Showing 25–36 of 559 results
Optimum Shape Design of Double-Layer Grids by Particle Swarm Optimization Using Neural Networks
In this paper, an efرایگان!
In this paper, an efficient method is proposed for optimum shape design of double-layer grids. In optimization process, the weight of structure is considered as objective function. The design variables are the number of spans divisions of grid in two directions, the height of between two layers and the cross sectional area of elements. The design constraints are considered as limitations of the stress and slenderness of elements and the displacement requirements of joints. The optimization is carried out by particle swarm algorithm that is suitable for discrete and continuous variables. To reduce the computational time of optimization process, the structural responses are predicted using properly trained radial basis function neural network. This network is a robust network for predicting the structural responses. The numerical results demonstrate the robustness and high performance of the suggested method for the optimum shape design of double-layer grids in.
Parametric study of concrete base isolated building in the near field earthquakes
Recently the experie...رایگان!
Recently the experience of recent near source earthquakes such as Northridge, Kobe and Tabas earthquakes have shown that the structures re more vulnerable in the near source earthquakes. This has also shown in many studies. The main reason for that is due to a strong and long period velocity pulse which generates in the near-field (NF) earthquakes. Base isolation systems are one of the methods for reducing the damage and vulnerable in the near source earthquakes, seismic isolation system increase period of vibration which reduce seismic force and the amount of energy transferred into the structure. In this paper, a parametric study has been carried out to study the behavior of based isolated concrete buildings in the near source earthquakes. One base isolated concrete building with 6 stories is considered. The behavior of selected structure has been studied using nonlinear dynamic analysis under three near and three far field (FF) earthquake recorders. A parametric study of various value of stiffness for the base isolation has been studied as well. The results have shown that the responses of building in the NF are very much than FF earthquakes, and the use of base isolation system reduces the base shear and story acceleration of building in NF in contrast FF, but displacement increased. Also the parametric study on the stiffness of base isolation showed that, decreasing stiffness of isolator’s causes the base shear and story acceleration reduced, but this subject for story displacements is not valid
Prediction of FRP Contribution to the Shear Resistance of RC Beams Using Artificial Neural Networks
Shear strengthening of reinforced concrete (RC) beams using fiber-reinforced polymers (FRPs) has been studied intensively in the last decade, even if shear for simple RC beams is not actually fully understood. Three main configurations of FRP strengthening including side bonding, U-wrapping, and complete wrapping may be used for externally bonded reinforcement of RC beams. In the present study, the FRP contribution to the shear resistance of RC beams is predicted using available experimental data by applying artificial neural networks (ANNs). With known combinations of input and output data, the neural network can be trained to extract the underlying characteristics and relationships from the data. Then, when a separate set of input data is fed to the trained network, it will produce an approximate but reasonable output. Neural networks are highly nonlinear and can capture complex interactions among input/output variables in a system without any prior knowledge about the nature of these interactions. A database containing the results from more than 200 tests performed in different research institutions across the world was collected. Having parameters used as input nodes in ANN modeling such as beam dimensions, compressive strength of concrete, type of FRP fiber, ultimate tensile strength of FRP, angle of inclination of FRP fibers with respect to the horizontal axis and thickness of FRP, the target/output nodes was shear contribution of FRP. The transfer functions were assumed to be Tan-sigmoid and Logsigmoid for hidden layers. The comparison of the new approaches with existing experimental data and available empirical models shows that the ANN model can accurately predict the shear contribution of FRP.
Seismic Retrofitting by using Friction damper in Horizontally Irregular Infilled Structures
Steel frames with maرایگان!
Steel frames with masonry infill walls are common systems in the ordinary residential structures. High stiffness value of the infill walls has significant effect on the behavior of structure, torsional problem is the one them. A friction damper device can be used to minimize torsional effects in the structure. Nonlinear analysis and modeling of the infill walls and the damper is done by “Opensees”. Results show that the presence of infill walls can lead to severe torsion increase through the frame which can be solved by using friction damper device. This technique can benefit the complete capacity of structure with minimum intervention in the structure and architecture.
Sensitive Analysis on Effective Parameters in Breakwater Design against Wave Diffraction
Beaches erode and th...رایگان!
