2017-09-19T22:18:50Z
http://ceij.ut.ac.ir/?_action=export&rf=summon&issue=7697
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Structural Reliability: An Assessment Using a New and Efficient Two-Phase Method Based on Artificial Neural Network and a Harmony Search Algorithm
Naser
Kazemi Elaki
Naser
Shabakhty
Mostafa
Abbasi Kia
Soroosh
Sanayee Moghaddam
In this research, a two-phase algorithm based on the artificial neural network (ANN) and a harmony search (HS) algorithm has been developed with the aim of assessing the reliability of structures with implicit limit state functions. The proposed method involves the generation of datasets to be used specifically for training by Finite Element analysis, to establish an ANN model using a proven ANN model in the reliability assessment process as an analyzer for structures, and finally estimate the reliability index and failure probability by using the HS algorithm, without any requirements for the explicit form of limit state function. The proposed algorithm is investigated here, and its accuracy and efficiency are demonstrated by using several numerical examples. The results obtained show that the proposed algorithm gives an appropriate estimate for the assessment of reliability of structures.
artificial neural network
Failure Probability
Harmony Search Algorithm
Implicit Limit State Function
Reliability Index
2016
06
01
1
20
http://ceij.ut.ac.ir/article_57581_f3e945db438e9cdb612d5492a37a5a50.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
The Elastic Modulus of Steel Fiber Reinforced Concrete (SFRC) with Random Distribution of Aggregate and Fiber
Reza
Saleh Jalali
Emran
Shadafza
The present paper offers a meso-scale numerical model to investigate the effects of random distribution of aggregate particles and steel fibers on the elastic modulus of Steel Fiber Reinforced Concrete (SFRC). Meso-scale model distinctively models coarse aggregate, cementitious mortar, and Interfacial Transition Zone (ITZ) between aggregate, mortar, and steel fibers with their respective material properties. The interfaces between fibers and mortar have been assumed perfectly bonded. Random sampling principle of Monte Carlo's simulation method has been used to generate the random size, orientation, and position of aggregate particles as well as steel fibers in concrete matrix. A total of 2100 two-dimensional and three-dimensional cube specimens (150 mm) with varying volume fractions of aggregate and fiber have been randomly generated. The commercial code ABAQUS has been used to analyze the specimens under tensile loading and the calculated elastic modulus has been compared to other analytical and experimental values. Results indicate that the non-homogeneity of the matrix and random distribution of aggregate and fibers manage to disperse calculated efficiency factor of fiber with a standard deviation of 2.5% to 3.0% (for 150 mm cube specimens, it can be different for other specimens). Nevertheless, the mean value of the calculated efficiency factor agrees well with the value, recommended by Hull (1981), for uniformly-distributed fibers, equal to 0.353, and 0.151 for two and three-dimensional models respectively.
Aggregate
Elastic Modulus
Mesoscopic
Random Distribution
Steel Fiber Reinforced Concrete
2016
06
01
21
32
http://ceij.ut.ac.ir/article_57582_7f1dad5345555fa57be04942ef3d569c.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
The Effect of Spandrel Beam's Specification on Response Modification Factor of Concrete Coupled Shear Walls
Mussa
Mahmoudi
seyed Mohammad Reza
Mortazavi
Saeid
Ajdari
Response modification factor (R factor) is one of the seismic design parameters to be considered in evaluating the performance of buildings during strong motions. This paper has tried to evaluate the response modification factor of concrete coupled shear wall structures with various length/depth ratios of spandrel beams. The effect of diagonal reinforcement of spandrel beam was also evaluated on the R factor. The R factor directly depends on overstrength factor and ductility reduction factor. For this purpose, three conventional structures with 5, 10 and 15 story buildings (having various spandrel beam's length/depth ratio with and without diagonal reinforcement) were selected and the nonlinear static analyses were conducted to evaluate their overstrength and ductility reduction factors. Also for a 5-story structure, nonlinear dynamic analysis (time history) was carried out in order to compare the results with nonlinear static analysis. It was concluded that the R factors using nonlinear time history analysis and nonlinear static analysis are almost the same. The results also indicate that by increasing the height of the structure, the overstrength reduction factor decreases; while the ductility reduction factor increases. Also, the response modification factor decreases with increasing length/depth ratio of spandrel beams. The coupled shear walls with diagonal reinforcement in spandrel beams have a greater R factor.
