Scientia Iranica
Year:2014 | Volume:21 | Issue:1 (TRANSACTIONS A: CIVIL ENGINEERING)|Papers Count:11

A simple node enrichment strategy using a gradient based error estimator is presented for the Collocated Discrete Least Squares (CDLS) meshless method. Also, a procedure is defined to distribute collocation points according to the field nodes position. Here, shape functions are constructed using Radial Point Interpolation Method (RPIM). As temporal discretization a first-order accurate scheme, named semi-incremental fractional step method is used. One of the advantages of this scheme is its capability to use large time step sizes for the solution of the governing equations on steady state problems. The capability of the presented strategy is shown by investigating Carreau-Yasuda fluid flow model in solving lid-driven cavity flow problem with different curve fitting indices values.

Dynamic analysis of rectangular thick plates on elastic foundations under partially distributed and centrally concentrated impulsive load is presented using Winkler foundation model. An 8-noded (PBQ8) Mindlin plate element are adopted for modeling the plate to account the transverse shear deformation effects neglected in the classical thin plate theory. Selective reduced integration technique is used to avoid shear locking problem which occurs as thickness/span ratio decreases. The results obtained from the study are compared with the solutions obtained by SAP2000 software to show the validity of the elements. The variation of the maximum displacement with various values of subgrade reaction modulus, aspect ratios, the ratio of plate thickness to shorter span of the plate and loaded area are investigated. Numerical examples show the applicability of the 8-noded element to dynamic analysis of thick plates on elastic foundation subjected to external loads using Winkler model.

The fault rupture propagation phenomenon, spreading from the base rock through different layers of soil, is a matter of concern in many natural and man-made soil structures. The focus of this paper is to investigate reverse fault rupture propagation through two layers of sand deposits by means of numerical modeling. For this purpose, analyses are carried out for different permutations of the three typical materials: dense sand, medium dense sand and loose sand, considering five fault dip angles, 30, 45, 60, 75 and 90 degrees. The validity of numerical model was verified by simulating an experimental model of homogeneous soil layer subjected to reverse faulting. Further to the general trends found in fault rupture propagation in a single layer of soil, special attentions are devoted to the refraction of fault path in the interface of two materials as well as its concavity in the continuation. Moreover, four patterns of fault rapture propagation in two-layered sands, depending on their arrangements and fault dip angles, were concluded from the results.

This paper examines gully growth and head advancement at Queen Ede gully Site Benin City. This is achieved by observing gully growth and head advancement between the year 2000 and 2012 using field surveys, aerial photographs and geographical information system. Also by using experimental models such as Thompson [1], American Soil Conversation Service, SCS (I), SCS (II) and FAO models, for estimating migrating headcuts over a study period. Results obtained, revealed that the gully width varied from 15.6m to 99.5m while the depth varied from 0.5m to 13.8m. The volume of soil loss was 372, 775m3 over an area of 104.4m2. A mathematical model is proposed for gully growth (GA) and head advancement (RA), which is hereby presented as:(i) GA =0:15R0.2679La0.0873Lw0.09179E0.009860P0.06773(ii) RA =0.15A0.5328S0.14P0.6778E.The model has been tested against the best existing theories and found to give the same order of error.

Liquefaction is a serious geotechnical hazard leading to catastrophic damages which cause life and property losses. In many instances it may be preferable to predict liquefaction susceptibility indirectly, by common in-situ tests such as cone penetration test (CPT). A new approach, for prediction of liquefaction susceptibility, is proposed which presents a polynomial model to correlate cyclic resistance ratio (CRR) predicated on subsoil geotechnical properties from CPT tests, viz. normalized cone tip resistance (qC1) and friction resistance (¦s). The derived model is applied to a total of 182 data sets, including field investigation records from eighteen earthquakes. The performance of the proposed approach is compared to other available methods within a quantitative validation framework (e.g., Precision, Recall, and F-Score). Results indicate the accuracy and generalization of the proposed new approach in predicting liquefaction susceptibility.