Beaches erode and the obvious environmental and landscape degradation of many coastal stretches are problems that coastal engineers are spending time solving. Different protection methods have been used over time, most on the basis of the artificial nourishment of beaches and the building structures such as groynes and detached breakwaters. Breakwaters are artificial structures, generally parallel to the coastline, ینسپیرد by the working of natural formations, protecting a certain stretch from wave action and being able to create accretion areas. This is why these structures have been in general use, with different results, since the 1970s in countries such as Japan, the United States, Spain, Italy, and Australia. Lakes coast confronts a wide range of natural hazards from severe storms, floods, landslides and shoreline erosion. All of these coastal hazards threaten both lives and property-a problem that becomes more pressing as the coastal population continues to rise. Coastal erosion, deposition, and flooding can also be exacerbated by lake level regulation, water diversion and coastal resource use. Structures like breakwaters always confront sea phenomenon like diffraction and refraction of waves. Diffraction, which be made by contact of water waves to breakwater structure and results almost concentric circles of waves, makes evaluating this phenomenon far more important on structures. By using the powerful software MIKE 21 in sea hydraulics problems, finding the optimized model of the breakwater arms can be obtained. Meanwhile other factors are playing role in this optimized model.
Static Response of Reinforced Soil Retaining Walls with Modular Block Facing
Effect of backfill cرایگان!
Effect of backfill compaction, reinforcement connection type, geogrid-soil interface properties, and facing inclination on static response of Geosynthetic Reinforced Soil Walls (GRSW), was investigated using finite difference method. The numerical simulation of wall was included sequential construction of the wall. Backfill soil was modeled with Elastic-plastic Mohr–Coulomb model and modular block was modeled with elastic model. Results include the facing displacement, maximum load reinforcement and lateral earth pressure. Numerical results show the magnitude of lateral displacement decrease with increasing facing inclination and compaction load, the maximum reinforcement load increased significantly with an increase in compaction load. It was found that finite difference procedure was able to simulate the static response of GRS wall ery well
The Behavior of Concrete Frames Retrofitted by Steel Plate Shear Walls in Earthquake
Steel plate shear waرایگان!
Steel plate shear walls have been used more frequently in recent years as the lateral load resisting system in the design and retrofit of high-rise buildings. Expected low cost fabrication, speedy erection, and good energy absorbing potential make the steel plate shear wall system an attractive alternative for the seismic upgrading of existing buildings. A new structural steel lateral load building system, called the steel plate shear wall (SPSW) currently under development in Canada, United States, Japan and other countries is gaining interest for its potential application in the seismic upgrading of buildings. While SPSW system can be easily integrated into existing steel frames, its suitability in concrete frames is still in the development stage. This paper concentrates on analytical studies of steel plate shear walls added to concrete frames. First using the fiber-based finite element analysis we propose an analytical model and verify this model by several experimental results (Numerical modeling has been developed in SeismoStruct). This model has been used to compare the behavior of concrete frames with and ithout steel shear wall. Then we continue our investigations with a parametric study on the behavior of concrete frames retrofitted by steel plate shear wall. We study the influence of changing in parameters such as concrete and steel plate characteristics, width to height ratio of frame and etc on behavior of such frames. Based on analytical results, some design recommendations for the structural system have been proposed.
The Investigation of Extra Seepage of Gheisaragh dam and Remedial Method
Gheisaragh dam is anرایگان!
Gheisaragh dam is an earth fill in East Azarbayjan province of Iran which is completed in 2005. The main problem with the dam operation is seepage with ascending rate through the foundation and abutments which leads to piping with considerable sinkholes in downstream. From the comprehensive geological studying in the dam site, it was disclosed that major part of dam foundation involved gypsum veins and pockets and gypsum marl. The chemical test of water sample obtained from piping sinkholes indicates significant increase in the amount of Mg++, Ca++ and So4– content which is a sufficient evidence for dissolving of the gypsum veins due to the seepage through the foundation ground. In this paper, at first geotechnical features of the dam site and foundation and result of the chemical tests are investigated. Then, the causes of piping occurrence are indicated. According to importance of dam safety, the treatment methods are investigated for rehabilitation of dam foundation. Then the effect of each method is evaluated by numerical analysis. Finally, best method economically and practically is selected. In this method, impervious concrete cover is established on the upstream slope and a cement-bentonite cutoff wall is constructed in upstream heel of dam.
Tuned Liquid Column Dampers with Period Adjustment Equipment for Earthquake Vibrations of High-rise Structures
This paper investigaرایگان!
