Modares Civil Engineering journal
Year:2016 | Volume:16 | Issue:1|Papers Count:22

Spur dikes are man-made transverse river structures. They divert the high velocity to the channel center and prevent undesirable bank erosion. In this paper, flow structure around a single spur dike with side slope is investigated experimentally. Three dimensional flow field around a single spurdike with 75o side slope located in a flat-bed rectangular laboratory flume has been measured using the Acoustic Doppler Velocimeter (ADV) and mean flow and turbulence parameters are investigated. Downstream of the spur dike due to the decrease of the flow velocity, a recirculation zone forms, while the flow accelerates at the middle zone of the channel. Upstream of the tested spur dike, flow is divided into two parts. A part of the approaching flow is diverted to the channel bed and the remaining form a bow wave near the water surface. Downward deflected flow interacts with the near bed approach flow and results in the horseshoe vortex. The horseshoe vortex is the main responsible for scouring at the upstream of the spur dike. Dye visualizations showed that due to the upstream side slope of the spur dike, the down flow is weaker than the spur dike with vertical side slope. Along the main channel two distinctly velocity amplification zones form. A velocity amplification along the outer boundary of the shear layer, downstream of the spur dike forms due to the local effects of the spur dike. Due to the spur dike constriction imposed to the channel, another high velocity zone forms. The second velocity amplification zone forms along the right channel wall. Flow velocity in the first amplification zone is higher than the second zone. The horse shoe vortex is strong near the lower layers and consequently the velocity amplification along the shear layer at the near bed layers is higher than the near water surface layers. By going from near bed layers to the water surface layers the extent of the second amplification zone increases. Flow streamlines at the near bed plane shows development of some oblique streamlines, after the reattachment zone. This stream lines are attributed to the coherent flow structures reported in the literature. The near bed streamlines are more diverted to the opposite channel wall, compared to the near water surface layers. By going from the near bed layers to the water surface layer the center of the recirculating zone moves downstream. The mean flow kinetic energy is amplified 2.5 times of the approach flow. The maximum mean flow amplification occurs at the central zone of the channel, while the maximum turbulent kinetic energy is measured along the outer boundary of the separation zone. The higher turbulent kinetic energy along the shear layer is responsible for the pickup and movement of the sediment particles at low mean velocity zones. Distribution of the Reynolds shear stresses show that the maximum-`pu’v’ stress occurs along the shear layer bounding the separation zone. Minus values of the `pv’w’ and `pv’w’ stresses shows that the sedimentation will occur at the downstream zone of the spur dike.

The existence of soft clay and dispersive soft clay at the site of engineering structures is regarded as one of the geotechnical problems. This study is performed on silty soft clay that according to the experimental results showed 100% dispersivity potential. Due to the low bearing capacity of this type of soil in the site, the slaked lime was used to stabilize the soil geotechnical properties, to increase its strength, to decrease plasticity behaviour of soil, and to overcome its dispersive properties. The main goal of the present study is to determine the growth rate and progress of lime-soil pozzolanic reactions in short and long terms from micro- and macro- structural point of view, as well as the measurement of the consumed lime rate over the time and its effect on mechanical parameters of the stabilized soil. The results of this study allow determining the minimum percentage of the lime that is necessary to react with clay minerals for making an acceptable change in long-term properties of stabilized soil. Since the hydration of cement produces lime, one would expect that a main element of the soil–cement interaction process can be studied in terms of interactions between lime and clay minerals. The addition of lime or cement to clay minerals and clayey soils – i.e. soils with a significant proportion of clay minerals – in the presence of water produces both short term and long-term reactions. In this regard, a number of tests carried out with different percentages (0 to 10 percent) of hydrated lime. The pH, electric conductivity (EC), unconfined compressive strength, and lime consumption rate determination by X-ray diffraction analysis were the tests used in this study to observe the progress of lime reaction with clay. In order to determine the microstructural and mineralogical changes, and reaction products formed in the modified soil, X-ray diffraction (XRD) evaluation and scanning electron microscopy images have been used. Among the most important results of the present study, this paper propose a simple criterion for the onset of pozzolanic reactions and determination of the consumed lime rate during the pozzolanic reaction process based on pH and electric conductivity measurements. Based on the results from pH, EC, XRD, and unconfined compressive strength (UCS) tests, the pozzolanic reaction occurs at EC³4 mS/cm. Following that, the formation of new components such as calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) causes an increase in soil strength. Over the time, with the reduction of EC£4 mS/cm and pH£12.4, the progress rate of pozzolanic reaction and the progress rate in soil strength suspend. The results show that for the dispersive soil around 3-4% lime is sufficient for its short-term reaction, which includes cation exchange. Based on the achieved results, the use of 6% lime for stabilization of sample gives EC³4.0 mS/cm and pH³12 after the first 14 days period. The unconfined compressive strength of the stabilized sample increased around 10 times in the same period, while only 5% increase in strength observed after 14 days (EC£4.0 mS/cm and pH£12).

Shaped charges are explosive devices with a high penetration capability and are used for both civilian and military purposes. In civilian applications shaped charge devices are used in demolition works, oil drilling and mining. In the military applications, shaped charges are used against different kinds of armors and Protective Structures. Analysis of forming and penetration of shaped charge projectiles issue is so complex that include explosion of charge, propagation of the shock wave in the charge, hitting the shock wave to the liner, liner deformation, projectile formation and finally striking projectile to target until it stops. According to the complexity of Behavior of the concrete during the Penetration of the Jet, the material models shoude be able to model the effect to large deformation, high hydrostatic pressure, high strain rate and failure. Although there are many references about Numerical simulation of shaped charge Jet in the armor targets, however it was not found any comprehensive sources about penetration of shaped charge in the reinforced concrete targets. Experimental results suggest that both kinetic energetic projectile and shaped charge are capable of destroying concrete targets, but the magnitudes of damage due to them are different. Compared with a kinetic energy projectile, a shaped charge has more significant effect of penetration into the target, and causes very large spalling area. In this paper, AUTODYN software was used to numerical simulation of shaped charge jet formation and target penetration. Different solver and modeling alternatives of AUTODYN were evaluated for jet formation and penetration problems. Euler solver of the AUTODYN was used to jet formation simulations and Lagrange solver was used for penetration simulations and both models were 2D axisymmetric. To simulate the penetration performance of the RPG – 7 charge, both the jet and the target were modeled by Lagrangian elements. The results of jet formation simulations, performed by the Euler solver were used to determine the properties of the jet. Penetration simulations were performed for a fixed 2 CD standoff distance. The jet material distribution obtained by the Euler solution at 2 CD standoff distance was mapped onto the Lagrange solver. The quality of this Euler-to-Lagrange mapping was limited to the mesh resolution of the Lagrangian jet part. The first goal of this research is presentation of a reliable method to numerical simulation of Penetration of shaped charge of RPG – 7 into the concrete targets by use of available software tools. Therefore, simulation results were compared to the experimental results in three stages that Include the jet formation, jet Penetration in armor targets and behavior of concrete target against Penetration. The second goal is determination of the safe thickness of conventional concrete targets against the Penetration of RPG – 7 weapen and investigation of the behavior of this concrete type of target in terms of penetration depth, hole diameter and failure of the front and rear surfaces of the target.

