سال:1391 | دوره: | شماره: |تعداد مقالات:11

Vehicle collision on bridge piers is no more a rare possibility with crowded city roads, encroached spaces, and lack of recommended margins around piers. An attempt is made through this study to investigate the plasticity induced in a pier due to a colliding vehicle. Responses of several piers with varying geometries are studied by finite element analysis. The piers are subjected to collision loads, static as well as dynamic in nature. The study aims at identifying the areas of damage and roughly estimating the damage sustained by the pier under consideration. A range of results in the form of graphs have been presented. Subroutines capable of handling material nonlinear effects in the static as well as dynamic zones were developed using MATLAB. The programs were validated using ANSYS.Separate results are presented for static and dynamic analysis. The forces considered for static analysis are based on specifications of several countries, while the force-time histories adopted for transient elastoplastic response of the pier are adopted from simulated crash test results. An attempt is made to get a better insight into quantifying damage with plasticity as an indicator.

In this paper, three artificial neural networks are presented using the experimental results from bolted moment connections among cold-formed steel members and the software MATLAB in order to predict the rotation at the connections. A common neural network which has a multilayer perceptron along with back propagation learning algorithm is applied in this research. Each of the networks consists of four layers including two hidden ones. The number of neurons in the first hidden layer is changed from 1 to 10 to achieve optimal results. The best results are obtained when the networks had 10, 10, and 9 neurons in the first hidden layer for column base and beam column connections (in positive and negative rotations), and they had the performance of 0.0001371, 0.00044, and 0.00047, respectively, after being trained in the software MATLAB. Thirty percent of the data from each test series were omitted randomly in order to verify the networks. The Mann-Whitney  r value tests are 0.9933, 0.9393, and 0.9653 for column base and beam column connections (in positive and negative rotations), respectively.

Structural durability is an important criterion that must be evaluated for every type of structure. Concerning reinforced concrete members, chloride diffusion process is widely used to evaluate durability, especially when these structures are constructed in aggressive atmospheres. The chloride ingress triggers the corrosion of reinforcements; therefore, by modelling this phenomenon, the corrosion process can be better evaluated as well as the structural durability. The corrosion begins when a threshold level of chloride concentration is reached at the steel bars of reinforcements. Despite the robustness of several models proposed in literature, deterministic approaches fail to predict accurately the corrosion time initiation due the inherent randomness observed in this process. In this regard, structural durability can be more realistically represented using probabilistic approaches. This paper addresses the analyses of probabilistic corrosion time initiation in reinforced concrete structures exposed to chloride penetration. The chloride penetration is modelled using the Fick's diffusion law. This law simulates the chloride diffusion process considering time-dependent effects. The probability of failure is calculated using Monte Carlo simulation and the first order reliability method, with a direct coupling approach. Some examples are considered in order to study these phenomena. Moreover, a simplified method is proposed to determine optimal values for concrete cover.

Under seismic loads on structures, the maximum drift without total collapse is called target displacement. Most of low- and medium-rise building structures are seismically designed using equivalent static method. In equivalent static method, design forces are obtained from elastic spectra which are reduced using response modification factor. This coefficient represents the structures’ inelastic performance and indicates strength and hidden ductility of structures in inelastic phase. The ultimate deformation of the structure to its deformation in yielding is called ductility coefficient which expresses the inelastic deformation capacity of structures. The larger this coefficient, the higher the level of energy absorption and the more the formation of plastic joints, so accurate determination of yielding points and ultimate displacements are very important. In this paper some failure criteria are used to estimate seismic demands for buildings. To investigate these criteria, pushover analysis is done on reinforced concrete frame buildings. Using a combination of these criteria will lead to displacements that are closed to the target displacement presented in FEMA-356.

The paper presents artificial neural network models to evaluate the fatigue life of unidirectional glass fiber-reinforced epoxy-based composites under tension-tension and tension-compression loading. The fatigue behavior of the composite materials was analyzed using three parameters: fiber orientation angle, stress ratio, and maximum stress. These parameters formed the input vectors, and the number of cycles corresponding to the failure was taken as the output parameter for the assessment of the fatigue life. The architecture of the network was selected based on a detailed parametric study and it was trained and tested with data generated analytically using finite element analysis. The predicted results of the neural network model were compared with the available experimental values and were found to be in good agreement. Three different networks such as feed forward, recurrent, and radial basis function networks were used in the present investigation, and a comparative study was carried out to get the optimum network. The significance of the present work is that the same network could be used for assessing the fatigue strength of unidirectional glass/epoxy composite specimens with different fiber orientation angles tested under different stress ratios.

The effect of length and thickness on dynamic stability analysis of cantilever cylindrical shells under follower forces is addressed. Beck’s, Leipholz’s, and Hauger’s problems were solved for cylindrical shells with different length-to-radius and thicknesses-to-radius ratios using the Galerkin method. First-order shear theory was used, and rotary inertias were considered in deriving the differential equations. Critical circumferential and longitudinal mode numbers and loads were evaluated for each case. Diagrams containing nondimensional load parameters vs. length and thickness parameters were plotted for each problem. For some shells with small length-to-radius ratios, flutter occurred in high longitudinal mode numbers where the first-order shear theory may not suffice to accurately evaluate the deformations. However, for long and moderately thick shells, there are ranges in which the shell can be analyzed using the simplified equivalent beam model.

