Local-average stress field concept in the post-crack analysis of RC members
Atefeh
Jahanmohammadi
دانشجوی دانشگاه تربیت مدرس
author
Masoud
Soltani
هیئت علمی دانشگاه تربیت مدرس
author
Abbas Ali
Tasnimi
هیئت علمی دانشگاه تربیت مدرس
author
text
article
2015
per
Common smeared crack approach, which is mainly defined on the basis of average stress field concept, represents average constitutive models for both concrete and steel bars, in the post-cracking phase. These models are highly dependent on the cracking state and the local mechanisms, so the smeared crack approach is not accurate enough in the analysis of the problems including highly localized mechanisms. These mechanisms appear in anisotropically-reinforced or under-reinforced members, members with large crack spacing or the ones include discrete cracking. The "local stress field concept" is proposed herein to introduce the effect of the local characteristics into the average models. To represent a combine local-average stress field concept, the state of local strain and stress in the RC domain must be determined. Based on several parametric studies and validation procedures, a proposed closed form slip-strain relation is introduced to find out the local strain state along the steel rebar embedded in RC domain. This relation includes the effect of rebar diameter, average tensile stress in steel, initial characteristics of concrete and steel and the cover effect. Adopting the local stress-strain model for the steel rebar, along with the known local strains, the local stress distribution is also determined. Afterward, two main stress states are introduced for the definition of the combined local-average stress algorithm, one in the center of the between-crack length and the other, on the crack surface. Introducing the participated local stresses locating on the crack surface in equilibrium with the related local stresses in the centerline of the crack spacing, the cracking growth is detected. The procedure of the cracking is stopped where the concrete’s maximum stress at the centerline is less than the cracking stress and the crack spacing is fixed afterward. Representing another stress equilibrium condition between the local stresses at the crack surface and the average stress of both steel bar and concrete in the centerline, the average tension softening/stiffening parameter of concrete (C) is updated by use of the relation adopted for the average constitutive model of concrete. By use of the yield slip value, corresponding to the crack spacing and average tensile strain, the average yield stress of the steel, as its main average characteristic, is determined by the application of the proposed slip-strain relation. Considering the effects of the local mechanisms by updating average characteristics of concrete and steel, the combined local-average stress field concept is interpreted in the finite element programming procedure. To express the importance of introducing the local effects into the average behavior, the accuracy of the concept is assessed for the analysis of several experimental specimens including RC shear panels and walls. The concept is also evaluated for some specific cases where the localized mechanisms directly affect the total response.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
53
66
http://mcej.modares.ac.ir/article_13711_b946222a1d189a7139fbf692237a3487.pdf
Comparison of Phosphorus Removal Efficiency in Reed, Bamboo & Cyperus
Bita
Ayati
P.O.Box 14155-4838
author
شیما
رضامند
دانشگاه تربیت مدرس
author
حسین
گنجی دوست
دانشگاه تربیت مدرس
author
text
article
2015
per
One of the major water pollution factors in receiving water bodies is the presence of excessive nutrients (nitrogen & phosphorous compounds) due to wastewater discharge to the environment. If phosphorus level exceeds its discharge standard (6 mg/L), it will cause eutirification which resulted in secondary water pollution due to algal blooming crisis. Development of different methods to remove phosphorus from the year 1950 was performed in response to the need of reducing the discharged phosphorus amount to surface waters. Phosphorus is removed using different chemical and biological methods that have disadvantages such as greater capital and operational costs, operational problems, high sludge production and safety operational & maintenance requirement. So phyto-remediation method can be used to overcome these disadvantages. This useful technology is actually a genneric term for several ways in which plants can be used to clean up contaminated soils and water. Considering this fact phyto-remediation is a bioremediation process in which a particular type of plant used to remove, transfer, stabilize, degrade and volatilize of contaminants (such as pathogens, heavy metals, pesticides, solvents, crude oil, arsenic, cyanide and radioactive elements) by accumulation, stabilization, extraction, rhizofiltration, rhizodegradation or volatilization mechanisms. Phytoextraction is the name given to the process where plant roots uptake polltants from the soil and translocate them to their above soil tissues. Rhizofiltration is similar in concept to Phytoextraction but is concerned with the remediation of contaminated groundwater rather than the remediation of polluted soils. The contaminants are either adsorbed onto the root surface or are absorbed by the plant roots. Phytostabilisation is the use of certain plants to immobilise soil and water contaminants. Contaminant are absorbed and accumulated by roots, adsorbed onto the roots, or precipitated in the rhizosphere. Selection of appropriate plant and microbial species, biological accumulation and transmission of pollutants, contaminant concentration and its disposal are the most important factors in phyto-remediation process. Environmental factors including ambient temperature, solar radiation, the presence of nutrients, water and oxygen and the type of material removal will also affect the process. In this study reed, bamboo and umbrella plant were evaluated in removal phosphorus from water in different concentration of 2,10, 25, 50 and 100 ppm in vitro condition (ambient temperature of 23-25 ◦C, DO of 4.5 – 6.5 and pH of 6.5- 8.5). According to the results, the maximum phosphorous removal was observed in reed plant pilot at concentration of 25 ppm. The percent removal efficiencies were found to be 17.3, 35.81, 87.94, 78.77, 48.63, 52.4, 92.01 for reed, 15.66, 21.07, 68.08, 57.89, 34.41, 48.33 and 73.69 for bamboo and 15.89, 21.5, 37.23, 32.41, 22.33, 30.48 and 54.47 for umbrella plant at mentioned concentrations, respectively. Overall phosphorous removal for reed plant, bamboo and umbrella plant were 59, 45.5 and 30.65, respectively.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
89
96
http://mcej.modares.ac.ir/article_13119_dc11db699069f0a45aa3d202b09c18f3.pdf
Introducing Comb-Teeth Yielding Metallic Dampers
Sadegh
Garivani
دانشجو/دانشگاه تربیت مدرس
author
علی اکبر
آقاکوچک
استاد/ دانشگاه تربیت مدرس
author
شریف
شاه بیک
استادیار/ دانشگاه تربیت مدرس
author
text
article
2015
per
Passive energy dissipation devices have been widely used in structures in the last decades, as effective and relatively low-cost systems to reduce the earthquake damage. Inelastic deformation of ductile metals in metallic dampers is a mechanism which may be used to dissipate seismic energy. The research on yielding metallic dampers was started by the pioneering works of Kelly et al. (1972), which was continuously followed by other researchers. These dampers, if used effectively, can dissipate significant portion of seismic energy through inelastic deformation of ductile metals. Generally, depending on the yielding mechanism, metallic dampers can be divided into four groups of flexural, axial, shear, and torsional. The most wide spread yielding dampers are Added Damping and Stiffness, ADAS, Triangular-ADAS. Yielding shear panels and slit dampers are other types of yielding dampers that are studied more recently. Slit dampers are known as a special type of metallic dampers, in which plates with a number of slits or openings are subjected to in-plane shear deformations. The slits/openings divide the steel plate to a series of links acting in flexure under the global in-plane shear deformation of damper. Based on the concept of slit dampers, researchers have proposed and tested various types of dampers. In addition some attempts have been made to find out the optimum geometry of openings and usually, rhombus-like openings have found to be more suitable than others. Considering the results and observations of previous studies on slit dampers, this paper presents a new yielding metallic damper called comb-teeth damper, CTD, which consists of a series of steel links/teeth acting in parallel and dissipating energy through in-plane flexural yielding deformation. Special attention is paid to the geometric design of links in order to generate uniform stress distribution along their length and to prevent strain localization and premature failure. The design is then checked out through a set of nonlinear finite element analyses and finally, experimental specimens are fabricated and tested under cyclic loads. Experimental studies have confirmed very stable hysteretic behavior of CTDs under cyclic loading with large displacement amplitudes. For example, a specimen was loaded under twenty fully reversed cycles at amplitude of 40 mm and even after these cycles, hysteretic curves were quite stable and thus displacement amplitude was increased to 60 mm. It should be noted that 40 and 60 mm in amplitude respectively correspond to more than 20 and 30 times the yield displacement of outer fiber of links. After numerical and experimental investigation of the behavior of CTD specimens, the behavior of three simple steel frames equipped with such dampers is studied under cyclic loading. In this regard, CTDs are installed between beams and Chevron bracing. The results of experiments show that the dampers can reproduce the satisfactory performance observed in the tests on individual devices and as a result the hysteretic behavior of frames is very stable. Therefore this type of dampers has a potential for application in building frames. The experimental set up and results will be reported in detail in the paper.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
