فهرست مطالب

  • Volume:13 Issue: 1, 2015
  • Transaction A: Civil Engineering
  • تاریخ انتشار: 1393/12/23
  • تعداد عناوین: 11
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  • A semi-theoretical approach for determining the maximum scour depth downstream of adverse stilling basins
    Hossein Khalili Shayan, Javad Farhoudi, Hossein Hamidifar Pages 1-15
    Because of the complexity of the physical processes in the vicinity of the hydraulic structures due to the separation of the flow, traditional methods for for prediction of maximum scour depth downstream of hydraulic structures are mostly based on empirical approaches. Hence, only a few theoretical works have been reported to study this phenomenon. The present paper describes a new approach based on the momentum principles to estimate the maximum local scour depth downstream of a submerged sluice gate flowing over horizontal or adverse stilling basin. A control volume of the fluid in the equilibrium state of the scour hole was considered and based on momentum principles, some equations are derived to estimate the scour depth at equilibrium state. To verify the proposed equations, large numbers of experiments were planned and conducted under wide range of characteristic parameters such as, incoming Froude number, sediment size, tailwater depth, length and slope of the apron. It was found that the proposed equations fall in a good agreement with experimental results. It was also observed that, in the case of horizontal apron, a specific tailwater depth exists with which the local scour depth attains a minimum value. However, in the case of adverse basins when the tailwater depth takes a specific value, the maximum depth of the scour hole reaches to its maximum and then decreases to a constant value as the tailwater depth increases. This critical tailwater depth was formulated using a semi-theoretical equation.
    Keywords: Local scour, Momentum principle, Sluice gate, Submerged jet, Adverse Stilling basin
  • NONLINEAR DYNAMIC ANALYSIS OF CONCRETE GRAVITY DAMS CONSIDERING ROTATIONAL COMPONENT OF GROUND MOTION
    Leila Kalani Sarokolayi, Bahram Navayi Neya, Javad Vaseghi Amiri Pages 16-29
    This study focuses on non-linear seismic response of a concrete gravity dam subjected to translational and rotational correlated components of ground motions including dam-reservoir interaction. For this purpose rotational components of ground motion is generated using Hong Non Lee improved method based oncorresponding available translational components. The 2D seismic behavior of the dam concrete is taken into account using nonlinear fracture mechanics based on the smeared- crack concepts and the dam-reservoir system are modeled using Lagrangian Lagrangian approach in finite element method. Based on presented formulation, Pine Flat concrete gravity dam is analyzed for different cases and results show that the rotational component of ground motion can increase or decrease the maximum horizontal and vertical displacements of dam crest. These results are dependent on the frequency of dam reservoir system and predominant frequencies of translational and rotational components of ground motion.
    Keywords: Rotational component of ground motion, Nonlinear analysis, Concrete gravity dam, Smeared crack, Dam, Reservoir interaction, Lagrangian, Lagrangian method
  • Progressive Collapse Evaluation of RC Symmetric and Asymmetric Mid rise and Tall Buildings under Earthquake Loads
    Somayyeh Karimiyan, Abdolreza Moghadam, Ali Husseinzadeh Kashan, Morteza Karimiyan Pages 30-44
    Plan irregularity causes local damages being concentrated in the irregular buildings. Progressive collapse is also the collapse of a large portion or whole building due to the local damages in the structure. The effect of irregularity on the progressive collapse potential of the buildings is investigated in this study. This is carried out by progressive collapse evaluation of the asymmetric mid rise and tall buildings in comparison with the symmetric ones via the nonlinear time history analyses in the 6, 9 and 12 story reinforced concrete buildings. The effect of increasing the mass eccentricity levels is investigated on the progressive collapse mechanism of the buildings with respect to the story drift behavior and the number of beam and column collapsed hinges criteria. According to the results, increasing the mass eccentricity levels causes earlier instability with lower number of the collapsed hinges which is necessary to fail the asymmetric buildings and at the same time mitigates the potential of progressive collapse. Moreover, the decreasing trend of the story drifts of the flexible edges is lower than those of the stiff edges and the mass centers and the amount of decrement in the story drifts of the stiff edges is approximately similar to those of the mass centers.
    Keywords: Progressive collapse, Symmetric, asymmetric reinforced concrete mid rise, tall buildings, Story drift
  • DYNAMIC PRESSURE ANALYSIS AT CHUTE FLIP BUCKETS OF FIVE DAM MODEL STUDIES
    Omid Nazari, Ebrahim Jabbari, Hamed Sarkardeh Pages 45-54
    To dissipate energy and invert excessive discharge flow away from high dams into plunge pool, flip buckets are commonly designed and optimized by hydraulic model studies. In the present study, performance of chute flip buckets in different hydraulic and geometry conditions was investigated using experimental data of five different physical models. The collected experimental data such as Froude number, radius of flip bucket and slope of chute covered a wide range of chute flip buckets in prototype. By analyzing the data, relations for dynamic values of maximum and minimum pressures and their location along the flip bucket were extracted. Moreover, pressure distribution along the central axis of flip bucket was defined. Finally, results of the present research were compared with that of the other researches. Results of this study could be used in the design of chute flip buckets in hydraulic engineering.
