AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2018 | Volume:50 | Issue:5 |Papers Count:20

Among the climate change impacts, changing hydrologic regime and increasing the probability of encountering extreme events are of the most important. This paper investigates extreme rainfall and runoff regime (intensity and frequency) under climate change impact in West Flood-Diversion (WFD) catchment in Tehran, and compares the changes in extreme rainfall and runoff return periods during future time period (2080-2090) with baseline period (1999-2000). To do this, the output of MRI-CGCM2. 3. 2a climate model under A1B emission scenario was extracted as a point (station scale) and change factor method was used for downscaling and producing daily rainfall time series. Afterwards by extracting extreme daily rainfall data, the value of 1-hour, 10-year rainfall of the catchment was calculated and then IDF curves of the catchment for base time period and also the future period were obtained. Finally by extracting PDFs of Maximum runoff, changes in catchment’ s runoff regime in future period compared to baseline period were analyzed. The results showed that extreme rainfall intensity at future decreases a little compared to base time period. In addition the results are representative of enhancing catchment’ s runoff discharges in 2090 time horizon compared to baseline period. By moving from baseline to the future, the catchment faces increasing in frequency and probability of a given amount of runoff discharge occurrence, and also for a given return period, urban flood flow-rate increases. Therefore employing measures for adaptation to climate change impacts in the catchment seems to be necessary.

By passing and strike flow with vegetation, pressure area in upstream of plant and low pressure area in its downstream is formed. The pressure difference created in this way triggers separation of the boundary layer and consequently formation of vortices downstream of vegetation. When the frequency of vortex rooted from vegetation becomes equal to the natural frequency of the channel, transverse stationary surface waves are generated. In natural channels in areas where the flow rate is on the wane, the probability of growing plants is on the rise, incontrovertibly there is a free flow beside a flow passing through the plants. In this study, the characteristics of the surface transverse oscillations caused by vegetation, introduced as rigid barriers, were investigated under different configurations of barriers and over a range of width percentage covered by obstacles (WPO). Totally, 378 experimental tests were conducted in a rectangular channel of 9 m length and 50 cm width. The variables studied included flow discharge, flow velocity and WPO. Moreover, flow discharges were ranged from 5 to 15 liters per second. It is shown that, as long as WPO increases, transverse oscillation are formed at larger depths, which also have a larger oscillation amplitude. For a certain flow depth, increasing WPO results in growth of oscillation amplitudes. Based on dimensional analysis, regression relationships were extracted to predict the relative amplitude of transverse oscillations as a function of WPO, among other affecting parameters. Overall, the empirical equations proposed in this study were found to reproduce experimental results with acceptable accuracy.

Desirable physical and behavioral characteristics of clay soils have resulted in their wide usage in engineering landfills. Clay soils are able to interact with the materials in contaminants thanks to their special mineral structure and adsorb part or all of the hazardous materials present in the leachate leaked in them. Previous studies have shown that changes in the physical and chemical characteristics of pore fluid in soil, given the type of minerals clay soils and the soil structure, significantly influence the properties of soil engineering including shear parameters, the extent of swell, and water adsorption percentage. The aim of this research is to study the effect of heavy metal contaminants on some strength and geotechnical parameters of sandy clays. For this purpose, following preparation of the samples, adsorption and direct shear experiments along with determination of the liquid limit were performed on the samples which had been exposed to the heavy metal contaminants of Pb and Zn. The results indicated that across the three studied clay types (the mixed sand kaolinite samples with different sand percentages), with the increase in the concentration of both contaminants, soil cohesion diminishes, while the internal friction angle of the samples was not affected by presence of heavy metal contaminants. When concentration of Zn increases to 25 cmmol, cohesion of samples with 90% and 60% of kaolinite decreased 20% and 23% respectively. While in the presence of Pb decrease in cohesion is 42% and 51%.

This study investigates the effect of seismic sequence on the behavior and increased response of concrete moment frames with/without shear walls. At first, three moment resisting concrete frames with 4, 7 and 10 stories are designed and analyzed under critical single and consecutive records. In order to investigate the effect of seismic sequence phenomena, frames were subjected to nonlinear time history analysis and some parameters such as, maximum ductility demand, inter-story drift and shear deformation of shear walls are calculated. It was seen that records with peak ground acceleration (PGA) ratio of consecutive records to single’ s less than 0. 46 do not have any significant effect on the response of frames. As PGA ratio increased, the effect of seismic sequence on the frames is more considerable. Results show that seismic sequence phenomena has more effective on the moment frames with shear walls compared to moment frames. Moreover, for both structural systems, its effectiveness decreased as the number of stories increased.

