• Geomechanics and Engineering
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• v.16 no.6
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• pp.569-575
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• 2018

The stability of shallow cavities with an arbitrary profile is a difficult issue in geotechnical engineering. This paper investigates this problem on the basis of the upper bound theorem of limit analysis and the Hoek-Brown failure criterion. The influence of pore pressure is taken into consideration by regarding it as an external force acting on rock skeleton. An objective function is constructed by equating the internal energy dissipation to the external force work. Then the Lagrange variation approach is used to solve this function. The validity of the proposed method is demonstrated by comparing the analytical solutions with the published research. The relations between shallow and deep cavity are revealed as well. The detaching curve of cavity roof with elliptical profile is obtained. In order to facilitate the application of engineering practice, the numerical results are tabulated, which play an important role in tunnel design and stability analysis of roof. The influential factors on potential collapse are taken into consideration. From the results, the impact of various factors on the extent of detaching is seen intuitively.

• Earthquakes and Structures
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• v.22 no.3
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• pp.289-304
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• 2022

During strong ground motions, adjacent structures with insufficient separation distances collide with each other causing considerable architectural and structural damage or collapse of the whole structure. Generally, existing design procedures for determining the separation distance between adjacent buildings subjected to structural pounding are based on approximations of the buildings' peak relative displacement. These procedures are based on unknown safety levels. This paper attempts to evaluate the influence of foundation flexibility on the structural seismic response by considering the variability in the system and uncertainties in the ground motion characteristics through comprehensive numerical simulations. Actually, the aim of this study is to evaluate the influence of foundation flexibility on probabilistic evaluation of structural pounding. A Hertz-damp pounding force model has been considered in order to effectively capture impact forces during collisions. In total, 5.25 million time-history analyses were performed over the adopted models using an ensemble of 25 ground motions as seismic input within OpenSees software. The results of the study indicate that the soil-structure interaction significantly influences the pounding-involved responses of adjacent structures during earthquakes and generally increases the pounding probability.

• Nuclear Engineering and Technology
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• v.55 no.7
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• pp.2670-2677
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• 2023

In the nuclear safety studies, a new trend refers to the evaluation of uncertainties as a mandatory component of best-estimate safety analysis which is a modern and technically consistent approach being known as BEPU (Best Estimate Plus Uncertainty). The major objectives of this study consist in performing a study of uncertainties/sensitivities of the major analysis results for a generic CANDU 6 Nuclear Power Plant during Station Blackout (SBO) progression to understand and characterize the sources of uncertainties and their effects on the key figure-of-merits (FOMs) predictions in severe accidents (SA). The FOMs of interest are hydrogen mass generation and event timings such as the first fuel channel failure time, beginning of the core disassembly time, core collapse time and calandria vessel failure time. The outcomes of the study, will allow an improvement of capabilities and expertise to perform uncertainty and sensitivity analysis with severe accident codes for CANDU 6 Nuclear Power Plant.

• Journal of the Korean Institute of Gas
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• v.27 no.4
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• pp.27-33
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• 2023

In a petrochemical plant, various mechanical equipments and structures are interconnected to ensure operability. Since the production activities of petrochemical plants have a great impact on the national economy, it is very important to maintain not only structural safety but also the operability of the facilities. However, the current seismic design standards present the design requirements of facilities mainly aimed at preventing collapse, and do not provide the requirements for securing operability of facilities. Depending on the behavioral characteristics of the facility, operability of the facility can be secured by seismic performance levels other than the collapse prevention level, so it is necessary to present seismic design methods that can apply various seismic performance levels. Spherical (ball) storage tanks are supported by columns and braces and exhibit complex nonlinear behavior because of buckling and yielding of support members. In this study, nonlinear seismic behavior characteristics were statistically analyzed and a new performance-based seismic design method was proposed based on them.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.6
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• pp.675-682
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• 2015

Current design codes such as AASHTO LRFD or Korean Highway Bridge Design Code recommend of using static force for designing bridge column against vehicle collisions. However, there was an accident that the bridge was collapsed shortly after vehicle impact on bridge pier in Nebraska(near Big Spring, 2003). It was found that the second largest cause of bridge collapse is collision after hydraulic causes. It can be thought that the possibility of truck-bridge collision are getting increasing as the size of truck increases and traffic condition are becoming improved. However, dynamic behavior under the impact loading seldom considered in bridge design procedure due to computational cost and time. In this study, in order to reduce the computational cost for dynamic impact analysis, model reduction method was developed. Obtained results of residual displacement were compared with the results of direct impact simulations.

• Structural Engineering and Mechanics
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• v.20 no.5
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• pp.505-526
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• 2005

The influence of the inter-story structural pounding on the seismic behaviour of adjacent multistory reinforced concrete structures with unequal total heights and different story heights is investigated. Although inter-story pounding is a common case in practice, it has not been studied before in the literature as far as the authors are aware. Fifty two pounding cases, each one for two different seismic excitations, are examined. From the results it can be deduced that: (i) The most important issue in the inter-story pounding is the local effect on the external column of the tall building that suffers the impact from the upper floor slab of the adjacent shorter structure. (ii) The ductility demands for this column are increased comparing with the ones without the pounding effect. In the cases that the two buildings are in contact these demands appear to be critical since they are higher than the available ductility values. In the cases that there is a small distance between the interacting buildings the ductility demands of this column are also higher than the ones of the same column without the pounding effect but they appear to be lower than the available ductility values. (iii) It has to be stressed that in all the examined cases the developed shear forces of this column exceeded the shear strength. Thus, it can be concluded that in inter-story pounding cases the column that suffers the impact is always in a critical condition due to shear action and, furthermore, in the cases that the two structures are in contact from the beginning this column appears to be critical due to high ductility demands as well. The consequences of the impact can be very severe for the integrity of the column and may be a primary cause for the initiation of the collapse of the structure. This means that special measures have to be taken in the design process first for the critically increased shear demands and secondly for the high ductility demands.

