Scientia Iranica
Volume:22 Issue: 5, 2015

In conventional elastic-plastic constitutive models for clays, elastic strains are usually calculated by isotropic hypo-elastic models. However, this class of elasticity has two major deficiencies: (a) it ignores the influence of shear stress-induced anisotropy and; (b) it does not conserve energy. Another class of the elasticity theory, the so-called hyper-elasticity theory, is capable of eliminating both deficiencies simultaneously. In this study, constitutive equations of a recently proposed elastic-plastic platform for clays named SANICLAY are generalized in order to enable it to consider the possibility of the anisotropic response in the elastic domain. The generalized formulation allows shear-volumetric coupling not existing in the basic platform. Then, the elastic moduli obtained from a hyper-elastic model are implemented within the generalized SANICLAY formulation. The refined model predictions are directly compared with the experimental data of various clays. It is shown that more realistic stress paths are achieved from the refined model.

Spatially continuous data is important in modeling, numerical and computational works. Since sampling points are not continuous, interpolation methods should be used to estimate data at unsampled points. In this paper, radial basis function (RBF) and Moving least square (MLS) interpolation methods are applied to estimate concentration of Nickel, Mercury, Lead, Copper, and Chromium in the Caspian Sea by programming. Cross validation results are also obtained by RBF and MLS methods and have been compared for Lindane, Total DDT, Total HCH, Total Hydrocarbons and Total PAH elements. Input data for MLS and RBF are longitudinal, latitude and depth (3D interpolation) at any point. Output of MLS and RBF is concentration of an element at any point. A new method is introduced for defining constant parameter in RBF. The number of sampling points for calibration and verification tests is analyzed with the values of root mean square error (RMSE) in pollutant parameters. Optimum selection of MLS parameters are used in this paper. The results of concentrations estimation of metal elements in sediments of Caspian Sea by MLS and RBF show that RBF method yields more accurate results than MLS method.

Hazard analysis is the prominent stage in performance-based earthquake engineering and properintensity measure selection is itssignificant phase. Despite diversity in recently proposed intensity measures, there are still significantvariations in the magnitude of structural responses used to assess performance especially according to the records with pulse-like characteristicsIn this study, several intensity measures for two groups of records, far-field and near-field, were evaluated in six scaling levels. In addition, a new scalar intensity measure,accounting for pulse-like characteristics of near-field records, have been generated based on spectral velocity at first-mode period of a structure and maximum amount of velocity. Utilized structural models are steel moment frames with different heights accounting for the effects of wave propagation.It is discovered that this new velocity-based intensity measure is the most convenient IM factor especially forthe stories under pulse propagation associated with near-field records,considering both efficiency and sufficiency aspects. Furthermore, it is found that utilizingnonlinear spectral values doesnot significantly amplify assessment precision in the moderate range of intensity measures, and considering their unavoidably complicating and timeconsuming required analyses; elastic spectral valuescan be adequately substituted.

In this study, stress-strain analyses of embankment dams with clay core in narrow valleys are evaluated by means of numerical modeling, considering the longitudinal section along an embankment dam centerline. Emphasis is placed on effects of cross valley differential settlements, and the end of construction core load-settlement behavior, particularly in vicinity of abutments. The effects of core material type (mixed clayey sand material versus pure clay), on stress-strain behavior are examined. As a case study the Masjed Soleyman clay core is analyzed considering different types of materials, and a range of core material deformation properties. A 70% reduction in depth of tensile zones near the core- abutment interface was achieved by inclusion of contact clay material at the core bottom. Comparison of analysis results and instrumentation data suggested a good agreement between results.

When a fault crashes, seismic body waves travel away the source to the ground surface. Seismic wave characteristics change due to source, path and site effects. Site effects consist of surface and subsurface irregularities such as cavities can affect the properties of seismic waves. Therefore, in this study the effects of underground cavities on surface ground motion amplification are investigated for circular and elliptical shapes. Underground cavities are subjected to the vertically propagating SV and P in-plane waves. The effects of dimensionless frequency, depth of cavity, geometry of cavity and also presence of the second cavity are studied in this research. Results show that increasing of dimensionless frequency, causes increase in ground motion amplification for both cases of incident SV and P waves. It is also resulted depth and geometry of cavity can cause very important effects on the ground seismic motion. Presence of second cavity can also aggravate the ground surface seismic motion in addition to the first cavity.

Using steel curbs and props is an appropriate method for strengthening the moment resisting reinforced concrete frames. In this paper, RC frames which were strengthened using steel prop and curb only, and in combination with beam''s revival steel sheets and column jacketing are investigated using numerical modeling. After verifying the models, local and global behavior of these frames, such as displacement, ultimate strength, ductility factor and reduction factor were studied. Analytical results show that ultimate lateral load of strengthened frames using the prop with sectional area of 1.2, 2.0 and 3.5 cm2, has grown up to 2.0, 2.66 and 3.3 times of the ordinary frame, respectively. According to the results, when the prop''s area increases, the ductility factor and the reduction factor of frames will decrease. The effect of column jacketing and beam revival sheet are opposite each other, while column jacketing increases the strength of the frame, the beam''s revival decreases it, and when column jacketing increases ductility, the beam''s revival decreases it.

