SEISMIC ASSESSMENT OF THE DAMAGE LIMIT STATES OF EXISTING HIGHWAY BRIDGES

The majority of existing bridges originate from various periods of design and construction. Due to their age, they have been exposed to environmental influences, often exacerbated by increased traffic loads and different hazards. For bridges located in areas prone to seismic activity, including our region, it is particularly important whether the structure was designed and built according to codes that do not meet modern seismic performance requirements. Environmental effects contribute to gradual deterioration, but de-icing salts and the aggressiveness of the environment lead to corrosion, which can often result in faster deterioration. Therefore, assessing the load-bearing capacity and seismic performance of beam bridges, which are the most common type of bridge, is crucial. For this purpose, it is necessary to apply appropriate assessment methods, especially for structures that were not built according to modern code requirements and for older bridges with a higher degree of deterioration and thus reduced load-bearing capacity. This paper presents a review of relevant literature, codes, and recommendations related to the pre-earthquake evaluation of bridges from countries frequently affected by strong earthquakes, including the USA, Japan, India, New Zealand, Turkey, and others. Based on this and the analysis of fragility curves (for substructures), this paper lists some recommendations for bridge evaluation as a case study, serving as a basis for making decisions on the type of structural intervention on the bridge or its demolition and removal. Considering that for bridges, unlike reinforced concrete buildings, the condition is set that the deck structure does not exhibit yielding, which dissipates the energy of an earthquake, it is recommended that yielding occurs first in the elements of the lower structure (columns, abutments, and even foundations). Therefore, numerical analyses are focused on the sub-structure. A comparative numerical analysis of six bridge mid-column models, featuring identical superstructures but differing substructures was performed in the paper. The prestressed concrete bridges, spanning 88 meters with configurations of 24.0+40.0+24.0m, were designed according to both old JUS (three models) and new EN standards (three models). The substructures consist of RC columns with foundations and a prestressed beam of variable height (1.40m to 2.60m). Models type 1 has massive rectangular mid-columns, while types 2 and 3 consist of two columns with a crossbeam—type 2 features rectangular columns, and type 3 has circular columns. Using nonlinear analysis, the study evaluates how these design choices impact seismic damage limit states and column responses for different damage limit states. The results show significant differences in structural resilience and vulnerability, emphasizing the importance of design factors in enhancing seismic performance and ensuring safety. Key words: Concrete road bridges, pre-earthquake evaluation, deterioration, damage state, performance, seismic fragility