eポートフォリオ(ePortfolio)

Bridges are one of the most critical components of transportation networks, which are highly vulnerable due to exposure to natural hazards. In addition, multiple degradation mechanisms can considerably affect the functionality of highway bridges during their service life. Therefore, accumulated damage could also arise continuously because of seismic loading and structural deterioration, which consequently can change system resilience over its life-cycle. This study presents a probabilistic methodology to systematically evaluate and develop the time-dependent seismic resilience curves for Reinforced Concrete (RC) bridges under chloride attacks. In this regard, different jacketing materials with varying thicknesses are chosen for retrofitting purposes. In each case, the time-dependent seismic fragility curves (four damage states) for calculating the time-dependent seismic resilience curves are established through Probabilistic Seismic Demand Models (PSDMs) by performing Incremental Dynamic Analysis (IDA). Finally, the time-dependent seismic resilience curves are evaluated based on the time-dependent seismic fragility curves using the restoration function for all the retrofitting strategies by considering the effect of structural deterioration over time. The results indicate that aging, earthquake intensities, and retrofitting strategies undeniably affect the time-variant seismic resilience of bridges, which is helpful for the long-term safety and reliability of bridges.

Bridges play an important role in providing essential services to communities as one of the most critical components of transportation infrastructure. In this regard, selecting reliable, robust, and efficient indicators is necessary to prepare a disaster management strategy. This study presents a multi-objective optimization framework for decision-makers to find the most optimal retrofit strategies that satisfy a given threshold of functionality/Resilience (R) while minimizing a structure's Life-Cycle Cost (LCC). Accordingly, various retrofit strategies include different materials (steel, Carbon Fiber Reinforced Polymer (CFRP), and Glass Fiber Reinforced Polymer (GFRP)), thicknesses, arrangements, and timing of retrofitting actions. In each scenario, the fragility curves are derived through nonlinear time-history Incremental Dynamic Analysis (IDA) to evaluate the LCC and resilience. In the subsequent step, the LCC analysis is conducted, considering the proposed formulation of multiple occurrences of seismic events, which incorporates the effects of complete/incomplete repair actions of damage conditions induced by previous seismic events. This study employs an elitist Non-dominated Sorting Genetic Algorithm II (NSGA-II) to identify the optimal set of solutions. The various aspects of the optimal retrofit strategies are thoroughly investigated and discussed for a bridge as a case study infrastructure. Results show that the considered objectives lead to reasonable and sense-making retrofit strategies.

Each of the total Life-Cycle Cost (LCC) and resilience index are valuable indicators of infrastructure management against hazard events during its service lifetime. In this study, the proposed multi-objective framework provides a systematic methodology for decision-makers to select the optimal retrofit strategies that minimize the LCC while satisfying a given level of resilience, for which various retrofit strategies are chosen. For each case, the fragility curves are established through IDA for calculating the resilience and LCC, which incorporates the effects of complete or incomplete repair actions of damage conditions induced by multiple occurrences of previous hazard events. This study employs a well-known ‘NSGA II’ to identify the optimal set of solutions. The various aspects of the optimal retrofit strategies are thoroughly investigated and discussed for an actual structure in the refinery sites as a case study infrastructure.

Curved bridges are commonly used for logistics and emergencies in urban areas such as highway interchange bridges. These types of bridges have complicated dynamic behaviors and also are vulnerable to earthquakes, so their functionality is a critical parameter for decision makers. For this purpose, this study aims to evaluate the bridge seismic resilience under the effects of changes in deck radius (50, 100, 150 m, and infinity), pier height irregularity (Regular and Irregular), and incident seismic wave angle (0°, 45°, and 90°) under short- and long-period records. In the first step, fragility curves are calculated based on the incremental dynamic analysis and probabilistic seismic demand models. Finally, seismic resilience curves/surfaces are constructed and their interpolated values of the log-normal distribution function presented for assessing system resilience. It is found that when long-period records are applied in one given direction, the angle of incidence has the most significant effect on seismic resilience, and bridges are most vulnerable when the angle of incidence tends to 0°. The effect of deck radius on seismic resilience became more remarkable as the angle of incidence increased. Additionally, results indicate that the bridge vulnerability in long-period records is more significant than that under short-period records.

Structural retrofitting is a common approach to increase the resilience of the existing buildings (e.g., office buildings) in the industrial (e.g., refinery) sites against earthquakes. In this study, a typical RC structure that used as operational office building is considered, for which a multi-objective framework is proposed to select the retrofit patterns that are optimized for seismic resilience index and cost of retrofit of these buildings. For this purpose, three different jacketing materials (i.e., Steel, CFRP and GFRP) with four various thicknesses for each one (1.2, 2.4, 3.6 and 4.8 mm for Steel, and 1 to 4 plies for CFRP and GFRP) are chosen to retrofit these buildings. In addition, six different plans are considered for the retrofit designs. Besides, three seismic intensity levels from low to severe seismic intensities with different distances ranging from near-to far-field are taken into account to determine the sensitivity of responses. For each scenario, the fragility values for calculating the seismic resilience index, and the cost of retrofit are obtained, and then the optimal set of solutions is calculated by applying the well-established non-dominated sorting genetic algorithm II. The results show that the structural retrofitting not only reduces the sensitivity of the structural response to different seismic inputs in a limited range, but also improves the performance of the structure in terms of resilience index especially at higher intensities. The proposed framework provides a method for decision makers to choose optimal retrofit strategies that minimize the corresponding costs, while achieving a predesigned resilience's level for an infrastructure system.

SMAs (Shape Memory Alloys) have been implemented about a decade in design of the concrete buildings and improving their behavior. Among the major advantages of reinforced concrete structures with SMA one could refer to their super-elasticity property and the reversibility of inelastic displacements in the structure. In this article the seismic behavior of RC buildings with SMAs in regular, torsional irregularity and extreme torsional irregularity cases for three height types of building is investigated. For this purpose the effects of SMA as longitudinal reinforcement in structures with different number of stories (3, 6 and 9) which represented the Low, Mid and High-Rise buildings are examined. For each building, three reinforcement arrangements including the case of full Steel, the case of SMA at the plastic region of the beams and Steel reinforcement in other regions and also the case of SMA rebar over the entire length of the beams are taken into consideration. In all of the above cases, the Steel rebar is used in columns for economic purposes. In continuation, nonlinear dynamic time history analysis method was performed where the parameters of the maximum drift, residual drift, amplification factor, residual amplification factor, and base shear were investigated for each case of the mentioned buildings. The obtained results indicate that application of SMA in irregular buildings mitigates the devastative effects of irregularity, including reduction in the base shear and drift in buildings.