• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.2
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• pp.1-13
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• 2010

This paper proposes an optimal design method for the nonlinear seismic isolated bridge. The probabilities of failure at the pier and the seismic isolator are considered as objective functions for optimal design, and a multi-objective optimization technique is employed to efficiently explore a set of multiple solutions optimizing mutually-conflicting objective functions at the same time. In addition, a stochastic linearization method is incorporated into the multi-objective optimization framework in order to effectively estimate the stochastic responses of the bridge without performing numerous nonlinear time history analyses during the optimization process. As a numerical example to demonstrate the efficiency of the proposed method, the Nam-Han river bridge is taken into account, and the proposed method and the existing life-cycle-cost based design method are both applied for the purpose of comparing their seismic performances. The comparative results demonstrate that the proposed method not only shows better seismic performance but also is more economical than the existing cost-based design method. The proposed method is also proven to guarantee improved performance under variations in seismic intensity, in bandwidth and in the predominant frequency of the seismic event.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.1
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• pp.17-26
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• 2009

The capacity spectrum method (CSM), which is known to be an approximate technique for assessing the seismic capacity of an existing structure, was originally proposed for simple building structures that could be modeled as single-degree-of-freedom (SDOF) systems. More recently, however, CSM has increasingly been adopted for assessing most bridge structures, as it has many practical advantages. Some studies on this topic are now being performed, and a few results of these have been presented as ground-breaking research. However, studies have until now been limited to symmetrical straight bridges only. This study evaluates the practical applicability of CSM to the evaluation of irregular curved bridges. For this purpose, the seismic capacities of 3-span prestressed concrete bridges with different subtended angles subjected to some recorded earthquakes are compared with a more refined approach based on nonlinear time history analysis. The results of the study show that when used for curved bridges, CSM induces higher inelastic displacement responses than the actual values, and that the gap between the two becomes larger as the subtended angle increases.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.5
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• pp.635-643
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• 2018

In the present study, influence of earthquake intensity range on seismic fragility analysis of a RC bridge has been evaluated. For this purpose, a RC bridge damaged by a past earthquake has been selected, and analytical model of the bridge has been developed for nonlinear dynamic time-history analysis. A total of 25 recorded earthquake motions have been employed for the nonlinear analysis from which maximum lateral drift ratio of piers are obtained. Then, seismic fragility analysis has been conducted for the bridge using the nonlinear analysis results. Probability of exceeding damage has been computed in terms of using the maximum likelihood estimation, and effect of earthquake intensity range of the motions on seismic fragility curves has been assessed analytically. Analytical predictions indicate that the earthquake intensity range is of utmost significance for rationale seismic fragility analysis reflecting a physical damage state of a bridge and seismic performance evaluation of such bridge.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.2
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• pp.75-84
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• 2003

Most structures are expected to deform beyond the limit of linearly elastic behavior when subjected to strong ground motion. Seismic evaluation of structure requires an estimation of the structural performance in terms of displacement demand imposed by earthquakes on the structure. The nonlinear response history analysis(NRHA) among various nonlinear analysis methods is the most accurate to compute seismic performance of structures, but it is time-consuming and necessitate more efforts. The nonlinear approximate methods, which is more practical and reliable tools for predicting seismic behavior of structures, are extensively studied. Among them, the capacity spectrum method(CSM) is conceptually simple, but the iterative procedure is time-consuming and may sometimes lead to no solution or multiple solutions. This paper considers a nonlinear direct spectrum method(NDSM) to evaluate seismic performance of mixed building structures without iterative computations, given dynamic property T from stiffness skeleton curve and nonlinear pseudo acceleration $A_{y}$/g and/or ductility ratio $\mu$ from response spectrum. The nonlinear response history analysis has been performed and analyzed with various earthquakes for estimation of reliability and practicality of NDSM with mixed building structures.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.4
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• pp.23-28
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• 2010

This study evaluated the effect of vibration, level of lateral yielding strength, site conditions, ductility factor, strain-hardening ratio, and post-capping ratio of the strength limited bilinear SDF systems on the inelastic displacement ratio. The nonlinear response history analysis was conducted using 240 ground motions which were collected at the sites classified as site classes B, C, and D according to the NEHRP. To account for the P-$\Delta$ effects, this study considered negative stiffness ratios ranging from -0.1 to -0.5 of elastic stiffness. Four different damping ratios are used: 2, 5, 10, and 20%. From this study, an equation of inelastic displacement ratio was proposed using nonlinear regression analysis.

