فهرست مطالب

Science and Technology Transactions of Civil Engineering - Volume:39 Issue: 2, 2015
  • Volume:39 Issue: 2, 2015
  • C2+
  • تاریخ انتشار: 1394/12/06
  • تعداد عناوین: 13
  • A. Kaveh, M. Ilchi Ghazaan Pages 395-408
    Natural frequency is one of the parameters that represent useful information about the dynamic behavior of structures. Controlling this parameter can decrease the probability of damage under dynamic loading. Weight optimization on layout and sizing with frequency constraints is a well known problem because of its highly non-linear behavior. Improved ray optimization (IRO) algorithm is utilized to solve truss layout and sizing optimization with multiple natural frequency constraints. This is a multi-agent algorithm and each agent is modeled as a ray of light with a location and direction. At each iteration, each light ray approaches a point which is defined based on the historically best position of the entire agents and the historically best positions of one agent to find the global or near-global optimum solution. To verify the efficiency of the IRO, five well-known benchmark problems are studied and their results illustrate the ability of the proposed algorithm in finding the optimal solution.
    Keywords: Improved ray optimization, multiple natural frequency constraints, layout, size optimization, truss structures
  • H. Beiraghi, A. Kheyroddin, M.A. Kafi Pages 409-422
    Verifying the behavior of shear walls in a tall building requires reliable response results. This paper examined nonlinear fiber element modeling of a slender reinforced concrete shear wall during large-scale shaking table testing. The goal was to understand and validate the inelastic responses given by fiber models using time history analysis. Reasonable agreement was found between the numerical and experimental responses. It was demonstrated that the spread of the second plastic hinge into the upper level of a shear wall can be adequately captured using fiber modeling in response to the effect of higher modes. The parameters of damping, shear stiffness, axial load, concrete strength, longitudinal reinforcement ratio and mass were examined. The shear and moment demand distribution were sensitive to axial loading, mass and reinforcement ratio. The drift distribution along the height, rotation, and top horizontal displacement were also investigated and it was found that the sole use of Rayleigh damping did not produce accurate responses. Increasing longitudinal reinforcement did not prevent nonlinear flexural behavior in the upper levels.
    Keywords: Reinforced concrete shear wall, fiber element model, nonlinear time history analysis
  • E. Ghiasvand, A.A. Ramezanianpour Pages 423-433
    The benefits of using mineral admixtures as a partial replacement of portland cement (PC) are well established in the literature. Economic and environmental advantages by reducing CO2 emissions are well known. This paper examines the influence of intergrinding and separate grinding on the amount of energy consumption, Blaine fineness and particle size distribution (PSD) of blended cements, namely portland pozzolana cement (PPC), portland limestone cement (PLC), and portland composite cement (PCC). In this study, 18 types of cements including two types of portland cement (PC), four types of portland -limestone cement (PLC), four types of portland -pozzolan cement (PPC), and eight types of portland -composite cement (PCC) were used. The results show that particle size distribution (PSD) of blended cements varies for each method. In intergrinding method, interactions between cements components can affect final product properties positively or negatively. In other words, proper use of these interactions not only promotes process of grinding in multi components cements, but also improves particle size distribution of these cements.
    Keywords: Intergrinding, separate grinding, blended cements, energy consumption, particle size distribution
  • M.Z. Kabir, H. Hejabi Pages 435-447
    The current study focuses on the experimental investigation of FRP strengthening of RC portal frame subjected to combined vertical and horizontal loads. The main target of this research is to enhance the proposed structural properties that the RC portal frame had before the seismic occurrences by providing retrofitting of both columns and joints with more deformation capacity. The effect of various parameters on the effectiveness of FRP is examined through 1/3 scaled testing of 6 single bay RC portal frames. Comparisons between intact and retrofitted specimens are discussed in detail in terms of local and global performance modes. The information about the crack development, the damage characteristics, the hysteretic curves, the skeleton curves of frame and energy dissipation curves were presented. In addition, the strength and stiffness of frames were measured. Test results indicate that the FRP rehabilitated frame shows a good hysteretic energy capacity which indicates that this frame has a better seismic behaviour. The results provide an important insight to the role of FRP in improving the earthquake resistance of frame buildings.
    Keywords: Reinforced concrete, portal frame, FRP strengthened frames, experimental, cyclic loading test
  • A. Nikoui, A. Dalvand, M.K. Sharbatdar, A. Kheyroddin Pages 449-468
    In the current study an experimental/statistical approach addressing key mechanical properties (compressive, tensile and flexural strength) and impact resistance of such new fibers with inclusion of different volume of polyphenylene Sulfide (PPS) fibers has been carried out on 288 specimens. Results from this study revealed that compressive, tensile and flexural strength exhibit a good fit with normal distribution with a coefficient of variation less than 10%. However, impact resistance results dispersed with no considerable conformity to normal distribution with a coefficient of variation around 40~50%. Additionally, higher percentage of fibers led to higher level of data scatter which may be attributed to the considerable effect of the presence of more fiber-concrete interfaces. Tests also proved a direct correlation between percentage of fibers versus mean and coefficient of variation values. Moreover, based on acquired results a General Linear Model (GLM) was developed for impact resistance of PPS fibers considering fiber content. Required replications of tests considering fiber content and required accuracy were also proposed.
