The effects of using different seismic bearings were investigated to reduce the seismic response of buildings by assuming the vulnerability of 20-story regular RC building in this paper. The method of this study was that the studied building was studied in three different models in terms of its connection to the foundation. In the first model, the structures were placed on the rigid bearing and in the second and third models; lead-rubber bearings and friction pendulum bearings were placed at the counter between the structure and foundation, respectively. Then, the dynamic analysis was used to assess the behaviour and seismic response of the mentioned models. The results of the study showed that the structures in the first model functioned like cantilever column that would become uniaxial and biaxial bending under the effects of earthquake around the vertical axis of structure. Due to the tensile (tension) weakness in concrete, seismic loads caused major cracks in the tension part of the structures according to the place of the neutral axis that could lead to the collapse of structure. In addition, the use of mentioned seismic bearings under the earthquake caused the structure like a semi-rigid box slid on this equipment that reduced the structure's stiffness and increased the period of the structure in comparison with the first model. Using the studied seismic bearings caused the displacement of the roof of the first and twentieth stories of the structure become approximately equal and prevented the creation of the bending moment in the first model. The results of non-linear time history analysis showed that using the studied seismic bearings caused the response of the structure reduced significantly when the structure was placed on rigid bearings. It could be very valuable regarding the limitation of the capacity of the structure's members.

This paper investigates the effects of earthquakes’ duration, intensity, and magnitude on the seismic response of reinforced concrete (RC) bridges retrofitted with seismic bearings, such as elastomeric bearings (EB), lead rubber bearings (LRB), and friction pendulum bearings (FPB). In order to investigate the effects of the seismic isolation, the condition of the deck with a rigid connection on the cap beams and abutments (i.e., without isolation) was investigated as the first model. The EB, LRB and FPB bearings are used between the superstructure and substructure of the studied bridge in the second, third and fourth models, respectively. First, the effects of using seismic bearings on the seismic retrofit of an RC bridge under the Tabas earthquake were investigated. The results of the nonlinear dynamic analysis showed that the use of seismic bearings leads to seismic retrofit of the studied bridge, and FPB and LRB had the best results among the studied isolation equipment, respectively. The same models were also studied subjected to the Landers and Loma Prieta earthquakes. The magnitude of the Landers and Tabas earthquakes is equal to 7.3 Richter, and the magnitude of the Loma Prieta earthquake is equal to 6.7 Richter. However, the duration and intensity of the Landers and Loma Prieta earthquakes are much larger than the Tabas earthquake. The Landers and Loma Prieta earthquakes caused instability in the isolated models due to their significant duration and intensity. This issue shows that using seismic bearings is very useful and practical for seismic retrofitting bridges subjected to far-fault earthquakes. According to most seismic codes, selecting earthquakes in far-region of faults is based on just magnitude criterion. However, this study indicates that there are two main factors in the features of far-fault earthquakes, including duration and intensity. Ignoring these factors in selecting earthquakes may lead to the instability of structures. Considering earthquakes’ duration, intensity, and magnitude are vital for selecting earthquakes in the far region of the fault.

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This paper investigated the effects of the duration, intensity, and magnitude of earthquakes in seismic retrofitting of RC bridges using seismic bearings. First, the seismic retrofit of an RC bridge using seismic bearings under the Tabas earthquake was investigated. Seismic bearings included elastomeric bearing (EB), lead rubber bearing (LRB), and friction pendulum bearing (FPB). In order to investigate the effects of this equipment, the condition of the deck with a rigid connection on the cap beams and abutments was investigated in another model. The results of the studies showed that the use of seismic bearings leads to seismic retrofit of the studied bridge, and FPB and LRB had the best results among the studied equipment, respectively. The same models were studied subjected to the Landers earthquake. The magnitude is equal to Landers and Tabas earthquakes, but the duration and intensity of the Landers earthquake are much larger than Tabas earthquake. The Landers earthquake caused instability of isolated models due to its significant duration and intensity. This issue indicates that in the far region of faults, considering the duration and intensity of earthquakes is very important to seismic retrofit of bridges using seismic bearings. Also, magnitude as the only criterion for selecting earthquakes is not suitable for seismic design and retrofit of bridges.

In this study, the effects of selection and scaling procedures of earthquake records on the dispersion of seismic response of structures are examined. This is according to the Standard No. 2800 seismic code and the ASCE code. So that during two case studies, seven earthquakes have been selected and scaled with the spectral acceleration of the seismic Standard No. 2800. Besides, the seismic response of a reinforced concrete (RC) bridge and a 7-story RC building is evaluated against scaled earthquakes. The results of the studies indicate that structures respond differently to earthquake records. However, in order to avoid designers' different decisions and align their views to choose suitable earthquakes and to evolve the selection and scaling methods of earthquake records for the seismic design of structures, in the end, some recommendations are presented. The results show that in selecting earthquakes, it is crucial to consider PGA, magnitude, and a classified range of intensities and durations of strong ground motion. In addition, to select earthquakes, paying attention to the frequency content of accelerograms and the shape of the response spectrum is also of particular importance. Considering the ranges of the scale of accelerograms depending on the importance of the structures is significant. By applying the mentioned recommendations, the methods of selecting and scaling earthquake records will be improved to some extent. In addition, seismic response dispersion will be prevented.