• Earthquakes and Structures
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• 제22권5호
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• pp.439-445
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• 2022

One of the best choice for transportation of oil and gas at the end of rivers or seas is concrete pipelines. In this article, a concrete pipe at the end of river is assumed under the earthquake load. The Classic shell theory is applied for the modelling and the corresponding motion equations are derived by energy method. An external force induced by fluid around the pipe is asssumed in the final motion equations. For the solution of motion equations, the differential quadrature method (DQM) and Newmark method are applied for deriving the dynamic deflection of the pipe. The effects of various parameters including boundary conditions, fluid and length to thickness ratio are presented on the seismic response of the concrete pipe. The outcomes show that the clamped pipe has lower dynamic deflection with respect to simply pipe. In addition, with the effect of fluid, the dynamic defelction is increased significantly.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.121-128
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• 1999

This paper presents a time domain method for soil-structure interaction analysis for seismic loadings. It is based on the finite element formulation incorporating analytical frequency-dependent infinite elements for the far field soil. The dynamic stiffness matrices of the far field region formulated using the present method in frequency domain can be easily transformed into the corresponding matrices in time domain. At first, the equivalent earthquake forces are evaluated along the interface between the near and the far fields from the free-field response analysis carried out in frequency domain, and the results are transformed into the time domain. An efficient procedure is developed for the convolution integrals to evaluate the interaction force along the interface, which depends on the response on the interface at the past time instances as well as the concurrent instance. Then, the dynamic responses are obtained for the equivalent earthquake force and the interaction force using Newmark direct integration technique. Since the response analysis is carried out in time domain, it can be easily extended to the nonlinear analysis. Example analysis has been carried out to verify the present method in a multi-layered half-space.

• 한국지반공학회논문집
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• 제19권6호
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• pp.85-97
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• 2003

본 논문에서는 건축물 하중기준 및 해설에서 제시된 지반분류 방법으로 지반 III 또는 IV에 해당하는 지반을 대상으로 등가선형해석을 수행하였고, 해석에서 얻어진 스펙트럴 가속도 값으로 지반계수를 역산하여 국내 각 기준에서 제시하고 있는 지반계수와 비교 검토하였다. 해석결과 고유주기 0.9초 이상 고층 건물의 경우 지반 III의 경우 지반 II의 지반계수의 사용이 가능하였고, IV의 경우 지반 III의 지반계수를 사용하여도 충분하였다. 또한, 대부분의 해석에서 얻어진 지반계수의 값이 국내 내진설계기준의 값보다 상당히 작게 나타났다. 이는 내진설계시 국내 내진설계기준을 그대로 적용하면 구조물 밑면전단력이 보수적으로 산정될 수 있음을 의미한다.

• Structural Engineering and Mechanics
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• 제23권5호
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• pp.543-562
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• 2006

Base isolation technology has been accepted as a feasible and attractive way in improving seismic resistance of structures. The seismic design of new seismically isolated structures is mainly governed by the Uniform Building Code (UBC-97) published by the International Conference of Building Officials. In the UBC code, the distribution formula of the inertial (or lateral) forces leads to an inverted triangular shape in the vertical direction. It has been found to be too conservative for most isolated structures through experimental, computational and real earthquake examinations. In this paper, four simple and reasonable design formulae, based on the first mode of the base-isolated structures, for the lateral force distribution on isolated structures have been validated by a multiple-bay three-story base-isolated steel structure tested on the shaking table. Moreover, to obtain more accurate results for base-isolated structures in which higher mode contributions are more likely expected during earthquakes, another four inertial force distribution formulae are also proposed to include higher mode effects. Besides the experimental verification through shaking table tests, the vertical distributions of peak accelerations computed by the proposed design formulae are in good agreement with the recorded floor accelerations of the USC University Hospital during the Northridge earthquake.

• Steel and Composite Structures
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• 제31권6호
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• pp.575-589
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• 2019

The main focus of this study is to numerically investigate the influence of strong earthquake and tsunami-induced wave impact on the response and behavior of a cable-stayed steel bridge with large caisson foundations, by assuming that the earthquake and the tsunami come from the same fault motion. For this purpose, a series of numerical simulations were carried out. First of all, the tsunami-induced flow speed, direction and tsunami height were determined by conducting a two-dimensional (2D) tsunami propagation analysis in a large area, and then these parameters obtained from tsunami propagation analysis were employed in a detailed three-dimensional (3D) fluid analysis to obtain tsunami-induced wave impact force. Furthermore, a fiber model, which is commonly used in the seismic analysis of steel bridge structures, was adopted considering material and geometric nonlinearity. The residual stresses induced by the earthquake were applied into the numerical model during the following finite element analysis as the initial stress state, in which the acquired tsunami forces were input to a whole bridge system. Based on the analytical results, it can be seen that the foundation sliding was not observed although the caisson foundation came floating slightly, and the damage arising during the earthquake did not expand when the tsunami-induced wave impact is applied to the steel bridge. It is concluded that the influence of tsunami-induced wave force is relatively small for such steel bridge with large caisson foundations. Besides, a numerical procedure is proposed for quantitatively estimating the accumulative damage induced by the earthquake and the tsunami in the whole bridge system with large caisson foundations.

