2020-11-28T03:17:56Z
http://scientiairanica.sharif.edu/?_action=export&rf=summon&issue=1051
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Investigation into stiffness degradation progress in glass/vinylester laminated beams under large deformations
A. R.
Nazari
Mohammad Z.
Kabir
H.
Hosseini - Toudeshky
There are many reports indicating that the maximum measured stress in the composite laminated beams under flexural loading appears different from that under tensile loading. The current study compares the results of Hashin failure criteria in the form of stress and strain components for prediction of failure strength in GFRP laminated beams. In the experimental program the composite laminates were tested under tensile and three-point-bending (3PB) loads. Then, it was trying to predict the flexural failure in laminates based on the measured ultimate stresses and strains in the tensile tests. The strain-based failure criteria employed in the FE models could achieve more admissible predictions for maximum load carrying capacity in the laminates compared to the stress-based criteria. Progressive failure analyses showed that due to higher elastic modulus of laminates under bending load, the maximum experienced stress under bending load becomes larger.
Flexural strength
GFRP laminate
Progressive failure
Hashin criteria
Large deformations
2018
10
01
2389
2403
http://scientiairanica.sharif.edu/article_4220_9c3a8e7a0aff00ae1d02e1708710a0b5.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Water reducing agent effects on the engineering performance of cement stabilized aggregates
Liqun
Hu
Zhuangzhuang
Liu
Aimin
Sha
Water reducing agents (WRAs) are usually utilized in cement concretes to reduce the water-cement ration, increasing mechanical strength and improving the durability of concrete structures. As a kind of widely used construction materials in pavement structures, i.e., base or subbase course, cement stabilized aggregates (CSAs) have to face their own problems, e.g., drying shrinkage at early ages. To evaluate the feasibility of water reducing agent in cement stabilized aggregates, and its effects on engineering performance, six groups of cement stabilized aggregates were prepared (water reducing content = 0, 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%). Engineering performances including density-water relationships, unconfined compressive strength (UCS), tensile splitting strength (TSS), compressive resilience modulus (CRM) and drying shrinkage strain(DSS) were measured. Result indicates that water reducing agents used in this study can significantly benefit the engineering performances of cement stabilized aggregates. The function or role of water reducing agent in cement stabilized aggregates were summarized, which would be beneficial to guide the water reducing agent utilization in cement stabilized aggregates.
Cement stabilized aggregate (CSAs)
Water reducing agents (WRAs)
Mechanical behavior
Vibration compaction method
2018
10
01
2404
2412
http://scientiairanica.sharif.edu/article_4213_323ea86acd00a10f5c4ae467411233eb.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Numerical modelling of flow field in compound channels with non-prismatic floodplains
B.
Rezaei
H.
Amiri
In this paper an attempt has been made to study flow field in compound channels with non-prismatic floodplains. A three dimensional computational fluid dynamic (CFD) model is used to calculate the velocity distribution, secondary flow circulation and boundary shear stress in non-prismatic compound channels with two different convergence angles of 3.81o and 11.31o. The ANSYS-CFX software and k-e turbulence model is used to solve Reynolds Averaged Navier-Stokes (RANS) equations. The results of the numerical modeling were then compared to the experimental data on non-prismatic compound channels with the same convergence angles. The study shows that, more or less, the k-e turbulence model is capable of predicting the velocity and boundary shear stress distributions along the flume fairly well, especially for convergence angle of 3.81o. Also by increasing relative depth, discrepancy between numerical and experimental data decreases. The results of modeling show that the k-e turbulence model is able to predict secondary flow circulations in the main channel, created by the mass exchange between the floodplains and the main channel.
Non-prismatic compound channel
Numerical Modeling
k-e turbulence model
velocity distribution
2018
10
01
2413
2424
http://scientiairanica.sharif.edu/article_4215_0a8a861f327d14d3f5b3bc4e4d71dced.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Earthquake ground-motion duration estimation using general regression neural network
Saman
Yaghmaei-Sabegh
Accurate prediction of earthquake duration could control seismic design of structures. In this paper, a new simple method was developed to estimate such important parameter by employing artificial neural networks (ANN) capability. A generalized regression neural network (GRNN) as a special class of RBF networks was implemented in this study to reduce the computation steps required for the searching process on sparse data sets. This network with quick-design capability does not need to impose a prescribed form for mapping of the observed data. The independent variables used in the predictive model of this study were earthquake magnitude, distance measure and site conditions. The designed models were trained using the 950 accelerograms recorded at Iranian plateau. The performance of proposed approach was compared with predicted results of feed forward back propagation networks. Analyses show that the designed GRNN performs well in estimating earthquake record duration and could be applied for prediction of common measures of earthquake ground-motion duration.
