نشریه مهندسی عمران امیرکبیر
سال پنجاه و دوم شماره 3 (خرداد 1399)

One of the efficient ways in order to reinforce the earth slopes is Geogrid Encased Stone Column (GESC). This technique can increase bearing capacity and decrease settlement rate of slopes. The aim of this study is to perform a three dimensional finite difference method (FLAC3D) for GESC in the stabilization of sand slopes. According to the results of 3D numerical analysis, the existence of geogrid-encased stone column, increases stability to an ideal level compared with ordinary stone column-reinforced slopes. Different parameters including stone column diameter, the coupling spring stiffness, coupling spring cohesion, coupling spring friction, S/D ratio, and the layout of encasements evaluated and discussed in this paper. The influential parameter in geogrid in order to reinforce stone column, is coupling spring cohesion. By increasing the parameter, slope bearing capacity of reinforced slope increases linearly. This indicate that use of geogrid reinforced stone column, based on type of geogrid characteristics, can enhance earth slope bearing capacity up to 1.8 times of slope reinforced by ordinary stone column. The maximum bearing capacity with a row of stone columns was obtained for S/D=2. However, the reduction of S/D does not necessarily imply the increase of bearing capacity of slopes.

Hybrid structures consisting of reinforced concrete columns and steel beams (RCS) have gained popularity because of reductions in concrete formwork, increased space availability, economics in construction, energy dissipation capacity of the structure and dead load reduction. On the other hand, the current provisions of codes for reinforced concrete columns to steel beams connections have led to some complex details in practice. In this paper, the behavior of RCS connections is examined, experimentally. Five real scale external connections of RCS with circular concrete columns were prepared and tested. The variable parameters in the specimens include the confinement of concrete columns around and inside the connection region and type of concrete. The confinement of concrete columns provided by the spiral reinforcement and CFRP sheets. The purpose of the study is to propose a connection with simple details and desirable behavior. The results show that the proposed connection can transfer the moment from the steel beams to concrete columns, appropriately. Also, the reinforcement in the connection region together with CFRP sheets increase the ductility and energy dissipation of the RCS connection.

Tuned Mass Dampers, TMDs, often reduce the displacement response of structures by influencing their first mode of vibration. The structure of these dampers consists of three main parameters: mass, damping, and stiffness. Since the parameters of TMDs are constant during the vibrations, optimal tuning of these parameters is very important. Finding the optimal values of the key parameters for a TMD in nonlinear structures using numerical methods involves numerous nonlinear dynamic analyses; therefore, the computations would be time-consuming. Recent studies, carried out on the application of TMDs in building structures, have mainly focused on reducing the lateral displacements of building structures. However in this research, the application of TMDs and their effectiveness are investigated for cables of the power transmission tower in both lateral and vertical directions simultaneously. In order to numerically study the behavior of the power transmission tower, the structure of the telescopic steel tower is modeled in the OpenSEES software and to reduce the volume of computation, a numerical search method is used to find the optimal values for the parameters of the TMDs to minimize the lateral displacement in the middle of the cable span. The mass ratio of the TMDs is equal to 0.5% of the total mass of the structure. Using this mass ratio, numerical analyses of the system indicate that the maximum reduction of lateral displacement at the middle of the cable mitigated due to implementing TMDs is about 50% under the applied earthquakes with 0.5g maximum acceleration.

Flexural strength test has significant effect on determinating failure strengths and cracking moment. According ASTM-C78, the size and shape of specimens used were cubes by size (700*150*150 mm). Here, the efficiency of the non-destructive Break-Off (BO) and Flexural strength tests was investigated for assessing the in-place compressive strength of steel fiber reinforced concrete. To provide a through and comprehensive database, 24 mixtures were designed. Then, effective parameters of SFRC and Break-Off and Flexural strength tests results were evaluated. The studies showed that volumetric percentage and features of steel fibers had a significant influence on concrete properties as well as Break-Off and Flexural strength tests results. According to the experimental results it could be generally concluded that the influencing factors, namely, SFRC properties due to presence of steel fibers and non-destructive tests significantly affect the results as follows:Generally, for a constant W/C ratio, it can be concluded that raising the cement content increase the mean values of Break-Off strength and Flexural strength. It can be stated that increasing the size of aggregate cause in increase of strength. Also, the steel fibers restrain the development of internal microcracks in concrete and thus contribute to increase in bending strength which causes improving Break-Off strength and Flexural strength. In addition to, conventional numerical regression model was developed in this study. Statistical indices were used to compare the efficiency and accuracy of model. The result of this study has confirmed the accuracy of artificial neural network models in determination of the compressive strength of concrete.

