• Earthquakes and Structures
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• 제8권6호
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• pp.1349-1362
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• 2015

This paper presents an analytical study aimed at evaluating the effectiveness of using buckling-restrained braces (BRBs) in mitigating the seismic response of a case study 6 storey reinforced concrete (RC) building. In the design of the BRBs with non-prismatic cross-sections, twelve combinations of ${\alpha}$ and ${\beta}$ design parameters that influence the strength and stiffness of the BRBs, respectively, were considered. The response of the structure with and without BRBs under earthquake ground accelerations were evaluated through nonlinear dynamic analysis. Two sets of ground motions representative of the design earthquake with 10% and 50% exceedance probability in fifty years were taken into account. By comparing the structural performance of the original and buckling restrained braced structures, it was observed that the use of the BRBs were very effective in mitigating the seismic response as a retrofit scheme. However, the selection of the strength and stiffness parameters of the BRBs had considerable effect on the response characteristics of RC structures. For instance, by increasing the value of ${\alpha}$ and by decreasing the value of ${\beta}$ of the buckling-restrained braces, the maximum deformation demand of the structures increased.

• 국제강구조저널
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• 제18권4호
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• pp.1252-1264
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• 2018

Long span bridges such as steel cable stayed and suspension bridges are usually more flexible than short to medium span bridges and expected to have large deformations. Deflections due to live load for long span bridges are important since it controls the overall heights of the bridge for securing the clearance under the bridge and serviceability for securing the comfort of passengers or pedestrians. In case of sea-crossing bridges, the clearance of bridges is determined considering the height of the ship master from the surface of the water, the trim of the ship, the psychological free space, the tide height, and live load deflection. In the design of bridges, live load deflection is limited to a certain value to minimize the vibrations. However, there are not much studies that consider the live load deflection and its effects for long span bridges. The purpose of this study is to investigate the suitability of live load deflection limit and its actual effects on serviceability of bridges for steel cable-stayed and suspension bridges. Analytical study is performed to calculate the natural frequencies and deflections by design live load. Results are compared with various design limits and related studies by Barker et al. (2011) and Saadeghvaziri et al. (2012). Two long span bridges are selected for the case study, Yi Sun-Sin grand bridge (suspension bridge, main span length = 1545 m) and Young-Hung grand bridge (cable stayed bridge, main span length = 240 m). Long-term measured deflection data by GNSS system are collected from Yi Sun-Sin grand bridge and compared with the theoretical values. Probability of exceedance against various deflection limits are calculated from probability distribution of 10-min maximum deflection. The results of the study on the limitation of live load deflection are expected to be useful reference for the design, the proper planning and deflection review of the long span bridges around the world.

• 대한토목학회논문집
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• 제13권2호
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• pp.141-149
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• 1993

수력에너지 생산량은 추계학적인 저수지 유입량에 지배되므로 전력량 판매 계약에는 이를 반영하여 합리성을 보장해야 할 필요가 있다. 본 연구에서는 유입량의 신뢰도별로 저수지조작(貯水池操作)을 수행하여 최적 신뢰도 및 이에 따른 최적 전력 판매계약량을 결정하는 방법을 제시하였다. 목적함수에는 전력생산량이 신뢰도를 벗어나는 위험에 대한 손실함수를 도입하고, 손실계수의 범위를 제시하였다. 여기서 손실은 계약량을 공급하지 못할 경우 지불해야 할 벌칙량을 의미하고 신뢰도는 저수지 유입량에 대한 초과 확률과 같고, 이 때 확률밀도함수는 대수정규분포를 5% 유의수준에서 채택하였다. 최적의 신뢰도를 결정하기 위하여 오목함수 범위에서 황금비 조사 기법을 썼으며, 신뢰도별 최대 수력 에너지를 얻기 위해 증분 동적계획 기법으로 저수지 조작을 수행하였다. 본 연구의 적용대상으로 대청 다목적댐 및 수력발전소를 택하여 손실계수, 최적 신뢰도 및 계약 발전량을 구하였다.

