• The Transactions of the Korean Institute of Electrical Engineers P
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• v.55 no.2
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• pp.94-102
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• 2006

This paper describes experimental analysis of UPQC, which is composed of cascaded H-bridges and single-phase multi-winding transformers. The operational characteristic was analyzed through experimental works with a scaled model, and simulations with PSCAD/EMTDC. The UPQC proposed in this paper can be directly connected to the distribution line without series injection transformers. It has flexibility to expand the operation voltage by increasing the number of H-bridge modules. The analysis results can be utilized to design the actual UPQC system applicable for the actual distribution system.

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.368-375
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• 2003

Now a days, the fabrication and election skills have improved in Korea. Due to taking the vertical clearance and a point of beauty, the election of the suspension and the cable-stayed bridges whose span length can be lengthened have been increased. Accordingly, there are link areas between the bridges by cables and other bridges. These dynamic behaviors are different from others. When the vehicles and trains run on the link area, the member force and the fatigue behavior which are occurred to the structure have different values depend on the velocity. On this paper, we analyze the bridge behavior by means of the tine history analysis depend on to velocity, the number of vehicles, single and double way.

• Structural Engineering and Mechanics
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• v.62 no.3
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• pp.281-289
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• 2017

Damping value has considerable influence on the dynamic and seismic behaviors of bridges. However, currently the constant damping ratios that are prescribed by most bridge seismic design codes can't truly represent the complicated damping character of actual structures. In this paper, a cyclic loading experiment was conducted to study the effect of stress amplitude on material damping of concrete to present an analyzing model of the material damping of concrete. Furthermore, based on the fundamental damping of structure measured under ambient vibration, combined with the presented stress-dependent material damping concrete, the seismic response of a bridge pier was calculated. Comparison between the calculated and experiment results verified the validity of the presented damping model. Finally, a modified design and analysis method for bridge was proposed based on stress-dependent damping theory, and a continuous rigid frame bridge was selected as the example to calculate the actual damping values and the dynamic response of the bridge under different earthquake intensities. The calculation results indicated that using the constant damping given by the Chinese seismic design code of bridges would overestimate the energy dissipation capacity of the bridge.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.6
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• pp.35-47
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• 2003

Seismic ground motion can vary significantly over distances comparable to the length of a majority of highway bridges on multiple supports. This paper presents results of fragility analysis of two actual highway bridges under ground motion with spatial variation. Ground motion time histories are artificially generated with different amplitudes, phases, as well as frequency contents at different support locations. Monte Carlo simulation is performed to study dynamic responses of the bridges under these ground motions. The effect of spatial variation on the seismic response is systematically examined and the resulting fragility curves are compared with those under identical support ground motion. This study shows that ductility demands for the bridge columns can be underestimated if the bridge is analyzed using identical support ground motions rather than differential support ground motions. Fragility curves are developed as functions of different measures of ground motion intensity including peak ground acceleration(PGA), peak ground velocity(PGV), spectral acceleration(SA), spectral velocity(SV) and spectral intensity(SI). This study represents a first attempt to develop fragility curves under spatially varying ground motion and provides information useful for improvement of the current seismic design codes so as to account for the effects of spatial variation in the seismic design of long-span bridges.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.149-156
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• 1999

Numerical studies were carried out to investigate the mechanical properties of competent hysteric isolators for seismic design of bridge. For dynamic analysis, bridges with isolator were simplified to a model with single degree of freedom. The initial stiffness and the yielding forces of hysteric isolators were varied. Seismic responses obtained by time history analysis show that about 4% of the weight acting as the inertia force is appropriate for the yielding force of isolator. And also better results could be achieved with the values about two times the weight per unit displacement for the initial stiffness of isolator.

• Steel and Composite Structures
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• v.17 no.6
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• pp.803-824
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• 2014

The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of the tower with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping, such as steel/concrete mixed structure - supporting soil coupled system. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. An analytical approach capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to define and investigate dynamic characteristics of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified approximation of two lumped masses to investigate the structure irregularity effects including damping of different material, mass ratio, frequency ratio on dynamic characteristics and modal damping; the second approach employs a detailed numerical step-by step integration procedure in which the damping matrices of the upper and the lower substructures are modeled with the Rayleigh damping formulation.

