فهرست مطالب

Scientia Iranica - Volume:27 Issue: 2, 2020
  • Volume:27 Issue: 2, 2020
  • Transactions on Civil Engineering (A)
  • تاریخ انتشار: 1399/02/28
  • تعداد عناوین: 14
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  • Osman Sonmez *, Hussein Bizimana Pages 517-528

    This study addresses the crucial variables contributing highly to the risk of flooding based on the flood characteristics of the Waverly region and develop a fuzzy logic and geographic information based urban flood map with flood zones in Waverly City, Iowa. The methodology emphasizes on weighting crucial variables using spatial analyst tools and fuzzy logic based GIS mapping. Local elevation, distance from Cedar River, land use and population density in Waverly city are recognized as effective variables to risk of flooding in Waverly city. Twenty three calibration tests for determination of weightages of these variables on the risk of flood were performed and compared to previously produced Waverly flood risk maps. Finally, weightages of these variables were assigned as 70 % for elevation, 20 % for distance from Cedar River, 5 % for Manning’s coefficient, and 5 % for population density. In a fuzzy environment they were assigned different fuzzy membership functions, for elevation, fuzzification technique Small was used, for distance, fuzzification technique MS Small was used, for Manning’s coefficient and population density, fuzzification technique Large was used. The flood hazard maps created were overlaid with 100 and 500-year flood maps of Waverly city for calibration and risk evaluation.

    Keywords: Flood, Weights, Zoning, Multi-criteria environment, Geographic Information System (GIS), Fuzzy logic, weighted linear combination
  • Morteza Esmaeili *, Masoud Yaghini, Shila Moslemipour Pages 529-540
    This paper is geared toward selection of the trough geometry (width and height) and elastic surrounding materials (elasticity modulus) as the optimization parameters along with selection of minimum environmental vibrations in the critical point of pavement system.  The optimum trough geometry and specification of surrounding materials were evaluated as the objective function .To this, a numerical finite element model of embedded slab track rail system was developed in consideration of the components of the substructure and superstructure of system under the plain strain conditions. In the first stepf, the numerical model was calibrated by comparing it with static lab results. In the next step, the vibration behavior was investigated after applying a harmonic load to the system at various amplitudes and frequencies corresponding to the real operation conditions. Maximum velocity of particles vibrations was evaluated at different points in the vertical direction, and the critical point of pavement determined. Then, the best trough section and elasticity modulus of surrounding materials corresponding to the load amplitude and frequency were determined by designing the experiments using the surface response method and limiting the maximum vibrations of critical points to 65 Decibel.
    Keywords: optimization, Embedded slab track rail system, Trough geometry, elasticity modulus, surrounding materials, Vibration environmental, Design of Experiments
  • Ali Pak *, MohammadAli Iranmanesh Pages 541-550

    Liquefaction is one of the consequences of earthquake in soil layers comprised of saturated loose sands. Various aspects of liquefaction have been investigated using different methods of field, laboratory, and numerical studies. Numerical simulation of liquefaction constitutes a major part of these researches. Application of a proper constitutive law in the numerical analysis is crucial for modeling thecomplicated undrained behavior of saturated sands during dynamic loading. Simplicity of formulation, limited number of parameters, and good performance are the main features of a proper constitutive law. In this study, an Endochronicbased model for simulating liquefaction of sand is implemented into the finite element program, PISA. Coupled dynamic field equations of Biot’s theory with u-p formulation are used to determine pore fluid and soil skeleton responses. Generalized Newmark method is employed for integration in time. The developed code is capable of predicting the magnitude of the generated pore water pressure, coupled with advanced constitutive laws such as critical state twosurface plasticity as well as simple models such as Mohr- Coulomb. Simulating cyclic simple shear and centrifuge tests using Endochronic model showed favorable performance of this model for predicting the variation of pore water pressure in saturated soil layers subjected to earthquake excitations.

