Scientia Iranica
Volume:24 Issue: 1, 2017

The behavior of SiO2 and metakaolin in aggressive environment when used separately as a supplementary cementitious material was studied for three different replacement levels: 5%, 10% and 15%. SiO2 and metakaolin were used in two states namely unground and ground (ultra-fine). Ultra-fine state was achieved by subjecting the mineral admixtures to grinding in a planetary ball mill for an optimum period of one hour. The microstructure of the unground and ground mineral admixtures was studied using Scanning Electron Microscope and X-Ray Diffraction. The compressive strength of these systems in normal and aggressive environment was tested after initial curing in water for a month and subsequent curing in acid or base environment for a period of three months to arrive the rate of deterioration. The rate of corrosion in rebars was also determined using Half-cell potential method. The results obtained from the tests were compared with control concrete. From the results it was understood that concrete with 10% ground SiO2 and 5% ground metakaolin provided better resistance to deterioration and corrosion. It also exhibited improved microstructure as well as filler action. Comparing the results of two admixtures, performance of concrete with ground metakaolin found to be better than ground SiO2

Structural engineers have recognized unstiffened Steel Plate Shear Wall (SPSW) as an economical lateral resisting system, due to the post-buckling capacity, energy dissipation and deformability. This study investigates practical application of an added Energy Absorbent Element (EAE), subjoined to the SPSW in order to improve seismic behavior of the SPSW.The EAE is an aluminum shear panel with or without bracings and surrounding frame. Furthermore, a series of parametric studies are implemented to examine the effect of dimensions, position and formation of the EAE. It is assumed that the lateral loading is applied as quasi-static loading. Further, nonlinearity of the material and the geometry are included in the models. The results reveal that by adding the EAE adjacent to the surrounding frame of the SPSW, not only dissipated energy but also ultimate strength of the system can be efficiently increased.

Ski jump is one of the most e ective structures in energy dissipation over spillways. Spillways have long been of practical importance to safety of dams. The major criteria in hydraulic design are based on the analytical and empirical methods. In the current study, in order to increase chute spillway eciency, a multi-objective evolutionary algorithm known as the Non-dominated Sorting Genetic Algorithm II (NSGA-II) has been utilized to design the optimal triangular bucket angle and chute width. In design method, two separate objective functions have been used. In the rst objective function, equations of dynamic pressure of the bucket, the jet length after bucket, and the scour depth have been used. The second objective function is related to construction volume of chute spillway. For calibrating the rst objective function, characteristics of Karoon III dam have been used as a case study. The di erence between design parameters of Karoon III spillway and those from NSGA-II algorithm method is less than 12 percent. According to the results, if the jet length is considered as the most impressive parameter in the rst objective function, design of the spillway becomes frugal.

In geostatistical analysis, spatial interpolation at any unmeasured point is done using the parameters of a variogram model that matches the experimental data. Several variogram models can be used and the accuracy of the spatial map produced depends on the selection of the most appropriate variogram model that fits the spatial distribution of the experimental data. Therefore, in this study, a multiple-criteria decision-making method, Analytical Hierarchy Procedure (AHP), is used to evaluate and select the best variogram model for mapping spatial rainfall in the upper reaches of the Kelang River basin in Malaysia. Using daily rainfall data from 71 rain gauge stations, geostatistical analysis was done with the Ordinary Kriging interpolation method and 5 alternatives of variogram models, namely Spherical, Tetraspherical, Pentaspherical, Exponential and Gaussian for spatial rainfall mapping. The accuracy of the spatial rainfall map was evaluated using four criteria of spatial interpolation error indicators, which are Root-Mean-Square Error (RMSE), Average Standard Error (ASE), Mean Standardized Error (MSE) and Root-Mean-Square Standardized Error (RMSSE). The results showed that the Spherical model was ranked at the top for producing the best spatial rainfall map of the study area.

Recently, there has been lots of studies about ductility reduction factor of CBFs, because AISCs seismic design provision has been changed significantly since 2010, So a comprehensive study is needed for seismic designing and ductility reduction factor of CBFs. In this study, about 160, 2D CBFs with different types of bracing are designed according to AISC-341, and ductility reduction factor of designed frames is compared for types and form of bracing in the height of frames. The results confirm that ductility reduction factor and response modification factor of CBFs, are mostly dependent on types and form of bracing. Also, maximum allowable height of OCBFs Can be reduced for some types of bracing and increased for some other types of bracings. for SCBFs ductility reduction factor depends on the bracing type and number of frame stories. For most of studied SCBFs, ductility reduction factor can''t be achived for more than ten-story frames, so for these kind of frames, maximum allowable height should be decreased or smaller response modification factor should be used. For double large scale CBFs, Because of the enormous stiffness of one to seven story frames, ductility reduction factor can''t be obtained and smaller response modification factor should be used.

