per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Suggestion of a New Link Element to Calculate the Impact Force and Energy Dissipation Based on CR-Factor and Impact Velocity
Hosein Naderpour
1
Rui Carneiro Barros
2
Seyed mohammad khatami
3
35149-53741 hekmat st. jalal al ahmad ave. farhangian. semnan
Nowadays, buildings are built without required separation distance as many engineers do not consider the building pounding effects. If adjacent buildings are not separated properly from each other, pounding can occur upon earthquake occurrence, and severe damages to the buildings can be observed even if they are well designed and constructed. Engineers should realize that building pounding is a serious hazard and it has to be considered during design and construction of buildings. There are many residential building complexes, service office, agencies, schools and hospital in cities around the world which are located next to each other as the cost of land is high. In this term, hospitals with emergency facilities and emergency centers have to be protected against the damages due to the significance of such structures prior and after earthquake. Many researchers have studied building pounding to calculate the dissipated energy and the impact force between two buildings during earthquake. For this challenge, they need to have a link element, which describes impact by using spring and dashpot. Several mathematical equations were suggested to calculate two mentioned parameters. In this paper, based on mathematic relation, a new relation of damping term of impact formula is simulated to measure impact force and energy dissipation. The results of this formula are compared with another suggested formula. As it was mentioned, different materials used in building constructions cause various dynamic behaviors during earthquake. Concrete structures are typically more rigid than steel structures in similar conditions. Consequently, lateral displacements of concrete buildings may also be less than lateral displacements of similar steel structures as stiffness of concrete buildings causes decrease in natural periods during earthquake. Naturally, large lateral nonlinear displacements under time history lateral loading in concrete structures may not be observed. Buildings can collide with adjacent buildings in left and right directions. For concrete buildings, however, the impact of pounding may be more significant than those on steel structures in most situations. Many researchers have suggested new relations in terms of impact to increase the dissipated energy. Based on mathematic relation, they showed that energy dissipation depends significantly on stiffness, impact velocity and coefficient of restitution. For this challenge, by using a suggested link element, a new formula is presented to calculate the impact force and energy dissipation. To optimize the results of dissipated energy, a new relation between CR and impact velocity is suggested. As it seems that it is a need to have a reference curve to select impact velocity based on coefficient of restitution, several impact velocity and CR were evaluated. Using this curve, all of results can be optimized. Finally, a new equation of motion is assumed to select the best impact velocity and coefficient of restitution.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-4045&slc_lang=en&sid=16
Impact
Impact Velocity
Dissipated Energy
Damping
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Suggestion of a New Link Element to Calculate the Impact Force and Energy Dissipation Based on CR-Factor and Impact Velocity
H. Naderpour
1
Rui C. Barros
2
S.M. Khatami
3
Semnan University
Semnan University
, Semnan University, Semnan, Iran
Nowadays, buildings are built without required separation distance as many engineers do not consider building pounding effects. If adjacent buildings are not separated properly from each other, pounding can occur upon earthquake occurrence, and severe damages to the buildings can be observed even if they are well designed and constructed. Engineers should realize that building pounding is a serious hazard and it has to be considered during design and construction of buildings. There are many residential building complexes, service office, agencies, schools and hospital in cities around the world which are located next to each other as the cost of land is high. In this term, hospitals with emergency facilities and emergency centers have to be protected against the damages due to the significance of such structures prior and after earthquake.
Many researchers have studied building pounding to calculate the dissipated energy and the impact force between two buildings during earthquake. For this challenge, they need to have a link element, which describes impact by using spring and dashpot. Several mathematical equations were suggested to calculate two mentioned parameters. In this paper, based on mathematic relation, a new relation of damping term of impact formula is simulated to measure impact force and energy dissipation. The results of this formula are compared with another suggested formula.
