Scientia Iranica
Volume:26 Issue: 3, May-Jun 2019

The effect of aging on dynamic properties of Municipal Solid Waste (MSW) including damping ratio and shear modulus was investigated in the current research. For this purpose, a series of cyclic Consolidated Undrained (CU) triaxial tests were performed on fresh and old reconstituted cylindrical specimens, taken from Mansoory Prototype Landll (MPL) placed in Kahrizak Landll, Tehran, Iran. The results showed that the shear modulus of old samples (7.5 years old) was more than that of the fresh ones. This trend can be attributed to decomposition of waste over time, which leads to reduction in organic content and, consequently, increment of brous waste particles (plastics) of the old samples. On the other hand, the results also indicated that the damping ratio was partially dependent on the composition of the specimen and it slightly decreased with increasing the age of MSW. The high percentage of organic content in fresh specimens can be consideredas the main reason for this behavior. Finally, the normalized shear modulus reduction and strain-dependent material damping curves were prepared for both ages of retrieved MSW from Kahrizak Center Landll (KCL). The results of the current study are in the range reported in the technical literature and can be used as reliable data for seismic purposes.

The masonry walls should have sucient in-plane strength and stiness to withstand the seismic loads during strong ground shakings. Dierent retrotting techniques have been proposed for improving in-plane behavior of the unreinforced masonry (URM) walls. This study focuses on experimental evaluation and numerical simulation of a simple practical retrotting technique employing Fiber Reinforced Concrete (FRC) surface layer.The simple FRC mix has conventional and available ber, low ber content, ordinary mix design, and applicable construction procedure. Eects of FRC mix properties, including ber type, ber content, and surface layer thickness, on in-plane behavior of masonry panels made up of conventional solid clay bricks are evaluated through experimental study in accordance with ASTM E-519 diagonal tension strength of masonry panels. In addition, a numerical simulation model for this retrotting technique in ABAQUS software is proposedand validated with test results of bare and retrotted panels.

Earth Dams are one of the most important and expensive civil engineering structures to which a considerable amount of budget is allocated. Their construction costs are mainly related to the size of embankments, which in turn depends on their cross section area. Therefore, reductions in cross section areas of earth dams would cause decreases in embankment volumes leading to a significant reduction in the construction cost of these structures. On the other hand, it is almost impossible to obtain optimum cross section in earth dams with desired stability and acceptable operational dimensions using traditional design methods. In this paper, ant colony optimization algorithm (ACO), a well-known and powerful metaheuristic method used to tackle problems in geotechnical engineering, was used to solve this complicated problem. The results showed that applying ideal and optimum slope and berm arrangements resulted from ACO in designing embankments and earth dams with different heights could lead to decreases in embankment volumes compared to those without any berms or those with berms resulting from usual designs with trial and error.

Oil and its derivatives such as gasoline, motor oil and gasoil are using in various industrial and non-industrial sectors as the main energy sources all over the world. However, within the process of exploration, transportation and storage they may spill or leaking into the soil. Among them the gasoil which is more widely used in different parts and machineries has the largest contribution in contaminating lands. Purgation of these areas is not always feasible or possible. Instead, they can be used in many engineering practices if the level of contamination is not high. In such cases knowing the geotechnical properties of these areas are of great necessity and importance. In this study, extensive laboratory tests were performed on remolded clayey samples mixed with gasoil to evaluate their geotechnical properties. The Response Surface Methodology (RSM) was used to analyze the data and find behavioral equations. According to testing results and RSM outputs a decrease in Atterberg limits, and increase in maximum dry density happen by increasing contamination. Also their shear strength parameters (c and f) both exhibit a turning change point at 8% gasoil content, while their variations trends are quite in opposite directions

Fragility curve, based on the performance-based earthquake engineering (PBEE), is a fundamental tool in assessing the probabilistic seismic performance of concrete gravity dams. Determination of the dam limit-states (LSs) is necessary for estimation of fragility curve. In this research, four LSs in seismic performance of massive structure have been utilized for Pine Flat dam. To address this, the Incremental Dynamic Analysis (IDA) method has been applied to the integrated dam-reservoir finite-element model. Evaluation of seismic behavior, demand and capacity of the tallest monolith has been investigated by implementing IDA. A new comprehensive method in terms of IDA and statistical analysis has been used for determination of each defined LS based on the certain value of the engineering demand parameter (EDP). To assess probabilistic performance of the dam, the exceeding probability of the LSs curves has been developed at various intensity measures based on the tree EDPs. It was found that the defined LSs have the capability indeed to be used in probabilistic framework.