Concrete Coupled Shear Wall
Ductility Reduction Factor
Response Modification Factor
Overstrength Factor
Spandrel Beam
2016
06
01
33
43
http://ceij.ut.ac.ir/article_55743_50d7805715f00777fcf6daca8da84173.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Investigating the Properties of Asphalt Concrete Containing Glass Fibers and Nanoclay
Hasan
Taherkhani
The performance of asphaltic pavements during their service life is highly dependent on the mechanical properties of the asphaltic layers. Therefore, in order to extend their service life, scientists and engineers are constantly trying to improve the mechanical properties of the asphaltic mixtures. One common method of improving the performance of asphaltic mixtures is using different types of additives. This research investigated the effects of reinforcement by randomly distributed glass fibers and the simultaneous addition of nanoclayon some engineering properties of asphalt concrete have been investigated. The properties of a typical asphalt concrete reinforced by different percentages of glass fibers were compared with those containing both the fibers and nanoclay. Engineering properties, including Marshall stability, flow, Marshall quotient, volumetric properties and indirect tensile strength were studied. Glass fibers were used in different percentages of 0.2, 0.4 and 0.6% (by weight of total mixture), and nanoclay was used in 2, 4 and 6% (by the weight of bitumen). It was found that the addition of fibers proved to be more effective than the nanoclay in increasing the indirect tensile strength. However, nanoclay improved the resistance of the mixture against permanent deformation better than the glass fibers. The results also showed that the mixture reinforced by 0.2% of glass fiber and containing 6% nanoclay possessed the highest Marshall quotient, and the mixture containing 0.6% glass fibers and 2% nanoclay possessedthe highest indirect tensile strength.
Asphalt Concrete
Glass Fiber
nanoclay
Tensile strength
2016
06
01
45
58
http://ceij.ut.ac.ir/article_57583_34037a27acd089c5e5e36190110ac064.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Investigation of Peak Particle Velocity Variations during Impact Pile Driving Process
Maryam
Rezaei
Amir
Hamidi
Abtin
Farshi Homayoun Rooz
Impact pile driving is a multi-component problem which is associated to multi-directional ground vibrations. At first, vibration is transferred from the hammer to the pile and then to the common interface of pile and soil. This is then transferred to the environment and has great impact on the adjacent structures, causing disturbance to residents and also damage to the buildings. It is of high importance to have sufficient estimation of pile driving vibration level in order to maintain the comfort of residents near the site and also to prevent the structural damage to buildings. In this study, a finite element model, using ABAQUS, with the ability of simulating continuous pile driving process from the ground surface, was introduced. The model was verified by comparing the computed peak particle velocities with those measured in the field. Parameters affecting the peak particle velocity (PPV), for example elastic modulus, shear strength parameters, impact force, pile diameter, etc. were considered, and variations of PPV was investigated. Results of present study indicated that PPV at the ground surface does not occur when the pile toe is located on the ground surface; as the pile penetrates into the ground, PPV reaches a maximum value at a critical depth of penetration. Moreover, the amplitude of vibration on the ground surface reduced logarithmically with increasing distance to the pile. Also, on the ground surface and radial distances of 3 to 20 m, maximum particle velocity occurred between 1 to 5 m depths of pile penetration. The results showed PPV as being directly proportional to the hammer impact force, pile diameter, friction angle and cohesion intercept and inversely proportional to the elastic modulus of the soil.
Abaqus
Numerical Analysis
Peak Particle Velocity
Pile Driving
2016
06
01
59
69
http://ceij.ut.ac.ir/article_57238_2432a8765d2c08c940e9759b696afea2.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Three-Dimensional Interfacial Green’s Function for Exponentially Graded Transversely Isotropic Bi-Materials
Farzad
Akbari
Ali
Khojasteh
Mohammad
Rahimian
By virtue of a complete set of two displacement potentials, an analytical derivation of the elastostatic Green’s functions of an exponentially graded transversely isotropic bi-material full-space was presented. Three-dimensional point-load Green’s functions for stresses and displacements were given in line-integral representations. The formulation included a complete set of transformed stress-potential and displacement-potential relations, with the utilization of Fourier series and Hankel transform. As illustrations, the present Green’s functions were analytically degenerated into special cases, such as exponentially graded half-space and homogeneous full-space bi-material Green’s functions. Owing to the complicated integrand functions, the integrals were evaluated numerically, and in computing the integrals numerically, a robust and effective methodology was laid out which provided the necessary account of the presence of singularities of integration. Some typical numerical examples were also illustrated to demonstrate the general features of the exponentially graded bi-material Green’s functions which will be recognized by the effect of degree of variation of material properties.
