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Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
Scientific Information Database (SID) - Trusted Source for Research and Academic Resources
Title: 
Author(s): 

Issue Info: 
  • Year: 

    0
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    -
Measures: 
  • Citations: 

    0
  • Views: 

    2044
  • Downloads: 

    0
Keywords: 
Abstract: 

Yearly Impact: مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    391-400
Measures: 
  • Citations: 

    0
  • Views: 

    3334
  • Downloads: 

    0
Abstract: 

Liquefaction triggered by earthquakes is a source of damage to structures resting on loose to medium sandy soils. During earthquakes soil structures and the ground are subjected to vibratory excitations which are to a high degree erratic and extremely irregular. The magnitude of shear stress that is applied to a soil element in a real earthquake will, therefore, vary at random from one second to another. In order to evaluate the effect of such randomness, averaging procedures have been employed. In this averaging method a complex stress time history can be converted to an equivalent number of constant harmonic stress cycles. The equivalent load pattern thus determined has been considered as a representative load. This concept tends itself considerably to the simplification of the laboratory method. The soil selected for this thesis is known as Firouzkouh Sand No. 161, that exerted by load pattern that recorded in Kojaeli earthquake in 1999. Finally by using the stress averaging method, the reduction coefficient of stress is proposed and compared to those of existing studies and codes.

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Author(s): 

PALASSI M. | ARASH M.H.

Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    401-410
Measures: 
  • Citations: 

    0
  • Views: 

    3866
  • Downloads: 

    0
Abstract: 

In this paper, using the data obtained from the measurement of convergence of Gavoshan Tunnel and its access galleries, the ratio of horizontal to vertical in-situ stresses have been estimated from back calculations. This tunnel with a length of about 20.2km is located in the west of Iran, and in the vicinity of the main road of Sanandaj to Kermanshah. This tunnel has been excavated from inlet and outlet and from eight faces created by four access tunnels including Haltooshan, Tavankesh, Sabenav and Kachaleh galleries. Several instruments have been used for monitoring the behavior of the tunnel including tape extensometers, rod extensometers, total pressure cells, piezometers and load cells. The convergence of the tunnel has been measured using tape extensometers in several stations in the main tunnel and the access galleries. For the numerical modeling, the computer software Plaxis with computational modeling of jointed rock (JR) and triangular elements of 6 nodes in plane strain has been used. Considering that Gavoshan Tunnel is located in the zone of Sannadaj-Sirjan fault, assessment of the ratio of horizontal to vertical stress is important. Therefore a back analysis to calculate K value has been carried out. The results obtained from convergence measurements are analyzed for the different stations and are combined with the numerical analyses to evaluate the coefficient of lateral pressures. It is concluded that in the outlet region of the tunnel, Sarbenav, Haltooshan and Tavankesh access galleries, the ratio of horizontal to vertical in-situ stress exceeds one and in the inlet region of the tunnel, this ratio is less than one.

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Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    411-416
Measures: 
  • Citations: 

    0
  • Views: 

    2884
  • Downloads: 

    0
Abstract: 

In this paper the volumetric behavior of four carbonate sands having different physical properties and crushable grains are investigated using isotropically consolidated-drained triaxial tests. Three sands were obtained from the north shores of the Persian Gulf, south of Iran, called Hormoz, Kish and Tonbak sands, and one was obtained from the south beaches of England and called Rock beach sand. The studied sands have different particle size distribution, shapes and physical properties. Shapes of the grains in these soils are as platy, needle, bulky, angular, subangular and porous, in which show the different sources and deposition environments of them. Tests results conducted on the studied carbonate sands show that different properties of them result in different particle breakage ratio during loading, so that it increases with confining pressure, axial strain, slenderness and area to thickness ratio of the soil grains. Volumetric response of these soils is complex due to interaction of dilation and contraction resulted from particle breakage during shear loading. Therefore, regarding the unknown values of void ratios changes from dilation and particle breakage, the critical state concept become complex. In fact, there is not a real critical state in these soils at least up to axial strain of %20. It is also impossible to reach the critical sate concept using the common triaxial tests apparatus considering of its axial strain limitation. The randomly observed deformation under constant volume is apparent and not real. Such a situation is the volumetric balance between dilation and contraction due to particle breakage. Considering the relative values of these two parameters, the location of the apparently critical state is variable and curve shape, and it is depend on the initial void ratio, dilation, particle breakage and confining pressure. It is expected that the dilation ends up fast, however, particle breakage occurs as the shear strains are applied.