Ground motion duration
significant duration
generalized regression neural network (GRNN), RBF network, Iran
2018
10
01
2425
2439
http://scientiairanica.sharif.edu/article_4217_4059f8e909732e5651d70e368865e50e.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Physical, mechanical, and durability properties of ternary blend concrete
G.
Dhinakaran
B.
Sreekanth
Production of high strength concrete with waste utilization attracted more attention of many researchers due to number of benefits in the present scenario. This paper discusses the effect of such waste utilization in strength, durability and structural behavior of high strength concrete by considerably replacing cement. Rice husk ash (RHA) (5 to 15%) and ground granulated blast furnace slag (GGBFS) (20 to 40%) were used as mineral admixtures in three different percentages. The range of replacement of cement with this dual mixture was kept 25% as minimum and 55% as maximum. Strength parameters such as compression & flexure and durability parameters such as sorptivity, porosity and freeze-thaw were studied. All the tests were conducted as per ASTM standards. Ten combinations of ternary mix were tested and among them mix with 30% GGBFS and 5% RHA exhibited better performance at par with control concrete by compromising characteristic compressive strength to an extent of 5%. It also yields better performance in terms of durability characteristics. Hence it was concluded that it could be possible to produce high strength concrete with 35% replacement of cement either with 20% of GGBFS and 15% of RHA or 30% of GGBFS and 5% of RHA.
Ternary blend, rice husk ash
GGBFS
compressive strength
freeze and thaw
Sorptivity
porosity
load deflection
2018
10
01
2440
2450
http://scientiairanica.sharif.edu/article_4210_57679603bc7c92dc50184924393e8637.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Performance of alkali activated slag concrete under aggressive environment
Parthiban
Kathirvel
Saravana Raja Mohan
Kaliyaperumal
The environmental effects of production of Portland cement (PC) have provoked to examine the growth of concrete with 100% replacement of cement with industrial byproducts containing high amount of Si and Al, which are activated by alkali solutions termed as geopolymer concrete. Concrete made with PC can be durable under mild exposure condition when properly designed whereas undergo deterioration under severe exposure condition. Since very few works have been performed on the ambient cured alkali activated slag concrete (AASC) under aggressive environmental condition, this work was intended to study the effect of binder content and sodium hydroxide concentration on AASC subjected to aggressive environment. In this regard, an experimental investigation was carried out to study the influence of AASC under chloride, acid and sulphate environment on its physical and mechanical properties. The results infer that the AASC mixes perform well under aggressive environment condition.
geopolymer concrete
alkali activated slag
aggressive environment
mechanical properties
sulphate
chloride
ambient temperature
2018
10
01
2451
2460
http://scientiairanica.sharif.edu/article_4221_383d840450ef3b0d1df43a150c9cacd7.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Loading frequency effect on dynamic properties of mixed sandy soils
Ata
Aghaei Araei
Ahmadreza
Ghodrati
Most of the previous studies focused on pure (clean) sands, silts and clays and less effort has been dedicated toward understanding the dynamic behaviors of natural sandy soils. The purpose of this paper is to evaluate the effect of loading frequency as one of the most important factors affects the dynamic properties especially stiffness and damping characteristics of natural sandy soils mixed with silt and gravel. For this purpose, 40 dynamic triaxial tests were carried out on the cylindrical samples prepared from three mixed sandy materials. Cyclic tests were performed using large triaxial apparatus under different confinement, waveforms and loading frequencies. Results showed that, shear modulus and damping ratio were dependent on confining pressure and loading frequency. Shear modulus and damping ratio increase as loading frequency increases. Moreover, the shear modulus increases as confining pressure increases but damping ratio decreases. However, the effect of triangle, sinusoidal and rectangle waveforms on the dynamic behavior was negligible. At the ranges of strains studied, the effects of number of cyclic loading and excess pore water pressure over and were negligible. There are considerable differences between obtained results for the tested soils and literature results, even for the almost same loading frequency.
frequency
mixed sandy soils
triaxial
shear modulus
damping ratio
2018
10
01
2461
2479
http://scientiairanica.sharif.edu/article_4209_290ef49ecaa6c3dd4a6cadcc6b17fb86.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Optimal domain decomposition using the global sensitivity analysis-based metaheuristic algorithm
A.
