نشریه مهندسی عمران
سال پنجاه و دوم شماره 12 (اسفند 1399)

Today, glasphalt technology is considered as an efficient way to reduce asphalt production costs, reduce fuel consumption, and reduce environmental pollution caused by the production of this type of waste. Despite the advantages of glasphalt, moisture damage is a weak point for these types of mixtures. The present study evaluated the moisture sensitivities of glasphalt and HMA and compared the performance of these two types of mixtures, along with the effects of two types of additives, nano hydrated lime and nano calcium carbonate on moisture damage. The moisture sensitivity of both types of mixtures was evaluated using a modified Lotttman test and a thermodynamic test of Wilhelm plate based on surface free energy methods. The results of the indirect tensile strngth test showed that the resistance of glasphalt in dry conditions was higher than that of HMA. However, glasphalt are exposed to wet conditions with a higher resistance to HMA. The results obtained from the thermodynamic test also showed that the modification of both types of asphalt binder (AC 60-70 and AC 85-100) using nano hydrated lime and nano calcium carbonate increases the total surface free energy and adhesion of the bonding of both types of base asphat binders. This increase improves the strength of mixtures made with this type of asphat binders against moisture damage of cohesion type, which is a positive effect in reducing the moisture damage.

The concrete structures used in various applications including iron and aluminum foundries and hazardous waste disposal lose performance when subjected to heat. As aluminum silicate materials however, geopolymers behave in a much more stable manner than normal concrete when exposed to high temperatures. Calcium silicate hydrate (C-S-H) and calcium-aluminum-silicate-hydrate nanostructures, which are products of the geopolymerization process that strengthens geopolymer concrete, undergo many changes when exposed to heat. The study therefore investigates the effect of high temperatures on geopolymer concrete’s strength parameters from a microstructural perspective and according to nanostructural changes of C-S-H and C-A-S-H.

In this regard, about 300 samples were cured in the humidity bath for 1, 3, 7, 14, and 28 days. All samples were then put in of 25, and 900°C temperatures for 2 hours. Length and weight change percentages, compressive strength, and ultrasonic and cracking behavior tests were performed on all samples. Images from the (SEM) and the energy-dispersive X-ray (EDX) analysis were also used to evaluate the microstructural behavior of samples in various temperatures.

According to the results, sample weight and length changes and compressive strength depended on the behavioral nature of C-S-H and C-A-S-H nanostructures. Nanostructural analysis of C-A-S-H points to high temperatures reducing compressive strength and weight as well as causing more cracks. The compressive strength of the 28 samples in 900°C temperature also decreased from 604 kg/cm2 to 75 kg/cm2. The complete disintegration of the C-S-H and C-A-S-H nanostructures.

As an essential infrastructure of cities, public transit networks have special importance in decreasing traffic congestion and air pollution. Metro network is known as the most efficient mode of public transit due to green. Usually, based on evaluation indices, a suitable approach to the development of a metro network is chosen. In this study, the mixed evaluation index is composed of two component that they are shape and service points. The shape point is calculated by utilizing network length, topology characteristics, station density, and average edge length (integer value between zero and ten). Also, annual passenger and passenger per unit length are utilized to calculate the service point (between zero and one). Metro network data of 52 cities in the world are collected. Based on the mixed index, the score of Tehran and New York metro network are equal to 4.390 (rank 29) and 8.506 (rank 1), respectively. Metro networks are classified into three groups based on connectivity and complexity indices with utilizing fuzzy c-means (FCM) clustering method. Results indicated that the Tehran metro network is a relatively developed system. Another classification with fuzzy boundaries based on average line length and total number of stations is accomplished. This classification results in the Tehran metro network is partly a regional accessibility system. Finally, Results of regression models based on the world trend indicate that currently, length and number of stations of the Tehran metro network should be equal to 206.3 km (31.1 km deficiency) and 147 (8 stations deficiency), respectively.