Buried pipelines, commonly used to transport water, gas and oil, are critical elements of the infrastructure of today’s modern cities and usually pass through large geographical distances. They are classified as lifelines as they carry materials that are essential to support human life. Due to the importance of maintaining the operability of these lifelines, it is of primary importance to study the effect of different hazards on their behavior in order to be able to mitigate any possible damages. Therefore, they could be subjected to different types of natural hazards such as earthquakes in the form of permanent ground displacement and/or wave propagation. Seismic waves could pose great threats to above ground facilities and perhaps to a lesser content to buried pipelines. Permanent ground displacement is often caused by surface faulting, landslides, or liquefaction. Over the past years, many researchers have attempted to study the behavior of buried pipelines crossing active faults. Many reconnaissance reports show that significant damages are observed in buried steel pipelines crossing active faults. The corresponding ground deformations are applied in a quasi-static manner, and are not necessarily associated with high seismic intensity. During the ground deformation, the pipeline may undergo severe deformation, well beyond the elastic range of pipe material and may cause pipeline failure, i.e. high tensile stresses may result in tensile fracture of the pipe wall, specifically at welds, whereas compressive stresses may cause local buckling or wrinkling of the pipe wall. In case of moderate buckling, deformation of the pipe cross-section can lead to flow restriction and high friction losses, and eventually require line replacement; while for severe buckling high localized strains can lead to pipe rupture, loss of contents, and possible pollution of surrounding soil. The present study investigates the mechanical behavior of buried steel pipelines, crossing normal faults of right angle in loose clay. The pipe is assumed to be normal to the fault plane. The interacting soil–pipeline system is modeled through three-dimensional finite element method, which accounts for large strains and displacements, nonlinear material behavior, friction and gap forming on the soil–pipe interface. The analysis is conducted through an incremental application of fault displacement. Considering steel pipelines of various diameter-to-thickness ratios, and typical steel material for pipeline applications, the present study concentrates on identifying the fault offset at which the pipeline fails considering different performance criteria and to use them for performance-based design purposes. The results are presented in the form of diagram showing the critical fault displacement, and the corresponding critical strain versus the pipe diameter-to-thickness ratio. Results show that for pipelines buried in loose clay, the governing failure mode is local buckling of the pipe wall, which occurs at two locations along the length of the pipeline. The distance between the two locations at which local buckling occurs increases with decreasing pipe diameter-to-thickness ratio. It is shown that with increasing pipe diameter-to-wall thickness ratio, longitudinal compressive strains in the pipe wall increases and consequently the capacity of the pipeline to accommodate the ground deformation decreases significantly.

Land subsidence caused by natural factors and human activities in different parts of the world. This phenomenon consists of collapse or settlement of the surface level that may occur due to some reasons such as the dissolution of subsurface formations, sediment compression, loading, drainage, vibration, subsurface mechanical erosion, shrinkage of clay soils, tectonic subsidence and etc. Land subsidence, as a serious crisis, has been observed in several Iranian plains in recent years. By the continuation of drought and excess withdrawal of water resources, land subsidence and gaps have slowly extended and it can impose expensive financial and social costs on the government gradually. Water consumption and withdrawal of under groundwater are important factors in the plain of Iran that is very irreparable and alarming. Low rainfall, nonexistence of appropriate nutrition for aquifers, continuous pumping is caused the groundwater level of plain in the most provinces during the past years has always reduced. The most important results of groundwater level dropping that can be noticed are land subsidence; increase the cost of drilling deeper wells and water pumping, drying and decreasing the water of wells, springs and water quality. On a global scale, hazard of land subsidence due to dropping water levels has reached its peak between 1950 and 1970, which coincided with industrialization and urbanization growth. This phenomenon has been observed in many parts of the world such as northern Greece, northern Italy, China, Mexico and japan in the past years. Hu et al. (2004) reported these phenomena in over 150 cities worldwide. And also regional land subsidence related to the groundwater level dropping has been reported in many parts of Iran such as Ardakan plains of Yazd, Moin Abad in Varamin and Shahryar in Tehran. Also, subsidence along with the drop of groundwater levels has been reported in many aquifers such as Sistan Plain, Kashmar plain in Khorasan and Mashhad plain. In this paper was shown that subsidence in recent years is appeared in Fars province due to indiscriminate withdrawal of groundwater, drought and other factors. Land subsidence caused lots of damages to agricultural lands, residential buildings, roads, and other structures and generally created environmental, social and financial problems. In this research a case study was performed on the villages of Marvdasht plain in order to study the effective factors and parameters and evaluate the influence of each one on land subsidence. And also was examined how to determine and evaluate the main effective parameters such as water levels falling, material and thickness of soil layers especially fine-grained, geotechnical properties of soil layers. Results showed to perform of subsidence calculations the data and requirement information should be prepared accurate and complete as much as possible. It should be noted that the characteristics and different statues of each parameter must be considered. For example, the amount of settlement is different in various depths due to same water falling or same thickness of layers.. Based on the analysis of the data, the most important factors which caused land subsidence in Marvdasht plain and damage to rural buildings were water table dropping due to excessive exploitation of water resources, the decrease of precipitation during the studied time and presence of thick clay.