In seismic resistant design of moment frames, the structure behavior under earthquakes has to be examined, considering various damage criteria. Damage indices can be estimated by using endurance time (ET) method with minimum computational effort. The quality of this estimation can be improved in different ways. In this paper, the graphs of a certain damage index versus natural period of the structure, called damage spectra, are produced applying intensifying ET records and scaled ground motions (GM). Then the excitation duration of ET acceleration functions (target time) is modified in order to reach acceptable consistency between ET and GM damage spectra. Moreover, various damage indices of a steel moment frame at two hazard levels are evaluated via nonlinear time-history analyses of the structure under scaled earthquakes and ET records. It is observed that the frame damage estimation can be improved by modifying the target time of ET records based on damage spectra; in addition, in most cases, there are negligible discrepancies between values of frame damage indices corresponding to ground motions and ET acceleration functions with the damage-based target time.

Waste tires are extensively being used in civil engineering applications to improve flexibility and elastic properties of the base foundation material. Moreover, by using pure tires or soil-tire mixtures, rubber stockpiles which cause lots of environmental contaminations are being consumed. The objective of this research is to study the strength and modulus variations of sands when combined with rubber materials in different sizes and percentages. To this reason, triaxial experiments were performed on various sand-rubber mixtures using static triaxial apparatus. Samples were constructed at the maximum dry density and optimum moisture content to consider engineering applications in dry regions. The results show that rubber content and rubber-sand particle size ratio,D50,r/D50,s, significantly affect the mixture behavior in the manner which increase in the former and decrease in the latter leads to more softening behavior. Furthermore, specific combination of sand and rubber which may improve the elastic properties of the mixture is proposed as a base flexible layer.

In this study, the effect of Styrene-Butadiene-Styrene (SBS) modification on physical and mechanical properties of hot mix asphalt, in terms of fatigue characteristics, are evaluated.As such, 87 samples were prepared using 15 different mixtures, and the repeated load-fatigue indirect tensile test was applied to these samples using a Süleyman Demirel University (SDU) asphalt tester apparatus. In addition, it is also used to analyze the effects of gradation, bitumen percentage, loading, and polymer type on fatigue behavior. 18 control samples were prepared to analyze the effect of SBS modification on fatigue performance. The other objective of the study is to present the reliability of the computer controlled repeated loading test apparatus. Linear regression and Adaptive Neuro Fuzzy Inference System (ANFIS) was used to analyze the results of the test, and models were developed and analyzed in terms of modeling. At the end of the study, the variables that are effective in improving the fatigue performance are addressed in detail, as well as the ANFIS environment likely to be used in non-linear modeling of such studies.

Dynamic compaction is a useful economic method for improving different soil types, especially loose sandy fills. However, the method has been rarely used in the vicinity of slopes due to stability concerns. In this research, dynamic compaction method adjacent to slope edge was numerically simulated using 2D plain-strain finite element models. Stability of slope models under different compaction energies and slope geometries at the same initial static factor of safety (FS) was investigated considering different stability criteria. These criteria include peak particle velocity (PPV) or peak particle displacement (PPD) on the slope, rate of change in plastic volumetric strains, yield stress ratio on the induced slip surface and the ratio of crater depths in flat and sloped models. Safe compaction distances from slope heel were calculated for different criteria and it was concluded that PPV criterion yields the most conservative distances but PPD criterion almost shows the smallest safe distances. Based on comparison of different criteria, it was concluded that combination of yield stress ratio and rate of plastic volumetric strain achieves the most acceptable safe compaction distance values for consideration in slope stability analyses.

