Modares Civil Engineering journal
Year:2016 | Volume:15 | Issue:4|Papers Count:15

Nowadays, the problems of water quality and quantity in different parts of the world, especially developing countries, have provided a great challenge for these countries. Preservation and optimal usage of water resources are that main aspects of sustainable development in each country. Knowing qualitative and quantitative problems in water resources monitoring systems is one of the most important steps in water resources system management and pollution reduction plan. Recent studies in the field of water quality monitoring network has shown the needs for more researches, despite the abilities and investments in this field. One of the most important problems is the difference between required data and provided data in monitoring networks. So, monitoring systems should be revised and modified in several cases. High monitoring expenses necessitates optimizing monitoring systems to prevent cost loss.Being aware of network properties is an essential step in evaluating existing quality monitoring network. Locations of sampling stations, time frequencies, qualitative variables specifications and sampling duration should be considered in these evaluations.Reduce the cost of monitoring networks and maximize the obtained information, is the common objectives of the monitoring networks planning. From a monitoring perspective, identification of the reservoir eutrophication situation is of particular importance. Eutrophication phenomenon affects water quality strongly and causes serious limitations on the water utilization ability. Autotrophic organisms and algae overgrowth increased turbidity, toxic substances, increased sedimentation rate, oxygen concentration in the middle of the day and reduced severely by decreasing sunlight from sunset until next day morning, which causes anaerobic regions creation in deeper areas of the reservoir as the result.In this study, locations of Karkheh dam reservoir that there was maximum variations in quality indices values using CE-QUAL-W2 model, was identified. PO_4, NO_3, chlorophyll A and dissolved oxygen was studied to eutrophication control in reservoir. Because of limited available data from the time frequencies and sampling location point of view, dam reservoir was modeled by CE-QUAL-W2, 2D qualitative model for a period of one year. Using time series developed in previous step in model cells, time variance of studied parameters in the entire model cells was calculated and was used as a measure of its value change during time. Critical path from monitoring point of view was obtained after fitting best curve to cells with maximum time variance for studied qualitative indices. Placement of monitoring stations on this route will get the maximum information about the quality of the monitoring operation. The results showed that the proposed methodology is efficient in determination of critical paths for quality indices from monitoring perspective, in the dam reservoirs. It is recommended that, the model developed in this study, links with optimization models such as genetic algorithm, particle swarm optimization and etc., .Also, uncertainties related to hydrologic characteristics of the model well-consideredin future studies. Furthermore, by using the three-dimensional water hydrodynamics and quality models, critical paths also be found in latitude of thereservoir. Also, the recommended methodology, can be extended for monitoring of the multi-reservoir systems. In addition, to determine the critical path for all quality parameters, multi-criteria decision-making techniques alsocan be used.

Shear modulus is one of the most important properties of soil deposit that should be evaluated as a preliminary step for site response analysis. Although numerous studies have been conducted to evaluate this parameter for silicate soils, there are considerably less studies on calcareous soils. However, extensive regions of the earth is covered with calcareous soils. This type of soil is typically observed near offshore hydrocarbon industries, such as the Persian Gulf. Calcareous sand is the accumulation of pieces of carbonate materials, originated from reworked shell fragments and skeletal debris of marine organism. These soils typically include huge oil and gas reservoirs which are continuously under an extending construction. Therefore, assessment of dynamic behavior of calcareous soils is a vital step for engineering projects. In this study, shear modulus of calcareous sand are investigated in the range of small and large strains using resonant column and cyclic triaxial tests, respectively. Bulk samples of Boushehr sand were collected from the North bank of the Persian Gulf near the Boushehr port. Preliminary mineralogy tests were conducted in order to estimate carbonate content of the samples. The sand contains considerable level of carbonate content and skeletal structure of the soil can be observed easily. Remolded samples of this sand were prepared via dry deposition method for either triaxial or resonant column tests. The results are presented in terms of shear modulus versus shear strain. The effects of confining pressure and relative density on the shear modulus of the calcareous soil are investigated. Moreover, for evaluating the effect of stress anisotropy on the shear modulus of calcareous soil, dynamic and cyclic tests were conducted under both isotropic and anisotropic conditions. The experimental results confirm that confining pressure has an important influence on the shear modulus of the tested samples. Increase of the mean confining pressure and relative density increases the shear modulus of the sand, as previously reported for the other sands. The results indicate that the effect of stress anisotropy on dynamic properties of calcareous sand is less important than those of mean confining pressure and relative density. With increasing mean confining pressure, the effect of relative density and initial stress anisotropy on the shear modulus increases. The normalized shear modulus are compared with the G-reduction ranges proposed for silicate sand by the previous researchers. This comparison show the need for some modification of the previous proposed ranges for normalized shear modulus curves. Finally, a modified hyperbolic model is presented for estimating the normalized shear modulus of Boushehr calcareous sand. It is demonstrated that the proposed model has more capability for prediction of the experimental G-reduction curves, compared with the models recommended for silicate soils. One advantage of the proposed model is the simple correlation developed for the reference shear strain in terms of initial effective confining pressure. The modified hyperbolic model presented in this study can be employed for site response analysis of the calcareous deposits of the Boushehr city.