Soil improvement techniques are mostly consisted of 5 groups including chemical, physical, mechanical, biological and electrical methods. Materials such as lime, cement, coal ash, enzymes and some type polymers are used for chemical stabilization, while geogrides, geotextiles, metal bars and polymer fibers are used to improve soil performance as the physical methods known as soil reinforcement. Several techniques have been used for soil reinforcement. In 1966, Vidal first used galvanized steel strips to improve the properties of cohesionless soils. Since then, numerous reinforced earth structures have been constructed throughout the world. One of the reinforced soil applications is the construction of reinforced soil retaining walls. Due to the advantages of reinforced soil retaining walls, the usage of such walls in civil engineering projects has shown an increasing trend over the past three decades. Nevertheless, more studies seem necessary to achieve optimal designs for such walls. The use of reinforced soil in strengthening foundations to bear and designing earth retaining structures is a method widely used in recent years. On the base of the studies done and comparison of different criteria in various retaining walls, it has become clear that the use of earth walls reinforced with geosynthetic is prior to other kinds of walls practically and economically. In this research study, an attempt was made to investigate the effect of tilted face, oblique reinforcements as well as anchorage of the end side of reinforcements on the performance of retaining wall using laboratory scale wall models. In this context, 14 models of the walls were constructed and their performance was determined under static loading. The models of retaining walls were built in a flexible laminar box to considerably reduce the boundary effects. Model retaining walls were constructed in the laminar box to a size of 60 cm×39 cm in plan and 60 cm deep. Locally available dry sand is used as the backfill material. The sand is classified as poorly graded sand with letter symbols SP as per the Unified Soil Classification System. The model walls are reinforced with geogrid layers. According to FHWA (2001), the length of reinforcements chosen is equal to 0.7H. In case of rigid-faced walls, the facing is constructed from 25 hollow rectangular wood box sections of 4 cm height and 5 cm width. On the base of the observed results, horizontal deformation of wall face is compared with the state of horizontal block to determine the optimum angle at which less deformation appears in wall face. The experimental results provided enough evidence that horizontal deformation of the wall face decreased with tilting it towards backfill. Moreover, using oblique reinforcements caused more reduction in the wall horizontal deformations. As a typical case, it was found that the reinforced soil wall model with oblique reinforcements of 10 degree and sloped face of 80 degree provided a 20% reduction in the maximum horizontal deformation of the wall model. Such a result may be considered as significant improvement in the wall performance. Moreover, the anchorage of end side of reinforcements within backfill presented beneficial but limited effects on the wall performance.

In this paper, the flow field between two straight groynes in shallow wide open channel has been measured using Particle Image Velocimetry method. Groynes with 25cm length, 5cm width and 7cm height with two aspect ratios (l) of 1 and 2 have been located in the fully developed zone of a 18m length flume and velocity measurements carried out in order to study the circulating flow, structure of the mixing layer and downstream separation zone. Surface Particle Image Velocimetry was conducted using two Procilica GE1910 CCD cameras with 37 Hz measuring frequency. Images resolution was 90*1660 pixeles. Image processing was performed using GPIV software and Westerweel, 2005 and Brevis, 2009 methods were used for filtering of the measured velocity fields. Matlab programs were developed for the post processing of the measured data. Results are presented in forms of time averaged values, turbulence intensities and the Reynolds stresses at the various zones of the groyne field. Results showed that due to the flow shallowness, most of the turbulent structures are two dimensional. Development of a back flow from downstream zone to the groyne field enhances the complexity of the mixing layer and mas exchange phenomenon compared to the groyne series configuration. In the l=1 case, a fully developed gyre forms inside of the groyne field. The circulation zone is connected to the mixing layer at the head of the upstream groyne. By increasing the distance between the groynes, i.e., for the l=2 case, another circulation zone forms inside of the mixing layer. Consequently the circulation zone inside of the groyne field is depressed in the transverse direction. In the both cases a single gyre forms inside of the groyne field. While, the previous works showed that in the groyne series case, by increasing the aspect ratio, number of the gyres between groynes increases. Furthermore, unlike to the two groynes case, gryres rotate in the clockwise direction.In two groyne case, the rotational energy is fed from the vorticity of the back flow to the circulation zone in the groyne field, while in the groyne series case, the momentum transfer between the free flow and the dead zone in the groyne field is responsible for the formation of multiple gyres inside of the groyne field. Two groynes field has complex dynamic flow features and it is not a suitable choice for modification of the river alignment or the bank stabilizing projects. On the other hand, they move the high velocity zone to the channel center and they could be used as protection measures for the river structures like bridge abutments.The mixing layer of two groynes case is fully dynamic and it can deeply penetrate into the groyne field. While, in the groyne series case, exchange processes between dead zones and main stream are governed by large coherent two-dimensional structures which are generated at the head of the upstream groyne. Consequently, in terms of the environmental issues, the retention time of the trapped pollutants in a two groynes field will be shorter than the groyne series case.

Tanks in water distribution networks are used to store water for emergency conditions, fire flow demand and demand oscillations control. Construction of tanks spends a lot of money and therefore using whole volume of tanks is essential while operation. Otherwise, if tank volume will be more or less than what is required during operation, tank reliability is reduced. Accordingly, in this paper, a new relationship for tank reliability according to water level variation in tanks is defined. Therefore, maximum water level in tanks is defined as the decision variable. The definition of tank reliability is as follows. At first, the values of maximum level for each tank is computed such a way that optimal use is provided from balancing volume of tanks. In fact, for these maximum level values, maximum reliability is achieved for each tank. Now if during optimization process, a value lower than these computed maximum level is selected for decision variables, tank reliability is reduced. To compute the value of tank reliability, the values of tank water level for the selected decision variables is divided by the values of tank water level for maximum tank reliability. Also, because water level variation can effect on pressure and water age in demand nodes, this effect is investigated by considering hydraulic and quality reliability. In fact, variation of water level in tanks changes node demand pressures and in result actual node demands. Also, variation of water level or on the other hand variation of storage volume affects on water age in demand nodes. Besides, in order to investigate the simultaneous effect of water level variation on hydraulic and quality reliability, a relationship is also defined for integrated reliability. Definition of integrated reliability is to investigate whether there is optimum maximum tank level values that both hydraulic and quality reliability is improved simultaneously while tank construction costs is minimum. Optimal management of tanks in water distribution networks to provide required water of consumers with desired quality is of high importance. To achieve this, optimization is defined as a powerful tool. In this paper, by focusing on operation phase, multi-objective optimization of water distribution performance is performed in which tank costs is considered as the first objective and tank reliability, node hydraulic reliability, node water age reliability and integrated reliability is considered as the second objective. Ant colony algorithm is codified in Microsoft Visual C++ for optimization due to its simplicity and high performance. The validity of the edited algorithm is tested on mathematical functions and proved to be applicable on water distribution networks. The created trade-off curve from multi-objective optimization helps the decision makers to select the top choice based on the importance of their own criterion whether it is hydraulic or quality. It should be mentioned that the created trade off curves have been produced under constant hydraulic conditions (i.e. pumps are On for 24 hours and nodal demands are constant). Further study should also consider pump rotation speed as the decision variable to achieve more accurate results. In fact these conditions help operators to make better decisions.