Ductility with direct effect on the response modification factor of buildings can influence their seismic performance. Moreover, some factors such as geometry and different types of irregularity can affect the ductility and seismic performance of structures. In this study, the effects of mass irregularity in height on the over strength, ductility, response modification factors and probabilistic seismic performance in steel Moment Resisting Frames (MRFs) are assessed. Then, the obtained results are compared with those of regular structures. For this purpose, incremental dynamic analysis (IDA) is implemented using ten records out of past worldwide earthquakes. The location of mass concentration in height is studied assessing 8-, 12- and 16-storey buildings with their mass concentrated at the first floor, mid-height and roof. Then, the probabilistic seismic responses of these structures are evaluated using the outputs of IDA. In this regard, probabilistic seismic demand analysis is conducted on each model. The obtained results are used to plot the seismic fragility and demand curves for both regular and irregular models. Based on the findings, mass irregularity causes the reduction of ductility and response modification factors. This effect increases when the heavier storey is located either at the first floor or at roof. Moreover, mass irregularity brings about the increase in probability of damage occurrence or its exceedance from a certain level.

Extremal hypotheses without bank stability constraint typically over-predict and under-predict channel width in large rivers and natural streams, respectively. In general, results obtained from unconstrained extremal hypotheses are indicative of inappropriate agreement between predicted and observed dimensions of the rivers. One of the important factors in disparity of the data may be lack of appropriate relationships to assess bank vegetation of the rivers. For this reason, a modified analytical model has been developed to reduce the effect of bias by considering bank stability and vegetation. The model takes into account channel shape factor, a wide range of bed load equations in the form excess shear stress and vegetation quantification is able to predict optimal channel geometry dimensions. Finally, developed model was calibrated using the field data of the United Kingdom and Iran. In addition to indicating the effect of bank stability and vegetation on estimation of the geometric characteristics of the channel, obtained results also confirmed the efficiency of the constrained model in comparison to the unconstrained model. This study also provides support for the use of the concepts of maximum sediment transporting capacity and minimum stream power for understanding the operation of alluvial rivers.

After drilling a well, the  stresses will be altered and the induced stresses present the new state of stress. These induced stresses which result in geomechanical problems. The studies indicate that the flow of hydrocarbon into the wellbore influences the induced stresses. Darcy equation has been used in the past; however, the laminar flow assumption embedded in this equation cannot correctly model the flow of fluid when a non-Darcy flow dominates near a wellbore. Example of such situation includes the gas wells. In this study, analytical equations are developed to incorporate the effect of non-Darcy flow on the induced stresses around a wellbore. These equations developed based on Forchheimer flow equation. Then the simplified solutions were presented by considering the second term of Forchheimer flow equation. It was found that the difference between the results from Darcy and non-Darcy flow models is proportional to the drawdown pressure. Further studies included numerical simulation of non-Darcy fluid flow in a typical reservoir. Comparison of the results with the analytical models indicated that the magnitude of stresses in non-Darcy flow is larger than of Darcy flow. Finally, sensitivity of the reservoir properties on the induced stresses in the non-Darcy flow regime was investigated.

Mathematical simulation of the nonlinear tri-dimensional mechanical behavior of quasi-brittle materials like concrete is one of the biggest challenges in the engineering science. It is vital to have the knowledge of the response of concrete specimens subjected to low and high strain rate deformation for the analysis of concrete structures under the static and dynamic loading cases. The behavior of this material is generally known to be strain rate sensitive. Among phenomena of different orientation, the multi plane models, like multi-laminate models using a constitutive equation in a vectorial form rather than tensorial form by means of capturing interactions, can meet this goal adequately. This paper suggests a robust rate dependent damage based model in the multi-planes framework accomplished with minimum parameters for calibration and appropriate for engineering purposes. This damage formulation has been built on the basis of two types of essential damage, axial damage and shear damage, that basically can happen on each sampling plane and based on this concept two new axial and shear damage functions are proposed. Model verification has been studied under different compressive and tensile loading rates, comparing the results of the proposed model with the experimental data and Mohr-Coulomb failure criterion envelope line.