    Keywords: Dams, Physical model, Flip bucket, Pressure distribution, Dynamic pressure
  • The combination of fuzzy electre and swot to select private sectors in partnership projects Case study of water treatment project in Iran
    Mohammadhosein Dadpour, Eghbal Shakeri, Hamidreza Abbasian Jahromi Pages 55-68
    Employer Organizations have increasingly interested in outsourcing their projects in the form of public-private partnership (PPP) due to various reasons such as compromising the resource limitations, entering new technologies to the organization and reducing risk. Choosing the private sector as one of the most basic steps in the formation of PPP is of great importance. The present study aims to introduce a hybrid model to evaluate and choose the private sector as one of the parties in PPP using a combination of SWOT-AHP analysis, as one of the most powerful tools in identifying the problem environment, and Fuzzy ELECTRE analysis to evaluate the existing candidates to participate in the partnership using the criteria resulted from SWOT analysis. In first step, criteria set by an organization, as a case, to choose appropriate private sector were identified using SWOT method during various meetings with qualified experts. Then, the best choice was selected using ELECTRE method. Finally, obtained results were compared with the PROMETHE method. The results showed the effectiveness of our proposed method to select private partnerships especially positive and negative inter organizational and outer-organizational factors significantly influence the private sector selection.
    Keywords: Participatory projects, Selection of private sector, Swot, AHP, Fuzzy electre
  • Investigation of Long Term Coupled Effect of High Temperature and Constant High Humidity on Corrosion Rehabilitated Patches of Reinforced Concrete Structures
    M. Wasim, Raja Rizwan Hussain *, M. A. Baloch Pages 69-75

    This paper aims at finding the long term coupled effect of high temperature and constant high relative humidity on the corrosion rehabilitated patches of chloride contaminated steel reinforced concrete. This paper is an extension of previous research in which the authors experimentally corroborated re-corrosion in the repaired reinforced concrete (RC) patches in the form of macro-cells. In previous research, the coupled effect was investigated by laboratory controlled experimentation at varying temperature of 30, 40 and 50°C and a high ambient relative humidity of 85% in environmental control chambers for duration of one year. The specimens were prepared having total chloride concentration in mixing water 3% and 5 % by mass of binder. In this present research paper, the two year results of the same specimens are presented to get a deep insight of the long term phenomenon of macro-cell corrosion under the coupled effect of high temperature and humidity on repaired RC patches.

    Keywords: Macro, cell corrosion, Electrochemistry, High temperature, High relative humidity reinforced concrete, Long term
  • Load Carrying System Characteristics of Existing Turkish RC Building Stock
    Hayri Baytan Ozmen, Mehmet Inel, Sevket Murat Senel, Ali Hayfar Kayhan Pages 76-91
    Seismic performance and loss assessment studies for stock of buildings are generally based on representative models due to extremely large number of vulnerable buildings. The main problem is the proper reflection of the building stock characteristics well enough by limited number of representative models. This study aims to provide statistical information of structural parameters of Turkish building stock for proper modeling using a detailed inventory study including 475 low and mid-rise RC building with 40351 columns and 3128 beams for member properties. Thirty five different parameters of existing low and mid-rise Turkish RC building stock are investigated. An example application is given to express use of given statistical information. The outcomes of the current study and previous studies are compared. The comparison shows that the previous studies have guidance for limited number of parameters while the current study provides considerably wide variety of structural and member parameters for proper modeling.
    Keywords: Earthquake, Seismic, Loss assessment, Modeling, Structural properties, Statistical data
  • Study on the flexural behaviors of RC beams after freeze-thaw cycles
    Dafu Cao, Wenjie Ge, B. Y. Wang, Y. M. Tu Pages 92-101
    In order to investigate the flexural behaviors of RC beams after freeze-thaw cycles, compressive strength test of concrete cubes after 0, 50, 100, 125 freeze-thaw cycles were made, and static flexural experiment of 48 RC beams after 0, 50, 100, 125 freeze-thaw cycles were made. The relationships of relative compressive strength, mass loss rate, relative dynamic elastic modulus and numbers of freeze-thaw cycles were analyzed. The influences of different numbers of freeze-thaw cycles on the flexural behaviors of RC beams with different concrete grades were studied. The results show that concrete cubes’ mass, relative dynamic elastic modulus and compressive strength decrease with the increasing of freeze-thaw cycles, and highstrength grade concrete could slow down the damage caused by freeze-thaw cycles. Experimental values of test beams stiffness under short-term load were smaller than theory value. Some under-reinforced RC beams occurs over-reinforced failure mode after freeze-thaw cycles. Boundary reinforcement ratio of RC beams after certain numbers of freeze-thaw cycles was derived and its correctness was verified by experiment. Current code for design of concrete structures about crack load and ultimate load are still suitable for RC beams after freeze-thaw cycles.