• Journal of the Korean Geotechnical Society
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• v.39 no.12
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• pp.7-22
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• 2023

In this study, the limit range of input acceleration was investigated based on time domain and response spectrum analyses by considering the relative density, groundwater depth, and soil type. Special attention was paid to the input acceleration and shear modulus of soil, which affect pile behavior. The surrounding soil was identified as an elastoplastic material and subjected to FLAC3D analysis using the Mohr-Coulomb and Finn models as well as FB-Multiplier analysis using a nonlinear p-y curve for soil spring. Based on the analyses, the limit range of acceleration on the pile is much higher for SP soil than for SM soil, and the groundwater level tends to reduce the limit range of input acceleration, irrespective of soil conditions. The limit range of acceleration was mainly affected by the shear modulus. The limit range of acceleration with nonlinear soil behavior is proportional to the relative density of the surrounding soil.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1695-1705
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• 2014

In the present study, a total of 275 tested specimens (149 of non-seismically designed and 126 of seismically designed) for reinforced concrete bridge piers with circular section have been investigated in order to suggest drift limits probabilistically according to damage states in seismic fragility analysis. Thus, quantitative damage states of the piers have been evaluated depending on details of the piers. Nonlinear time-history analyses have been conducted for a damaged bridge in terms of using the suggested drift limits. Then, seismic fragility analysis for a reinforced concrete bridge structure has been conducted using both suggested and existing drift limits. Comparative analyses have revealed that median values by the suggested limits is smaller than those by the existing limits. This implies that seismic performance of the structure can be overestimated when the existing limits are used.

• The Journal of Engineering Research
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• v.6 no.1
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• pp.53-63
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• 2004

In this paper, influence of shear on the seismic performance and failure mode of reinforced concrete piers subjected to earthquake loading is investigated. Comparative study has been carried out for reinforced concrete column tests to verify the shear-axial interaction model presented in this paper. Comparison shows that predicted shear hysteretic response agrees well with the test results. Also conducted is a nonlinear time-history analysis of a reinforced concrete bridge damaged by the Kobe earthquake using the current development. Displacement response for piers reveals that maximum displacement is considerably increased due to the effect of shear coupled with axial force variation, which leads to overall stiffness degradation and period elongation. It is therefore concluded that the response considering both shear and axial force gives better explanation regarding the seismic damage evaluation of reinforced concrete bridge piers.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.2
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• pp.105-112
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• 2023

In this study, structural analyses were conducted to analyze the performance of a bridge to which friction pendulum systems (FPSs) were applied using different friction models. A Coulomb friction model and a rate dependent friction model were constructed using the friction coefficient of a PVDF/MgO friction material to analyze the effect of different friction analysis models. The Coulomb friction model uses a single friction coefficient regardless of friction velocity, while the rate dependent friction model can reflect the change in the friction coefficient with friction velocity. Nonlinear time history and seismic fragility analyses were conducted to confirm responses of the bridge. The seismic responses of a deck and a column were used to evaluate the performance of the base isolated bridge, and a friction model that can effectively evaluate the performance of isolated bridges was analyzed.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.1
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• pp.1-10
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• 1997

Current seismic design philosophy for reinforced concrete (RC) structures on energy dissipation through large inelastic defomations. A nonlinear dynamic analysis which is used to represent this behavior is time consuming and expensive, particularly if the computations have to be repeated many times. Therefore, the selection of an efficient yet accurate alogorithm becomes important. The main objective of the present study is to propose a new technique herein called the prediction approach with siffness measure (PASM) method in the convetional direct integration methods, the triangular decomposition of matrix is required for solving equations of motion in every time step or every iteration. The PASM method uses a limited number of predetermined decomposed effective matrices obtained from stiffness states of the structure when it is deformed into the nonlinear range by statically applied cyclic loading. The method to be developed herein will reduce the overall numerical effort when compared to approaches which recompute the stiffness in each time step or iteration.