Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Experimental study of flow around spur dike with side slope
1
11
FA
Experimental study on effect of single spur dike side slope on flow structure carried out. In the study, 3D flow dynamics around the single spur dike with side slope of 75 degree has been studied experimentally in straight fixed bed channel. In order to analysis of flow characteristics, turbulence parameters flow around the scour have been measured using Acoustic Doppler Velocimeter (ADV). In behind of the spur dike, due to reduction of flow velocity that leads to formation of stationary zone, flow velocity will be increased in central zones. Therefore, a part of the flow is conducted upward and another part will be directed downward, where the pressure is lower. Downward flow is the cause of horseshoe vortex formation. Two velocity intensifier zones is formed, one is located in the main core of flow which is caused by reduction of flow width and the other one is a high velocity zone that is related to local velocity intensifying in outer layer of shear zone in the downstream of the spur dike. This is stemmed from increase in velocity of flow caused by reduction in flow width and leads to scour initiation from this zone. The maximum amount of “-ρ(u^' v^' ) ̅” stress element in shearing layer direction is occurred. Regarding to negative amounts of “-ρ(v^' w^' ) ̅” and “-ρ(u^' w^' ) ̅” stress elements, accumulation of deposits is happened in circular zone behind the spur dikes. Increases in both the speed, a core area to increase the speed of the flow and reduce the width of the high-speed flow and other areas related to the intensification of local rapidly down the breakwater and in the area the outer layer the shear is formed. The maximum mean flow velocity at the bottom of the breakwater 55/1 is the mean flow velocity is approaching. In the upstream region of the breakwater a rotating flow in the leg is shaped breakwater. It has small dimensions and rotational flow near the breakwater body rotation power was concentrated in the can be high. Upstream of the nose, the lines of the horseshoe vortex, the rotation around the nose, the hands move downward and adjacent layers come to be intertwined with the shear. The average flow field, the maximum kinetic energy in the central part of the channel and away from the shear layer form is the maximum kinetic energy of turbulence along the shear layer will occur. Increase in kinetic energy along the shear layer plays an important role in the sediment bed holds it down, so that the kinetic energy due to the formation of vortex turbulence the total flow depth have been developed. In behind of the spur dike, due to reduction of flow velocity that leads to formation of stationary zone, flow velocity will be increased in central zones. Therefore, a part of the flow is conducted upward and another part will be directed downward, where the pressure is lower.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Microstructural Assessment of Lime Consumption Rate and Pozzolanic Reaction Progress of a Lime-Stabilized Dispersive Soil
11
22
FA
Vahid
Ouhadi
Bu-Ali Sina University, Faculty of Eng., Civil Eng. Department, Iran
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. 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 EC ≥ 4 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 EC ≥ 4.0 mS/cm and pH ≥ 12 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).
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Numerical simulation of shaped charge Jet formation and penetration in the reinforced concrete targets
23
34
FA
ahmad
heidarian khorzoughi
ghasem
Dehghani Ashkzari
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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Seismic response of buried pipelines subjected to normal faulting
35
44
FA
nader
K.A. Attari
Dept. of Structural Eng., Road, Housing and Urban Development Research Center
mohamad
Deljavan Anvari
Earthquake Eng. department, Road, Housing and Urban Development Research Center
himan
hojat jalali
Dept. of Civil Eng., Sharif University of Technology
mehdi
Momeni
Retrofit expert, Tehran Gas Company
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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Analysis and evaluate the effective parameters on land subsidence
45
54
FA
sohrab
mirassi
Shiraz university of technology
HOSSEIN
RAHNEMA
shiraz university of technology
Land subsidence phenomenon caused by natural factors and human activities in different parts of the world. This phenomenon in recent years is appeared in Iran, especially 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 economicAL 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 depth due to same water falling or same thickness of layers. Land subsidence phenomenon caused by natural factors and human activities in different parts of the world. This phenomenon in recent years is appeared in Iran, especially 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 economicAL 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 depth due to same water falling or same thickness of layers. Land subsidence phenomenon caused by natural factors and human activities in different parts of the world. This phenomenon in recent years is appeared in Iran, especially 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 economicAL 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.this part have a problem
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Evaluation of Performance Reinforced Soil Retaining Wall with Oblique Reinforcements, Slope Facing and Reinforcements Anchor
55
68
FA
mohammad
shabani rameneti
