Scientia Iranica
Volume:23 Issue: 1, 2016

To support evaluation and selection processes in engineering, formal decision making methods can be used. A great number of works applying diverse multiple criteria decision making (MCDM) techniques for engineering problems have been published recently. A new approach of hybrid MCDM methods has been developing rapidly during the past few years. The current paper aims at filling the gap and to summarize publications related to applications of hybrid MCDM for engineering. The study is limited solely on papers referred in Thomson Reuters Web of Science Core Collection academic database. It aims to review how the papers have been distributed by period of publishing and by country, which multiple criteria decision making methods have been used the most frequently in developing hybrid approaches and in what domains the methods have been applied. For a more detailed analysis of applications, journal articles from engineering research area were grouped by research domains and further by analyzed issues. Findings of the current review paper confirm that hybrid MCDM approaches, due to their abilities in integrating different techniques, can assist in handling miscellaneous information taking into account stakeholders’ preferences when making decisions in engineering.

This paper describes a methodology to develop the interface between a finite element software and optimization algorithm for optimization of concrete high arch dams. The objective function is the volume of the dam. The numbers of design variables are 31 including the thickness and upstream profile of crown cantilever, left and right abutment thickness, radius of curvature of water and air face left and right by use of polynomial curve fittingand cubic spline function. The constraint conditions are the geometric shape, stress and the stability against sliding. Initially, a program is developed in MATLAB in order to generate the coordinate of nodes, then finite element software ANSYS is taken for modeling the geometry of dam. Finally, the optimization technique is performed by Simultaneous Perturbation Stochastic Approximation algorithm. To include dead weight of dam body, stage construction is considered. The proposed method is applied successfully to an arch dam and good results are achieved. The results indicate that the concrete volume of the dam optimized is reduced by an average 21%. Compared with the initial shape, the time of convergence of this method is very short and the method is fairly effective. It can be applied to practical engineering design.

This paper aims to investigate the likely effects of geogrid reinforcement configuration on footings bearing capacity. Using geogrids reinforcement layers with certain total areas in various uniform and non-uniform arrangements, the bearing capacities of footing models on reinforced sand beds were determined and compared. The first arrangement was the conventional uniform layout in which 3 geogrid layers of equal dimensions were considered. In the second group the same amount of geogrids were used in a trapezoidal profile in which smaller size geogrid were placed at upper layers and the geogrid dimensions increased with embedment depth. The third group consisted of arrangements in which the same amount of geogrids were used in an inverse trapezoidal layout i.e. the layer sizes decreased with embedment depth. The effect of soil density on the footing performance was also investigated. The tests results indicated that in all soil densities, the greatest bearing capacities were obtained for the sand beds reinforced with inverse trapezoidal reinforcement layouts while the least bearing capacities were determined for trapezoidal arrangements.The improvement ratio of bearing capacity due to geogrid reinforcement varied from 1.8 to 5.35 depending on the reinforcement layout and the sand bed density.

Imputation of missing data is a critical part of accurate data analysis and modeling. This paper presents 3D imputation as a new data-driven methodology to estimate missing values in time series data. The method is based on the assumption that all the observed data in a time series are related with each other and with data of the some other series. The available data is placed in a three-dimensional space so that the increasing or decreasing relationships between the observed data are appropriately represented. For the estimation of each missing value, the method searches and determines the best possible group of estimator data within the data space. Di erent data groups are found and used for the estimations of each individual group of missing data. The method is validated by removing and estimating all the observed monthly flow data of Saraykoy station on Buyuk Menderes River in Turkey. Data of the downstream Burhaniye station constituted the second data layer in the model. High correlation values were obtained for all years between observations and estimations and the missing data of Saraykoy station was also estimated by using the proposed method.