As it was mentioned, different materials used in building constructions cause various dynamic behaviors during earthquake. Concrete structures are typically more rigid than steel structures in similar conditions. Consequently, lateral displacements of concrete buildings may also be less than lateral displacements of similar steel structures as stiffness of concrete buildings causes decrease in natural periods during earthquake. Naturally, large lateral nonlinear displacements under time history lateral loading in concrete structures may not be observed. Buildings can collide with adjacent buildings in left and right directions. For concrete buildings, however, the impact of pounding may be more significant than those on steel structures in most situations
Many researchers have suggested new relations in terms of impact to increase the dissipated energy. Based on mathematic relation, they showed that energy dissipation depends significantly on stiffness, impact velocity and coefficient of restitution. For this challenge, by using a suggested link element, a new formula is presented to calculate the impact force and energy dissipation. To optimize the results of dissipated energy, a new relation between CR and impact velocity is suggested. As it seems that it is a need to have a reference curve to select impact velocity based on coefficient of restitution, several impact velocity and CR were evaluated. Using this curve, all of results can be optimized. Finally, a new equation of motion is assumed to select the best impact velocity and coefficient of restitution.
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-10&slc_lang=en&sid=16
Impact
Impact Velocity
Dissipated Energy
Damping
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Improvement of Moisture Sensitivity of Asphalt Concrete Mixtures Using Nano- Composites
B. Amini
1
M.J. Rajab Bolookat
2
International University (IKIU),
International University (IKIU
Abstract:
High traffic volumes and diverse weather conditions cause defects in the asphalt concrete surfaces such as excessive deformation, fatigue, rutting, ravelling and asphalt bleeding. Many researchers have examined moisture susceptibility of asphalt mixtures, because the high moisture sensitivity of asphalt pavement leads to the separation of bitumen and aggregates, and concluded that this phenomenon reduces the internal resistance of asphalt mixtures leading to failures such as rutting, raveling, and fatigue cracks under the traffic load stresses Styrene butadiene rubber, as a commonly used polymer has been focused by many researchers, and different methods have been developed for production of its composites based on nano-clay materials. According to the research results, styrene butadiene rubber nano-clay composite (SBR/NC) shows better properties compared to pure SBR.
Despite extensive studies carried out on the impacts of SBR/NC on various properties of bitumen, asphalt concrete moisture susceptibility has not been addressed adequately. In this study, SBR/NC nano-composites with different ratios were prepared and used for modification of bitumen, and the indirect tensile strength, which can measure moisture sensitivity of asphalt mixtures, is being addressed.
SBR/NC composite was prepared using the internal mixer apparatus and melting process method. Mixing was carried out for 12 minutes at a temperature of 140°C and 60 rpm rotation speed. Then the mixture was placed in a roller mill for 3 minutes to complete the mixing operation and cooling the resulting product.
To evaluate the distribution structure of silica plates in polymer, X-ray diffraction tests were performed on the composites prepared with different ratios of SBR/NC.
According to the obtained XRD spectrum the peak intensity has decreased, indicating a break down in regular layer structure. The wide range of peaks in this spectrum shows that, due to irregularity of layers, SBR is located between them. Thus it can be concluded that the silica plates to be well-distributed in the nano-composite structure.
The ITS improvement of samples in dry state were up to 6 .6 percent and in wet state up to 25.30 percent and the ratio of wet to dry state up to 96.25 percent. These values indicated a significant improvement in asphalt properties against moisture permeability, which is one of the most detrimental factors in premature failure of asphalt concrete pavements.
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-9&slc_lang=en&sid=16
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Hydraulic Design of a Trapezoidal Labyrinth Spillway Using Computational Hydrodynamics
M. Azhdari Moghadam
1
E. Jafari Nadoushan
2
Sistan & Balochestan University
Sistan & Balochestan University
Abstract:
Labyrinth spillways as appropriate hydraulic structure to pass PMF discharge have been considered. To replace existing spillways of reservoirs which in terms of capacity they are not hydraulically suitable, these types of spillways are recommended. In a certain width with similar head these spillways with nonlinear crest can pass greater discharges compare to spillways with frontal crest. The Labyrinth spillway is a type of hydraulic structure which can be used for the existing and new reservoirs. This structure is considered for hydraulic engineers as a good alternative to keep the water level of the reservoirs in an acceptable position when there is a limit on the maximum level of the water surface of the reservoir. The plan shape of the labyrinth spillway consists of broken lines in the form of triangular, trapezoidal, semi circular and rectangular with several repeating cycles. The main objective of using this type of spillway is to increase the flow capacity of the reservoir while keeping the crest and the water surface of the reservoirs in a reasonable level. The use of this type of reservoir goes back to the early 1920’s; however, the real studies and research in this field started form 1968. The majority of researches in this field are for those with triangular or trapezoidal in plan.
