• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.2
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• pp.73-87
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• 2019

Ocean waves are the driving force for the sediment transport and the beach process. However, wave actions are nonlinear and non-stationary, and the response of the beach is inconsistent in terms of reaction rate and magnitude. Therefore, the beach process is difficult to predict accurately. The purpose of this study is to identify the correlations between the shoreline change and ocean waves observed in the east coast of Korea. The relation of the beach width obtained from video monitoring at five sandy beaches and the wave data obtained from nearby wave monitoring at three points was analyzed. Although the correlations estimated over the whole data sets was not significant, the correlations estimated based on the seasonal period or wave conditions provided more noteworthy information. When the non-exceedance probability of the wave height was greater than 0.99, the wave period and beach width showed strong negative correlations. In case the non-exceedance probability of the wave period was greater than 0.99, the wave height and beach width showed strong negative correlations as well. Furthermore, the erosion rate of the beach width increased when the primary wave direction was close to normal to the coastline. Little significant seasonal or monthly change was found between the beach width and the wave, but it was greatly affected by intensive events such as typhoons. Thus, it is necessary to analyze in detail the wave height or period level explaining the change of beach width for more relevant and practical information.

• Earthquakes and Structures
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• v.7 no.2
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• pp.201-216
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• 2014

In this paper the vulnerability of the confined masonry buildings is evaluated analytically. The proposed approach includes the nonlinear dynamic analysis of the two-story confined masonry buildings with common plan as a reference structure. In this approach the damage level is calculated based on the probability of exceedance of loss vs a specified ground motion in the form of fragility curves. The fragility curves of confined masonry wall buildings are presented in two levels of limit states corresponding to elastic and maximum strength versus PGA based on analytical method. In this regard the randomness of parameters indicating the characteristics of the building structure as well as ground motion is considered as likely uncertainties. In order to develop the analytical fragility curves the proposed analytical models of confined masonry walls in a previous investigation of the authors, are used to specify the damage indices and responses of the structure. In order to obtain damage indices a series of pushover analyses are performed, and to identify the seismic demand a series of nonlinear dynamic analysis are conducted. Finally by considering various mechanical and geometric parameters of masonry walls and numerous accelerograms, the fragility curves with assuming a log normal distribution of data are derived based on capacity and demand of building structures in a probabilistic approach.

• Earthquakes and Structures
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• v.8 no.2
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• pp.443-462
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• 2015

Some model building codes stipulate that the design displacement of a building can be computed using the elastic static analysis results multiplied by the deflection amplification factor, $C_d$. This approach for estimating the design displacement is essential and appealing in structural engineering practice when nonlinear response history analysis (NRHA) is not required. Furthermore, building codes stipulate the consideration of accidental torsion effects using accidental eccentricity, whether the buildings are symmetric-plan, or asymmetric-plan. In some model building codes, the accidental eccentricity is further amplified by the torsional amplification factor $A_x$ in order to minimize the discrepancy between statically and dynamically estimated responses. Therefore, this warrants exploration of the reliability of statically estimated design displacements in accordance with the building code requirements. This study uses the discrepancy curves as a way of assessing the reliability of the design displacement estimates resulting from the factors $C_d$ and $A_x$. The discrepancy curves show the exceedance probabilities of the differences between the statically estimated design displacements and NRHA results. The discrepancy curves of 3-story, 9-story, and 20-story example buildings are investigated in this study. The example buildings are steel special moment frames with frequency ratios equal to 0.7, 1.0, 1.3, and 1.6, as well as existing eccentricity ratios ranging from 0% to 30%.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.15 no.1
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• pp.35-42
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• 1979

This paper concerns the receding of the eastern coastline of Korean peninsula at a macroscopic point of view, the result is as following. 1. Eastern coast is gradually developed from maturity stage to full maturity stage. 2. The coastline recession due to sea level rise is amounted to the receding distance, x=0.045 m per yr. 3. The author proposes another classification from the new view point, which is classified by comparing quantities between river supplying sediment loads, and the littoral drifting due to wave actions. According this, eastern coast is receding(Type Q-A), and we could find it's geomorphological characteristics. 4. The general piofile of eastern coast sand beach is erosional storm profile(Type I) which accompany offshore bar. 5. From the wave measuring data of eastern coast(Hoopo port), I can derive the linear regression line of the exceedance probability of wave height from the log-normal distribution. $z=O. 113+4.335 log_lo H, r=0.983.$ Above equation made it possible to estimate $\omega[=P(H>H_c)]for the effective wave height H_c=2. Om4, 4. Om and their corresponding values are considerable (7.8%, 0.3%) 6. Eastern coastline certainly have the tendency of erosive and receding, owing to the sea level rise, poor sediment source and effective wave actions. It's very desirable to survey coastline evolution for a long time systematically, in order to make more elaborate diagnosis.

• Structural Engineering and Mechanics
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• v.25 no.3
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• pp.311-330
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• 2007

Model-based predictions of structural behavior are negatively affected by uncertainties of various type and in various stages of the structural analysis. The present paper focusses on dynamic analysis and addresses the effects of uncertainties concerning material and geometric parameters, mainly in the context of modal analysis of large-scale structures. Given the large number of uncertain parameters arising in this case, highly scalable simulation-based methods are adopted, which can deal with possibly thousands of uncertain parameters. In order to solve the reliability problem, i.e., the estimation of very small exceedance probabilities, an advanced simulation method called Line Sampling is used. In combination with an efficient algorithm for the estimation of the most important uncertain parameters, the method provides good estimates of the failure probability and enables one to quantify the error in the estimate. Another aspect here considered is the uncertainty quantification for closely-spaced eigenfrequencies. The solution here adopted represents each eigenfrequency as a weighted superposition of the full set of eigenfrequencies. In a case study performed with the FE model of a satellite it is shown that the effects of uncertain parameters can be very different in magnitude, depending on the considered response quantity. In particular, the uncertainty in the quantities of interest (eigenfrequencies) turns out to be mainly caused by very few of the uncertain parameters, which results in sharp estimates of the failure probabilities at low computational cost.