Kaveh
V.R.
Mahdavi
In this paper, an efficient approach is presented for finding optimal domain decomposition in conjunction with k-median method. Using the clique graph, the connectivity properties of finite element meshes is represented. In order to divide the nodes of the graph or the meshes of the finite element model into k subdomains, k-median approach is employed. For optimal subdomaining, a recently developed metaheuristic algorithm so-called Global Sensitivity Analysis Based (GSAB), is utilized. The performance of the proposed method is investigated through three finite element models for minimize the cost of k-median problem. A comparison of the numerical results obtained using the proposed method with standard Colliding Bodies Optimization (CBO) and Particle Swarm Optimization (PSO) algorithms indicates that the proposed technique is capable of locating more promising solutions using less computational efforts.
Optimal domain decomposition
Global sensitivity analysis based (GSAB)
k-median method
Finite elements meshes
2018
10
01
2480
2487
http://scientiairanica.sharif.edu/article_4508_77c7f2b5cca18972e25a498833d833b3.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Geometrical nonlinear analysis by plane quadrilateral element
Mohammad
Rezaiee - Pajand
Majid
Yaghoobi
Various corotational schemes for solid, shell, bending plate and beam elements have been proposed so far. Nevertheless, this approach has rarely been utilized for membrane problems. In this paper, a new quadrilateral element will be suggested for solving nonlinear membranes. The simplicity, rapid convergence and high accuracy of the formulation are the three main characteristics of the presented element. It is worth emphasizing; the recommended element can solve structures with irregular geometry and distorted mesh. This element is insensitive to the aspect ratio. In addition, using this element leads to high-accuracy results. Several numerical examples will be tested to prove the high precision of authors' element in coarse distorted meshes with a large aspect ratio.
Corotational method
Geometrical nonlinear
Strain states
Membrane problem
Quadrilateral element
2018
10
01
2488
2500
http://scientiairanica.sharif.edu/article_4219_cf18170df64b8220ae74ebd058524a58.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Response of buried oil and gas pipelines subjected to reverse faulting: A novel centrifuge-finite element approach
Reza
Yeganeh Khaksar
Majid
Moradi
Abbas
Ghalandarzadeh
Buried pipelines, transporting fuels, inevitably face active faults when they pass through various seismic regions. These faults may damage the pipelines severely; hence numerous analytical, physical and numerical studies have been conducted with their own pros and cons to investigate the pipeline response due to the faulting. In the present study, an innovative combination of centrifuge and numerical modeling methods has been employed to overcome the geometrical limitation of the small scale physical modeling. Then, it is applied for investigation of buried pipelines response due to reverse faulting. Initially, two centrifuge tests with the fixed end pipelines have been conducted and employed as the benchmarks for the verification of a numerical model. Then, the calibrated numerical model has been used to develop the novel pipeline spring-like end connection system which is supposed to represent the response of the omitted pipeline parts. Eventually, a centrifuge test was conducted, employing the novel end connection system which verified the proper performance of the system. Then, the model is employed for investigation of buried pipelines response due to reverse faulting and the results are also presented.
steel buried pipeline
reverse faulting
centrifuge modeling
Numerical Modeling
end connection
2018
10
01
2501
2516
http://scientiairanica.sharif.edu/article_4214_607a0a6766b3ee2190e19bec44e4bb03.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Influence of random inclusion of treated sisal fibres on the unconfined compressive strength of highly compressible clay
Evangelin
Ramani Sujatha
E
Lakshmi Priya
A. R
Sangavi
K.V
Poonkuzhali
Reinforcement in the form of strips, grids and fibres enhances the engineering properties of soil. In this study, an attempt has been made to use treated sisal fibres to reinforce the soil so that unconfined compressive strength is enhanced. The compaction characteristics, stress-strain behavior, strength and failure pattern of the unreinforced and reinforced sisal fibre reinforced soil were investigated. The inclusion of sisal fibres increases the strength and modifies compressibility and permeability of the soil. The results of the study show that addition of sisal fibres to soil causes an increase in optimum moisture content and a decrease in dry density. The unconfined compressive strength and post peak strength of the reinforced soil increase with fibre content of 2 %. Failure pattern shows that fibre has a significant control over the development of cracks. Fibre inclusion suppresses the development of long cracks as they act as tension reinforcements. The use of sisal fibres gives the advantage of an eco-friendly material that aids sustainable development in addition to the beneficial modification of soil properties.
unconfined compressive strength
Random Inclusion
Sisal Fibre
Post Peak Strength
Failure Pattern
2018
10
01
2517
2524
http://scientiairanica.sharif.edu/article_4208_ca3cfe2c89a9ca998b5129a7df1dbe87.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Analytical approach to evaluate stability of pile-stabilized slope
Mohammad
Hajiazizi
Ahmadreza
Mazaheri
Rolando P.