The most advantages of using labyrinth spillway in the reservoirs and channels are as follows:
1- If the width of the spillway or channels cannot be chosen enough wide due to upstream or downstream site condition;
2- If the maximum level of the water in the reservoir during the flooding season is limited;
3- If it is desirable to provide larger water storage of the reservoir by making the crest level of the spillway higher without causing floodplain of upstream lands during high inflow to the reservoir;
4- If the capacity of the existing spillways are not large enough with respect to current standards of dams safety;
5- It is more economical due to the need of smaller discharge channel downstream of the spillway; and
6- If the reservoir needs to have spillways with the gates to provide larger amount of water storage, in the case of labyrinth spillway the needs of the gates can be eliminated which is very advantageous both in terms of primary costs and maintenance costs.
In this study by considering various angles of walls and lengths of nose different types of trapezoidal labyrinth spillways were designed. Applying Flow-3D software which is analytical software to solve equations of flow domain passed over spillway based on Eulerian viewpoint, numerical models were constructed. In order to model turbulence, the K-ε model in RNG state was used. Also to identify position of free surface profile, the VOF method was applied. To verify the results, experimental data of Tullis and Amanian (1995) was employed which the model results showed good agreement with the experimental data.
Passing various discharges over the spillway variation of discharge coefficient was studied. It was showed with increase in length and angle of the spillway wall in flow direction the discharge coefficient would increase which is due to less interaction between the flow layers. This increase in small angles due to the reduction in over lapping layers is a considerable loss. At the end based on the obtained results a procedure to design a trapezoidal labyrinth spillway with choosing the angle of wall along the length of the nose was developed.
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-8&slc_lang=en&sid=16
Trapezoidal Labyrinth Spillway Design
Coefficient discharge
CFD method
Flow-3D
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
The Optimum Support Selection for Access Tunnel of Gushfill Mine using LINMAP Method
M. Hayati
1
M. Ataei
2
Z. Ranjbar
3
Shahrood University
Shahrood University
Shahrood University
Select a support system of tunnels has an important role safety and economic status. This choice usually based on experience of designer engineers. But the question is always whether the best choice has been done?. In this study, Linear Programming for Multidimensional Analysis of Preferences (LINMAP) as one of the most important method of multiple Attribute decision making (MADM), to select optimum support system of tunnels has been used and finally to achieve a single rating for the support system integration methods are used. In this way the tunnel support system selection as a multi attribute decision making has been considered and the criteria for selection optimum support system include: support cost, safety factor, applicability, time installation, displacement and capable of mechanization. For this purpose, first, using the finite difference numerical method) FLAC2D (, various support systems based on technical parameters and stability of the tunnel has been identified. Then based on considered criteria, using the aforementioned optimum support system has been selected. The study considered eight criteria that include: Vertical displacement in the roof of the gallery (C1), vertical displacement of the gallery floor (C2), the horizontal displacement at the corner of the side wall of the gallery (C3), vertical displacement at the corner of the side wall of the gallery (C4), safety factor (C5), maintenance (C6 ), the need for human resources (C7) and ease of implementation (C8). Since the access tunnel consists of two perpendicular tunnels, and each of the two tunnels to be divided into two areas are mineralized dolomite and dolomite The storage system of choice for the four regions are considered. In the first decision, the lowest safety factor storage system, a team of specialists is recommended; Then based on the results obtained with smaller amounts of the several options are proposed, decisions are removed from the list. Displacement parameters in different parts of the walls, floors and crown of the tunnel, safety factors and system maintenance cost indices are slightly And the economic analysis and numerical modeling have been achieved. Thus, the matrix is directly related Drays these numbers will be. Indices requires human resources and facilitate the implementation of quality indicators that are qualitative terms such as very low, low, medium, high and very high, have been evaluated. Quality indicators used for quantifying the scale is bipolar. Thus, instead of words is very low, low, medium, high and very high order of the numbers 1, 3, 5, 7 and 9 are used. Accordingly, the final decision matrix (slightly) related to the number one and two tunnels in the area of mineralized dolomite and dolomite, respectively. In this matrix, the indices of displacement in different parts of the walls, floors and crown of the tunnel, system maintenance costs and manpower