2018-08-15T13:38:30Z
http://scientiairanica.sharif.edu/?_action=export&rf=summon&issue=1002
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Current efforts for prediction and assessment of natural disasters: Earthquakes, tsunamis, volcanic eruptions, hurricanes, tornados, and floods
J.P.
Amezquita-Sanchez
M.
Valtierra-Rodriguez
H.
Adeli
This article presents a state-of-the-art review of different methods, signal and image processing techniques, and statistical analyses used for prediction and assessment of natural disasters including earthquakes, tsunamis, volcanic eruptions, hurricanes, tornadoes, and floods. Application of the big data paradigm to the aforementioned natural disasters is also discussed. The research for increasingly more sophisticated computational models will continue to achieve more accurate predictions of various natural disasters.
Natural disasters
Big data
Prediction
Assessment
Earthquakes
Tsunamis
Volcanic eruptions
Hurricanes
Tornadoes
Floods
2017
12
01
2645
2664
http://scientiairanica.sharif.edu/article_4589_b0ee16cdfc25c1b0235159d2c129cacc.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Dynamic behavior of large-diameter piles with considering liquefaction under clay layer
M.
Oliaei
A.
Ghotbi
Marine structures are mostly constructed on deep foundations, namely large-diameter piles. Such support structures are driven into deposits of saturated granular soil, which is vulnerable to liquefaction under loadings of dynamic nature, e.g., earthquakes. Although numerous studies have been accomplished to obtain a comprehensive understanding of their performance during liquefaction, a conclusive study has not been presented for the specific case of large-diameter piles under a clay layer. This issue has great importance in case of offshore wind turbines, since they are very sensitive to dynamic loadings. In this study, a 3D FEM model was constructed by OpenSeesPL to explore soil and pile responses throughout liquefaction. To capture the precise behavior, a constitutive law based on a multi-surface plasticity was utilized for soil. The described model used in this study is capable of accurate prediction of sand behavior in undrained conditions. Different scenarios were tested: variations in pile dimensions, loading frequency and influence of clay layer. Sensitivity analyses show that loading frequency, presence of clay layer and pile diameter could significantly affect behavior of large-diameter piles in saturated soil conditions.
numerical investigation
soil-pile interaction
large-diameter piles
liquefaction
clay layer
2017
12
01
2665
2683
http://scientiairanica.sharif.edu/article_4170_92ed720df57844cb65f792915501df9d.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Assessment of labor productivity in construction projects using system dynamic approach
M.
Khanzadi
A.
Kaveh
Majid
Alipour
Reza
Khanmohammadi
Labor productivity is one the most important factors in achieving project success at different stages of a project. In this research a new method is presented to model labor productivity for different types of contractors based on system dynamic (SD) simulation. Using cause and effect feedback loops, a qualitative model is constructed. The relationships between different parameters are then determined by expert judgment and real data obtained from several real projects, and the quantitative model is built. The labor productivity is simulated by the proposed SD model considering all affecting factors. For higher accuracy, the model is examined on two types of contractors and two models are constructed. The total productivity of each contractor is obtained and the effect of different parameters on the labor productivity is investigated.
labor productivity
Contractors
System dynamic
Construction Projects
simulation
Total productivity
2017
12
01
2684
2695
http://scientiairanica.sharif.edu/article_4164_2dfe4fe4c7c3fdbe97220650e3f9eeca.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Experimental study on relation between scour and complex 3D flow field
Mojtaba
Mehraein
Masoud
Ghodsian
In this paper scour and flow fields around two spur dikes with different submergence ratios located in a 90° developed bend were experimentally investigated. The spur dike and the scour rate around the low submerged spur dike is higher than that around the high submerged condition. The ejection and sweep events are the predominant events in the upstream region of the spur dike. The larger peak of the power spectrum and the higher frequencies of sweep and ejection events in low submerged condition increase the scour rate at the early stages of the scour process. Interaction events are the main events in the downstream recirculation zone and may be the principle reasons for the sediment deposition process. The scour initiation region cannot be predicted using variance of the vertical velocity component. However, the estimation of the bed shear stress using the Reynolds stresses can predict the scour initiation region correctly. Strong relationships between the scour rate and triple correlations, quadrant analysis, turbulent kinetic energy flux and power spectrum were found based on the fact that the scour rate increases in the low submergence condition by the latter parameters increments.