General attention to carbonate sandshas been begun since the early 1960 in Iran. When the first bore drilled the Persian Gulf’s bed, it drew out layers of this soil type along with sand and shell. However, the large amount of carbonates in this soil was not first diagnosed.The first knowledge of the unique behavior of this type of soil was obtained during pile driving in the construction of an oil platform in Lavan Island, Persian Gulf, in 1968. In this operation, after a number of 30 inch pipe sank into the cemented soil for about 25 feet, they suddenly had a free fall with no resistance up to depth of 50 feet.Carbonate materials and aggregates can be found in nature in different shapes. The majority of them are made of calcium carbonate or other types of carbonate with soft and loose grains that can break easily. These soils are of remarkable importance in offshore engineering.Since early 70s, a great amount of studies have globally been conducted for identifying the unique engineering characteristics of carbonate sands. Different behavioral parameters including strain-stress behavior, shear strength, internal friction angle, volumetric behavior, elastic and shear modulus, Poisson’s ratio, carbonate content, shape of carbonate grains andetc have been studied.No certain laboratory methods or field study plan have yet been provided to obtain appropriate parameters for designing foundations in carbonate soils. Despite this, performing a number of laboratory and field experiments can be helpful. Executing at least amount of experiments to determine the following matters are essential:- Material composition, especially calcium carbonate content- The origin of the materials to distinguish between skeletal and non-skeletal deposits- The properties of the gains such as angularity, porosity, and initial void ratio- Compressibility of materials (using consolidation test)- Strength parameters of the materials, especially internal friction angle- Cementation, at least quantitativelyIn this paper, shear behavior of four skeletal carbonate sand samples obtained from the northern coasts of Persian Gulf and Oman Sea are investigated. Regarding some parameters of samples such as particle size distribution, physical properties, microscopic images of grains, compressibility, drained triaxial shear behavior, elastic modulus and internal friction angle it was attempted to promote geotechnical knowledge and improve civil engineers understandings of carbonate soils in this part of the world. On the basis of experimental tests like one-dimensional consolidation and triaxial tests, it was determined that despite a number of similarities between the shear behavior of carbonate sands, behaviorally they depend on the grains shape and size, initial particle size distribution and void ratio, calcium carbonate content, confining stresses and applied strains. Although all specimens were selected from the southern coasts of Iran, but a large number of difference was observed between them in terms of shear behavior and strength.