199
212
http://mcej.modares.ac.ir/article_13712_35afa5de7c8a706a3e34758d02303299.pdf
Numerical Evaluation of the Retrofit Effectiveness for Fiber Reinforced Polymers (FRPS) Retrofitted Concrete Slab Subjected to Blast Loading
marjan
gordan
kordestan university
author
mahammad
Nia omran
kordestan university
author
text
article
2015
per
For retrofitting structures against blast loads, sufficient ductility and strength should be provided by Using high-performance materials such as fiber reinforced polymer (FRP) composites. The effectiveness of retrofit materials needs to be precisely evaluated for the retrofitting design based on the dynamic material responses under blast loads. The structural behavior of reinforced concrete (RC) slab retrofitted with fiber reinforced polymer (FRP) under blast pressure is simulated using nonlinear transient analysis of Ls-Dyna software. And the analysis results are verified with the previous experimental results. It was determined that overall the FRP retrofitted panels performed better than the companion control panels. Parametric studies are performed to examine the influence of FRP thickness, FRP strength, Compressive strength of concrete, ratio of steel bars on the response of retrofitted panel. Improvement on slab blast load resistance capacity is achieved by increasing all of parameters. But effect of increasing Compressive strength of concrete is more than another, In other words, increasing Compressive strength of concrete is economical. The relative effectiveness of CFRP and GFRP in strengthening deficient slabs can be evaluated by comparing the behavior of specimens. The two slabs in each set of specimens are similar in every aspect except that one slab was retrofitted by CFRP whereas the other one was confined by GFRP. The layers of the GFRP were as those of the CFRP. Comparisons of the ductility parameters show that both slabs in each set behaved in a similar manner and had comparable ductility parameters, the ultimate tensile strength of the CFRP fabric was higher than that of the GFRP fabric. The effectiveness of CFRP measured was larger than that of GFRP. From these test results, it appears that the effectiveness of FRP in enhancing slab ductility closely relates to its ultimate tensile strength..For retrofitting structures against blast loads, sufficient ductility and strength should be provided by Using high-performance materials such as fiber reinforced polymer (FRP) composites. The effectiveness of retrofit materials needs to be precisely evaluated for the retrofitting design based on the dynamic material responses under blast loads.The structural behavior of reinforced concrete (RC) slab retrofitted with fiber reinforced polymer (FRP) under blast pressure is simulated using nonlinear transient analysis of Ls-Dyna software. And the analysis results are verified with the previous experimental results. It was determined that overall the FRP retrofitted panels performed better than the companion control panels. Parametric studies are performed to examine the influence of FRP thickness, FRP strength, Compressive strength of concrete, ratio of steel bars on the response of retrofitted panel. Improvement on slab blast load resistance capacity is achieved by increasing all of parameters. But effect of increasing Compressive strength of concrete is more than another, In other words, increasing Compressive strength of concrete is economical. The relative effectiveness of CFRP and GFRP in strengthening deficient slabs can be evaluated by comparing the behavior of specimens.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
19
30
http://mcej.modares.ac.ir/article_13129_fbca21773c32349b5ff660b11d80acdf.pdf
Experimental Investigation of Flow and Scour Pattern around Submerged Attracting and Repelling T head Spur Dike
Hossein
Alizadeh Armaki
student
author
Masoud
Ghodsian
professor
author
Mohamad
Vaghefi
Assistant professor
author
mojtaba
Khosravi
Graduation M.Sc
author
text
article
2015
per
Abstract In this paper, flow and scour pattern around submerged and attracting T head spur dike in a straight bend has been studied. For measuring 3D velocities and bed topography, Vectrino+ and Point gauge machines were utilized. 3D velocities were measured in rigid bed state. Flow pattern experiments were conducted in a way in which after installation of spur dike in their place the sediments of the bed were flattened and then the sediments around the spur dike were covered with a thin layer of cement grout using anairbrush. After 6 hours, once the cement grout dried, the experiments are initiated. During velocity record times no scour was observed. In this research, electrical current was plotted in lateral and horizontal plans and flow pattern was studied. The findings of this research showed that the maximum scour in attracting spur dike is stronger than that of repelling spur dike and in both states it occurs in the edge of upstream wing of spur dike. Besides, flow pattern results suggest presence of a separation plane in upstream spur dike where a part of flow acts as up flow and another part acts as down flow. Moreover, flow and scour pattern in lateral, vertical, and different other plans were presented in this research. Furthermore, the finding of this study revealed that dimensions of downstream scour hole for attracting spur dike are larger. The length of this hole for attracting and repelling spur dike is 3.8 and 3.1 times to the effective length of spur dike. This suggests stronger effect of attracting spur dike on downstream flow. Besides, the width of scour hole in repelling spur dike (4.2 times to the effective length of spur dike) was larger than that of attracting spur dike (5 times to the effective length of spur dike). The length of sediment ridge in the attracting spur dike, due to its stronger effect on its downstream area, was larger (20 times to the effective length of spur dike) than that of repelling spur dike (16.4 times to the effective length of spur dike). Moreover, through this research it was found that the down flow area in upstream spur dike in repelling spur dike is larger than that of the attracting spur dike - 0.77 and 1.4 times to the effective length of spur dike for attracting and repelling spur dike, respectively. This length corresponds with the vastness of down flow. Also, the length of circulation zone in downstream of attracting and repelling spur dikes were 3.8 and 3.1 times to the effective length of spur dike, respectively and this length is in consistent with length of scour hole in downstream spur dike in vicinity of the spur dike. Finally, through this research, it was found that the center of clockwise vortex developed in downstream of repelling spur dike, compared to the attracting spur dike, is closer to the spur dike and due to initiation of deposition in a distance closer to the spur dike in repelling spur dike.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
254
254
http://mcej.modares.ac.ir/article_13130_19667d87883146e435d716c4c754fff3.pdf
Influence of concrete behavior modeling on the nonlinear response of oscillators
Alireza
Azarbakht
ARAK University
author
فاطمه
معصومیان
دانشگاه اراک
author
text
article
2015
per
Reinforced concrete structures are one of the most commonly used structures all over the world. However, the high nonlinear behaviour of this kind of structures still needs more research, e.g to shed light into the effects of nonlinear modelling and the structure characteristics. One of the most common methods to predict the nonlinear response of concrete structures is the simplified nonlinear spectra. The nonlinear spectra have been widely used in the seismic design and rehabilitation procedures e.g, ATC40 and FEMA 274. A set of closed-form formulas have been proposed in this manner to predict the strength reduction factor for a given period and ductility. The design and rehabilitation procedures can significantly simplified by using this kind of closed-form formulas. The aim of this paper is to evaluate the seismic behaviour of a set of 4620 single-degree-of-freedom (SDOF) oscillators, which was taken into account based on their period, damping and nonlinear backbone curve parameters. Eleven different periods, three damping ratios, five cracking states, seven ductility ratios, five hardening slopes and two collapse negative slopes were taken into account to cover a wide range of nonlinear behaviour of oscillators. The all combination of nonlinear characteristics with eleven periods and three damping ratios produces 4621 different oscillators to be investigated. The SDOF oscillators were analyzed for two sets of ground motion records which are representative of far and near field records. The far-field records contain 30 strike-slip records with moment magnitude of 6.5 to 6.9. The records are corresponding to the firm soil without any directivity effects. The near-field set contain 31 strike-slip records corresponding to four different earthquake events. They were all recorded within 16 kilometre of the earthquake epicentre. The incremental dynamic analysis was employed to calculate the system demand ductility in a wide range of earthquake intensity levels. The relationship between the strength reduction factor and the ductility factor was then derived for all considered SDOF systems. The results show that the natural period of vibration as well as the primary concrete cracking can significantly influence on the predicted strength reduction factors. The incremental dynamic analysis was employed to calculate the system demand ductility in a wide range of earthquake intensity levels. The relationship between the strength reduction factor and the ductility factor was then derived for all considered SDOF systems. The results show that the natural period of vibration as well as the primary concrete cracking can significantly influence on the predicted strength reduction factors. The incremental dynamic analysis was employed to calculate the system demand ductility in a wide range of earthquake intensity levels. The relationship between the strength reduction factor and the ductility factor was then derived for all considered SDOF systems. The results show that the natural period of vibration as well as the primary concrete cracking can significantly influence on the predicted strength reduction factors.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