experimental study
Turbulent 3D flow
Quadrant analysis
Scour
ADV
2017
12
01
2696
2711
http://scientiairanica.sharif.edu/article_4165_157159f2f25dbf4664b79046b7b27d6e.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
The effect of gusset plate in moment-rotation behavior of double-web angle connection, in braced frames
Massood
Mofid
Amir Reza
Tabkhi Wayghan
Double web angle connection is one of the most rudimentary connections in simple structural systems such as braced frame system. Essentially, it is presumed in conventional designs, which actually double web angle connection behaves as a hinge connection. However, in braced frames, due to existence of braces in some bays, in specified locations where gusset plates of brace placed with beam to column connection in one joint, this contemplation may not be accurate. This is due to the restraining of the beam from rotation by gusset plates that is placed on top and bottom of the beam or only on one side. In such cases, the simple beam to column connection may be transformed into a semi-hinge or fixed connection. In this paper, double web angle connection is investigated in the mentioned locations using the FEM method along with the calculating moment rotation behavior of connection and subsequently type, as well as the rigidity of connection. Furthermore, an analytical model is proposed to predict the characteristics of the double web angle connection in the view of the relevant case.
Double web angle connection
Moment rotation curve
Braced frame
Semi-hinge connection
Gusset plate
2017
12
01
2712
2725
http://scientiairanica.sharif.edu/article_4172_2c0b540ae81068338f63d9934fb4db79.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Tubular Web RBS Connection to Improve Seismic Behavior of Moment Resisting Steel Frames
Seyed Mehdi
Zahrai
Seyed Rasoul
Mirghader
Aboozar
Saleh
A new type of Reduced Beam Section (RBS) connection called "Tubular Web RBS (TW-RBS)" is proposed in this research. TW-RBS is made by replacing a part of web with a tube at the expected location of the beam plastic hinge. In addition to analytical study, the proposed section is numerically studied under cyclic load using ABAQUS finite element software and a test specimen is used for calibration of numerical results. The results show that using TW-RBS not only creates a ductile fuse far from the beam-to-column connection components but it also increases story drift capacity up to 9%. Furthermore, the tubular web like corrugated sheet can improve both the out-of-plane stiffness of the beam longitudinal axis and the flange stability condition due to the smaller width to thickness ratio of the beam flange in the plastic hinge region. Thus, the tubular web improves lateral-torsional buckling stability of beam. On the other hand, the tubular web provides a better condition than other accordion web with sharp corners in terms of low-cycle fatigue, because change of direction of strain in arc shape of the tubular web section is smaller than the accordion web with sharp corners.
Cyclic behavior
moment resisting steel frames
rigid connection
reduced beam section
Tubular Web RBS (TW-RBS)
2017
12
01
2726
2740
http://scientiairanica.sharif.edu/article_4168_0ad0b988b389a73103573d60a228409c.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Reliability analysis of foundation settlement by stochastic response surface and random finite element method
A.
Johari
A.
Sabzi
This paper presents a reliability-based analysis of strip footing settlement by Stochastic Finite Element Method (SFEM). The Stochastic Response Surface Method (SRSM) and Random Finite Element Method (RFEM) are used as two formulation of SFEM. The elastic properties of soil are considered as spatial random variables and modeled as cross correlated log–normal random fields. Random field discretization is done by Karhunen–Loeve (K-L) expansion. Two programs were coded by MATLAB so as to take full advantages of its matrix operations and in an illustrative example; it was shown that the results of SRSM are close to RFEM however the consumed time in RFEM is at most 50 times longer than SRSM. Using the faster method, SRSM, it is concluded that considering the spatial variability of soil parameters in stochastic analysis is necessary.
Foundation settlement
Spatial variability
Random fields
Stochastic response surface method
Random finite element method
Karhunen–Loeve expansion
2017
12
01
2741
2751
http://scientiairanica.sharif.edu/article_4169_254b6b06071dd4e989a8704b5e913a5f.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Modeling Labor Productivity in Construction Projects using Hybrid SD-DES Approach
Saeed
Moradi
Farnad
Nasirzadeh
Farzaneh
Golkhoo
Labor productivity is one of the most significant factors in the evaluation of construction projects performance. Improvement of labor productivity is believed to have direct impact on outperformance of the project. This research argues about a hybrid SD-DES approach to model labor productivity considering the effects of both the context and operational level factors. The complex inter-related structure of different context factors affecting the labor productivity is modeled using system dynamics (SD) approach. Discrete event simulation (DES) is implemented to model the operational variables and their effects on labor productivity. Using the proposed hybrid SD-DES model, the labor productivity can be determined more precisely since the effects of both context and operational variables are taken into account. The proposed hybrid model is implemented in a real world case and the value of labor productivity is simulated considering the effects of both context and operational variables.
