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earthquake-loadings
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Evaluation of variation of permeability in liquefiable soil under earthquake loading
, Article Computers and Geotechnics ; Volume 40 , 2012 , Pages 74-88 ; 0266352X (ISSN) ; Pak, A ; Taiebat, M ; Jeremić, B ; Sharif University of Technology
2012
Abstract
Liquefaction phenomenon is usually accompanied by large amounts of settlement owing to disruption of soil structure. In addition to that, large settlement also occurs by a significant increase in soil permeability during seismic excitation. To properly simulate the post-liquefaction settlement, it is important to take the compressibility properties of the liquefied sand as well as the permeability increase into account. Using initial permeability coefficient in the course of simulation of liquefaction leads to underestimation of settlement. In addition to that, using unrealistic values for permeability may cause erroneous predictions of other aspects of soil behavior. Therefore, an accurate...
Performance of Jacket Platform Equipped with BRB (Buckling Restrained Brace) under Earthquake and Wave Loads
,
M.Sc. Thesis
Sharif University of Technology
;
Golafshani, Ali Akbar
(Supervisor)
;
Tabeshpour, Mohamad Reza
(Co-Advisor)
Abstract
Offshore platforms are one of the most important structures in oil-rich countries, so that their economic benefit makes it very expensive to stop their usage. Therefore, it is essential that their performance is not disrupted by earthquake or the tidal waves made by severe storms. In the conventional bracing systems, it is assumed that the braces buckle under compressive forces; but Buckling Restrained Brace (BRB) does not buckle under pressure. In this study performance of BRB in jacket platform, with a case study of Resalat platform, has been investigated under earthquake load and powerful wave. The modeling of jacket equipped with this brace has been done in Abaqus software, and results...
Numerical Study of Pile Behavior under Seismic Loading
, M.Sc. Thesis Sharif University of Technology ; Ahmadi, Mohammad Mahdi (Supervisor)
Abstract
Numerous structures which are involved in seismic soil-pile-structure interaction have been destroyed. Considering complexities which exist in soil-pile interaction problems and lack of precise methods without imperfect bases, it is necessary to use numerical methods for analyzing soil-pile interaction problems. In this research, three-dimensional modeling and studying the effect of changing soil and pile parameters on the behavior of pile under earthquake loading is performed using finite difference software, FLAC3D. The soil in this model has a softening behavior. Real earthquake spectrum has been applied into the model as the acceleration time history at the bedrock level. The results of...
Numerical study of steel box girder bridge diaphragms
, Article Earthquake and Structures ; Volume 11, Issue 4 , 2016 , Pages 681-699 ; 20927614 (ISSN) ; Mohammadinia, P ; Dolati, A ; Sharif University of Technology
Techno Press
2016
Abstract
Steel box girders have two webs and two flanges on top that are usually connected with shear connectors to the concrete deck and are also known as tub girders. The end diaphragms of such bridges comprise of a stiffened steel plate welded to the inside of the girder at each end. The diaphragms play a major role in transferring vertical and lateral loads to the bearings and substructure. A review of literature shows that the cyclic behavior of diaphragms under earthquake loading has not been studied previously. This paper uses a nonlinear finite element model to study the behavior of the end diaphragms under gravity and seismic loads. Different bearing device and stiffener configurations have...
Effects of concurrent earthquake and temperature loadings on cable-stayed bridges
, Article International Journal of Structural Stability and Dynamics ; Volume 16, Issue 6 , 2016 ; 02194554 (ISSN) ; Maghsoudi Barmi, A ; Sharif University of Technology
World Scientific Publishing Co. Pte Ltd
Abstract
This paper discusses the necessity of considering the concurrent effects of uniform temperature and earthquake loadings in the design of cable-stayed bridges. This load combination is not foreseen in current design standards such as AASHTO and Eurocode. Three-dimensional finite element models of cable-stayed bridges are employed for nonlinear time history analyses. A load combination is proposed that adds uniform temperature loading to the existing extreme event load combination. The proposed combination is compared with existing extreme event load combination and the changes in forces and displacements are noted. A parametric study is then conducted by varying a number of properties of the...