    Keywords: Liquefaction, Endochronic Model, numerical simulation, Constitutive Laws, Centrifuge Test
  • Fardin Jafarzadeh, Mostafa Zamanian * Pages 551-565
    Geotechnical design may be unsafe if the anisotropic behaviour of soil is not considered. The behaviour of anisotropic materials depends on the principal stresses and their directions. A detailed experimental programme was conducted to study the effect of stress direction on the monotonic and cyclic behaviour of dense sand. A total of 20 undrained tests were performed at a constant mean confining stress (σ'0m) constant intermediate principal stress ratio (b= (σ2-σ3)/(σ1-σ3)), and principal stress directions (α). Two fine sands, Babolsar and Toyoura, were selected as the test materials. The isotropic consolidated specimens were prepared using the wet tamping technique. The results showed that the major principal stress direction had little considerable effect on the mobilized friction angle at steady state or phase transformation. The results showed that stress direction had a significant effect on the non-coaxiality between the principal strain increment direction and the principal stress direction. The soil fabric was led to significant non-coaxiality value before the peak shear strength. Increasing the octahedral shear strains decreased the non-coaxiality value due to destruction of the soil particle interlock (soil fabric). The effect of stress direction on non-coaxiality and excess pore water pressure generation was also investigated.
    Keywords: direction of major principal stress, Sand, pore water pressure, non-coaxiality, internal friction angle
  • A. Akhtarpour, M. Salari* Pages 566-587

    The Masjed-e-Soleyman dam is a high rockfill dam with clay core, located in Iran. During construction and first impounding, a considerably high excess pore water pressure has been developed inside the core and has been being dissipated with a very slow rate, so the consolidation deformations have been insignificant. However, there have been reports of noticeable internal deformations in the dam, the crest has also exhibited quick settlements during the first impounding. The main objective of this paper was to identify the deformation mechanism of this dam. For this purpose, the data recorded by its instruments were carefully studied and then a three-dimensional numerical model of the dam was developed. The mechanical behavior of materials was idealized by a hardening strain constitutive model. A numerical method was proposed, based on this constitutive model and Rowe’s stress–dilatancy theory, to simulate the deformation behavior of coarse-grained materials, like rockfills, due to particle size distribution, particle breakage, rotation, and rearrangement under shearing. The results show that significant development of pore pressure in the core and its insignificant dissipation, plastic shear deformations inside the core and extensive collapse settlements of the upstream shell are the main causes influencing the deformation mechanism.

    Keywords: high rockfill dam, hardening strain constitutive model, Particle breakage, collapse settlement
  • Gh. Khademghaeinya, Jalil Abrishami, Amir Zarrati *, Mojtaba Karimaei Tabarestani, M. Mashahir Pages 588-595
    In previous studies, sizing riprap layer around bridge pier as scour countermeasure was for 100% protection against scouring. However, in many cases limited scour depth around a pier maybe accepted if only smaller riprap sizes are available. In the present work the effects of smaller size of riprap stones than the stable size on the scour depth is studied. Circular and oval shapes for riprap extent as well as both round and angular stone shape were tested. All tests were conducted at the threshold of bed sediment motion and the maximum scour depth was measured. The results of these experiments showed that with stone sizes closer to stable riprap, the efficiency of both round and angular stone shape was identical. As, size of riprap was reduced, deeper scour holes were observed with both round and angular shape material. The results also indicated that increasing the extent of the riprap layer from circular to oval with 5 times more riprap volume had insignificant effects on scour hole for angular shape riprap meanwhile reduced the scour depth with round shape material. Based on experimental data a method was developed to calculate a smaller riprap size based on an accepted limited scour hole.
    Keywords: Bridge Piers, Local scour, Riprap protection, Round, angular shape riprap, Oval, Circular extent, limited scouring
  • Hamed Sadeghi *, Abraham C.F. Chiu, Charles W.W. Ng, Fardin Jafarzadeh Pages 596-606
    Real-time measurement of soil water pressure has been recognized as an essential part of investigating water flow in unsaturated soils. Tensiometry, amongst different measuring techniques, is a common method for direct evaluation of water pressure. However, the lower limit of measurable water pressure by a conventional tensiometer becomes even more limited by increasing its length in the vertical installation. This paper describes development of a vacuum-refilled tensiometer (VRT) for monitoring soil water pressure independent of installation depth. This is achieved by fixing the distance between pressure sensor and ceramic cup together with incorporating an ancillary vacuum-refilling assembly into its design. The assembly allows for more efficient replacement of diffused air into the ceramic cup and reservoir with water. The new tensiometer is designed to withstand both negative and positive water pressure of up to almost one bar. In addition, the response time of the tensiometer to a change in negative water pressure for its working range (≥ -80 kPa) is very quick, in the order of seconds and one minute at most. The long-term performance of the new tensiometer is evaluated through a five-month monitoring program in the laboratory, simulating cyclic wetting and drying in the field.
    Keywords: Deep tensiometer, vacuum-refilling, pore water pressure, field monitoring, cyclic wetting, drying, long-term performance
  • Ha Sung Kong, Woong Jae Ra * Pages 607-613