In this research, numerical analysis of the hybrid lead rubber bearing system with shape memory alloy was investigated by Abaqus software and the effectiveness of various parameters on its performance was examined. The parameters studied are the bearing dimensions, the type of shape memory alloy and its cross-sectional area, the lead core diameter, the thickness of the rubber layer and the compressive stress. In this hybrid bearing, memorable form shape memory alloy are used as a recovery unit and lead core is used as a unit of energy dissipation. For this purpose, a finite element model of the bearing is modeled using the Abaqus software and the effect of the various parameters mentioned on the bearing performance has been investigated. The results show that the structures equipped with this bearing have better seismic performance than lead rubber bearing. Finally, depending on what kind of performance is required from the bearing, the parameters can be obtained optimally. As a result, in order to achieve a combination of behavior, both the suitable absorption capacity of lead and the recentring property of the shape memory alloy, it is necessary to balance the stiffness between the lead core and the shape memory alloy wire.

In arid and semi-arid regions, like Iran, water is one of the main factors limiting economic development. In the present study, a new high-performance method was used for optimal water allocation in the agricultural sector during the 2002 to 2016 years. Election Algorithm is an iterative population based algorithm, which works with a set of solutions known as population. The results of this method were compared with the results of Imperialist Competitive Algorithm (ICA). The objective function was determined for each product in the agricultural sector as well as product performance, each product benefits and cultivated area of the demand function, then maximization of the objective function and optimal water resources allocation were performed using EA and ICA algorithms. The results of the application of the EA and ICA algorithms to the optimal water allocation problem, showed that in this section, higher benefits could be obtained through economic policies as well as changing the cultivation pattern. Generally, in the case of Moghan plain can be expressed by applying a coefficient of 0.9, 135 Billion Rials, that is, about 40% of the optimal water resources allocation benefits improving between the agriculture sectors compared to the current situation.

Accident prone segments have a significant role in the occurrence and the numbers of road accidents. And they impose negatively social and environmental effects on the performance of transport system. Thus, identification and prioritization these segments play positively a role in reducing accidents, costs, and improvement of safety level on roads. Due to the importance of determining the accident prone segments, the aim of this study is to use dynamic segmentation and prioritization methods including wavelet theory and cause-oriented methods. Therefore, results from the segmentation and wavelet signal theory on the Kermanshah-West Islamabad Road indicated that accident prone segments are classified as main and local segments. Then, the cause-oriented prioritization method based on the analytical hierarchy process method for main and local segments showed that the S2 section, which ranges from about 2.5 km to 11.5 km from the beginning of the road is in the higher priority. However, S3 section which ranges from about 7.5 km to 10.5 km from the beginning of the road is the lower priority of the improvement of the road safety. In the future, this paper may help researchers in order to examine combination of arithmetic’s functions with artificial intelligence methods, logical reason methods, and SVM (Support Vector Machines) algorithm for segmentation accident prone segments as dynamic segmentation methods.

The present study evaluates the behavior of concrete gravity dams against the hydrodynamic pressure of shock waves produced by the explosion in the reservoir. To this end, several arbitrary points are selected at lower, middle, and upper elevations along the dam height, and the explosives are placed at 10, 20 and 30 meters distances from the dam face. Numerical analysis is carried out under various scenarios. The cracking profiles of the dam are extracted and the probable cracking areas under various explosive loads are determined. By investigating the crack profiles, it is concluded that the shock wave from the explosion at the middle elevation and near the dam base has more destructive effects with respect to the locating the explosives near the dam crest. It is observed that when the explosives are located near the dam base with the horizontal distance of 10 meters the most failure is imposed to the dam body. The areas susceptible to cracking are determined at the heel and neck of the dam. After the sudden explosion load is completed, the effects of the explosion remain, and the resulting waves can damage the dam body for the next few seconds. If more explosive materials are located at lower altitudes near the dam bottom, the change in the crown of the dam is increased, such that the rate of change of crest displacement rises by placing explosives on the floor of the reservoir.