    Keywords: Fiber reinforced concrete, PPS fibers, statistical, impact resistance, mechanical properties
  • M. Veiskarami, J. Kumar, F. Valikhah Pages 469-483
    Following the recent work of the authors in development and numerical verification of a new kinematic approach of the limit analysis for surface footings on non-associative materials, a practical procedure is proposed to utilize the theory. It is known that both the peak friction angle and dilation angle depend on the sand density as well as the stress level, which was not the concern of the former work.In the current work, a practical procedure is established to provide a better estimate of the bearing capacity of surface footings on sand which is often non-associative. This practical procedure is based on the results obtained theoretically and requires the density index and the critical state friction angle of the sand. The proposed practical procedure is a simple iterative computational procedure which relates the density index of the sand, stress level, dilation angle, peak friction angle and eventually the bearing capacity. The procedure is described and verified among available footing load test data.
    Keywords: Foundation, sand, non, associated flow rule, limit analysis, stress characteristics
  • K. Badv, K. Mohammadzadeh Pages 485-496
    The electro-osmotic consolidation is a method to improve geotechnical properties of soft clayey soils. The feasibility of electro–osmotically induced consolidation can be examined through the soil coefficient of electro–osmotic permeability (ke) and the electro–osmotic coefficient of water transport (ki). Using an electro-osmotic testing cell, ke and ki parameters were measured in Urmia Lake west coast sediments. Three electric field intensities of 40, 60 and 80 V/m were used and salinity and pH change was monitored in cathode and anode reservoirs during the tests. ke and ki increased when soil void ratio increased. The results showed that increasing applied electric field intensity increased the rate of water pH and salinity change at cathode reservoir. The results for soil hydraulic conductivity (kh) and ke showed that kh is in the range of 10-10 m/s to 10-9 m/s for the range of void ratios between 0.5 to 0.8, respectively, and ke is in the range of 5.5×10-9 to 6.6×10-9 m2/sV for the range of void ratios between 0.72 to 0.83, respectively. The ratio of ke/kh controls electro–osmotically induced negative pore water pressure. The higher the ratio, the higher the pore water pressure difference and the faster the consolidation is. The range of ke/kh was between 5.2 to 9.4 m/V at the void ratios between 0.83 and 0.72, respectively. The ratio of ke/kh increased when void ratio decreased. The high range of ke/kh proved the effectiveness of electro-osmosis consolidation for the Urmia Lake sediments.
    Keywords: Electro–osmotic consolidation, Urmia Lake sediments, electro–osmotic permeability, hydraulic conductivity
  • M. Ajdari, A. Esmail Pour Pages 497-510
    In this study, a bearing capacity device is designed and fabricated to determine the load-settlement behavior of three circular footing models resting above the ground water table. Capillary rise in the studied well graded sand is measured and the level of the water table is controlled at the desired heights during each bearing capacity test. Moreover, shear strength parameters and soil water retention curve of the soil are also determined.Experimental results show that using the conventional equations available in the literature of foundation engineering to determine the bearing capacity of footings built above the ground water table can be highly conservative. Moreover, despite the conventional theories, lowering of the ground water table can result in a decrease in the bearing capacity of shallow foundations. Therefore, utilizing the in situ experiments such as cone penetration test performed while the ground water table is at its highest level can lead to a quite non-conservative estimation of the bearing capacity of footings. In addition, an empirical relationship is proposed to simulate the bearing capacity factor,, of circular footings based on the experimental results.
    Keywords: Bearing capacity, circular footing, ground water table
  • M. Jahanandish, D. Azan Pages 511-522
    Soil slopes are sometimes curved in plan rather than being straight. This curvature, especially when it is convex, decreases the bearing capacity of the slope. Finite element method has been used here in this research to investigate the reducing effect of curvature on bearing capacity of a slope. Failure of soil has been assumed to be according to Mohr-Coulomb criteria; but the flow rule of the soil has been considered unassociated. Both cohesive and frictional soils have been used in these investigations to observe the effect of soil type on the problem. Investigations consist of four types of cohesive soils having different strengths and four types of frictional soils having different friction angles. The finite element model consisted of a square footing adjacent to a slope that is convex in plan. Besides changing the curvature; the slope angle and the footing to slope distance have also been varied to see their effects as well. Based on the results of these investigations it has been concluded that convex curvature generally reduces the bearing capacity and this effect is more pronounced in steeper slopes. While this reduction is limited to 7% in case of cohesive soils it can be as high as 15% in case of frictional soils. Therefore this effect should be considered in design of slopes that are convex in plan.
