2020-11-29T16:55:22Z
http://scientiairanica.sharif.edu/?_action=export&rf=summon&issue=1044
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Evaluation of effective parameters on lateral buckling of subsea pipelines on a rigid seabed
Mohammad
Vaghefi
Marjan
Keshavarzi
Maryam
Akbari
In this study, the lateral buckling of pipelines on a rigid seabed under temperature and internal pressure is discussed regardless of the effects of waves and currents. The analytical results in some cases are compared with the numerical results obtained from ABAQUS software. Then the influence of effective parameters (such as: internal pressure, friction, initial imperfection, diameter and thickness of the pipe and the pipe material) on the lateral buckling of pipelines on a rigid seabed is evaluated in order to determine the level of importance. The most important results indicate a reduced possibility of lateral buckling with an increased coefficient of friction between the pipe and seabed, reduction of the internal pressure, and reduction of the amplitude of the initial imperfection in the pipeline. For example, compared to the models with coefficients of friction equal to 0.5 and 0.3, the safety temperature in the model with a coefficient of friction equal to 0.7 has increased 13.6% and 50% respectively. Compared to the models with initial imperfections equal to 0.3, 0.5, and 0.7 m, the safety temperature in the model with an initial imperfection of 0.1 m has increased 4.49%, 15.32%, and 40.65% respectively.
Subsea pipeline
Lateral buckling
Initial imperfection
Internal pressure
Temperature
2018
08
01
1891
1906
http://scientiairanica.sharif.edu/article_4610_71d831e82f6efed92581cbec8b82b447.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
A numerical investigation of the effect of the temperature on the seepage calculation
Alireza
Tabarsa
Mohsen
Lashkarbolok
Temperature difference in the soil and its environments is a common phenomenon. The permeability of the soil changes with the temperature mostly because of the variation of the viscosity of water in different temperatures. More realistic estimation of the seepage value through and beneath hydraulic structures leads to more efficient design of them. In this paper, the heat conduction equation is solved by a least squares based meshfree method to calculate the distribution of the temperature in a soil. The distribution of the permeability coefficients can be varied irregularly that may make some difficulties in the mesh-based methods. In these methods the permeability changes in each mesh and finer mesh or some kinds of interpolation are required in the solution procedure. Since there is no need to form elements or grids in a meshfree method, it can handle this irregular variation simply. Here, the seepage equation is solved by the same least squares based meshfree method. The method is integral free, simple and efficient in calculation thanks to its sparse and positive definite matrices. The scheme is validated by solving a simplified version of the governing equations. More complicated problems are dealt with to investigate the phenomenon numerically.
temperature distribution
meshfree method
seepage
Permeability
least squares
2018
08
01
1907
1915
http://scientiairanica.sharif.edu/article_20421_834af46b531bbaa6bbc7b01cccec3d61.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Robust model and solution algorithm for the railroad blocking problem under uncertainty
Reza
Mohammad Hasany
Yousef
Shafahi
The railroad blocking problem emerges as an important issue at the tactical level of planning in freight rail transportation. This problem consists of determining the optimal paths for freight cars in a rail network. Often, demand and supply resource indicators are assumed to be certain, so the solution obtained from a certain model might not be optimal or even feasible in practice because of the stochastic nature of these parameters. To address this issue, this paper develops a robust model for this problem with uncertain demand and uncertain travel time as supply resource indicators. Since the model combines integer variables and nonlinear functions, a branch-and-cut algorithm is used to solve the linearized version of the robust model. The performance of the proposed algorithm in several instances is discussed. A comparison with a well-known solver shows the high efficiency and effectiveness of the proposed algorithm. Finally, this algorithm is applied to a blocking problem of the railways of Iran. The results show that, by ignoring approximately 10% of the optimal value of the deterministic model, we have an optimal solution that remains unchanged with a probability of more than 0.98.
