• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.3
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• pp.149-158
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• 2022

As a bridge ages, its mechanical properties and structural performance deteriorate, degrading its seismic performance during a strong earthquake. In this study, the aging of piers and bridge bearings was quantified in several stages and reflected in the analysis model, enabling the evaluation of the member-level seismic fragility of these bearings. Moreover, by assuming that the failure mechanism of a bridge system is a series system, a method for evaluating the system-level seismic fragility based on the member-level seismic fragility analysis result is formulated and proposed. For piers with rubber and lead-rubber bearings (members vulnerable to aging effects), five quantitative degrees of aging (0, 5, 10, 25, and 40%) are assumed to evaluate the member-level seismic fragility. Then, based on the result, the system-level seismic fragility evaluation was implemented. The pier rather than the bridge bearing is observed to have a dominant effect on the system-level seismic fragility. This means that the seismic fragility of more vulnerable structural members has a dominant influence on the seismic fragility of the entire bridge system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.3
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• pp.173-184
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• 2023

Presently, the general seismic fragility evaluation method for a bridge system composed of member elements with different nonlinear behaviors against strong earthquakes has been to evaluate at the element-level. This study aims to develop a system-level seismic fragility evaluation method that represents a structural system. Because the seismic behavior of bridges is generally divided into transverse and longitudinal directions, this study evaluated the system-level seismic fragility in both directions separately. The element-level seismic fragility evaluation in the longitudinal direction was performed for piers, bridge bearings, pounding, abutments, and unseating. Because pounding, abutment, and unseating do not affect the transverse directional damages, the element-level seismic fragility evaluation was limited to piers and bridge bearings. Seismic analysis using nonlinear models of various structural members was performed using the OpenSEES program. System-level seismic fragility was evaluated assuming that damage between element-levels was serially connected. Pier damage was identified to have a dominant effect on system-level seismic fragility than other element-level damages. In other words, the most vulnerable element-level seismic fragility has the most dominant effect on the system-level seismic fragility.

• Smart Structures and Systems
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• v.14 no.5
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• pp.847-867
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• 2014

There are continuous efforts to mitigate structural losses from earthquakes and manage risk through seismic risk assessment; seismic fragility curves are widely accepted as an essential tool of such efforts. Seismic fragility curves can be classified into four groups based on how they are derived: empirical, judgmental, analytical, and hybrid. Analytical fragility curves are the most widely used and can be further categorized into two subgroups, depending on whether an analytical function or simulation method is used. Although both methods have shown decent performances for many seismic fragility problems, they often oversimplify the given problems in reliability or structural analyses owing to their built-in assumptions. In this paper, a new method is proposed for the development of seismic fragility curves. Integration with sophisticated software packages for reliability analysis (FERUM) and structural analysis (ZEUS-NL) allows the new method to obtain more accurate seismic fragility curves for less computational cost. Because the proposed method performs reliability analysis using the first-order reliability method, it provides component probabilities as well as useful byproducts and allows further fragility analysis at the system level. The new method was applied to a numerical example of a 2D frame structure, and the results were compared with those by Monte Carlo simulation. The method was found to generate seismic fragility curves more accurately and efficiently. Also, the effect of system reliability analysis on the development of seismic fragility curves was investigated using the given numerical example and its necessity was discussed.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.6
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• pp.293-303
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• 2020

Seismic fragility was assessed for non-seismic reinforced concrete shear walls in Korean high-rise apartment buildings in order to implement an earthquake damage prediction system. Seismic hazard was defined with an earthquake scenario, in which ground motion intensity was varied with respect to prescribed seismic center distances given an earthquake magnitude. Ground motion response spectra were computed using Korean ground motion attenuation equations to match accelerograms. Seismic fragility functions were developed using nonlinear static and dynamic analysis for comparison. Differences in seismic fragility between damage state criteria including inter-story drifts and the performance of individual structural members were investigated. The analyzed building had an exceptionally long period for the fundamental mode in the longitudinal direction and corresponding contribution of higher modes because of a prominently insufficient wall quantity in such direction. The results showed that nonlinear static analyses based on a single mode tend to underestimate structural damage. Moreover, detailed assessments of structural members are recommended for seismic fragility assessment of a relatively low performance level such as collapse prevention. On the other hand, inter-story drift is a more appropriate criterion for a relatively high performance level such as immediate occupancy.

• Earthquakes and Structures
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• v.12 no.6
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• pp.653-663
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• 2017

A seismic margin assessment evaluates how much margin exists for the system under beyond design basis earthquake events. Specifically, the seismic margin for the entire system is evaluated by utilizing a systems analysis based on the sub-system and component seismic fragility data. Each seismic fragility curve is obtained by using empirical, experimental, and/or numerical simulation data. The systems analysis is generally performed by employing a fault tree analysis. However, the current practice has clear limitations in that it cannot deal with the uncertainties of basic components and accommodate the newly observed data. Therefore, in this paper, we present a Bayesian-based seismic margin assessment that is conducted using seismic fragility data and fault tree analysis including Bayesian inference. This proposed approach is first applied to the pooltype nuclear research reactor system for the quantitative evaluation of the seismic margin. The results show that the applied approach can allow updating by considering the newly available data/information at any level of the fault tree, and can identify critical scenarios modified due to new information. Also, given the seismic hazard information, this approach is further extended to the real-time risk evaluation. Thus, the proposed approach can finally be expected to solve the fundamental restrictions of the current method.