One of the common bracing systems in our country is Y-shaped bracing system. Because of architectural advantages, it attracts more attention in comparison to x shape concentric braced frame (CBF). But, its stiffness is less and it has more potential for out of plane buckling. One of the extensively used methods for improving the seismic behavior of the structural systems is using the passive control systems. By reducing seismic demand and increasing ductility, this control way can reduce the rate of seismic damage. Yielding dampers are one of the elements to achieve this kind of control in the structures. Because of good ability of yielding dampers in earthquake energy dissipation, the use of these dampers is increased through recent decade in passive control of structures. Due to development of passive control methods for earthquake energy dissipation and for preventing the structures from earthquake losses, this paper proposes a new improved dissipating element for Y shape bracing systems which could be used for structural rehabilitation of steel structures. The basis of the proposed element operation is its operation as a fuse element to improve the bracing elements behavior. The operation of the proposed element is in such a way that before formation of a hinge in bracing element, the presented element is yielded and by absorbing appropriate energy, prevents the bracing elements from inappropriate performance. Before inserting the proposed element in the bracing frames, using the ANSYS software, the element performance is studied for different dimensions and appropriate dimensions are determined. The energy absorbing element is inserted into two different positions in the bracing systems of interest. 2D steel frames with three different number of stories (4, 6 and 8 story frames) are modeled in SAP 2000 software, using conventional braced frames and their behavior is compared to braced frames with the proposed energy absorbing element. The frames are analyzed through nonlinear time history analysis, using appropriate time history records from near source and far source locations. The results show the appropriate ductility of the proposed element, the improvement of bracing elements behavior and also, the higher energy dissipation of the new bracing system, which can be shown through comparison of the hysteresis loops of the bracing frames, solely and those with proposed elements. It could be shown that the ductility of the system is affected by the position of the proposed element. Reducing the base shear due to earthquake records and also decreasing the permanent displacement of the structural stories after earthquake occurrence are some of other advantageous of the presented element. Inserting the new proposed elements in bracing system can also reduce the input energy of the system, during the earthquake. In general view, it can be concluded that by appropriate design of the proposed element, the other structural elements behave elastically and the inelastic behavior is happened in the presented elements, which is resulted in improving the seismic structural performance of the new system.The results of this study can be used in seismic design of earthquake resistant structures.

Bridges are exposed to damage during their service life which can severely affect their safety. Thus, it is important to monitor bridges for existence of damage. A damage in a structure alters its dynamic characteristics. Changes in properties such as the flexibility or stiffness matrices derived from measured modal properties and changes in mode shape curvature have shown promise for locating structural damage. Since damage alters the dynamic characteristics of a structure, namely its eigenproperties (natural frequencies and modes of vibration), several techniques based on experimental modal analysis have been developed in recent years. Therefore vibration characteristics of a structure can be used as the basis for vibration based damage detection (VBDD) techniques. These techniques have been recently subjected to a considerable amount of attention for damage detection due to their relative simplicity and the moderate cost of dynamic measurements. Damage detection methods based on the dynamic measurements of structures are one of the most important techniques for damage evaluation in bridges. VBDD methods use damage-induced changes to the dynamic properties of a structure to detect, locate, and sometimes quantify the extent of damage.VBDD methods are able to detect damage with information from the dynamic response of the bridge only. The performance of these methods for damage detection in bridges has not been fully proven so far and more research needs to be done in this direction. In this article a new method base on developing the Co-Ordinated Modal Assurance Criteria and Damage Inedx (DI) is present. For applying these methods, mode shapes and natural frequencies that came from health bridges model and damage bridges model are used. The bridges that used are a two-span bridge and a five-span bridge that modeled and verified. To verifying the models, five natural frequencies of the models that created with software, copmared to natural frequencies of the original models. In this article just one element defined as damage location. The damage created by redusing stiffness in one element near the abutments. The four level damage that considered are 15%, 30%, 70% and 90% reduce in module of elasticity. At first the unability of COMAC and DI methods to detecting the damage near the abutment is shown. Then the new method base on these method is presented. This new method is use of mode shapes that obtained from several longitudinal section instead of one longitudinal section. Results confirmed that if mode shapes are just extract from one longitudinal section like before, methods can not always detecting the damaged cross section or damaged longitudinal section. But if mode shapes obtain from several longitudinal sections, these methods will be able to assessment the damaged cross section plus damaged longitudinal section. Although in the most of the times these methods detecting the elements at the abutment as damage location wrongly. So it is necessarily to eliminate the result of the element at the abutment and then decided for the damage location. Besides it is concluded that for detecting the damage near the abutment, COMAC method has better result than DI method.