1
8
http://mcej.modares.ac.ir/article_13131_fc283b0bc5bc9b6221b49b2b9e3732a4.pdf
Modeling of surcharge due to building on a liquefaction soil
جواد
شریفی
دانشگاه فردوسی مشهد
author
سعید
اردشیری لاجیمی
تربیت مدرس
author
ناصر
حافظی مقدس
دانشگاه فردوسی مشهد
author
text
article
2015
per
Soil liquefaction describes a phenomenon whereby a saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid. If the pressure of the water in the pores is great enough to carry all the load, it will have the effect of holding the particles apart and of producing a condition that is practically equivalent to that of quicksand the initial movement of some part of the material might result in accumulating pressure, first on one point, and then on another, successively, as the early points of concentration were liquefied.The phenomenon is most often observed in saturated, loose (low density or uncompacted), sandy soils. This is because a loose sand has a tendency to compress when a load is applied; dense sands by contrast tend to expand in volume or 'dilate'. If the soil is saturated by water, a condition that often exists when the soil is below the ground water table or sea level, then water fills the gaps between soil grains ('pore spaces'). In response to the soil compressing, this water increases in pressure and attempts to flow out from the soil to zones of low pressure (usually upward towards the ground surface). However, if the loading is rapidly applied and large enough, or is repeated many times (e.g. earthquake shaking, storm wave loading) such that it does not flow out in time before the next cycle of load is applied, the water pressures may build to an extent where they exceed the contact stresses between the grains of soil that keep them in contact with each other. These contacts between grains are the means by which the weight from buildings and overlying soil layers are transferred from the ground surface to layers of soil or rock at greater depths. This loss of soil structure causes it to lose all of its strength (the ability to transfer shear stress) and it may be observed to flow like a liquid (hence 'liquefaction'). The effect of structure on liquefaction potential of soil is very important, because it may prevent the occurrence of liquefaction phenomena or may to increase the intensity of liquefaction in the lower layers; hence the surcharge due to structures can be an important factor in the occurrence of liquefaction. Therefore in this study to model the surcharge of constructing a structure on liquefiable soil, first introduced the finite difference numerical analysis, then using FLAC 2D nonlinear dynamic analysis modeling of surcharge is carried. In this analysis, the modeling of surcharge due to building on a liquefaction soil and the effect of liquefaction potential of the economy has been studied. Also, the validation process and ensure the results of numerical analysis, modeling and comparing the results with a numerical model of centrifuge tests have been conducted. Results showed a significant decrease in the use of numerical modeling cost structures will be studied.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
9
18
http://mcej.modares.ac.ir/article_13224_cb119e96487e0f1e22d6a670990c9f09.pdf
Introduction and evaluation a combined system in order to a two-level performance
Mehdi
Alirezaei
دانشجوی دکترای سازه- پژوهشگاه بین المللی زلزله شناسی و مهندسی زلزله
author
Behrokh
Hoseini Hashemi
International Institute of Earthquake Engineering and Seismology,
author
text
article
2015
per
In this paper a new and innovative configuration of lateral bracing for steel frame construction is presented and discussed. Eccentrically Knee Bracing (EKB) frame, as it is called in this paper, is made up of four structural elements, the knee element, the diagonal brace element, the link element and the columns. The knee and link elements are a fuse-like element that dissipates energy by the formation of plastic shear hinges or flexural hinges when the building is subjected to moderate and severe lateral loads, respectively. The diagonal brace element, on the other hand, provides the required level of lateral stiffness and remains in the elastic range at all time. In order to examine this system behavior, ANSYS, which is a well-known finite element software is used. Also two half-scale EKB were tested using the SAC loading protocol and an innovative loading protocol. The experimental and numerical results indicated that in this system, ductility and cumulative dissipated energy can be significantly increased. Eccentrically braced frames (EBFs) have been indicated as the excellent elements of a structural typology suitable for satisfying the different design objectives of modern performance-based seismic engineering in medium or high-rise steel buildings. EBFs address the desire for a laterally stiff framing system with significant energy dissipation capability to accommodate large seismic forces. EBFs combine the high elastic stiffness of concentrically braced frames (CBFs) with the high ductility and energy dissipation capacity of moment resisting frames (MRFs). The excellent seismic behavior of EBFs reported in the first numerical studies on traditional eccentrically braced structures subjected to lateral static forces. To improve the seismic performance and behavior of the steel framed structures, further modification and innovation to enhance the structural performance is essential. For this purpose, a modified structural form that adopts eccentrically knee brace elements in the corner regions of the beams and columns, namely Eccentrically Knee Braced frame (EKB) is considered in this study. In an EKB, one end of the brace is connected to a short knee element instead of beam-column joint and other end of brace is connected to a short link element. The link element which is the short beam segment between the brace-beam and beam-column joint, is designed to dissipate energy through shear yielding during severe earthquakes. Thus, the link element acts as a ductile fuse to safeguard the brace against possible buckling. In this study, the knee element is designed in such a way that the knee yields in shear instead of flexure under moderate excitation and link element is designed to yield under severe excitation. The seismic performance and ductility of this proposed system is of great concern, which is covered in the current paper. All tests were of the cyclic quasi-static type for which similar displacement time histories were considered.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
127
136
http://mcej.modares.ac.ir/article_13132_26a824e9a8f987348b29c0e6ad8e8055.pdf
Assessing the Setting Times and Strength
Development of Concrete containing Pozzolanic Materials
Mahmoud
Nili
Associate Professor Civil Eng., Dept., Bu-Ali Sina University
author
محسن
تدین
عضو هیات علمی -دانشگاه بوعلی سینا
author
مجتبی
نیلی
کارشناس ارشد- دانشگاه بوعلی سینا
author
text
article
2015
per
.Setting time is considered as an identification boundary of fresh and hardened of concrete. Initial set refers to a change from a fluid to a rigid state, accompanied by a rapid temperature rise in the body of concrete structures. The early hydration of C3A and C3S in presence of gypsum plays an important role in concrete rheology, and setting points of concrete. The final set, on the other hand, express the start of strength development. Knowledge of the initial setting time will help not only in determining the time available for the transportation, placement, and consolidation of concrete; but also in identifying the effectiveness of various admixtures and pozzolanic materials. The use of different types of pozzolanic materials has allowed to reduce the carbon dioxide emission per ton of produced cement. In the present work, the effects of silica fume, fly ash and slag on the setting times and strength development of different concrete mixtures are examined. The setting times were conducted accordance to ASTM C403. The Concrete specimens were prepared with three water cement ratios of 0.35, 0.45, and 0.55. Silica fume at 7%, fly ash at 15% and 25% and slag at 25% and 35%, by weight of cement, were used as replacement for cement. The results showed that the setting times of the concrete increased as water-cement ratio increased and the lowest setting times corresponded to the specimens with 0.35 water-cement ratio. The setting time of the specimens with water cement ratios of 0.45 and 0.55 increased by 10% and 18%, respectively, compared to that for 0.35. Using silica fume, fly ash and slag, as replacement for cement, retarded the setting times of the mixtures. The more replacement contents led to increase of setting times. The setting time of the fly ash specimens at 15% and 25% increased by 6% and 12%, whereas addition of slag at 25% and 35% retarded the setting time by 11% and 18%, respectively, compared to those for reference specimens with 0.45 water-cement ratio. Silica fume caused a slight increase of setting time by 5.5% compared to those without pozzolan materials. These may attributed to the low cement content in the pozzolanic specimens which resulted to the low friction surface between cement particles and on the other hand enhancement of effectiveness of the super-plasticizer in the mixtures which led to the increase of setting times. The results also indicated that silica fume, as a very fine supplementary cementitious material, enhanced both the early and later age strength. Fly ash and slag, as replacement for cement, increased the later stage strength of the specimens, but had a negative impact on the early- age strength. This may attributed to the low pozzolanic activity of these cementing materials in the early age, however in the later ages which calcium hydroxide content increased in the mixtures the secondary induced gel enhanced the compressive strength. A power relationship was proposed for the early age strength and the final setting time relationships
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
235
243
http://mcej.modares.ac.ir/article_13134_747ef409aa6e449aa53c3954bd1b0584.pdf
Effects of distance between pontoons on wave transmission coefficient of dual floating breakwaters.