Bi-Material
Displacement Potential
Exponentially Graded
Functionally Graded Material
Green’s Function
Transversely Isotropic
2016
06
01
71
96
http://ceij.ut.ac.ir/article_55744_4651af5ab40f057d52a0b43a634f84b8.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Ultimate Load Capacity and Behavior of Thin-Walled Curved-Steel Square Struts, Subjected to Compressive Load
S.Mohammad Reza
Mortazavi
Behrouz
Zaeimdar
There have been some experimental tests on hollow curved-steel struts with thin-walled square sections, in order to investigate their general behavior, particularly their capacity for bearing differing loads. One set of square tubes are cold-formed into segments of circular arcs with curvature radii, equal to 4000 mm. Different lengths of curved struts are fabricated so as to cover a practical range of slenderness ratios. The struts tests were pin-ended and had slenderness ratios, based on the straight length between ends ranging from 31-126. The cold-forming operation induces initial inelastic behavior and associated residual stresses. There is, therefore, an interaction among material effects, such as the strain hardening capacity, the Bauschinger effect, strain aging, and residual stresses, together with the significant geometrical effect of the initial curvature, caused by the cold-forming operation. Eventually the results from three series of tests, which are taken on fully-aged and stress-relief-annealed square curved struts, are compared. The variations in load carrying response are discussed.
Bauschinger Effect
Curved Strut
Residual Stresses
Square Hollow Section
Strain Aging
Thin Walled
Ultimate Load Capacity
2016
06
01
97
109
http://ceij.ut.ac.ir/article_57584_eeea52ca3a7cb8e7cd333e3cb31d9e79.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Seismic Bearing Capacity of Strip Footings on Pile-Stabilized Slopes
Maryam
Haghbin
Mahmoud
Ghazavi
This paper develops an analytical method to calculate seismic bearing capacity of a strip footing, which is located on a slope reinforced with rows of pile. The resistance of passive pile is determined based on normal and shear stress of the soil around the pile, which is then compared to other analytical methods. This comparison indicates an acceptable agreement. The variants of the study include location of pile rows, location of footing with respect to the slope crest, foundation depth, and horizontal seismic coefficient. The footing seismic bearing capacity is calculated based on seismic slope stability with limit analysis method (yield acceleration coefficient of reinforced slope with pile row) as well as soil stability beneath the footing by means of virtual retaining wall method. The main objective is to determine and establish the relation between various parameters and seismic bearing capacities of the footing, and to find the best location of the pile row that gives the best improvement in the footing seismic bearing capacity. Results indicate that stabilizing the earth slope with rows of piles has a significant effect on the improvement of seismic bearing capacity of the footing. In addition, the results of the present method are compared with those, reported by others, to demonstrate a reasonable agreement.
analytical method
Footing
Footing Bearing Capacity
Pile
Seismic
slope
Yield Acceleration
2016
06
01
111
126
http://ceij.ut.ac.ir/article_57585_697f5931b758d794e874e9f520d0628c.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Bending Solution for Simply Supported Annular Plates Using the Indirect Trefftz Boundary Method
Amin
Ghannadiasl
Asadollah
Noorzad
This paper presents the bending analysis of annular plates by the indirect Trefftz boundary approach. The formulation for thin and thick plates is based on the Kirchhoff plate theory and the Reissner plate theory. The governing equations are therefore a fourth-order boundary value problem and a sixth-order boundary value problem, respectively. The Trefftz method employs the complete set of solutions satisfying the governing equation. The main benefit of the Trefftz boundary method is that it does not involve singular integrals because of the properties of its solution basis functions. It can therefore be classified into the regular boundary element method. The present method is simple and efficient in comparison with the other methods. In addition, the boundary conditions can be embedded in this method. Finally, several numerical examples are shown to illustrate the efficiency and simplicity of the current approach.
