PIANC Smart Rivers 2022

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Hydraulic structures are long usable infrastructure assets that have been designed for a long service life since time immemorial. Age statistics with approx. 30 % of hydraulic structures that have exceeded so far the service life of 100 years to be applied today should rather fill with pride than indicate the obsolescence of the structures. Nevertheless, structural verifications are necessary for existing hydraulic structures, because some structures show damage, others have changed their boundary conditions in the course of time, and others were built according to ear-lier standards, in whose verifications changes and further developments were made (conceptual ageing).

In many cases, normative safety can no longer be verified with the relevant standards. From the discrepancy that structures can no longer be verified numerically, i.e. they are "unsafe", and the fact that they have been operated inconspicuously for decades in some cases, a frame-work was developed to get to the bottom of this discrepancy and to clarify the facts leading to the uncer-tainty. A subsequent adjustment or change of the procedures and standards that have been maintained for a long time cannot be ruled out.

The framework for a more realistic assessment provides for the following three categories:
1. observations, experimental tests and monitoring,
2. revision of actions and verification formats in current standards,
3. considerations of the safety concept and reliability.

As an example for category 1, the application of test loads that exceed normal actions and a sub-sequent post-calibration can be mentioned. The middle wall of an existing twin ship lock, built in 1925, in the Neckar River has already been proven to be unsafe under service loads, i.e. for characteristic actions and resistances. The concrete has low strength. Higher water levels, which occurred several times in the past, could be used as test loads to calibrate a minimum safety lev-el by calculation, from which a remaining service life was determined.

Within the framework for category 2, the application of tensile strength in massive concrete cross-sections is investigated, which is not yet permitted in the current codes. Applying tensile strength, even if only to a limited extent, reduces the tensile zone in the concrete cross-section and thus the crack and pore water pressure, which would lead to iterative cracking of the cross-section. With the application of a tensile strength, not only bending verifications but also shear force verifications would succeed more reliably.

The safety level for hydraulic structures is based on that for buildings and engineering struc-tures; an independent reliability level BETA for hydraulic structures has not yet been defined. In particular, if existing hydraulic structures would have to be upgraded to a considerable extent, the question of economic efficiency and acceptable risk within category 3 arises. A risk-based methodology allows a decision to be made on necessary upgrading measures.

The individual investigations within the above criteria for the evaluation of existing hydraulic structures are shown and some of them are explained by way of examples.

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