The high costs of meshing, required problem dependent fundamental solutions, singularity, modeling all over the domain and … are the most important weaknesses in the common numerical mesh methods for solving continuum mechanics problems. In this study, aiming for eliminating some of these shortcomings, one of the well-known Radial Basis Functions (RBF) methods, Multiquadric (MQ), was developed for analyzing 2D seismic waves in reservoirs of rigid dams. In this regard, the Helmholtz equation and the governing complex boundary conditions are reproduced using MQ function in the frequency domain. The results showed that using the real and complex forms of the MQ function, the computational time will be optimized for frequencies smaller and larger than the natural frequency of the reservoir, respectively. Also, to determine the most important factor in accuracy and convergence of MQ method, the optimal shape parameter, firstly the inefficiency of some of the previously introduced methods was shown, then a new high-speed algorithm was presented. The results of this research show that the optimal shape parameter can be formulated in terms of the frequencies of earthquake loads. This advantage simplifies considerably application of MQ method in this particular problem and reduces its computational time. The high accuracy of the present method compared to the exact solutions was shown in two different examples with and without considering effects of sediment absorption. The achieved high accuracy is due to a continuous estimation function defined all over the domain and using an exact algorithm for finding the optimal shape parameter.

In this study, lateral response of masonry walls with openings is studied. The numerical modeling and analysis is followed and the developed models are validated using available experimental results.Samples selected for validation analysis include two masonry walls confined with reinforced concrete perimeter ties and one masonry wall with no ties. Validity of the numerical models has been established against the experimental samples within Abaqus software using nonlinear static analysis. Variation in the size, location and aspect ratio of the opening are taken into account and the lateral stiffness and strength of the walls are calculated. In addition, a series of equations have been developed based on strength of materials for simple calculation of lateral stiffness, strength and ductility of masonry walls with opening. This has the important advantage of avoiding complex and time consuming 3D nonlinear finite element analysis for the same purpose. To do this task, three different cases of failure are accounted for the walls including: when presence of the opening is not effective, when behavior of the two piers besides the opening is governing, and when the overhead lintel governs the lateral behavior of wall. Each of the mentioned cases are in turn divided into other sub-cases and several nonlinear finite element analysis have been undertaken. Results of the developed analytical equations are compared and calibrated with those of the finite element analysis and desirable accuracy of the relations developed in this study is confirmed.

Impacts of climate change on water resources will force decision-makers to adopt climate change adaptation policies in order to reduce social-economic problems and difficulties resulting from it and water resource sustainable development. One of the adaptation methods is to increase water use efficiency in agriculture that will adjust climate change impacts include decreasing runoff and increasing water demands. In this study, the impact of water use efficiency as a climate change adaptation approach is assessed in the optimal operation of JAREH dam. Fifteen climate change scenarios were generated by using downscaling technique on CMIP5 data for the near (2020-2044) and far (2070-2094) future. Based on these scenarios, time series of reservoir inflow and downstream water demand were projected for both future periods. An optimization model is developed considering the water efficiency coefficient parameter in order to define four water use efficiency scenarios (0-S1, 0.1-S2, 0.3-S3, 0.5-S4). Results show that reservoir inflow decreases up to 18.8% and water agriculture demand increases up to 29%. The amount of water allocation would increase up to 18.7% in the future periods than in the baseline period under S1 scenario to supply the increased water demand, which may decrease reliability of reservoir system for water allocation. Increasing water use efficiency coefficient up to 0.5 in the future periods would increase system reliability up to 20% that will reduce social-economic problems caused by climate change impact in this study area.