Productivity
Construction simulation
Hybrid simulation
system dynamics
Discrete event simulation
2017
12
01
2752
2761
http://scientiairanica.sharif.edu/article_4171_e4d3a1ea9bfe4985bb44cd17d0bb4a12.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Modal Analysis of Two-Dimensional Beams Using Parallel Finite Element Method
Soroush
Heydari
Saeed
Asil Gharebaghi
Modal analysis is the process of determination of the natural frequencies and mode shapes of structures. In practical problems, modal analysis may be repeated many times, which results in a huge amount of computations. Although parallel processing technique can reduce the analysis time, it is rarely implemented by civil engineers because it requires more programming skills as well as designing parallel algorithms. In the present paper, the Davidson algorithm is adapted for parallel modal analysis of two-dimensional beams. More precisely, the parallel version of the Davidson algorithm is implemented from scratch. A new proposed method, which is called "Modified Checkered Method" (MCM), is introduced, and four versions of the algorithm, are implemented. Two out of four versions use Row-wise and MCM in combination with Compressed Sparse Row algorithm, while the others utilize the aforesaid methods without matrix compression. It is shown that the speedup increases when the main matrix of the standard form of eigenvalue problem is not compressed. Moreover, the speedup will increase in comparison to the Row-wise division method when MCM is used. It is notable that the implemented Parallel Finite Element source code is capable of being used in companion with a wide variety of finite elements.
Eigenvalue problem
Parallel processing
FEM
CSR matrix compression
Davidson algorithm
Modified Checkered Method
2017
12
01
2762
2775
http://scientiairanica.sharif.edu/article_4529_2093824a2f3305fb058ceef1735fc90a.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Generalized Implicit Multi Time Step Integration for Nonlinear Dynamic Analysis
javad
alamatian
This paper deals with a generalized multi time step integration used for structural dynamic analysis. The proposed method presents three kinds of implicit schemes in which the accelerations and the velocities of the previous steps are utilized to integrate the equations of motion. This procedure employs three groups of weighted factors calculated by minimizing the numerical errors of displacement and velocity in Taylor series expansion. Moreover, a comprehensive study on mathematical stability of the proposed technique which is performed based on the amplification matrices proves that the new method is more stable than existing schemes such as IHOA. For numerical verification, wide range of dynamic systems including linear and nonlinear, single and multi degrees of freedom, damped and undamped, forced and free vibrations from finite element and finite difference methods are analyzed. These numerical studies demonstrate that efficiency and accuracy of the proposed method are higher than other techniques.
multi time step
numerical integration
implicit method
Dynamic Analysis
conditional stability
higher accuracy
2017
12
01
2776
2792
http://scientiairanica.sharif.edu/article_4167_d21d2835f3e39389052033e1a781ee30.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Adaptive mesh-free lower bound limit analysis using non-linear programming
Seyed Mohammad
Binesh
S.
Rasekh
An adaptive mesh-free approach is developed to compute the lower bounds of limit loads in plane strain soil mechanics problems. There is no pre-defined connectivity between nodes in the mesh-free techniques and this property facilitates the implementation of h-adaptivity. Nodes may be added, moved or discarded without complex changes in the data structures involved. In this regard, the Shepard mesh-free method is used in conjunction with the nodal stress rate smoothing technique and the lower bound limit analysis theory to establish a non-linear optimization problem. This problem is solved by second order cone programming technique and the result is a stress field that satisfied the lower bound requirements in non-rigorous manner. The lack of rigorousness arises from relaxation during nodal stress rate smoothing process. An error estimator is introduced by the application of Taylor series expansion and, by controlling the local error via a user-defined tolerance, the adaptive refinement strategy has been established. To demonstrate the effectiveness of proposed method, the procedure is applied to the examples of purely cohesive and cohesive-frictional soils.
adaptive
mesh-free
Lower bound
non-linear programming
plane strain
2017
12
01
2793
2802
http://scientiairanica.sharif.edu/article_4163_1f834856a89be71751ad51fe393f6d11.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Evaluation of behavior of bucket foundations under pure loading
Vali
Ghaseminejad
M.A.