    The existing arc fault circuit interrupters have the function to interrupt overloads, ground fault, arc fault and all but neither is there the monitoring function to allow external monitoring nor the notification function to notify the fire safety manager. This is a study on arc fault circuit interrupters with the network function that have not been studied so far. We intend to install these arc fault circuit interrupters in places such as server rooms, pigsties, chicken farms, markets, cultural assets, skyscrapers, and facto-ries where large loss may occur if the fire safety managers do not recognize the electricity shutdown in order to increase the efficiency of electricity management. If an overload, a short circuit or an arc is detected while power is supplied to the load, the microprocessor generates a trip signal and cuts off the power by this trip signal. This situation is monitored in real time by ex-ternal monitoring and notified to the fire safety manager. The fire safety manager can immediately recognize the situation where the arc fault circuit interrupter interrupts the circuit and take the necessary action to manage the electricity efficiently.

    Keywords: Network, Arc Fault Circuit Interrupter (AFCI), Electricity Management, External Monitoring, Interruption Cause Analysis
  • Bo Liu *, Fu Hua Sun Pages 614-624

    When identifying PPP project risks using the decomposition analysis method, the PPP project risks are considered to include government risk, market risk, and project risk. Based on these facts, a constructed list of PPP project risks is established, which can be divided into three first-class indexes and 27 second-class indexes. Based on the analysis of the traditional matter element model limitations, the evaluation model of PPP project risk assessment of the improved matter element model is established, in order to provide effective support for effective PPP project risk management, contract management and other work. Lastly, the feasibility of theoretical research is verified by a case study.

    Keywords: PPP project risk management, risk assessment, risk identification
  • Ali Hekmatzadeh *, Hatef Keshavarzi, Nasser Talebbeydokhti, Ali Torabi Haghighi Pages 625-638
    This article addresses the abilities and limitations of the Lattice Boltzmann (LB) method in solving advection-dominated mass transport problems. Several schemes of the LB method, including D2Q4, D2Q5, and D2Q9, were assessed in the simulation of two-dimensional advection-dispersion equations. The concept of Single Relaxation Time (SRT) and Multiple Relaxation Time (MRT) in addition to linear and quadratic Equilibrium Distribution Functions (EDF) were taken into account. The results of LB models were compared to the well-known Finite Difference (FD) solutions, including Explicit Finite Difference (EFD) and Crank-Nicolson (CN) methods. All LB models are more accurate than the aforementioned FD schemes. The results also indicate the high potency of D2Q5 SRT and D2Q9 SRT in describing advection-controlled mass transfer problems. The numerical artificial oscillations are observed when the Grid Peclet Number (GPN) is greater than 10, 25, 20, 25, and 10 regarding D2Q4 SRT, D2Q5 SRT, D2Q5 MRT, D2Q9 SRT and D2Q9 MRT, respectively, while the corresponding GPN values obtained for the EFD and CN methods were 2 and 5, respectively. Finally, a coupled system of groundwater and solute transport equations were solved satisfactorily using several LB models. Considering computational time, all LB models are much faster than CN method.
    Keywords: Lattice Boltzmann method, Grid Peclet Number, Crank-Nicolson, Artificial oscillation, Multiple relaxation time, Equilibrium distribution function
  • Ehsan Ghorbani, Ali Mohammad Rajabi * Pages 639-656

    Liquefaction is a serious natural hazard in susceptible regions which are prone to earthquakes. According to empirical and field studies, insufficiency of liquefaction assessment methods in determining liquefaction through clays and high prediction errors has caused an unceasing new development. In this article we present a comprehensive history review to organize literature on the liquefaction potential evaluation published prior to 2017. We consider deterministic approach based on SPT (Standard Penetration Test) records to create an appropriate connection between the different methods, facilitate reviewing the development of correlations in the past and current decades, assess both the cyclic stress and the flow liquefactions in a unified system, compile the latest research developments and identify the main sources as a database for the future investigators. The study attempts to assess cyclic stress method (1971) and Chinese criteria (1982) in evaluating the liquefaction potential and to discuss the insufficiencies of these methods with reference to the liquefactions caused by the Chi-chi (Taiwan) and Adapazari (Turkey) earthquakes in 1999. Besides, the absence of soil improvement on the basis of vulnerability and performance is identified as a research gap in this study.