Railroad blocking problem
robust optimization
branch-and-cut algorithm
uncertainty
railway planning
2018
08
01
1916
1930
http://scientiairanica.sharif.edu/article_4199_cc6e5e8def3a9db33c8caec1a2f043ba.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Reservoir's geometry impact of three dimensions on peak discharge of dam-failure flash flood
Ahmad
Tahershamsi
Farhad
Hooshyaripor
Sahand
Razi
Once a dam fails, large amount of water at rest in the reservoir releases to downstream river and can cause extensive inundation areas, damage to properties, and loss of lives. The outflow hydrograph influences from variety of factors; e.g. dam’s properties, failure mode, and reservoir specification. This paper aims to analyze the effect of two latter factors on the peak outflow discharge focusing on the relative size of the failed part employing failure ratio (a/A0) and shape of the reservoir employing shape factor (Sf) and cross section index (λ). Doing so, instantaneous experimental dam break and historical gradual failure were considered and separate analyses were carried out. Results showed that a higher peak-discharge is expected when Sf decreases or a/A0 and λ increase. Based on the experimental and historical dam failure data two distinct regression equations were developed and verified for peak-discharge estimation. The sensitivity analysis demonstrated that peak-discharge is highly sensitive to changes of the failure ratio and shape factor and it to some extend affects from cross section index.
Dam failure
Failure ratio
Peak-discharge
Reservoir shape
cross section index
2018
08
01
1931
1942
http://scientiairanica.sharif.edu/article_4467_c6ec34eb9ea4addc93f6afeb9ad392f2.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Predicting shear wave velocity of soil using multiple linear regression analysis and artificial neural networks
OMOLBANIN
ATAEE
NASER
HAFEZI MOGHADDAS
GHOLAM REZA
LASHKARI POUR
MEHDI J
ABBARI NOOGHABI
In this paper, the correlation between shear wave velocity and some of the index parameters of soils including standard penetration test blow counts (SPT), fine-content (FC), soil moisture (W), liquid limit (LL) and depth (D) is investigated. The study attempts to show the application of artificial neural networks and multiple regression analysis in the prediction of the shear wave velocity (VS) value of soils. New predicting equations are suggested to correlate VS and mentioned parameters based on a dataset collected from Mashhad city in the north east of Iran. The results suggest that better and more exact correlations in the estimation of VS are acquired when ANN method is used. The predicted values using ANN method are checked against the real values of VS to evaluate the performance of this method. The minimum correlation coefficient obtained in ANN method is higher than the maximum correlation coefficient obtained from the MLR. In addition, the value of estimation error in the ANN method is much less than the MLR method indicating the higher confidence coefficient of the ANN in estimating the VS of soil.
Shear wave velocity
SPT
depth
Fine-content
artificial neural network
Multiple Linear Regression
and Mashhad
2018
08
01
1943
1955
http://scientiairanica.sharif.edu/article_4263_57852cf72ee0384832b234269900f3bf.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Importance of bed roughness in transversal variability of the flow patterns and bed shear stress due to secondary currents
Seyed Hossein
Mohajeri
Akbar
Safarzadeh
Seyed Ali Akbar
Salehi Neyshabouri
Laboratory experiments were carried out in order to study the influence of the bed roughness on secondary circulations and lateral flow variability in a straight open channel. Flow field and bed shear stress were measured using an acoustic doppler velocimeter and a particular type of the Preston tube, respectively. All experiments attest presence of noticeable lateral variations of the flow characteristics due to the secondary currents. The observations also reveal that the lateral variations in the experiments with larger bed roughness are more intense. This implies the formation of a more stable mechanism for the maintenance of the cellular pattern in the experiments with larger bed roughness elements. Regarding formation of the secondary currents, application of double averaging method (averaging of the time averaged turbulence parameters within a thin spatial slab parallel to the bed) is also discussed. It was found that, to properly consider the lateral variations of the flow characteristics, spatial averaging should be implemented among the measured data at different spanwise locations. As such secondary current enhancements can also affect more complex and natural flow like river flows, it can also be recommended to examine the importance of such phenomenon in those areas respecting double averaging method.