Mehdi
صنایعی
دانشگاه تربیت مدرس
author
text
article
2015
per
Abstract In spite of the large amount of work that has been done on coastal regions, a specific design for low-cost shore protection was serious need in small ports. Coastal protection structures are using to provide secured area for navigation and berthing of vessels. Using the breakwaters is the most popular method of coastal protection. Floating breakwaters are also using to provide partly calm water area by less cost in comparison with other breakwaters. Mentioned breakwater type is usually performed in small craft harbors that need impermanent calmness with low costs. Floating pontoons are one of the most usual floating breakwater types that composed of connected pontoons. Reports show that pontoon type floating breakwaters have appropriate performance in order to coastal protection. Floating breakwaters used to create tranquility in port. The floating breakwater use plenty in marine works, military operations, fishery activities, and recreational ports are abundant. In many ports, output ports are significantly affected by influx of waves, hence the existence of a floating breakwater seems to be necessary to increase efficiency and provide a safe environment for the ship. Breakwaters made in practical work, trying to reduce wave’s height in a specific location. The first record about a floating structure as a breakwater dates back to the early19th century. In 1811 General Bentham, the Civil Architect and Principle Surveyor of the Royal Navy of Great Britain, proposed a breakwater model for the British fleet at Plymouth. The Breakwater would consist of triangular sections of floating wooded frames moored with iron chain. The project cost was about one-tenth the cost of the rubble and granite mound structure which was finally adopted. The idea was rejected due to the concerns about its effectiveness during severe storms. In present research that conducted at hydraulic and marine structures laboratory of Tarbiat Modares University, two separated pontoons with variable distances, have been used as floating breakwater system. Considering the wave transmission coefficient as a main performance parameter, performance of the floating breakwater studied under the effect of the variation of distances between pontoons. In order to this, 160 tests lead in the wave flume and their results were compared with each other. Frequency domain method was used to analysis the raw data to decrease errors that may occur in time domain analysis method. In present research effects of distance between pontoons have been examined and the optimum distance of pontoons that leads to minimum transmission coefficient have studied. Results show that wave transmission coefficient of dual floating breakwaters is minimum at the range of the relative distance about 0.8 – 0.9 and its quantity will be maximum when relative distance of dual floating pontoons is at the range of 1.3-1.4. Keywords: irregular wave, dual pontoon floating breakwater, wave transmission coefficient, distance between pontoons.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
107
116
http://mcej.modares.ac.ir/article_13135_ab92aa3ebfe1612709478ab99b488918.pdf
Simulation of flow and sediment in bend and lateral intake of bend
معصومه
رستم آبادی
دانشگاه
author
Seyed Ali Akbar
Salehi Neyshabouri
Tarbiat Modares University
author
Amir Reza
Zarrati
Amir Kabir University
author
text
article
2015
per
Flow and sediment analysis is required for organizing or managing research projects in rivers. Due to fully three-dimensional nature of the flow in the river bend, streams and sediment are difficult to analyze. Development of three-dimensional numerical models and advanced computing power of computers has led to the increasing use of numerical modeling studies of hydrodynamic and sediment flow. But accuracy and validity of numerical results of flow especially in conjunction with the sediment at complex Geometry has not been determined yet. In the present study, in order to simulate the hydrodynamic of flow and sediment in the bend and lateral intake of bend, three-dimensional numerical model SSIIM2 has been used. Simulation results show that the model's prediction accuracy of hydrodynamic flow and the secondary flow in the bend, hydrodynamic flow in the lateral intake of the bend, and water surface in the lateral intake of the bend is acceptable. Model error in predicting the topography of the bed in the bend with lateral intake is relatively high. The error of the numerical model is due to using two-equation turbulence model k- ε and the sediment transport equations. Flow and sediment analysis is required for organizing or managing research projects in rivers. Due to fully three-dimensional nature of the flow in the river bend, streams and sediment are difficult to analyze. Development of three-dimensional numerical models and advanced computing power of computers has led to the increasing use of numerical modeling studies of hydrodynamic and sediment flow. But accuracy and validity of numerical results of flow especially in conjunction with the sediment at complex Geometry has not been determined yet. In the present study, in order to simulate the hydrodynamic of flow and sediment in the bend and lateral intake of bend, three-dimensional numerical model SSIIM2 has been used. Simulation results show that the model's prediction accuracy of hydrodynamic flow and the secondary flow in the bend, hydrodynamic flow in the lateral intake of the bend, and water surface in the lateral intake of the bend is acceptable. Model error in predicting the topography of the bed in the bend with lateral intake is relatively high. The error of the numerical model is due to using two-equation turbulence model k- ε and the sediment transport equations. Flow and sediment analysis is required for organizing or managing research projects in rivers. Due to fully three-dimensional nature of the flow in the river bend, streams and sediment are difficult to analyze. Development of three-dimensional numerical models and advanced computing power of computers has led to the increasing use of numerical modeling studies of hydrodynamic and sediment flow. But accuracy and validity of numerical results of flow especially in conjunction with the sediment at complex Geometry has not been determined yet.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
77
88
http://mcej.modares.ac.ir/article_13136_d347681139ca20bbed7e405a3d1fe464.pdf
The study of workability of lime on improvement of oil materials contaminated soils around the Tabriz oil refinery
Seyed Davood
Mohammadi
Assistant Prof./Bu-Ali Sina University
author
khalil
Moharamzade Saraye
فارغ التحصیل مقطع کارشناسی ارشد
author
text
article
2015
per
This paper has investigated the affect of quicklime on engineering behaviour of contaminated soils from the Tabriz Oil Refinery. The type of contamination of studied soil was alkali hydrocarbons that had more than 14 carbon atoms (C14) and is classified in the solid phase. The laboratory tests that were undertaken are included the pH, Atterberg limits, standard compaction, uniaxial compressive strength and direct shear test. The quicklime is added to samples in 1%, 3%, 5%, and 7% of values based on weight percentages and the results of tests are investigated at curing time of 1, 3, 7, 14, 21 and 28 days. Base on the results of improvement process of contaminated soils using quicklime, the soil plasticity has been decreased. To assessment of accuracy of the affect of quicklime on contaminated soils, pH values are determined. Based on results, with addition of 5% of quicklime, the pH value was increased and then stabled that is showing the stopping of reaction between quicklime and soil. The pH values of improved contaminated clayey for 1%, 3% and 5% of added quicklime were 10.56, 11.87 and 12.52, respectively. Also, the pH values of improved silty sand for the same of added quicklime were 10.13, 11.63 and 12.17, respectively. According to the results of different researcher, the suitable pH for reaction between soil and quicklime is 12.4. Thus, adding of quicklime to the contaminated soils from Tabriz oil refinery is efficient for soil improvement. The results of compaction test indicated a decrease in maximum dry density and an increase in optimum water content for improved contamination soils. The results of compaction test are according to the results obtained by other researchers on uncontaminated soils. According to the values of UCS measured in the uniaxial compression strength tests on improved contaminated soils, there is a direct correlation between UCS and quicklime content. Base on the relationship of consistency and compression strength of soils, the CL and SM samples changes from soft consistency to hard consistency at the quicklime content of 5%. Regarding to results, the clayey soils with contamination of 66.4 mg/kg and the clayey soils with contamination more than 66.4 mg/kg, by 3% and 5% of added quicklime showed maximum strength, respectively. The optimum quicklime for contaminated silty sandy soil is not under the contamination effect and was 3% of values based on weight percentages. Comparing the uniaxial compressive strength of improved soil samples showed that the sample with low oil material contamination had high strength. Also, with increase of curing time, the uniaxial compressive strength has been increased. Direct shear test were carried out to find the effect of quicklime on strength parameters of contaminated soils from Tabriz oil refinery. The present results show a direct correlation between quicklime content and both internal friction angle and cohesion with increasing of quicklime content. The result indicate that oil material contaminated soils of Tabriz oil refinery can be stabilized satisfactory with addition of 3% and 5% quicklime.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