In the present study, the effect of vertical drop, gradually expanding and vertical screens are investigated to increase the efficiency of the energy dissipation of the flow. The experiments were carried out in a horizontal laboratory flume with a rectangular cross section, two vertical drop heights, and the wall expanding ratios of 0.5 to 1, the porosity ratio of the screens of 40% and 50%, and The range of Froude number of 0.86-0.92. The results showed that the use of screens and expansion of the walls would increase energy dissipation and decrease the pool depth and the downstream depth. The application of expanding wall, screen and the effect of simultaneous use of screens and expanding walls increases the efficiency of energy dissipation by 25, 44 and 48 percent, respectively. The porosity ratio of the screen is not much efficient in energy dissipation, but it reduces the pool depth and increases the downstream depth. In the same hydraulic conditions, energy dissipation is increased and the depth of the pool decreases by increasing the height of the drops due to the increased jet severity over the drop striking the downstream bed. By increasing the discharge, the hydraulic jump formed in the upstream of the screens with a porosity ratio of 40% is submerged and moves upwards. However, in screens 50% of the jump is free and moves downward.

This work uses the H_∞ static output-feedback controller with linear matrix inequality (LMI) theory and some variations in LMI variables for retrofitting the shear structures against a variety of uncertainties as well as the dynamic forces of the earthquake and wind. To prevent the system from losing control due to the failure of the central controller, preventing the large amount of data transfer between sensors and controller, as well as economic issues, the discussion of the replacement of a centralized control with decentralized control in various types, including fully decentralized controller, partial coupled and uncoupled decentralized controllers is studied. Then the robustness of the method is evaluated both in centralized control and in decentralized control against dynamic forces such as earthquakes, uncertainty in earthquake excitations and failure of sensors, and are compared with each other. Finally, the responses obtained from the control algorithm used are compared with the results of the linear quadratic regulator control (LQR). Two numerical examples are solved for this assessment. A 5-story shear building structure and a 20-story bench mark structure. Based on the results, the algorithm is completely resistant to the failure of the sensors, as well as decentralized controllers have very close results to the central controller. The uncertainty of earthquake provokes changes in responses, but the controlled responses are significantly less than uncontrolled responses. It should be noted that the method used reduces the responses considerably less than the LQR control method.

The purpose of this study was to evaluate the environmental risks of Alborz Dam on Bababrood River in Babol city, using multi-criteria decision making methods. Initially, environmental identification of the study area was carried out, Then a list of environmental risks identified in the construction and exploitation phase was prepared and presented to environmental experts familiar with the Alborz dam area in the form of a questionnaire. environmental risks scored by environmental experts based on three indicators, Severity of occurrence, Probability of occurrence, Then environmental risks ranking was performed using TOPSIS and Fuzzy TOPSIS methods. The most important risks of Alborz dam using TOPSIS method in the construction phase, respectively: Was Obtained, Destruction of forest within the dam with a score of 0.926, Displacement of reservoir residents with a score of 0.837 And in the phase of operation: Thermal stratification of dam reservoir with a score of 0.847, Landslide with a score of 0.751. Also, the most important risks of the Alborz dam using the Fuzzy Topsis method in the construction phase, respectively: Was Obtained, Displacement of reservoir residents with a score of 0.682, Demolition of forest within the dam with a score of 0.677, And in the phase of operation, respectively: Thermal stratification of dam reservoir with a score of 0.645, Landslide with a score of 0.630. Finally, one method of integration (average rating method) was used to resolve the conflict between the results.

In this study, the effect of geogrid on the ultimate bearing capacity of strip footing, which was imbedded on sandy soil and under eccentric loads (VM) was investigated by using PLAXIS 2D finite element software. After numerical verification, the effect of parameters, such as the amount of eccentricity, applied vertical force, the number of reinforced layers and layout of the layout of geogrid layers on the ultimate bearin capacity of strip footing were studied. The results of analyzes were presented in the form of dimensionless graphs. Based on the analyses result, the optimum depth of first geogrid layer from foundation (u), the vertical intervals of the layers (h), the number (N) and layout of the geogrid layers have been determined. The results of the analysis show that by adding the geogrid layers, the bearing capacity of footing under the eccentric load increases significantly. The amount of the effectivity is related to the layout of layers and and the amount of the eccentricity. In the optimum layout of the layers, the position of geogrid layers depends on the number of layers. Also, the optimum number of layers for obtaining the maximum bearing capacity at eccenric load condition was obtained to be 4 layres in the present study. The optimum depth for the first, second, third and fourth layers, at the optimal layout, was 0.5, 0.7, 0.3 and 0.9 meters from the base of the footing, respectively.