Rough bed
turbulent flow
Flow variability
Open-channel
Secondary
2018
08
01
1956
1967
http://scientiairanica.sharif.edu/article_4204_0d25389dd9e362a044a6d453fe93a63e.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Behavioral analysis of vehicle-pedestrian interactions in Iran
Abbas
Sheykhfard
Farshidreza
Haghighi
Statistics upon injured and killed pedestrian accidents in recent years expresses a high vulnerability of this group of road users. By identifying influential factors on the interactions of pedestrians-vehicles and representing appropriate solutions to reduce the impact of these factors, the possibility of such interactions and consequently, the relative accidents can be reduced. In present research, based on naturalistic driving studies (NDS), the driving behavior of 29 drivers of vehicles was investigated. 289 vehicle-pedestrian interactions in the local urban routes of Babol City in Mazandaran, Iran at the traffic peak hours were determined. By analyzing the interactions using the DREAM method (Driving Reliability and Error Analysis Method), the risk factors were identified and two causal patterns were determined for pedestrian crossings and places lacking pedestrian crossings. Drivers talking to passengers and listening to music were among the factors influencing occurrence of interactions at pedestrian crossings. Unexpected behaviors by pedestrians while crossing (such as sudden running, crossing careless of the traffic flow, and crossing without obtaining the permission from the vehicle driver) played a substantial role in occurrence of interactions in places without pedestrian crossings. Finally, some solutions were proposed for reducing the chances of occurrence of interactions.
Pedestrian accidents
Vehicle-pedestrian interaction
Vehicle driver behavior
Pedestrian behavior
DREAM method
2018
08
01
1968
1976
http://scientiairanica.sharif.edu/article_4201_f1a87f8a9cb273014ce2937b455370a1.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Experimental and numerical study of a proposed moment-resisting connection for precast concrete frames
Mojtaba
Fathi
Mahdi
Parvizi
Javad
Karimi
M.Hossein
Afreidoun
This paper presents the test results of a proposed ductile moment-resisting beam-column connection for precast concrete frames and a developed3D nonlinear finite element model of this connection in several different details of connection, to predict its behavior under cyclic loading, based on the loading of the ACI T1.1-01. In this connection, precast concrete beam and column are connected to each other by steel linkage element. This method is able to create concrete structures with higher quality through minimizing in-situ concreting and maximizing the speed of construction as well as usage of ductile and exchangeable elements in sensible locations of the connection. Two types of bolted and welded connections were compared to monolithic connection in terms of stiffness, strength, energy dissipation capacity and ductility factor. All specimens satisfied all criteria of ACI T1.1-01.To investigate the behavior of these connections a 3D nonlinear finite element model has been simulated. Numerical results showed a good agreementwith experimental results. The initial stiffness of monolithic connectionspecimen wasgreater thanboltedconnection and welded connectionspecimens.Even though, the beam moment capacity factors for two welded and bolted samples were a little more than monolithic sample; but the ductility factors of these samples were a little less than that of monolithic sample.
Experimental Study
Precast Concrete Frame
Moment-Resisting Connection
cyclic loading
Finite Elements Analysis
2018
08
01
1977
1986
http://scientiairanica.sharif.edu/article_4200_134c8a8b6c8e1c2c25473d247e3f5010.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Near-fault ground motion effects on the responses of tall reinforced concrete walls with buckling-restrained brace outriggers
Hamid
Beiraghi
In this paper, responses of reinforced concrete core-wall structures connected to the outside columns by buckling-restrained brace (BRB) outriggers in tall buildings were investigated. These buildings are subjected to forward directivity near fault (NF) and ordinary far-fault (FF) ground motions. According to the current codes for the DBE level, the response spectrum analysis procedure was applied to analyze and design the structures. The nonlinear fiber element approach was used to simulate the reinforced concrete core-walls. Nonlinear time history analysis was implemented using 14 NF as well as 14 FF records at MCE level. In the core-wall, the results show that the mean moment demand envelope as well as the mean shear demand envelope obtained from the NF records are approximately similar to the corresponding demand envelope from FF records. The reason has to do with extending plasticity all over the RC core-wall which is subjected to both sets of records. The overall responses of the reinforced concrete core-wall with BRB outrigger system is in acceptable range both for NF and FF earthquakes. In this study, the largest curvature ductility demand in the reinforced concrete core-wall took place at levels just above the outriggers.