The rigid steel connections were suffered severe damage because of low rotational capacity during earthquakes. Hence many investigations have been performed on the connections of steel structures. In order to prevent brittle failure of connections and damage of main structural members, steel slit dampers with uniform strip width are used in the beam-to-column connections. Slit damper is a plate or a standard section with a number of slits in the web. The remaining strips in the web of damper, dissipate the seismic energy with inelastic deformation absorption and also prevent seismic energy transmission to the main structural members. No special fabrication technique was involved in the slit dampers, thus the device can be easily used in practice. To verify the accuracy of finite element modeling, the obtained results of ABAQUS finite element software were compared with an experimental study done by Oh et al (2009). The analytical results have a good agreement with experimental ones and the average error is about 2%. According to the analyses performed in the ABAQUS, using steel slit dampers with uniform strip width is resulted in stress concentration at the ends of the damper strips, unbalanced distribution of Von-Mises stresses along the strips length and low participation of middle parts of slit damper strips in the energy dissipation. Therefore, to resolve these problems and energy-absorbing area rise in the end parts of strips, elliptic slit damper is proposed and compared with the previous investigated slit damper. Slits dimensions of elliptic slit damper are calculated as such that both of present and previous slit dampers have the same weight. The objective of this paper is to improve the seismic performance of steel slit dampers. Nonlinear analyses are carried out in the beam-to-column connections equipped with slit dampers. Effects of geometrical and material nonlinearity are considered in the analyses. Nonlinear characteristics of steels are defined with stress-strain curves. Bilinear stress-strain curves are used for all steel parts except the slit damper which is defined with completed stress-strain curve. Plasticity behavior of steel materials is based on the Von-Mises yielding criteria. To simulate the behavior of rigid connections, pin boundary conditions are assigned to both ends of the column. Loading protocol recommended by FEMA-350 is used for cyclic analyses. All parts of connection are modeled using shell elements except the split-T plates and the upper plate of slit dampers which are modeled using solid elements. The results of connections analysis under cyclic loading show that the proposed elliptic slit damper causes better distribution of stresses along the damper strips, better hysteresis performance and increase the amount of energy dissipation in the beam-to-column connection. In the proposed slit damper with elliptic slits, stress concentration is decreased in the end parts of strips. Also elliptic slit damper leads to strength and ductility increment in the connection. Additionally, it is concluded that in the proposed elliptic slit damper compared to the slit damper with uniform strip width, the energy dissipation and the maximum plastic rotation of connection increase about 99.6 and 26.8%, respectively.

Abstract -----------------------------Many bridge engineers assume that vertical ground motions during seismic events are unimportant. Current seismic design requirements do not attempt to account for vertical motion effects. Of earthquakes. However the Study on the Accelerometers of the past earthquake indicates that the vertical acceleration can reach values comparable to (and sometimes even higher than) the horizontal accelerations.Some of design codes presume that vertical ground shaking effects can be crudely included in design codes by increasing or decreasing the dead load actions in load combination equations. The current application of this approach is found in the AASHTO Seismic Isolation Guide Specification that uses ±20% of the dead load, in the testing requirements to represent vertical effects of earthquake, irrespective of its magnitude, fault distance, and soil type.For ordinary standard bridges constructed on sites where the peak rock acceleration is expected to be more than 0.6 g, SDC-2006 requires consideration of vertical effects, but does not require analysis of the structure under combined horizontal and vertical components of the ground motion Instead, it stipulates the check of the nominal capacity of the structure subjected to an equivalent vertical load with a magnitude of 25% of the dead load (DL) of the structure applied separately in the upward and downward directions to account for vertical effects.In some other design approaches, that attempt to consider vertical component of earthquake explicitly in the design, a vertical response spectrum with ordinates arbitrarily set at two-thirds of the appropriate horizontal response spectrum at the site is considered. However, recent studies including the present study have clearly demonstrated that this vertical-to-horizontal ratio in many cases underestimates the severity of the vertical component in the near-fault region and at short periods.This study investigates the effect of vertical component of near fault and far fault earthquakes on three span railway bridges of variable spans with box girder cross sections.Results of bridge analyses when vertical motions of earthquake are included in earthquake effects are compared to the case when vertical motions are excluded.Comparison of the results show that the vertical components of ground motions cause significant amplification in the axial force demand in the columns and moment demands in the box girder at both the midspan and at the face of the joints to column. Another finding from the linear analytical study is the fact that the effect of vertical component is completely uncoupled to the horizontal effects.Comparison of the results obtained, with the results obtained from SDC-2006 suggestions shows that a unit multiplier of the dead load effect for compensation of vertical effect of earthquake is not always appropriate. Therefore, for considering the effect of an earthquake's vertical component, preferably it is suggested that the vertical and horizontal components of earthquake is considered simultaneously. On behalf of such analysis, this study suggests different Dead Load Multipliers for different internal forces depending on their positions on the bridge.