Orense
Many studies have been conducted to examine the factor of safety of a slope reinforced by a row of piles and the forces acting on these piles. This paper presents an analytical approach to calculate the forces acting on piles and the corresponding factor of safety of slopes stabilized by a row of piles. The proposed approach is based on force equilibrium within the upslope wedge above the pile location and would require knowledge of the upper wedge weight before application. The validity of the proposed analytical approach was verified by comparing the results with those obtained using available approaches in the literature as well as from physical experiments and numerical analyses using available software. Additionally, the effect of arching phenomenon was examined and the optimum pile spacing for use in reinforcing slopes was investigated. The optimum pile spacing depends on the properties of the soil comprising the slope, but the most cost-effective pile spacing was found to be between 4-5 times of the pile diameter, corresponding to the largest spacing that can generate arching between piles. Thus, the proposed analytical approach can be used in practical applications to determine the stability of slopes reinforced by a row of piles.
Slope stability
pile
safety factor
Stability analysis
Arching
2018
10
01
2525
2536
http://scientiairanica.sharif.edu/article_4218_93eb17677e52db7c83694663c9bcdab9.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
Field study of flow resistance in step-pool streams (case study of Dizin River)
Ahmad
Tahershamsi
Mohammad Reza
Majdzadeh Tabatabai
Abbas
Torabizadeh
A series of steps and pools are ubiquitous bed forms in mountain stream channels, occurring where gradients exceed 2% and materials are in the gravel to boulder size range. Flow resistance, reflected by roughness elements, appears to be an important control on bed load transport rates and mean flow velocity. To estimate flow resistance some morphological features and velocity were measured in the step-pool channel of Dizin River, located in Karaj River watershed in Iran. Topographic surveys and bed sediment sampling were made in low flow condition while three-dimensional velocity measurements were made in low, medium and high flow conditions. Gradient variations are in the range of 7% to 14%. As flow resistance is a function of geometric, bed material size, longitudinal slope and hydraulic radius, dimensional analysis was conducted to develop a non-dimensional relationship for flow resistance in step-pool reaches. Thereafter, it was calibrated for the measured data set of Dizin river and validated for Rio Cordon data set. Comparable results of validation with a river located in a different environment may suggest that flow resistance features in semi arid and humid streams may have similar effects on non-dimensional resistance coefficient
Step-pool
Flow Resistance
Mountain Streams
Chezy Coefficient
Dizin River
2018
10
01
2537
2549
http://scientiairanica.sharif.edu/article_20441_d38efb18bc3769279fb3ed72a132dc95.pdf
Scientia Iranica
Scientia Iranica
1026-3098
1026-3098
2018
25
5
The effect of fixed-tip piles on stabilization of earth slopes
Mohammad
Hajiazizi
Masoud
Nasiri
Ahmad Reza
Mazaheri
A recent widely researched solution is slope stabilization using a row of piles. In this study, the effects of fixed-tip pile and the subsequent pile length reduction, which finally bring about a reduction in stabilization costs were considered. This paper, presents novel analyses that were carried out in static condition. The analyses were performed using the limit equilibrium (LE) method and shear strength reduction (SSR) method, which approve of one another. Fixing pile tip was an efficient and applicable method for stabilizing earth slopes and reducing pile length. Results of these analyses were acceptable and were properly consistent with the results obtained by other researchers. The process of fixing end of pile were also carried out experimentally, and a new method proposed for this purpose, besides its simplicity, is cost effective and practical. The result of this investigation shows the effectiveness of the proposed method, in which, fixing the pile tip could enhance factor of safety (FOS) up to 55 percent.
Earth slope
Fixed-tip pile
Pile length reduction
Stabilization
Experimental modeling
2018
10
01
2550
2560
http://scientiairanica.sharif.edu/article_4211_342331787b6d7ca61b6d107cd37f8b55.pdf