• Earthquakes and Structures
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• v.15 no.3
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• pp.295-306
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• 2018

Reinforced concrete containment (RCC) building has long been considered as the last barrier for keeping the radiation from leaking into the environment. It is important to quantify the performance of these structures and facilities considering extreme conditions. However, the preceding research on evaluating nuclear power plant (NPP) structures, particularly considering mainshock-aftershock seismic sequences, is deficient. Therefore, this manuscript serves to investigate the seismic fragility of a typical RCC building subjected to mainshock-aftershock seismic sequences. The implementation of the fragility assessment has been performed based on the incremental dynamic analysis (IDA) method. A lumped mass RCC model considering the tri-linear skeleton curve and the maximum point-oriented hysteretic rule is employed for IDA analyses. The results indicate that the seismic capacity of the RCC building would be overestimated without taking into account the mainshock-aftershock effects. It is also found that the seismic capacity of the RCC building decreases with the increase of the relative intensity of aftershock ground motions to mainshock ground motions. In addition, the effects of artificial mainshock-aftershock ground motions generated from the repeated and randomized approaches and the polarity of the aftershock with respect to the mainshock on the evaluation of the RCC are also researched, respectively.

• Journal of the Korean Geotechnical Society
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• v.34 no.8
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• pp.51-64
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• 2018

Korean peninsula is known to be far from the plate boundary and not to generate large-scale earthquakes. However, earthquakes recently occurred in Gyeongju (2016/09/12, $M_L=5.8$) and Pohang (2017/11/15, $M_L=5.4$). The interest in earthquake engineering has increased, and various studies are actively underway by recently events. However, the seismic station network in Korea is less dense than that of the western U.S., resulting in the lack of data for detailed analyses of earthquakes. Therefore, KMA (Korea Meteorological Administration) set up temporary seismic stations and recorded ground motions from aftershocks. In this study, characteristics of Pohang seismic propagation and generation of bedrock motion are analyzed through the aftershock ground motion records at both permanent and temporary stations, as well as through the collected geological structure and site information. As a result, the response at Mangcheon-Li shows evidences of basin effects from both geology structures and measured aftershock motions.

• Earthquakes and Structures
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• v.15 no.5
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• pp.529-540
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• 2018

The influences of initial damage paths and aftershock (AS) spectral shape on the assessment of AS collapse fragility are investigated. To do this, a four-story ductile reinforced concrete (RC) frame structure is employed as the study case. The far-field earthquake records recommended by FEMA P695 are used as AS ground motions. The AS incremental dynamic analyses are performed for the damaged structure. To examine the effect of initial damage paths, a total of six kinds of initial damage paths are adopted to simulate different initial damage states of the structure by pushover analysis and dynamic analysis. For the pushover-based initial damage paths, the structure is "pushed" using either uniform or triangle lateral load pattern to a specified damage state quantified by the maximum inter-story drift ratio. Among the dynamic initial damage paths, one single mainshock ground motion or a suite of mainshock ground motions are used in the incremental dynamic analyses to generate a specified initial damage state to the structure. The results show that the structure collapse capacity is reduced as the increase of initial damage, and the initial damage paths show a significant effect on the calculated collapse capacities of the damaged structure (especially at severe damage states). To account for the effect of AS spectral shape, the AS collapse fragility can be adjusted at different target values of ${\varepsilon}$ by using the linear correlation model between the collapse capacity (in term of spectral intensity) and the AS ${\varepsilon}$ values, and coefficients of this linear model is found to be associated with the initial damage states.

• Earthquakes and Structures
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• v.16 no.4
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• pp.425-436
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• 2019

Successive ground motions having short time intervals have occurred in many earthquakes so far. It is necessary to investigate the effects of this phenomenon on different types of structures and to take these effects into consideration while designing or retrofitting structures. The effects of seismic sequences on the structures with combined reinforced concrete shear wall and moment resisting frame system have not been investigated in details yet. This paper has tried to analyse the seismic performance of structures with such structural systems subjected to mainshock-aftershock sequences. The effects of the seismic sequences on the investigated models are evaluated by strong measures such as IDA capacity and fragility and vulnerability curves. The results of this study show that the seismic sequences have a significant effect on the investigated models, which necessitates considering this effect on designing, retrofitting, decision making, and taking precautions.

