• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.109-116
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• 2012

The dynamic properties of lead rubber bearings, which are used as isolator, are dependent on the main rubber's dynamic behaviors and nonlinear qualities. Rubber materials tend to undergo an aging process under the influence of mechanical or environmental factors, so they can end up inevitably facing damage. A main cause of such aging is known to be oxidization, which occurs through the heat of reaction at high temperatures. Accordingly, in this study an accelerated thermal aging test was carried out in order to compare the characteristic values of the bearings with each other before and after thermal aging occurs. As a result of this experiment, it was found that a thermal aging phenomenon could have an effect on shear stiffness, energy absorption, and equivalent damping coefficients. Furthermore, a decline in the dynamic properties of the lead rubber bearings by means of the thermal aging process was applied to an actual bridge and the effects of such thermal aging on the seismic performance of the bridge were also compared and analyzed based on numerical analysis. As a result of this analysis, it was found that the changes in the basic properties of the lead rubber bearings have a minor effect on the seismic performance of bridges.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.102-110
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• 2023

PSC-I girder bridges constitute the largest proportion among highway bridges in Korea. According to the precision safety diagnosis data for the past 10 years, approximately 41.3% of the PSC-I bridges have been graded as C. Furthermore, with the increase in the aging of bridges, preemptive management is becoming more important. Damage and deterioration to the deck and girder with a long replacement cylce can have considerable impacts on the service and deterioration of a bridge. In addition, the high rate of device damages, including expansion joints and bearings, necessitates an investigation into the influence of the device damage in the structural members of the bridge. Therefore, this study defined representative PSC-I girder bridges with single and multiple spans to evaluate heterogeneous damages that incorporate the damage of the bridge member and device with the deterioration of the deck. The heterogeneous damages increased a crack area ratio compared to the individual single damage. For the single-span bridge, the occurrence of bearing damage leads to the spread of crack distribution in the girder, and in the case of multi-span bridges, expansion joint damage leads to the spread of crack distribution in the deck. The research underscores that bridge devices, when damaged, can cause subsequent secondary damage due to improper repair and replacement, which emphasizes the need for continuous observation and responsive action to the damages of the main devices.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.2
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• pp.15-21
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• 2010

Structural analysis used to evaluate the load carrying capacity of a bridge should implement behavioral characteristics similar to the actual behaviors of the structure through loading tests, but it is not feasible in many cases due to the behavioral characteristics of points, inadequate modeling method in structural analysis, errors in loading tests, changes in strength and rigidity resulting from cross-sectional damage, etc. This problem can be more serious if bridge bearings have been damaged or were not installed and, consequently, the bearings do not function properly. This study produced results similar to actual behaviors using a structural analysis model built with support moment derived from the difference $\Delta{\delta}$ between measured deflection obtained by confining the cantilever segment of a solid beam and calculated deflection under a unrestrained condition. When the load carrying capacity of a bridge in operation was evaluated in consideration of the confinement condition of supports, the result was 15~19% lower than load carrying capacity calculated by the existing method.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.77-85
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• 2020

In this study, the seismic fragility curve according to the boundary conditions is created for a two-pylon concrete cable-stayed bridge, and the effect of the boundary conditions on the seismic fragility of the target bridge is evaluated. An analysis model for the target bridge is constructed using Midas Civil, and a nonlinear time history analysis is performed by applying the fiber element, concrete and rebar material models. The boundary conditions between the pylon and the stiffened girder are classified into four types: rigid, unconstrained, pot bearing, and seismic isolation bearing, and the seismic fragility curves are created for each boundary condition. The plastic hinge section of the pylon, the connection part, and the cable are selected as weak members, and the earthquake vulnerability curve is created for them. As a result of the analysis, it is found that the seismic isolation bearing model shows the lowest damage probability in the pylon and the connection part, and the seismic fragility of the cable is less affected by the boundary conditions than other members.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.243-250
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• 2005

In elevated irrigation aquaducts, one can observe a common damage pattern. That is, cracks, and crushing of concrete are usually repeated at a certain interval even if no faults are found in the design and construction of the structures. To investigate the causes of this damage, longitudinal deformations of several aquaducts have been measured. The analysis of the measured data suggests that the damages are mainly caused by cumulative repetition of extension and contraction due to temperature changes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.4
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• pp.135-144
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• 2006

In performing a risk analysis of structures under earthquakes, it is imperative to identify the vulnerability of structures associated with various damage stages considering structural properties, soil-structure interactions, site condition, and so on. In this paper, the method to derive a representative fragility curve of seismic isolated LRB(lead rubber bearing) bridges is proposed. In which, the curve is assumed log-normally distribution with two parameters. The risk analysis of seismic isolated LRB bridges considering earthquake effects such as PGA, PGV, SA, SV, and SI is also performed to assure the earthquake resisting capability of the structures. An practical way for constructing the representative fragility curves is also recommended combining fragility curves of structures.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.287-294
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• 2001

Dynamic responses of multi-span simply supported bridges are investigated to examine the effect of damaged bearings under seismic excitations. The damaged bearings are modeled as sliding elements with friction between the super-structure and the pier top. Various values of the friction coefficients for damaged bearings are examined with increasing magnitudes of peak ground accelerations. It is found that the g1oba1 seismic behaviors are significantly influenced by the occurrence of bearing damage. It should be noticed that the most possible location of unseating failure of superstructures differs with that in the model without consideration of the bearing damage. It can be concluded that the bearing damage may play the major role in the unseating failure of a bridge system, so that the damage of bearings should be included to achieve more rational seismic safety evaluation.

• Journal of the Society of Disaster Information
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• v.11 no.3
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• pp.406-412
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• 2015

Recently, frequent earthquakes can cause serious damage to the bridge. So newly constructed bridge is considered earthquake resistant design, and for the existing old bridge evaluation of damage state is needed. In this paper, replacement of US-artificial earthquakes which are used for the construction of fragility curve for evaluating damage state to Korean artificial earthquakes to meet the Korean specifications is studied. For the generation of artificial earthquakes, the fragility curves are constructed for the PGA, for the cases of having isolated bearing and not having that.

• 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 Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.145-152
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• 2009

In performing a risk analysis on structure for earthquake, it is imperative to identify the vulnerability of structures associated with various stages of damage. And the earthquake resisting capability is needed for structures like bridge. So the damage analysis of bridges with or without isolator for earthquake effects is necessary. In this paper, the risk analysis of seismic isolated LRB bridges considering earthquake effects such as PGA, PGV, SA, SV, and SI is performed using fragility curves to assure the earthquake resisting capability of the structures. And, the stability of fragility curve is investigated with respect to input earthquake.