فهرست مطالب

Scientia Iranica - Volume:26 Issue: 1, Jan-Feb 2019
  • Volume:26 Issue: 1, Jan-Feb 2019
  • Transactions on Civil Engineering (A)
  • تاریخ انتشار: 1397/11/22
  • تعداد عناوین: 13
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  • Hamid Mohammadnezhad, Hamid Zafarani, Mohsen Ghaemian * Pages 145-156
    Numerical simulation of dam-foundation-fault system, considering the earthquake source, propagation path, and local site eects, was carried out for realistic and reasonable seismic safety analysis of concrete dams. The Domain Reduction Method (DRM) was used for seismic analysis of Dam-Foundation-Fault (DFF) system, in which a modular two-step methodology for reducing the computational costs in large domain analysis was introduced. In this method, seismic excitation is directly applied to the computational domain such that assigning arti cial boundary to the nite element models is more comfortable. In order to verify the implementation of the DRM in Finite Element Method (FEM), a simple 2D half-space under the Ricker wavelet excitation was examined. Then, to investigate the DRM as an appropriate method in seismic analysis of DFF system, the Koyna concrete gravity dam was modeled. Comparing the obtained results by using both the DRM in a small domain and the traditional approach in the large domain containing the source shows the eciency of the DRM in terms of computational costs, such as running time and number of elements for seismic analysis of concrete gravity dams.
    Keywords: Domain reduction method, dam-foundation-fault system, seismic wave propagation, numerical method
  • Saleh Noui* , Abdelkrim Kadid, Abderrahim Bali Pages 157-166
    Due to architectural considerations, openings are required in masonry infill panels. In this study, a pushover analysis is carried out to assess the behavior of RC infilled frames with emphasis on the effect of openings in the infills. The main parameters that will be considered concern the size, the location and the aspect ratio of the openings. Three reinforced concrete structures representative of rigid, semi-rigid and flexible structures are designed according to the Algerian seismic code. The numerical model of the structures consists of frame elements with concentrated plastic hinges at the ends and a nonlinear layered shell for the infills. The results obtained show that the presence of infills can drastically change the overall behavior of the structures by enhancing the strength capacities but with limited ductility and the presence of openings can modify the hinges locations and patterns according to their size, location and aspect ratio.
    Keywords: Infills, openings, plastic hinges, capacity curves, Nonlinear layered shell
  • Elif Cicek* , Erol Guler, Temel Yetimoglu Pages 167-177
    In this study, the performance of the first reinforcement layer depth for sand subbase of a road or construction was investigated with plate load laboratory tests. Unreinforced and reinforced experiments for different reinforcement types were made by changing the first reinforcement layer depth ratio. One type of geotextile and two different geogrid specimens were used in the research. Load-settlement curves and Bearing Ratios were studied by measuring the results for different settlement ratios. Finally, laboratory measurements of unreinforced and reinforced soil using geotextile reinforcement were compared with Finite Element Model (FEM) analyses modeled under similar conditions. The results demonstrated the effects of different types of reinforcements for different first reinforcement layer locations. The number of reinforcement layers was another parameter which affected the bearing ratio along with the first reinforcement layer depths. It was also observed that the Bearing Ratio (BR) and load-settlement behavior changed significantly with the first reinforcement depth and settlements. Effects on failure modes for unreinforced and reinforced sand soils were compared for each test.
    Keywords: First reinforcement depth, Settlement, reinforcement, Sand soil, Geosynthetic, Plate load test
  • Amir Hossein Zaji, Hossein Bonakdari * Pages 178-187
    One of the most important parameters in designing of sewer structures is the ability to accurately simulation the discharge and velocity field of them. Among the various sewer receiving inflow methods, open channel junctions are mostly occurring. Because of the separation and contraction zone that occur at the open channel junctions, the fluid flow has a complex behavior. Modeling is carried out by Radial Basis Function (RBF) neural network, Gene Expression Programming (GEP), and Multiple Non-Linear Regression (MNLR) methods. Finding the optimum situation for GEP and RBF models are done by examining the various mathematical and linking functions for GEP and different number of hidden neurons and spread amount for RBF. In order to use the models in practical situations, three equations were conducted by using the RBF, GEP, and MNLR methods in modeling the longitudinal velocity. Then, the surface integral of the presented equations is used to simulate the flow discharge. The results showed that the GEP and RBF method perform significantly better than the MNLR in open channel junction characteristics simulations. The GEP method has higher performance in modeling the longitudinal velocity field compare with the RBF. However, the RBF presented more reliable results on the discharge simulations.
