hardness and ductility of corroded RC beam decrease with corrosion ratio,and the structure failure mode may change from flexural failure to shear failure when stirrup ratio is low.(5) Simplified calculation method without considering degradation of bond strength and response surface method using analysis output by FEM is carried out to calculate the time-dependent reliability of corroded structure separately. The influenceof chloride diffusion rate and steel corrosion ratio on structure reliability is discussed. The applicable scope and the calculation difference between the two methods are compared. A practical method based on reliability for durability appraisal of concrete structures is provided. For the structure,which can continue to service,the resistance was simulated by FNN,then its residual service life was predicted.(6) According to the requirements of safety,serviceability and durability,a reliability-based optimum model of reinforced concrete beam with limited corrosion was presented. Then Genetic Algorithm (GA) optimized the design parameters. The influence of climate,service condition and curing time on durability is analyzed. The relationship between cost and estimative failure cost is discussed.