Reinforced concrete
core-wall
plastic hinge
BRB
outrigger
NLTHA
near-fault
2018
08
01
1987
1999
http://scientiairanica.sharif.edu/article_4205_e80a45a71a5fb39088c2898416c68381.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Collocated Mixed Discrete Least Squares Meshless (CMDLSM) method for solving quadratic partial differential equations
Saeb
Faraji
M.
Kolahdoozan
M.H.
Afshar
In this paper, a Collocated Mixed Discrete Least Squares Meshfree (MDLSM) method is proposed and used for efficient solution of engineering problems. Background mesh is not required in the MDLSM method; hence the method is a truly meshfree method. Nodal points are used in the MDLSM methods to construct the shape functions while collocated points are used to form the least squares functional. In the original MDLSM method, the location of the nodal points and collocated points are the same. In the proposed Collocated Mixed Discrete Least Squares Meshfree (CMDLSM) method, a set of additional collocated points is introduced. It is expected that the accuracy of results is improved by using the additional collocated points. It is noted that the size of coefficient matrix is not increased in the proposed CMDLSM method compared with the MDLSM method. The required computational effort for solving the linear algebraic system of equations, therefore, is the same as that of MDLSM method. A set of benchmark numerical examples, cited in the literature, is used to evaluate the performance of proposed method. The results indicate that the accuracy of solutions is improved by using additional collocated points in the proposed CMDLSM method.
Meshfree
PDEs
DLSM
MDLSM
Collocated points
CMDLSM
2018
08
01
2000
2011
http://scientiairanica.sharif.edu/article_4203_6f92c0efb8788f8cf01aa3a39f2f8b84.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Flexural and shear strengthening of RC beams with NSM technique and manually made CFRP bars
Mohammad Kazem
Sharbatdar
M.
Jaberi
In this paper, the efficiency of NSM method for both flexural and shear strengthening of RC beams were examined by applying an innovative manually made CFRP bar (MMFRP) as an alternative reinforcement composite material through experimental and numerical investigation. Experimental program was consisted of three inverted T-section RC flexural-dominated beams and three rectangular section RC shear-dominated beams with parameters of the length and anchoring of MMFRP bars and their inclination to the longitudinal axis of the beams. The structural performance of the tested beams and the Finite Element (FE) modeling approach including modes of failure, load-deflection response and ultimate load capacity are presented and discussed. Test results indicated that using proposed MMFRP bars significantly improved the flexural resistance and shear capacity of deficient concrete beams. Furthermore reduction of the crack width and increase in the quantity and propagation of new cracks was observed in strengthened beams compared to control beam.
Beams
Shear
Flexural strengthening
Composite Materials
numerical
NSM
2018
08
01
2012
2025
http://scientiairanica.sharif.edu/article_4207_e016ef7b57c3a66d1a2e9083405649db.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Estimation of van Genuchten SWCC model for unsaturated sands by means of the genetic programming
A.
Taban
M . Mirmohammad
Sadeghi
M.A.
Rowshanzamir
The van Genuchten Model (1980) is widely-used for the description of the Soil-Water Characteristic Curve (SWCC) of a variety of soils. This study uses the Genetic Programming (GP) for the presentation of equations estimating the van Genuchten (vG) Model fitting parameters for unsaturated clean sand soils. Moreover, this study uses the data derived from the valid dataset of Benson et al. (2014), including 95 measured SWCCs in both drying and wetting phases. The data on the particle size distributions includes the fine-grain percentage (Fines %), d60, d10, besides the residual and saturated volumetric water content and ), as the GP model inputs of set of terminal. As for the model outputs of set of terminal, the fitting parameters for the vG model include a and n. The functions used in the GP training were 'plus', 'minus', 'times', taken from the MATLAB default functions, 'mydivide' proposed by Silva (2007), and some other new power functions included by this study. Accordingly, new equations were presented for the estimation of vG Model fitting parameters for both forms of wetting and drying. Finally, to evaluate the accuracy of the proposed estimation equations, the GP results were evaluated and verified in different procedures.