• Computers and Concrete
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• 제24권2호
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• pp.125-135
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• 2019

Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use of nano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that SiO2 nanoparticles can improve the mechanical behavior of concrete. Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton's principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load. The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method. The effects of different parameters such as SiO2 nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluid pressure and earthquake intensity are discussed on the seismic response of the structure. From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of SiO2 nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.

• Earthquakes and Structures
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• 제16권5호
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• pp.611-623
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• 2019

A set of mid-rise bare and uniformly infilled reinforced-concrete frame buildings are analyzed for two different seismic intensities of ground-motions (i.e., 'Design Basis Earthquake' and 'Maximum Considered Earthquake') to study their floor response. The crucial parameters affecting seismic design force for acceleration-sensitive non-structural components are studied and compared with the guidelines of the European and the United States standards, and also with the recently developed NIST provisions. It is observed that the provisions of both the European and the United States standards do not account for the effects of the period of vibration of the supporting structure and seismic intensity of ground-motions and thereby provides conservative estimates of the in-structure amplification. In case of bare frames, the herein derived component amplification factors for both the design basis earthquake and the maximum considered earthquake exceeds with their recommended values in the European and the United States standards for non-structural components having periods in vicinity of the higher modes of vibration, whereas, in case of infilled frames, component amplification factors exceeds with their recommended value in the European standard for non-structural components having periods in vicinity of the fundamental mode of vibration, and only for the design basis earthquake. As a consequence of these observations, as well as capping on the design force (in case of United states standard and NIST provisions), in case of the design basis earthquake, the combined amplification factor is underestimated for non-structural components having periods in vicinity of the higher modes of vibration of bare frames, and also for non-structural components having periods in vicinity of the fundamental mode of vibration of infilled frames. At the maximum considered earthquake demand, excepting non-structural components having periods in vicinity of the higher modes of vibration of bare frames, all provisions generally provide conservative estimates of the design floor accelerations.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 춘계학술대회 논문집
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• pp.144-151
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• 2001

The development history of seismic design and analysis methods considering seismic force in soil-structure dynamic interaction are presented. Determination of seismic intensity in static analysis of both seismic and modifided seismic methods is discussed and preferable method in future seismic design is proposed.

• Structural Engineering and Mechanics
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• 제5권2호
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• pp.149-165
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• 1997

A dynamic time-history analysis of the coupled internals and core in the vertical direction is performed as a part of the fuel assembly qualification program. To reflect the interaction between the fuel rods and grid cage, friction element is developed and is implemented. Also derived here is a method to calculate a hydraulic force on the reactor internals due to pipe break. Peak responses are obtained for the excitations induced from earthquake and pipe break. The dynamic responses such as fuel assembly axial forces and lift-off characteristics are investigated.

• Smart Structures and Systems
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• 제5권3호
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• pp.209-221
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• 2009

A control algorithm for seismic protection of building structures based on the theory of variable structural control or sliding mode control is presented. The paper focus in the design of sliding surface. A method for determining the sliding surface by pole assignment algorithm where the poles of the system in the sliding surface are obtained on-line, based on the frequency content of the incoming earthquake signal applied to the structure, is proposed. The proposed algorithm consists of the following steps: (i) On-line FFT process is applied to the incoming part of the signal and its frequency content is recognized. (ii) A transformation of the frequency content to the complex plane is performed and the desired location of poles of the controlled structure on the sliding surface is estimated. (iii) Based on the estimated poles the sliding surface is obtained. (iv) Then, the control force which will drive the response trajectory into the estimated sliding surface and force it to stay there all the subsequent time is obtained using Lyapunov stability theory. The above steps are repeated continuously for the entire duration of the incoming earthquake. The potential applications and the effectiveness of the improved control algorithm are demonstrated by numerical examples. The simulation results indicate that the response of a structure is reduced significantly compared to the response of the uncontrolled structure, while the required control demand is achievable.