Retaining walls are one of the most common geotechnical structures. Horizontal displacement at the top of the retaining wall is an important parameter in design of retaining structures because of serviceability of the wall and adjacent structures. In this research, the Gene Expression Programming (GEP) is used for developing a model to predict this design parameter of retaining wall. The input parameters of the model consist of e ective period of adjacent structure, horizontal and rocking sti ness of the foundation of adjacent structure, density, Young''s modulus, and friction angle of granular soil as well as the thickness and height of retaining wall. The output of the model is maximum lateral displacement of retaining wall. A database including 240 cases, created from 3D nite element modeling of a soil-retaining wall with an adjacent steel structure modeled as surcharge, is employed to develop the model. Comparison of the GEP-based model predictions with the simulated data indicates a very good performance and ability of the developed models in predicting maximum lateral displacement of retaining walls. Sensitivity and parametric analyses are conducted to verify the results. It is shown that soil density is the most in uential parameter in the maximum lateral displacement of retaining wall.

RC beams strengthened by external bonded FRP reinforcement often fails by one of several possible debonding modes. Although many experimental studies have been performed to assess the flexural behavior and failure modes of FRP-strengthened RC beams under monotonic loads, the flexural performance of these elements under cyclic loads have rarely been examined. The present paper illustrates the results of an experimental study aimed at better understanding of the structural behavior and debonding failure mechanisms of FRP-strengthened RC beams under monotonic and cyclic loads. This experimental research program is made of flexural tests carried out on eight RC beam specimens with dimensions of 150 mm width, 200 mm height, and 1800 mm length externally strengthened with CFRP laminates and tested under monotonic and cyclic loading. Three specimens were considered as control specimens. The remaining five specimens were strengthened in flexure by CFRP laminates. This program investigated structural behavior and debonding failure trends in the FRP-strengthened beams. Results of this investigation are presented in the form of load-deflection curves and FRP strain profiles.

In this paper, optimal design and assessment of the capability of tuned mass dampers (TMDs) in improving the seismic behavior of confined masonry walls as the main element of historical buildings has been studied. For this purpose, the design parameters of TMDs have been determined through the minimization of wall response using Genetic algorithms (GAs). For simulation the behavior of confined masonry wall under earthquake, the triple linear shear beam model has been used. For illustration, the method has been tested on confined masonry walls equipped with linear TMDs. To study the effects of frequency content and peak ground acceleration (PGA) of earthquake records on the performance of TMDs, the controlled walls have been subjected to different earthquake records. Results have shown that the proposed method has been effective in designing optimal TMDs regarding the convergence and simplicity behavior of GA in solving the optimization problem. It has also been shown that using TMD enhances the seismic behavior of confined masonry walls which its efficiency depends on the earthquake characteristics and the mass ratio. Finally, it can be concluded that the results of this research could be used as guides to design TMDs for historical and heritage buildings.

In most construction projects, human resources account for 30 to 50 percent of all project costs, thus it is an important cost element in construction projects. However, the complexities and uncertainty of work ow have made it dicult to predict human resource costs. The most e ective and economic management approach is computer simulation which has a better ability to understand and identify the dynamics and statics of a case research system. One of the steps of simulation is modeling, and choosing the best modeling approach for prediction is very important. Agent-based modeling, which is referred to by some as a third way of doing science«, was chosen to predict labor cost impacted by many factors in the work flow. In our research, the increased labor cost, based on factors a ecting work ow, is 16 percent on average, which is predicted more accurately by the simulated model than by planned cost.

This research introduces an approach to predict maximum scour depth, scour hole length, and the length of the deepest point of the scour hole at equilibrium conditions at downstream of stilling basins by using the GEP. Five non-dimensional parameters in terms of physical properties of bed sediments, stilling basin length, tail water depth, and discharge of spillway were considered as input variables to evaluate the scour hole geometry. The GEP model was developed using experimental datasets collected from literature. Results of the GEP models were compared with those obtained using ANFIS and non-linear regression analysis. Performances indicated that the proposed GEP models to characterize scour hole geometry produced more accurate results than the other methods. In addition, results of sensitivity analysis to de ne the most e ective independent parameters on scour hole geometry were reported. Finally, proper application of the proposed model has been con rmed as the GEP-based best formulation, which is a useful soft computing tool for prediction of scour hole geometry at downstream of a stilling basin.

