• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.718-725
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• 2002

A wall type friction damper is newly Proposed in this paper to improve the performance of R/C framed structures under earthquake loads. Although traditional dampers are usually placed as bracing members, the application ot bracing-type dampers into R/C structures is not as simple as those of steel structures due to the connection between R/C members and dampers and the stress concentration in connection region. Proposed damper is consisted of Teflon-sheet slider and R/C shear wall. The damper can also avoid stress concentration and reduce P-Δ effect. To evaluate the performance of proposed damper, nonlinear dynamic analyses are carried on 10 story and 3 bay R/C structures with numerical model for the damper. It is shown that the damper reduces the inter-story drifts and the time-historic responses; especially the damper prevents from forming plastic hinges on the lower columns.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.611-620
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• 1997

The history of Tidal Bench Mark(TBM) at four major tide observation stations on the the Korea West Coast is reviewed. The data concerned with the local mean sea level(LMSL), the datum level(DL), and TBM is collected and checked. The values of LMSL surveyed by Rural Development Corporation(RDC), Office of Hydrographic Affair(OHA), and Office of Port Affair(OPA) are compared so that their unbiased MSLs at four stations are determined. Kriging model is introduced to estimate the design levels for tide; DL, MSL, and high water spring tide(HWOST). The estimated design level is well fitted with the sample data. The value of the identified drifts increase with the latitude. The estimated semi-variograms ${\gamma}(h)$ show self similarity. The values of the ${\gamma}(h)$ for DL and HWOST are 0.005 times as much as the values of ${\gamma}(h)$ of MSL.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.529-534
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• 2009

Climate models, both global and regional, have increased in sophistication and are being run at increasingly higher resolutions. The Land Surface Models (LSMs) coupled to these climate models have evolved from simple bucket models to sophisticated Soil-Vegetation-Atmosphere Transfer (SVAT) schemes needed to support complex linkages and processes. However, some underpinnings of terrestrial hydrologic parameterizations so crucial in the predictions of surface water and energy fluxes cause model errors that often manifest as non-linear drifts in the dynamic response of land surface processes. This requires the improved parameterizations of key processes for the terrestrial hydrologic scheme to improve the model predictability in surface water and energy fluxes. The Common Land Model (CLM), one of state-of-the-art LSMs, is the land component of the Community Climate System Model (CCSM). However, CLM also has energy and water biases resulting from deficiencies in some parameterizations related to hydrological processes. This research presents the implementation of a selected set of parameterizations and their effects on the runoff prediction. The modifications consist of new parameterizations for soil hydraulic conductivity, water table depth, frozen soil, soil water availability, and topographically controlled baseflow. The results from a set of offline simulations are compared with observed data to assess the performance of the new model. It is expected that the advanced terrestrial hydrologic scheme coupled to the current CLM can improve model predictability for better prediction of runoff that has a large impact on the surface water and energy balance crucial to climate variability and change studies.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.1
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• pp.49-58
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• 2004

Drift design of a high-rise building is a governing factor in the determination of structural weights and lateral resisting systems. However, high-rise buildings are composed of tens of thousands of structural member, designer can not know which members are active to lateral drift control and how much they contribute to lateral drifts. Resizing technique was proved to be a practical method for drift design of high-rise buildings. However, no resizing algorithm has been considered the effect of vertical loads in drift designs. Thus, in this paper, a resizing algorithm has been developed for drift designs of high-rise buildings subjected to both lateral and vertical loads. The drift design model has been applied to drift designs of two high-rise building examples.

• Journal of the Korean Vacuum Society
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• v.20 no.5
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• pp.322-326
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• 2011

Etch process of silicon dioxide layer by using capacitively coupled plasma (CCP) is currently being used to manufacture semiconductor devices with nano-scale feature size below 50 nm. In typical CCP plasma etcher system, plasmas are generated by applying the RF power on upper electrode and ion bombardment energy is controlled by applying RF power to the bottom electrode with the Si wafer. In this case, however, etch results often drift due to heating of the electrode during etching process. Therefore, controlling the temperature of the upper electrode is required to obtain improvement of etch repeatability. In this work, we report repeatability improvement during the silicon dioxide etching under extreme process conditions with very high RF power and close gap between upper and bottom electrodes. Under this severe etch condition, it is difficult to obtain reproducible oxide etch results due to drifts in etch rate, critical dimension, profile, and selectivity caused by unexpected problems in the upper electrode. It was found that reproducible etch results of silicon dioxide layer could be obtained by controlling temperature of the upper electrode. Methods of controlling the upper electrode and the correlation with etch repeatability will be discussed in detail.

• Structural Engineering and Mechanics
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• v.56 no.4
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• pp.569-588
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• 2015

A comprehensive methodology is proposed for design of metallic dampers in seismic retrofit of earthquake-damaged frame structures. It is assumed that the metallic dampers remain elastic and only provide stiffness during frequent earthquake (i.e., earthquake with a 63% probability of exceedance in 50-year service period), while in precautionary earthquake (i.e., earthquake with a 10% probability of exceedance in 50-year service period), the metallic dampers yield before the main frame and dissipate most of the seismic energy to either prevent or minimize structural damages. Therefore by converting multi-story frame to an equivalent single-degree-of-freedom system, the added stiffness provided by metallic dampers is designed to control elastic story drifts within code-based demand under frequent earthquake, and the added damping with the combination of added stiffness influences is obtained to control structural stress within performance-based target under precautionary earthquake. With the equivalent added damping ratio, the expected damping forces provided by metallic dampers can be calculated to carry out the configuration and design of metallic dampers along with supporting braces. Based on a detailed example for retrofit of an earthquake-damaged reinforced concrete frame by using metallic dampers, the proposed design procedure is demonstrated to be simple and practical, which can not only meet current China's design codes but also be used in retrofit design of earthquake-damaged frame with metallic damper for reaching desirable performance objective.

