Reliability of Existing Hydraulic Structures

Claus Kunz

Wednesday 1 july 2015

12:00 - 12:15h at Africa (level 0)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 9F. Engineering - River

Hydraulic structures are long-living infrastructure assets which have to some extent a high risk potential. Waterway structures in Germany have an average lifespan of 65 years already, about 25% of the structures have already passed their theoretical service life of 100 years. By aging and degradation, by changing of environmental conditions with time, but also by changes of safety concepts and proof formats in codes existing structures must be evaluated within a statical verification or a risk analysis. This is not possible with the standards that have often been usually designed only for new structures. The application of these “new structure” standards leads to a conceptional aging, where the bearing capacity is not given by computational figures. However this does not correspond to reality. In addition, limited resources prohibit to meet the safety standard ever for new structures during a cycle of use, and thus to negate the aging. A concept for the reliability of massive hydraulic structures had been developed, where - the remaining lifetime, - the possible modification of basic variables on the action and resistance side after some detailed on-site inventory and - risk considerations are comprised. For example, the required total reliability according Eurocode for a new structure which implies several uncertainties is recognized for the remaining lifetime as the structure experienced had shown no failure up to the valuation date. The equivalent reliability index beta can be adapted for the remaining service time.Measurements and stochastical treatments of relevant actions, such as (flood) water levels and groundwater levels, but also soil properties and material testing of concrete and steel properties allows updated base variables (means, standard deviations). For proof in a semi-probabilistic way modified partial safety factors for actions and resistances are gained. An appropriate safety evaluation of existing hydraulic structures is aimed.