Injection in soils using traditional materials, such as cement grout, has its inherent problems and has not shown the potential for further development in industrial applications. Accordingly, application of novel materials for injection in soils with considerable content of fines for stabilizing and even making them impermeable is suggested. Among different stabilizers that are injectable in soils with fine, colloidal silica seems very suitable due to its very low viscosity, nontoxicity in the nature, and adjustability of the setting time for slow injection in soils with fine. Based on laboratory tests performed in this research, the effect of colloidal silica on the strength parameters and the short-term behaviour of silty sand was examined. For characterizing the soil stabilized by colloidal silica, the silty sand samples with different silt values, in both unstabilized and stabilized conditions, were prepared with different concentrations of the stabilizer. 45 Uniaxial tests and 75 unconsolidated- undrained compressional triaxial tests were conducted. An increase in the undrained cohesion of all samples was observed. On the other hand, two different trends were observed in the alteration of the undrained internal friction angle of soils with low and high fines content.

This paper proposed a practical approach for reliability analysis of vertical cut in unsaturated soil. This approach extends the application of conditional random field into the unsaturated soils. A real case study of vertical cut was considered and three boreholes were drilled to investigate the subsurface layers. The Sequential Gaussian Simulation (SGS) was used to generate conditional random field with considering the possible fluctuation of soil properties between known data. The undersampled parameters were estimated by cokriging method, while Kriging method was used to estimate other stochastic parameters. In order to verify the efficienty of simulations, it was checked that all data were reproduced at their locations and the input semivariogram model was reproduced within acceptable fluctuations. To predict the unsaturated soil behaviour, the Soil Water Retention Curve (SWRC) was estimated using physico-empirical method with the aim of determining suction stress for finite element stability analysis. The vertical cut was analyzed with and without considering suction. It was concluded that considering unsaturated condition shifts the mean of safety factor from the unsafe ranges to the safe ranges. It was illustrated that the number of known data effects the construction of conditional random fields and leads to different probability of failure.

Considering both size and dimensions of the offshore wind turbine structures, design optimization of such structures is a fruitful yet, simultaneously, onerous task due to the tempestuous complexity of the problem, which mostly comes from their environment. However, in this study, a computerized methodology based on meta-heuristic algorithms, consisting of the Colliding Bodies Optimization (CBO), Enhanced Colliding Bodies Optimization (ECBO), and Vibrating Particle System (VPS), is presented such that more economic upshots can be accomplished. Hence, minimization of the total weight of the structure subjected to a number of structural constraints, including a frequency constraint, by applying the above mentioned algorithms is the underlying goal of this study. Using the data from Horns Rev I offshore wind farm, which is located in the coastlines of Denmark in the North Sea, this study is performed based on a simplified structural model of a monopile offshore wind turbine structure, which can be utilized in preliminary stages of pertinent projects for conducting suitable comparisons.

The charged system search algorithm is a relatively new optimization algorithm developed based on some principles from physics and mechanics. This paper presents an approach in which Pareto dominance is incorporated into the charged system search in order to allow this algorithm to handle problems with some multi-objective functions; the proposed algorithm will be called Multi-Objective Charged System Search (MOCSS). Well-known mathematical and engineering benchmarks are used to evaluate the proposed algorithm and the results have been compared with other new approaches. The results of implementing the new algorithm on some test problems show that the proposed algorithm outperforms the other algorithms in terms of Generational Distance, Maximum Spread, Spacing, Coverage of two Set and Hypervolume Indicator. Results of well-known mathematical examples indicate that the new approach is highly competitive and can be considered as a viable alternative to solve multi-objective optimization problems. These results encourage the application of the proposed method to more complex and real-world multi-objective optimization problems. The proposed method can deal with highly nonlinear problems with complex constraints and diverse Pareto optimal sets.

Structural Health Monitoring (SHM) as a process in order to implement a damage detection strategy and assess the condition of structure plays a key role in structural reliability. In this paper, we aim to present a methodology for online detection of damages which may occur during a strong ground excitation. In this regard, Empirical Mode Decomposition (EMD) is superseded by Ensemble Empirical Mode Decomposition (EEMD) in the Hilbert Huang Transformation (HHT). Albeit analogous, EEMD brings about more appropriate Intrinsic Mode Functions (IMFs) than EMD. IMFs are employed to assess the first mode frequency and mode shape. Afterward, Artificial Neural Network (ANN) is applied to predict story acceleration based on previously measured values. Because ANN functions precisely, any congruency between predicted and measured acceleration indicates onset of damage. Then, another ANN method is applied to estimate the stiffness matrix. Though the first mode shape and frequency are calculated in advance, the process essentially requires an inverse problem to be solved in order to find stiffness matrix, which is done by ANN. This algorithm is implemented on moment-resisting steel frames, and the results show that the proposed methodology is reliable for online prediction of structural damage.