223
234
http://mcej.modares.ac.ir/article_13137_2c337f3085dfb2c7a996ea9697e8f94d.pdf
Experimental Study of prestressed RC Deep Beams retrofitted by CFRP
Abolfazl
Arabzadeh
هیات علمی دانشگاه تربیت مدرس
author
Asghar
Amani Dashlejeh
دانشجوی دکترای دانشگاه تربیت مدرس
author
Iraj
Mahmoudzadeh Kani
عضو هیات علمی دانشگاه تهران
author
text
article
2015
per
Deep beams are the members that their behavior is different from conventional beams due to their special geometry and loading condition. Due to the low thickness compared with the height of the beams, the flexural reinforcement’s ratio is usually high and need to be placed in several layers. One of the most effective ways to reduce the ratio of the flexural reinforcement is to use of the prestressed reinforcement instead of conventional reinforcement which more conventional reinforcement can be replaced by a prestressed reinforcement. If that happens, there will be discussion of prestressed deep beams. In recent decades, along with the serious discussion of prestressed deep beams, reinforced concrete members retrofitted with FRP are also considered and in the last years the similar studies have also done on deep beams. The girders are usually prestressed deep beams in the structures such as reinforced concrete bridges, and if the retrofitting of them is considered, it will encounter with prestressed deep beams and it is necessary to have knowledge of the behavior of such members. However, the simultaneous effect of prestressing together with retrofitting has not been studied. For this, the experimental study was carried out in this paper for a better understanding of their behavior and comparing of their behavior with other deep beams. This paper study the behavior of simply supported deep beams experimentally by different conditions and has been examined their behavior compared to conventional deep beams, prestressed deep beams, and deep beams strengthened with CFRP. For this purpose, 10 deep beams with span to depth ratio of 2 are constructed and subjected to single-point failure load. Considering of this span to depth ratio is due to more compatibility with existing codes. The concrete cylindrical strength is considered greater than 400 kg/cm2 because of prestressed specimens. The test indicates that the idea of replacing of the prestressing cable instead of conventional reinforcements is appropriate and can increase the shear strength and initial stiffness of deep beams in addition to their bending strength. The analysis of experimental results shows that the effects of prestressing and strengthening are not the sum of prestressing and strengthening individually. Moreover, if two conventional and prestressed deep beams with equal shear capacity strengthen with the appropriate arrangements of CFRP, ultimate strength of prestressed deep beam will be 7% higher than conventional deep beam. The energy absorption and ductility of prestressed deep beams strengthened with CFRP are higher than strengthened conventional deep beams. Furthermore, the comparison of experimental results with existing codes and relations in the literature shows that none of the relations have the ability to predict the behavior of deep beams tested in this paper. It is necessary to generalize the existing relations to obtain to the accurate prediction.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
117
126
http://mcej.modares.ac.ir/article_13138_cd8c4e7f5bacadb8849e114071c4e275.pdf
Evaluation of the Application Distributed and Lumped Hydrologic Models in Simulation of Mean Daily Flow Discharge in Gharasoo river basin in Ardebil (Iran)
FARZIN
nasiri
T.M.U
author
Maryam
Afkhami
Tarbiat Modares University
author
text
article
2015
per
In this research, MIKE SHE distributed hydrologic model and MIKE NAM lumped hydrologic model has been used for simulation of mean daily flow discharge in Gharasoo river basin in Ardebil province (Iran). Generally in the distributed models, the whole watershed is divided to small elements and the amount of each effective parameter on watershed for each element is considered separately. While in lumped models, watershed is considered as an integrative unit and effective parameters on watershed are considered with their intermediate quantity. Progressed and comprehensive hydrological models for more accurate calculation of flow discharge in watershed have been highly applied in recent years and progresses performed in the development of distributed and physically based models, oriented the research towards the evaluation and comparative studies with other models including lumped models.Because of the lack of the correct knowledge of complex hydrologic cycle in consequence of incorrect planning of water resources in watersheds, it is necessary to take an effective act for calculating flow discharge by using progressed and comprehensive models in direction of stable development of watersheds in our country. As mentioned above, the application of distributed and lumped models has been evaluated in simulation of mean daily flow discharge in Gharasoo river basin.The watershed area is about 4100 Km2 and its elevation ranges from 1200 to 4788 m above the mean sea level. the study area lies between 470 45' and 480 40'E longitude and 370 49' and 380 30' N latitude. The average annual precipitation of this study area is about 284 mm. The most part of the study area has been covered by grass lands and crop lands. For confidence of correct simulation of hydrological processes by both models, the simulated discharge has been compared with observed discharge related to Samiyan hydrometry station that situated in out of the watershed for calibration and validation periods by using of evaluation criteria. The evaluation criteria including Root Mean Squre Error (RMSE), Standard Deviation of the Residuals (STDres), Correlation Coefficient (r) and Nash Sutcliffe Correlation Efficiency(E) have been used for evaluation of the application of the modeles along calibration and validation periods.The MIKE SHE model simulated daily discharge well as corroborated by correlation coefficients of 0.85 and o.80, root mean square errors of 4.0571 and 1.598 m3/s, standard deviation of the residuals of 4.0523 and 1.6m3/s and nash sutcliffe correlation efficiencyof 0.71 and 0.63 respectively for calibration and validation periods. The MIKE NAM model simulated daily discharge well as corroborated by correlation coefficients of 0.87 and o.78, root mean square errors of 3.13 and 1.6651 m3/s, standard deviation of the residuals of 3.122 and 1.6650m3/s and nash sutcliffe correlation efficiencyof 0.83 and 0.60 respectively for calibration and validation periods. The results of comparision between two models show that both of the models have appropriate application in simulation of mean daily flow discharge in the watershed. Also according to the calculated coefficient of efficiency in validation period, MIKE SHE distributed model had more appropriate application than the MIKE NAM lumped model.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
31
40
http://mcej.modares.ac.ir/article_13139_8a189b30b2104fcff1aafb98bfa61a5e.pdf
Removal of methylene blue from aqueous solution using graphene oxide nanosheets: kinetic and isotherm study
افسانه
شهبازی
دانشگاه شهید بهشتی
author
حبیب
کولیوند
دانشگاه شهیدبهشتی
author
سید حسین
هاشمی
دانشگاه شهید بهشتی
author
text
article
2015
per