Rowshanzamir
Offshore wind turbine as a green renewable resource can have important roles in changing energy structure. In this study the results of three-dimensional finite element analyses of the pure horizontal, vertical and moment loading of bucket foundations in medium-dense sand are presented. Sensitivity analyses have been performed at different bucket diameters and length-to-diameter aspect ratios (L/D) and the responses for pure horizontal, vertical and moment loading have been compared. To determine the pure horizontal, vertical and moment bearing capacities of the bucket foundation, different methods have been compared. Charts and functions derived from finite element results and responses are presented as failure envelopes in M-H plane. The results show that pure ultimate capacity of the bucket significantly depends on bucket geometry and aspect ratio.
Offshore wind turbines
Bucket foundations
Finite element analyses
Pure bearing capacity
Medium dense sand
2017
12
01
2803
2816
http://scientiairanica.sharif.edu/article_4166_baff98b3adcb234791d4eb67dcc3723f.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
On the Evolutionary Characteristics of the Acceleration Records Generated From Linear Time-Variant Systems
Zakariya
Waezi
Fayaz
R. Rofooei
This paper discusses the time-varying characteristics of the output signals resulted from linear time variant (LTV) systems using level crossing properties. These systems which are used for generating synthetic records based on a target record contain two identification processes: 1) amplitude modulating function, 2) time-varying impulse response function (IRF) parameters. For efficient tracking of the IRF parameters, the zero-crossing and positive minima/negative maxima cumulative curves are usually utilized as the measures of the instantaneous spectral power. Using spectral moments, analytic relations for zero-crossing and positive minima/negative maxima cumulative count are developed with respect to the IRF’s evolutionary power spectrum. In order to efficiently investigate the low-frequency components of the output records, the zero-crossing rate of the velocity and the displacement records are tracked and rigorous analytic equations for their descriptions are developed. Some of the issues concerning application of the developed equations are explored using two LVT models, and the limitations of the proposed procedures are explained. Through introduction of new compatibility measures, the necessity of implementing Monte Carlo simulations would no longer be needed and it would be possible to generate the synthetic acceleration records with desirable evolutionary characteristics with much less computation time.
Non-stationary records
Ground motion simulation
Linear time variant
Zero crossing
Positive minimum and Negative maximum
Lower-level crossings
2017
12
01
2817
2831
http://scientiairanica.sharif.edu/article_4254_92a5577457dd70f1b45552ed573b2995.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2017
24
6
Increasing the flexural capacity of geopolymer concrete beams using partially deflection hardening cement-based layers: Numerical study
M.
Mastali
M..
Mastali
Z.
Abdollahnejad
A.
Dalvand
Experimental research has demonstrated the great flexural performance of deflection hardening cement based composites for strengthening the beams. This paper numerically investigates the feasibility of adding thin deflection hardening fiber reinforced layers to the bottom of geopolymer concrete beams to enhance the flexural performance. To properly predict the structural behavior and crack patterns of beams, the smeared crack approach was adopted to simulate the beams. The numerical simulations executed in the FEM-based computer program. To validate the developed numerical models, the tested experimental tests beams with two layers cross section were numerically simulated. Regarding the results obtained , the models would well predict the structural behavior and crack patterns of beams. Ensuring the efficiency and accuracy of the adopted constitutive model to predict the structural behavior and crack patterns of beams, the numerical FE models used to simulate the added hardening deflection fiber reinforced layer to the bottom of geopolymer concrete beams. The numerical results revealed that adding a thin fiber reinforced layer to geopolymer concrete beams results in increasing ultimate load capacity, ultimate deflection, and ductility. The greatest enhancement in the flexural performance of the strengthened beams was found in the ultimate load capacity of the strengthened beams.
FEM
Material nonlinear analysis
Flexural strengthening
DHCC
enlargement method
2017
12
01
2832
2844
http://scientiairanica.sharif.edu/article_4530_7814a0e43a0dbeff2a4084b4a3a419eb.pdf