Computational Methods in Engineering

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The paper presents the results of casting and testing of 264 GFRC specimens. The glass fibers were 25 mm long, with the aspect ratio (L/D) ranging between 1250 and 3570. The parameters studied were the ratio (by weight) of fibers to cement, i.e. F/C=0%, 1.5%, 3%, and 4.5%, and the ratio of coarse to fine aggregates (gravel to sand), i.e. G/S=1.1, 0.7 and 0.2. In total, 12 mix designs were selected for GFRC specimens while the water-cement ratio was constant and equal to W/C=0.4. The balling of glass fibers in the mix was overcome by using adequate and sufficient antistatic agents. The specimens were tested under compressive, tensile and flexular loading at the ages of 7 and 28 days. Furthermore, the modulus of elasticity and the absorption of the concretes were determined. Finally, the mechanical and physical properties of the GFRC specimens were analysed and an empirical expression describing the modulus of elasticity of the GFRC was proposed.

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In most cases, structural engineers assume a concrete floor to be a rigid diaphragm. Although this simplification is in most cases acceptable, it should be noted that such an assumption may be distrusted due to certain problems. Concrete structures with staggered shear walls are among those whose analysis should be conducted with special concern for the behavior of their floor diaphragms. However, in the structures with staggered shear walls, the horizontal shear due to lateral loads is transmitted to the lower stories through the floor diaphragm since the walls are not usually located over each other in consecutive stories. Therefore, the rigidity of the floor diaphragm is of great importance. In the present study, a parametric analysis was performed to investigate the effect of the rigidity of the floor diaphragm on the load-carrying procedure of the structures with staggered shear walls. The investigated parameters were the number of stories, the ratio of length to width of the plan, and the thickness of walls and diaphragms. Furthermore, the study was carried out for both rectangular and I-shaped plans. All analyses were dynamically performed by ANSYS 5.4 using acceleration spectrum recommended by Iranian Building Code Standard No. 2800. Finally, the behavior of these structures and comparison of the frequencies, the maximum lateral displacements and the shear in the walls and columns as the responses of rigid and flexible diaphragms were highlighted and outlined. Keywords: Reinforced concrete, staggered shear wall, load carrying, floor diaphragm, rigidity.

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In the Present study, attempt will be made to propose a new method for prediction of long-term essential creep of concrete utilizing some short-term creep tests under high temperature. To do so, regarding the similarities between essential creep of concrete and creep in viscoelastic materials, the time–temperature equivalence relation in viscoelastic materials is evaluated for concrete. This relation states that experimental curves of creep at different temperatures fit into a single curve when shifted along the axis of logaritmic time. To develop the model, an equation was first developed taking into account the effect of temperature and the maturity of concrete. Then, an appropriate method was proposed for transmission of the creep curve of concrete under a specific temperature to fit in the creep curve of the same concrete under a temperature. The proposed model was verified using existing experimental data which very good agreement was observed.

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Five methods are introduced for design of castellated I beams encased in concrete. One of the methods, plastic analysis, is thoroughly explained and the relevant equations are developed. Eight castellated I beams encased in concrete are made and tested. The theoretical design methods are all compared with the test results and the safety factor for each method is calculated. The results show that the plastic method of analysis and design is the most economical, which also gives a reasonable safety factor against beam failure

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Silica fume has been largely used in concrete in recent decades due to its effect on improvement of strength and durability of concrete. On the other hand, attention has been recently paid to the use of limestone powder as a substitute for part of cement in concrete, basically because of its low price and its positive effect on the durability of concrete. The aim of the current study is the investigation of the interactive effect of silica fume and limestone powder on the compressive strength of concrete and the optimization of the mix design. To do so, 27 mix designs including 3 water-to-cementitious materials ratios (W/CM=0.25, 0.3 and 0.4) 3 silica fume-to-cementitious materials ratios (SF/CM=%0, %5 and %10) and 3 limestone powder-to-cement ratios (LP/C=%0, %15 and %30) were used and 28-day compressive strength of the cubic concrete specimens were determined. Then, the interactive effect of silica fume and limestone powder on compressive strength of concrete was investigated using isoresponse curves. Furthermore, the optimization of the mix design for concretes containing silica fume and limestone powder was carried out using “cost effective factor” (CEF) which is defined compressive strength divided by cost of concrete.

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Bridges are potentially one of the most seismically vulnerable structures in the highway system during earthquake events. It is known that the seismic performance of transportation systems plays a key role in the post-earthquake emergency management. Hence, it is necessary to evaluate both physical and functional aspects of bridge structures. The physical aspects of the seismic performance of bridges are evaluated by seismic fragility functions or damage probability matrices of transportation facilities. The fragility curves represent the probability of structural damage due to various levels of ground shaking. The fragility curve describes a relationship between a ground motion and a level of damage. In this paper, the fragility curves (F.C) are developed. The vulnerability of a railway prestreed concrete bridge is assessed using fragility curves derived from dynamic nonlinear finite element analysis. A software package is developed in MATLAB to study the results obtained. Modeling of the bridge using 3D nonlinear models and modeling of abutments, bearings, effect of falling of girder on its bearings, and nonlinear interaction of soil-structure are some of the advantages of this research compared to previous ones. Reliability curves developed in this study are unique in their own kind. The proposed method as well as the results are presented in the form of vulnerability and structural reliability relations based on two damage functions.