3D Numerical Modeling of Dynamic Instability Induced by Liquefaction in Loose Sand Deposit when Earthquake Occurs Perpendicular to the Slope
, M.Sc. Thesis Sharif University of Technology ; Pak, Ali (Supervisor)
Abstract
Soil liquefaction occurring in loose saturated sand deposits during seismic loadings is one of the most destructive earthquake-induced phenomena in the field of earthquake geotechnical engineering. Catastrophic destructions due to this phenomenon that have been observed in the earthquakes such as Kobe (1995), Chi-Chi (1999), etc. has led to extensive studies in this field. In case of soil slopes prone to liquefaction hazard, detailed analysis of this phenomenon requires considering soil-related factors (e.g. shear strength, relative density, permeability, slope geometry) on the one hand, and earthquake-related characteristics (e.g. amplitude, frequency, duration) on the other. Numerical...
Interaction Effects of Gravity and Lateral Loads in Reinforced Concrete Slab
, M.Sc. Thesis Sharif University of Technology ; Kazemi, Mohammad Taghi (Supervisor)
Abstract
Reinforced concrete slabs carry both vertical gravity loads and in plane forces due to seismic loads. In this study interaction of bending and in plane forces will be considered. Lee et al. in 2007 studied the floor diaphragm behavior. They considered combination of both in plane and out of plane loadings. In the most previous studies, the diaphragm behavior of a floor slab was represented by its behavior under in-plane forces only. With this assumption, analysis of the floor diaphragm was simplified to the two dimensional plane stress problem. For low-rise buildings, the lateral stiffness of the structure is usually higher than high-rise buildings.Tena et al. in 2014 assessed ment the...
Liquefaction-induced settlement of shallow foundations on two-layered subsoil strata
, Article Soil Dynamics and Earthquake Engineering ; Volume 94 , 2017 , Pages 35-46 ; 02677261 (ISSN) ; Pak, A ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
Geotechnical design codes have been shifted from classical limit equilibrium analysis toward the performance-based procedures. In foundation design, settlement is the most representative parameter for its performance. Settlement of shallow foundations subjected to earthquake loading and its consequences is one of the most outstanding issues which should be considered in designing different structures. In this study, settlement of shallow footing on two-layered subsoil strata under earthquake loading is of concern. The numerical study presented in this research by means of a 3D dynamic fully coupled u-p analysis, addresses the effect of different parameters on shallow foundation settlement...
Local and global buckling condition of all-steel buckling restrained braces
, Article Steel and Composite Structures ; Volume 23, Issue 2 , 2017 , Pages 217-228 ; 12299367 (ISSN) ; Nazeryan, M ; Bahrani, M. K ; Nooralizadeh, A ; Montazerian, L ; Naserifard, M ; Sharif University of Technology
Techno Press
2017
Abstract
Braces are one of the retrofitting systems of structure under earthquake loading. Buckling restrained braces (BRBs) are one of the very efficient braces for lateral loads. One of the key needs for a desirable and acceptable behavior of buckling-restraining brace members under intensive loading is that it prevents total buckling until the bracing member tolerates enough plastic deformation and ductility. This paper presents the results of a set of analysis by finite element method on buckling restrained braces in which the filler materials within the restraining member have been removed. These braces contain core as the conventional BRBs, but they have a different buckling restrained system....
More efficient lateral load patterns for seismic design of steel moment-resisting frames
, Article Proceedings of the Institution of Civil Engineers: Structures and Buildings ; Volume 171, Issue 6 , 2018 , Pages 472-486 ; 09650911 (ISSN) ; Hajirasouliha, I ; Hosseini Gelekolai, S. M ; Sharif University of Technology
ICE Publishing
2018
Abstract
The preliminary design of building structures is normally based on the equivalent lateral forces provided in seismic design guidelines. The height-wise distribution of these loads is predominantly based on elastic vibration modes. However, as structures exceed their elastic limits in severe earthquakes, these design load patterns may not necessarily lead to efficient distribution of strength within the structures. To address this issue, several alternative load patterns have been proposed for the seismic design of non-linear structures. However, due to the simplifications involved in the development of these design load patterns, their adequacy needs to be assessed for different structural...