    Keywords: Freeze, thaw cycles, Concrete beams, Flexural behaviors, Experimental study
  • Shape Optimization of Arch Dams with Frequency Constraints by Enhanced Charged System Search Algorithm and Neural Network
    A. Kaveh, R. Gaffarian Pages 102-111
    The main aim of this paper is to find the optimum shape of arch dams subjected to multiple natural frequency constraints by using an efficient methodology. The optimization is carried out by charged system search algorithm and its enhanced version. Computing the natural frequencies by Finite Element Analysis (FEA) during the optimization process is time consuming. In order to reduce the computational burden, Back Propagation (BP) neural network is trained and utilized to predict the arch dam natural frequencies. It is demonstrated that the optimum design obtained by the Enhanced Charged System Search using the BP network is the best compared with the results of other algorithms. The numerical results show the computational advantageous of the proposed methodology.
    Keywords: Arch dam, Finite element, Frequency constraint, Enhanced charged system search, Optimum shape design, Neural
  • FINITE ELEMENT MODELING OF INCREMENTAL BRIDGE LAUNCHING AND STUDY ON BEHAVIOR OF THE BRIDGE DURING CONSTRUCTION STAGES
    Arman Shojaei, Hossein Tajmir Riahi, Mohammadreza Hirmand Pages 112-125
    Incremental launching is a widespread bridge erection technique which may offer many advantages for bridge designers. Since internal forces of deck vary perpetually during construction stages, simulation and modeling of the bridge behavior, for each step of launching, are tedious and time consuming tasks. The problem becomes much more complicated in construction progression. Considering other load cases such as support settlements or temperature effects makes the problem more intricate. Therefore, modeling of construction stages entails a reliable, simple, economical and fast algorithmic solution. In this paper, a new Finite Element (FE) model for study on static behavior of bridges during launching ispresented. Also a simple method is introduced to normalize all quantities in the problem. The new FE model eliminates many limitations of some previous models. To exemplify, the present model is capable to simulate all the stages of launching, yet some conventional models of launching are insufficient for them. The problem roots from the main assumptions considered to develop these models. Nevertheless, by using the results of the present FE model, some solutions are presented to improve accuracy of the conventional models for the initial stages. It is shown that first span of the bridge plays a very important role for initial stages; it was eliminated in most researches. Also a new simple model is developed named as "semi infinite beam" model. By using the developed model with a simple optimization approach, some optimal values for launching nose specifications are obtained. The study may be suitable for practical usages and also useful for optimizing the nose-deck system of incrementally launched bridges.
    Keywords: Incremental bridge launching, Finite element method, Nose – deck system, Optimization, Semi infinite beam model
  • Aging Effect on Physical Properties of Municipal Solid Waste at the Kahrizak Landfill, Iran
    Nader Shariatmadai, Amir Hossein Sadeghpour, Maryam Mokhtari Pages 126-136
    The physical properties of the municipal solid waste (MSW) in Kahrizak Landfill (Tehran, Iran) and its changes due to aging were investigated in this research. A study of the components of the fresh MSW in this landfill showed that more than 60% of it was made from the wastes of foods, fruits, vegetables and organic materials. Next to that, paper/cardboard and plastics, with contributions of 14% and 11%, comprised the greatest parts of the waste materials. Meanwhile, the results obtained from these studies revealed that the contribution of the organic part has been decreased during the last two decade by about 20% while the plastics and paper/cardboard contribution has been increased by the same amount. In order to investigate the effect of aging on the physical properties of MSW, waste samples of 5.5, 14 and 21 years of age were obtained by excavating the aged waste burial regions of this landfill. A study of the changes in the composition of waste materials through aging also revealed that the portion of paste was decreased from 25% to 40% due to the decomposition process, while the contribution of plastics and fabrics was increased up to 200%. Particle size became finer with the mean size being reduced from 70 mm in the fresh wastes to 20 mm in 21-year-old wastes due to the decomposition process. The moisture content of the fresh waste samples was reported to be more than 150%, which was considerably larger than that of other existing landfills. Along with the increase in the age of the waste samples, the moisture content was decreased by as much as one third of the initial value. Furthermore, since the waste mass became more homogeneous by age, the variation of the moisture content was reduced. The organic content of the 14-year-old waste was found to be 20%, which was less than 0.3 of the initial value. Moreover, the variation of the organic content in the waste samples was directly related to the moisture content of the samples with both parameters being reduced to less than one third of the initial value in the older samples. Investigation of the moisture content and the organic content of the aged samples showed that the burial location had a significant effect on the trend of variations. The average density of the fresh waste was measured to be 3.5 and 7.3 kN/m3 after production and burial, respectively. It was found that the average density of the fresh waste grew to about 12kN/m3 as the age was increased.
    Keywords: Municipal solid waste, Aging, MSW compositions, Organic content, Degradation, Kahrizak landfill