The vulnerability of bridges and the effectiveness of suitable mitigation techniques in regions exposed to different seismic scenarios, while lacking reliable fragility assessment studies for existing bridge inventory, need focused attention. Further, while several retrofit techniques were proposed for improving the seismic performance of existing bridges, the limitations of such approaches need further investigation. Thus, this study assesses the seismic vulnerability of a benchmark structure representing pre-seismic code multi-span bridges in an earthquake-prone region before and after the retrofit to mitigate earthquake-related losses. The numerical modeling approaches of the selected bridge and retrofit systems were verified using the results of previous experimental studies. Detailed three-dimensional fiber-based (3DFB) simulation models were then developed to assess the seismic response of the benchmark bridge under the effects of diverse earthquake records representing far-field and near-source seismic scenarios in both longitudinal and transverse directions. The obtained results from several inelastic pushover analyses (IPAs) and incremental dynamic analyses (IDAs) confirmed the vulnerability of the benchmark bridge and the pressing need for mitigation actions to reduce the expected seismic losses under different seismic scenarios. Higher damage probabilities were observed under the effects of far-source events and at lower intensities than their near-field counterparts. Based on the probabilistic assessment study, it is concluded that retrofitting the bridge with buckling restrained braces (BRBs) is an effective mitigation measure to increase the lateral strength and overcome the high curvature ductility (CD) demands observed in bents, particularly under the most critical seismic scenario. The study provides insight into the impacts of contemporary retrofit techniques on improving the seismic performance of substandard bridges and presents a range of fragility functions for the assessment and mitigation of earthquake risks.
This study aims to select an effective mitigation approach from different alternatives to upgrade substandard RC bridges to meet the seismic performance objectives of current design standards. The performance assessment results for an existing benchmark bridge confirmed that the bent curvature ductility and bearing displacement control the seismic response. Thus, five contemporary retrofit solutions were investigated, including adding different supplementary lateral force-resisting systems (SLFRSs), replacing old bearings with those equipped with shape memory alloy (SMA), and combinations of these retrofit options. Fourteen earthquake records representing long- and short-period seismic events and the seismo-tectonic characteristics of a moderate seismic region were progressively scaled and applied separately in the two orthogonal directions of detailed simulation models representing the retrofitted benchmark bridge. This study provided insights into the impact of combining contemporary seismic risk mitigation techniques on improving the seismic performance of substandard bridges and presented a range of fragility functions for delaying structural damage and minimizing disruption of existing bridges to avoid traffic interruption. The dynamic response simulation results in the longitudinal direction (LD) confirmed that utilizing SMA bearings reduces curvature ductility and bearing displacement demands. Although the probabilistic assessment study in the transverse direction (TD) indicated that SMA bearings adequately reduce displacement demands, the bridge should be equipped with SLFRSs to overcome the bents’ high curvature ductility demands. Therefore, the most effective retrofit technique in TD is achieved using both SMA bearings and steel bracings.
Observations from previous earthquakes indicated that substandard bridges in different parts of the world could be severely damaged or even suffer a collapse under strong earthquakes. Potential damage to substandard and pre-seismic code bridges can be identified using detailed inelastic assessment procedures, which supports the selection of suitable seismic mitigated approaches. In this study, a five-span simply supported typical bridge located in the UAE, which is selected as a case study representing moderate seismic zones, is investigated numerically for seismic vulnerability. The fiber-based modeling approach adopted in this study is verified using a bridge bent tested in another study using quasi-static cyclic loading experiments. A three-dimensional (3D) model is developed to consider the bridge components' geometric non-linearities and material inelasticity, including multi-column piers, superstructure, gaps, and bearings. A set of diverse input ground motions are selected, scaled, and applied to the bridge model with increasing intensities to develop fragility curves. Lower strength and higher deformation demands are observed in the longitudinal direction of the bridge compared to its transverse counterpart. The fragility analysis also confirmes the higher vulnerability in the longitudinal direction. The study highlights the pressing need for seismic retrofit to ensure the post-earthquake functionality of substandard bridges in the study region.
Observations from previous earthquakes indicated that substandard bridges in different parts of the world could be severely damaged or even suffer a collapse under strong earthquakes. Potential damage to substandard and pre-seismic code bridges can be identified using detailed inelastic assessment procedures, which supports the selection of suitable seismic mitigated approaches. In this study, a five-span simply supported typical bridge located in the UAE, which is selected as a case study representing moderate seismic zones, is investigated numerically for seismic vulnerability. The fiber-based modeling approach adopted in this study is verified using a bridge bent tested in another study using quasi-static cyclic loading experiments. A three-dimensional (3D) model is developed to consider the bridge components' geometric non-linearities and material inelasticity, including multi-column piers, superstructure, gaps, and bearings. A set of diverse input ground motions are selected, scaled, and applied to the bridge model with increasing intensities to develop fragility curves. Lower strength and higher deformation demands are observed in the longitudinal direction of the bridge compared to its transverse counterpart. The fragility analysis also confirmes the higher vulnerability in the longitudinal direction. The study highlights the pressing need for seismic retrofit to ensure the post-earthquake functionality of substandard bridges in the study region.
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