In this study, graphene oxide nanosheets have been used for the adsorption of methylene blue, a cationic dye from aqueous solution. The physical characteristics of graphene oxide nanosheets studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The adsorption of the methylene blue onto the graphene oxide nanosheets has been carried out at different experimental condition such as contact time (1- 4 hours), adsorbent dosage (0.05 - 0.7 g/l), pH of solution (3 - 9) and initial concentration of dye (50 – 400 mg/l). The results show that the maximum adsorption (910 mg/g) under these conditions; adsorbent dosage of 0.05 g/l, initial concentration of 50 mg/l, two hours contact time and pH=6. The kinetic of adsorption data analyzed using three kinetic models such as elovich model, pseudo first-order model and pseudo second order model. Kinetic study indicated that the maximum adsorption was reached at two hours and follows the linear form of pseudo second-order kinetic model. The adsorption isotherm has been investigated in the pH range of 3 to 9, initial concentration of 50 to 400 mg/l and the adsorbent dosage of 0.05 to 0.7 g/l in 25 °C. The equilibrium data fitted to the Langmuir isotherm model well. Thus, graphene oxide nanosheets can be known as a good adsorbent for the adsorption of cationic pollutants. In this study, graphene oxide nanosheets have been used for the adsorption of methylene blue, a cationic dye from aqueous solution. The physical characteristics of graphene oxide nanosheets studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The adsorption of the methylene blue onto the graphene oxide nanosheets has been carried out at different experimental condition such as contact time (1- 4 hours), adsorbent dosage (0.05 - 0.7 g/l), pH of solution (3 - 9) and initial concentration of dye (50 – 400 mg/l). The results show that the maximum adsorption (910 mg/g) under these conditions; adsorbent dosage of 0.05 g/l, initial concentration of 50 mg/l, two hours contact time and pH=6. The kinetic of adsorption data analyzed using three kinetic models such as elovich model, pseudo first-order model and pseudo second order model. Kinetic study indicated that the maximum adsorption was reached at two hours and follows the linear form of pseudo second-order kinetic model. The adsorption isotherm has been investigated in the pH range of 3 to 9, initial concentration of 50 to 400 mg/l and the adsorbent dosage of 0.05 to 0.7 g/l in 25 °C. The equilibrium data fitted to the Langmuir isotherm model well. Thus, graphene oxide nanosheets can be known as a good adsorbent for the adsorption of cationic pollutants. Thus, graphene oxide nanosheets can be known as a good adsorbent for the adsorption of cationic pollutants.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
191
198
http://mcej.modares.ac.ir/article_13232_e2f7fb51094c15098ec370be7c665ed5.pdf
Devolopment of Decoupled Equations Methods for calculating hydrodynamic pressures on concrete gravity dams
Naser
Khaji
Tarbiat Modares University
author
رضا
بابایی
دانشگاه تربیت مدرس
author
محمدتقی
احمدی
دانشگاه تربیت مدرس
author
text
article
2015
per
Dams as one of the most important structures are always exposed to various hazards such as earthquake. As dam failure may lead to financial damages and fatalities, it should be designed with most economical and accurate methods. An earthquake causes hydrodynamic pressure waves exerting on the dam. This is one of the important factors in design of dams that are always considered by consulting engineers. Helmholtz equation is the governing relation on the propagation of hydrodynamic pressure waves in dam reservoirs during an earthquake. In order to solve the Helmholtz equation to calculate hydrodynamic pressures on dams, the reservoir’s boundary conditions (BCs) should be taken exactly into account. The BCs include (a) the interface boundary of dam and reservoir (as initial zone of reservoir excitation), (b) bottom boundary (with partial absorption of wave energy by accumulated sediments), (c) upstream boundary (with radiation of another part of the wave energy from the reservoir), and (d) formation of surface waves in the upper boundary of the reservoir. The purpose of present study is to model the mentioned physical phenomena in the frequency domain, using a new semi-analytical method, called Decoupled Equations Method (DEM). In the DEM, only the domain boundaries are discretized by specific high-order non-isoparametric elements. The main features used for modeling of geometry and physics of the problem consists of: (1) high-order Chebyshev polynomials as mapping functions, (2) special shape functions of 2n_η+1 degree polynomials for (n_η+1)-node elements , (3) Clenshaw-Curtis quadrature, and (4) integral forms produced by weighted residual method. By using these features and their properties, coefficient matrices of the system of governing equations become diagonal. This means that the governing partial differential equation for each degree of freedom (DOF) becomes independent from other DOFs of the domain to be analyzed. Therefore, this reduction in space dimensions of the main problem may significantly reduce computational costs in comparison with other available numerical methods. In this study, for the first time in order to provide a solution by low costs to calculate the hydrodynamic pressure distribution on the gravity dams, the relations of reservoir’s BCs are derived in local coordinates by using of the DEM and, the process of applying derived equations is then expressed into the solution of Helmholtz equation. To verify this method, an example of this field is solved by using the DEM, where dam and its rigid foundation are excited by horizontal harmonic vibration. The obtained responses from the solution of this example indicates that the present method for modeling of the potential problems with natural boundary conditions under earthquake excitations, by considering propagation of hydrodynamic waves in the reservoir, show acceptable accuracy and feasibility in comparison with the available analytical solution. The results of the DEM should be developed for more general condition of dam-reservoir interaction, which include flexible concrete gravity dams with inclined dam-reservoir interaction boundary conditions along with partial absorption of wave energy by accumulated sediments. These features are being followed by the authors, and will be disseminated in new papers soon.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
41
52
http://mcej.modares.ac.ir/article_13720_d5b0d37ee3f27f1181f4d94905257843.pdf
select preventive maintenance treatments using AHP
amir
khajepour
دانشجوی کارشناسی ارشد
author
hamid
behbahani
استاد دانشگاه علم و صنعت
author
text
article
2015
per
In addition to existing rehabilitation and maintenance treatments, new treatments must be identified to optimize maintenance and management of pavement. Preventive maintenance treatments are used to reduce pavement distress rate and improve the pavement surface. These treatments can be effective when the pavement has no structural distress, so choose of optimum preventive maintenance is difficult. In addition, choose of optimum preventive maintenance treatment is dependent on many factors that makes choosing more difficult. Identifying these factors and knowing the fact that how preventive maintenance methods affect these factors, can significantly help managers to select the best method. In this paper, these factors have been identified and models for selecting the best preventive maintenance treatment have been presented. Due to lack of measuring devices, a simple calculation method for these factors has been presented. Finally, the importance of each factor has been analyzed by Analytical Hierarchy Process and models for selecting the best preventive maintenance method have been presented.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
67
76
http://mcej.modares.ac.ir/article_13721_bc63f3df9463e88051decefd42534e4c.pdf
Determination of Seismic Response of Structures based on Spectral Analysis using Elliptic Envelope
Jalal
Akbari
Deputy of Faculty of Engineering
author
text
article
2015
per