A damage plastic constitutive model for metals is proposed in this paper. Anisotropic damage tensor and damage surface are adopted to describe the degradation of mechanical properties of metals. The model is developed within the thermodynamic framework and implements an anisotropic damage plastic model with ability to describe the plastic and damage behavior of iron based materials. According to the principle of strain energy equivalence between the undamaged and damaged material, the linear elastic constitutive equations for the damaged material expressed stiffness tensor in damaged configuration. The damaged material is modeled using the constitutive laws of the undamaged material in which the stresses in undamaged configuration are replaced by the stresses in damaged configuration. To simulate the onset of plastic deformation and damage, yield and damage surfaces are applied and in accordance with the normality rule, evolution laws for the damage variables are achieved to complete the proposed damage plastic model. The implementation of the model in the form of a practical method, based on the forward Euler integration scheme (modified forward Euler integration with error control) is discussed. Finally, the constitutive response is compared with some experimental results and classical plasticity results for validating the capability of the proposed model, and a good agreement between the experimental results and the model is obtained.

The objective of this paper has been to study the improvement in the seismic behavior of concrete gravity dams by optimization of concrete mechanical properties. The criteria to measure the improvement have been: 1) reduction in the extent of cracks and 2) increase in the time the dams are able to tolerate earthquakes before failure. The mechanical properties considered have included the density and modulus of elasticity of concrete. Pine Flat dam has been selected for this numerical study. During a high intensity earthquake, dams enter nonlinear phase where the cracks open and close repeatedly. Smeared crack model has been used for the simulation of nonlinearity. For the purpose of optimization, the dam has been divided into horizontal layers where the concrete has been assumed to have the same properties at every point within each layer. The results of this study have shown that by using lower density concrete at upper layers and in the region of the crest of the Pine Flat dam, it has been possible to both reduce the extent of the induced cracks and increase the time to failure of the dam. The same methodology can be applied to other concrete gravity dams.

This paper deals with the modeling of a vertically coupled vehicle-slab track using finite element method. The slab track system is represented by a two layer Euler-Bernoulli beam model including rail and concrete slab. The vertical stiffness of track bed is assumed to be random variable using Monte Carlo simulation. The vehicle is simplified as a multi-body system with 10 degrees of freedom. The accuracy of the simulation is verified by deterministic and random approaches as well. Sensitivity analyses on the various parameters such as slab thickness, coefficient of track bed stiffness, vehicle velocity are performed. It is demonstrated that the uncertainty in track bed stiffness has a major effect on rail and slab deflections. From a practical point of view, the obtained results of the present study can be utilized efficiently in the analysis and design of slab track systems.

In this study, numerical simulation of flow over a chute spillway is presented using the computational fluid dynamics (CFD) method. The flow characteristics such as velocity, pressure and depth through the spillway have been calculated for four different flow rates. Since the actual flow is turbulent, the RNG turbulence model has been used for simulation. The numerical computed results of piezometric pressure and flow velocity along the spillway were compared with the results from the hydraulic model tests. The maximum difference between calculated and experiment results in average velocity values was 5.47% and in piezometric pressure values was 7.97%, and the numerical results agreed well with experiments.

The oscillatory diameter of the charged jet during the bubble electrospinning results in beads on the obtained nanofibers. We demonstrate that the applied voltage and the initial flow rate of the jet are the crucial parameters that are necessary to control morphology of the nanofibers. We also find that there is a criterion for production of smooth nanofibers without beads. The theory developed in this paper can be extended to the classical electrospinning and the blown bubble-spinning.

Identifying the contribution of each part of the railway to total lateral resistance is considered the most important issue in choosing type of sleeper for providing lateral stability of ballasted railway track. On the other hand, identifying the percentage of effect of each part can help to present new methods for increasing lateral resistance of ballasted railway track. Methodology of this study was based on experimental work in the laboratory. In this paper, the contribution of each part of the sleeper comprised of base, crib and shoulder was determined in the total lateral resistance by STPT tests. In all of the measurements, the greatest value of lateral resistance was related to the area under the sleeper (base zone) and its corresponding valuesin concrete, steel and wood sleepers were 62%, 56% and 51%, respectively. The contributions of shoulder and crib area to the lateral resistance were28% and 9% for concrete sleeper, 27% and 22% for wooden sleeper and 18% and 26% for steel sleeper, respectively.