AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2020 | Volume:51 | Issue:4 |Papers Count:20

Performance-Based Earthquake Engineering (PBEE) attempts to improve seismic risk through assessment and design methods that are more informative than current approaches. However, little work has been performed investigating the seismic response of buried steel pipelines within a performance-based framework. In this paper the seismic response of buried steel pipelines are studied in a performance-based context. Multiple nonlinear dynamic analyses of three buried steel pipes with different D/t and H/D ratios, steel grade and various soil characteristics carried out using an ensemble of near-field ground motion records were scaled to various intensities to capture the behavior of buried pipeline in the range of elastic response to dynamic instability. Peak axial compressive strain in critical section of the pipe was considered as engineering demand parameter (EDP) of pipelines. Several ground motion intensity measures (IMs) are considered to investigate their correlation with EDP. Using the regression analysis in logarithmic space the efficiency and sufficiency of investigated IMs are studied. Among the models investigated in this study it was seen that VSI[w1(PGD+RMSd)]^0. 5, PGV and SMV are the most sufficient IMS. For buried steel pipelines investigated in the studied it was concludede that PGD is the most sufficent IM for near-field fround motions. It was seen that VSI[w1(PGD+RMSd)]^0. 5 followed by SMV are the optimal IM for buried steel pipelines under near-field ground motions based on both efficiency and sufficiency conceptions.

In regions where seismic activity is not high, the weight of the tower and the wind load are main loads for the cooling tower design. However, the effect of thermal load cannot be ignored. Due to the microcracks caused by thermal loads, the ultimate strength of the cooling towers at the end of wind loading may decrease. In this study, the cooling tower of Shahid Rajaee Power Plant was simulated using ABAQUS finite element software. Damage plasticity model which is capable of modeling cracks was used to model the tower shell. The effects of two load combinations were calculated and compared. In the first load combination, gravity, wind and thermal loads, and in the second, gravity and wind loads were applied to the given tower. According to the results, the differences of tower shell displacement toward the wind direction, compression-induced damage, and tensile damage in two loadings were 6. 4%, 3%, and approximately 10%, respectively. It was revealed that compressive and tensile damages spread out over a wider area in the presence of thermal loading. The highest impact of thermal loading was upon the bending moment of the shell and the back-winded side, such that the difference of bending moment in two loadings was estimated to be more than 40%. Moreover, in the presence of thermal loads, the tower reached its ultimate strength with lower wind pressure.

Prediction of flow through the compound open channel is one of the main problems in the field of hydraulic engineering. One of the main parameter related to the flow properties in the compound open channel is Shear Stress. The shear stress is because of difference of velocities between the main channel and floodplains. The Shear Stress causes of turbulence and vortex creation on the border of main channel and floodplains. The difference between the roughness of main channel and floodplains intensities the shear stress in the border zone and also decreases total discharge. In this paper, the discharge of flow in compound open channels was predicted using group method of data handling technique. To this end, related dataset were collected from literature. Involved parameters in modeling are relative hydraulic depth ( ), relative hydraulic radius ( ), and relative roughness ( ) and relative area ( ). To compare the performance of GMDH with other types of soft computing methods, the MLPNN as most well-known soft computing technique is developed as well. Results indicate that the GMDH model with coefficient of determination 0. 91 and root means square error 0. 057 is more accurate than the MLPNN. Reviewing the structure of developed GMDH model shows that and are the most effective parameters on prediction of discharge in compound open channels.

Investigating soil characteristics and models for better design and performance of construction projects is very important. In this paper, the ability and capability of the behavioral model of Manzari and dafaliais, which is an advanced model in the field of soil behavioral model, is evaluated to predict the shear behavior of carbonate sand with brittle seeds. Soil parameters are examined and their effects on soil behavior display. By comparing strain stresses obtained from a tri-axial test and a model in loose and dense samples, it was observed that the results of the behavioral model are in good agreement with experimental results. However, by examining the volumetric strain graphs against the axial strain, the outcomes of the Manzari and dafaliais behavioral model in comparison with the experimental results are not sufficiently accurate; the main reason for this is that the crushing of soil grains and its effect on soil volume variation in the Dafalias model, there is no perspective on the prediction of the volumetric strain. Nevertheless, the above-mentioned behavioral model predicts the trend of change. This behavioral model in high imbibed tensions has better results in comparison with the immensely low stresses in the study of strain volumes of samples.