In the design or analysis of structures for seismic loads, the effects of forces acting simultaneously in a member must be considered. The most common case is the interaction of bending moments and axial load in columns. The usual response spectrum method provides the maximum values of individual responses, but the critical combination of these responses may not involve any of these maxima. In this Paper, the response-spectrum-based procedure for predicting the envelope that bounds two or more responses in a linear structure is implemented. It is shown that, for an assumed orientation of the principal axes along which the ground motion components are uncorrelated, this envelope is an ellipsoid. For the case when the orientation of the principal axes is unknown, a ‘‘supreme’’ envelope is derived, which corresponds to the most critical orientation of the axes. The response envelope can be superimposed on the capacity curve to determine the adequacy of a given design. In the commercial softwares such as SAP and ETABS seismic designs of structures are based on rectangular spectrums that they are usually over estimated ones. Therefore, implementation of such accurate envelope instead of rectangular one is felt in design softwares. In the design or analysis of structures for seismic loads, the effects of forces acting simultaneously in a member must be considered. The most common case is the interaction of bending moments and axial load in columns. The usual response spectrum method provides the maximum values of individual responses, but the critical combination of these responses may not involve any of these maxima. In this Paper, the response-spectrum-based procedure for predicting the envelope that bounds two or more responses in a linear structure is implemented. It is shown that, for an assumed orientation of the principal axes along which the ground motion components are uncorrelated, this envelope is an ellipsoid. For the case when the orientation of the principal axes is unknown, a ‘‘supreme’’ envelope is derived, which corresponds to the most critical orientation of the axes. The response envelope can be superimposed on the capacity curve to determine the adequacy of a given design. In the commercial softwares such as SAP and ETABS seismic designs of structures are based on rectangular spectrums that they are usually over estimated ones. Therefore, implementation of such accurate envelope instead of rectangular one is felt in design softwares. It is shown that, for an assumed orientation of the principal axes along which the ground motion components are uncorrelated, this envelope is an ellipsoid. For the case when the orientation of the principal axes is unknown, a ‘‘supreme’’ envelope is derived, which corresponds to the most critical orientation of the axes. The response envelope can be superimposed on the capacity curve to determine the adequacy of a given design. In the commercial softwares such as SAP and ETABS seismic designs of structures are based on rectangular spectrums that they are usually over estimated ones. Therefore, implementation of such accurate envelope instead of rectangular one is felt in design softwares.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
213
222
http://mcej.modares.ac.ir/article_13727_600d8640781469b0a13a1d1822e06462.pdf
An Integrated Fleet Scheduling and Allocation Model to Bus Rapid Transit Network
sajjad
mazloom
کارشناس ارشد
author
mahmood
saffarzadeh
استاد گروه راه و ترابری دانشگاه تربیت مدرس
author
text
article
2015
per
In this article has been tried to find a new solution for fleet assignment to BRT network through scheduling assigned fleet to routes. Vehicle scheduling in each route is done with regard to passenger waiting time at stations and in consequence assigned vehicle dispatching model is related to the first station at each route. In designing the model, it has been tried to develop it in a way that it can be extended and be useful on a worldwide scale. The proposed model for Tehran BRT network has been developed by lingo software with data acquired from the Tehran municipality transportation department and the results analyzed. One of the important finding in this research is that a necessity of using buses with high capacity in BRT systems.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
97
106
http://mcej.modares.ac.ir/article_13722_2dec5431e08fbd133ba0926f52541250.pdf
Renovation of Orthotropic steel decks to control fatigue in rib-to-deck joints
mohammad
abbasi
دانشجوی کارشناسی ارشد سازه، دانشکده فنی و مهندسی، دانشگاه رازی کرمانشاه
author
mojtaba
fathi
عضو هیات علمی گروه عمران، دانشکده فنی و مهندسی، دانشگاه رازی کرمانشاه
author
text
article
2015
per
One of the main reasons for the fatigue problems in Orthotropic steel decks is the low stiffness of the deck plate. In this study, By increase the deck plate stiffness with three methods of renovation, Reducing stress in the rib-to-deck connections is investigated. For this purpose, a orthotropic steel deck is modeled with ABAQUS finite element Software, and According to the AASHTO LRFD Bridge Design Specification is simulation of fatigue and Then with the help of three methods of Renovation Bonded steel plate, Sandwich steel plate and Reinforced High Performance Concrete ,This reduction of Stresses is studied. The analysis results indicate that at the rib-to-deck joints, Stresses on the deck plate can be reduced by 80% and on the rib web can be reduced by 70% using this renovation methods, As a result, fatigue life of the deck will increase significantly. Also, The comparison of the Renovation methods shows that among renovation methods, Reinforced High Performance Concrete method will give the best results. An orthotropic bridge deck (OBD) consists of a deck plate supported in two perpendicular directions by a system of longitudinal stiffeners and transverse crossbeams which are, in turn, spanned by main girders. All these elements are connected by welding. Fatigue is a well-known phenomenon in orthotropic bridge decks. Several welded details appeared to be extremely sensitive to fatigue loading and shortened drastically the life span of orthotropic bridge decks. One of the most threatening fatigue cracks concerning the traffic safety running on the bridge is the one at the longitudinal welds between the deck plate and trapezoidal stiffener. The main reason is the low stiffness of the deck plate, which is insufficient to deal with the wheel loads of heavy traffic. Moreover, the increase of heavy traffic in the last decades makes the fatigue phenomena an even greater concern. It became clear that existing orthotropic bridge decks needed to be stiffened in order to decrease the stresses at the welds and extend their fatigue life. In the past decades, this subject attracted international attention and several studies have been performed on the fatigue phenomena and on the possible reinforcement systems. The transverse distribution of wheel loads in orthotropic decks generates significant out-of-plane bending moments in the deck plate and rib wall at the rib-to-deck joint. Due to the relatively small thickness of both the deck plate and rib wall, the out-of-plane bending moments result in high local flexural stresses causing fatigue cracks to develop at the joint. in the rib-to-deck connections, Due to the geometry of the welding, there are four potential spots around the weld where the fatigue cracks may initiate, wherein: Crack 1 initiates in the weld root and propagates through the deck plate Crack 2 initiates in the weld toe in the deck plate and propagates through the deck plate Crack 3 initiates in the weld toe in the trough web and propagates through the trough web Crack 4 initiates in the weld root and propagates through the weld throat.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
149
160
http://mcej.modares.ac.ir/article_13723_c1b1923445708e2d8cfbb16a2ec55726.pdf
Analysis of friction and texture of asphalt pavement by British pendulum tester and sand patch test
mansour
fakhri
associate professor, faculty of civil engineering, Khaje Nasireddin-e Toosi University
author
abolfazl
hassani
professor, , Faculty of Civil and Environmental Eng, Tarbiat Modares University
author
mohammad
kari
M.Sc. of civil Engineering, faculty of civil engineering, Islamic Azad University south Tehran branch
author
text
article
2015
per
Slipperiness of the road surface is one of the factors which increase the risk of accident. In fact slip occurs when the coefficient of friction between the tire and road surface is not enough to keep the adherence between the two. Skid should not be considered as a separate issue, but to solve this problem, we should optimize properties of tire and road which leads to decrease in possibility of skid. This is a fact that the less the skid resistance value, the more accidents in fall and winter which have more rain. Road friction changes with change of many factors such as properties of pavement surface, properties of tire, moisture of road and performance of vehicle. There is a need to manage skid resistance systematically to maintain the level of safety performance of roadway surfaces. This study focused on the development of a skid resistance deterioration model based on the analysis of skid data inventory collected in Tehran. This field study has been performed by examining the statistical information related to traffic and accidents and case study of a street with heavy trafficin inTehran as follows. Hot mix asphalt was provided from factories of municipality of Tehran and was distributed and tests of hot mix asphalt were done by Marshal test; then British pendulum method was used to determine the microtexture, and sand patch test was used to determine mean surface macrotexture depth. Finally by repeating the test in time intervals within 18 months and investigating the relationship between the data and test results, charts of state of changes of skid resistance over time were presented which indicated that slip resistance of asphalt pavement decreases by time and traffic crossing. First this decrease is more and then gradually declines. By comparing the results with standard it is concluded that the skid resistance of asphalt pavement should be improved after 7 months. result shows the variation of pavement skid resistance versus pavement age. Also by investigating the statistical reports given by the road police in the aforesaid street it was found that about 50% of the accidents are related to function of brakes of vehicles and friction resistance and comparing the statistics reveals that after the road surface is improved by asphalt, accidents in case study street decreased by 25%. After that with comparing the number of accidents in the studied street in the second 6-month of year and during the year especially in accident prone points it was found that number of accidents in the second 6-month is 70% of the whole year. This indicates the particular effect of weather condition in rainy season and decrease of skid resistance of pavement due to roads surface wetting on number of accidents.