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In recent years, destructive earthquakes have shown the deficiencies of the existing buildings. One of the most effective mechanisms for dissipating the earthquake energy is inelastic deformation of the steel components. The objective of this research is to study the application of metallic dampers for dissipation of the earthquake energy and to investigate the behavior of concrete structures incorporating these dampers. Therefore, the metallic dampers and the behavior of concrete structures having these dampers are studied first. Afterwards, a typical metallic damper is used in four different types of concrete structure. The required dampers are designed and nonlinear earthquake analysis is applied to investigate the behavior of the structures. Finally, the buildings are subjected to various earthquakes to generalize the results. The results show that the incorporation of the metallic dampers significantly decreases the relative and absolute drift, the structure and the stories damage indices and, finally, the number of plastic hinges. Furthermore, the hysteretic energy dissipation demand also decreases in structural components. Despite the reduction in the inner forces of structural components, story shear forces slightly increase due to increase of lateral stiffness, but much of these forces will concentrate in dampers. Moreover, the combination of moment resisting frame, shear wall, and metallic dampers are studied. The results show a similar trend in the stated parameters- especially the drift and the hysteresis energy dissipation demand.

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Deterioration of concrete, which is mainly due to ignorance of environmental and service conditions, causes considerable costs for the construction industry. With this in mind, in this paper, results of investigation into the major causes of concrete deterioration in the Urumie Lake are presented. For the purposes of this investigation, samples were obtained by mixing two types of cement (OPC types 1&2), micro silica, anti oxide, water proof and air entraining agent, with different w/c ratios and tested at the ages of 7,14, and 28 days. In addition to compression strength, tensile strength of the samples was measured. Regarding the durability studies, abrasion resistance, electrical resistivity, chloride penetration, water absorption and freeze-thaw tests were carried out under both laboratory and real conditions in the Urumieh lake. Based on our findings recommendations are made about optimum w/c ratio, most suitable types of cement, optimum percentage of micro silica content, and additive .

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Although studies on RC beams under shear have a history record of more than 100 years, many important issues in this context still remain that have evaded attention. The aim of the current study is to study a number of these less investigated aspects of the behavior of RC beams under shear. For this purpose, and based on the modified compression field theory, a computer program has been written to study the effects of transverse and longitudinal steel reinforcement and shear span, a/d, on the behavior of RC beams under shear. The results show that the shear capacity of the beam cannot be increased beyond an optimum amount of transverse steel ratio. This paper will try to provide a precise definition of this optimum transverse steel ratio. Another finding of the present study is that increasing tensile longitudinal steel ratio increases the amount of the optimum transverse steel ratio, while increasing a/d decreases the optimum transverse steel ratio.

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In this research, nonlinear dynamic analysis of concrete shear wall using a new nonlinear model based on damage mechanics approach and considering bond slip effects is presented. Nonlinear behavior of concrete is modeled by a rotational smeared crack model using damage mechanics approach. The proposed model considers major characteristics of the concrete subjected to two and three dimensional loading conditions. These characteristics are pre-softening behavior, softening initiation criteria and fracture energy conservation. The model was used in current research analysis after verification by some available numerical tests. Reinforcements are modeled by a bilinear relationship using two models: Discrete truss steel element and Smeared model. In Discrete model the effects of bond-slide between concrete and rebar is mentioned using the bond-link element model concept. Based on the presented algorithms and methodology, an FEM code is developed in FORTRAN. The validity of the proposed models and numerical algorithms has been checked using the available experimental results. Finally, numerical simulation of CAMUS I and CAMUS III reinforced concrete shear walls is carried out. Comparisons of deduced results confirm the validity of proposed models. The obtained results, both in the expected displacements and crack profiles for the walls, show a good accuracy with respect to the experimental results. Also, using discrete truss element model with respect to the smeared steel model leads to increasing the accuracy of maximum displacement response to 7% in analysis.

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In this paper, Lattice-Discrete Particle Model (LDPM) of concrete has been extended in 2-D to account for the effect of non-circular aggregates. To this end, the flexible equation of super-ellipse is employed for generating aggregates in order to add the simulation possibility of a greater spectrum of aggregate samples in 2-D to lattice-Discrete particle Model. Alongside this extention, required procedures for the generation of aggregates, their packing in space, the determination of influencing region of each particle, the definition of interacting surfaces and computational points and the definition of strains are outlined. Finally, the effects of aggregates geometry on macro-scale compressive strength and softening curve and also cracking pattern of concrete under uniaxial compression are discussed.

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With respect to the great application of pipes conveying fluid in civil engineering, presenting a mathematical model for their stability analysis is essential. For this purpose, a concrete pipe, reinforced by iron oxide (Fe₂O₃) nanoparticles, conveying fluid  is considered. The goal of this study is to investigate the structural stability to show the effects of the inside fluid and the nanoparticles. The structure was modeled by a cylindrical shell and using Reddy theory. To obtain the force induced by the inside fluid, the Navier-Stokes equation was used. To assume the effect of the nanoparticles in the pipe, the Mori-Tanaka model was utilized so that the effects of agglomeration of nanoparticles could be considered. Finally, by applying energy method and the Hamilton's principle, the governing equations were derived. For the stability analysis of the structure, differential quadrature method (DQM) was proposed and the effects of different parameters such as volume fraction of the nanoparticles and agglomeration of the nanoparticles inside fluid and geometrical parameters were investigated. The results showed that the existence of the nanoparticles as the reinforcement for the pipe led to the delay in the pipe instability.