This paper presents the results of static vertical load tests carried out on a model building frame with plinth beam supported by pile groups embedded in cohesionless soil (sand). The effect of soil interaction on displacements and rotation at the column base and also the shears and bending moments in the building frame were investigated.The experimental results have been compared with those obtained from the finite element analysis and conventional method of analysis. Soil nonlinearity in the axial direction is characterized by nonlinear vertical springs along the length of the pile (t-z curves) and at the tip of the pile (Q-z curves) and in the lateral direction by the p-y curves. The results reveal that the conventional method gives the shear force in the column by about 20%, the bending moment at the column top about 10%, and at the column base about 20% to 30%, more than those from the experimental results. The response of the frame from the experimental results is in good agreement with that obtained by the nonlinear finite element analysis.

The transverse vibration of a single-walled carbon nanotube (SWCNT) with light waviness along its axis is modeled by the nonlocal Euler-Bernoulli and Timoshenko beam theory. Unlike the Euler-Bernoulli beam model (EBM), the effects of transverse shear deformation and rotary inertia are considered within the framework of the Timoshenko beam model (TBM). The surrounding elastic medium is described as both Winkler-type and Pasternak-type foundation models. The governing equations are derived using Hamilton’s principle, and the Galerkin method is applied to solve these equations. According to this study, the results indicate that the frequency calculated by TBM is lower than that obtained by EBM. Detailed results show that the importance of transverse shear deformation and rotary inertia become more significant for stocky SWCNTs with clamped-clamped boundary conditions. Moreover, the influences of the amplitude of waviness, nonlocal parameter, medium constants, boundary conditions and aspect ratio are analyzed and discussed. It is shown that waviness in the curved SWCNT causes an obvious increase in the natural frequency in comparison with the straight SWCNT, especially for a compliant medium, pinned-pinned boundary condition, short SWCNT and large nonlocal coefficient.

Flat-slab building structures exhibit significant higher flexibility compared with traditional frame structures, and shear walls (SWs) are vital to limit deformation demands under earthquake excitations. The objective of this study is to identify an appropriate finite element (FE) model of SW dominant flat-plate reinforced concrete (R/C) buildings, which can be used to study its dynamic behavior. Three-dimensional models are generated and analyzed to check the adequacy of different empirical formulas to estimate structural period of vibration via analyzing the dynamic response of low- and medium-height R/C buildings with different cross-sectional plans and different SW positions and thicknesses. The numerical results clarify that modeling of R/C buildings using block (solid) elements for columns, SWs, and slab provides the most appropriate representation of R/C buildings since it gives accurate results of fundamental periods and consequently reliable seismic forces. Also, modeling of R/C buildings by FE programs using shell elements for both columns and SWs provides acceptable results of fundamental periods (the error does not exceed 10%). However, modeling of R/C buildings using frame elements for columns and/or SWs overestimates the fundamental periods of R/C buildings. Empirical formulas often overestimate or underestimate fundamental periods of R/C buildings. Some equations provide misleading values of fundamental period for both intact and cracked R/C buildings. However, others can be used to estimate approximately the fundamental periods of flat-plate R/C buildings. The effect of different SW positions is also discussed.

This paper presents the structural behavior of composite concrete slabs with CRIL DECKSPANTM (Colour Roof India Limited (CRIL), Mumbai, INDIA) type profiled steel decking by experimental and analytical studies. The slab is created by composite interaction between the concrete and steel deck with embossments to improve their shear bond characteristics. However, it fails under longitudinal shear bond due to the complicated phenomenon of shear behavior. Therefore, an experimental full-size tests has been carried out to investigate the shear bond strength under bending test in accordance to Eurocode 4 - Part 1.1. Eighteen specimens are split into six sets of three specimens each in which all sets are tested for different shear span lengths under static and cyclic loadings on simply supported slabs. The longitudinal shear bond strength between the concrete and steel deck is evaluated analytically usingm-k and partial shear connection (PSC) methods and compared the values. The experimental results is verified and compared with the results of bothm-k and PSC methods. Comparison of experimental and analytical results of the load-carrying capacity of composite slabs revealed that agreements between these values are sufficiently good. As a result, m-k method proved to be more conservative than PSC method.

The seismic response of linearly elastic, single-storey, one-way asymmetric building with linear and non-linear viscous dampers is investigated. The response is obtained by numerically solving the governing equations of motion. The effects of eccentricity ratio, uncoupled lateral time period, ratio of uncoupled torsional to lateral frequency and supplemental damping eccentricity ratio are investigated on peak responses which include lateral, torsional and edge displacements and their acceleration counter parts as well as control forces. To study the effectiveness of dampers, the controlled response of asymmetric system is compared with the corresponding uncontrolled response. Further, to study the effects of torsional coupling, the controlled response of asymmetric system is compared with the corresponding symmetric system. It is shown that the non-linear viscous dampers are quite effective in reducing the responses and the damper force depends on system asymmetry and supplemental damping. Also, the effectiveness of dampers significantly depends on structural and damping eccentricity ratio and torsional to lateral frequency ratio and the effects of torsional coupling are found to be more significant for torsionally flexible and strongly coupled systems. Further, effects of torsional coupling are less for asymmetric systems with non-linear dampers as compared to linear dampers.