One of the most damaging natural disasters is earthquake which random process of its motions has made predicting and preventing of its occurrence impossible; but it is possible to reduce the probable damages caused by earthquakes through probabilistic seismic hazard studies. The experiments of many countries that are at high risk of earthquakes, has shown that damages can be reduced when seismic hazard analysis is achieved in structural design process. Seismic hazard analysis requires earthquake data and obviously more accurate data can lead to results with more precision. The magnitude, location and focal depth of earthquake are the most basic data that needs to be updated carefully. These parameters have a major role in the estimation of probabilistic seismic hazard analysis in different regions. The current research includes a history of more than 300 earthquakes in the past 117 years, which has been analyzed for Tehran and its suburbs with the aim of conducting a new FOSM (First Order Second Moment) algorithm. Based on given design seismic levels and the Iranian Standard No.2800, the present study has PGA in two levels. The first level which is, Design Basis Earthquake(DBE) defines the peak horizontal accelerations with 10%probability of exceedance in 50years that is expected to occur once in approximately 475 years. The second is Maximum Considered Earthquake(MCE) that defines the peak horizontal accelerations with 2%probability of exceedance in50years which is expected to occur once in approximately 2,475years. According to the FOSM algorithm the estimated PGA for both level are0.30061g and0.55666g, respectively.

One of the important benefits of using warm-mix asphalt is to reduce the asphalt production temperature, but this is also generating a pavement problem such as a higher moisture potential, due to the lower production temperatures, all moisture in the aggregate does not evaporate, subsequently. The purpose of this study is to evaluate the effect of zycotherm on the moisture susceptibility reduction in warm-mix asphalt. In addition, waste crumb rubber was used as a substitute for fine-aggregates. In total, 9 mixtures were made of 0.1%, 0.15% and 0.2% of zirconium, 10% and 20% of waste crumb rubber, and their combination with bitumen, 70/60 grading and silica aggregate. To evaluate the moisture susceptibility, boiling water tests, indirect tensile test (ITS) and the resilient modulus test were used. Boiling water test results show that the increase in zycotherm improves the moisture susceptibility, but due to the low density of crumb rubber, the crumb rubber hasn’t significant effect on the final result of boiling water test. Based on the results of ITS test and the TSR, a model was generated to predict TSR. According to this model, the minimum required percentage of zycotherm with the replacement of 10% and 20% of crumb rubber, is equal to 0.128% and 0.149%, respectively. According to the experimental results, the addition of a zycotherm increases the Mr, while the substitution of the waste crumb rubber causes a slight increase. Additionally, based on the Mr ratio (RMR), all mixtures have a proper performance against moisture damage.

The behavior of steel frames during earthquakes depends on the performance of their joints. In this study, the event of damages in beam-to-column connections of steel frames subjected to an earthquake ground motion is detected, which is related to the numbers of spikes in wavelet results. The proposed method is based on the detection of abrupt changes in seismic vibration responses by the analysis of velocity responses using wavelet analysis. In order to model damage at the joints, beam-to-column connections are considered to be semi-rigid and damage is considered based on the end-fixity factors. In the proposed method, velocity responses for the different damage cases under Kocaeli (1999) earthquake was analyzed using wavelet transform. The peak values of the details of the response can be expressed the time of damage occurrence in the beam-to-column connections. To illustrate the effectiveness of the proposed method, a five story and ten story steel frames have been used. The results indicate that the proposed method has been able to identify the damage occurrence in the connections with high accuracy.

