Quality Control And Reassessment Techniques Of Durability Of Concrete Structures In Hong Kong-Zhuhai-Macau Bridge

Durability is one of the most important concerns of reinforced concrete structuresin chloride environment. Probabilistic performance-based durability design provide areasonable way to get specified service life of structures. Quality control in constructionstage make the assumptions and estimations in design be reality. And reassessment ofstructural durability based on the inspection data is the foundation of maintenancestrategy design in life-cycle. This paper focus on the engineering practice of HongKong-Zhuhai-Macau (HZM) bridge which has a design working life of120years, andthe content studied are as follows:(1) Brief introduction of the effecting factor, degradation mechanism, andmathematical model of chloride ions transportion of structural durability. Discuss thetheory and computing method of structural reliability. Based on the statistical propertiesof design variables which have been obtained from long term exposure tests, therelationship between the cover thickness and the chloride diffusion coefficient under atarget reliability is established using full probabilistic method, and the sensitivityanalysis of the statistical parameters of design variables is carried out. The procedure ofsafety factors calibration using the first-order reliability method for the durability designformula in a partial factor format is also provided. And the above reliability computingfunctions are integrated into a program named “Reliability-based computing programmeof bridge durability version1.0”.(2) The concept of quality control is discussed in the scope of statistical theory.The difference and connection of concrete strength quality control and the coverthickness as well as the chloride diffusion coefficient control is analyzed, where theformer is relatively mature. The precision of field experiment and measuring methodsare also analyzed, and the uncertainty relationship is obtained between the designparameter and in-situ parameter of control variables. A quality control functionconforming to the target reliability is proposed, thus the relationship of the mean valueand variability of variables for the design demands can be set up. The acceptancecriteria in codes and standards in and abroad are used to calibrate the consumer’s andthe producer’s risk. Then, after probability statistics analysis, the acceptance sampling criteria and the switching rules with and without the standard deviation are obtained,and alternative combination of sampling size and construction quality level for theproducer is given. Based on the design-construction consistent reliability quality controlplan above, an example is given using the construction data of HZM project.(3) The inspection data in construction and the exposure tests under the sameconditions of HZM project provide a possiblity of utilizing bayesian approach to adjustthe assumptions and estimations of model and parameters in design. On the basis ofinspection data, the statistical parameters of durability design variables for specificstructural members in each exposure zone are updated. The additional corrisionprevention measures used in the current project design scheme are explained and thequantitative analysis model are given. Moreover, taking Jiuzhou Channel Bridge andimmersed tube tunnel as examples, the time-dependent reliability in design, afterupdating and if taking additional corrision prevention reserve into account are compared.At last, the alternative time of first repair is discussed.