فهرست مطالب

Scientia Iranica - Volume:27 Issue:6, 2019
  • Volume:27 Issue:6, 2019
  • تاریخ انتشار: 1398/09/30
  • تعداد عناوین: 15
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  • J.P. Amezquita Sanchez *, H. Adeli Pages 3051-3059

    In the past twenty-five years, structural health monitoring (SHM) has become an increasingly significant topic of investigation in the civil and structural engineering research community. An SHM schema involves three main steps: (a) measurement and acquisition of signals related to the structural response, (b) signal processing consisting of pre-processing and feature extraction employing nonlinear measurements, and (c) interpretation using machine learning. This article presents a review of recent journal articles on nonlinear measurements used for feature extraction in SHM of building and bridge structures. It also reviews three recently-developed nonlinear indexes with potential applications in SHM.

    Keywords: Civil structures, structural health monitoring, Nonlinear Measurements, Vibrations
  • Mehralah Rakhshanimehr *, Hamed Mirkamali, Mohsen Rashki, Abdolhamid Bahrpeyma Pages 3060-3071

    Reliability analysis of structures is often problematic for the structures with nonlinear and complex limit state functions (LSF). For these cases, simulation methods often provide accurate failure probability, but with high number of structure’s LSF analysis. This paper presents an efficient combination of Monte Carlo Simulation (MCS) method and Univariate Dimension Reduction (UDR) based Meta-model to approximate the failure probability of structures with few LSFs evaluation. For this purpose, the design of experiment used in the Meta model is adapted such that the expected failure samples in MCS being approximated with higher accuracy. Several numerical and engineering reliability problems are solved by the proposed approach and the results are verified by MCS. Results show that the proposed approach highly reduces the required number of structural analysis to provide proper results.

    Keywords: Structural Reliability, Simulation Methods, Univariate Dimension Reduction, Design of Experiment, Monte Carlo simulation
  • Parisa Shadan, Mohammad Zaman Kabir * Pages 3072-3084

    During an earthquake diagonal braces are designed to dissipate energy by yielding in tension and buckling in compression. However, local buckling occurring in the middle of the brace leads to immediate fracture. With the aim of strengthening braces against local buckling, wrapping FRP sheets in transverse direction is proposed in this study. Hitherto, the effect of FRP strengthening on the post-buckling behaviour of Square Hollow Section (SHS) tubes has not been investigated. A numerical model was generated and verified by previous research. Then, a comprehensive parametric study was conducted and the effect of slenderness ratio, number of FRP layers and FRP coverage percentage on post-buckling response of strengthening brace was explored within the study. Results indicate that utilising FRP is certainly successful at mitigating local buckling mode of long SHS braces Moreover, for short braces, applying enough numbers of FRP layers can change the mode of buckling from local to overall. Finally, an optimized length of FRP was suggested for strengthening of braces in accordance with their slenderness ratio.

    Keywords: stability, strengthening, CFRP, square hollow section brace, numerical study
  • Bong Ho Cho, Dae Jin Kim *, Taehyu Ha Pages 3085-3096

    Military quarters and barracks are representative of housing units where the same plan is repeated, and thus prefabricated housing production can be effectively applied. These housing units are required to be disassembled and recycled as military forces are frequently reorganized and deployed to perform military actions. In order to meet these needs, this study proposes a systematic approach for the design of modular military housing units based on Six-Sigma concept. The application of the Six-Sigma to modular military housing units allows customers’ needs to be reflected on the critical to quality, which summarizes the main design requirements, and the design concept of the modular units can be developed based on the derived critical to qualities. To evaluate the effectiveness of the proposed approach, a representative example of military housing units is chosen and designed by utilizing the new modular units developed through this procedure. The weight of frames per unit area and factory manufacturing ratio of the new design are analyzed. The results of the comparison show that the use of the new modular units not only reduces construction cost significantly, but also greatly improves the quality of construction.