Inweight optimizitaion of double-layer grids, various parameters such as the members cross-sectional areas, the height between the two layers, the structure meshing in two directions and topology of the structure should be considered. In this study, for simultaneous optimization of size, shape and topology of double-layer grids, genetic algorithm is employed and is modified based on fuzzy inference system. First, to efficiently search in design space at each stage, some solutions are generated in the neighborhood of the best sample, which enhances searching operation in the neighborhood of the optimum solution. Then, in order to achieve the possible solutions, the penalties for violation of constraints and the number of violated constraints are considered to choose the next generation. The value of objective function and the values of genetic algorithm parameters have a great effect on the result of the algorithm. In order to adaptive setting of these parameters, the fuzzy inference system is employed. The efficiency of these improvements has been confiremd by presenting some examples of truss structures and comparison with the other algorithms.

Labyrinth spillway has become an appropriate choice to increase an existing spillway’s capacity. Thus, it is necessary to understand the hydraulic performance of labyrinth spillways/weirs. This paper numerically solves turbulent flow over labyrinth spillways/weirs and determines the discharge coefficients. Reynolds governing equations, turbulence k-ε model, and the volume of fluid (VOF) model are numerically solved to define pressure, velocity, and the free surface flow profiles. The numerical results are comparable to those obtained from physical modeling with maximum 6.43% error relative to results of physical modeling. Present study indicates that numerical simulation can be used to supplement physical modeling. Thus, by using numerical solutions the site specifics of the spillway which are often different from the conditions of design curves can be investigated. Also, the effect of different shapes of apex on discharge capacity of the labyrinth spillway is investigated in this study. The analyses show that labyrinth spillways with round apex shape are the most efficient spillways. Numerical determination of free water surface is presented and discussed, which is helpful for optimum design of stilling basin and leading walls.

In this paper, a General Hybrid Cellular Automata (GHCA) model is hybridized with two of the most reliable heuristic search methods, namely Genetic Algorithm (GA) and Ant Colony Optimization Algorithm (ACOA), for the simultaneous optimal design of layout and size of pumped and/or gravity sewer networks. GHCA model is recently proposed by the authors for the optimal size determination of the sewer network with fixed layout. The model has shown to be able to optimally design pumped and/or gravity sewer networks, if required. In proposed hybrid models, the heuristic search algorithms are used to create trial layout for the network while GHCA is used to design the network by determining the pipe diameters, pipe slopes, drop height and pump height, if required. An ad-hoc engineering based method is used to determine feasible layouts by GA, while a Tree Growing Algorithm (TGA) is used to construct feasible layout using ACOA. The proposed hybrid models are tested against two benchmark sewer networks and the comparison of results to those of some existing methods indicates that proposed models, and in particular the ACOA-GHCA method, are more efficient and effective than some alternative methods for the optimal design of layout and size of sewer networks.

Estimation of crushing stress is important to understand the crushing mechanism and shear strength of granular material. One simple constitutive model using the reference crushing stress had been proposed for describing the variation in strength and deformation behavior of sand before and after particle crushing occurrence. The prediction capacity of the constitutive model is examined for representing the variation in mechanical behavior of relative high crushable sand. This study presents the parametric analysis on the reference crushing stress and examines its effect on the mechanical behavior of Cambria sand. Numerical results demonstrate that peak stress ratio increases and contractive behavior becomes less obvious with larger reference crushing stress. The stress ratio and dilatant ratio at failure with variable reference crushing stresses and confining pressures are also demonstrated. Predicted results indicate that reference crushing stress is basically dependent on the inherent feature and type of sand but has some relationship with the ultimate strength of a single particle. The linear relationship between the reference crushing stress and the yield stress decided in one dimensional compression test has been obtained on the logarithmic plot. The reference crushing stress can be applied as one effective strength index for sand in macro viewpoint.

Hydraulic network solver simulates the behavior of water distribution network for a given set of geometric and hydraulic parameters such as pipe length, pipe diameter, tank size, pump capacity, demand, pipe roughness, etc. Over the years, many researchers have developed number of hydraulic simulation models (software) for analysis and design of water distribution networks, but most of them are based on demand driven analysis (DDA). This paper reviews the existing approaches and examines the usefulness of emitter feature available in hydraulic network solver (EPANET) as tool for pressure driven model. The emitter based method determines the possible supply at all deficient nodes based on the availability of energy at that node by introduction of an emitter. This method along with three existing approaches has been applied to three benchmark networks and important findings from the study in terms of convergence and numerical results are presented. The framework of head-flow based approaches and proposed method is carried out using toolkits feature available in EPANET hydraulic solver.

Spillways play an important role in the safety of dams. To ensure the safety of dams, spillways should be designed considering floods with long return periods. To increase the discharge capacity of a spillway, a designer can increase the crest length using the labyrinth spillway. For high head conditions, the local submergence may decrease the efficiency of a labyrinth spillway. In this study, the hydraulic characteristics of linear and arced labyrinth spillways are compared and the effect of the downstream bed level on the discharge coefficient of labyrinth spillways is studied numerically. The numerical simulations are done using Flow-3D software. RNG k-ε model is used for turbulence simulations and the free surface profiles are calculated by VOF method. Experimental data of pervious researchers are used for validation of the proposed numerical model. The results show that in the high head conditions, lowering the downstream bed level of a labyrinth spillway increases its efficiency, especially in the case of an arced labyrinth spillway.