Semiactive viscous tensile bracing system
, Article Journal of Structural Engineering ; Volume 135, Issue 4 , 2009 , Pages 425-436 ; 07339445 (ISSN) ; Bakhshi, A ; Golafshani, A.A ; Sharif University of Technology
2009
Abstract
Structural control using energy dissipater devices is emerging as a heavily researched strategy in earthquake engineering. Among several control systems, semiactive control is usually possible and efficient. In this research, a semiactive energy dissipating bracing system based on a viscous damper is proposed. In the conventional bracing systems, it is assumed that the braces can buckle under compression. Therefore, a semiactive on-off brace strategy is implemented to improve the conventional brace performance. Further, an energy absorbing mechanism is implemented. In the proposed system, the buckling of the member is prevented by implementing a one-way valve device. The permanent story...
Numerical investigation of the effects of soil densification on the reduction of liquefaction-induced settlement of shallow foundations
, Article Scientia Iranica ; Volume 16, Issue 4 A , 2009 , Pages 331-339 ; 10263098 (ISSN) ; Pak, A ; Sharif University of Technology
2009
Abstract
The liquefaction phenomenon is usually accompanied by a large amount of settlement. Based on the observations made in past earthquakes, ground improvement by densification is one of the most useful approaches to reduce the liquefaction-induced settlement. Currently, there is no analytical solution for evaluation of the amount of settlement and tilting of footings that are constructed on densified ground surrounded by liquefiable soil. A number of factors, such as underlying soil properties, dimensions of the footing and earthquake loading characteristics, cause the problem to become complicated. In this paper, the dynamic response of shallow foundations on both liquefiable and...
Definition of Performance Levels and Risk Level of Fixed Offshore Platform
, M.Sc. Thesis Sharif University of Technology ; Golafshani, Ali Akbar (Supervisor)
Abstract
Offshore platforms are one of the most important structures in oil-rich countries, so that their economic benefit makes it very expensive to stop their usage. Therefore, it is essential that their performance is not disrupted by earthquake or the tidal waves made by severe storms. According to statistics many of the offshore platforms of their design life pass and need an important loss inspection. The assessment of existing platforms is a relatively new process. The lack of comprehensive standard creates some difficulty in establishing performance requirements, on a case by case basis depending upon the risks associated with the future operations of the platform. In this study the criteria...
Nonlinear seismic behavior of RC frames with RC braces
, Article Asian Journal of Civil Engineering ; Volume 9, Issue 6 , 2008 , Pages 577-592 ; 15630854 (ISSN) ; Mohseni, M. M ; Sharif University of Technology
2008
Abstract
Braced frames, besides other structural systems, such as moment resisting frames or shear walls, have been an effective and valuable method to enhance structures against lateral loads. In wind or seismic excitations, inclined elements react as truss web elements which would bear compression or tension stresses. This axial reaction results in less moments and therefore smaller sizes in beam and column sections with respect to members in similar moment resisting frame. However, low tensile strength of concrete material, made it a challenge to use in inclined members. In practice, there have been various methods to consider this defect such as disengagement of brace elements in tension or...
Application of fuzzy set theory to evaluate the effect of pore pressure build-up on the seismic stability of Karkheh Dam, Iran
, Article Journal of Earthquake Engineering ; Volume 12, Issue 8 , 2008 , Pages 1296-1313 ; 13632469 (ISSN) ; Bahador, M ; Bahrami, R ; Sharif University of Technology
2008
Abstract
It is a current practice to employ composite claya mixture of clay and aggregates that float within the clayey matrixas the core of embankment dams that have classically been constructed from pure clays. Experience has shown that significant pore pressures could build up during cyclic undrained loading in composite clays. This may threaten dam stability during earthquake loading. However, it is difficult to attribute a single value to excess pore pressure in conventional seismic stability analysis because of the random nature of earthquake loading, leading to uncertainty in the evaluation of factor of safety against sliding. This article evaluates the importance of pore pressure build-up in...
Vibration Analysis of Kish Island Elevated Water Storage Tank
, M.Sc. Thesis Sharif University of Technology ; Selk Ghafari, Ali (Supervisor)
Abstract
Elevated water tanks are one of the most critical elements in civilized society to provide safe servicing resources of drinking water after natural and human-made disasters. Dynamic analysis plays a vital role in investigating structural behavior of the elevated storage system subjected to the earthquake-induced vibration. The main scope of this paper is to address the structural stability analysis of the Kish Island’s elevated reinforced concrete water tank employing finite element method. A complete solid model of the structure with detailed design was constructed, and finite element analysis was carried out utilizing ABAQUS software. To investigate the dynamic behavior of the structure, a...