• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.3
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• pp.21-28
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• 2008

To evaluate the seismic performance of multi-degree of freedom(MDF) systems, repeated nonlinear response history analyses are often conducted, which require extensive computational efforts. To reduce the amount of computation required, equivalent single degree of freedom(SDF) systems representing complex multi-degree of freedom(MDF) systems have been developed. For the equivalent SDF systems, bilinear models and trilinear models have been most commonly used. In these models, the P-$\Delta$ effect due to gravity loads during earthquakes can be accounted for by assigning negative stiffness after elastic range. This study evaluates the adequacy of equivalent SDF systems having these hysteretic models to predict the actual response of steel moment resisting frames(SMRF). For this purpose, this study conducts cyclic pushover analysis, nonlinear time history analysis and incremental dynamic analysis(IDA) for SAC-Los Angeles 9-story buildings using nonlinear MDF models(exact) and equivalent SDF models(approximate). In addition, this study considers the strength limited model.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.415-421
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• 2003

With the increasing possibility of earthquake occurrence, seismic safety of bridges has become one of the most important social issues in Korea. In this study, a nonlinear earthquake response analysis is carried out for a real bridge by incorporating soil-structure interaction and pier nonlinearity. The material nonlinearity of the bridge pier is realized by utilizing SAP2000 whereas the soil-structure interaction is analized in time domain by adapting KIESSI. The numerical results are compared to those of the models without considering the effects.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.617-627
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• 2011

This paper presents the results of analytical simulation of shake-table responses of a 1:5 scale 10-story reinforcement concrete(RC) residential building model by using the PERFORM-3D program. The following conclusion are drawn based on the observation of correlation between experiment and analysis; (1) The analytical model simulated fairly well the global elastic behavior under the excitations representative of the earthquake with the return period of 50 years. Under the design earthquake(DE) and maximum considered earthquake(MCE), this model shows the nonlinear behavior, but does not properly simulate the maximum responses, and stiffness and strength degradation in experiment. The main reason is considered to be the assumption of elastic slab. (2) Although the analytical model in the elastic behavior closely simulated the global behavior, there were considerable differences in the distribution of resistance from the wall portions. (3) Under the MCE, the shear deformation of wall was relatively well simulated with the flexural deformation being overestimated by 10 times that of experiment. This overestimation is presumed to be partially due to the neglection of coupling beams in modeling.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.3 s.73
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• pp.239-245
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• 2006

In this paper, the performance of a toggle brace-MR damper system is evaluated for the control of the structure excited by earthquake load and the non-linearity of the toggle system is investigated. Considering that the control force of MR damper described by Bingham model is a function of velocity, velocity amplification factor by the toggle brace system is calculated and the effect of toggle configuration on the amplification factor is also evaluated. Numerical results show that the control performance can be largely enhanced using toggle brace system especially for the case that the MR damper installed with conventional brace system such as Chevron and diagonal cannot provide enough control force under severe earthquake load.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.17-24
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• 2020

In this study, series of nonlinear seismic analysis were performed on a reinforced concrete intake tower surrounded by water. To consider the fluid effect around the structure, analysis models were composed using an added mass and CEL approach. At this time, the implicit method was used for the added mass model, and the explicit method was used for the fluid structure interaction model. The input motions were scaled to correspond to 500, 1000, and 2400 years return period of the same artificial earthquake. To estimate the counteractivity of the fluid coupled model, models without fluid effect were constructed and used as a reference. The material models of concrete and reinforcement were selected to consider the nonlinear behavior after yielding, and analysis were performed by ABAQUS. As results, in the acceleration response spectrum of the structure, it was found that the influence of the surrounding fluid reducing the peak frequency and magnitude corresponding to the fundamental frequency of the structure. However, the added mass model did not affect the peak value corresponding to the higher mode. The sectional moments were increased significantly in the case of the added mass model than those of the reference model. Especially, this amplification occurred largely for a small-sized earthquake response in which linear behavior is dominant. In the fluid structure interaction model, the sectional moment with a low frequency component amplifies compared to that of the reference model, but the sectional moment with a high requency component was not amplified. Based in these results, it was evaluated that the counteractivity of the additive mass model was greater than that of the fluid structure interaction model.

• 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.