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
161
168
http://mcej.modares.ac.ir/article_13724_9e814bb1d1807364f106bf46de0185ad.pdf
EXPERIMENTAL AND NUMERICAL INVESTIGATION OF CRACK PROPAGATION IN PARTICLE SIZE HETEROGENEOUS ROCK LIKE MATERIAL
Mansour
sabri
دانشجو دانشگاه تربیت مدرس
author
Abdolhadi
Ghazvinian
دانشیار دانشگاه تربیت مدرس
author
Hamidreza
nejati
دانشجو دانشگاه تربیت مدرس
author
text
article
2015
per
An experimental and numerical approach on crack propagation and fracture toughness of Central Straight-through Crack Brazilian Disk (CSCBD) samples under compression is carried out to be investigated the effect of particle size heterogeneity. To accomplish this goal, six type of specimens with different silica sand particle size but same combination are used for preparation CSCBD specimens. Diametrical compression load with a rate of 0.3 mm/min in two directions respect to the central crack orientation is applied to the discs and the failure loads corresponding to the each test are recorded. Also In this study, a numerical simulator based on RFPA (Rock Failure Process Analysis) is used to study the crack propagation path and fracture load in simulated CSCBD specimens with different particle size (Similar laboratory specimens). In this simulator, the heterogeneity of specimens is considered by assuming that the material properties of elements conform to a weibull distribution. Result of laboratory tests indicates a nonlinear relation between specimen’s particle size and mode I and mode II fracture toughness. The specimen whit medial particle size (2-2.38 mm) has the maximum fracture toughness in two fracture mode. Toughness of specimens decreased with increase and decrease of silica sand particle size. Numerical results shows, the trajectory of crack path for fine particle are more regular and initiated from the crack tip, propagate parallel to the load direction. But it’s for coarse particle, initiated from the boundary of grains in whole of the specimen and lead it to failure in an unexpected path. An experimental and numerical approach on crack propagation and fracture toughness of Central Straight-through Crack Brazilian Disk (CSCBD) samples under compression is carried out to be investigated the effect of particle size heterogeneity. To accomplish this goal, six type of specimens with different silica sand particle size but same combination are used for preparation CSCBD specimens. Diametrical compression load with a rate of 0.3 mm/min in two directions respect to the central crack orientation is applied to the discs and the failure loads corresponding to the each test are recorded. Also In this study, a numerical simulator based on RFPA (Rock Failure Process Analysis) is used to study the crack propagation path and fracture load in simulated CSCBD specimens with different particle size (Similar laboratory specimens). In this simulator, the heterogeneity of specimens is considered by assuming that the material properties of elements conform to a weibull distribution. Result of laboratory tests indicates a nonlinear relation between specimen’s particle size and mode I and mode II fracture toughness. The specimen whit medial particle size (2-2.38 mm) has the maximum fracture toughness in two fracture mode. Toughness of specimens decreased with increase and decrease of silica sand particle size. Numerical results shows, the trajectory of crack path for fine particle are more regular and initiated from the crack tip, propagate parallel to the load direction. But it’s for coarse particle, initiated from the boundary of grains in whole of the specimen and lead it to failure in an unexpected path.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
169
180
http://mcej.modares.ac.ir/article_13725_520e6d30a8a85856e355bbb0735723bc.pdf
Application of Artificial Neural Networks in Prediction of Expansive Behavior of Clay Soils
Hamed
Komakpanah1
T.M.U
author
, Seyyed Sahahboddin
Yasrebi
Tarbiat Modares University
author
Aliakbar
Golshani
Tarbiat Modares University
author
text
article
2015
per
In the recent years, new techniques such as artificial neural networks were used for developing of the predictive models to estimate the needed parameters in Geotechnical Engineering such as swelling potential. If over 50% of the particles in a sample are able to pass through a number 200 screen or sieve then the sample is classified as either silt or clay or some combination of both. Regardless of the percentage of “fines” in a particular sample, a significant presence of clay minerals in a sample can indicate a possible expansive soil problem. When they absorb water they increase in volume. The more water they absorb the more their volume increases. Expansions of ten percent or more are not uncommon. This change in volume can exert enough force on a building or other structure to cause damage.
Cracked foundations, floors and basement walls are typical types of damage done by swelling soils. Damage to the upper floors of the building can occur when motion in the structure is significant.
Expansive soils will also shrink when they dry out. This shrinkage can remove support from buildings or other structures and result in damaging subsidence. Fissures in the soil can also develop. These fissures can facilitate the deep penetration of water when moist conditions or runoff occurs. This produces a cycle of shrinkage and swelling that places repetitive stress on structures. Determination of swell potential of soil is difficult, expensive and time consuming and also involves destructive tests. Multi-layer Perceptron model is one of the most sufficient methods of the Artificial Neural Networks in most of the research applications in engineering etc. In this research, Multi-layer Perceptron model and Radial Basis Function model of ANN (artificial neural networks) were used in order to predict expansive behavior of clayey soils (i.e., swell percent). All data have been modeled by using many types of architectural Multi-layer Perceptron network. Then, the output result of these networks are compared with each other according to the assessment indexes which has been leaded to the best architectural network selection in viewpoint of accusation and usage. It is noticeable that the parameters such as Natural Water Content, Plastic Index, Dry Density and Fine Soil Percent are considered as input parameters and swell percent (S%) is considered as output parameter.
The Soils which are selected for this research is clayey soils from different areas of Iran. Consequently this ANN has the ability to predict expansive behavior of diverse types of clayey soils. To train this network, results of previous researches, geotechnical consultant engineering data and the available thesis about Expansive soils are used. It was found that the Multi-layer Perceptron (MLPst and MLPdy) models exhibited a higher performance than Radial Basis Function (RBF) model for predicting expansive behavior of clayey soils. Also, the comparison of the MLPst and MLPdyn network models indicates that their accuracies are almost the same. However, the time taken by MLPst is less than that of MLPst in this study.
Since the population of the analyzed data is relatively limited in this study, the practical outcome of the proposed models could be used with acceptable accuracy at the preliminary stage of design.
Modares Civil Engineering journal
Tarbiat Modares University
2476-6763
15
v.
ویژهنامه تابستان
no.
2015
181
190
http://mcej.modares.ac.ir/article_13726_9d4033cbc44592b3bae2c754fd1cd91f.pdf