    Keywords: Three dimensional analysis, stability, finite element method, curved slopes, convex
  • M. Saridemir., M.H. Severcan, M. Ciflikli, S.Acer Pages 523-538
    In this paper, the effect on the strength properties of high strength concrete (HSC) manufactured with silica fume (SF) and ground pumice (GP) is investigated. Portland cement was replaced with SF, GP and combination of SF and GP up to 25%. 22 different concrete mixtures with these replacement ratios were produced by using 0.25 water-binder ratio. The ultrasound pulse velocity, compressive, splitting tensile and flexural strengths of these concretes were determined. The experimental results show that producing HSC is feasible with SF and GP. Besides, the experimental results indicate that SF and SF in combination with GP can enhance both the short-term and the long-term properties of concrete, whereas GP needs a comparatively longer time to obtain a suitable effect. The results are also supported by scanning electron microscope analysis. The optimum replacement ratios of SF and GP are found to be 15% and 5% of cement, respectively. The relationships between ultrasound pulse velocity, compressive, splitting tensile and flexural strengths are investigated by considering the effects of SF and GP.
    Keywords: Strength properties, high strength concrete, silica fume, ground pumice
  • L. Abrari, N. Talebbeydokhti, S. Sahraei Pages 539-558
    Throughout history dams have been important structures in water storage. To avoid overtopping, damage, and or failure of a dam, adequate spillway is needed to release excess water from upstream floods. Researchers found that spillways have to be made nonlinear in order to reach an economic structure with high performance. A piano key weir is one of the best solutions. Piano key weirs are the modified and developed labyrinth spillways which can discharge greater volume of water than the common spillways in limited width and can be used as economic structures with high efficiency. In this article, a calibrated Flow-3D modeling by laboratory results has been used to evaluate and analyze the discharge coefficient of piano key weirs as related to the variation in width at inlet and outlet keys. According to the researches, the geometrical and hydraulic parameters are the most important factors for evaluating the performance of piano shaped weirs. In this study, the analytical effects of these parameters on discharge coefficient, and also the capability of discharge in these models have been investigated. Moreover, the important hydraulic parameters including depth, velocity and pressure have been studied through 3D numerical simulation. From the numerical results, a practical formula is proposed to obtain the discharge coefficient for the release capacity of the piano key weirs.
    Keywords: Piano key weirs, discharge coefficient, numerical simulation, hydraulic performance, flow, 3D
  • S. Mohammadiun, S.A.A. Salehi Neyshabouri, Gh. Naser, H. Parhizkar, H. Vahabi Pages 559-573
    Open-channel junctions have a broad application in civil and environmental engineering. Formation of a low-pressure zone with recirculating flow (high sedimentation) accompanied by a high-velocity zone (high erosion) is the most characteristic feature of flow in junctions. A large number of researches have been performed to study the complexity of the flow in junctions in open-channel flows. In this research, four new geometrical modifications, based on streamlinization concept, are investigated to understand their effects on reducing the sedimentation and erosion potential in a 90° open-channel junction. First, the numerical model was validated based on previous experimental studies. Then, effects of the mentioned modifications were evaluated and some efficiency measures were devised to improve their performance. The results show that employing the proposed geometrical modifications improves the flow pattern significantly via eliminating the recirculation zone and reducing the maximum flow velocity after the junction. Thereby a comprehensive reduction in sedimentation and erosion potential is produced as well as contracting the stagnation zone.
    Keywords: Open, channel junction, geometrical modification, numerical model, sedimentation, erosion
  • M. Noshadi, M. Kazemizadeh Pages 575-587
    Effluent from RO (Reverse Osmosis) systems during recovery gradually becomes concentrated and supersaturated with soluble salts such as calcium carbonate (CaCO3), calcium sulfate (CaSO4), barium sulfate (BaSO4) and silica (SiO2). Thus we were looking for procedures to prevent precipitation of soluble salts on the membrane surface and decrease membrane permeability. Therefore, recovery could be limited by the precipitation potentials of these salts. The objective of this research was to investigate methods to achieve maximum efficiency for precipitation of soluble salts in RO effluent by ZLD process. This research was conducted on samples collected and tested from RO system effluent in Tange Alhad, Hajiabad, Zarin Dasht, Darab city, Fars province, Iran. In bench-scale for Ca removal, chemical precipitation with sodium hydroxide and fluidized bed crystallization and for silica removal adsorption with alum and sodium aluminate were used. The optimum ZLD processes for Ca and silica removal was fluidized bed crystallization with 100 mg/L of sodium aluminate and 100 mg/L NaOH. In this ZLD method Silica and Calcium concentrations reduced by 90 and 55 percent, respectively.
    Keywords: Fluidized bed crystallization, alum, calcium, sodium aluminate, silica