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

• 국제강구조저널
• /
• 제18권5호
• /
• pp.1598-1606
• /
• 2018

An integrated optimal structural design method for a diagrid structure and control device was developed. A multi-objective genetic algorithm was used and a 60-story diagrid building structure was developed as an example structure. Artificial wind and earthquake loads were generated to assess the wind-induced and seismic responses. A smart tuned mass damper (TMD) was used as a structural control system and an MR (magnetorheological) damper was employed to develop a smart TMD (STMD). The multi-objective genetic algorithm used five objectives including a reduction of the dynamic responses, additional stiffness and damping, mass of STMD, capacity of the MR damper for the integrated optimization of a diagrid structure and a STMD. From the proposed method, integrated optimal designs for the diagrid structure and STMD were obtained. The numerical simulation also showed that the STMD provided good control performance for reducing the wind-induced and seismic responses of a tall diagrid building structure.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2003년도 추계 학술발표회논문집
• /
• pp.107-114
• /
• 2003

There are many problems in the prediction of dynamic behaviors of saturated soils because undrained excess pore water pressure builds up and then the strain softening behavior is occurred simultaneously. A few analytical constitutive models based on the effective stress concept have been proposed but most models hardly predict the excess pore water pressure and strain softening behaviors correctly In this study, the disturbed state concept (DSC) model proposed by Dr, Desai was modified to predict the saturated soil behaviors under the dynamic loads. Also, back-prediction program was developed for verification of modified DSC model. Cyclic triaxial tests were carried out to determine DSC parameters and test result was compared with the result of back-prediction. Through this research, it is proved that the proposed model based on the modified disturbed state concept can predict the realistic soil dynamic characteristics such as stress degradation and strain softening behavior according to dynamic process of excess pore water pressure.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2001년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2001
• /
• pp.107-114
• /
• 2001

When group pile supporting structures are to be subjected to large lateral loads, generally, hatter piles are used in group pile with vertical piles. It is well known that batter piles resist lateral static loads which are acted upon the piles as axial farces quite well but, they show a poor performance under seismic loads. However, it is not yet known how the batter piles behave under dynamic loading and how to strengthen the batter piles to improve the seismic performance. Shaking table tests were performed to investigate the seismic behavior of the batter pile and to bring up the countermeasures to improve the seismic performance. As the result of the shaking table tests, batter piles failed due to not only the excessive increase of compressive force near the pile head but also that of tensile force. In case that the pile head was connected with pile cap by rubber joint, the max. acceleration at the pile cap was reduced due to the high damping ratio of rubber and the max. moment and max. axial farce at the pile head was decreased remarkably. When the inclinations(V:H) of the batter pile were 8:3 and 8:4, max. moment, max. shear force, and max. axial farce were reduced notably and max. acceleration and max. displacement at the pile cap was diminished, too.

• 한국지진공학회논문집
• /
• 제7권1호
• /
• pp.65-72
• /
• 2003

이 연구의 목적은 무리보행하중을 받는 구조물의 주요 지점에 대한 응답을 계측하고 분석하여 하중의 특성을 파악하는 것이다. 이를 위하여 먼저 건축구조물의 동특성을 파악하였으며 이를 바탕으로 무리보행하중의 주파수 특성을 파악할 수 있는 식을 유도하였다. 그리고, 단위보행하중의 주파수 특성을 바탕으로 무리보행하중의 크기를 평가할 수 있는 방법을 제안하였다. 유도된 식은 무리보행하중의 진동수 및 크기를 잘 나타내었으며, 단위보행하중을 기준으로 한 무리보행하중의 크기를 평가하는 경우에는 고차모드형상을 포함하여야 좋은 결과를 얻을 수 있는 것으로 나타났다.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
• /
• pp.565-570
• /
• 2001

Base shear and roof drift relation was acquired from experiment of 3 story ordinary moment resisting frame which was designed using gravity loads. To evaluate the dynamic behavior of the frame, analytical model was generated from experimental result. Dynamic analysis was performed using the analytical model subjected to earthquake ground motions with 500, 1000, and 2400 years of return period. And capacity spectrum method was adopted to find the performance points of the frame. Both dynamic analysis and CSM showed that the performance of the frame meet the life safety objectives suggested by FEMA 273 and ATC 40.