Azo dyes are widely used in a variety of industries such as textile. These compounds constitute the largest class of dyes and contains one or various azo groups conjugated with aromatic systems such as acid azo dyes which have sulfonic groups causing strong attachment to the cationic groups of fibers. The characteristics of these materials are high color intensity and visibility in very low concentrations, complex chemical structures, and light resistance and hard to biodegradability, variability in pH range and above of these they have high carcinogenic and mutagenic potential. Generally, the physical, chemical and biological methods are considered as textile wastewater treatment techniques such as electrocoagulation, absorption, advanced oxidation, Fenton, photo-Fenton, photo electrochemical and photo electro catalytic. Electro-Fenton is an indirect oxidation process and is based on in situ electrochemical generation of peroxide hydrogen due to electrochemical reduction of dissolved oxygen next to graphite cathode. In this process hydroxide radicals are generated by reaction of hydrogen peroxide and iron ions in acidic condition. Hydroxide radicals are the most powerful radicals with high oxidation potential lead to degrade organic matters into simple compounds like water and carbon dioxide. Recently carbonic material like carbon felt, graphite, activated carbon fibers, carbon nanotubes, carbonic sponge and graphite-PTFE are used to improve electro-Fenton process. Enhancement of surface area, reaction rate and electron transfer are the main reasons which Carbon nanotubes are used to improve electrochemical production of hydrogen peroxide in electro-Fenton process.Dye removal increased at initial reaction time by increasing current intensity, aeration rate and electrode surface due to enhancing electro-Fenton regents, meanwhile it decreased with increasing pH and electrolyte concentration. Reduction in dye degradation is usually caused by scavenging role of hydrogen peroxide and iron ions due to reaction of these compounds with hydroxyl radicals which decreased its concentration in reactor. Dye degradation increase by enhancement of Initial dye concentration from 35 to 100 mg/L but when initial dye concentration increased further to 200 mg/L, degradation rate was reduced. On the other hand energy consumption reduced by decreasing current intensity from 2 to 1 mA/cm2 and enhancing electrode surface from 30 to 90 cm2. It has been shown that carbon nanotubes coated on graphite cathode could enhance dye removal rate by increasing hydrogen peroxide concentration due to increase electrode surface area, electron transfer and reaction rate. The results showed that dye and COD removal efficiency was obtained 98% and 95% after 180 and 360 minutes respectively at the optimal condition of effective parameters such as current density of 1 mA/cm2, pH of 6.5, no aeration, initial dye concentration of 100 mg/L, electrode surface of 90 cm2, electrolyte concentration of 0.01 M, temperature of 25oC and energy consumption of 0.13 KWh/ppm. Electro-Fenton process seems to be an economic and environmental friendly process to remove the toxicity of the persistent organic pollutants from water due to generation of hydrogen peroxide and hydroxyl radicals. It has been demonstrated that electro-Fenton process with the use of stainless steel anode and graphite cathode coated with carbon nanotube is a very effective and operative method to degrade Acid Orange 7.

Ductility demands of structures are increased during strong ground motion as a consequence of the dissipation of hysteretic energy caused by cyclic load reversals. This phenomenon is called Low-cycle fatigue. The monotonic ductility capacity could not take into account Low-cycle fatigue. Hence this ductility capacity should be reduced in design procedures (equivalent ductility factor) and should be used instead of the conventional monotonic ductility supply in design procedures. The equivalent ductility factor is applied for determination of force reduction factor. In this study, the effect of low-cycle fatigue on ductility capacity factor is examined. For this reason the replies of a single degree of freedom system was evaluated using nonlinear dynamic analysis. Seven records related to soil type II from strong ground database are extracted. Three models have been proposed to determine the equivalent ductility factor taking into account cumulative damage. The first two models based on the maximum displacement and maximum dissipation energy are the upper and lower values. The third one model is Park-Ang model. According to the Park-Ang model, the damage is related to hysteretic energy and concluded of maximum displacement and maximum dissipation energy. The parameter γ controls the hysteretic energy and depends on maximum displacement and natural frequency of the system. In order to obtain the quantity of the parameter g, a parametric study of the inelastic response of SDOF systems was carried out. In the parametric study, input ground motion, as well as the initial stiffness (period), strength, ductility, hysteretic behavior and damping of SDOF systems, was varied. In this paper the variation of this parameter was considered and the effect of the ductility factor, force reduction factor, time history acceleration and damping ratio was evaluated.The results show that the reduction of the ductility factor due to low-cycle fatigue (controlled by parameter g) is significant. It is proved that the parameter is relatively stable during all length of periods. If approximate values for γ are used, the determination of equivalent ductility is very simple, and thus appropriate for design purpose. The parameter g varies from 0.6 to 1.2. For practice peruses it is assumed that the value of g is 0.9. Using this assumption it is possible to determine equivalent ductility factor taking into account low cycle fatigue.

To determine the future condition of pavements in a pavement network, the deterioration rate of pavement condition should be estimated with accordance to traffic volume, environmental condition, pavement type and its thickness. The pavement condition index (PCI) can be used in order to estimate the pavement condition. PCI is a practical index that used in Pavement Management System (PMS) and ranges between 0 to 100. The severity and quantity of pavement disteresses increase as it gets older. As the result of it, PCI decreases with the pavement age increase. PCI can be predicted in future by applying different models. These models consist of deterministic and probalistic models. Deterministic models yield a single value of future pavement condition while the probalistic ones yield a probability for any value of the future pavement condition. Empirical, mechanistic and imperical mechanistic models can be used for pavement condition calculation. Among them empirical models are more practical because of their simpilisity in development and application. In this paper, empirical deterministic model is used to predict the future pavement condition. A lot of research has been done on this subject in the developed country and results are presented presented by performance diagrams. In such diagrams, pavement condition changes within the years are plotted. Performance diagrams can significantly contribute to the road authorities to reduce their costs by right time selection for maintenance and rehabilitation actions, remaining life determination and pavement condition improvement in the road network. In this paper, type, severity and quantity of distresses are collected by visual inspection in Tehran NO.1 district and Sabzevar city. There are up to 5 years old pavements in Tehran district NO.1 which are all rehabilitated or overlayed pavements. In contrast, Sabzevar have mainly initial pavements Rezaa the Rezaa 15 years and consequently are in more deteriorated condition with lower PCI. The least PCI for Tehran NO.1 district is 61 percent and for Sabzevar city is 11 percent. Pavement condition index, as an indicator of pavement condition, is then calculated according to the collected data and Performance diagram, which is the pavement condition change during pavement life, is interpolated using different typical functions including exponentioal, linear and multi polynomial equations up to 3th order on.1th order polynomial diagrams is Rezaa descriptive diagram for Tehran and Sabzevar which are selected based on Adjusted R square and Root mean square error parameters. All the plotting performance diagram, Adjusted R Square and Root Mean Square Error calculation are done by SPSS. Adjusted R square equal to 1 and Root Mean Square Error of 0 are the ideal conditions which means the interpolated diagram passes through the scattered points. To obtain more precise estimation of scattered Rezaa both parameters should be considered as it is done in this paper. The results indicate that if the minimum desirable level of the pavement condition index is assumed 40, then the useful life of the pavement in the Tehran NO.1 district and Sabzevar city will be estimated 7.6 and 11.5 years, respectively.

