Probability And Performance Based Durability Study For Reinforced Concrete Structures In Chloride Environment

Concrete structures generally make up an important part of the national infrastructures. A majority of concrete structures in marine environment and road condition with de-icing salt application shows signs of performance degradation even premature failure due to corrosion of reinforcement in the presence of chloride.In some cases,the degradation is visible within a few years of construction completion.Despite the fact that the exposure condition is particularly severe,other factors affect the premature deterioration caused by the steel corrosion,such as:poor construction quality as a result of poor workmanship;poor design as a result of insufficient information with regards to the parameters that influence the degradation process.The main objective of this research work is to develop the models for assessing the performance deterioration and predicting the life cycle of RC structures in chloride environment based on the performance criteria and reliability analysis.This dissertation presented here focus on the following aspects:1.A probability-based model for the chloride ingress into concrete,based on the Fick's second law of diffusion,is developed that takes into account the uncertainties in the relevant material and environment factors influencing the diffusion process of chloride.From the previous laboratory and field data reported by other researchers,the quantitative effect of these factors,e.g.temperature,relative humidity,time of moist curing,test methods and loading condition,on the diffusion coefficient of chloride is estimated statistically. Furthermore,in order to avoid adverse effect on accuracy in predicting chloride profiles affected by the convection zone,which deviates from diffusion behavior,the two parameters regarding convection zone are introduced into the probabilistic model.2.By introducing the concept of smeared crack and considering the bilinear softening traction-separation curve for cracked concrete,an analytical model for concrete cracking caused by corrosion of reinforcement is developed.In the model,cover concrete with embedded reinforcing steel bar is modeled as a thick-wall cylinder subjected to the uniform internal pressure build-up of expansive corrosion products.By solving the corresponding differential equation,the analytical solutions for the variables with respect to cover cracking due to corrosion are derived.These variables include the corrosion-induced pressure,radial displacement of concrete cylinder,critical amount of rust products,and width of corrosion crack.Moreover,based on the critical amount of corrosion products and rate of rust production,the time-to-cracking for cover concrete can be estimated. 3.An effective anchorage coefficient is defined to express the influence of corrosion-induced cracking in anchorage zone on the effective anchorage capacity for RC members.Both length and width of corrosion crack and cover depth significantly affect the effective anchorage coefficient.In addition,an anchorage reliability analysis approach for simply supported RC members under corrosion attack in anchorage zone is developed.The effect of various parameters,including both length and width of cover cracking due to corrosion,cover thickness,tensile strength of concrete,anchorage length,and stirrup ratio,on the anchorage reliability was analyzed by the first-order second-moment method.The results show that the effect of corrosion-induced crack length on the reliability index?for anchorage,β₀,is negligible when the crack on the concrete surface was just appearing,but with the crack widening,theβ₀ value is reduced significantly;the considerable changes inβ₀ can result from a variation in cover depth and anchorage length;the effect of changes in diameter or space of stirrups on the anchorage resistance is very limited,and the variation inβ₀ is also very low.4.A reliability and performance based life cycle model for corrosion-affected reinforced concrete members located in the chloride environment is presented.The performance can be defined by serviceability requirements,which includes issues such as deflections,cracks and spalling,vibrations,or by load bearing capacity.In the model,the life cycle of structures consists of four phases of lifetime,e.g.,the time periods from the completion of a newly built structure to corrosion initiation in the structure,from the initiation of corrosion to corrosion induced concrete cracking,from the concrete cracking to acceptable serviceability limit states,and from loss in serviceability to acceptable minimum level of safety.Reliability analysis method is employed to determine the time periods for each phase of lifetime.The estimate criteria are established to identify the end of every phase in terms of serviceability and ultimate limit states.