The existence and extension of the cracks in structural materials is one of the issues to be considered to prevent the devastating effects of cracks. Cracks can be subjected to different types of fracture modes that considering these modes help us to predict the behavior of cracks. This paper investigates the effects of the fracture modes (opening, shearing and tearing) on the annular crack in an infinite transversely isotropic solid. In each mode, by substituting the boundary conditions into governing equations of the medium, the problem reduced to triple integral equations. With the aid of Hankel and Abel integral transforms, the triple integral equations reduced to two Fredholms integral equations which are amenable to numerical solutions. The inner and outer stress intensity factors of the annular crack are obtained for different ratios of inner-outer radius of the annular crack. Some limiting cases such as the penny-shaped crack and external crack are considered. From the results, it can be concluded that the stress intensity factors (SIFs) are independent of material properties; additionally, loads play major role in the variation of SIFs which may lead to change in the direction of crack extension.

Using anti-striping additives is the most optimal method to improve the strength of asphalt mix against moisture. In this survey, it is tried to review the effect of using polymeric materials as bitumen modifiers on the reduction of moisture damage of hot asphalt mix. To investigate the effect of polymeric materials, repetitive loading test in dry and wet condition together with thermodynamic parameters have been used. The results showed that using Styrene-Butadiene Rubber (SBR) have led to improve the ratio of wet to dry module of asphalt mixes, showing their strength against moisture damage. Moreover, SBR have increased the conjunction free energy and have decreased the released energy of system in striping event and this indicates drop in system’ s tendency to striping. Moisture susceptibility index which is the surface percent of aggregates exposed to moisture have been obtained according to the measuring the components of surface free energy of bitumen and aggregate and asphalt mix module in loading cycles. The results of this index showed similar results to the ratio of dry module to wet module. Obtained results represents that SBR has led to considerable decrease in striping percentage in samples of controlled asphalt mixes.

Ore sorting Proposed proposed as an important step in the plant of chromite processing and the reported results in this field bounded. By using this method, substantial energy savings and increasing in production take place in the comminution stage. Ore sorting is done in three stages including entrance to the primary crusher, the output of the primary crusher and entrance to gravity separation which the primary crusher output stage has more favorable results. In this study, for separation with designed device, the identification and characterization of chromite ore is performed. Firstly, minerals imaged with three-dimensional scanner and by creating a cloud of points, the volume of chromite ore achieved and the equivalent diameter of stone pieces are determined. Then ores placed on the device’ s conveyor and the mass of each pieces are measured by load cell sensor and the density of minerals determined. Finally, according to the size and specified conditions of each fraction, the grade of stone pieces determined and according to the limit specified for the grade of the ore driven to concentrate or tailings. The results showed that Sabzevar chromite with a grade of 26. 16 percent with gaunge minerals after ore sorting, produces an initial concentrate with 33. 11 and 83. 92 percent of the grade and recovery respectively.

Excessive column shortening in conventional one-step analyses is one of the most important aftereffects of ignoring the real behavior of concrete columns. This real behavior could only be achieved by staged application of gravity loads considering the long-term inelastic strains of concrete. Thereupon, consideration of adaptation between high-rise reinforced concrete structures’ design and practical stages of construction has always been staunchly held forth by researchers. Neglecting the fact above may lead to serious incorrect outcomes of analyses especially in high-rise structures. Some of these adverse structural effects are extra induced bending moments in beams, expansion of progressive cracks in second or non-structural elements, and wasting the intended capacity for structural elements in the design stage. This paper deals with comprehensive nonlinear staged analyses of structures with various geometrical specifications and represents simple empirical equations to evaluate column shortening caused by creep, shrinkage, and time changes of modulus of elasticity in such a way that the proposed relations could be independent of conventional variables of CEB-FIP code. Results of validation process show high conformity of all proposed equations for up to 30 floors and also demonstrate the accuracy of proposed shrinkage relation even for the structures higher than the aforementioned limit.

Externally Bonded Reinforcement (EBR) is known as a conventional method for flexural strengthening of concrete beams with Fiber Reinforced Polymer (FRP) composites. The present study has been conducted to investigate the flexural behavior of RC beams strengthened by CFRP sheets. Eight beam specimens strengthened by EBR method having the cross sectional dimensions of 250*300 mm and length of 2200 mm with two different reinforcement ratios (low and high) were evaluated under four point bending test. The compressive strength of four specimens was 25 MPa and other four specimens were made using high strength concrete with the compressive strength of 55 MPa. Additionally, the tensile reinforcement arrangement varied in different specimens with two bar sizes. In order to strengthen the specimens, two CFRP layers with dimensions of 160*1700 were used. Based on the results of the present study, in the case of low reinforcement ratio while maintaining the total reinforcement ratio constant, by decreasing the bar size and increasing the number of bars, the load carrying capacity of the specimen increases. In contrast, in the case of high reinforcement ratio, this results in the decrease of load carrying capacity. Finally, utilizing the smaller bar size in the tensile region of the specimens with low reinforcement ratio results in a more uniform distribution of cracks in the beam.