Hydraulic jump is a rapid and sudden transition from a high-velocity supercritical flow to a subcritical flow in an open channel flow. Stilling basins are used to control the hydraulic jump at the downstream of chutes, sluice gates, … End Sills, baffle blocks and negative steps are often used to control hydraulic jumps in stilling basins. The present study focuses on the formation of hydraulic jump in the new type of stilling basins with stepped sills. Extensive experiments were conducted in a rectangular flume 0.6 m wide, 12.0 m long and 1.0 m deep, with various discharges from 30 to 120 l/s. Water was pumped from an underground sump into a head tank and the discharge was measured with a ultrasonic flowmeter. At the downstream end of the head tank there was a sluice gate into the flume. The edge of the sluice gate has a streamlined lip in the shape of a half-cylinder of diameter 20 cm to minimize flow contraction and provide a uniform supercritical flow. A point gauge with an accuracy of 0.1 mm was used to measure water depths. In order to visualize the flow field, the dye-injection method and a high speed camera were employed. A tailgate located at the downstream end of the flume was used to control the tailwater depth. The effects of stepped end sills on hydraulic jumps were investigated experimentally. Firstly, dimentionless parameters affecting the hydraulic jump on stepped sill introduced using Buckingham π theorem. The effect of important parameters such as approach Froude number (Fr1), relative tailwater depth (gt/g2*) and the end sill geometry (shape and relative height of sill (s/y1)) on hydraulic jump were investigated. The hydraulic jumps over stepped end sills were classified into A-jump, B-jump, minimum B-jump, C-jump and minimum C-jump. By changing the type of flow from A-jump to minimum C-jump, the jump is going to sweepout from basin. A-jump is entirely formed in the basin and at the upstream of sill. In the case of minimum C-jump, most of the surface roller of jump formed at the downstream of sill. The flow types are presented in the form of 6 different diagrams as functions of the relative step height s/y1. By increasing the tailwater depth, sill height, the probability of occurance of hydraulic jump in the stilling basin increased. It was found that the sill with 2 steps have better performance in stabilizing the jump in the stilling basin as compare to sill with 3 steps. By increasing the approach Froude number, the jump began to sweep away from basin. By knowing the initial condition like upstream velocity and upstream froude number, tailwater depth, sill height and its number of steps the toe distance from sill can be found out with desirable accuracy.

Many of the past experimental research on the design of road pavement layers was confined to the behavior of saturated pavements materials. Among the experimental studies to determine the road layers properties, California bearing ratio (CBR) has been one of the most common and applicable parameter for determination of the resistance of roads subgrade in both design and practical purposes. An extensive amount of research exist in the literature that explains the behavior of California bearing ratio of saturated soils. However, any change in the degree of saturation of subgrade materials and in particular different hydraulic response in wetting and drying paths can affect the CBR value of a pavement material. In compare to the extensive previous studies on the California bearing ratio of soils, this phenomenon is rarely concerned in the previous studies. The goal of this laboratory research is to examine the influence of the initial compaction void ratio, moisture content, degree of saturation, matrix suction and hydraulic hysteresis on the California bearing ratio of a pavement material. To this end, California bearing ratio of a sand-kaolin mixture was measured in a range of initial void ratios and initial water contents along drying and wetting portions of the soil-water characteristic curve. The CBR tests along wetting paths was performed on the soil samples that were dynamically compacted and wetted in a range of initial void ratios and initial water contents. The CBR tests for drying paths was also carried out on the soil samples that were compacted identically to the samples used in wetting tests, but they were air dried for seven days before CBR measurements. The air drying process was achieved from the both ends of soil samples as to maintain a homogenous moisture distribution thorough the soil. This was experimentally verified by measuring the moisture contents of top, middle, and bottom portions of the specimens. The CBR values of soil samples were measured within the loading speed of 1.2 mm/min both for wetting and drying paths. The results of a comprehensive study in past by Mirzaii & Yasrobi (2012) on the soil-water characteristics of this soil mixture was used in this study as to estimate the matrix suctions within the specimens on CBR tests performed on wetting or drying paths. According to the laboratory results, it is observed that the CBR value is increased within the increment of initial soil compaction and matrix suction. Based on the results, it is also observed that the value of California bearing ratio of the understudying soil is decreased within increment of the degree of saturation and initial moisture content of the soil. The experimental data also revealed that the California bearing ratio of the pavement material along the drying and wetting paths are not identical, and for a given suction, the CBR values for drying paths possess lower values than the wetting paths. This hysteretic trend for the change of CBR along drying and wetting paths is explained with regard to the hysteretic behavior of the soil-water characteristic curve.

Among four basic load-bearing mechanisms of reinforced concrete structural elements, namely, axial, flexure, shear and torsion, only the latter is truly a three-dimensional problem. Consequently, studies of pure torsion serve to verify three-dimensional modeling as a pre-requisite for general solutions of combined loads. To our best knowledge, however, few studies have been conducted on torsional behavior of concrete beams which most of them are experimental investigations or simplified analytical models based on early and modified version of Compression Field Theory (M-CFT). Previous researchers focused on the torsional behavior of plain and reinforced concrete beams as well as FRP strengthened RC beams. However, the focus of this study is to find a rational set of constitutive laws of materials to simulate a three-dimensional reinforced concrete element. From the viewpoint of constitutive modeling of RC elements, there are two approaches; discrete crack and continuum level models. The major disadvantage that adheres to discrete crack models is the fact that these models focus on a local crack behavior and seeking to detect the crack paths, requiring a high computational cost. By contrast, continuum level models taking advantage of the spatially averaged macroscopic models to predict the structural behavior of the entire member (i.e. columns, beams etc.). In this method, the control volume of simulation is a finite domain between two primary transverse cracks which contains several secondary bond cracks, leading to relatively low computational cost along with acceptable accuracy. Furthermore, there are two major approaches for simulation of RC elements in continuum level; smeared cracks models and the models based on classical theory of plasticity. Smeared cracks models originally have been developed as a solution for 2D problems. Nevertheless, most of plasticity based models originally have been developed for 3D problems. The downside of plasticity based models however, is the uncertainty in calibration of material constant because most of these models are phenomenological models, not a physical consistent rule. Taking advantage of classical theory of plasticity along with damage mechanics, Lubliner et. al. (1989), proposed an isotropic Damage Plasticity Model for simulating the plain concrete. However, variety of researchs have been conducted on reinforced concrete members based on damage plasticity model. This model, includes material parameters such as dilation angle, yield surface factors etc,. which should be calibrated for each problem.The aim of this study is to investigate the effect of each parameter on the numerical response of the beam. Hence, solid RC beams under pure torsion have been simulated using nonlinear finite elements. Concrete material is simulated using isotropic plastic-damage model integrated in ABAQUS software. The constitutive laws of materials is modified using present methods to take into account for anisotropic behaviour of RC elements under torsion. The torque – twist curves, crack patterns and detected failure modes obtained from the proposed nonlinear finite element analysis are in good agreement with experimental results.