Due to the advantages of reinforced soil retaining walls, the using of type of the walls has increased in civil projects over the past three decades. One of the reinforced soil applications is the construction reinforced soil retaining walls. The major advantages of the reinforced soil walls are their flexibility and absorbency of deformations. Regarding experiences derived from previous studies, it attempted to investigate the effect of facing slope, oblique reinforcements and reinforcements anchoring on the performance retaining wall by experimental. In this study, 14 models of the walls were constructed. Results of the study provide evidence that horizontal deformation of the wall facing decreased with decreasing of the facing slope. Moreover, with increasing of the reinforcements slope the horizontal deformation reduced. Results showed that reinforced soil wall with oblique reinforcements of 10 degree and facing slope of 80 degree reduce the maximum horizontal deformation of the facing by 20%.Due to the advantages of reinforced soil retaining walls, the using of type of the walls has increased in civil projects over the past three decades. One of the reinforced soil applications is the construction reinforced soil retaining walls. Regarding experiences derived from previous studies, it attempted to investigate the effect of facing slope, oblique reinforcements and reinforcements anchoring on the performance retaining wall by experimental. In this study, 14 models of the walls were constructed. Results of the study provide evidence that horizontal deformation of the wall facing decreased with decreasing of the facing slope. Moreover, with increasing of the reinforcements slope the horizontal deformation reduced. Results showed that reinforced soil wall with oblique reinforcements of 10 degree and facing slope of 80 degree reduce the maximum horizontal deformation of the facing by 20%.Due to the advantages of reinforced soil retaining walls, the using of type of the walls has increased in civil projects over the past three decades. One of the reinforced soil applications is the construction reinforced soil retaining walls. The major advantages of the reinforced soil walls are their flexibility and absorbency of deformations. Regarding experiences derived from previous studies, it attempted to investigate the effect of facing slope, oblique reinforcements and reinforcements anchoring on the performance retaining wall by experimental. In this study, 14 models of the walls were constructed. Results of the study provide evidence that horizontal deformation of the wall facing decreased with decreasing of the facing slope.Due to the advantages of reinforced soil retaining walls, the using of type of the walls has increased in civil projects over the past three decades. One of the reinforced soil applications is the construction reinforced soil retaining walls. Results of the study provide evidence that horizontal deformation of the wall facing decreased with decreasing of the facing slope. Moreover, with increasing of the reinforcements slope the horizontal deformation reduced. Results showed that reinforced soil wall with oblique reinforcements of 10 degree and facing slope of 80 degree reduce the maximum horizontal deformation of the facing by 20%
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Experimental Study of Turbulent Flow Structures in Two Groyne Field using PIV Method
69
80
FA
Zolfaghar
Safarzadeh
a
صفرزاده
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 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. Image processing is conducted using GPIV software and Westerweel and Brevis methods are used for filtering of the measured velocity fields. Results are presented in form of time averaged values, turbulence intensities and Reynolds stresses at 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 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 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. Image processing is conducted using GPIV software and Westerweel and Brevis methods are used for filtering of the measured velocity fields. Results are presented in form of time averaged values, turbulence intensities and Reynolds stresses at 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 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 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. Image processing is conducted using GPIV software and Westerweel and Brevis methods are used for filtering of the measured velocity fields. Results are presented in form of time averaged values, turbulence intensities and Reynolds stresses at 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. enhances the complexity of the mixing layer and mas exchange phenomenon compared to the groyne series configuration.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Ant Colony Optimization of Tank Maximum Level Considering Hydraulic and Quality Reliability of Water Distribution Networks
81
92
FA
mahmood
Fotuhi
Tanks in water distribution networks are used to store water for emergency conditions, fire flow demand and demand oscillations controll. 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 acheived 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 devided 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 simultaneusly 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 acheive this, optimization is defined as a powerful tool. In this paper, by focusing on operation phase, multiobjective 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 multiobjective optimization helps the decision makers to select the top choice based on the importance of their own criterion whether it is hydraulic or quality.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Application of Elliptic Slits for Development of Slit Damper in Beam-to-Column Connection
93
102
FA
Saeed
Farahi Shahri
University of Sistan and Baluchestan
Seyed Roohollah
Mousavi
Assistant Professor, University of Sistan and Baluchestan
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. 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. 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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Effects of Near-Fault and Far -Fault Vertical Ground Motions on three span railway bridges
103
116
FA
Modar
Feddah
hamid
Moharrami
Director of Structural Eng. group, Tarbiat Modares University
Farhad
Daneshjoo
Tarbiat Modarres University
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. This study investigates the effect of vertical component of earthquakes on the railway bridges with box girders cross section. 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. With the results obtained, the comparison of the results with SDC-2006 suggestions shows that a unit multiplier of the dead load effect for compensation of vertical effect of earthquake. Finally, for considering the effect of an earthquake's vertical component, Dead Load Multipliers have been suggested; they are used in designing bridges.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Analysis of degradation of Acid Orange 7 by Electro-Fenton process with graphite cathode coated by carbon nanotubes