Many industrial wastewater containing various cationic pollutants including heavy metals and organic dyes with non-degradable structures that are considered as a serious threat to public health and the environment. In this study, nano-absorbers including graphene oxide (GO) and graphene oxide modified with 3-aminopropyltriethoxysilane (GO-NH2) was successfully synthesized and characterized by Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) analysis. GO and GO-NH2 were applied to remove Pb2+ and Cd2+ metal ions, and methylene blue (MB) cationic dye from aqueous solution in single and binary component systems (Pb2+-Cd2+, Pb2+-MB, Cd2+-MB). In the single component system, the maximum absorption of 99%, 72. 5% and 49. 5% was obtained for MB, Cd2+ and Pb2+, respectively, by using GO. In the case of GO-NH2, maximum absorption of 90%, 73% and 35% was obtained for Pb2+, Cd2+ and MB, respectively, in single-component system. In the presence of MB dye, removal percentage of Pb2+ and Cd2+ showed a reduction of 10% compared to the single component system (Rq <1) by using GO. By using GO-NH2, in the metal-dye binary systems, the removal percentage of Pb2+ and Cd2+ showed a reduction of 15% and around zero, respectively, to the single component system. The adsorption rate of MB onto GO and Pb2+ onto GO-NH2 were in good agreement with pseudo-second order model (R2=99; k2=0. 0002g mg-1 min-1, R2=95; k2=0. 001g mg-1 min-1 respectively).

During the past years researchers have conducted a number of comprehensive in-situ and laboratory tests on municipal solid waste (MSW). Following these investigations, for the purpose of measuring shear wave velocity and small-strain shear modulus a set of bender element device mounted on cyclic triaxial test apparatus located in Iran University of science and technology was employed. Tests were conducted on medium-sized samples of fresh MSW in order to primarily evaluate the influence of fiber content (fiber contents of 0, 3 & 6 %), confining stress (75, 150 & 300 kPa confining stress) and unit weight (9 & 12 kN/m3) on shear wave velocity and small-strain shear modulus. The influence of fiber content on movement of shear wave velocity was observed using bender element tests. Although increasing the fiber content of MSW samples caused a higher shear wave velocity, the energy of received wave by bender element device had lower magnitude this could be attributed to lower capacity of plastic fibers to transmit the wave, however the increased shear wave velocity of samples with greater fiber content could be attributed to higher compaction effort. It is considerable that the effect of fiber content is more significant under higher confining stress.

Traditional techniques such as burning leads to some highly durable non-degradable synthetic materials that cause unrepairable environmental damages by releasing heavy metals such as arsenic, chromium, lead, manganese, and nickel. Today, scrap tires are used as lightweight alternative materials in many applications such as retaining wall backfilling. In the present study, several laboratory models were carried out to evaluate the stability of retaining walls reinforced with plate anchors. Then, the effect of adding different contents (10 and 20 wt. %) of crumb rubber to fill of a mechanically stabilized retaining wall with plate anchors were investigated including its effect on bearing capacity and wall horizontal displacements during static loading. To visualize the critical slip surface of the wall, particle image velocimetry (PIV) technique was employed. The results showed that the circular anchor plates provide a higher bearing capacity and wall stability in comparison to square plates. Also, it was found that the backfill with 10 wt. % crumb rubber provides the wall with the maximum bearing capacity. In addition, increasing the weight percentage of crumb rubber to 20 wt. % resulted in a significant reduction in bearing capacity and horizontal displacement of the wall, which occurred due to a decrease in lateral pressure against the whole walls. Moreover, an increase in weight percent of crumb rubber results in a decrease in failure wedge formation and expansion of wall slip surface while the failure wedge is not formed in mix of sand-20 wt. % crumb rubber.

It has been of great interest among the researchers to investigate the behavior of soil_geogrid interface. Due to the wide use of geogrids between different layers of soil; these investigations are very important. This paper shows the results of experimental tests on soil_geogrid interface. This study conducts a series of large scale direct shear tests to investigate the interface shear strength of granular soil with various degrees of compaction and various sizes of geogrid apertures. The shear stress versus shear displacement curves and peak shear strength are important for evaluating the results. The interactions between soil and geogrid may include the following mechanisms: 1) shear resistance between soil and the surface of the geogrids; 2) internal shear resistance of the soil in the opening area; and 3) passive resistance of the transverse ribs. The value of α was defined to evaluate the effect of geogrid on the shear strength of the soil which is the ratio of geogrid_soil shear strength to internal shear strength of soil. The results showed that a larger degree of compaction reduces the resistance in soil_geogrid interface and shear strength of soil_geogrid interface will be reduced further by reducing the distances of transverse ribs of geogrid.

