AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2015 | Volume:47 | Issue:1|Papers Count:15

The need for thermo-hydro-mechanical studies of soils at high temperatures has increased in environmental geomechanics these years. An important case is the behavior of engineering clay barrier or natural host rock in deep nuclear waste repositories that undergo high temperatures up to 120°C. Only an apparatus designed for high temperatures can do this kind of studies. This research reviews design, assemble and calibration of a triaxial set that has been made for the first time in Iran. Triaxial tests at high temperatures indicated that sand-bentonite with unit weight in the range of density for engineering barrier of nuclear waste repositories, has contractive behavior. When this mixture was heat up to 110°C, both peak and critical state shearing strength reduced about 20 percent and critical state friction angle decreased too. These results were similar to other authors' results that show the apparatus has worked conveniently.

This paper presents the results of oil spill simulation in the northwest of the Persian Gulf, next to Al-Ahmadi oil wells. A two-dimensional depth averaged flow and oil pollution model is developed for coastal water simulation. To increase accuracy advective terms in transport equation were discretized by applying third-order upwind scheme and modified by using GH limiter. The oil spill is considered in two different layers: surface smudge layer and depth emulsion part. The model takes into account the major physiochemical phenomena of oil spill including wind and current speed, oil evaporation, dissolution and coastline deposition. Average monthly wind speed has been used for long-term prediction in the Persian Gulf. Comparing the model result with the actual measured data in the incident sight revealed good agreement for predicting oil spill behavior and model accuracy.

This paper expresses the effects of silica fume, super plasticizer and GFRP on the torsional strength of self-compacting concrete (SCC) beams. SCC and control concrete mix designs in this study are based on 20 different mixes with the water-cement ratios of 0.35 and 0.45. For Torsion tests, beams with the dimensions of 40 × 10 × 10 cm were casted. To determine the compressive strength and Pundit tests, Cubic specimens with the dimensions of 10 × 10 × 10 cm and standard cylindrical specimens with the dimensions of 15 × 30 cm height were made and cured for 28 days before testing. The obtained experimental results show that the effect of silica fume in w/c=0.45 was more than the other on torsional capacity was. The torsional strength of concrete beams with GFRP was increased about 43%. The error of estimating the compressive strength of concrete by pundit test was 2%. In addition, the existing equations for estimating the torsional strength of ordinary concrete can be used for Self Compacting concrete.

During a destructive earthquake, beam-column connection ought to be the last part of whole system that be damaged. In this study, exterior beam-column connection of the five story building designed by the current seismic concrete design code was chosen. The selective connection was subjected to cyclic (seismic type) loading. For studying the more influencing parameters which effect connection behaviors, a FEM model was prepared. The FEM model was calibrated by using the experimental specimens at same loading history. Two different axial load quantities ( 0.1f’c Ag, 0.25 f’c Ag) were applied on top of column. Increasing loads and concrete compressive strength cause an increase in the shear strength of connection. Transverse beam not only affect the confinement of beam-column connection but also increases the system rigidity. In all the models used, the shear factor (g in t = g Öf’c) without axial load is more than the values suggested by ABA (Iranian concrete design code) and more than the minimum value of (NZS 3101-1995).The results was shown that in concrete structures the chosen one value for effective stiffness of cracked element without considering ductility of element is not reliable.

Because of the happenings such as accidents and road repairs, the traffic level of some links of the network can strongly be changed. Therefore, routing on the basis of merely historical traffic data is not always useful. On the other hand, routing based on real-time data is not adequate either. The reason is that the real-time data regarding near links can be trusted. However, this is not the case for the distant links; since their present traffic will certainly be changed before the vehicle gets there. The main goal of this research is to propose a new method of routing based on fuzzy integration of historical and real-time traffic data. In this method, the basis of routing for normal situations is the historical data. In case of an accident in the network, before getting to the vicinity of the accident, the shortest path will be recalculated. The weights allocated to the links are calculated based on the integration of historical and real-time traffic data, using a fuzzy inference system. These weights are variable and are a function of the distance between the present location of the vehicle and the accident location. The results of the research show that, using this method, in the case of accidents, the calculated path is clearly deviated from the location of the accident.

