In seismically active areas, knowledge of the actual behavior of bridges under seismic load is extremely important, as they are crucial elements of the transport infrastructure. To assess their seismic resistance, it is necessary to know the key indicators of their seismic response. Bridges built before the adoption of standards for seismic detailing may still contain structural reserves due to the properties of the used materials and construction approach. For example, smooth reinforcement which is found in older bridges due to the material properties, detailing principles, and lower bond strength compared to ribbed reinforcement, allows for greater deformations. In bridges, columns are vital elements employed in the dissipation of seismic energy. Their cross-sections often deviate from the regular square, rectangular, or round cross-sections, which are typically found in building. Based on the behavior of the columns in the vicinity of potential plastic joints, we can determine their deformability. This paper presents an experimental study of seismic resistance indicators around a potential plastic joint for a column with an atypical cross-section, without seismic details and with smooth reinforcement. The experimental results are compared with the numerical and analytical, but also with the experimental results on samples with ribbed reinforcement. Conclusions are made about the behavior of such column elements and their seismic resistance indicators, allowing for the application of an analytical or numerical method with realistic material and element properties and derivation of correction factors due to the effect of the smooth-reinforcement slippage from the anchorage area.

Many concrete arch bridges in Croatia are located in seismically active areas. The last two strong earthquakes that struck central Croatia prompted consideration of the seismic resistance of several dozen arch bridges situated on important traffic routes. Seismic assessment of existing arch bridges presents a significant challenge. Most of these structures were designed and built without seismic guidelines, and their resistance decreases over time due to deterioration. Meanwhile, new regulations increase construction requirements but do not provide a clear procedure for seismic assessment of such structures. Pushover analysis is a nonlinear static procedure used in structural engineering to estimate the seismic performance of bridges by subjecting them to monotonically increasing lateral loads. This method serves as a computationally efficient alternative to complex nonlinear dynamic time-history analysis, while offering insights into structural behaviour beyond the elastic limit. Pushover analysis yields good results for bridges with uniform stiffness in the substructure elements and a dominant horizontal direction of earthquake action. This is generally not the case for arch bridges; therefore, it is necessary to adapt this method. This paper presents the application of pushover analysis in the seismic assessment of an existing arch bridge according to the requirements of current seismic regulations and guidelines. The bridge was built in the 1960s in accordance with the regulations and materials valid at that time, which are no longer in use today.