One of the important factors a ecting the quality of concrete is the placement of fresh concrete inside the formwork. Inadequate compaction is a common problem in concrete technology. In this study, the e ect of inadequate compaction on compressive strength and ultrasonic pulse velocity of concrete exposed to elevated temperature is examined. For this purpose, various compaction rates were applied during the casting stage of concrete in order to simulate various levels of inadequate compaction. Four di erent water-cement ratios (0.50, 0.40, 0.38, and 0.35) were selected. All concrete specimens were exposed to 450 or 900C for one hour. The Taguchi approach was used to reduce the number of samples. The results were evaluated by the Analysis of Variance (ANOVA) method. Test results showed that inadequate compaction played a signi cant role, more than curing time, in the compressive strength after high temperature exposure.

During recent years, processed used tires such as tire shreds, tire chips, tire bungs, and tire crumbs have been applied in order to improve the mechanical properties of soil mixtures. Finding more bene cial ways of using waste tires, this paper assessed the influence of adding tire crumbs to a clayey soil which was a ected by freeze-thaw cycles. Freeze-thaw cycling is a weathering process which occurs in cold climates during winter and spring and considerably changes the engineering properties of soils. In the present study, a clayey soil was mixed with six di erent percentages of tire crumbs (0, 0.5, 1, 1.5, 2, 2.5) and evaluated by triaxial compression tests under three di erent con ning pressures (30, 60, 90 kPa) after the soil was subjected to 1, 3, 6, and 9 cycles of freeze-thaw. It has been found that for the investigated soil, using 2.5% of tire crumbs decreases the cohesion reduction ratio by about 24% and the resilient modulus reduction ratio by about 6-42% during the cycles. Hence, although the addition of tire crumbs does not considerably a ect the strength reduction of soil during freeze-thaw cycles, it can reduce the changes of cohesion and resilient modulus of the soil, e ectively.

In this article, transverse vibration of an Euler-Bernoulli beam carrying a series of traveling masses is analyzed. A semi-analytical approach based on eigenfunction expansion method is employed to achieve the dynamic response of the beam. The inertia of the traveling masses changes the fundamental period of the base beam. Therefore, a comprehensive parametric survey is required to reveal the resonance velocity of the traversing inertial loads. In order to facilitate resonance detection for engineering practitioners, a new simpli ed formula is proposed to approximate the resonance velocity.

The method of Zero Extension Lines (ZEL) has been used to evaluate the static and seismic active lateral earth pressure on an inclined wall retaining inclined c-f backfill. The equilibrium equations along the Zero Extension Lines have been solved using the finite difference method. A computer code is prepared to analyze the retaining wall, calculate the ZEL network and the distribution of the active lateral earth pressure behind the retaining wall. The total active force on the retaining wall was defined as the lateral earth pressure coefficients due to the soil unit weight, the surcharge and the soil cohesion. The variation of the active lateral earth pressure coefficients with changes in different parameters, such as the inclination of the earth and wall, the friction angle of the soil, the adhesion of the soil-wall interface, the horizontal and vertical pseudo-static earthquake coefficients have been obtained. The results have been obtained for soils with associated and non-associated flow rules. The effect of the dilation angle has also been considered. The results obtained in this study are very close to those of other methods and confirm that the ZEL method can be successfully used to evaluate the lateral earth pressure of retaining walls.

In this paper, the approximate analytical solutions of Camassa-Holm, modified Camassa-Holm and Degasperis-Procesi equationswith fractional time derivative are obtained with the help of approximate analytical method of nonlinear problem called the Homotopy Perturbation Method (HPM). By using initial condition, the explicit solution of the equation has been derived which demonstrate the effectiveness, validity, potentiality and reliability of the method in reality. Comparing the methodology with exact solution shows that the present approach is very effective and powerful. The numerical calculations are carried out when the initial condition in the form of exponential and transcendental functions and the results are depicted through graphs.