This study proposes a novel model to quantitatively evaluate functionality loss in railway network systems during earthquakes and assesses its applicability to a hypothetical railway network system. The model combines seismic fragility functions and restoration curves to assess functionality loss, deriving a time-dependent recovery function to propose a functionality loss model based on earthquake magnitude. The proposed model uses a hypothetical railway network to calculate the overall functionality loss of the network under various earthquake scenarios. The hypothetical railway network was designed with three lines, allowing different routes to remain operational depending on the damaged sections and increasing the diversity of network impact scenarios based on the functionality loss. This model provides a framework for analyzing the functionality loss and recovery processes of railway networks during seismic events and assessing the socioeconomic impacts of earthquakes.

In this study, a series of 1-g shaking-table tests was performed for a single pile in soft clay deposit with various conditions. Based on the test results, the dynamic p-y curve was determined by connecting the peak points of dynamic p-y loops. To construct the p-y curve for practical forms, Matlock's p-y for clay deposit was utilized to represent the initial stiffness (k(ini)) and the ultimate capacity (p(u)) of the clay. These two terms are required to formulate the p-y curve as a hyperbolic function. The suggested p-y curve was compared with p-y curves in the literature, and verified with centrifuge test results and numerical analysis results.

Load and resistance factor design (LRFD) is a limit state design method that has been applied worldwide. Because the data for determining LRFD factors in Korea has been insufficient, the resistance factors suggested by American Association of State Highway and Transportation Officials (AASHTO) in the US have been used for design in Korea; however, these resistance factors were defined based on the characteristics of the predominant bedrock types in the U.S. As such, it remains necessary to determine resistance factors that reflect the bedrock conditions in Korea. Accordingly, in this study, LRFD resistance factors were determined using 13 sets of drilled shaft load test data. To obtain accurate resistance factors, calibration of the elastic modulus of the drilled shaft and the equivalent load–displacement curve considering the axial load and elastic settlement was conducted. After determining accurate resistance values, a reliability analysis was performed. The resistance factors were determined to be within 0.13–0.32 of the AASHTO factors for the shaft resistance, 0.19–0.29 for the base resistance, and 0.28–0.42 for the total resistance. This is equivalent to being 30–60% of the AASHTO-recommended values for the shaft resistance and 40–60% of the AASHTO-recommended values for the base resistance. These differences in resistance factors were entirely the result of discrepancies in the conditions of the rock in the US and Korea in which the shafts were founded.

This study presents a technology used for the prediction of economic losses to facilities in a given area during an earthquake, thereby enabling the efficient application of performance-based maintenance and seismic strengthening. We also propose an algorithm for the establishment of a reinforcement plan that minimizes earthquake-induced economic losses within a constrained budget. The algorithm incorporates fragility functions from prior research and utilizes an optimization technique for budget allocation, leveraging the target damage ratio concept and constrained optimization. Based on the fragility curve, the probability of occurrence for each damage state for a specific PGA value and the damage rate for each damage state are calculated. From these values, the expected damage ratio (EDR) is estimated. An optimization-based budget allocation algorithm is developed to find the elements that would result in the lowest damage rate for a limited cost. To validate the applicability of the model, we created a hypothetical city with a 30 km × 30 km area containing bridges, embankments, and buildings. The estimated pre- and post-reinforcement damage was assessed in two earthquake scenarios, allowing us to test the effectiveness of the optimization-based budget allocation model in reducing damage. These results suggest that the proposed model offers a viable strategy for efficient seismic strengthening within budgetary constraints.

Foundation reinforcement using micropiles can enhance the bearing capacity of foundations and reducing the settlement of structures in building remodeling with vertical extension. However, in the process of vertical extension following foundation reinforcement, the allowable bearing capacity of the existing piles is still likely to be exceeded due to the additional load. This study presents a preloading method used to carry a partial load from the existing piles and to mobilize skin friction along the reinforcing piles in advance to ensure that the carried load on the existing piles does not exceed the pile’s allowable bearing capacity. Two cases, foundation underpinning without preloading and with preloading, were compared using FEM analysis with PLAXIS 3D. The analysis results showed that the preloading method using jacking equipment had a significant influence on mobilizing the skin friction along the reinforcing pile and reducing the carried load on the head of the existing piles.

This study investigates the seismic fragility of railway tunnels intersecting fractured geological zones using a nonlinear numerical approach. A series of dynamic analyses was performed on tunnel models subjected to multiple ground motions with varying frequency contents. The structural response was evaluated in terms of maximum bending moment, and the resulting damage indices were used to classify damage states. Based on these classifications, seismic fragility functions were developed for tunnels passing through fractured zones using a lognormal cumulative distribution with peak ground acceleration (PGA) as the intensity measure. The fragility curves indicated that the probabilities of exceeding minor, moderate, and extensive damage states surpassed 50% at PGAs of approximately 0.289 g, 0.578 g, and 0.91 g, respectively. These findings highlight the elevated seismic risk in tunnels intersecting fractured ground and emphasize the necessity of incorporating geological conditions into seismic design frameworks.