    Keywords: Six-Sigma, modular construction, quality function deployment, military housing unit, steel structure
  • Ali R. Kazerounian *, Mohammad T. Kazemi Pages 3097-3108

    Present codes of practice do not consider the effect of arrangement of partitions in the plan of structure on the seismic demands of these non-structural components. In this paper, a modification factor has been proposed to modify provisions for those seismic demands. Seventy two regular low-rise reinforced concrete moment frames, supporting some partitions, exposed to seven appropriate ground motions. The nonlinear seismic response history analysis considering out-of-plane behavior of partitions has been conducted using the OpenSees platform. The average values of peak responses from those earthquakes were obtained. The forces generated using the analytical method, which some of them verified with existing study results, were compared with the values from the code and a factor denoted as seismic force modification factor, W, was proposed. A parametric study has been carried out to study the effect of dominent parameters such as the arrangement of partitions, partition to structure height ratio, and length to height ratio of partitions on the W values. For the majority of the models, the W values are larger for partitions located further with respect to the center of floor. Moreover the modification factor could be as large as 1.85 for the partitions located in the middle floors.

    Keywords: partition arrangement, out-of-plane, low-rise structures, modification factor, nonlinear seismic response history
  • Saeed Darvishi Alamouti, Majid Moradi *, Mohammad Reza Bahaari Pages 3109-3124

    Monopiles are the most common foundation type used for fixed-bottom substructures in offshore wind installations. In an offshore environment, the predominant load is cyclic, which affects the stiffness and deformation properties of foundation systems, especially monopiles. To investigate the effect of cyclic loading on a short (rigid) steel monopile, a set of displacement-controlled ηg laboratory tests were designed. This paper presents the procedure and results of eight centrifuge tests investigating monopile behaviour when subjected to lateral monotonic and cyclic loading. The general trend of monotonic response is in good agreement with the results of similar experimental studies, however, much softer behaviour was observed compared to the equivalent Winkler model on API p-y curves. The cyclic tests focused on the stiffness and deformation properties of a soil-pile system under fatigue loading. Increases, decreases or no changes in secant stiffness were observed depending on the regime of the applied cyclic displacements which are in contradiction to current design methodology where only cyclic degradation is assumed. Influence of load cycling on cyclic bending moments along the pile shaft was discussed and found to be of minor significance

    Keywords: Monopile, lateral loading, short pile, centrifuge modelling, p-y curve, secant stiffness
  • Hamed Amini Tehrani, Ali Bakhshi *, Moustafa Akhavat Pages 3125-3139
    This paper presents a method for structural damage localization based on signal processing using generalized S-transform (SGS). The S-transform is the combinations of the properties of the short-time Fourier transform (STFT) and wavelet transform (WT) that has been developed over the last few years in an attempt to overcome inherent limitations of the wavelet and short time Fourier transform in Time-Frequency representation of non-stationary signals. The generalized type of this transform is the SGS-transform that has adjustable Gaussian window width in the time-frequency representation of signals. In this research, the SGS-transform has been employed due to its favorable performance in detection of the structural damages. The performance of the proposed method has been verified by means of three numerical examples and also the experimental data obtained from the vibration test of 8-DOFs mass–stiffness system. By way of the comparison between damage location obtained from the proposed method and simulation model, it was concluded that the method is sensitive to the damage existence and clearly demonstrates the damage location.
    Keywords: Damage localization, signal processing, Generalized S-transform, Time-frequency representation, Non-stationary signals
  • Hossein Rahnema *, Mehdi Hashemi Jokar, Hadi Khabbaz Pages 3140-3158

    The effective stress parameter (χ) is applied to obtain the shear strength of unsaturated soils. In this study, two adaptive neuro-fuzzy inference system (ANFIS) models, including SC-FIS model (created by subtractive clustering) and FCM-FIS model (created by Fuzzy c-means (FCM) clustering), are presented for prediction of χ and the results are compared. The soil water characteristic curve fitting parameter (λ), the confining pressure, the suction and the volumetric water content in dimensionless forms are used as input parameters for these two models. Using a trial and error process, a series of analyses were performed to determine the optimum methods. The ANFIS models are constructed, trained and validated to predict the value of χ. The quality of the ANFIS prediction ability was quantified in terms of the determination coefficient (R2), Root Mean Square Error (RMSE) and Mean Absolute Error (MAE). These two ANFIS models are effectively able to predict the value of χ with reasonable values of R2, RMSE and MAE. Sensitivity analysis was used to acquire the effect of input parameters on χ prediction, and the results revealed that the confining pressure and the volumetric water content parameters had the most influence on the prediction of χ.