Experiencing several earthquakes around the world indicate that, for a specific earthquake, the amount of structural damages, with almost identical features, is highly influenced by the condition of the site, which is called as the site effects. In fact, something which exists in reality and practice is, in most cases, the non-prismatic canyons in line with the longitudinal axis of the valley so that narrowing parts of the canyons are usually selected as the appropriate sites for a variety of structures, and then studied .In this study, the dynamic behavior of prismatic and non-prismatic canyons, using three-dimensional boundary element method in triangular, trapezoidal, and semi-circular forms under the SH waves, are studied. The Results indicate that the movement of non-prismatic canyons, which have narrowing in the middle and opening in two ends of the canyon, based on the frequency and wave angle, are in some cases more than prismatic canyon. Therefore, to obtain accurate values of site effects, it is necessary to do a realistic and three-dimensional modeling of the canyon.

Using FRP material, due to their excellent features like high strength to weight ratio, resistance to corrosion, convenience of transportation and installation, is developing rapidly. Using FRP bar instead of steel rebar significantly prevents corrosion in concrete members specifically for the seashore concrete structures.In this research, in order to investigate the benefits of replacing steel rebar with FRP bars in concrete columns, some column specimens were modeled in finite element computer program and the effects of parameters like FRP bar ratio and compressive strength of concrete on the flexural capacity and ductility of column were discussed. The investigations on the concrete columns strengthened with CFRP bar and steel rebar, indicate that the FRP bar ratio is significantly less than the steel rebar ratio to achieve the acceptable strength.

The recent earthquakes exhibit that the uses of seismic design codes of practice yet do not provide sufficient comprehensive safety for buildings. This means that during earthquakes all structures would behave various performances, while the design objectives in current building codes address life safety, control damage in minor and moderate earthquakes, and prevent collapse in a major earthquake. In this respect, evaluation of performance of existing buildings designed in accordance with the current seismic code of practices could improve these codes and provide ample precision related to the expected structural behavior. This paper investigates the various performances of 72 reinforced concrete moment resisting frames (RCMRF) with low and moderate ductility. These structures are designed in accordance with Iranian seismic standard 2800 and Iranian concrete code of practice. The seismic performances of all structures investigated, discussed and compared under the nonlinear static (pushover) and nonlinear dynamic analysis. The moderate ductile structures (except two stories) due to earthquake hazard level 1 exhibit life safety level of performance, which transfers to immediate occupation level by increasing the height of the structure. Among the low ductile structures, all regular six, eight and ten stories have life safety performance while the two and four stories show low level of performance expected by standard 2800. The general comparisons among all moderate and low ductile structures show the better performance for that of moderate structures.

Linear-repetitive projects are in which one or more group of activities repeat in different parts of project. Because of their special nature and importance of factors such as resource work continuity, personnel's variable productivity rate and effect of learning curve on efficiency of human resources, these projects scheduling is very particular and traditional methods cannot achieve optimum results herein. Personnel’s learning phenomenon has been underlinein past researches but they have less set to this matter. In present study, an approach for modeling learning rate and considering it in line of balance technique was processed. For this end, fuzzy sets theory has been apply here. After calculating the learning rate, it has been use for estimating amount of required worker-hours, variable productivity rate of labor and expected duration of activities in each unit of project. Based on outputs, it was obvious that effect of learning due to repetition results in reduction of total project duration and scrounging in its total cost.

Organic solvents of TBP and D2EHPA were used to extract copper from aqueous phase in the buffer solution. This study was performed in order to obtain optimized conditions for copper extraction from low grade copper oxide ores by hydrometallurgical processes. In this regard, the following parameters were studied: the effect of organic solvents synergism, the ratio of TBP:MIBK, the buffer solution pH, the concentration of buffer solution agent (sodium acetate) and the ratio of aqueous to organic phase (A:O). The results showed that under conditions of: synergism of TBP (Tri-n-Butyl Phosphate), MIBK (Methyl Iso-Butyl ketone) and D2EHPA (D-2-Ethyl Hexyl phosphoric acid), TBP:MIBK= 7:3, pH=5, concentration of sodium acetate= 1 milli mole and A:O= 1:1; more than 99% of copper could be extracted.