Bucking restrained braced frame (BRBF) is a special type of concentrically braced frames that the braces do not buckle in compression and as a result shows a desirable energy dissipation behavior. However, low post-yield stiffness of these braces causes large residual deformations at high levels of earthquake itensities. The aim of this article is to evaluate the seismic behavior of a new steel structural system known as hybrid buckling-restrained braced frame (HBRBF). Nonlinear static analysis, nonlinear time history analysis and nonlinear incremental dynamic analysis (IDA) methods are used for standard and hybrid core BRBFs with different stories. The average values of seismic behavior factor (R) for HBRBFs are obtained as 10. 2 and 14. 7 for ultimate limit state and allowable stress design methods, respectively. In order to carry out response history analyses, past earthquakes records were used with different hazard levels. Hybrid buckling-restrained braced frames are shown to have a significant improvement over standard BRBFs in terms of behavior factor and damage measures including inter-story drift ratios and residual displacements.

Re-centering is an exclusive characteristic of superelastic Shape Memory Alloys (SMAs) which can be used in manufacturing and retrofitting of reinforced concrete elements. Reinforced concrete beams retrofitted with SMA bars have more ductility and higher energy dissipation compared to conventional RC beams. Furthermore, these beams experience less damage in consecutive loading-unloading cycles. The current research aims to investigate the behavior of reinforced concrete beams retrofitted with SMA bars using Near-Surface Mounted (NSM) flexural retrofitting method. Eleven RC beam specimens with the cross section of 200*150 mm and length of 1150 mm were cast. Three of the specimens had no external strengthening, four of them were retrofitted with SMA bars and other four beams were retrofitted with GFRP reinforcements. The specimens were subjected to three-point bending test under either monastic or loading-unloading. Different parameters including load-carrying capacity, energy dissipation, deformation recovery and reduction capability of crack width were investigated. The results showed that RC beams retrofitted with SMA bars had more mid-span deflection and higher energy dissipation compared to other specimens under monotonic loading. Moreover, under loading-unloading, RC beams retrofitted with SMA bars method experienced less damage.

Statistical quality control is a method for monitoring the process to identify the underlying causes of changes and carrying out corrective actions. Process and capability control charts are two important applied tools for statistical quality control. In many actual systems in which accurate and certain information is not always available and the information is vague and fuzzy, fuzzy based methods can survey production process more precisely using appropriate linguistic terms and fuzzy numbers. In this study, fuzzy control charts are developed using fuzzy rules, and then the fuzzy actual capability index of process ( ) is investigated to evaluate the precision, accuracy and performance of production process in the fuzzy state. The results of the study on the quality of water flowmeters in the urban water and wastewater company of West Azarbaijan province showed that using fuzzy rules compared to the crisp data, provides more decision-making options to decision-makers and provides more precise division about the product quality. Also, the fuzzy actual capability index of process can propose a more precise analysis of the process taking into account the average, target value and process variance, simultaneously. The values of the fuzzy actual capability index of process in the studied case are less than one, showing that the conditions of the production process are unfavorable.

Current design of Geo synthetic-reinforced soil (GRS) walls, shows that the horizontal deformations in the walls increases rapidly with height. To take advantage of both the aesthetics and the economics of GRS walls while considering high heights, multi-tiered walls are often used. In this context, 12 models of the walls were constructed and their performance was determined under static loading. This study presents a series of model tests on the GRS walls in a tiered configuration, to evaluate the effects of factors, including the offset distance between adjacent tiers and number of tiers, on the lateral displacements of the wall facing and ultimate bearing capacities of the strip footings on the multi-tiered GRS walls. The ultimate bearing capacity and wall deflection can be significantly improved by increasing the number of tiers wall and increase of tier-offset. Interaction between the upper and lower walls significantly influences the tier-offset, and the interaction between the walls, significantly increase in the horizontal deformation in the wall face for the upper wall. With an increase in the offset distance, the lateral displacement decreased significantly, particularly in the upper tier. The experimental results showed that, the Performance in Four layers of reinforcement, and two tier walls, the optimum offset distance obtained for D/H= 0. 35. When the offset becomes significantly large, each tier functions independently