This paper investigates the application of a bi-directional vibration system, namely Tuned Liquid Column Damper with Period Adjustment equipment (TLCD-PA), which is used to decrease the vibrations of highrise buildings due to earthquake oscillations. The TLCD-PA is a two degree-of-freedom (2DOF) system consists of two U-shaped tubes filled with water (2TLCDs) and a pendulum. The second TLCD, namely Period Adjustment equipment (PA), is smaller than the first one and placed above it. The two TLCDs are connected through the air tubes at the top of vertical columns. The liquid displacement in the PA system moves the plate at the middle radially, which is connected to the pendulum. The liquid columns, the air tubes and the pendulum provide spring stiffness for the system. On the other hand, the liquid movement in the two TLCDs provides nonlinear damping for the equipment. The liquid mass in the two TLCDs and the pendulum provide the required mass for the system. Therefore, this type of damper consists of many adjustable parameters that help for the better tuning of requency and damping coefficients. In this paper, the effect of various important parameters of the TLCD-PA on the earthquake vibrations of tall buildings is investigated. The structure is modeled as a single DOF system equipped with TLCD-PA at the top of the building. Kobe arthquake data is employed for the modeling of earthquake oscillations, and the nonlinear Newmark method is applied for the displacement, velocity and acceleration calculations. The effects of area ratios and length ratios for the U-shaped tubes of two TLCDs are investigated. Moreover, the effects of pendulum parameters such as mass, spring stiffness and length of the pendulum are discussed.
Using NSM Method in R/C Beams Strengthening by FRP Strips
Reinforced concrete flexural elements may be required to strengthen during their service life due to various reasons, e.g. defect or decay in mechanical materials properties, imperfections on construction, or increasing of design loads due to changing in utilization or rules of the codes. Various FRP products – as composite materials- are recently used in different technique to strengthen the structural elements. In a very newest technique, which is called Near-Surface-Mounted (NSM) method, the FRP strips (or rods) are laid down on the epoxy filled grooves which already created on the external surfaces (top or bottom) of the concrete beams or slabs. Compare to the traditional use of FRP sheets adhering to the external surfaces, this method cause better transferring of the loads to the surrounding concrete by enhancing the bonding stresses, as well as better protecting the mechanical properties of the FRP strips against any environmental defects. In this study, behavior of nine reinforced concrete beams (in three groups of different reinforcing ratios) which already strengthened by FRP strips (by NSM method), were simulated numerically by Finite Element Method. The numerical results were compared to the experimental ones. Results show impressive compatibility between the numerical and the experimental loaddisplacement curves from the initial stage of loading, up to the peak load and further down to total strength degradation. Crack pattern and deformation, and also the failure process, all reproduced in a good and reasonable estimate of the experimental results. Increase in strength along with decrease in ductility was shown by both results. Strength and stiffness of all the strengthened beams (by FRP strips) were higher compare to the control beams (with no FRP), the same as observed in the experiments. Also, it shown that for the specimens with higher reinforcements, increase in CFRP strips resulted lower efficiency in strength, the same trend in the experiments
آزمون روند و تحلیل دگرگونی در سري هاي زمانی آب دهی رودخانه کارون در ایستگاه اهواز (رویکرد ناپارامتري)
حوضه کارون و دز بستر...رایگان!
حوضه کارون و دز بستر تغییرات گسترده اي در حوضه آب و خاك شامل احداث سد، تغییر کاربري زمین، تغییر پوشش زمین و … بوده است. به منظور بررسی اثر این تغییرات بر آب دهی رود کارون، سري هاي زمانی مشخصه هاي جریان براي تعیین نقطه شکست و روند مورد آزمون قرار گرفت. اگر چه وجود نقاط شکست در سري هاي مورد بررسی از لحاظ آماري معنی دار نبود ولیکن با توجه به در نظر گرفتن نقاط پتانسیل شکست مشخص شد که بر خلاف روند مثبت نشان داده شده در کل سري، همه جز سري ها داراي روند نزولی است.
آناليز استاتيكي سيستم تركيبي قاب محيطي، هسته مركزي و كمربند خرپايي در برابر نيروهاي جانبي در سازه هاي بلند
يكي از مناسبترين سيس...رایگان!
يكي از مناسبترين سيستمهاي مقاوم در برابر بارهاي جانبي در سازه هاي بلند سيستم تركيبي قاب محيطي، هسته مركزي و كمربند خرپايي ميباشد. كمربند خرپايي در تركيب با قاب محيطي و هسته مركزي همانند يك فنر خمشي در تركيب با تير طره عمل ميكند. در اين مقاله با در نظر گرفتن توابع جابجايي محوري براي ستونها و نوشتن رابطه انرژي، روابطي براي تنش هاي موجود در ستونها در ارتفاع بيان شده است. سپس با مينيمم كردن تغييرمكان جانبي بالاي سازه محل بهينه كمربند خرپايي به دست آمده است. در ادامه دقت نتايج روش پيشنهادي با روش آناليز كامپيوتري مقايسه گرديده است.