Earth dam is a structure as homogeneous or non homogeneous forms for raising water level or water supply. Earth dam consist of different parts that one of the main parts is clay core. Choosing an optimal non permeable core which causes reduction of seepage through dam body and also being stable is necessary. The objective of this research is to optimize the geometry of earth dam clay core such that, beside of reduction of seepage through dam body, the volume of core material is minimized. For access of this objective a consolidated model consist of a simple model which obtained by linear regression and SA algorithm were used. So the necessary model has been written in Matlab 7.8 and using SA algorithm, to optimize the Birjand Hesar Sangi dam. Optimal parameters such as seepage through dam body, hydraulic gradient and safety factor of stability access from model compared by the values access from the direct run of the software modeling that show a good agreement. Also the result of access by modeling have been compared by real dimensions of Birjand Hesar Sangi dam, that cause reduction of material volume for construction core dam about 21% and shell dam about 8% with satisfactory stability.Result show that the consolidated model have successful operations and a general optimal plan design of clay core dimensions in stable condition can be achieved.

Threshold shear strain is one of the basic parameters of soil during cyclic loading condition. The threshold shear strain should be determined for evaluating pore water pressure generation due to earthquake, vibrating machine and all the cyclic loading which apply permanently or temporary on the soil. According to many scientific researches, the threshold shear strain is the strain, which there is no pore water pressure generation at the saturated soils and no volume changes at the dry conditions during cyclic loading. By increasing the shear strain more than threshold shear strain (gt), pore pressure increase is noticeable at the saturated soil and the soil microstructure starts to change. In this study, the effects of plastic and non-plastic fines on the threshold shear strain of saturated sands were evaluated by performing a number of cyclic triaxial tests with strain control method at small shear strain. All the specimens contained 0%, 10%, 20% and 30% plastic and non-plastic fines prepared by wet tamping undercompaction method. As a result, by increasing plastic fines more than 20%, threshold shear strain increased significantly. Moreover, by increasing non-plastic fines, threshold shear strain fluctuated. It first increased and then decreased.

Usually the cost of sewer rehabilitation is large but the budget is limited. Owing to the importance of sewer networks in the functioning of society, the current state of the networks, and given the enormous cost of replacement of these systems, actions need to be taken to restore and/or improve the systems and to prolong their service-lives. For a holistic and sustainable rehabilitation planning, a reliable assessment model is needed which grades existing defects according to the real defect severity and gets most out of the exiting information, being tolerant to imprecise data. Hence, engineers can limit rehabilitation costs by producing software components based on asset management systems and assess thousands of kilometers of sewer each year. Little effort to date has focused on devising methodologies for gathering information about the condition of pipelines. It was not until the mid-1980s that the use of decision support tools emerged as an important element in pipeline rehabilitation. The tools range from simple ranking algorithms to information management systems and rehabilitation models. However, the basic concept of assessing the condition is to measure the type and extent of deterioration that the sewer is currently experiencing. This paper reviews some widespread decision support systems used in sewer asset management and the stages they cover. It also reviews the related studies on sewer network management in Iran. In addition, the article presents a framework and future research’s needs in this field. It is argued that the methodology presented in this paper would help the decision makers/sewer inspectors enormously.

High attractive surface forces between particles of nanosilicas could lead to significant aggregation of these materials. This study is thus focused on the aggregation status of pyrogenic nanosilicas and nanosilica sols, as two main types of nanosilicas used in concrete. The results show that unlike nanosilica sols, which are in the form of monodispersed particles, serious aggregation of pyrogenic nanosilicas in water occurs. Increasing dispersion forces, particularly the use of ultrasonic waves, has considerable effect in breaking aggregates into smaller aggregates. Increasing the pH was found to be very effective in improving dispersion of nanosilicas and through combined use of high pH and high dispersion forces such as ultrasonic method it is possible to break all the aggregates into primary aggregates.

Tunnel construction in soft ground causes ground displacements around it. Displacements influence surface and subsurface structures in urban areas and cause serious damages and injuries. So prediction of ground deformations and involved possible damages on surrounding structures are major parts of designing and planning in soft ground tunnelling. In this paper, O7 station of line7- Tehran metro was modeled using FLAC3D. This station is located in residential and commercial region with high density. Station excavated using underground method. At first, a gallery was excavated in middle of station in order to access and excavation of lateral piles and concrete arcs. To control the settlement, piles and concrete arcs created as temporary support with 1.2m spacing. In the next stage inside of station excavated and permanent support installed. It found that two buildings located in influence area of the station. Since the obtained value of settlement for both buildings was higher than 10mm, so in first stage assessment of risk damage these buildings were in unsafe region. Then second stage assessment of risk damage conducted using relative stiffness method. In this stage, building located in safe region. Therefore, It can be concluded that excavation of station has no risk damage on surrounding structures.