This study has been conducted to investigate the effect of reinforcing on the bearing capacity of circular footing resting on granular soil. For this purpose, a total number of seven large-scale plate load tests were carried out on a circular plate with a diameter of 300 mm. In order to prepare specimens, a portable curtain rain system is used which is calibrated by 60 raining tests. In the current designed and developed experimental system, a new method is used to measure the normal pressure at footing base. In all loading experiments on soil reinforced with geogrid, only one geogrid layer is used and the effect of depth of this layer from footing base is investigated. The results showed that with provision of geogrid, the bearing capacity of circular footing increases up to 1. 56 times of unreinforced mode. In addition, it is shown that by increasing the ratio of u/DF, the slope of load-settlement curve (stiffness) decreases. For values of u/DF>0. 67, the effect of this parameter (dimensionless depth of geogrid) on bearing capacity of the footing is constant, which indicates that the reinforcing mechanism has been changed and the failure occurs at the upper soil mass (above the geogrid). Also, the results showed that with increasing of the distance from center of the footing, the value of normal pressure applied at footing base reduces.

This study has been conducted to investigate the effect of reinforcing on the bearing capacity of circular footing resting on granular soil. For this purpose, a total number of seven large-scale plate load tests were carried out on a circular plate with a diameter of 300 mm. In order to prepare specimens, a portable curtain rain system is used which is calibrated by 60 raining tests. In the current designed and developed experimental system, a new method is used to measure the normal pressure at footing base. In all loading experiments on soil reinforced with geogrid, only one geogrid layer is used and the effect of depth of this layer from footing base is investigated. The results showed that with provision of geogrid, the bearing capacity of circular footing increases up to 1. 56 times of unreinforced mode. In addition, it is shown that by increasing the ratio of u/DF, the slope of load-settlement curve (stiffness) decreases. For values of u/DF>0. 67, the effect of this parameter (dimensionless depth of geogrid) on bearing capacity of the footing is constant, which indicates that the reinforcing mechanism has been changed and the failure occurs at the upper soil mass (above the geogrid). Also, the results showed that with increasing of the distance from center of the footing, the value of normal pressure applied at footing base reduces.

Rapid growth of performance-based earthquake engineering has caused increasing interest in Non-linear Time History Analysis (NLTHA) as an effective tool for the estimation of engineering demand parameters (EDPs) and capacity. Focusing on the selected set of strong ground motions (SGMs) as an important source of uncertainty on the results; there are a variety of studies, the purpose of which is to introduce a standard scheme for efficient selection of appropriate SGMs as the input of NLTHA. A part of existing differences, most of these methods suffer from a common limitation that is the application of simplifying assumptions in their contextual framework that may not be correct always. Although, the use of such simplifications is unavoidable, the effect of them on the reliability of the results estimated by performing NLTHA under proposed set of SGMs by method must be evaluated. In this paper, a recently proposed structure-specific record selection method is investigated in terms of its ability to keep the claimed efficiency in case of structures that may challenge the correctness of reducing a MDOF nonlinear system to an equal SDOF. Among different influencing parameters that are considered in this study such as the type and pattern of irregularities, as well as, initial stiffness of the frames; the results confirm that ductility plays the chief role on the selection output. Also, the application of the proposed subsets by the selection method does not necessarily result in the reduction of the statistical dispersion in the estimated EDPs.

There is a long history of occurrences for events and natural &/ un-natural crisis in Iran. Some natural crisis are as earthquake, flood, storm, reaper, landslide and fire. Generally, in every crisis the homes and accommodations of majority of people are damaged and some people getting into financial and psychological damages. Temporary accommodation of injured people in every crisis is the main task for the authorities of each country. Temporary accommodation operation should be conducted with due observance on the rules such as time, cost and operation of the site. Nowadays, much progresses has been conducted in the world in building of the temporary accommodations and then construction velocity and quality were improved. In this research, Iran’ s country conditions were studied and optimization of time and cost of building of temporary accommodations were investigated using both of particle size optimization algorithm (PSOA) and MATLAB software. The aim of research was optimal distribution of demographic blocks in residences so that firstly, do not exceed the capacity of any settlement and secondly, the minimum distance and cost for moving the population is spent. The obtained results showed finally that for optimization of time and cost of operation which demographic block should be moved to what accommodation. Regarding to the limited capacity of every settlement, the population overflow for some demographic blocks should be moved to several settlements. Some advantages for settlements structures compared to others, are as fast installation, low cost, and convenient storage.