One of the necessary parameters in designing and scaling up flotation columns is carrying capacity (Ca) which can be determined in terms of mass of solids per unit time per unit column cross sectional area. The prediction of Ca for a given flotation technology has been commonly achieved using a simplified expression based on a representative particle size and density of the floatable material, regarding several assumptions in limited data ranges. In determining the Ca, the effect of operational parameters, such as particle size, pulp solids rate, bubble diameter, air flow rate, pulp solid content, frother dosage and froth height should be considered. In this study, the effect of these parameters on the Ca was investigated in column flotation. The studied sample was obtained from rougher circuit concentrate of Sungun copper complex flotation plant. It was found that when the pulp solid rate increased up to 1. 4 cm/s, more surface of bubbles is covered by entering more solid particles to the column and Ca increased, but it decreased in higher rates. In lower speed of input pulp, the increase of frother dosage led to higher Ca, but in pulp rate higher than 1. 2 cm/s, the maximum Ca was obtained in frother dosage of 45 ppm. By decreasing the froth height and increasing the solid percent up to 30%, Ca increased. Likewise, the results of the experiments with particles of different size distribution showed that the input pulp with size 44-63 μ m had the maximum Ca.

An accurate assessment of the behavior of structures by an analytical method should be able to estimate the initial stiffness of the structure, the maximum capacity and the local and global ductility. In this research, in order to simulate the nonlinear behavior of reinforced concrete structures under monotonic loading, a new fiber beam-column element has been developed with a displacement control method using linearized arc-length approach. The formulation of the implemented element is based on the combination of Bernoulli and Timoshenko's theory along with the axial, flexural, and shear interaction effects of each element. The cross-sectional area of each element in Gaussian points is equivalent to a set of discrete fibers with uniaxial constitutive behavior in the process of nonlinear solution. Also, in order to consider the elemental shear deformation, the four-way smeared cracked approach and the modified compression field theory (MCFT) have been considered in nonlinear shear analysis by using the direct-displacement control algorithm in the main sub-program. The reference configuration of numerical formulation is considered according to the configuration of the previous step and the initial configuration, simultaneously. The analytic approach of the algorithm has the ability to change the updated Lagrangian formulation to the total Lagrangian in accordance with the problem-solving convergence. The developed fiber element has been validated by numerous experimental experiments and the evaluation of the proposed analytical method has been tested. The proposed method leads to an appropriate solution and an acceptable convergence process with high processing speed for problems with mixed combinational mechanisms.

Gabion stepped weir is a simple hydraulic and environment friendly structure that can be used to dissipate flow energy in different dams or to control downstream erosion of various structures. Most researches have been related to concrete and rigid stepped spillways, so studies on gabion stepped weirs are very small. In this research using the experimental method and physical model various components that affect the energy loss in gabion stepped weirs have been studied and comparisons with other studies by researchers have also been made. The flow passes in gabion stepped weir was carried out both in overflow and inflow (both simultaneously) and the amount of energy dissipation along the structure was calculated based on the energy relation. In this study, completely uniform particles with three diameters ( ) of 10, 25 and 40 mm were used. The height and width of physical models made of gabion stepped weirs were 60 cm and 40 cm respectively, with stairs of 3, 6 and 12 and height of stairs 5, 10 and 20 cm and the slope of the weirs are 1: 1, 1: 2 and 1: 3 (2 and 3 horizontals, 1 vertical). In the gabion stepped weirs, the downward slope of the weir has a negligible impact on the energy dissipation. As the number of steps increases (for constant ), the energy loss decreases. The average diameter of the particles of 10 mm for and the average diameter of the particles of 40 mm for has the highest of relative energy loss.

Vulnerability assessment and seismic retrofit of bridges as lifelines is of great importance. In recent years, performance based procedures in bridges is taken into consideration by researchers. In this paper after evaluating proposed methods for seismic performance assessment of bridges, first a laboratory model of box-shaped steel bridge piers was analyzed for verification and results were compared with laboratory data. Then based on the properties of a real bridge, several bridges were designed for parametric studies. The mentioned bridge is continuous and consists of steel moment frames in longitudinal direction. Further, after evaluating performance levels of the bridges, obtained results were compared with damage indices and difference between structural specifications and mentioned indices was indicated. The nonlinear static analysis procedure was used to analyze models. For evaluating damages, energy, effective stiffness and, Park-Ang damage indices were used. Independence of indices from geometric changes of structures, high adaptation of Park-Ang index with energy index due to use of energy as a common concept and more accurate results of energy damage index in each performance level are some of results.

Cable-stayed bridges are vital structures which need significant maintenance and repair costs every year. Therefore, health monitoring of such structures can mitigate human and financial losses. In this paper, a damage detection method for cable-stayed bridges is proposed using signal processing and clustering. Since the accuracy of signal processing can considerably affect the accuracy of damage detection results, in the first part of the paper, a comparison is carried out between the popular FDD method and two newer AFDD and TDD methods which have improved some of the FDD drawbacks. Then, the most effective method is selected. Among these procedures, FDD is successfully implemented in signal-based procedures. However, the two newer ones have not adequately investigated in comparison to FDD. In the second part, by using competitive neural network for clustering, a new damage index is introduced by calculation of the Euclidian distances of cluster centers. Results show that the proposed damage detection algorithm can differentiate healthy and damage states with acceptable accuracy.

