Showing 6 results for Eis
Behrouz Asgarian, Mahdi Boroumand, Mohamad Zarrin,
Volume 1, Issue 0 (6-2013)
Abstract
In this paper, pile behavior embedded in layered soil deposits subjected to seismic loadings is analyzed using a nonlinear fiber element for simulation of soil – pile interactions. In the created model, both pile and surrounding soil are modeled using fiber elements in a practical Beam on Nonlinear Winkler Foundation (BNWF) concept. Herein, the features of DRAIN–3DX finite element software are utilized in order to develop the model. In the presented approach for performing of Seismic Soil-Pile-Superstructure Interaction (SSPSI) analysis, the constitutive behavior of soil and steel pile are assigned to fiber elements using available soil p-y backbone curves and steel stress-strain relationship. The effect of radiation damping is incorporated into the model by adding a dashpot in parallel with nonlinear p-y element. In order to consider the effects of free field site response in different soil layers, EERA and NERA programs are used. Results of the analyses are compared with available experimental data. The results are in good agreement with the available centrifuge test results. The main purpose of the proposed method is to make DRAIN–3DX software capable of performing SPSSI analysis of any pile supported structure especially Jacket Type Offshore Platforms (JTOP).
Hamid Heidary Torkamani, Khosrow Bargi, Rouhollah Amirabadi,
Volume 1, Issue 0 (6-2013)
Abstract
This study aims to develop seismic fragility curves for a typical pile-supported wharf. Fragility curve is one of the popular tools in seismic performance evaluation of a structure. The software FLAC2D was used to simulate the seismic performance of the wharf structure. Using eight time history records, occurred in past, as seismic loading, incremental dynamic analysis (IDA) was applied for seismic demand estimation. Based on the resulted seismic response matrix the analytical fragility curves were developed. As a prevailing tool, adopted fragility curves are useful for seismic risk assessment. They can also be used to optimize wharf-retrofit methods.
Samira Babaei, Roohollah Amirabadi, Touraj Taghikhany,
Volume 6, Issue 0 (8-2016)
Abstract
In this study, mass, stiffness and damping matrices of the Nosrat jacket; located in Persian Gulf; equipped with Semi Active Tuned Mass Damper (SATMD) system have been derived after modeling the structure in SACS software. Owing to huge number of the degrees of freedom in the model, computation of on-line control of SATMD was time consuming. For this purpose, the size of the model was reduced in the finite time and frequency intervals by programming in MATLAB software. The SATMD utilized in this study, contains a passive Tuned Mass Damper (TMD) and two Magneto Rheological (MR) dampers in order to illustrate the control effect of SATMD. The selected algorithm to control and optimize the performance of MR damper is Linear Quadratic Gaussian (LQG). Time history responses of the platform in cases with and without SATMD have been compared under three different ground motions. Results indicate that jacket equipped with SATMD can dramatically reduce the seismic-induced dynamic responses.
Karim Akbari Vakilabadi, Hosein Khanzadi,
Volume 12, Issue 0 (7-2019)
Abstract
Aluminum–magnesium alloys are specially used in high speed boats, submarines, desalination systems, etc. In this re-search the electrochemical impedance spectroscopy technique was utilized to study the flow accele-rated pitting corrosion behavior of this alloy in 3.5% NaCl solution. To do so, impedance spectra of the samples after 20h of exposure to the test solution at a rotation speeds were investigated. SEM (scanning electron microscopy) method was utilized to investigate the changes in the surface of the samples. Results indicated that under static and dynamic con-dition, the surface growth rate of the pits increases with time. Moreover, at -0.9 V upon altering the flow condition from static to dynamic, the surface growth rate of the pits and their surface fraction increases while the corrosion resistance of the passive layer is time dependent.
Samira Babaei, Rouhollah Amirabadi, Mahdi Sharifi,
Volume 15, Issue 0 (4-2021)
Abstract
Probabilistic seismic demand models (PSDMs) for typical South Pars fixed pile-founded offshore platforms, utilizing probabilistic seismic demand analysis (PSDA) have been presented in this study. It expresses the probability that a system experiences a certain level of engineering demand parameter (EDP) for a given intensity measure (IM) level. Utilizing Bin approach, 80 ground motion records have been selected. A three dimensional (3D) nonlinear model has been generated considering the effects of soil-pile-structure interaction (SPSI) and analyzed for each ground motion. The process involves a modal analysis to determine natural frequency as well as a static pushover analysis to establish yield values, and mode shape information, and finally 80 dynamic time-history analyses to determine demand, given IMs. With the probabilistic models being traditionally conditioned on a single seismic IM and single EDP, the degree of uncertainty in the models is dependent on the IM and EDP used. The present study evaluated optimal PSDMs build from 16 IMs against a wide range of EDPs in levels of local, intermediate and global. From a large combination of IM-EDP pairs, a selection of the optimal pairs has been made owing to the criteria of practicality, effectiveness, efficiency, and sufficiency. Results indicate the absolute superiority of velocity-related IMs compared to acceleration, displacement and time-related ones for most of EDP types. In particular, Housner Intensity-Global Drift and Specific Energy Density-Global Ductility (in global level), Housner Intensity-Jacket Drift (in intermediate level) and Housner Intensity- TopDeck Differential Settlement (in local level) result in optimal pairs. Conversely, Sa(T1, 5%), the widely used IM in probabilistic assessment of fixed pile-founded offshore platforms, demonstrates relatively poor performance in predicting the demand parameters.
Amirreza Zafarjoo, Ruhollah Amirabadi,
Volume 18, Issue 0 (5-2023)
Abstract
Most of the fixed offshore platforms in the Persian Gulf have survived more than 25-year design life and have suffered from significant damages in this period. Seismic acceleration modifications and changes in seismic criteria of API-2EQ-2014 increase the importance of seismic assessment of the offshore platforms in the Persian Gulf. This paper presents a case study for modeling and evaluating the seismic behavior of an existing damaged fixed offshore platform in the Persian Gulf with consideration of actual structural damages as per provided subsea inspection reports and comparing with the intact condition of the platform to obtain the effect of assessment initiators like; actual damages and increased spectral acceleration as per API2EQ 2014 in the structural integrity of the fixed offshore platforms under the seismic loads in Persian gulf. Following the actual jacket inspection reports, Excessive corrosion, flooding of some members, marine growth, and anode wastage are the significant damages on this platform. Spectral nonlinear and static-dynamic analysis with SACS12.00 software considering the pile-soil interaction in the three following scenarios have been performed to verify structural seismic assessment. The first scenario contains a damaged platform with a lighter topside, the second scenario is a damaged platform with a heavier topside, and the third one includes the intact platform with initial design assumptions and criteria. The evaluation of the structure in three parts of the jacket members, joints, and piles has been done under the ALE & ELE earthquake levels. According to the results, jacket legs have the significant effect on the structural seismic strength. In abnormal level earthquake, the first plasticization occurs in the deck legs which are connected to the topside and the piles below the seabed. The comparison of the RSR values indicates that the initial assumption in platform design criteria has been stringent and uneconomical in the past. Also, the actual presented damages do not have much effect on the seismic strength of the structure. A Comparison of the Joint and member capacity illustrates a more significant impact of uniform corrosion on joint capacity than member strength. Finally; buckling in the deck legs at the splash zone and yielding in the Piles near the sea bed causes the global collapse of the structure.