Safety is an area of increased attention within transportation engineering. The development of cities caused increasing of vehicles and accidents. The accident statistics show that the intersection points are one of the most eventful that occur 50 percent of all accident and 25 percent of human casualties.The first step in improving traffic safety is identifying hazardous situations. Based on trafficaccidents’ data, identifying hazardous situations in roads and network is possible. However, in small areas such as intersections, especially in maneuvers resolution, identifying hazardous situations is impossible using accident’s data. Due to shortcomings of traffic accident data, using surrogate measures such as traffic safety indicators have been taken into consideration. Therefore, in this study was used the traffic conflict. According to different problems of traditional traffic safety evaluation, the using of necessary methods is needed. In recent years, using of traffic conflict indicator has increased. Time-to-Collision (TTC) is one of the first and most widely used time-based indicators. For using of these indicators the users’ speed, moving direction is needed. For high attention in safety evaluations and considering the type of the vehicle, two dimensional modeling of vehicle is presented. The critical interactions density index was based on the TTC indicator and traffic volume. The hazardous situations were identified three-dimensional by using ARC GIS software in the physical area of the intersection. By using this method, there is possible to identify hazardous situations based on critical traffic conflict. By using information obtained, determined how to improve intersection safety. Four-leg unsignalized intersection located at the crossroad of Vessaleshirazi-Bozorgmehr in Tehran has been selected as study location. By video analyzing, data was recorded and hazardous situations were determined by using the method proposed in this paper. The evaluation results show that at the entrance minor path to major path the hazardous situations has been located because of conflict of the right movement minor path with the direct movement of the major path and the left movement minor path with the direct movement major path. The risk of right movement of minor path, conflict to direct movement of the major path is 245.1 that about 8 times the average risk of all movements and, the risk of similar conflict on the other side of the intersection is 89.These conflict are the main reason for the increasing of the intersection risk.

The lateral spreading of mildly sloping ground and the liquefaction induced by earthquakes can cause major destruction to foundations and buildings, mainly as a result of excess pore water pressure generation and softening of the subsoil. During many large earthquakes, soil liquefaction results in ground failures in the form of sand boils, differential settlements, flow slides, lateral spreading and loss of bearing capacity beneath buildings. Such ground failures have inflicted much damage to the built environment and caused significant loss of life. The risk of liquefaction and associated ground deformation can be reduced by various ground improvement methods, including densification, solidification (e.g., cementation), vibro-compaction, drainage, explosive compaction, deep soil mixing, deep dynamic compaction, permeation grouting, jet grouting, piles group and gravel drains or SCs. Nowadays, using pile foundation is one of the popular solution for soils vulnerable to liquefaction. the pile with enough length more than liquefiable soil depth can reduce the large deformation and unacceptble settlements. Liquefaction and lateral deformation of the soil has caused extensive damage to pile foundations during past earthquakes. Several example of significant damages in pile foundation have been reported in the literature from the 1964 Niigata,1983Nihonkai-Chubu,1989 Manjil and 1995 kobe earthquakes. These damage have been observed mainly in coastal areas or sloping ground. evaluation of liquefaction in order to develop the northern and southern ports and implement coastal and offshore structures in Iran is of particular importance due to locating in a high seismic hazard zone and Liquefactable soil in coastal areas. Although, in recent years many studies have been conducted to understand the various aspects of this phenomenon, yet a lot of uncertainties have remained about the lateral deformations of the soil and its effects on deep foundations. In this study, behavior of pile groups (2 × 1, 1 × 3, 2 × 2 and 3 × 3) were evaluated using fully coupled three-dimensional dynamic analysis. Therefore, the influence of effective parameters such as number of piles, ground slope angle on soil and pile behavior has been studied using the finite element software Opensees SP v2.4. results indicate that most of the factors affecting the behavior of the pile, soil are not considered in the current design codes (such as JRA 2002) and these issues indicate the need to revise the current design and analysis methods.Lateral Pressures compared to that of JRA regulations show that these regulations cannot exactly predict pressures on pile and pile groups. Altogether comparing the results of numerical model of this research to various laboratory observations indicate that the use of numerical method can be reliable to predict the behavior of the soil and pile qualitatively and quantitatively using appropriate constitutive model and parameters for soil and pile.