A designer needs to design a structure with the aim of obtaining the maximum possible load expected for the structure during its lifetime. In this paper, with regards to the information obtained from the earthquakes, the critical earthquakes were computed for a shear frame building, equipped with a belt truss system and subjected to two constraint scenarios. For this purpose, a nonlinear optimization problem has been solved, in which the objective function was the maximization of the roof displacement. In the first constraint scenario, the computed critical earthquake was known as the first state critical earthquake. In addition, for the second constraint scenario, the earthquake was named as the second state critical earthquake. In the first scenario, the energy and peak ground acceleration was considered as the constraints, while in the second scenario, the upper bound Fourier spectrum was added to these constraints. Finally, properties of the initial and critical earthquakes were investigated using the Fourier analysis method and continuous wavelet transform. The numerical results showed that the Fourier spectrum of the first critical earthquake was 6.86 times higher than the maximum values for the same parameter for other earthquakes at a frequency near the first natural frequency of the structure. Also, using time-frequency curve, it was shown that duration of the strong ground motion of all earthquake places within the dominant duration of the frequencies of the same earthquake was more than 10 sec.

Several factors can affect the responses of structures under seismic loads. The properties of the materials can be different from the parameters required in the design of the structures. This difference can affect the response of the structures. In this research, it is tried to investigate the effect of changing the characteristics of materials on the seismic response of a suspended cable bridge equipped with a RNC separator whit sensitivity analysis. A cable bridge with and without an RNC isolator has been analyzed dynamically nonlinear after initial modeling under a San Fernando record. Then, the effect of random variables on the response of these structures was investigated using Monte Carlo sensitivity tests and the second-order second moment (FOSM). Finally, the accuracy of the FOSM analysis method is evaluated in a Monte Carlo method. Two basic parameter, maximum deck displacement and maximum base shear was considered as structural responses. The results show that, among the specification of concrete strength materials, the yield stress of the reinforcement and the modulus of elasticity of the cables, the most effect on the seismic response of these structures. Also, the sensitivity of these parameters to the isolated bridge is less than the bridge without isolation.

In recent earthquakes, masonry structures have not been resistant to earthquake due to high weight and low ductility and low shear resistance, and they have experienced a lot of damage. The improvement and strengthening of masonry structures is a serious discussion in urban construction. The walls of masonry are not resistant to the earthquake and their basic weakness is in ductility; its ductility is reduced when the length ratio increases to the wall height, in addition to the wall resistance. The purpose of this study is to investigate the seismic performance of masonry structures with two aspect ratio of 0.5 and 0.7 with scale 1: 2 and strengthening of masonry walls using different layouts of steel tie. The analytical evaluation of seismic behavior of reinforced masonry structures has been done using ABAQUS finite element software. In the FEMA356 method, the displacement curve of all samples is bilinear. Analytical results were compared in dominant resistance, effective stiffness and ductility. The ultimate strength, effective stiffness and ductility of strengthened specimens using steel tie increased in comparison to the control sample.

