Analytical study on hydrodynamic motions and structural behaviors of hybrid floating structure

Jeong, Youn-Ju,Lee, Du-Ho,Park, Min-Su,You, Young-Jun Techno-Press 2013 Ocean systems engineering Vol.3 No.1

In this study, a hybrid floating structure with cylinder was introduced to reduce the hydrodynamic motions of the pontoon type. The hybrid floating structure is composed of cylinders and semi-opened side sections to penetrate the wave impact energy. In order to exactly investigate the hydrodynamic motions and structural behavior of the hybrid floating structure under the wave loadings, integrated analysis of hydrodynamic and structural behavior were carried out on the hybrid floating structure. Firstly, the hydrodynamic analyses were performed on the hybrid and pontoon models. Then, the wave-induced hydrodynamic pressures resulting from hydrodynamic analysis were directly mapped to the structural analysis model. And, finally, the structural analyses were carried out on the hybrid and pontoon models. As a result of this study, it was learned that the hybrid model of this study was showed to have more favorable hydrodynamic motions than the pontoon model. The surge motion was indicated even smaller motion at all over wave periods from 4.0 to 10.0 sec, and the heave and pitch motions indicated smaller motions beyond its wave period of 6.5 sec. However, the hybrid model was shown more unfavorable structural behavior than the pontoon model. High concentrated stress occurred at the bottom slab of the bow and stern part where the cylinder wall was connected to the bottom slab. Also, the hybrid model behaved with the elastic body motion due to weak stiffness of floating body and caused a large stress variation at the pure slab section between the cylinder walls. Hence, in order to overcome these problems, some alternatives which could be easily obtained from the simple modification of structural details were proposed.

해저지진의 수직지반운동에 의한 부유식 해양구조물의 지진응답 해석기법 개발

이진호,김재관,진병무 한국지진공학회 2014 한국지진공학회논문집 Vol.18 No.6

Considering a rigorously fluid-structure interaction, a method for an earthquake response analysis of a floating offshore structure subjected to vertical ground motion from a seaquake is developed. Mass, damping, stiffness, and hydrostatic stiffness matrices of the floating offshore structure are obtained from a finite-element model. The sea water is assumed to be a compressible, nonviscous, ideal fluid. Hydrodynamic pressure, which is applied to the structure, from the sea water is assessed using its finite elements and transmitting boundary. Considering the fluid-structure interaction, added mass and force from the hydrodynamic pressure is obtained, which will be combined with the numerical model for the structure. Hydrodynamic pressure in a free field subjected to vertical ground motion and due to harmonic vibration of a floating massless rigid circular plate are calculated and compared with analytical solutions for verification. Using the developed method, the earthquake responses of a floating offshore structure subjected to a vertical ground motion from the seaquake is obtained. It is concluded that the earthquake responses of a floating offshore structure to vertical ground motion is severely influenced by the compressibility of sea water.

Experimental study on viscous effect in roll and heave motions of a rectangular structure

Kim, Mingyu,Jung, Kwang-Hyo,Park, Sungboo,Suh, Sung-Bu,Park, Il-Ryong,Kim, Jin,Kim, Kwang-Soo Elsevier 2019 Ocean engineering Vol.171 No.-

<P><B>Abstract</B></P> <P>This study focuses on the interaction between roll and heave motions of a rectangular structure, and the heave influence on the viscous effect on the roll motion experimentally in a two-dimensional wave tank. The dynamic responses were investigated with a range of regular wave periods, including longer, equal to, shorter than the natural roll wave period of the structure with wave steepness in beam sea conditions. The velocity fields were obtained using particle image velocimetry in the vicinity of the structure to elucidate the viscous effect on the roll motion, and its different features between the heave fixed and free conditions. Velocity maps were compared systematically to understand the heave and roll influences on the viscous effect for four motion conditions of all fixed, roll fixed and heave free, roll free and heave fixed, and roll and heave free. It is found that the heave motion has a significant impact on the viscous effect and the roll motion. The roll motion has the nonlinearity and the vortex strength was intensifying with the increase of the wave steepness at the natural roll period. The heave motion should be considered to estimate accurate roll damping and motion of floating structures.</P>

Seismic Response of Long Span Cable-stayed Bridge to Near-fault Vertical Ground Motions

Bipin Shrestha 대한토목학회 2015 KSCE Journal of Civil Engineering Vol.19 No.1

In design and analysis of seismic resistant structures and particularly the bridge structures vertical ground motion tends, in general,to be ignored or underestimated. However, during recent earthquakes high amplitude of motions were recorded in vertical directionnear to the fault, invalidating such design assumptions of neglecting the vertical motion. This paper presents an analyticalinvestigation on the effect of the near fault vertical ground motions on seismic response of a long span cable-stayed bridge. Responses of the bridge subjected to ground motions with and without vertical ground motion is carried using near fault groundmotions on three dimensional bridge model. A suite of five near field ground motion with varying V/H (Vertical to Horizontal) ratioof peak ground acceleration is used. Influence of vertical motion on global and local structural response is presented. The study alsotakes into consideration the arrival time of peak vertical motion which has received little attention previously. Effects of coincidenceof peak vertical motion with the peak horizontal motion in time domain are also analyzed. The study reveals that influence of verticalmotion on the seismic response of the Karnali Bridge is slight and coinciding peak vertical motion with peak horizontal motion alsohave slighter effects compared to the motion without such coincidence.

