DESIGN OF REBAR COVERS IN MARINE STRUCTURES BY PROBABILISTIC MODELLING APPLYING CORNELL'S RELIABILITY INDEX

摘要

Research into the phenomenon of chloride ingress into concrete of marine structures has led to reliable mathematical models. Even if there is still a need for standard test methods to measure the various parameters of the chloride diffusivity of concrete exposed to a given chloride laden environment, it is time to determine how the cover of reinforcement in marine reinforced concrete structures could be designed applying a certain safety level e.g. as the design of the reinforcing bars of load bearing reinforced concrete structures. This paper describes how Cornell's reliability index, cf., is applied to the design of cover of reinforcement by the mathematical models 'LIGHTCON', cf. [2] and [3], and 'HETEK', cf., of chloride ingress into marine reinforced concrete structures and assuming the initiation of the reinforcement to be critical. At the moment there is no general requirement for the reliability index, but examinations by Karlsson et al, cf., have shown that for accepted marine reinforced concrete structures the reliability index is significantly smaller than that of load carrying reinforced concrete structures. When the reinforcement starts to corrode there is an early warning before failure, e.g. by spalling of rebar cover, and there is no risk of loss of human life. For the load capacity of a load carrying reinforced concrete structures the reliability index ought to be approximately 4.0, but it seems realistic that the reliability index ought to be approximately 3.0 for the initiation time of marine reinforced concrete structures since the corrosion consequences is 'not serious with reserve capacity', cf.