• Structural Engineering and Mechanics
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• v.56 no.1
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• pp.27-47
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• 2015

In this study, the accuracy and reliability of fully nonlinear method against equivalent linear method for dynamic analysis of soil-structure interaction is investigated comparing the predicted results of both numerical procedures with the results of experimental shaking table tests. An enhanced numerical soil-structure model has been developed which treats the behaviour of the soil and the structure with equal rigour. The soil-structural model comprises a 15 storey structural model resting on a soft soil inside a laminar soil container. The structural model was analysed under three different conditions: (i) fixed base model performing conventional time history dynamic analysis, (ii) flexible base model (considering full soil-structure interaction) conducting equivalent linear dynamic analysis, and (iii) flexible base model performing fully nonlinear dynamic analysis. The results of the above mentioned three cases in terms of lateral storey deflections and inter-storey drifts are determined and compared with the experimental results of shaking table tests. Comparing the experimental results with the numerical analysis predictions, it is noted that equivalent linear method of dynamic analysis underestimates the inelastic seismic response of mid-rise moment resisting building frames resting on soft soils in comparison to the fully nonlinear dynamic analysis method. Thus, inelastic design procedure, using equivalent linear method, cannot adequately guarantee the structural safety for mid-rise building frames resting on soft soils. However, results obtained from the fully nonlinear method of analysis fit the experimental results reasonably well. Therefore, this method is recommended to be used by practicing engineers.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.2
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• pp.11-17
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• 2000

The drift and movement of oil slick in the sea are closely related to the flows at the sea surface (at 0m depth) because specific gravity of an oil is lighter than that of sea water. As an effort toward a development of realistic model for oil spill drift on the sea surface, a study on sea surface wind-induced drift (skin drift) at 4 coastal regions of Korea was carried out. In this study, skin drifts were inferred from difference between the flow at the sea surface and that in underwater (at 1.5m depth). The average speed of skin drift in our experiments was 2.9% of wind speeds and the average direction of skin drift to wind was deflected to the right by 18.6°. The results of this experiment were used in the modelling of the skin drift as a prompt response of time-variable wind. The modelled skin drift, which corresponds to observed wind, successfully reproduced the observed trajectories of sea surface flows.

• Earthquakes and Structures
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• v.12 no.1
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• pp.13-21
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• 2017

Recent seismic events occurred in Italy (Emilia-Romagna 2012, Abruzzo 2009) and worldwide (New Zealand 2010 and 2011) highlighted some of the weaknesses of precast concrete industrial buildings, especially those related to the connecting systems traditionally employed to fasten the cladding panels to the internal framing. In fact, one of the most commons fails it is possible to observe in such structural typologies is related to the out-of-plane collapse of the external walls due to the unsatisfactory behaviour of the connectors used to join the panels to the perimeter beams. In this work, the strengthening of a traditional industrial building, assumed as a case study, made by precast reinforced concrete is proposed by the adoption of a dual system allowing the reinforcement of the structure by acting both internally; by pendular columns and, externally, on the walls. In particular, traditional connections at the top of the walls are substituted by devices able to work as a slider with vertical axis while, the bottom of the walls is equipped with two or more hysteretic dampers working on the uplift of the cladding panels occurring under seismic actions. By means of this approach, the structure is stiffened; obtaining a reduction of the lateral drifts under serviceability limit states. In addition, its seismic behaviour is improved due to the additional source of energy dissipation represented by the dampers located at the base of the walls. The effectiveness of the suggested retrofitting approach has been checked by comparing the performance of the retrofitted structure with those of the structure unreinforced by means of both pushover and Incremental Dynamic Analyses (IDA) in terms of behaviour factor, assumed as a measure of the ductility capacity of the structure.

• Earthquakes and Structures
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• v.12 no.1
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• pp.67-77
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• 2017

In this paper, it is aimed to present a comparative study about the structural behavior of tall buildings consisting of different type of materials such as concrete, steel or timber using finite element analyses and experimental measurements on shaking table. For this purpose, two 1/60 scaled 28 and 30-stories wooden building models with $40{\times}40cm$ and $35{\times}35cm$ ground/floor area and 1.45 m-1.55 m total height are built in laboratory condition. Considering the frequency range, mode shapes, maximum displacements and relative story drifts for structural models as well as acceleration, displacement and weight limits for shaking table, to obtain the typical building response as soon as possible, balsa is selected as a material property, and additional masses are bonded to some floors. Finite element models of the building models are constituted in SAP2000 program. According to the main purposes of earthquake resistant design, three different earthquake records are used to simulate the weak, medium and strong ground motions. The displacement and acceleration time-histories are obtained for all earthquake records at the top of building models. To validate the numerical results, shaking table tests are performed. The selected earthquake records are applied to first mode (lateral) direction, and the responses are recorded by sensitive accelerometers. Comparisons between the numerical and experimental results show that shaking table tests are enough to identify the structural response of wooden buildings. Considering 20%, 10% and 5% damping rations, differences are obtained within the range 4.03-26.16%, 3.91-65.51% and 6.31-66.49% for acceleration, velocity and displacements in Model-1, respectively. Also, these differences are obtained as 0.49-31.15%, 6.03-6.66% and 16.97-66.41% for Model-2, respectively. It is thought that these differences are caused by anisotropic structural characteristic of the material due to changes in directions parallel and perpendicular to fibers, and should be minimized using the model updating procedure.