Showing 25–36 of 726 results
Modeling of welded angle connections in fire
In this paper, the bرایگان!
In this paper, the behavior of welded angle connections is studied at elevated temperatures using ABAQUS finite element software. In this study, steel members and connection components are considered to behave nonlinearly; the degradation of steel properties with increasing temperature is considered according to EC3 recommendations. The results of finite element and experimental tests conducted on welded angle connections in furnace fire conditions are compared, and the obtained failure modes and moment-rotation-temperature characteristics are in good agreement with those associated with experimental tests. Temperature loading similar to real fire condition is applied to each specimen to study the behavior of these connections in fire condition and the stiffness change with temperature increase under real fire condition is studied. The numerical results show that, in addition to material properties and connection geometry, the applied moments and temperature have significant effects on the stiffness of this kind of steel connection
Near-source ground motions effect on seismic reliability of reinforced concrete framed buildings
Near-Source ground mرایگان!
Near-Source ground motions have characteristics like pulse-like feature which make them distinctive from ordinary records. This paper discusses near-source ground motions effect on seismic reliability of reinforced concrete framed buildings. Since there are significant uncertainties in capacity of structural members and seismic excitations, reliability analysis can be an efficient method for assessing the seismic performance of a structural system. In this study the reliability evaluation is carried out by response analysis. Nonlinear dynamic analysis is used for assessment of structural seismic demands. Two sets of ordinary and near- source records are selected for focusing on comparison of near source ground motion effects with ordinary ones. A vector-valued intensity measure (IM) is adopted for applying the ground motions, which takes into account the spectral shape. Four example buildings with different heights are analyzed through three-dimensional nonlinear time history method, and capacity curves are obtained by incremental dynamic analysis (IDA). The P-Delta effect was considered in nonlinear analysis. In considering the effect of added shear walls on structural seismic reliability in near-source ground motions, the example buildings had two different kind of lateral load resisting systems, moment resisting frame system (MRF) and dual system consisting of moment resisting frames and shear walls. These approaches lead to a more general conclusion about the probability of failure of reinforced concrete framed buildings in near-source ground motions in comparison with ordinary ground motions. The results show that the added shear walls have a little effect on seismic reliability of high-rise reinforced concrete framed buildings subjected to near-source ground motions, but the added shear walls are relatively more beneficial for low-rise buildings against near-source ground motions.
NUMERICAL INVESTIGATION ON FAILURE MECHANISM OF SLENDER STRUCTURAL WALLS
The overall behavior...رایگان!
The overall behavior of the slender structural wall is determined by the behavior of the plastic hinge region at the wall base. A slender structural wall subject to a lateral load is damaged at the wall base. The failure of a slender structural wall with confined end-zones is caused by the crushing of the confined concrete, crushing of the unconfined concrete, fracture and buckling of the flexural re-bars, and fracture of the lateral re-bars. In this study, the crushing of the confined concrete and crushing of the unconfined concrete are investigated by section analysis. Moreover, the slender structural walls have flexural behavior and the behavior of bending members can be explained by moment– curvature relation. The moment-curvature relation for a section is determined using an analysis procedure that satisfies the requirements of strain compatibility, equilibrium of forces, and the stress-strain relations. The proposed moment-curvature relation is extended well into failure stage. Finally, correlation studies between analytical and experimental results are conducted with the objective to establish the validity of the proposed procedure. The occurrence of each failure modes depends on the quantity of confinement reinforcement, the depth of compressive zone, the depth of confined zone and properties of concrete and steel
Numerical investigation on shear strengthening of RC beams using Near Surface Mounted (NSM) FRP
A recent and promisiرایگان!
A recent and promising method for shear strengthening of reinforced concrete (RC) members is the use of near-surface mounted (NSM) fiber- reinforced polymer (FRP) reinforcement. So far, numerical studies concerning the NSM FRP strengthening method have been rather limited. Moreover, virtually no comprehensive analytical research is available on the behavior of shear-strengthened beams considering NSM FRP. This paper illustrates a numerical research program on shear strengthening of RC beams with NSM reinforcement, aimed to investigate individual parameters effecting numerical analysis and capture the effect of important issues. The proposed numerical analysis is validated against published experimental results. Maximum load bearing capacity of proposed numerical models was shown very good conformity to experimental results. As a result, the behavior of the FRP systems predicted by the analytical modeling was slightly stiffer than the values recorded experimentally; probable differences in stiffness are discussed in this study. In general, comparison between the numerical predictions and test results shows desirable agreement
Numerical simulation of flow in open channel with a 90o bend
A new methodology foرایگان!
A new methodology for resolve complex problems in fluid mechanics has been known as computational fluid dynamics (CFD). CFD investigates parameters such as velocity field, pressure, shear stresses, effect of turbulence and etc in flow field. In this paper, a three- dimensional CFD model was used to investigate of flow patterns, velocity profiles and also accuracy of numerical models in 1phase and 2 phases was investigated. For numerical simulation ANSYS-CFX software was used. The k-ε turbulence model was used to solve turbulence equations. The results showed that secondary flow and centrifugal force influenced flow pattern and have good agreement with experimental.
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.
Sediment Extraction and Flow Structure of Vortex Settling Basin
The paper presents tرایگان!
The paper presents the results of an investigation conducted in a vortex chamber and the flow structure along with sediment extraction efficiency were observed. During the experiments, various flow discharges were employed. Three sizes of sediment were fed at three different rates. It was observed that the increase in the flow and sediment feeding rates result in the increase of sediment extraction efficiency of the settling basin. An ADV velocity measuring equipment was utilized to determine flow structure inside the settling basin. It was also found that various types of flow patterns were developed in radial sections which may play a positive or negative role in sediment trapping process.
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