Woody debris accumulates in front of bridge piers, reduces the flow area, deviates the flow and increases the velocity around the bridge piers. Debris accumulation in front of bridge piers increases the downward flow, and shear stress around the bridge pier, therefore, the scour hole depth increases and bed degradation accelerates. Most of previous researchers focused on the scour depth around the bridge piers, and less researchers have investigated the effect of debris accumulation on the scour depth. To the best of our knowledge, the effect of debris accumulation on the scour depth has not been reported in previously published literature, as explored in this work. The purpose of this study is to experimentally investigate the effect of accumulation of woody debris in front of a square pier with a parabolic nose on the scour depth. The experiments were performed in clear water condition, with and without debris accumulation and with 20, 30 and 40 l/s discharges and for different debris dimensions. The experiments were performed in a sixty centimeter width channel at the hydraulic laboratory of Shahrekord University. Previous field studies showed that most debris accumulates in front of bridge piers in rectangular shapes, therefore three different rectangular shapes debris are designed and are placed in front of bridge piers during the experiments. Since, performed experiments at twelve hours showed the maximum equilibrium scour depth occurs at the first seven hours, therefore, all experiments are done in 420 minutes. The results showed that when woody debris is placed over, at, and below the water surface respectively, the ratio of scour depth to the scour depth of control sample is 2.2, 2.36 and 1.44, respectively. Moreover, when the percentage of blockage (ratio of the occupied flow area by debris to the flow cross section) is 30% and when debris is located below the water surface, the maximum scour depth will occur (2.36 with respect to the control sample). Also, the comparison between a square pier with parabolic nose and a sharp nose piers at the same hydraulic condition, show when there are no debris, the scour depth around the square pier with a parabolic nose is less than the scour around a sharp nose square pier (1.5 times). For the case in which debris are placed in front of bridge pier, the scour depth, width, and length around a square pier with a parabolic nose are significantly decreased with respect to a sharp nose square pier (2.3 times). Also, using dimensional analysis an equation is presented for predicting the maximum scour depth around a square pier with a parabolic nose in presence of woody debris accumulation. The results show that there is good agreement between predicted and observed scour depth.

Mercury is a highly toxic and accumulative metal and its compounds, especially methyl mercury, are neurotoxins which cause blockage of the enzyme sites and interfere in protein synthesis. The fate of inorganic, mercury ions in nature is its turning into methyl mercury due to the aerobic action of microorganisms. Mercury is a toxic metal that causes the serious environmental problems. The main sources of mercury ions in aquatic ecosystems are divergent, chloralkali wastewater, oil refineries, power generation plants, paper and pulp manufacturing, rubber processing and fertilizers industries. Various methods have been used for removing heavy metals from aqueous environment such as reverse osmosis, chemical precipitation, ion exchange, coagulation and adsorption. Among these methods, adsorption process is extensively used for the uptake and pre-concentration of heavy metal ions from aqueous solutions. Many carbon-based nanoparticles (CNTs) have been developed to remove heavy metals from aqueous media. They are promising material for numerous applications due to their unique electrical, mechanical, thermal, optical and chemical properties. In addition, CNTs are proven to be superior adsorbents for several divalent metalions in water, because of their capability to establish ( p-p) electrostatic interactions as well as for their large surface areas. Therefore, they have received considerable attention for usage in analytical chemistry and environmental remediation. Multi-walled carbon nanotubes (MWCNTs) were the first observed CNTs involving of up to several tens of graphite shells. The sorption capability of MWCNTs is related mainly to the functional groups attached on its surface. Generations of functional groups on the surface carbon nanotubes improves the reactivity and provides active sites for further chemical modifications. Many researchers have developed amino and thiol functionalization on carbon-based adsorbents and CNTs in order to increase the