• Earthquakes and Structures
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• v.14 no.5
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• pp.437-447
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• 2018

Computational cost is one of the major obstacles for detailed risk analysis of structures. This paper puts forward a methodology for efficient probabilistic seismic loss assessment of structures using the Endurance Time (ET) analysis and the first-order reliability method (FORM). The ET analysis efficiently yields the structural responses for a continuous range of intensities through a single response-history analysis. Taking advantage of this property of ET, FORM is employed to estimate the annual rate of exceedance for the loss components. The proposed approach is an amalgamation of two analysis approaches, ET and FORM, that significantly lower the computational costs. This makes it possible to evaluate the seismic risk of complex systems. The probability distribution of losses due to the structural and non-structural damage as well as injuries and fatalities of a prototype structure are estimated using the proposed methodology. This methodology is an alternative to the prevalent risk analysis framework of the total probability theorem. Hence, the risk estimates of the proposed approach are compared with those from the total probability theorem as a benchmark. The results indicate a satisfactory agreement between the two methods while a significantly lower computational demand for the proposed approach.

• Earthquakes and Structures
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• v.12 no.1
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• pp.109-118
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• 2017

A novel post-tensioned self-centering (SC) concrete beam-column connection with web friction devices has been proposed for concrete moment-resisting frames. This paper presents a probabilistic performance evaluation procedure to evaluate the performance of the self-centering concrete frame with the proposed post-tensioned beam-column connections. Two performance limit states, i.e., immediate occupancy (IO) and repairable (RE) limit states, are defined based on peak and residual story drift ratios. Statistical analyses of seismic demands revealed that the dispersion of residual drifts is larger than that of peak drifts. Due to self-centering feature of post-tensioning connections, the SC frame was found to have high probabilities to be recentered under the design basis earthquake (DBE) and maximum considered earthquake (MCE) ground motions. Seismic risk analysis was performed to determine the annual (50-year) probability of exceedance for IO and RE performance limit states, and the results revealed that the design objectives of the SC frame would be met under the proposed performance-based design approach.

• Earthquakes and Structures
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• v.15 no.3
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• pp.319-334
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• 2018

In this paper, an analytical study was carried out to propose an optimum base-isolated system for the design of steel structures equipped with lead rubber bearings (LRB). For this, 5 and 10-storey steel moment resisting frames (MRFs) were designed as Special Moment Frame (SMF). These two-dimensional and three-bay frames equipped with a set of isolation systems within a predefined range that minimizes the response of the base-isolated frames subjected to a series of earthquakes. In the design of LRB, two main parameters, namely, isolation period (T) and the ratio of strength to weight (Q/W) supported by isolators were considered as 2.25, 2.5, 2.75 and 3 s, 0.05, 0.10 and 0.15, respectively. The Force-deformation behavior of the isolators was modelled by the bi-linear behavior which could reflect the nonlinear characteristics of the lead-plug bearings. The base-isolated frames were modelled using a finite element program and those performances were evaluated in the light of the nonlinear time history analyses by six natural accelerograms compatible with seismic hazard levels of 2% probability of exceedance in 50 years. The performance of the isolated frames was assessed in terms of roof displacement, relative displacement, interstorey drift, absolute acceleration, base shear and hysteretic curve.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.1 s.139
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• pp.43-49
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• 2005

in this paper a dolphin-fender moored pontoon-type floating structure in shallow water depth is studied focusing on mooring force. The pontoon-type floating structure is 500m long, 300m wide. The structure has partially non-uniform drafts of 2.0m and 3.0m. The employed mooring system is a guyed frame type dolphin-fender system. The 1/125 scale model fender system is made of rubber tube to have hi-linear load deflection characteristics. A series of model tests has been conducted focusing on motion and fender force responses in regular and irregular waves at KRISO's ocean engineering basin Non-linear numerical simulation of fender reaction force has been carried out and the results are compared with those of model tests. The simulated rigid body motion and mooring forces also have been compared with the test results.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.3
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• pp.271-276
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• 2009

Under current design standard, sewers are designed to drain stormwater generated up to 10 year return period of storms. This implies sewer flooding could occur from rainfall exceeding a 10 year return period. 5, 10, 20 and 30 year return period of storm intensities were calculated for 22 locations (cities) of meterological stations over the nation and compared to the recorded rainfall intensities for the last 30 years. The comparison resulted in the numbers of year maximum rainfall intensities exceeded each return period. Using the questionnaire survey for "the incidences of flooding since 1980" of the previous paper (Survey on sewerage operation/management planning for flooding (I)), the actual rainfall records on the date of flooding events were analyzed to demonstrate the number of flooding events caused by the exceedance of sewer capacity. For the last 30 years, more than 6 years of year maximum rainfall intensity (20%) were larger than the 10 year return period of storm in 4 cities of the 22 used for the first analysis. The number of rainfall records that exceeded the 10 year return period was 50 of the 260 actual flooding events investigated from the survey.