required to have a negative aspect Safety and ease of implementation of aspect ratio and the indices are positive. Important factor in determining the indicators, the indicators were paired comparison matrix (a matrix of 6 × 6). Based on expert opinion and using the geometric mean weight of each of the indicators were. It is necessary to keep the system in selecting the weights for the two tunnels in two ranges, are the same. As was pointed out to select optimum maintenance system, the methods LINMAP as an important characteristic of decision methods have been used. As a general conclusion can be stated that in selecting a storage system for the tunnel, several indicators are considered. Way too many of the numerical method for determining the storage system, are used. Although many indicators are effective in the maintenance system But all these indices in a numerical analysis cannot be removed, Although one of the good work, behavior of the tunnel with the different options for a tunnel system is maintained. In a process of decision making using multiple indicators Evaluations to be made more scientific. In this study, eight different types of storage systems for the four different levels of access tunnels Goshfill mine was in 1565, Then consider the safety factor of at least 1.2 for access tunnels, storage systems, 2 to 5 because of the safety factor of 1.2 were excluded from the decision making process. The method according to other criteria LINMAP maintenance systems 1, 6, 7 and 8 were studied. Finally, the option 1 "to 4 meters in length and spacing of rock bolts have 1.5 m in the roof and walls." As the best system for the maintenance of the access tunnel was aligned Goshfill 1565.
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-7&slc_lang=en&sid=16
LINMAP
Multi criteria decision making
LINMAP
access tunnel
mine of Goshfill
Support System
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Evaluating of X-Shaped Bars and Top Layer Concrete on Rigidity of Jack Arch Slabs
M. Mahmoudi Sahebi1
1
A. Khaki
2
M. Haji Azizi
3
Shahid Rajaee Teacher Training Uni
, Shahid Rajaee Teacher Training Uni.,
Shahid Rajaee Teacher Training Univ
Abstract:
A large number of slabs (floor and roof) in industrial and residential buildings were constructed by steel I-beam, brick Jack arch slab in Iran. Jack arch masonry flooring system consists of a number of closely-spaced, parallel steel I-beams and a number of shallow brick arches filling the spaces between the steel beams. The spaces over the arches are then filled to create a flat floor. This kind of slab did not indicate suitable reaction during past earthquakes. Collapse of a large number of these non-homogeneous one-way slabs during past earthquakes has highlighted their poor seismic performance. They do not behave as rigid elements. However, due to their easy construction together with low cost, the jack-arch slab is still widely used in many countries. Thus it is necessary to study the rigidity of this kind of slabs by more accuracy. The objective of this paper is to evaluate the rigidity of the jack arch slab and influence of X-shaped bars and top layer concrete in their rigidity using nonlinear analysis (Ansys software). Finite element numerical analyses are then conducted to investigate the effects of a number of parameters on the rigidity of the slabs. In addition, appropriate tables and figures are presented to facilitate the investigation of the jack arch slabs. For this purpose, several steel-framed structures constructed by jack arch slab with different terms were selected. These terms consist of, number of buildings stories (one, two and three stories), diameter of bars (14, 16, 18 and 20 mm), thickness of top layer concrete (6, 8 and 10 cm) and different areas of slabs (3.6×3.6, 3.6×4.5, 3.6×5.4 and 3.6×6.3 m). To consider the rigidity of slabs, the 2800 standard's regulations were applied. According to the rules and regulations of standard no. 2800, the slab will be rigid if the ratio of relative story displacement and diaphragm displacement to be less than 0.5 and the slab will be flexible, if this ratio to be greater than 0.5. The result of an experimental model was used to clarify the result of this research. It was shown that the result of experimental model was in conformity with this research one. At the end two expressions was suggested for determination of bars diameters and the concrete layer's thickness needed for rigidity of jack arch slab
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-6&slc_lang=en&sid=16
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Predicting ultimate and yield strength of the plain concrete arch bridge of Akbar-Abad on the basis of nonlinear analysis
M.S. Marefat
1
M. Yazdani
2
Tehran University
Tehran University
Abstract:
Assessment of the remaining load carrying capacity of masonry arch bridges has been studied by many researchers in the recent years. Most of the masonry bridges have been built several decades ago, and have been designed for live loads and service conditions that have been changed over time. The residual strength of those structures cannot be predicted, in a reliable manner, because of time dependent effects such as fatigue and creep, environmental defects such as cracking and corrosion, participation of non-structural elements such as fill material and pavement layers, variation in restrain conditions, and differences between as-built and design specifications. To overcome such restrictions, field tests provide a dependable solution. On the basis of construction material, masonry arch bridges may be divided into three groups, namely, brickwork arch, stone arch, and plain concrete arch. Numerical and experimental studies of brickwork and stone arches have been reported frequently. Despite frequent study of brick masonry arches, load test of plain concrete arches have been published only in a few documents. There are a large number of old arch bridges in Iran that have been serving as railway bridges for more than seventy years. Field load testing of an old railway bridge in km 24 of Tehran-Qom railway has revealed important characteristics of the bridge and has proven that there is still large capacity under service load. This paper reports results of a study to predict the maximum and yield load capacity of a plain concrete arch bridge. The bridge has already been tested under vertical load static up to 5000 KN. For figure out the behavior of these types of structures, model updating is necessary. Appropriate modeling of arch bridges is the subject that is highly regarded by researchers in recently year. The complexity in the behavior of these structures will seek more accurate studies and researches, so the field tests are an integral part. In this article, uses numerical modeling in order to determine yield strength and ultimate strength of Akbar Abad Bridge. This bridge is a plain concrete arch and consists of five identical 6m and formerly has tested, due to operational and field limitation, possibility of loading until limit ultimate and Set maximum load capacity and yield strength has not been possible. In this paper with ANSYS software, an accurate modeling has done. In this model has used strain analysis. Considering the existence of initial cracks in bridge, they have been modeled as empty space. Behaviors of the material are assumed nonlinear and have used Dracker-Prager criterion. Finally, according to pattern of cracks appeared in test and result of field testing of a similar bridge (km-23 of Tehran-Qom railway), the ultimate load and yield strength is estimated and The pattern of formation of plastic hinges conforms to the patterns reported in the literature for arch masonry bridges.
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-5&slc_lang=en&sid=16
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Investigation of Grouping Effect in Seismic Behavior of R. Concrete Frames
m Karimi
1
A. Kheyroddin
2
One of the problems that influence on seismic behavior of structures and associate designing to itself is the grouping of structural element within analyzing and design of structures. Generally this grouping is due to facilitate of performing the structures. This paper investigates these grouping effects on behavior of concrete structures with RC bending frame systems andmoderate ductility scale. Study cases that is used for assessment of these grouping effect contains buildings with 4, 8 and 12 story RC structures. Each of these buildings designed one time without grouping and several times with grouping consideration about columns of structures in the height direction of buildings.Codes that are used for design purposes are Iranian Seismic code and RC structure design code. IDARC program V7.0 is utilized for estimation of damage indices, maximum story drifts or displacements and energy dissipated by building structural systems to comparing thenonlinear seismic behavior of column grouped and non-grouped structures. Damage indices calculated by this program is based on modified Park-Ang-Wen model and represented individually by elements, stories and a total damage index. The selected structures are analyzed with nonlinear dynamic analyzing method under Tabas earthquake record using several peak ground accelerations (0.35g, 0.50g, 0.75g and 0.90g) and pushover analysis with force-control and displacement-control methods. Maximum responses such as maximum displacements, damage indices(with grouping and non-grouping design method) were used to realization result of this designing method.Comparing the result of nonlinear analysis showed increasing of damage with increasing of PGA. This is due to a better distribution of forces in the elements of structures in case of non-grouped designed structures. Analytical results showed that the effect of grouping in PGA less than 0.5g is not sensible, but in larger PGA the grouped designed structures suffer more damages. The grouping of structural elements causes to concentration of energy in elements that their demand to capacity ratio (DE/CE) is greater than others.This causes that these elements embroil more damage and save other element from greater damage.One of the other results of this designing method (Grouping of element) is formation of soft stories in the structure. Also the reason of this behavior is due to lumping of hysteretic energy on these stories. This subject causes to generate soft and weak story in the structure and increase the overall damage indices.Furthermore result of pushover analysis showed that grouped element structures have a more stiffness and so in a weak earthquake (a low PGA) have a less or equal damage index in comparison to non-grouped element structures. As an overall result determined when DE/CE for all elements is close to each other distribution of damage is uniform and vice versa.