117
126
FA
Bita
Ayati
P.O.Box 14155-4838
Azo dyes 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, photoelectrochemical and photoelectrocatalytic. 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 25 ◦C 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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
The Effect of Low-Cycle Fatigue on Ductility Demand Factor
127
136
FA
Mussa
Mahmoudi
Lavizan, Shahid Rajaee Teacher Trainig University
Ductility demands of structures are increased during strong ground motion as a consequence of the dissipation of hysteretic energy caused by cyclic load reversals. In other word, the cumulative damage of the structures due to cyclic loading reduces the ductility capacity of the structures. This phenomenon is called Low-cycle fatigue. If the real force-deflection model of members is used to nonlinear analysis; the effect of cumulative damage will be concluded in design automatically. But 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. Also in order to assess the effect of low-cycle fatigue on ductility factor, various models of damage have been selected. 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 γ, 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 γ) 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 formulae for equivalent ductility factors include damage indices. In design procedures only life safety limit states are considered and the other purposes such as serviceability, immediate occupancy and collapse prevention limit states do not. A more rational design procedure should permit the designer to choose rational limit state. This idea has been realized by including damage indices into the formula for equivalent ductility factors. The parameter γ varies from 0.6 to 1.2. For practice peruses it is assumed that the value of γ is 0.9. Using this assumption it is possible to determine equivalent ductility factor taking into account low cycle fatigue.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Determining Pavement Performance Diagram Using Case Study
137
146
FA
Reza
Imaninasab
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 to estimate the pavement condition. PCI is a practical index widely 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 decrease by the pavement age increase. PCI can be predicted in future by applying different models. These models consist of deterministic and probalistic models. Deterministic models yields a single value of future pavement condition while the probalistic ones yields 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 its 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 its result is presented by performance diagrams. In such diagrams, pavement condition changes within the years are shown. 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 is 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 pavements. In contrast, Sabzevar’s mainly initial pavements reaches the age 15 years and consequently 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 best descriptive diagrams 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 is 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 data both parameters should be considered as it is done in this paper. The results indicate that if the minimum desirable level of pavement condition index is assumed 40, then the useful life of the pavement in the Tehran NO.1 district and Sabzevar city will be 7.6 and 11.5 years.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Experimental Investigation of Hydraulic Jump in stilling basin with Stepped Sill
146
156
FA
afshar
minaei gigloo
student of tarbiat modares university
masoud
ghodsian
mojtaba
mehraein
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 (〖y_t/y〗_2^*) 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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Experimental investigation on the influence of hydraulic hysteresis on the California Bearing Ratio of an unsaturated deformable clayey sand
157
166
FA
Meghdad
Negahban
M.Sc. of Highway and Transportation Engineering, Department of Civil Engineering., Isfahan (khorasgan) Branch, Islamic Azad University, Isfahan, Iran
Ali
Mirzaii
Assistant Professor, Department of Civil Engineering, Faculty of Engineering, University of Kashan
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 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. 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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Plastic – Damage Modeling of RC Beams under Torsion
167
178
FA
1
1
1
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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
performance of environmentally friendly fiber concrete in concrete pavement
179
188
FA
mohsen
ahmadi
abolfazl
hassani
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. The study showed that in addition of crushed concrete, brick and other materials such as, small ceramic rubble and other debris are present. The current study investigates the use of recycled materials resulting from construction debris as aggregate in concrete. Steel fibers recycled from old car tires are used to reinforce concrete and ordinary concrete. Samples with different percentages of recycled fibers and aggregates were made and tests such as compressive strength, tensile strength, flexural bending strength were adopted. Test results showed that the use of this type of fiber concrete as a structural concrete is acceptable. Yield line theory was used to investigate the role of steel recycled fiber and recycled aggregate concrete in slab design thickness. The design method showed that the addition of steel recycled fibers in the concrete reduces the thickness of slabs approximately by 20%. 