• Structural Engineering and Mechanics
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• v.78 no.3
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• pp.333-350
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• 2021

Motivated by the demand of seismic protection of museum collections and development of performance-based seismic design guidelines, this paper investigates the seismic fragility of sliding artifacts based on incremental dynamic analysis and three-dimensional finite element model of the artifact-showcase-museum system considering nonlinear behavior of the structure and contact interfaces. Different intensity measures (IMs) for seismic fragility assessment of sliding artifacts are compared. The fragility curves of the sliding artifacts in both freestanding and restrained showcases placed on different floors of a four-story reinforced concrete frame structure are developed. The seismic sliding fragility of the artifacts within a real-world museum subjected to bi-directional horizontal ground motions is also assessed using the proposed IM and engineering demand parameter. Results show that the peak floor acceleration including only values initiating sliding is an efficient IM. Moreover, the sliding fragility estimate for the artifact in the restrained showcase increases as the floor level goes higher, while it may not be true in the freestanding showcase. Furthermore, the artifact is more prone to sliding failure in the restrained showcase than the freestanding showcase. In addition, the artifact has slightly worse sliding performance subjected to bi-directional motions than major-component motions.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.161-168
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• 2005

Torsional behavior of eccentric structure under seismic loading may cause the stress and/or deformation concentration. Hence it is hard to estimate the seismic behavior of the structure with plan irregularity. This study suggests the method to setup the seismic fragility curve of the torsionally irregular structures. The suggested fragility curve may be acquired from the fragility surface defined on the D-R plan according to the estimated torsional behavior. The torsional behavior is predicted considering the inelastic region by adapting the inelastic stiffness of each wall. Finally the system displacement is converted to the spectral acceleration and the fragility curve for the seismic excitation level is presented. In addition, the fragility curve considering the excitation direction is proposed.

• International Journal of High-Rise Buildings
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• v.9 no.2
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• pp.175-185
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• 2020

Currently, few studies have been conducted to comprehend the seismic reliability of post-tensioned (PT) CLT shear wall structures, due to the complexity of this kind of structural system as well as due to lack of a reliable structural model. In this paper, a set of 4-, 8-, 12-, and 16-storey benchmark PT CLT shear wall structures (PT-CLTstrs) were designed using the direct displacement-based design method, and their calibrated structural models were developed. The seismic reliability of each PT-CLTstr was assessed based on the fragility analysis and based on the response surface method (RSM), respectively. The fragility-based reliability index and the RSM-based reliability index were then compared, for each PT-CLTstr and for each seismic hazard level. Results show that the RSM-based reliabilities are slightly less than the fragility-based reliabilities. Overall, both the RSM and the fragility-based reliability method can be used as efficient approaches for assessing the seismic reliabilities of the PT-CLTstrs. For these studied mid- and high-rise benchmark PT-CLTstrs, following their fragility-based reliabilities, the 8-storey PT-CLTstr is subjected to the least seismic vulnerability; while, following their RSM-based reliabilities, the 4-storey PT-CLTstr is subjected to the least seismic vulnerability

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.2
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• pp.91-99
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• 2023

Structural vibration induced by earthquake hazards is one of the most significant concerns in structure performance-based design. Structural hazards evoked from seismic events must be properly identified to make buildings resilient enough to withstand extreme earthquake loadings. To investigate the effects of combined earthquake-resistant systems, shear walls and five types of dampers are incorporated in nineteen structural models by altering their arrangements. All the building models were developed as per ACI 318-14 and ASCE 7-16. Seismic fragility curves were developed from the incremental dynamic analyses (IDA) performed by using seven sets of ground motions, and eventually, by following FEMA P695 provisions, the collapse margin ratio (CMR) was computed from the collapse curves. It is evident from the results that the seismic performance of the proposed combined shear wall-damper system is significantly better than the models equipped with shear walls only. The scrutinized dual seismic resisting system is expected to be applied practically to ensure a multi-level shield for tall structures in high seismic risk zones.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.1
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• pp.33-41
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• 2013

Due to a high level of system ductility, steel moment resisting frames have been widely used for lateral force resisting structural systems in high seismic zones. Earthquake field investigations after Northridge earthquake in 1994 and Kobe earthquake in 1995 have reported that many steel moment resisting frames designed before 1990's had suffered significant damages and structural collapse. In this research, seismic performance assessment of steel moment resisting frames designed in accordance with the previous seismic provisions before 1990's was performed. Buckling-restrained braces and shear walls are considered for seismic retrofit of the reference buildings. Increasing stiffness and strength of the buildings using buckling-restrained braces and shear walls are considered as options to rehabilitate the damaged buildings. Probabilistic seismic performance assessment using fragility analysis results is used for the criteria for determining an appropriate seismic retrofit strategy. The fragility contour method can be used to provide an intial guideline to structural engineers when various structural retrofit options for the damaged buildings are available.