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In recent years, there has been a growing seismic demand for existing bridges and the final redesign of bridges, especially after a major earthquake One method to strengthen concrete frames on bridges is to use steel sheets or profiles to use the confining force. During this study, a sample at 30% scale under gravity and lateral cycle loading was examined within the laboratory. A finite element model is additionally used to compare the behavior of laboratory samples. The laboratory sample was a model of a typical bridge in iran that was generally designed with deficient detailing requirements in agreement with the typical regulations of the 1970s. A finite element analysis set was used to evaluate various parameters in improving the behavior of the laboratory sample. The finite element model correctly predicted the weakness of the model. Subsequently, a reinforced specimen was investigated by increasing the prestressing force within the concrete beam and the thickness of the frp sheets utilized in the bridge pier by the finite element method. The results show the energy absorbed within the hysteresis curves improved the propagation of the failure. The result also showed that a 100% increase in the prestressing load caused a 67% increase in resistance .

The need for seismic retrofitting of bridges after severe earthquakes has become important in recent years. This study examines the seismic evaluation of concrete bents of highway bridges designed and implemented according to the 1990s regulations. Compared with the older codes, 1990s codes have more complex details for connections which are evaluated by experimental and numerical methods in this research. Significant improvement was observed in the behavior of the specimens designed with 1990s codes; however, this improvement is not enough as strength degradation was also reported in the inner cycles of the hysteresis curves. Therefore, seismic improvement was performed using performance levels. Results showed that in the connection zone, the longitudinal bar slippage occurs and the performance of connection is weak. In experimental phase, a specimen was constructed with external pre-stressing in a transverse direction for retrofitting. The level of improvement in behavior was also evaluated using parameters such as energy dissipation, performance levels and force-displacement curves.