Annular Plates
Indirect Trefftz Method
Kirchhoff Plate Theory
Reissner Plate Theory
2016
06
01
127
138
http://ceij.ut.ac.ir/article_55742_7c0b743709a9306bf156e3f6292f2c34.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Mechanical Behavior of Concrete, Made with Micro-Nano Air Bubbles
Amir
Arefi
Seyed Fazlolah
Saghravani
Reza
Mozaffari Naeeni
Nano materials have been widely used in laboratory and industrial scales in order to improve various properties of concrete and concrete mixture. The mainstream practice of the researches in this field is to add metallic nano-particles into the concrete mixture. The present research focuses on adding Micro-Nano Air Bubbles (MNAB) into water before mixing it with aggregate and cement mixtures. It studies the compressive and tensile strength as well as other engineering properties of the concrete such as the initial and final setting time and the variation in temperature during the setting. The ratio of water/cement was 0.6 with three specimens, prepared for each mixed design to ensure the data quality. Results showed that MNAB-made concrete had 19% higher compression and 16% tensile strength, while the initial and final setting times were significantly shorter (approximately a half) and hydration temperature was notably lower than ordinary concrete.
Compression Strength
Concrete
Micro-Nano Air Bubble
Setting Time
Tensile Strength
Workability
2016
06
01
139
147
http://ceij.ut.ac.ir/article_57586_afeb319dd13451561c626ce65eada1e5.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Permeability Characteristics of Compacted and Stabilized Clay with Cement, Peat Ash and Silica Sand
Seyed Esmaeil
Mousavi
Leong Sing
Wong
The present paper investigates the influence of stabilization with cement, peat ash, and silica sand on permeability coefficient (kv) of compacted clay, using a novel approach to stabilize the clay with peat ash as a supplementary material of cement in the compacted and stabilized soil. In order to assess the mentioned influence, test specimens of both untreated and stabilized soil have been tested in the laboratory so that their permeability could be evaluated. Falling head and one dimensional consolidation tests of laboratory permeability were performed on the clay specimens and the chemical compositions of the materials as well as microstructure of the stabilized soil with 18% cement, 2% peat ash, and 5% silica sand were investigated, using X-ray fluorescence and scanning electron microscopy respectively. Results show that for soil stabilization with up to 8% cement content (of the dry weight of the soil), the average value of coefficient of permeability (kv) is very close to that of untreated soil, whereas the kv value decreases drastically for 18% cement under identical void ratio conditions. It is further revealed that addition of 18% cement, 2% peat ash, and 5% silica sand had decreased the coefficient of permeability by almost 2.2 folds after 24 h, while about 1.7 folds increase was observed in coefficient of permeability once 13.5% of cement, 1.5% of peat ash, and 20% of silica sand were added. The partial replacement of cement with the 2% peat ash can reduce the consumption of cement for soil stabilization.
Falling Head
One Dimensional Consolidation
Peat Ash
Permeability
Silica Sand
2016
06
01
149
164
http://ceij.ut.ac.ir/article_57587_baaec551b267280caa4b649d90e897bc.pdf
Civil Engineering Infrastructures Journal
CEIJ
2322-2093
2322-2093
2016
49
1
Damage Detection of Axially Loaded Beam: A Frequency-Based Method
Omid
Rezaifar
Mohammad Reza
Doostmohammadi
The present study utilizes an analytical method to formulate the three lowest modal frequencies of axially-loaded notched beam through both crack location and load level in a specific format that can be used in existing frequency-based crack-identification methods. The proposed formula provides a basis to shift into two states, one with axial loading and the other without any loading whatsoever. When any two natural frequencies in simply-supported beam with an open crack, subjected to axial load, are measured, crack position and extent can be determined, using a characteristic equation, which is a function of crack location, sectional flexibility, and eigenvalue (natural frequency). Theoretical results show high accuracy for service axial loads. In this range, errors for crack location and extent are less than 12% and 10%, respectively.
Axial Load
Characteristic Equation
Damage Detection
Eigen Frequency
Notched Beam
2016
06
01
165
172
http://ceij.ut.ac.ir/article_57588_3c70f686ba5a3f5c8945184c1699a0e5.pdf