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-4&slc_lang=en&sid=16
Grouping
Concrete structure
nonlinear dynamic analysis
Damage Index
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Simulation of the Interaction Effect of Masonry Infill Panels - RC Frame on the Progressive Collapse Potential
S. Rahimi
1
M. Soltani Mohammadi
2
A.A. Aghakochak3
3
, Tarbiat Modares University
, Tarbiat Modares University
, Tarbiat Modares University
Progressive collapse is a rare event during which all or a part of the structure is destroyed due to damage or failure of a small section of the structure. Progressive collapse due to abnormal loading or the design and construction errors can lead to great financial and human losses. Therefore, during the past decades many engineers have been interested in this type of failure. Although a great research effort has been done to investigate the effect of masonry infill panels on the seismic response of frame buildings, there is not so much work on evaluating progressive collapse potential of masonry infill frames.
Reinforced concrete structures are considered as bare frames in analysis and design process, including the main structural members such as beams, columns and shear walls. However, in the urban areas, structural frames are filled with masonry walls as acoustic and thermal insulation in the middle or peripheral areas of the buildings therefore they have not the same behavior as the bare frames.
This research aims at investigating the effect of unreinforced masonry infill panels on the response of RC frames against the progressive collapse. For this purpose a micro based modeling approach is adopted for numerical simulation of the masonry infill panels and through a parametric study, the effect of influencing parameters is numerically investigated. Also an equivalent compressive strut model is proposed for macro modeling of masonry infill panels. The comparison between numerical and available experimental results confirms the reliability of the developed model. Finally, the developed macro model is used to investigate the influence of masonry infill panels on the progressive collapse resistance of two reinforced concrete frames with different ductility capacity. It is shown that, under the progressive collapse phenomenon, the ductility of RC frame is the main effective parameter and masonry infill panel plays an important and non-ignorable role in structural response.
In this paper also progressive collapse resistance is studied for two six-story reinforced concrete frame structures. The first structure has been designed according to Iranian concretecode (ABA) with high ductility and in the second building, seismic design load has not been considered and the structure was designed only against gravity load. The critical column has been removed from the models to numerically investigate the progressive collapse potential of the structures. Because of the lack of national regulations for evaluating the effect of progressive collapse, in this article nonlinear static analysis method of the U.S department of defense regulations (UFC) is used to evaluate the progressive collapse potential. The result of the analysis shows that the structure with high ductility is resistant under remove of column, but the structure designed without considering seismic effects needs to retrofit against progressive collapse.
