1st Croatian Conference on Earthquake Engineering 1CroCEE 2021

Croatian bridges have been built in different times, always in step with or even ahead of the world's achievements.
In seismically active areas it is of paramount importance to design bridges with ductile behavior. Many bridges built before the modern Eurocodes came into force were designed to standards which did not offer provisions for structural detailing allowing for their ductile behavior.
Unfortunately, we learnt hard way that earthquake is a natural phenomenon which can be expected to happen in our country, and which needs to be appropriately considered in the management of the existing transport infrastructure. This is because bridges are often its key elements, and the ability to use them immediately after an earthquake is extremely important. The first and most important step in the strategy of bridge infrastructure anti-seismic management is to determine the present state and capacity of existing bridges in regard to their seismic resistance.
Depending on the structural system and the materials used, existing bridges may have advantages (e.g., hidden reserves in integral/frame bridges), but also disadvantages (large displacements, insufficient overlap lengths in girder bridges). Ductility levels of older bridges columns missing current structural detailing for ductile behavior, especially those of non-standard cross-sections, the development of plastic hinges and in general their non-linear behavior, are still subject of research. Thereby, one of the key indicators of seismic capacity is the bending moment-curvature curve.
One of the best ways to gain insight into the condition of bridges and to assess seismic vulnerability are fragility curves, which express the probability of a bridge element reaching a certain damage state for a given earthquake parameter. The process of obtaining data for fragility curves involves performing incremental dynamic analyses on a bridge model for different levels of seismic intensity. Thereby, it is important to determine the input parameters, especially the properties of the elements, as accurate as possible, in order to determine advantages or disadvantages of a single bridge or a group of bridges with similar properties.
The behavior of selected types of existing bridges in regard to seismic action, limit states which may occur and the load-bearing capacity of individual bridge elements are investigated in the paper.