adsorption capacity, selectivity and removal efficiency of heavy metals and organic compounds. Among these functional groups, the thiols have an excellent binding ability to some metals such as silver, mercury, copper, nickel and zinc. In present study, multi-walled carbon nanotubes were functionalized in four stages to create thiolated multi-walled carbon nanotubes (MWCNTs-SH). The synthesized amino and thiolated MWCNTs were characterized by Fourier transform infrared spectroscopy (FT-IR) and elemental analysis (CHNS) to ensur successfully entailing the functional groups on MWCNTs surface. The efficiency of all synthesized MWCNTs in mercury removal was investigated. MWCNTs-SH was more efficient rather than other synthetized adsorbents in mercury removal from aqueous solutions. Furthermore, increasing in adsorbent dosage concluded an enhanced mercury removal and the MWCNTs-SH in a low dosage can give a high mercury removal. Solution pH has a more effect on mercury removal. When the pH increased from 2 to 8 the removal percentage ranged from 9.8 to 92%. The data fitted by Langmuir isotherm model (R2=0.966) better than Freundlich model (R2=0.935). The obtained maximum adsorption capacity (qm) by Langmuir model was 206.64 mg/g while its experimental value was 160.90 mg/g and was higher than that reported in other literatures. Thus the prepared synthetized adsorbent has high efficiency for mercury removal from aqueous solutions.

The anchored walls consist of nongravity cantilevered walls with one or more levels of ground anchors. Nongravity cantilevered walls employ either discrete (e.g., soldier beam) or continuous (e.g., sheet-pile) vertical elements that are either driven or drilled to depths below the finished excavation grade. For nongravity cantilevered walls, support is provided through the shear and bending stiffness of the vertical wall elements and passive resistance from the soil below the finished excavation level. Anchored wall support relies on these components as well as lateral resistance provided by the ground anchors to resist horizontal pressures (e.g., earth, water, seismic, etc) acting on the wall. A prestressed grouted ground anchor is a structural element installed in soil or rock that is utilized to transmit an applied tensile load into the ground. The basic components of a grouted ground anchor include the anchorage, free stressing (unbonded) length, and bond length. It is of note that the anchor bond length should be located behind the critical failure surface. The first use of ground anchors in the US was for temporary support of excavation systems. The use of permanent ground anchors for public sector projects in the US did not become prevalent until the late 1970s and today, represent a common technique for earth retention and slope stabilization. Anchors play a vital role in geotechnical structures such as excavations. The anchor section in soil is generally divided into five areas including reinforcement element, grout, grout and surrounding soil mixture, shear zone and soil media. Most of the common geotechnical software such as PLAXIS utilizes limited parameters in order to model the complex behavior of anchors; contrarily, modeling the soil-anchor interaction by means of FLAC yields conspicuous accuracy due to considering over ten various parameters. The main objective of the present research is to determine the soil-anchor interaction parameters for numerical modeling of anchored walls using FLAC2D software. Fundamentally, the main challenging issue in estimation of the anchor force is to determine the injection area diameter. According to the proposed method, the diameter of the injection area is determined based on the injection pressure, grout volume, porosity and shear zone thickness. It is demonstrated that the diameter of the injection area in soil medium is approximately 40% greater than the drilling diameter; nonetheless, that of the injection area in rock media is equal to the drilling diameter. The other parameters are determined by equalization of rock media formulas for soil media. In order to ensure the validity of the proposed methodology, the pull-out test was numerically simulated in FLAC2D, besides the numerical results have been then verified with anchor tension data in a field excavation project. The results indicate that the ultimate load of the anchor calculated from the numerical model is in fair agreement with equations postulated by many of former researchers. Correspondingly, there is a negligible difference between the displacement value obtained in the numerical simulation and the field pull-out test results. Henceforth, this method can be utilized in numerical modeling of anchored walls in soil media with high precision.