Due to the increasing production of plastic materials, there is an international concern about disposal or recycling of plastic waste in the world. One of the ways to reuse plastic waste is to use it in the engineering works to modify mechanical properties of loose soils. The purpose of this research is to find a way to reuse a particular kind of plastics (bottles of dough, soft drinks, mineral water, etc.) in geotechnical works to improve soil.In this paper, the mechanical behavior of Anzali Port sand, reinforced with 1×1 cm polyethylene terephthalate crumbs and 1×5cm strips, to 0, 0.1 , 0.5 , 1 and 2% and polyethylene terephthalate fibers to 0 and 0.1 and 0.5% of the dry weight of the soil which were arranged separately, was evaluated. Samples were prepared at the relative density of 75%. The effects of parameters such as dimensions, the weight percentage of reinforcers in the soil and vertical stress were investigated. The results of the experiments showed that although the polyethylene terephthalate crumbs and strips improve the mechanical behavior of sandy soil, but the effect of fiber reinforcers on soil mechanical properties has been much higher. Also, the optimum percentage of polyethylene terephthalate crumbs and strips reinforcers was 1% of sand dry weight. The comparison between reinforced and unreinforced samples showed that reinforced specimens had more ductility and resistance.

In this study, the effect of soil material parameters including soil specific weight (γ), cohesion (C) and angle of internal friction (∅) and geometric parameters of slope including angle with the horizontal (β) and slope height (H) on factor of safety (Fs) are investigated. Slope factor of safety is considered in two scenarios: (i) slope with dry condition and (ii) slope with steady-state saturated condition that comprises water level drawdown circumstances. In addition, the type of slip circle investigated. For this purpose, the limit of equilibrium method (LEM) is implemented. Results indicated that, decreasing of water level and omitting the hydrostatic pressure on the slope, would result in safety factor decrement such a way that with drawdown of 5.5 m water level, the factor of safety decreases about 41.42 % and also the type of slip circle is changed. Comparison of the plane and circular failure surfaces showed that plane failure method has good results for near-vertical slopes only. Determination of clip type showed that for β〖60〗^o only toe circle can happen. Application of the LEM in Bishop’s method resulted the values of R2 and RMSE equal to 0.93 and 0.121, respectively that the error of this method is 1.3% respect to other methods, which can be neglected in comparison with the complex and accurate methods.

A series of experimental data and two series of field data which have been extracted by USGS in the MONOCACY River and ANTIETAM creek have been utilized to compare source identification accuracy of the Gaussian, ADZ, and VART models. To achieve the object of the study, the theoretical solution of the VART model for sudden release, and the second-order central moment equation of the Gaussian and ADZ models have been operated For all of the experimental and field data series, firstly, all of the model parameters have been computed and then by operation of the extracted parameters and the mentioned relationships, the accuracy of them have been calculated. The results showed that the accuracy of the VART model for experimental and field data is 25% and 4.8% respectively. Also, the average relative errors of the Gaussian and ADZ models are 1.65% and 14%, respectively, which confirms the desirable accuracy of the Gaussian model. The results of the present study have been revealed that the Gaussian model in both of the model parameter numbers and the calculation accuracy is superior to the others. Also, to assess the goodness of fit between experimental and field data series and the theoretical Breakthrough curves, the average Nash-Sutcliffe parameters have been calculated about 0.97, which exhibits the favorable goodness in the fits.

There are different methods for soil stabilization, such as using windbreak, planting and use of mulch. The use of new soil stabilization methods, due to reduced environmental impacts, is a suitable alternative for oil mulch. Soil stabilization by using Nano polymer Polylatice creates a uniformly coherent cortex that is resistant to high wind speed and has less environmental degradation effects. In this research, the soil of the Hossein Abad area, near the salt lake of Qom, has been used for wind erosion test to verify the stabilization with the use of nano polymer Polylatice. After passing through a 2 mm sieve, the soils were stabilized with concentrations of 1, 1.5 and 2 L/m2 of Polylatice in trays with dimensions of 80*80*3 cm. These specimens were exposed to wind by three different velocities, including 10, 15 and 20 m/s, during 7 and 30 days and their stabilities were analyzed against wind. The concentration of dust of the Hossein Abad area in the 7 and 30-day stabilization decreased by 60 and 50 times at a wind speed of 20 m/s, respectively and as time passed by after adding mulch, the amount of particles deposited along the channel were also decreased significantly.