Kadir Ozakgul

Aftershocks are inevitable phenomena following a mainshock, especially after a major earthquake. However, the cumulative damage caused by aftershocks and its impact on structural performance evaluation has only recently received significant attention. This study explores the effects of mainshock–aftershock (MS–AS) sequences, including multiple consecutive aftershocks, acting on 3D steel moment-resisting frame structures. Following nonlinear time history analysis, several fundamental variables such as residual interstory drift, maximum displacement, plastic hinge formation, and base shear are evaluated to examine cumulative damage. In this context, the findings depicted in terms of aftershocks play a significant role in exacerbating plastic deformations and damage accumulation in steel moment frames. Subsequently, to mitigate cumulative damage on steel moment frames, retrofitting strategies were implemented. Retrofitting strategies effectively reduce cumulative damage and improve seismic resilience under multiple earthquake events. This research highlights the limitations of single-event seismic assessments and the need to incorporate sequential earthquake effects in design and retrofit practices. Furthermore, it provides new insights into mitigating further damage by retrofitting existing structures under multiple earthquakes.

Bridges are an essential component of the transportation system and safety and sustainability of bridges are critical for the efficient operation thereof. Due to scarcity of resources, an economical way should be determined to design and maintain bridges and the transportation system in general. Reliability indexes are widely used in the analysis of these concepts within a semi-probabilistic approach. However, advances in computer technology allow implementing a fully-probabilistic approach. This study represents a simulation-based reliability analysis of steel girder bridges in the railway lines. Statistical parameters of the bridges are determined both analysing the existing body of knowledge available in the literature and conducting specimen tests. The Bayesian approach is used to update the statistical properties of the steel material. Basic Monte Carlo Simulation (MCS) is used to simulate the load and resistance of the bridge. The reliability of the bridges is determined according to their ultimate limit states and statistical load distribution. By using simulation, the consistency of the log-normal marginal distribution obtained is analysed herein.

In this study, fragility analysis of a reinforced concrete arch railway bridge with a total length of 285 m having seven spans of 35 m, a height of 34 m and 15 ‰ slope were performed. The bridge constructed in 1928 still continues to give service. Because the bridge is located in a seismically active region in the southern part of Turkey and on a road, which is critical and important for national railway transportation, it was aimed to perform a probabilistic seismic assessment of the bridge. For this purpose, firstly, 3D finite-element model of the bridge was generated with the software SAP2000 according to the original constructional drawings. Then, the initial FE model was verified using its natural frequencies and mode shapes obtained from in-situ field acceleration measurements. Nonlinear time-history analyses were performed to obtain the seismic demands for 60 different real earthquake records. Probabilistic seismic demand model (PSDM) was derived to determine relations between engineering demand parameter (EDP) and intensity measure (IM). Lateral displacements of the mid-spans were considered as a damage state for three different service velocities. Finally, fragility curves of the bridge were derived.

In this paper, in situ field measurements and analytical model verification studies of a railway bridge that spans Karakaya Dam Lake between the cities of Malatya and Elazig in Turkey are presented. The bridge consists of 29 simply-supported steel trusses, each having a 64 m span length, giving a total bridge length of 2029.60 m. To understand the actual behaviour of the bridge, static and dynamic tests on the bridge spans were performed. The bridge was instrumented with strain-gauges mounted on the surface of the bridge members, accelerometers placed on the piers, abutments, and truss members and an optical laser based displacement sensor located at mid-span. Then, a three-dimensional finite element model of the bridge was generated using commercially available finite element analysis software using frame elements, a thick shell, and spring and rigid bar elements. The initial numerical model was calibrated using an optimization procedure based on automatically adjusting the spring constants and rigid bar rigidities with the help of MATLAB. Finally, the validity of the calibrated FE model was examined by the vertical displacement measurements.