PIANC Smart Rivers 2022

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Existing hydraulic structures may show damage with increasing age and operation, so that a structural verification is indicated. In addition, repair measures must be planned and their effectiveness demonstrated. The advent of improved structural analysis methods and subsequent standardization processes facilitate the verification of existing structures  to ensure sufficient reliability of infrastructure. Among the existing inland navigation hydraulic structures, older ship locks had been constructed with primitive construction materials such as damped plain concrete. Where visual inspections is deemed inadequate as at times it was observed that the structure exhibited neither any serious damages nor indication for failure but failed to satisfy the limit states prescribed by the latest standards. 
This contribution considers a similar ship lock build in 1925 as a case study. The ship lock has a half-frame structural system with plain concrete gravity walls and lightly transverse reinforced base slab. Cross section based static verification revealed that the structure does not provide sufficient resistance in case of sliding and overturning limit states which could be attributed to crack and pore-water pressures in the cross section. Consequently rehabilitation for the lock walls with vertical anchoring system was proposed to conform to required standards. 
Similar problems are expected for other existing locks in the German waterway system; there-fore a methodology was developed to investigate the structural reliability of similar structures using full probabilistic methods while considering standard-based limit state functions. This involved uncertainty quantification of parameters for relevant loads (self-weight, water pressure, earth/ groundwater pressure, temperature, etc.) and materials (concrete, steel). For calculation of probability of failure and reliability indexes First Order Reliability Methods (FORM) was applied considering it computational efficiency and by-product parameter importance factors. Additionally Monte Carlo based simulation method i.e. Subset Simulation was employed to root out any possible influence of non-linearity on FORM results.
For the lock from 1925, shown as an example, it can be shown for various verification formats that the minimum reliability index (Beta) without repair was 1.31 which does not meet today's reliability requirements, but that after reinforcement a reliability index of at least 4.05 can be achieved, so that the structure can achieve a further service life like a new hydraulic structure.   
The contribution provides methodology and application of probabilistic approach to verification of structural reliability of hydraulic structures without rehabilitation, the additional gain in case of rehabilitation and reliability based optimization of measures to achieve certain target reliability.

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