The Public complaint about odor pollution against local authorities has started for many years. Several industries generate odor such a poultries, livestock industries and landfill. Odor emission is one of the important problems of compost production and landfill sites. Therefore, study of the determination of odor emission from residential, institutional and commercial centers, considering geographical conditions and local climate of composting site or center of odor generation, is vital. Ammonia emits from landfill and composting plant and generate a bad smell. Toxicity, corrosion and sharp odor are the major specifications of ammonia, considered as the most common odors found in composting and landfill. We studied developing and extending of the odor emissions model of the landfill site and composting production site base on the Gaussian theory of pollution emission. The odor emission equations of Kahrizak composting and landfill sites was analyzed. For solving the equations of odor emission, we applied Pasquill Gifford and Gaussian equation.The coefficient of dispersion in vertical and lateral directions, using local meteorological data was determined according to the Pasquill Gifford method and odor emission was solved using the Gaussian equation. To determine the dominant wind direction, we used WRPLOT view software. For obtaining a velocity of ammonia emission, the first order equation was used. For the identification of stability class specification for the day and specified location, Monin–Obukhov length and net radiation were used. The effect of radiation angle and topography parameters of the area in our calculation was considered. For solving the Gaussian equation, we established a coding program. Limitation of our study was a lack of data in the study area for testing our model. Therefore, we compared our results with similar research in the world and also used a sensitivity analysis to prove the validity of our model. The results indicated that the ammonia emission rate from the Kahrizak Complex was about 163 g/s. By solving the Gaussian equation, we obtained the instant maximum ammonia emission equal to 180mg/m3 from 80 meters from the source at an effective height of 1.5 meters. The emitted ammonia could be detected up to 2 km away from the complex center. A comparison of our results with outcome of similar studies indicates the reliability of the model. Considering the location of residential area which is at 8.1 km far from the Kahrizak landfill center; therefore, no any danger will occur for people live in the area due to ammonia emission from Kahrizak landfill site.

One of the important aspects which may affect the seismic response of gravity dams is dam-reservoir-foundation interaction. The dam-reservoir interaction must be taken into account, since the dam undergoes deformation which influences the motion of water in the reservoir. Due to the complexity of a dam¬reservoir-foundation system, the finite element method is an efficient tool for studying the dynamic response of such a system not only due to the complicated geometry of the dam-reservoir-foundation system but also due to the mechanism of incident earthquake waves and different boundary conditions which can be simulated more appropriately. In order to seismic analysis of gravity dams, a computational procedure for two-dimensional finite-element analysis of damreservoir foundation systems subjected to seismic excitations is developed using Ansys software in this research. Water is assumed as a compressible, inviscid fluid with small amplitude displacements and the dam is modeled as an elastic solid. The analysis is carried out in time domain considering dynamic excitations. Newmark time integration scheme is developed to solve the time-discretized equations which are an unconditionally stable implicit method. An application of the procedure to a study of the seismic optimization of concrete gravity dams using hydrodynamic isolation layer under horizontal and vertical ground motions is presented and discussed. In this study, the hydrodynamic isolation layer is used for the geometry and seismic optimization of concrete gravity dams. For this purpose, the volume of dam body is considered as the objective function and constraints of various geometrical and structural behaviors in order to optimize the concrete gravity dam under seismic loading. To demonstrate the effectiveness of the developed numerical model, the response of Koyna dam in India due to Taft ground motion is presented as a case study to show the hydrodynamic isolation effects on seismic optimization of concrete gravity dams. The model was analyzed and compared for the cases in which the isolation layer attached along the upstream face of dam for different conditions.Consider to obtained results, it is revealed that the isolation layer can have the reducing effect on responses of dam model because of damping the induced hydrodynamic pressure due to earthquake.The layer reduces the dam response due to the hydrodynamics effect of the reservoir in essentially two different ways: (a) the layer serves as a boundary for the reservoir with a low reflection coefficient which results in reduction in the developed hydrodynamic pressure in the reservoir compared with the case of a completely reflective boundary. This effect was addressed in the previous part of the theoretical solution excluding the layer's isolation effects. (b) the isolation of the dam from the hydrodynamic pressure is the result of the layer thickness as well as its material properties which alter the amplitude of the transmitted pressure wave across the layer.