    Keywords: Deterministic, Liquefaction, Risk Management, SPT
  • Hosein Naderpour *, Masoomeh Mirrashid Pages 657-670
    In complex engineering problems, there are some inexact conceptions, or a lot of parameters which must be considered. Soft computing is an approach that successfully applied to solve such problems. Determination of fuzzy rules for many problems has not been quite possible by an expert human. In this case, a neuro-fuzzy system which is the combination of neural network (for its ability to learn by datasets) and fuzzy system (for solving the drawback of the neural network) can be enhancing the performance of the system with several parameters or complex conditions. This paper shows the capability of a neuro-fuzzy system namely ANFIS to predicting the shear strength of reinforced concrete beams with steel stirrups. For this propose, the collection of laboratory results which was published in literatures used to train and finally test the proposed system. For this purpose, the sub-clustering approach (SC) applied for generating ANFIS. The results indicated that the considered neuro-fuzzy system was able to predict the shear strength of the RC beams which have been reinforced with steel stirrups.
    Keywords: Adaptive neuro-fuzzy inference system (ANFIS), sub-clustering, shear strength, reinforced concrete beams
  • Hamed Javdanian *, Hamed Reza Zarif Sanayei, Leila Shakarami Pages 671-681
    Settlement and deformation of the embankment dams are among the major damages caused by earthquakes, eventually leading to dam instability. Therefore, accurate assessment of the seismic settlement of embankment dams is of particular concern. This study aims to evaluate the settlement of embankment dams subjected to earthquake loads using regression-based methods. A wide-ranging real data on crest settlement of embankment dams caused by earthquakes was collected and analyzed. Yield acceleration of dam, maximum horizontal earthquake acceleration, fundamental period of dam body, predominant period of earthquake, and earthquake magnitude were considered as the most influential parameters affecting the seismic crest settlement of embankment dams. Using support vector regression method as well as multiple linear regression method, two models were developed to estimate earthquake induced crest settlement of embankment dams. Subsequently, sensitivity analysis was conducted in order to assess the behavior of the proposed models under different conditions. Finally, the accuracy of the proposed models was compared with the existing relationship for estimation of earthquake induced crest settlement of embankment dams. Although both MLR- and SVR-based models have an acceptable accuracy in estimation of the crest settlement of embankment dams under earthquake loading, the SVR-based model has a higher accuracy.
    Keywords: Embankment dam, earthquake, Crest settlement, Support vector regression
  • Saber Piroti, Mohsen Najarchi *, Emadaldin Hezavehi, MohammadMahdi Najafizadeh, Seyyed Mohamad Mirhosseini Hezaveh Pages 682-692

    In this study the influence of water-cement ratio on the mechanical properties (compressive, abrasion, tensile, flexural strength and permeability) of Nano-silica concrete reinforced with polypropylene fibers is evaluated. The specimens contain 4% of Nano-silica, 0.30, 0.35, 0.40, 0.45 and 0.50 of water-cement ratios and 0, 0.10, 0.15, 0.25 and 0.35 percent by volume of polypropylene fibers. Other design features remained fixed in all concrete samples. The results of the experiments showed that with decreasing the ratio of water to cement from 0.50 to 0.30, all the mechanical properties of the concrete were improved. In addition, the test results showed a significant increase in mechanical properties improvement of concrete by using polypropylene fibers. Tensile strength, flexural strength and abrasion resistance of concrete increased up to 22%, 40%, and 27% respectively for 28 days age specimens. Also, considerable reduction of hydraulic conductivity coefficient to 51% indicates high durability of these types of concrete. Compressive strength had increment of 22%, 15% and 14% for 7, 28 and 90 days age specimens respectively.

    Keywords: Water-cement ratio, Nano-silica, Polypropylene fiber, Mechanical properties of concrete