Tsunami waves can be generated in any coastal area, including inland seas and large lakes. Although there exists enough information about the generation and propagation of tsunami in ocean environment, the assessment of such phenomenon in lakes with finite depth still suffers from the lack of theoretical work and sufficient measured data. The Caspian Sea is the largest lake in the world and has gone through different historical tsunami events. A numerical study for prediction of tsunami wave height time series for ten locations in the Caspian Sea is presented in this work. Unlike tsunamis generated by earthquakes, submarine landslide tsunamis generated in shallow waters are more destructive compared to those generated in deep water. This is due to the higher energy that can be converted from the slide to the water in shallow areas. Moreover, shallower waters are usually closer to the coasts and thus a shorter available distance exists for radial damping. The dispersion of short waves and also radial spreading decrease the far-field effects of landslide tsunamis in contrast to tsunamis of seismic origins. However, shorter waves are more prone to coastal amplification with higher local effects. The results of predictions are consistent with the previous finding reported in the literature indicating the possibility of tsunami occurrence in large lakes due to landslide which can affect the neighboring ports and area located particularly in the central and southern area of the Caspian Sea.

Functionally Graded Materials (FGMs) are kinds of composite materials that due to the continuity of mixture of constituent materials, have more effective mechanical properties which leads to eliminate the interlayer stress concentration. The most common usage of such materials is in thin-wall structures, such as plates and shells. One of the most effective factors in behavior of such structures especially in single-curved shells, thermal loads or Impact loads is caused by explosion. Also, due to some executive needs, make opening in shells and their behavioral changes are important and suggesting solution will be necessary. Therefore, in order to prevent large displacement and resistance improvement, using shells made of FGM and suitable stiffeners, will be suggested. In this study, ABAQUS finite element software has been used to survey the Effect of opening and stiffener on geometric nonlinear dynamical behavior of single-curved FGM shells under the blast loads. In order to do this, the effect of volume fraction index, the effect of different openings and stiffeners has been studied. Results show that by increasing the volume fraction index, the maximum amount of displacement of the shell decreased. Making opening in the center of the shells, has better function in contrast with making opening distribution in the level of shells. By increasing moment of inertia of longitudinal and circular stiffeners, the maximum displacement has been decreased. Also, by utilizing opening distribution and longitudinal stiffeners, the maximum amount of displacement can be reduced.

In this study, the numerical Discrete Element Method (DEM) is used for simulating drained and undrained behavior of 2D polygonal granular materials in order to find critical state line. For undrained behavior simulation, two methods including constant volume and cylinder methods have been used. In the constant volume method, it is assumed that the volume of the soil remains constant during the loading due to the incommensurability of water. In the cylinder method, however, a pipe is considered among adjacent pores that provides the water transformation between them. Undrained simulation was performed for sandy samples at the confining pressure of 200 kPa by both methods. Simulations show that the results obtained by cylinder method have good conformity with those of the constant volume method. As the water becomes less compressible, i.e., stiffer, the results of both methods become closer. Also, the effect of confining pressure on the drained and undrained behavior by constant volume and cylinder methods was investigated. The results of the simulations showed that by increasing the confining pressure, the deviatoric stress and the contraction tendency increase in drained and undrained simulations. To achieve critical state, the simulations were performed until large strains where the deviatoric stress and void ratio become constant. Then the critical state line locus and also its parameters are determined. The results show that the critical state line locus does not depend on the stress path and the simulation method for undrained condition has very little impact on the critical state line locus.

The first and the most important step in preparation of seismic retrofit plan for existing buildings is the analysis of their vulnerability by conducting retrofit studies. However, most of the existing buildings in Tehran are in urgent need of retrofit studies due to reasons such as high seismicity, upgration of building and seismic codes, the abundance of old buildings and so on. In these studies, it is very important to identify the seismic status of the buildings which are in the first priority of seismic retrofit, especially the ones with public use like schools. A seismic risk prioritization technique for steel buildings is proposed in this paper, using a risk assessment hierarchical structure and fuzzy inference system. Afterward, this technique is applied in a case study, validating the results obtained for the steel buildings of the schools in Tehran. At the first of the prioritization process, the required information of the buildings is classified according to the designed hierarchical structure; Then, after quantification of the qualitative data and the fuzzification, the data are modeled, evaluated and defuzzificated based on the fuzzy inference system; This process is performed for all stages of the hierarchical structure to obtain the seismic risk parameter. After the qualification, this parameter indicates the risk of buildings and their requirement for retrofit or rehabilitation. The results that are distinguished by urban districts, determined the high-risk steel school buildings requiring retrofit studies and have shown the role of each effective parameters on the seismic risk of the buildings.