• Computers and Concrete
• /
• 제21권6호
• /
• pp.717-726
• /
• 2018

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 $SiO_2$ 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 $SiO_2$ 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 $SiO_2$ nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.

• Earthquakes and Structures
• /
• 제4권2호
• /
• pp.157-179
• /
• 2013

Vulnerability studies on the existing building stock require that a large number of buildings is analyzed to obtain statistically significant evaluations of the seismic performance. Therefore, analytical evaluation methods need to be based on simplified methodologies of analysis which can afford the treatment of a large building population with a reasonable computational effort. Simplified Pushover-Based Earthquake Loss Assessment approach (SP-BELA), where a simplified methodology to identify the structural capacity of the building through the definition of a pushover curve is adopted, was developed on these bases. Main objective of the research work presented in this paper is to validate the simplified methodology implemented in SP-BELA against the results of more sophisticated nonlinear dynamic analyses (NLDAs). The comparison is performed for RC buildings designed only to vertical loads, representative of the "as built" in Italy and in Mediterranean countries with a building stock very similar to the Italian one. In NLDAs the non linear and degrading behaviour, typical of the structures under consideration when subjected to high seismic loads, is evaluated using models able to capture, with adequate accuracy, the non linear behaviour of RC structural elements taking into account stiffness degradation, strength deterioration, and pinching effect. Results show when simplified analyses are in good agreement with NLDAs. As a consequence, unsatisfactory results from simplified analysis are pointed out to address their current applicability limits.

• 한국지진공학회논문집
• /
• 제7권3호
• /
• pp.39-45
• /
• 2003

본 논문에서는 구조물의 효율적인 동적해석을 위한 수정된 Lanczos 벡터중첩법을 제안하였다. 제안방법은 강성행렬에 직교하는 Lanczos 벡터를 생성하는 수정된 Lanczos 알고리즘에 기초하고 있다. 단일입력하중을 받는 구조물의 해석에 있어서 제안한 Lanczos 벡터중첩법은 기존의 Lanczos 벡터중첩법과 동일한 정확도와 효율성을 갖는 반면 다중입력하중을 받는 구조물의 경우 제안방법이 기존의 방법보다 더욱 효율적이다. 수치예제를 통해 제안방법의 효율성을 검증하였다.

• Computers and Concrete
• /
• 제26권3호
• /
• pp.227-237
• /
• 2020

Strain rate investigations are needed to calibrate strain-rate-dependent material models and numerical codes. An appropriate material model, which considers the rate effects, need to be used for proper numerical modeling. The plastic concrete cut-off wall is a special underground structure that acts as a barrier to stop or reduce the groundwater flow. These structures might be subjected to different dynamic loads, especially earthquake. Deformability of a structure subjected to dynamic loads is a principal issue which need to be undertaken during the design phase of these structures. The characterization of plastic concrete behavior under different strain rates is essential for proper designing of cut-off walls subjected to dynamic loads. The Cowper-Symonds model, as one of the most commonly applied material models, complies well with the behavior of a plastic concretes in low to moderate strain rates and will be useful in explicit dynamics simulations. This paper aims to present the results of an experimental study on mechanical responses of one of the most useful types of plastic concrete and Cowper-Symonds constant determination procedures in a wide range of strain rate from 0.0005 to 107 (1/s). For this purpose, SHPB, uniaxial, and triaxial compression tests were done on plastic concrete samples. Based on the results of quasi-static and dynamic tests, the dynamic increase factors (DIF) of this material in different strain rates and stress state conditions were determined for calibration of the Cowper - Symonds material models.