    Keywords: Unsaturated soils, Effective stress parameter, ANFIA, Fuzzy clustering, Subtractive clustering, FCM clustering
  • Raghunath P.N, Suguna K, Karthick J *, Sarathkumar B Pages 3159-3164
    Concrete is a construction material consisting of cementitious material, fine aggregate, coarse aggregate and water. Now-a-days, the cost of these materials is increasing. We need to look at a way to reduce the cost of building materials especially cement. One of the recent advancement in construction industry is the replacement of cement with waste materials in concrete. This replacement offers cost reduction, energy savings and protection of environment. To achieve the above objective, an attempt has been made to replace cement with waste marble powder (WMP) produced from marble industries. The present investigation aims to study the mechanical and durability properties of high strength concrete (HSC) with cement partially replaced by waste marble powder. Cement has been replaced with marble powder at 0%, 5%, 10%, 15% and 20%   in this study. The properties of concrete such as compressive strength, modulus of elasticity and flexural strength were determined. The durability characteristics such as water absorption, acid resistance and rapid chloride permeability were also determined.
    Keywords: Marble powder, Durability, High strength concrete, Waste material
  • Mohammad Vaghefi *, Maryam Akbari Pages 3165-3180
    A laboratory flume in the hydraulics laboratory is necessary in order to investigate and model different hydraulic and hydrodynamic phenomena which govern the river. Hence, this article provides a description on construction and setting up a 180 degree flume, as the first 180 degree sharp bend flume containing multiple lateral intakes, in the Hydraulic Laboratory of Persian Gulf University, Iran. Also, employing the constructed flume, it includes a number of case studies which have been conducted on flow pattern. Such experiments utilized a Vectrino velocimeter in order to obtain the 3D flow velocity. As the primary stage, an experiment was conducted without any hydraulic structures installed at the bend so that flow characteristics could be analyzed in a 180 degree sharp bend. An increase was revealed in the secondary flow strength and velocity as a result of an increase in the flow depth. Therefore, it can result in an attack towards the outer wall. Consequently, a T-shaped spur dike was installed at the apex of the bend in order to provide protection for the outer wall against streams of high velocity, and a study of the flow pattern around the protective structure was conducted under clear water conditions.
    Keywords: Multipurpose flume, Sharp Bend, Lateral intake, Acoustic Doppler Velocimeter, Spur dike, Open channel, Secondary flow strength
  • Seyed Mohsen Haeri, Seyed Ali Shahcheraghi *, Hamed Sadeghi Pages 3181-3195
    A new computer controlled flow pump is developed to continuously mitigate the adverse effects of membrane compliance in conjunction with implementation of image processing for volume change measurement. The flow pump eliminates the membrane compliance by injecting or pumping out the required volume of water into or from the gravelly specimens to compensate for the erroneous volume change associated with the membrane compliance during undrained cyclic triaxial tests. This error is compounded in gravelly soils due to the large size of the grains and voids. In order to measure the volume of the specimen during the isotropic consolidation stage and calibrate the flow pump for cyclic loading, an image processing technique was used for measuring the volume change during the isotropic consolidation stage of loading while calculating membrane compliance associated with the amount of input water from the flow pump into the specimen. The results of image processing show that the increase in density of the specimens leads to an increase in the ratio of volumetric skeletal strains to axial strains and a decrease in the normalized membrane penetration. The study yields promising results for minimizing the errors associated with membrane compliance during undrained cyclic loading on gravels.
    Keywords: Gravelly soil, Cyclic Triaxial Test, Membrane Compliance, Image processing, Liquefaction Resistance
  • Murat MOLLAMAHMUTOĞLU, Eyubhan AVCI * Pages 3196-3206
    In this study, some geotechnical properties of microfine and ordinary Portland cements stabilized high plasticity clayey soil (HPCS) were investigated. The results showed that liquid limit, permeability, swelling potential and compressibility of HPCS were reduced and HPCS’s plastic limit and unconfined compressive strength (UCS) was increased by both microfine Portland cement (MPC) and ordinary Portland cement (OPC) stabilizations. Besides, liquid limit, permeability, swelling potential and compressibility of HPCS were further reduced by MPC. Although dry UCS of MPC stabilized HPCS was almost the same as the dry UCS of OPC stabilized HPCS, the plastic limit and wet cured UCS of MPC stabilized HPCS was higher than that of wet cured UCS of OPC stabilized HPCS. In general, as the size of cement particles became finer, the stabilization of HPCS became more effective.