• Journal of Wetlands Research
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• v.25 no.4
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• pp.345-352
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• 2023

Recently, the risk of snow disasters has been increasing South Korea. The damages of heavy snow were categorized into direct and indirect. Direct damage is usually the collapse of buildings as houses, greenhouse or barns. Indirect damage is various, for example, traffic congestion, traffic acident, drop damage, and so on. In South Korea, direct damage is severe in rural area, mosty collapse of greenhouse or barns. However, indirect damage such as traffic accident is mostly occurred in urban area. Therefore, the regional characteristics should be considered when vulnerability is evaluated. Therefore, in this study, the PSR and DPSIR method were applied by regional scale in South Korea. The PSR evaluation method is divided into pressure, state, and reaction index. however, the DPSIR evaluation method is divided into Driving force, Pressure, State, Impact, and Response index. the DPSIR evaluation method is divided into Driving force, Pressure, State, Impact, and Response index. Data corresponding to each indicator were collected, and the weight was calculated using the entropy method to calculate the snowfall vulnerability index by regional scale in South Korea. Calculated heavy snow damage vulnerabilities from the two methods were compared. The calculated vulnerabilities were validated using the recent snow damage in South Korea from 2018 to 2022. Snow vulnerability index calculated using the DPSIR method showed more reliable results. The results of this study could be utilized as an information to prepare the mitigation of heavy snow damage and to establish an efficient snow removal response system.

• Journal of the Korea Concrete Institute
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• v.25 no.5
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• pp.485-496
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• 2013

In recent years, frequent terror or military attacks by explosion or impact accidents have occurred. Examplary case of these attacks were World Trade Center collapse and US Department of Defense Pentagon attack on Sept. 11 of 2001. These attacks of the civil infrastructure have induced numerous casualties and property damage, which raised public concerns and anxiety of potential terrorist attacks. However, a existing design procedure for civil infrastructures do not consider a protective design for extreme loading scenario. Also, the extreme loading researches of prestressed concrete (PSC) member, which widely used for nuclear containment vessel, gas tank, bridges, and tunnel, are insufficient due to experimental limitations of loading characteristics. To protect concrete structures against extreme loading such as explosion and impact with high strain rate, understanding of the effect, characteristic, and propagation mechanism of extreme loadings on structures is needed. Therefore, in this paper, to evaluate the impact resistance capacity and its protective performance of bi-directional unbonded prestressed concrete member, impact tests were carried out on $1400mm{\times}1000mm{\times}300mm$ for reinforced concrete (RC), prestressed concrete without rebar (PS), prestressed concrete with rebar (PSR, general PSC) specimens. According to test site conditions, impact tests were performed with 14 kN impactor with drop height of 10 m, 5 m, 4 m for preliminary tests and 3.5 m for main tests. Also, in this study, the procedure, layout, and measurement system of impact tests were established. The impact resistance capacity was measured using crack patterns, damage rates, measuring value such as displacement, acceleration, and residual structural strength. The results can be used as basic research references for related research areas, which include protective design and impact numerical simulation under impact loading.

• Explosives and Blasting
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• v.30 no.2
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• pp.9-20
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• 2012

These days, mining industry prefers underground development for large mining because of exhaustive minning resources and large drafts and mining cavities thanks to extensive distribution of heavy excavation machines. In a mining design, to control collapse of cavities and secure stability, design of cavities and pillars are considered as very important. Therefore, this study obtained a prediction equation of blasting vibration through instrumentation for underground cavities. And we obtained theoretical shock vibration imposed on pillar through fragmentation analysis and measurement of flyrock distance. To examine the influence of pillar in underground mining blasting, we carried a finite element analysis and compared the result with prediction equation of blasting vibration, and shock vibration of flyrock when a impact was imposed on pillar and theoretical shock vibration.

• Earthquakes and Structures
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• v.1 no.4
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• pp.371-390
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• 2010

Historical buildings in seismically active regions are severely damaged by earthquakes, since they certainly were not designed by the original builders to withstand seismic effects. In particular the reports after major ground motions indicate that earthquake-induced pounding between buildings may lead to substantial damage or even collapse of colliding structures. The research on structural pounding during earthquakes has been recently much advanced, although most of the studies are conducted on simplified single degree of freedom systems. In this paper a detailed pounding-involved response analysis of three adjacent structures is performed, concerning the main bodies of the "Quinto Orazio Flacco" school. The construction includes a main masonry building, with an M-shaped plan, and a reinforced concrete building, separated from the masonry one and realized along its free perimeter. By the analysis of the capacity curves obtained by suitable pushover procedures performed separately for each building, it emerges that masonry and reinforced concrete buildings are vulnerable to earthquake-induced structural pounding in the longitudinal direction. In particular, due to the geometric configuration of the school, a special case of impact between the reinforced concrete structure and two parts of the masonry building occurs. In order to evaluate the pounding-involved response of three adjacent structures, in this paper a numerical procedure is proposed, programmed using MATLAB software. Both a non-linear viscoelastic model to simulate impact and an elastic-perfectly plastic approximation of the storey shear force-drift relation are assumed, differently from many commercial softwares which admit just one non-linearity.