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. The study showed that in addition of crushed concrete, brick and other materials such as, small ceramic rubble and other debris are present. The current study investigates the use of recycled materials resulting from construction debris as aggregate in concrete. Steel fibers recycled from old car tires are used to reinforce concrete and ordinary concrete. Samples with different percentages of recycled fibers and aggregates were made and tests such as compressive strength, tensile strength, flexural bending strength were adopted. Test results showed that the use of this type of fiber concrete as a structural concrete is acceptable. Yield line theory was used to investigate the role of steel recycled fiber and recycled aggregate concrete in slab design thickness. The design method showed that the addition of steel recycled fibers in the concrete reduces the thickness of slabs approximately by 20%. 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. The study showed that in addition of crushed concrete, brick and other materials such as, small ceramic rubble and other debris are present. The current study investigates the use of recycled materials resulting from construction debris as aggregate in concrete. Steel fibers recycled from old car tires are used to reinforce concrete and ordinary concrete. Samples with different percentages of recycled fibers and aggregates were made and tests such as compressive strength, tensile strength, flexural bending strength were adopted.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
A New Method for Estimating of displacement and Lateral Force Acting on Stabilizing Piles in Earth Slope
189
198
FA
A. Reza
Mazaheri
Ph.D Student
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. 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. 1. The assumptions are considered in this paper are, 2. The suitable location for installing of piles is middle of slope. 3. The pile behavior is considered as elastic. 4. The soil behavior is considered as elastoplastic. 5. The pile tip is embedded in the stable soil by the length 5D.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Analysis of the Behavior of Tubular T Joints Strengthened by FRP under Compressive axial Load
199
208
FA
m
حسین نژاد
a
آقاکوچک
In recent decades, 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 so far limited. 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 enable 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 method was 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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Study of Interfacial Bond between Aggregate and Cement paste in Concrete
209
218
FA
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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Evaluation of steel moment frame seismic behavior
With concentric brace associated by initial looseness
219
226
FA
hesam
azizi
jamal
ahmadi
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 (L_b) should be in the range of 3/4 L≤L_(b )≤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.
Tarbiat Modares University
Modares Civil Engineering journal
16
1
2016
3
1
Effect of Cylindrical Frictional Dampers on Seismic Response of Steel Structures
227
236
FA
hamid
mirzaeeafrd
m
میرطاهری
h
رحمانی سامانی
In this investigation, seismic response of steel structures utilizing Cylindrical Frictional Dampers (CFD) is studied. CFD is an innovative frictional damper which comprises two principal elements, the shaft and the hollow cylinder. These two elements are assembled such that one is shrink-fitted inside the other. If the damper’s axial force overcomes the static friction load, the shaft inside the cylinder will move and results in considerable mechanical energy absorption. To assess the efficacy of CFD, various steel frames are constructed and analyzed . Nonlinear time history analyses and Incremental Dynamic Analysis (IDA) are applied to the frames and clear distinction has been drawn between the frames comprising CFD and the counterparts without CFD to emphasize the effectiveness of CFD in altering seismic responses. The results show that CFD extremely improves the seismic response of the structure. Frictional devices dissipate energy through friction caused by two solid bodies sliding relative to each other. The idea of using frictional dampers was first proposed by Pall (1979). Pall and Marsh (1982) proposed frictional dampers installed at the crossing joint of the X-brace. Tension in one of the braces forces the joint to slip thus activating four links, which in turn force the joint in the other brace to slip. This device is usually called the Pall frictional damper (PFD). B. Wu et al. (2005) introduced improved Pall frictional damper (IPFD) which replicates the mechanical properties of the PFD, but offers some advantages in terms of ease of manufacture and assembly. Sumitomo friction damper (1990) utilizes a more complicated design. The pre-compressed internal spring exert a force that is converted through the action of inner and outer wedges into a normal force on the friction pads. Fluor Daniel Inc., has developed and tested other type of friction device which is called Energy Dissipating Restraint (EDR) (1994). The design of this friction damper is similar to Sumitomo friction damper since this device also includes an internal spring and wedges encased in a steel cylinder. The EDR utilizes steel and bronze friction wedges to convert the axial spring force into normal pressure on the cylinder. Constantine et al. (1990) proposed frictional dampers composed of a sliding steel shaft and two frictional pads clamped by high strength bolts. Grigorian et al. (1998) studied the energy dissipation effect of a joint with slotted holes both analytically and experimentally. Mualla and Belev (2002) proposed a friction damping device and carried out tests for assessing the friction pad material. Cho and Kwon (2004) proposed a wall-type friction damper in order to improve the seismic performance of the reinforced concrete structures. Recently Mirtaheri et.al. (2011) proposed an innovative type of frictional damper called cylindrical friction damper (CFD). In contrast with other frictional dampers the CFDs do not use high-strength bolts to induce friction between contact surfaces. This reduces construction costs, simplifies design computations and increase reliability in comparison with other types of frictional dampers.