    Keywords: Discharge prediction, gene expression programming, Multiple non-linear regression, Open channel, Radial Basis Neural Network, Sewer junction, Velocity field
  • Mohammad Hossain Mohammadi, Ali Massumi *, Afshin Meshkat , Dini Pages 188-201
    Strong ground motions of near-fault earthquakes are mostly generated by forward-directivity effects. Forward-directivity effects develop energetic pulses particularly in horizontal velocity history of fault-normal component. The narrow-band nature of the pulses results in revealing at least two peaks on the response spectra and also increasing seismic demand especially for mid-rise and high-rise buildings. Iranian seismic code (IS 2800-14) presents the coefficient N, for considering near-fault effects. It seems that the N is not efficient for designing in near-fault zone. The accurate near-fault demands can be determined by using nonlinear response history analyses. In the present paper, two 3-D reinforced concrete framed structures (RC buildings) are designed according to ACI 2014 and IS 2800-14. Then, the demands are estimated by employing linear response history analysis (LRHA) and also nonlinear response history analysis (NRHA) under an ensemble of 11 near-fault ground motions. The results reveal that the design spectrum of IS 2800-14 is incompatible with near-fault spectra and underestimates demands in the long periods range. Further, implementation of LRHA using response modification factor (Ru) and deflection amplification factor (Cd) leads to insufficient inter-story drift ratios. Finally, the influence of enhancing ductility is studied by determining ductility reduction factors for near-fault records.
    Keywords: Near-fault ground motion, Seismic demand, linear response history analysis, nonlinear response history analysis, ductility
  • Zhuo Li *, Yongjun He, Hongen Li, Yanqiao Wang Pages 202-212
    We present a case study of antecedent rainfall-induced failure of engineering slope. The impact of pore-water pressure, the increment of pore-water pressure, and water content, the factor of safety are investigated by numerical models for an actual slope in Yunnan, China. The results indicate that antecedent rainfall played an important role in the stability of the slope. The model reasonably explains the time lag between the occurrence of rainfall and landslides. Pore-water pressures have significantly changed at the upper layer of red clay slope, the cracks phenomenon at the upper of the slope agrees with the field observations before landslide. The saturated zone of the slope gradually expands from the top to bottom of the slope, the major reason for landslide is that the surface stagnant water after rainfall gradually infiltrates into the weathered gneiss rock, resulting in the decrease of the strength of weathered gneiss rock, and then the weight of later rainfall caused the landslide of the slope. The factor of safety of the slope was evaluated by the modified limit equilibrium methods, it was shown that the actual failure occurred when the calculated factor of safety approaches its minimum 0.97. The landslide is characterized by shallow landslides.
    Keywords: antecedent rainfall, landslide, Numerical Modeling, Slope stability, unsaturated soil
  • Aghileh Khajeh, Hossein MolaAbasi* , Safora Naderi Semsani Pages 213-223
    Treating soil with cement and zeolite is widely used in soil stabilization. This research intends to quantify the impact of cement and zeolite contents, porosity index, voids/cement ratio on zeolite cemented sands by the splitting tensile strength (σt) assessment. A program of splitting tensile tests using specimens by different zeolite replacement percentages is performed. Results indicate that cement replaces by zeolite at optimum proportion of 30%, then the value of improved σt of the cement sand specimens due to zeolite and cement chemical properties are exploited. Zeolite can effect more on a compacted mixture if its cement content and porosity increase. In this paper, it is shown that for the zeolite cemented sands, σt increases by cement content (C) raise and porosity (n) reduction and a power function is well-adapted to fit both σt-C and σt-n. Afterwards, good correlations are observed between voids/cement ratio (n/c) and the splitting tensile strength(σt)of the sand-zeolite-cement studied. Finally, based on a number of input variables as porosity (n), replacement of cement by zeolite (Z) and cement content (C), considering the regression approach, an equation is suggested to predict σt. Moreover, it is shown that the evolved equation could successfully predict .
    Keywords: Stabilization, Zeolite, Cement, tensile strength, Babolsar sand
  • Ariel Catalan, Dora Foti* , David Melendi Pages 224-233
    In this paper a new free on-line seismic database is presented. The database has 15 seismological and 26 deducted engineering parameters to search for available records for structural seismic analysis. As known, the selection and scaling of seismic records acquire primary importance in seismic analysis. Moreover, the application and development of Performance-based earthquake engineering (PBEE) implies finding records in different levels of the return period. This is a time-consuming and cumbersome procedure and the whole process is affected by great randomness. A database with specific parameters that permit finding best-suited records would prove very useful. As a consequence, both the randomness in the seismic action and in the results of the dynamic behavior of the structure can be strongly reduced. This is the objective of the new database.
    In this work the authors describe the new database and develop a numerical application with 3 different bins of parameters of selection for records and results of structural analyses. The great usefulness of the database is shown.
    Keywords: Seismic database, Selection of records, PBEE, Engineering parameters, Strong ground motion
  • Erfan Karimian, M. Oliaei * Pages 234-245
    Smoothed finite element method (SFEM) was introduced by application of the stabilized conforming nodal integration in the conventional finite element method. In this method, integration is performed on “smoothing domains” rather than elements. Smoothing domains are created based on cells, nodes or edges for two dimensional problems. Based on the smoothing domain creation method, different types of SFEM are developed that have different properties. It has been shown that these methods are insensitive to mesh distortion and are generally more computationally efficient than mesh-free and finite element methods for the same accuracy level. Because of their interesting features, they have been used to solve different problems. This paper investigates the performance of these methods in coupled hydro-mechanical (consolidation) analysis, by solution of some problems using a developed SFEM/FEM code. Biot’s consolidation theory is reviewed, and after introduction of the idea and formulation of SFEMs, discretized form of equations is given. Requirements for creation of stable coupled hydro-mechanical models are discussed and based on them, two methods for creation of stable SFEM models are introduced. To investigate the effectiveness of the methods, a number of examples are solved and results are compared with the finite element and analytical ones.