SWCC
van Genuchten Model
Unsaturated soils
Genetic programming
Fitting Parameters
2018
08
01
2026
2038
http://scientiairanica.sharif.edu/article_4206_941a3b4ae8ad623078c06dc2c5d32da0.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Probabilistic model of unsaturated slope stability considering the uncertainties of soil-water characteristic curve
A.
Johari
A.
Hooshmand Nejad
S.
Mousavi
Many soil slopes are unsaturated and failure of them can be a major cause of damage to structures. Apart from soil properties, the Soil-Water Characteristic Curve (SWCC) is the backbone of any unsaturated slope analysis. Uncertainties of these effective parameters of unsaturated slopes cause the probabilistic analysis to be more realistic rather than deterministic. In this research, the stochastic analysis of unsaturated slope stability is carried out based on simplified Bishop’s method. The stochastic parameters are the input parameters of SWCC in addition to effective internal angle of friction, effective cohesion and unit weight of soil. Based on the collected results from hundreds of stochastic analyses, the probability of failure is presented as a three dimensional surface. Finally, probabilistic model is developed to model this surface and evaluate the probability of failure as function of safety factor and its correlation of variation.
Unsaturated soils
Slope stability
Soil-water characteristic curve
Artificial intelligence
Probabilistic model
2018
08
01
2039
2050
http://scientiairanica.sharif.edu/article_4202_0b160133988f58a644442ca7c6c43767.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Efficient multi-objective optimization algorithms for construction site layout problem
A.
Kaveh
M.
Rastegar Moghaddam
M.
Khanzadi
Construction site layout planning is one of the managerial aspects of the construction industry and has significant impacts on performance of the sites. Since in real site layout optimization, many objectives are involved, therefore multi-objective algorithms are needed. In this study, multi-objective version of two meta-heuristics, CBO and ECBO, are developed and their applicability and performance are checked on a case study. The quality of the results obtained, verify the ability of these algorithms in finding optimal pareto front on this problem. Another tool that is utilized in this study is data envelopment analysis (DEA) which by calculating the efficiency of optimal pareto front layouts, can help decision makers to select the final layout among the candidates. It should be mentioned that the DEA has previously been used in models with multiple inputs and outputs.
site construction layout problems
multi-objective optimization
colliding bodies optimization
Data envelopment analysis
optimal pareto front
2018
08
01
2051
2062
http://scientiairanica.sharif.edu/article_4216_32853e6bc8b6176c321a748f76555129.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
4
Improving shallow foundations resting on saturated loose sand by a zeolite-cement mixture: A laboratory study
Sina
Salamatpoor
Yaser
Jafarian
Alborz
Hajiannia
Improvement of sands is frequently carried out by cement together with several other additives. The common additives have high manufacturing costs and negative environmental impacts during their manufacturing process and recycling in nature. Zeolite as a mineral substance for cement replacement can improve the strength parameters of a treated sand, without the negative deficiencies of the common additives. In this study, unconfined compression strength (UCS) and small-scale 1g model tests were conducted to evaluate the mechanical features of zeolite-treated sand and to study the behavior of shallow foundations rested on zeolite pad, respectively. The results of this study demonstrate that the UCS of the cemented sand samples increase when the cement is replaced by zeolite at an optimum proportion of 40% with 14 and 28 days curing times. Adding this amount of zeolite to cemented sand mixture causes an increase in terms of the improvement rate between 40% and 125% and increases the bearing capacity ratio (BCR) of the strip foundation treated by zeolite pad in the range of 11% and 420%. In addition, zeolite pad leads to decline the settlement of the treated strip footing from 16% to 86% in terms of the settlement reduction ratio (SRR).
Stabilized sand
Shallow footing
Zeolite
Unconfined compression strength
Small-scale 1g test
2018
08
01
2063
2076
http://scientiairanica.sharif.edu/article_20208_728e2d7f57b68449e3f7265021687a8f.pdf