    Keywords: Clay stabilization, Cement type, Strength, Permeability, Compressibility, Swelling
  • Shengjie Liu *, Shengbo Zhou, Yinshan Xu Pages 3207-3218
    Although several studies have been carried to discover the asphalt mixture performance when Alumina Trihydrate (ATH) as a flame retardant was added into, the moisture susceptibility of asphalt mixture containing ATH is still not fully clear. In this study, the moisture susceptibility of binders containing ATH were assessed through the surface free energy (SFE) obtained by the sessile drop method. A commonly used SBS modified asphalt with different dosages (0%, 6%, 8%, 10%, 12%, and 14%) of ATH were prepared to determine the physical properties, flame retardancy and SFE parameters. Experimental results indicated that the addition of ATH increased the viscosity, softening point, G*/sinδ and limiting oxygen index, but decreased the penetration and ductility. What's more, increases in total SFE, cohesive energy and work of adhesion were observed with the addition of ATH. Conversely, the work of debonding, wettability and energy ratio decrease due to the addition of ATH. It is concluded that the ATH has a significant negative effect on the moisture-induced damage potential of asphalt mixture from the view of micromechanisms. The recommended percentage of ATH was 6-8% in consideration of physical properties, flame retardation and moisture susceptibility
    Keywords: Asphalt binder, flame retardant, surface free energy, moisture susceptibility
  • Ali Hosseini, Alireza Hajiani Boushehrian * Pages 3219-3232
    This research studies the behavior of circular foundations rested on the soils contaminated with gas oil and kerosene oil under cyclic loading. The final goal of this study was to determine the influence level of the foundation of the reservoirs rested on oil-contaminated sand due to their filling and discharging. The contaminated sand layers were mixed with different percentages of contamination from 2 to 6 of kerosene oil and gasoline. The effect of the contamination percentage, the value of the applied load, as well as the depth and type of contamination is investigated in this study. To validate the numerical studies performed by finite element software, small-scale laboratory tests is carried out. The results showed that the pollutants could affect the amount of final settlement and the number of loading cycles to reach this value. Increasing depth, the number of load cycles and the contamination content increased the final settlement and the number of loading cycles to reach that level increases. Numerical results showed a good compatibility in the load-settlement charts with the experimental results.
    Keywords: Circular footing, oil contamination, Cyclic Loading, Permanent settlement, Laboratory study, Numerical analysis
  • Danial Rezazadeh Eidgahee, Abdolhosein Haddad *, Hosein Naderpour Pages 3233-3244
    Utilizing rubber shreds in civil engineering industry such as geotechnical structures can accelerate generated waste tire recycling process in an economical and environmentally friendly manner. However, understanding the rubber grains strength parameters is required for engineering designs and can be acquired through experimental tests. In this study, small and large direct shear test was implemented to specify shear strength parameters of five rubber grains group which are different in gradation and size. Moreover, artificial neural networks (ANN) are developed based on the test results and optimized networks which best captured the shear stress (τ), and vertical strain (εv) behavior of rubbers, are introduced. Additionally, a prediction model using the combinatorial algorithm in group method of data handling (GMDH) is proposed for the shear strength and vertical strain in the arrangement of closed-form equations. The performance and accuracies of the proposed models were checked using correlation coefficient (R) between the experimental and predicted data and the existing mean square error (MSE) was evaluated. R-values of the modeled τ and εv are equal to 0.9977 and 0.9994 for ANN, and 0.9862 and 0.9942 for GMDH models, respectively. The GMDH proposed models are presented as comparatively simple explicit mathematical equations for further applications.
    Keywords: Rubber Materials, size effect, shear strength, Vertical Strain, Direct Shear Test (DST), artificial neural network (ANN), Group Method of Data Handling (GMDH), Combinatorial (COMBI)