    Keywords: Smoothed Finite Element Method, The Finite Element Method, Coupled Hydro-mechanical Analysis, Consolidation, Biot’s Theory
  • A. Kaveh *_S . R . Hoseini Vaez_P . Hosseini Pages 246-256
    Vibrating particles system (VPS) optimization is a recently developed metaheuristic algorithm for optimization. This algorithm is inspired by the free vibration of freedom systems’ single degree with viscous damping. In this method, each answer is modeled as a particle that moves to its equilibrium position; new positions of the vibrating particle system are updated according to a historically best position. Enhanced Vibrating Particles system (EVPS) uses new approaches to improve the performance of the VPS algorithm. In this study, a dynamic method and modal based approach consisting of natural frequencies and mode shapes are used in the objective function formulation. To demonstrate the performance of the VPS and EVPS, different truss structures including several multiple elements scenarios with noise and without noise in modal data are considered for detecting damage problems. Additionally, all scenarios are studied with significant mutations. Results show that the EVPS algorithm has reached better answer compared to the VPS algorithm for damage detection problems.
    Keywords: VPS algorithm, Enhanced VPS algorithm, Damage detection, truss structures, Inverse problems, Optimization
  • Maalek Saafizaadeh, Mohammad Hossein Bagheripour * Pages 257-272
    In this paper, Probabilistic Seismic Hazard Analysis (PSHA) approach is used to evaluate the distribution of Peak Ground Acceleration (PGA) and their corresponding probabilities for Kerman region in S-E of Iran. The geological and seismological data were integrated into a probabilistic seismic hazard model for the region. Historical and instrumental earthquake data, geology, tectonics, fault activity and seismic source models related to seismic events are taken into account. Foreshocks and aftershocks are rationally eliminated and main shock records are used to evaluate seismicity parameters using Kijko method. The use of such method is advantageous since it accounts for incomplete or inaccurate seismic data related to various seismic sources in the region. CRISIS2007 software is also used to carry seismic hazard analysis for the region and to develop the maps of iso-acceleration contours and for various return periods.
    The results have been displayed as the probabilistic estimates of PGA for the return periods of 50, 75 and 475 years. Comparison of the results obtained here with those suggested by Iranian Code of Practice for Seismic Resistance Design of Buildings (Standard No. 2800 Version 1393) are also presented. Results obtained in this study provides the basis for the preparation of seismic risk maps.
    Keywords: seismic hazard assessment, PGA, Kerman, earthquake hazard parameters, CRISIS2007, Kijko method
  • Masoud Pourbaba, Abdolreza Joghataie * Pages 273-282
    In this research, nineteen specimens of ultra-high performance fiber-reinforced concrete rectangular beams are made and their shear resistance is determined experimentally. The results are compared with estimations by ACI 318, RILEM TC 162-TDF, Australian guideline and Iranian national building regulations. To compare the code estimations, the ratio of experimental shear strength to predicted shear strength is calculated for each code. This ratio is actually a measure of safety factor on one hand and a measure of precision of the estimation on the other hand. Based on the results of both studies, the authors conclude that the Australian guideline with a ratio of 2.5 provides the minimum experimental to predicted ratio while the Iranian National Building Regulations with a ratio of about 10 provides the highest experimental to predicted ratio. This ratio obtained for ACI and RILEM was about 8 and 3.6 respectively. The Iranian and ACI codes provide basically the same strength estimation but both are very conservative, which may be interpreted as mainly because the codes are dubious about the precision of their own estimations. However, RILEM and Australian codes, estimate the shear resistance with reasonable margin of safety.
    Keywords: Ultra-High Performance Fiber-Reinforced Concrete Beams (UHPFRC), shear strength, Steel fibers, Regulations, Experimental to predicted shear strength
  • Reza Fatahi, Alkouhi, Babak Lashkar, Ara* Pages 283-294
    The effects of non-dimensional parameters on the characteristic curves of a ram pump were evaluated in this study using an experimental model. To do so, after providing dependent and independent parameters using dimensional analysis, effect of each independent parameter was examined on the dependent parameter. Experimental observations showed that relative pumping discharge (q/QT), relative wasting discharge (Q/QT) and pump efficiency (η) were depended on length to diameter ratio of drive pipe (L/D) and pressure head ratio (h/hm). Impulse valve parameter (nD/v0) was depended on L/D, h/hm and Reynolds number of flow in drive pipe. Characteristic curves were presented for ram pump used in this study to estimate dependent parameters as function pressure head ratio for various ratios of length to diameter. In addition, characteristic equations of the used ram pump were introduced using nonlinear regression. Evaluation of results showed that the characteristic curves and equations can be designed a ram pump system with high accurate, and this design method can be proposed for any kinds of ram pumps to use in engineering purpose.
    Keywords: Ram pump, dimensional analysis, Characteristic curves, non-linear regression, and impulse valve