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-3&slc_lang=en&sid=16
Progressive collapse
Infill panel
Compression strut
RC frame
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Evaluation of Earth Dam Construction on Mitigation of Liquefaction Potential within Alluvial Foundation
H.R. Paseh
1
, M. Yazdani
2
R. Mahin Roosta
3
, Tarbiat Modares University
Tarbiat Modares University
Abstract:
The evaluation of the liquefaction risk of soil during earthquake and its consequences on the structures as well as the mitigation methods are major tasks for the safety of populations. In construction of earth dams, the alluvium deposit usually removed so that the dam lays on the rocky foundation. This solution in the case of thick deposits is expensive. On the other hand, it is possible to construct the moderate height dams on mitigated alluvium foundations, if the seismic behavior of system is guaranteed. In this study, the construction effect of earth dam on liquefaction potential of its alluvial foundation and reciprocally the effect of liquefied foundation on the stability of dam have been investigated for two different geotechnical conditions. The analyses are nonlinear and the constitutive law of the foundation material was assumed to follow Finn model incorporated into “Flac 2D” finite difference analysis program. The factors such as initial shear modulus, variation of shear modulus versus shear strain, generation and dissipation of pore pressure and hysteretic damping are considered in this study. The results of these analyses then compared with the results of dynamic analysis of earth dam on a rocky foundation. The evaluations show that the dam construction increases the relative density, effective stress, shear modulus, and thus decreases the shear strain and water pore pressure within alluvial foundation under the crest of dam. Depending on the relative density, depth of layer and level of applied acceleration, this may lead to mitigation of liquefaction potential. This effect decreased toward the upstream and downstream of the dam. It was observed that the liquefaction could be mitigated in the region close to dam crest when the relative density of soil is 65% to 85% and subjected to a maximum acceleration of 0.3g. However, the construction of dam finds little decreasing effect on liquefaction when the relative density of alluvial foundation is less than 65%. The main settlement and maximum horizontal displacement in foundation is occurred under the core and downstream of the dam, respectively and reached up to the depth of 10-15 m of foundation. In spite of the good performance of dam weight on lowering the liquefaction potential during earthquake loading, a large deformation and even instability condition can be achieved within the alluvial foundations. However, deformation of dam and its foundation are strongly dependent on the geotechnical specification of alluvial foundation, density, thickness and depth of liquefiable layer and the level of applied acceleration. The results present that in very good quality alluvial foundation where the liquefiable layer has small thickness and is located at a deep position, and in the case of acceleration lower than 0.2g, the effect of liquefaction in deformation of dam will be insignificant.
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-2&slc_lang=en&sid=16
Liquefaction
Alluvial Foundation
earth dam
Finn Model
Nonlinear analysis
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2013-10
13
3
123
123
article
Experimental Investigations of Hydraulic Fracturing Propagation in Multi-layer Formation
M. Behnia
1
K. Goshtasbi
2
A.A. Golshani
3
M. Fatehi
4
Tarbiat Modares University
Tarbiat Modares University
Tarbiat Modares University
Yazd University
Abstract:
Hydraulic fracturing as a method for reservoir stimulation depends on the properties of the media that fracture propagates in it. Discontinuities in the media and their mechanical properties greatly affect the geometry and propagation of hydraulic fractures. In this research, the interaction between the hydraulic fractures with the media layers interface, fracture propagation pattern and termination in multi-layered media were investigated. The true tri-axial cell was utilized to conduct experimental tests on cube multi-layered samples with discontinuities. The tests were aimed to investigate propagation of fractures from soft to stiff, stiff to soft media and also the effect of elastic properties of rocks in hydraulic fracturing. Results showed that the condition of discontinuities (healed, open or filled) and elastic properties of the layers influences the geometry and propagation pattern of hydraulic fractures. In the block with the bonded interfaces, the fracture propagates and interacts with the interfaces, then penetrates in the adjacent layers. However, for the block with unbonded interfaces the fracture propagates from the borehole up to the interface, then after filling the interface with the fluid the new fracture will propagate in the adjacent blocks. In sample where the interface was filled, the fracture propagation was terminated and then the fluid started to leak off in the interface. The results also show when the fracture reaches the interface, the pressure increased immediately and more pressure is needed for fracture propagation across the interface. In comparison between the length and width of fractures in soft and stiff layers, the study displays that the fracture width and its penetration length in soft layers are greater than those in stiff layers.
http://journals.modares.ac.ir/browse.php?a_code=A-10-10789-1&slc_lang=en&sid=16
Hydraulic Fracturing
layered formation
fracture propagation
Experimental investigation