• Geomechanics and Engineering
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• v.36 no.3
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• pp.303-316
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• 2024

Seismic records are composed of mainshock and a series of aftershocks which often result in the incremental damage to underground structures and bring great challenges to the rescue of post-disaster and the repair of post-earthquake. In this paper, the repetition method was used to construct the mainshock-aftershocks sequence which was used as the input ground motion for the analysis of dynamic time history. Based on the Daikai station, the two-dimensional finite element model of soil-station was established to explore the failure process of station under different seismic precautionary intensities, and the concept of incremental damage of station was introduced to quantitatively analyze the damage condition of structure under the action of mainshock and two aftershocks. An arc rubber bearing was proposed for the shock absorption. With the arc rubber bearing, the mode of the traditional column end connection was changed from "fixed connection" to "hinged joint", and the ductility of the structure was significantly improved. The results show that the damage condition of the subway station is closely related to the magnitude of the mainshock. When the magnitude of the mainshock is low, the incremental damage to the structure caused by the subsequent aftershocks is little. When the magnitude of the mainshock is high, the subsequent aftershocks will cause serious incremental damage to the structure, and may even lead to the collapse of the station. The arc rubber bearing can reduce the damage to the station. The results can offer a reference for the seismic design of subway stations under the action of mainshock-aftershocks.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.1159-1164
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• 2005

Seismic analysis methods in use on ground structure are equivalentstatic analysis, response-displacement method and dynamic analysis etc. Equivalentstatic analysis does not considerdynamic effect, and dynamic analysis process is very complex. then 'Urbanrail transit earthquake-resistance design standard (2005.06)' is persuading that analyze by response displacement method that consider enough dynamic effect of ground structure statically. But, It is very complex and difficult to apply response-displacement method in the field. So, modified equivalentstatic analysis or pseudo static analysis that is easy to apply in the field and have rationality of design is practically used. In this study, I try to prescribe the applicable scale of structure and static analysis that have calculative effectiveness about response-displacement method by comparing and analyzing the result of each analysis method according to the scale of urban rail transit' box type concrete structure and by performing seismic analysis that apply modified equivalentstatic analysis, pseudo static analysis and response-displacement method changing the kind of ground, depth of bedrock, size of structure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.5
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• pp.397-403
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• 2016

During the rapid economic growth in Korea since the 1970s, many underground facilities were constructed such as under passes and railways. Seismic design has been mandated in 1988, but the structures built before 1988 were not reflected on the seismic design. Accordingly, these underground structures require effective seismic reinforcing methods to ensure safety when the earthquake happens. By these reasons, in this study, using the proposed pre-flexed members, RC box structure was analyzed for seismic reinforcement of the corner. This method is based on a principle that enlarging the resistance against the external force by installing the pre-flexed member to the box structure corner. To evaluate validity, a newly developed member with CornerSafe was compared with traditional type reinforcement using experiments and finite element analysis. In finite element mode, nonlinearity of steel was modeled based on J2 plasticity model and concrete was based on CEB FIP MODEL CODE 1990. Also, composite ratios of box and pre-flexed member were computed for design application. The reinforcement and box structure were analyzed under the bond condition completely attached by the tie, and the results of experiment and finite element analysis were same in the force-displacement curve.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.1061-1071
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• 2018

A subsea tunnel, being a super-sized underground structure must ensure safety at the time of earthquake, as well as at ordinary times. At the time of earthquake, in particular, of a subsea tunnel, a variety of response behaviors are induced owing to relative rigidity to the surrounding ground, or difference of displacement, so that the behavior characteristics can be hardly anticipated. The investigation aims to understand the behavior characteristics switched by earthquake of an imaginary subsea tunnel which passes through a fault zone having different physical properties from those of the surrounding ground. In order to achieve the aim, dynamic response behaviors of a subsea tunnel which passes through a fault zone were observed by means of indoor experiments. For the sake of improved earthquake resistance, a shape of subsea tunnel to which flexible segments have been applied was considered. Afterward, it is believed that a D/B can be established through 3-dimensional earthquake resistance interpretation of various grounds, on the basis of verified results from the experiments and interpretations under various conditions. The present investigation performed 1 g shaking table test in order to verify the result of 3-dimensional earthquake resistance interpretation. A model considering the similitude (1:100) of a scale-down model test was manufactured, and tests for three (3) Cases were carried out. Incident seismic wave was introduced by artificial seismic wave having both long-period and short-period earthquake properties in the horizontal direction which is rectangular to the processing direction of the tunnel, so that a fault zone was modeled. For numerical analysis, elastic modulus of the fault zone was assumed 1/5 value of the modulus of individual grounds surround the tunnel, in order to simulate a fault zone. Resultantly, reduced acceleration was confirmed with increase of physical properties of the fault zone, and the result from the shaking table test showed the same tendency as the result from 3-dimensional interpretation.

• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.1
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• pp.69-76
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• 2017

Seismic analyses of a pile under a large rigid basement foundation embedded in the homogeneous soil layer were performed practically by a response displacement method assuming a sinusoidal wave form. However, it is hard to take into account the characteristics of a large mat foundation and a heterogeneous soil layer with the response displacement method. The response displacement method is relevant to the 2D problems for longitudinal structures such as tunnel, underground cave structure, etc., but might not be relevant with isolated foundations for building structures. In this study, seismic pile analysis by a pseudo 3D finite element method was carried out to compare numerical results with results of the response displacement method considering 3D characteristics of a foundation-soil system which is important for the building foundation analyses. Study results show that seismic analyses results of a response displacement method are similar to those of a pseudo 3D numerical method for stiff and dense soil layers, but they are too conservative for a soft soil layer inducing large soil pressures on the foundation wall and large pile displacements due to ignored foundation rigidity and resistance.

• Steel and Composite Structures
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• v.20 no.3
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• pp.719-729
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• 2016

There are great needs of simple but reliable mechanical nonlinear behavior analysis and performance evaluation method for frames constructed by steel and concrete composite beams or columns when the structures subjected extreme loads, such as earthquake loads. This paper describes an approach of simplified macro-modelling for composite frames consisting of steel-concrete composite beams and CFST columns, and presents the performance evaluation procedure based on the pushover nonlinear analysis results. A four-story two-bay composite frame underground is selected as a study case. The establishment of the macro-model of the composite frame is guided by the characterization of nonlinear behaviors of composite structural members. Pushover analysis is conducted to obtain the lateral force versus top displacement curve of the overall structure. The identification method of damage degree of composite frames has been proposed. The damage evolution and development of this composite frame in case study has been analyzed. The failure mode of this composite frame is estimated as that the bottom CFST columns damage substantially resulting in the failure of the bottom story. Finally, the seismic performance of the composite frame with high strength steel is analyzed and compared with the frame with ordinary strength steel, and the result shows that the employment of high strength steel in the steel tube of CFST columns and steel beam of composite beams benefits the lateral resistance and elasticity resuming performance of composite frames.

• Tunnel and Underground Space
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• v.20 no.2
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• pp.105-111
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• 2010

This study is to consider applicability of spiral bolt strain gauge as an instrument measuring behavior of soft ground foundation and rock slope. When the instrument was installed on the ground, it can be useful to identify the state of ground behavior because it has the characteristics of flexibility, as well as to apply the ground reinforcement because it has higher pull-out resistance to the ground. From the measurement of behavior to soft ground foundation, the strain shows a stable state in the beginning, then was observed significant change in the upper and the middle of spiral bolt strain gauge after 400 days. This is analyzed that ground loosening, which is due to occurred frequent earthquake of magnitude 1~2 with increased rainfall, lead to the instability of the ground. From the measurement of behavior to rock slope, the strain shows a stable state with very little change in a period of 0~50 days and the biggest strain at 4.2 m (P6) in a period of 50~100 days, then other places except P6 was maintained at a stable state in a period of 100~160 days. The reason is analyzed because that blasting for excavated limestone surrounding was affected to the largest at P6. However, based on the size of strain change by behavior of the soft ground foundation and rock slope, it is considered that the present condition are not effected on stability of retaining structure and rock slope. In conclusion, the proposed spiral bolt strain gauge can be useful to measure behavior of soft ground foundation and rock slope, and also to be measured behavior as well as reinforcement of the target ground.

• Journal of the Korea Institute of Building Construction
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• v.23 no.3
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• pp.295-303
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• 2023

South Korea has recently witnessed an increasing number of seismic events, leading to a surge in studies focusing on seismic earth pressures, as well as the attributes of geological layers and ground where foundations are established. Consequently, earthquake-resistant design has become imperative to ensure the safety of subterranean structures. The slurry wall method, due to its superior wall rigidity, excellent water resistance, and minimal noise and vibration, is often employed in constructing high-rise buildings in urban areas. However, given the separation between panels that constitute the wall, slurry walls possess limited resistance to seismic loads in the longitudinal direction. As a solution, several studies have probed into the possibility of interconnecting slurry wall panels to augment their seismic performance. In this research, we developed and evaluated a method for linking slurry wall panels using mechanical joints, including concrete-confined steel pipes and headed bars, through mock-up tests. We also assessed the constructability of the suggested method and compared it with other analogous methods. Any challenges identified during the mock-up test were discussed to guide future research in resolving them. The results of this study aid in enhancing the seismic performance of slurry walls through the development of an interconnected panel method. Further research can build on these findings to address the identified issues and improve the efficacy and reliability of the proposed method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.4
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• pp.243-254
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• 2021

In this study, the conservatism of the response displacement method (RDM) for the seismic response analysis of box-shaped power cable tunnels was evaluated. A total of 50 examples were used considering the cross-sections of 25 power cable tunnels and two soil conditions for each power cable tunnel. The following three methods were applied for the analysis by the RDM: (1) single cosine method, (2) double cosine method, and (3) dynamic free-field analysis method. A refined dynamic analysis method considering soil-structure interaction (SSI) was employed to compare the conservatism of the RDM. The double cosine method demonstrated the most conservative result, while the dynamic free-field analysis method yielded the least deviation. The soil stiffness reduction factor, C, for the double cosine method was recommended to be 0.9 and 0.7 for the operational performance and collapse prevention levels, respectively, to ensure a probability of at least 80% that the member force by the RDM is larger than that of dynamic SSI analysis.