부유구조체 형상에 따른 동요감소 특성분석

이두호(Lee, Du Ho),정연주(Jeong, Youn Ju),유영준(You, Young Jun),박민수(Park, Min Su) 한국해안해양공학회 2013 한국해안해양공학회 논문집 Vol.25 No.6

이전 연구에서는 부유구조체의 동요저감을 위해 폰툰과 반잠수식 부유구조체 형식을 결합하여 하이브리드 부유구조체를 제안한 바 있다. 하이브리드 부유구조체는 입사파랑에 대한 동요감소에는 효과적이었으나 부유구조체에 충분한 부력을 제공할 수 없는 단점이 있었다. 이와 같은 단점을 보완하기 위해 본 연구에서는 새로운 형식의 콤비네이션 부유구조체를 제안하였다. 입사 파랑하중에 대한 부유구조체의 동요감소 효과를 비교하기위해 폰툰, 콤비네이션 그리고 하이브리드 부유구조체에 대한 수치해석을 동수역학 해석프로그램 ANSYS AQWA를 이용하여 수행하였다. 본 연구에서 제안된 콤비네이션 부유구조체가 다른 부유구조체에 비해 동요감소에 효과적인 것을 확인할 수 있었다. 따라서 콤비네이션 부유구조체는 앞으로 개발될 초대형 부유구조체 건설을 위한 신형식 부유구조체로서 매우 유용하게 사용될 것으로 판단된다. In previous study, the hybrid floating structure composed of a pontoon and a semi-submersible was suggested to reduce the motions of floating structure. It was reported that the suggested hybrid floating structure could reduce the motions. However, the hybrid floating structure could not support enough buoyancy. In this study, the combination floating structure is newly suggested to resolve the problem. In order to adopt the shape of floating structures reducing the motions, the hydrodynamic analysis of various floating structures such as the pontoon, the hybrid and the combination of floating structure is carried out through hydrodynamic analysis program ANSYS AQWA. It is found that the combination floating structure is remarkably effective to reduce the motions compared to the other cases. Thus, the suggested combination floating structure may be a useful offshore structure for constructing a very large floating structure.

The effects of vertical earthquake motion on an R/C structure

Selcuk Bas,Ilker Kalkan 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.59 No.4

The present study investigated the earthquake behavior of R/C structures considering the vertical earthquake motion with the help of a comparative study. For this aim, the linear time-history analyses of a high-rise R/C structure designed according to TSC-2007 requirements were conducted including and excluding the vertical earthquake motion. Earthquake records used in the analyses were selected based on the ratio of vertical peak acceleration to horizontal peak acceleration (V/H). The frequency-domain analyses of the earthquake records were also performed to compare the dominant frequency of the records with that of the structure. Based on the results obtained from the time-history analyses under the earthquake loading with (H+V) and without the vertical earthquake motion (H), the value of the overturning moment and the top-story vertical displacement were found to relatively increase when considering the vertical earthquake motion. The base shear force was also affected by this motion; however, its increase was lower compared to the overturning moment and the top-story vertical displacement. The other two parameters, the top-story lateral displacement and the top-story rotation angle, barely changed under H and H+V loading cases. Modal damping ratios and their variations in horizontal and vertical directions were also estimated using response acceleration records. No significant change in the horizontal damping ratio was observed whereas the vertical modal damping ratio noticeably increased under H+V loading. The results obtained from this study indicate that the desired structural earthquake performance cannot be provided under H+V loading due to the excessive increase in the overturning moment, and that the vertical damping ratio should be estimated considering the vertical earthquake motion.

Comparison of uniform and spatially varying ground motion effects on the stochastic response of fluid-structure interaction systems

Bilici, Yasemin,Bayraktar, Alemdar,Adanur, Suleyman Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.33 No.4

The effects of the uniform and spatially varying ground motions on the stochastic response of fluid-structure interaction system during an earthquake are investigated by using the displacement based fluid finite elements in this paper. For this purpose, variable-number-nodes two-dimensional fluid finite elements based on the Lagrangian approach is programmed in FORTRAN language and incorporated into a general-purpose computer program SVEM, which is used for stochastic dynamic analysis of solid systems under spatially varying earthquake ground motion. The spatially varying earthquake ground motion model includes wave-passage, incoherence and site-response effects. The effect of the wave-passage is considered by using various wave velocities. The incoherence effect is examined by considering the Harichandran-Vanmarcke and Luco-Wong coherency models. Homogeneous medium and firm soil types are selected for considering the site-response effect where the foundation supports are constructed. A concrete gravity dam is selected for numerical example. The S16E component recorded at Pacoima dam during the San Fernando Earthquake in 1971 is used as a ground motion. Three different analysis cases are considered for spatially varying ground motion. Displacements, stresses and hydrodynamic pressures occurring on the upstream face of the dam are calculated for each case and compare with those of uniform ground motion. It is concluded that spatially varying earthquake ground motions have important effects on the stochastic response of fluid-structure interaction systems.