One of the most efficient energy dissipatoion structures in open channel flow are block ramps; which have been considered and used most often recently because of the simple performance. This kind of energy dissipators can be assumed as a particular type of baffle block chutes, but with natural base materials like sands and gravels and without cement. In laboratories, several physical models have been built and examined regarding their efficiencies to dissipate energy of flow. These experimental studies are not only too expensive and time consuming, but also some of the hydraulic conditions like higher velocities could not be obtained in controlled conditions of laboratories. Moreover, there are always problems with changing scales in laboratory studies. Hence, using computational fluid dynamics (CFD) codes are to some extent more favorable to engineers with which fluid hydraulic behavior is more widely examined. This paper at first, reviews the classifications of these structures regarding their fabrication and roughness from various point of views, and then deals with the formation of some types of flow regimes with different volume flow rates on them. In continuation, to study the three dimensional flow field around block ramps, Flow-3D software is utilized and hence, the mechanism of energy dissipation on various flow regimes on these structures has been surveyed. In this research, incompressible fluid assumption is made and Large Eddy Simulation (LES) turbulence model is used. Since it was a shallow water condition, Volume of Fluid (VOF) method is used to calculate the free surface elevation. The numerical results showed the more energy dissipation with more turbulence and more turbulence with forming the recirculating flow and extending the distance of the reattachment point from the boulders. Consequently, energy dissipation is maximum for lower volume flow rate and higher slope of the ramp. Since in these two conditions, the flow involves with roughness of the ramp more and more; hence it gets easier for turbulent flow to happen. In other words, energy dissipation is also maximum for the non-submerged boulders. Flows for the cases in which boulders are submerged have different mechanism of energy dissipation. In these types of flows, energy dissipation is maximum for the wake-interface flow condition and isolated roughness flow condition, respevtively. Therefore, in order to enhance the energy dissipation in flow over block ramps, it is advised to reduce the effective cross section or reduce the submergence of scale roughness while maintaing the same effective cross section and the volume of fluid flowing over the structure. Changing the boulder ordering from rows to staggered would be another way to increase the energy dissipation.

The importance of fire effect on stability of steel structures has become one of the major issues for structural engineering researchers. Since steel is very susceptible to high temperature and cost of strengthening the elements with use of fire proofing material or any other provision, the need for rigorous investigation of the behavior of steel frames at elevated temperature in order to reduce unfavorable effect is well understood. To achieve this goal, researchers have carried out both experimental and theoretical investigations. It is clear that the cost of experimental research is high and is not available in all the institutions. It is also know that due to the limitation of the parameters to be studied, finite element procedure can be used as a powerful method of investigating structural behavior under extreme loading. It has been approved that the modeling of structural elements can be performed by this procedure that will best represent the structural behavior under fire. In this research the effect of fire on steel beams considering the softening behavior of connection and reduction of strength of material is studied. ANSYS software is used for this purpose and beam sub-assembly that has been used by Bradford, with the same assumptions has been adopted considering different boundary conditions. The standard variation of temperature is imposed at the geometrical center while linear temperature gradient is considered though the beam cross section. Uniform gravity load representing service load is also imposed on the beam. Restrained ends are modeled by elastic springs with calculated stiffness. Bredford beam is first modeled with the same assumption to calibrate the modeling. In this research a four story steel building with concentrically bracing is designed and one of the exterior frames is selected for the study. ISO 834 as an standard fire is imposed on the beam. Cardington natural fire curve showing the variation of the temperature with time is also used on the beam. One of the beams of the frame is assumed to be in compartment and a uniform as well as partial fire are imposed on the beam. At the end of the beam both translational and rotational springs are provided. Nonlinear moment-rotation curve obtained from Yahyai and Saedi experiment is used. For linear spring behavior, lateral stiffness of the frame is considered. The results are obtained in the form of displacement and axial load at the center of the beam under partial and uniform fire loading. Endurance time of the beam at various temperature is obtained. As the results shows the displacement and axial loading at 500 degree increases considerably due to the reduction of the modulus of elasticity under both partial and uniform loading. This increase is more for uniform loading case. Endurance time is more in case of natural fire as compared to standard one. This is due to the steep slope of the standard fire curve.