• Earthquakes and Structures
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• v.15 no.6
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• pp.701-713
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• 2018

Many bridges in Algeria were constructed without taking into account the seismic effect in the design. The implantation of a new regulation code RPOA-2008 requires a higher reinforcement ratio than with the seismic coefficient method, which is a common feature of the existing bridges. For better perception of the performance bridge piers and evaluation of the risk assessment of existing bridges, fragility analysis is an interesting tool to assess the vulnerability study of these structures. This paper presents a comparative performance of bridge piers designed with the seismic coefficient method and the new RPOA-2008. The performances of the designed bridge piers are assessed using thirty ground motion records and incremental dynamic analysis. Fragility curves for the bridge piers are plotted using probabilistic seismic demand model to perform the seismic vulnerability analysis. The impact of changing the reinforcement strength on the seismic behavior of the designed bridge piers is checked by fragility analysis. The fragility results reveal that the probability of damage with the RPOA-2008 is less and perform well comparing to the conventional design pier.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1077-1092
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• 2007

The structural analysis model for estimate of load carrying capacity of railway bridge on service line is important to determine safety of bridges in service, we need to take response of bridge exactly, applying analysis model similar to the real railway bridge most. Track structure which is to distribute loads and decrease vibrations occurred from running train is constructed on the railway bridges. And it is important factor which should be considered to understand exact dynamic and static responses of bridge. But track structure is currently classified as a none structural members in the structural analysis model for estimating load carrying capacity of railway bridge and not considered in analysis model. That's the reason it is difficult to understand exact behavior of bridges. Therefore, the major objective of this study is to develop an analytical track-bridge model which is similar to real railway bridges considering track structure for safety assessment of railway bridge on service line to be effectively done.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.319-325
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• 2003

The fragility curves of seismic retrofitted bridges by steel jacketing of bridge columns and restrainers at expansion joints after the 1994 Northridge earthquake are developed. Fragility curves are represented by lognormal distribution functions with two parameters(fragility parameters consisting of median and log-standard deviation) and developed as a function of peak ground acceleration (PGA). Two parameters in the lognormal distribution are estimated by the maximum likelihood method. The sixty ground acceleration time histories for Los Angeles area developed for FEMA SAC project are used for the dynamic analysis of the bridges and a computer code is developed to calculate hysterestic parameters of bridge columns before and after steel jacketing. The effect of retrofit is expressed in terms of the increase of the median value of the fragility curve for the retrofitted bridge from that of the bridge before retrofit. The comparison of fragility curves of the bridges before and after column retrofit demonstrates that the improvement of the bridges with steel jacketing on the seismic performance is excellent for the damage states defined in this study. The comparison of fragility curves of the bridges before and after restrainers at expansion joints also shows the improvement in the seismic performance of restrained bridges for the severe damage states.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.67-74
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• 2019

In this paper the response factor is investigated for middle and small size-RC slab aged bridges. The response factor consists of static and dynamic response factors and is a main parameter in the frequency based-bridge load carrying capacity prediction model. Static and dynamic response factors are determined based on the frequency variation and the impact factor variation respectively between current and previous (or design) states of bridges. Here, the impact factor variation is figured out using the impact factor response spectrum which provides the impact factor according to the natural frequency of bridges. In this study, four actual RC slab bridges aged over 30 years after construction are considered and their span length is 12m. The dynamic loading test in field using a dump truck and eigenvalue analysis with FE models are conducted to identify the current and previous (or design) state-natural frequencies of the bridges, respectively. For more realistic considerations in the moving loading situation, the impact factor response spectrum is developed based on tri-axle moving loads representing the dump truck load distribution and various supporting conditions such as simply supported and both ends fixed conditions. From the results, the response factor is widely ranged from 0.21to 0.91, showing that the static response factor contributes significantly on the results while the dynamic response factor has a small effect on the result. Compared to the results obtained from the impact factor response spectrum based on the single axle-simply supported condition, the maximum percentage difference of the response factors is below 3.2% only.