Failure probability of tall buildings with TMD in the presence of structural, seismic, and soil uncertainties

Sadegh Etedali,Mohammad Seifi,Morteza Akbari 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.85 No.3

The seismic performance of the tall building equipped with a tuned mass damper (TMD) considering soil-structure interaction (SSI) effects is well studied in the literature. However, these studies are performed on the nominal model of the seismic-excited structural system with SSI. Hence, the outcomes of the studies may not valid for the actual structural system. To address the study gap, the reliability theory as a useful and powerful method is utilized in the paper. The present study aims to carry out reliability analyses on tall buildings equipped with TMD under near‐field pulse-like (NFPL) ground motions considering SSI effects using a subset simulation (SS) method. In the presence of uncertainties of the structural model, TMD device, foundation, soil, and near‐field pulse-like ground motions, the numerical studies are performed on a benchmark 40-story building and the failure probabilities of the structures with and without TMD are evaluated. Three types of soils (dense, medium, and soft soils), different earthquake magnitudes ( = 7,0. 7,25. 7,5 ), different nearest fault distances ( = 5. 10 and 15 km), and three seismic performance levels of immediate occupancy (IO), life safety (LS), and collapse prevention (CP) are considered in this study. The results show that tall buildings built near faults and on soft soils are more affected by uncertainties of the structural and ground motion models. Hence, ignoring these uncertainties may result in an inaccurate estimation of the maximum seismic responses. Also, it is found the TMD is not able to reduce the failure probabilities of the structure in the IO seismic performance level, especially for high earthquake magnitudes and structures built near the fault. However, TMD is significantly effective in the reduction of failure probability for the LS and CP performance levels. For weak earthquakes and long fault distances, the failure probabilities of both structures with and without TMD are near zero, and the efficiency of the TMD in the reduction of failure probabilities is reduced by increasing earthquake magnitudes and the reduction of fault distance. As soil softness increases, the failure probability of structures both with and without TMD often increases, especially for severe near-fault earthquake motion.

장주기 지진동을 고려한 건축물 및 비구조요소의 가속도 응답 증폭비

오상훈,김주찬 한국지진공학회 2023 한국지진공학회논문집 Vol.27 No.1

Structures of high-rise buildings are less prone to earthquake damage. This is because the response acceleration of high-rise buildings appears to be small by generally occurring short-period ground motions. However, due to the increased construction volume of high-rise buildings and concerns about large earthquakes, long-period ground motions have begun to be recognized as a risk factor for high-rise buildings. Ground motion observed on each floor of the building is affected by the eigenmode of the building because the ground motion input to the building is amplified in the frequency range corresponding to the building's natural frequency. In addition, long-period components of ground motion are more easily transmitted to the floor or attached components of the building than short-period components. As such, high-rise buildings and non-structural components pose concerns about long-period ground motion. However, the criteria (ASCE 7-22) underestimate the acceleration response of buildings and non-structural components caused by long-period ground motion. Therefore, the characteristics of buildings’ acceleration response amplification ratio and non-structural components were reviewed in this study through shake table tests considering long-period ground motions.

Non-linear dynamic assessment of low-rise RC building model under sequential ground motions

Syed Muhammad Bilal Haider,Zafarullah Nizamani,Chun Chieh Yip 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.74 No.6

Multiple earthquakes that occur during short seismic intervals affect the inelastic behavior of the structures. Sequential ground motions against the single earthquake event cause the building structure to face loss in stiffness and its strength. Although, numerous research studies had been conducted in this research area but still significant limitations exist such as: 1) use of traditional design procedure which usually considers single seismic excitation; 2) selecting a seismic excitation data based on earthquake events occurred at another place and time. Therefore, it is important to study the effects of successive ground motions on the framed structures. The objective of this study is to overcome the aforementioned limitations through testing a two storey RC building structural model scaled down to 1/10 ratio through a similitude relation. The scaled model is examined using a shaking table. Thereafter, the experimental model results are validated with simulated results using ETABS software. The test framed specimen is subjected to sequential five artificial and four real-time earthquake motions. Dynamic response history analysis has been conducted to investigate the i) observed response and crack pattern; ii) maximum displacement; iii) residual displacement; iv) Interstorey drift ratio and damage limitation. The results of the study conclude that the low-rise building model has ability to resist successive artificial ground motion from its strength. Sequential artificial ground motions cause the framed structure to displace each storey twice in correlation with vary first artificial seismic vibration. The displacement parameters showed that real-time successive ground motions have a limited impact on the low-rise reinforced concrete model. The finding shows that traditional seismic design EC8 requires to reconsider the traditional design procedure.