• Architectural research
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• 제14권3호
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• pp.99-108
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• 2012

An innovative multi-story Semi-Active Tuned Mass Damper (SATMD) building system is proposed to control seismic response of existing structures. The application of adding new stories as large tuned mass and semi-active (SA) resettable actuators as central features of the control scheme is derived. For the effective control of the structures, the optimal tuning parameters are considered for the large mass ratio, for which a previously proposed equation is used and the practical optimal stiffness is allocated to the actuator stiffness and rubber bearing stiffness. A two-degree-of freedom (2-DOF) model is adopted to verify the principal efficiency of the suggested structural control concept. The simulations for this study utilizes the three ground motions, from SAC project, having probability of exceedance of 50% in 50 years, 10% in 50 years, and 2% in 50 years for the Los Angeles region. 12-story moment resisting frames, which are modified as '12+2' and '12+4' story structures, are investigated to assess the viability and effectiveness of the system that aims to reduce the response of the buildings to earthquakes. The control ability of the SATMD scheme is compared to that of an uncontrolled and an ideal Passive Tuned Mass Damper (PTMD) building system. From the performance results of suggested '12+2' and '12+4' story retrofitting case studies, SATMD systems shows significant promise for application of structural control where extra stories might be added.

• Structural Engineering and Mechanics
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• 제33권6호
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• pp.725-745
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• 2009

In this paper, probabilistic seismic performance assessment of a typical non-seismic RC frame building representative of a large inventory of existing buildings in developing countries is conducted. Nonlinear time-history analyses of the sample building are performed with 20 large-magnitude medium distance ground motions scaled to different levels of intensity represented by peak ground acceleration and 5% damped elastic spectral acceleration at the first mode period of the building. The hysteretic model used in the analyses accommodates stiffness degradation, ductility-based strength decay, hysteretic energy-based strength decay and pinching due to gap opening and closing. The maximum inter story drift ratios obtained from the time-history analyses are plotted against the ground motion intensities. A method is defined for obtaining the yielding and collapse capacity of the analyzed structure using these curves. The fragility curves for yielding and collapse damage levels are developed by statistically interpreting the results of the time-history analyses. Hazard-survival curves are generated by changing the horizontal axis of the fragility curves from ground motion intensities to their annual probability of exceedance using the log-log linear ground motion hazard model. The results express at a glance the probabilities of yielding and collapse against various levels of ground motion intensities.

• Earthquakes and Structures
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• 제8권3호
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• pp.681-697
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• 2015

Iran as one of the countries located on the Alpine-Himalayan seismic belt has recently experienced a few number of catastrophic earthquakes. A well-known index of how buildings are affected by earthquakes is through assessment of probable Peak Ground Acceleration (PGA) and structures' response spectra. In this research, active faults around Kerman and Birjand, two major cities in eastern parts of Iran, have been considered. Seismic catalogues are gathered to categorize effects of surrounding faults on seismicity of the region. These catalogues were further refined with respect to time and space based on Knopoff-Gardner algorithm in order to increase statistical independency of events. Probabilistic Seismic Hazard Analysis (PSHA) has been estimated for each of cities regarding 50, 100, 200 and 500 years of structures' effective life-span. These results subsequently have been compared with Deterministic Seismic Hazard Analysis (DSHA). It has been observed that DSHA not necessarily suggests upper bound of PSHA results. Furthermore, based on spectral Ground Motion Prediction Equations (GMPEs), Uniform Hazard Spectra (UHS) and spectral acceleration were provided for 2% and 10% levels of probability of exceedance. The results show that increasing source-to-site distance leads to spectral acceleration reduction regarding each fault. In addition, the spectral acceleration rate of variation would increase if the source-to-site distance decreases.

• Earthquakes and Structures
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• 제15권3호
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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.

• 상하수도학회지
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• 제23권3호
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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.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2008년도 춘계 종합학술대회 논문집
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• pp.285-288
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• 2008

본 연구는 도시유역에서 강수계측망 밀도에 따른 빈도해석으로부터 관계곡선을 유도하여 최적 설계홍수량을 추적하고자 한다. 이를 위한 해석에는 도시전체를 한 개의 유역으로 하는 저밀도망과 13개 소구역으로 분할한 고밀도망에서 실측된 각기 다른 강우사상이 적용되었다. 저밀도망에는 39년간의 기상청 자료를 사용하였고, 고밀도망에는 6년간의 지자체 자료를 연초과치 계열로 확대하여 구성하였다. 그 결과 저밀도망은 지속기간 1시간에서 79.1mm, 24시간에서 329.1mm, 고밀도망은 93.0mm, 245.0mm가 각각 최대값으로 나타났으며, 빈도 관계곡선을 유도하기 위한 주요 6개 확률 분포형의 해석에서는 Gumbel 분포가 가장 적합한 것으로 나타났다.

• 대한조선학회논문집
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• 제42권1호
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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.