Nowadays the use of recycled materials in the industry is increasing. An example of this is production of environmentally friendly green concrete. So far, various studies regarding the use of concrete debris from demolished concrete as aggregate in concrete have been utilized. Fibers in concrete pavements not only reduce the thickness of slab but also are useful economically as controls the shrinkage cracks and reduces the latitude satures which ends in reduction of water penetration to the base of the pavement, which means the reduction of repair and maintenance costs. Fiber ability to improve the characteristics of concrete with recycled aggregates depends on the fiber type, its percentage, fiber aspect ratio, surface friction, and tensile strength of fibers. The recycle materials are composed of crushed concrete, brick and other materials such as, small ceramic rubble and other debris. In this study recycled aggregate are used in a range of 0, 50 and 100 percent to replace natural aggregate. Recycled steel fibers from worn-out tire of vehicles also are used in two type of concrete, the ordinary one and the concrete containing recycled aggregates with volume percentage of 0.5 and 1 percent of the concrete. To investigate the effect of aggregate on concrete strength similar grading for both natural and recycled aggregate were used. After 28 days curing of the concrete, compressive strength, indirect tensile strength and bending strength tests were carried out. Evaluation of the role of fibers and recycled aggregate in slab thickness of concrete pavement of industrial floors was conducted. The amount of increase or reduction of concrete strengths with recycled aggregates are depend on the water/cement ratio, the percentage of recycled aggregates, aggregate charactristics and humidity condition. The loss of concrete strength containing recycled aggregates is remarkable by reduction of water/cement ratio, increasing the percentage of recycled aggregates and reduction of aggregates strength. Test results showed that the use of this type of fiber concrete as a structural concrete is acceptable. Concrete samples containing recycled aggregates represent different behavior under compressive strength, indirect tensile and bending test in a way that by increasing the percentage of recycled aggregates, bending strength would be increased on the contrary of the two other test. Yield line theory was used to investigate the role of steel recycled fiber and recycled aggregate to determine slab thickness Concrete containing recycled aggregates would result in a thinner slab thickness due to higher bending strength compare to ordinary concrete. Adding fibers in order of 0.5% or 1% would not have meaningfull effect on the reduction of slab thickness. The calculation based on Yield line theory showed that the addition of recycled steel fibers to the concrete reduces the slab thickness approximately by 20%.

What should be considered at the beginning of any stabilization process besides slope safety is the minimization of expenses. Therefore, excavation on slope upstream and/or filling slope downstream and/or moderating slope angle are the primary and effective stabilization methods. If these methods cannot provide the desirable factor of safety it would be necessary to put effort in other methods such as increasing soil strength parameters, draining surface water and sub-surface (ground) water at embankments, and installing retaining walls and piles. Implementation of these solutions is usually costly and sometimes in order to achieve a desirable factor of safety it is necessary to combine one or several methods. Anyway, the aforementioned solutions are aimed at mitigating the driving force behind ruptures and/or increasing resistive forces. Slopes stabilization methods can be studied as empirical, analytical, and numerical methods. This classification has been so far used by researchers and has undergone numerous studies. One of the methods used for improving resistive forces is the installation of piles in earth slopes. Installing piles for stabilizing susceptible earth slope is an effective way of preventing the imbalance of force and instability. Stabilizing effect by using pile is provided by the passive resistance of the pile below the slip surface and load transfer from the sliding mass to the underlying stationary soil or rock formation through the piles due to soil arching mechanism. Moreover, slope stability and optimizing pile location by installing a row of piles have been studied by many researchers. The piles are embedded in the stable soil by the length 5D (D=pile diameter), because the zone of influence of each pile has been demonstrated not to exceed 5D and the length of the pile is restricted to 10D. Huang et al. have studied the Shuping landslide in the Gorges Dam Reservoir which was active in 2003. They installed instruments at different parts of the landslide and recorded landslide behaviors under the influence of rainfall and changes in the dam reservoir water level for 10 consecutive years. The slope motion velocity was about 0.5 mm per day.In this paper a new method is presented for estimating of displacement and lateral force acting on stabilizing piles in earth slopes. The growth mechanism of lateral force acting on stabilizing piles in a row due to the surrounding ground undergoing plastic deformation is discussed, and its theoretical analysis is carried out considering the interval between the piles (Ito and Matsui, 1975). Several methods have been proposed to determine the force exerted on the pile in addition to having the merits, defects such as lack of accuracy required in a particular interval between the piles. In this paper with regarded to initial slip surface and acting force due to weight of failed soil is proposed lateral force acting on piles. The assumptions are considered in this paper are, 1. The suitable location for installing of piles is middle of slope.2. The pile behavior is considered as elastic.3. The soil behavior is considered as elastoplastic.4. The pile tip is embedded in the stable soil by the length 5D.