Geocell is an effective type of geosynthetics for improving the performance of reinforced soil foundations due to provision of lateral confinement for the infill soil. In this research, in order to study the bearing pressure-settlement response of geocell reinforced sand, a reduced-scale physical model is developed and geocells with various geometrical dimensions (height, pocket size and width) produced from woven geotextile are used to reinforce sand bed. Strip footing model is then loaded monotonically to ultimate failure level and the influence of geocell geometrical properties on the improvement in bearing capacity and settlement of footing is described. The results show that by increasing height and decreasing pocket size of geocell, the beneficial effect of geocell reinforcement increases substantially. For the highest geocell used in the tests at settlement level of 6%, improvement in bearing capacity and percentage reduction in footing settlement is obtained as 2.1 and 48% respectively. The optimum width of geocell is determined five times the foundation width beyond which the improvement effect is negligible. It is also concluded that substituting a single layer of geocell reinforcement with 2 half-height and 4 quarter-height geocell layers results in 10% and 22% decrease in the ultimate bearing capacity respectively.

Topographical and mechanical properties of soil layers can lead to amplification or attenuation of seismic waves. Such a phenomena can be theoretically explained by means of ground response analysis. Definition of boundaries is of great concern in modeling ground response and application of boundaries with any constrain can lead to so called “trap box” effect in seismic waves in the model and hence to fictitious results. In present study, two-dimensional Finite Element Method (FEM) is applied in which boundaries known as “absorbing boundaries” are used to study the effect of wave scatter in valleys with different forms on the amplification or attenuation of SV waves. Comparison of the results is conducted for the current approach and those of the coupling Finite Element and the Infinite Element (sometimes called as FE-IFE) method. The results are also presented in non-dimensional diagrams of Au and Av for horizontal and vertical displacement amplitude respectively, through the valley span and its surrounding area. Comparison of the results also indicated that the proposed boundaries can improve the seismic analysis when coupled with the FEM. Also because of topographic irregularities, variations of displacement are seen inside the valley and around it.

In this article, a new approach is presented to solve the double-track railway rescheduling problem, when an incident occurs into one of the block sections of the railway. The approach simultaneously considers three rescheduling policies: cancelling, delaying and reordering. To find the optimal conflict-free timetables compatible with the approach, a mathematical model and an exact three-phase solution method are proposed. The method is based on Branch-and-Bound (B&B) algorithm. The lower bound consists of two cost parts: the cost of deviation from the primary timetable and the cost of train cancellation. To generate an appropriate upper bound, the method exploits an innovative algorithm called «Local Left Shifting». A heuristic beam search technique is also developed for tackling the large-scale problems. An experimental analysis on two double-track railways of the Iranian network indicates that the proposed solution method provides the optimal solution in much shorter time, compared with the time taken to solve the mathematical model by CPLEX software. Based on the findings of this research, it is possible to optimally retrieve the primary timetable after incident occurrence during a pre-determined time horizon.

In the present study, the non-metal acoustic waves monitor, TH204 has been used to determine P-wave velocity of compacted expansive soil under the condition of drying-wetting cycles with constant amplitude, to explore the change in P-wave velocity of compacted expansive soil with the cyclic number, cyclic amplitude and control moisture content. The results show that the P-wave velocity of the compacted expansive soil follows a non-linear decrease with increasing the cyclic number and tends to be stable. Also, under the conditions of equivalent control moisture rate and cyclic number, the cyclic amplitude has a great effect on the P-wave velocity of expansive soil. Thus, with increase in the cyclic amplitude, the P-wave velocity is decreased. Secondly, under the same cyclic number, the P-wave velocity changes with the control moisture rate monotonously. Further, the study shows that the peak values of P-wave velocity appear near the optimum moisture rate, and the peak value position remains unaltered with change in cyclic amplitude

In this paper, a node adaptive rearrangement is presented based on the estimated error in various domains for some problems in the fracture mechanics by Discrete Least-Squares Meshless method (DLSM). This method is one of the approximate methods recently introduced and used in the various elds. The method is based on minimization of the least-squares functional with respect to the nodal parameters, and it uses moving least-squares method for calculating the shape functions. Due to the natural process of problem solving, after calculating the shape functions, the residuals are calculated and their values are considered as an objective function for rearrangement of the nodes. There are three popular methods for constructing shape functions in discontinuous domains, and here, the transparency method is utilized. Similar to other numerical methods, there are di erent procedures for re nement and improvement of the results; however, adaptive rearrangement can be employed without increasing the computational cost. In this paper, the Charged System Search (CSS) algorithm is used as a tool for adaptive rearrangement or repositioning process. Eciency and e ectiveness of the proposed adaptive rearrangement technique is tested by some benchmark two-dimensional crack examples with available analytical solution around crack tips.