• Journal of the Korean Geotechnical Society
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• v.26 no.6
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• pp.57-70
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• 2010

Recent earthquakes have demonstrated that the tunnels, which were once considered to be highly resistant to earthquakes, are susceptible to substantial damage under severe seismic loading. Among various modes of deformation under an earthquake loading, the response of the tunnel in the transverse direction is known to be the critical mode. This paper investigates the seismic response of the tunnel in the transverse direction using the method of seismic displacement, which is a type of pseudo-static analysis. Firstly, the methods of calculating the ground deformation are compared. It is shown that the single and double cosine may not provide an accurate estimation of the ground deformation, and that a one-dimensional site response analysis needs to be performed for a more reliable evaluation. Secondly, the tunnel responses are calculated using the simplified, analytical, and numerical solutions. It is demonstrated that the simplified method provides poor estimates of the tunnel response ground deformation. The analytical solution is shown to be effective in modeling circular tunnels in uniform ground, but has serious limitation in modeling tunnel response in non-uniform ground. Numerical analyses are shown to be applicable to all cases, and give the most accurate estimates of the tunnel response. It is also demonstrated that the linear solutions can be so conservative that the soil nonlinearity needs to be accounted for more accurate evaluation of the tunnel response.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.4
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• pp.51-63
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• 2002

This paper presents a hybrid control strategy for seismic protection of a benchmark cable-stayed bridge, which is provided as a testbed structure for the development of strategies for the control of cable-stayed bridges. This benchmark problem considers the cable-stayed bridge that is scheduled for completion in Cape Girardeau, Missouri, USA in 2003. Seismic considerations were strongly considered in the design of this bridge due to the location of the bridge in the New Madrid seismic zone and its critical role as a principal crossing of the Mississippi river. Based on detailed drawings of this cable-stayed bridge, a three-dimensional linearlized evaluation model has been developed to represent the complex behavior of the bridge. A set of eighteen evaluation criteria has been developed to evaluate the capabilities of each control strategy. In this study, a hybrid control system is composed of a passive control system to reduce the earthquake-induced forces in the structure and an active control system to further reduce the bridge responses, especially deck displacements. Conventional base isolation devices such as lead rubber bearings are used for the passive control design and Bouc-Wen model is used to simulate the nonlinear behavior of these devices For the active control design, ideal hydraulic actuators are used and on $H_2$/LQG control algorithm is adopted. Numerical simulation results show that the performance of the proposed hybrid control strategy is quite effective compared to that of the passive control strategy and slightly better than that of the active control strategy. The hybrid control method is also more reliable than the fully active control method due to the passive control part. Therefore, the proposed hybrid control strategy can effectively be used to seismically excited cable-stayed bridges.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.3
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• pp.259-266
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• 2012

In this paper the seismic performance of a flat plate wall system structure was evaluated based on the ATC-63 approach, and the results were compared with those of a wall slab structure having the same size. As analysis model structures, a twelve story flat plate wall structure and a wall slab structure were designed based on the KBC-2009, and their seismic performances and collapse behaviors were evaluated by nonlinear static and incremental dynamic analyses(IDA). It was observed that the flat plate wall structure was designed with smaller amount of reinforced concrete, and showed slightly larger displacement response compared with those of the wall slab structure. The collapse margin ratios of the two structures obtained from the incremental dynamic analyses satisfied the limit states specified in the ATC-63, and the structures turned out to have enough capacity to resist the design level seismic load.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.5 s.57
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• pp.149-159
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• 2009

The main purpose of this study is to evaluate the seismic safety of Korean R/C school buildings built in the 1980s, based on "the Japanese Standard for Evaluation of Seismic Capacity of Existing R/C Buildings", the nonlinear static and the nonlinear dynamic analyses. The evaluation result of the Japanese Standard showed that R/C school buildings built in the 1980s have 0.2 through 0.4 of seismic indices($I_S$). This result indicates that more than medium damage could be potentially occurred under a medium intensity level of ground motion(150g). The results of the nonlinear analyses and the post-earthquake damage evaluation method showed that Korean R/C school buildings can be suffered moderate and severe damages under a 150gal and a 200gal intensity levels of ground motions, respectively. These results reveal that R/C school buildings should be urgently required a actual earthquake preparedness measures including seismic strengthening for future earthquake.