• Earthquakes and Structures
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• v.11 no.4
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• pp.649-664
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• 2016

A seismic damaged bridge may be hit again by a strong aftershock or another earthquake in a short interval before the repair work has been done. However, discussions about the impact of the unrepaired damages on the residual earthquake resistance of a steel bridge are very scarce at present. In this paper, nonlinear time-history analysis of a steel arch bridge was performed using multi-scale hybrid model. Two strong historical records of main shock-aftershock sequences were taken as the input ground motions during the dynamic analysis. The strain response, local deformation and the accumulation of plasticity of the bridge with and without unrepaired seismic damage were compared. Moreover, the effect of earthquake sequence on crack initiation caused by low-cycle fatigue of the steel bridge was investigated. The results show that seismic damage has little impact on the overall structural displacement response during the aftershock. The residual local deformation, strain response and the cumulative equivalent plastic strain are affected to some extent by the unrepaired damage. Low-cycle fatigue of the steel arch bridge is not induced by the earthquake sequences. Damage indexes of low-cycle fatigue predicted based on different theories are not exactly the same.

• Earthquakes and Structures
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• v.10 no.3
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• pp.495-521
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• 2016

Ancient monuments of Greek and Roman classical architecture usually consist of multi-drum columns that are constructed of stone blocks placed on top of each other. Several research studies deal with the seismic behaviour of such structures, since earthquakes are common causes of destruction of such monuments. This paper investigates the effect of multiple earthquakes on the seismic performance of multi-drum columns, through numerical simulations and parametric analyses. The Discrete Element Method and an appropriate contact model have been implemented in a specially developed software application that is able to efficiently perform the necessary simulations in two dimensions. Specifically, various strong ground excitations are used in series for the computation of the collective final deformation of multi-drum columns. In order to calculate this cumulative deformation for a series of ground motions, the individual deformation of the column for each excitation is computed and then used as initial conditions for the next earthquake excitation. Various multi-drum columns with different dimensions are also considered in the analyses in order to examine how the geometric characteristics of columns can affect their seismic sequence behaviour, in combination with the excitation frequency content.

• Earthquakes and Structures
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• v.18 no.2
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• pp.147-162
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• 2020

This paper presents a novel precast energy dissipation shear wall (PEDSW) structure system that using mild steel dampers as dry connectors at the vertical joints to connect adjacent wall panels. Analytical studies are systematically conducted to investigate the seismic performance of the proposed PEDSW under sequence-type ground motions. During earthquake events, earthquake sequences have the potential to cause severe damage to structures and threaten life safety. To date, the damage probability of engineering structures under earthquake sequence has not been included in structural design codes. In this study, numerical simulations on single-story PEDSW are carried out to validate the feasibility and reliability of using mild steel dampers to connect the precast shear walls. The seismic responses of the PEDSW and cast-in-place shear wall (CIPSW) are comparatively studied based on nonlinear time-history analyses, and the effectiveness of the proposed high-rise PEDSW is demonstrated. Next, the foreshock-mainshock-aftershock type earthquake sequences are constructed, and the seismic response and fragility curves of the PEDSW under single mainshock and earthquake sequences are analyzed and compared. Finally, the fragility analysis of PEDSW structure under earthquake sequences is performed. The influences of scaling factor of the aftershocks (foreshocks) to the mainshocks on the fragility of the PEDSW structure under different damage states are investigated. The numerical results reveal that neglecting the effect of earthquake sequence can lead to underestimated seismic responses and fragilities, which may result in unsafe design schemes of PEDSW structures.