In recent years, significant progress has been made on the use of Fiber Reinforced Polymers (FRP) in civil infrastructures. These materials have been used widely for the repair of concrete members, but their application to steel structures has been limited so far. Offshore structures, especially offshore platforms are very important and expensive ones, due to rising demand of energy. These structures may require repair and strengthening due to damages they may suffer in service. Searching for methods which are faster, more reliable, and less expensive led to application of FRP in repairing of offshore structures. Durability and high resistance against fatigue as well as high ratio of strength to weight make these material superior to other conventional materials for this purpose. In addition high resistance of these materials against corrosion is an advantage for their use in marine environment. Composite materials are being increasingly used for the strengthening and repair of offshore structures. More recently, carbon fiber reinforced laminates have been used to upgrade fire walls in Mobil's Beryl Bravo platform to enable them to withstand blast loading. Also a number of corroded conductors and caissons have been repaired by composites on several Gulf of Mexico and North Sea platforms.In current research, the behavior of T-shaped tubular joints reinforced with FRP material under compressive axial load is studied to evaluate the efficiency of these materials in strengthening the connections. For this purpose and in order to examine the effect of different variables, a numerical study was carried out using the non-linear finite element program. An elastic-perfectly plastic stress-strain curve was used for steel and glass/epoxy composite was used as the FRP. A four-node quadrilateral shell element was used to model the tubular members and composite. A perfect bond between steel and composite was considered. For considering different modes of FRP failure, the criteria proposed by Hashin is used. The numerical model was verified using the data available for a T- joint which was tested earlier. The model showed acceptable accuracy especially up to the level of maximum strength of the joint. Using the verified model a number of joints with different strengthening scheme ware analysed under a monotonically increasing axial compression loads. Material and geometric nonlinearities were considered in the analyses. The analysis was carried out using the modified RIKS algorithm. The effect of number of FRP layers and the fibers direction on the ultimate capacity of reinforced tubular joints was studied. The results of numerical analysis showed improvements in the capacity of reinforced joints which were further enhanced by increasing the number of layers. Comparing FRP failure initiation load with ultimate capacity of joint, it was found FRP can bear a considerable amount of ultimate load without breaking. In addition, by comparing the Von-Misses stress and the vertical and horizontal displacement (ovalization) of chord in reinforced joints were observed that a substantial reduction in mentioned factors led to hindering the yielding of steel and increased the stiffness and ultimately the strength of connections.

Mechanical and durability properties of concrete depend on paste composition, paste volume, the physical characteristics of aggregate, and the nature of the interfacial transition zone (ITZ). The ITZ is usually regarded as the weakest region in concrete, influencing both mechanical properties and durability, and is the reason why the stress deformation behavior of concrete differs from that of its individual components, i.e., hydrated cement paste and aggregate. The processes responsible for the formation of the ITZ are not well understood. Indirect evidence of the bonding mechanisms due to mechanical interlocking aided by the aggregate surface texture has been established by comparing the bond strength of fractured rock surfaces with that of polished rock surfaces. Due to the importance of interfacial transition zone on the mechanical properties of concrete and the lack of a simple and accurate method of measurement, it is necessary to develop a test for measurement of aggregate-cement paste interface. For this purpose, an apparatus was designed, based on the direct shear test and aggregate-cement paste interface strength of different concrete aggregates was measured. For this purpose, test specimens were preparing in based of direct shear test. Due to the difficulties involved in studying ITZ in normal concrete, laboratory specimens were prepared by casting cement paste on aggregate specimen. The aggregates were sawed into cylinder with height and diameter of 60 mm. A thin layer of cement with the same diameter was applied over aggregate in cylinder mould, and then layer of concrete apply over it. Therefore upper aggregate part was sawed aggregate and the other part consists of concrete and cement paste interlayer. The later procedure was used to prepare all specimens. Based on above discussions, 90 samples were made by ten aggregate types for three curing time. To measure the interfacial force, the shear box was positioned inside the servo-controlled direct shear machine and the specimens after 7, 14 and 28 days of curing in surface saturated-dry condition. The test was carried out using shear box with 30×30 cm2 dimensions. After carrying out test, The test results of ITZ strength showed values between 1 and 18 MPa at 7, 14 and 28 days. The highest ITZ strength of 15.64 Mpa at 28 curing days was measured in the concrete specimens prepared with the dolomite aggregates while the lowest ITZ strength was in diorite and lumashele aggregates. The result show that, ITZ strength of concrete is strongly influenced by the aggregate properties such as mineralogical source, compressive strength, porosity, water adsorption, shape, and surface texture. Mineralogical source of aggregate caused high degree of hydration in concrete at all ages, but is more appreciable in old age. Shape and surface texture porosity and water adsorption controls ITZ strength of concrete in all ages. Therefore surface texture porosity of aggregate has important in physical interlocking of aggregate with cement paste. Also, mechanical properties of aggregate are important in ITZ strength in all ages, this effect is visible in late age. In order to prepare high-strength concrete, the aggregate with high ITZ strength could be used. Therefore, in high-strength concrete, the aggregate-cement paste interface plays an important role in the strength.

Although, concentric braces have proper stiffness, but ductility and energy absorption of these are low and under pressure and lateral forces exhibit poor performance and also structural ductility will reduce due to buckling when these braces are used for retrofitting of structural frames. Several methods have been proposed for improving of concentric braces performance, especially increasing energy dissipation capacity. The uses of connections with especially performance such as connections with the initial loosening at the end of concentric braces are among these methods. The main objectives of this paper are comparison of the seismic behavior of concentric brace frames with and without initial looseness and calculation of optimal looseness besides the review of analytical studies conducted on no friction brace looseness. For this purpose, the braced frames with and without initial looseness have been modeled and studied using nonlinear static and time history analysis and then the behavior coefficient was calculated. The studied models in this research are concentric moment frames with and without initial looseness. As briefly, the method which is used in this research based on the principle that the moment frames resist against the seismic lateral load at first and then (if it is necessary) braces are activated for carrying lateral load when the lateral displacement is increased and exceeded from the certain level. To achieve this goal, at the junction of the moment frame and brace initial looseness with a certain amount is applied. After reaching to the desired displacement in frame, the bolts at the junction of the moment frame and brace reached to the end of slotted joint and brace will participate with moment frame in bearing lateral forces. In this case the amount of lateral force that can be tolerated by the concentric moment frame with initial looseness is significantly more than the brace without loosening. Based on the results obtained in this investigation the use of loosening in concentric brace frame connection, in addition to reduction of operational complexity of friction dampers, improves seismic performance and also increases seismic energy dissipation capacity of frames which were studied. Also behavior coefficient obtained for this type of frames is greater than behavior coefficient of conventional concentric brace frames. The study of desired frames in this paper indicated that the optimal value of looseness (Ld) should be in the range of 3/4 L£Ld£L to achieve maximum flexural capacity of moment frame and maximum axial resistance of brace simultaneously. Also, if the ratio of concentric brace stiffness to the stiffness of moment resistance frame is about 1.0, in the concentric moment frame with initial looseness, energy absorption and dissipation capacity is more than the other axial to moment stiffness ratios. In this state the value of load resistance and also behavior coefficient increase although the coefficient of ductility and reduction coefficient due to ductility don't follow any particular trend and are almost constant. It has been observed also that at the all studied models in this research, frames with looseness connection caused an average 17% energy dissipation more than frames without looseness connection.