Settling basins are one of the most important structures is commonly used for deposition of sediment particles in water and wastewater systems, in order to prevent the damage of sediment particles. The purpose of this study is to provide a one-dimensional numerical model for simulating flow and sediment in a rectangular sedimentation tanks. The governing equations are depth averaged equations of flow and sediment transport. In order to the numerical solution, the finite difference method has been used. The model can be used for non-uniform flow and non-uniform particles and could predict important information such as removal efficiency, thickness, and distribution of particle size of sludge. Comparison of the results of the proposed numerical model with the results of other researchers stated the acceptable accuracy of the proposed model, so that in all cases the error rate was less than 3%. The results of the sensitivity analysis showed that more than 50 percent of suspended sediment deposited at the first 5 meters of the basin; therefore, the increase in the dimensions of the rectangular reservoir is not the best way to improve the performance of the pond. In fact, increasing the removal efficiency can be achieved by reducing the depth of the settling basin, increasing the cross-sectional area of flow and reducing the surface loading rate.

In recent years the rupture of landfill centers has resulted in the importance of studying the behavior of municipal solid waste (MSW). MSW as the main constituent element in landfills has a complicated performance. In this study, by using the results of large – scale direct shear experiments with dimensions of 300 mm x 300 mm x 150 mm, 2 models to predict the behavior of MSW with ages of fresh and 3 months are presented. The purpose of this investigation is to predict MSW stress-strain behavior for kahrizak landfill as a sample of developing countries landfills under aging and by structural models. These models are Hyperbolic model and Evolutionary polynomial regression (EPR). In these collection of experiments, aging process up to 3 months, was artificially applied to samples. Three normal stresses 20, 50, 100 kpa and three shear strain rates 0. 8, 8, 19 mm per minute were used for samples with different ages. The results of these two models, in addition to predict MSW behavior under aging and degradation, shows high accordance with experimental results by direct shear apparatus. Finally this study states the advantage of EPR model relative to Hyperbolic model in higher accuracy for all experiments.

The Mixed Least Squares Meshfree (MDLSM) method has shown its appropriate efficiency for solving Partial Differential Equations (PDEs) governing the engineering problems. The method is based on the minimizing the residual functional. The residual functional is defined as a summation of the weighted residuals on the governing PDEs and the boundaries. The Moving Least Squares (MLS) is usually applied in the MDLSM method for constructing the shape functions. Although the required consistency and compatibility for the approximation function is satisfied by the MLS, the method loss its appropriate efficiency when the nodal points cluster too much. In the current study, the mentioned drawback is overcome using the novel approximation function called Mapped Moving Least Squares (MMLS). In this approach, the cluster of closed nodal points maps to standard nodal distribution. Then the approximation function and its derivatives compute noting the some consideration. The efficiency of suggested MMLS for overcoming the drawback of MLS is evaluated by approximating the mathematical function. The obtained results show the ability of suggested MMLS method to solve the drawback. The suggested approximation function is applied in MDLSM method, and used for solving the Burgers equations. Obtained results approve the efficiency of suggested method.

Various uncertainties exist in the engineering problems, so it is necessary to study these problems from probabilistic point of view. This paper aims to evaluate the interactions between new tunnel over – crossing the underlying existing tunnel. Metro line-6 tunnel above-crossing line-7 tunnel in Tehran was chosen as a case study project. In this study the numerical investigation was performed using the FLAC3D software and cohesion and friction angle of third layer and the surcharge on the ground level were assumed as random variables. Generating the random numbers and fitting the probabilistic distributions to the geotechnical variables was done using the Monte – Carlo method. The displacements at four points of existing tunnel (line 7) were recorded due to new tunneling and the appropriate probabilistic distribution was fitted according to the mean, median and skewness of each set of random numbers. According to these probabilistic distributions the probability of occurrence of the displacements more or less than a specific displacement can be determined. The results indicated that although input parameters have normal distributions, not all the outputs have symmetric or normal distributions and the results of deterministic method aren’ t as the same of mean values of stochastic approach. For all random parameters the probability of displacements greater than the mean value at the bottom and right side of the existing tunnel due to the new tunneling is 56 % and 55/5 %, respectively.