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Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    417-427
Measures: 
  • Citations: 

    0
  • Views: 

    4897
  • Downloads: 

    0
Abstract: 

Pre-stressed concrete beams are frequently used in structures such as bridges etc. The theory for analysis and design of these structures has been developed in recent decades. Furthermore, optimization in design has recently been considered with the aim of energy conservation. Optimization of pre-stressed concrete beams (OPCB) with box and T shapes is presented in this paper. For this purpose Genetic Algorithm Optimization method is used in which design properties such as cost, weight and section characteristics are included in the objective function. Furthermore, the cost objective function represented by the overall cost of the OPCB in terms of concrete, pre-stressing steel, mild steel, formwork and construction pre-stressing and placing of concrete is minimized subjected to 14 reliability constraints and 4 geometrical constraints. The design variables consist of three or five dimensions relative to section shape (T and box shapes respectively), two items that represent the percentage and amount of pre-stressing and three or seven items for tendon profile related to number of spans. Analysis is performed using a computer program with an automated design optimization package in which new exact equations are developed to calculate pre-stressing force losses analytically. Using this program, the design of an optimized pre-stressed concrete beam can be carried out according to the provisions specified by the British Standard (BS8110 and BS5400).

Yearly Impact: مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    429-436
Measures: 
  • Citations: 

    0
  • Views: 

    2049
  • Downloads: 

    0
Abstract: 

For seismic control of structures, energy dissipation systems are basically used to facilitate repair and seismic retrofit as well as limiting inelastic behavior in specific ductile devices designed accordingly. The main advantage of using passive control is to switch from earthquake resisting structural design to seismically controllable design of structures. In this paper, influence of using three passive control schemes: Visco Elastic Damper (VED), Tuned Mass Damper (TMD) and base isolation on reduction of seismic structural response like displacement, acceleration and base shear is investigated. The properties of a linear visco-elastic material can be determined by applying a periodic excitation and monitoring the response that involves both an amplification and a phase shift. The frequency of a TMD is tuned to a particular structural frequency so that when that frequency gets excited, the damper will resonate out of phase with the structural motion, thus energy is dissipated by the damper inertia force acting on the structure. The act of isolating an object involves providing an interface between the object and its neighbors which minimizes interaction. Therefore, it is logical to isolate the structure at its base and prevent the ground motion from acting on the structure. For this purpose, 6 moment frames of 5 to 30 stories were modeled using nonlinear finite element software. To study numerical behavior of frames in different cases, typical sections were selected for models subjected to the El Centro earthquake for time-history analysis. Based on the results, using base isolation significantly reduced base shear, story drift and acceleration while the other two methods, although convincingly reduced lateral displacements, generally increased the accelerations. Due to lateral stiffness increase, adding VED increased the frame base shear but TMD showed no major drawback.

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Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    437-442
Measures: 
  • Citations: 

    0
  • Views: 

    1535
  • Downloads: 

    0
Abstract: 

Building industry is one of the most energy consuming parts of the developed and developing countries. Cooling, heating and ventilating systems devote a great amount of this consumption so studying natural ventilation systems have become more important in order to improve their performance. In this paper, air flow has modeled by a computational fluid dynamic model with finite volume method in solar chimney as a new kind of natural ventilation system and in a combined system with Baadgir. For this reason, different turbulent models have been compared by a valid statistical test in order to find a suitable turbulent model in these systems and at the end a ke-RNG model has been selected. Also the effect of increasing height, span width and thermal gradient of the walls on improvement of solar chimney's performance have been studied by computing parameters like mass flow rate and mean velocity.

Yearly Impact: مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Author(s): 

SANEEI NIA Z. | GHASSEMIEH M.

Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    443-454
Measures: 
  • Citations: 

    0
  • Views: 

    711
  • Downloads: 

    0
Abstract: 

In seismic regions, steel tubular bracing members have widely been used in steel structures. Although there are some shortages with such systems, due to their economical advantages, they are being used in many structures. The steel hollow brace members exhibit stable hysteretic behavior up to the point of first local buckling, and subsequently they exhibit significant degradation in strength and ductility. Comparing composite braces with steel braces, the presence of concrete infill has shown to influence the possible mode of failure in the specimens. It is also found that the infill supplies the extra compression resistance of the brace after several load reversals, consequently improves ductility capacity of the system. In this research, using the finite element method, the seismic behavior of the composite bracing system with and/or without the infill is simulated. Analytical models with the capability of displaying the cyclic behavior are utilized for concrete filled tubular bracing members. The analysis has been implemented numerically by employing the general purpose finite element software. Overall, it is shown that the difference in improvement gained by concrete infilling was attributed to pertinent variables such as the width to thickness ratio, shape of the section and concrete compressive strength, yield stress of the steel tube and the axial load level on the stiffness, strength and ductility of concrete-filled steel tube braces. In addition, this paper provides information on key response parameters, including tensile and compressive strength and post-buckling capacity, as well as, ductility and energy dissipation capabilities. Particular attention is given to the influence of member slenderness. The analytical findings are compared with the recommendations of a number of international codes of practice, and areas of agreement or discrepancy are highlighted. Finally, special considerations for enhancing the seismic performance goals are discussed.

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Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    455-466
Measures: 
  • Citations: 

    0
  • Views: 

    799
  • Downloads: 

    0
Abstract: 

Vulnerability of masonry buildings to seismic activities has been observed during the past earthquakes. A large number of these structures in Iran are residential buildings, hospitals and schools, and their damage ends to massive human being causalities. Therefore, seismic evaluation and strengthening of masonry structures is crucial in seismic regions. Coating the walls with thin reinforced concrete layer(s) is an ordinary technique in retrofitting the masonry buildings in Iran. However, due to the lack of appropriate design guidelines, the rehabilitation procedures are mostly carried out following empirical procedures. Mechanical continuum elastic properties of a masonry wall are needed for modeling it as a continuum media in the elastic range. These properties can be achieved through the homogenization techniques. The homogenization theory for periodic media allows derivation of global behavior of masonry from the behavior of the constitutive materials (brick and mortar). In other words homogenization is the technique of describing the composite behavior of masonry in terms of macro or average stresses and strains. Homogenization techniques can be done in two main directions called experimental homogenization and analytical homogenization. Experimental homogenization needs so many costly tests and the obtained results are limited to the tests conditions. Analytical homogenizations have been used by many authors in different frame works (elastic, plastic, limit states and …) and with a variety of methods like single step homogenization, two-step homogenization and engineering methods and in most cases only in plane behavior in a two dimensional framework is considered. Single-step homogenization needs numerical solution that can be obtained through finite element analysis and it contains a great number of computations, also the results are not in close-form. In this paper the elastic properties of bare and retrofitted masonry walls, which can be used in linear seismic evaluation procedures, are derived from a simple analytical homogenization method. The adopted homogenization method can be used easily in any kind of bond patterns, the solution is in closed-form and the results are in good agreement with the complex homogenization procedures used by other authors. The obtained relations for computing the orthotropic elastic properties of the bare and retrofitted masonry wall are presented. The accuracy of the proposed relations for bare masonry walls are verified by comparing the results with the results obtained with a more complex homogenization method. Moreover, the verification for both bare and retrofitted masonry wall is conducted by comparing the elastic behavior of masonry walls following macro and micro modeling approaches.

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Author(s): 

GHASSEMIEH M. | KARI A.

Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    467-478
Measures: 
  • Citations: 

    0
  • Views: 

    863
  • Downloads: 

    0
Abstract: 

Shape memory alloys are such materials that are able to undergo large strains of up to 8 percent without leaving residual strains. Therefore, their recentering feature prevents the structure from permanent deformations when it is subjected seismic loadings. Having those key features, it makes shape memory alloy an ideal bracing to be utilized in the steel frame structures. Also, another form of the bracing system being buckling restrained braces provides more ductility and stability for the steel structure when subjected to earthquake loading. In this paper, seismic behavior of structures using shape memory alloy braces and/or buckling restrained braces has been investigated. It has been shown that in relatively short structures, priority of using one bracing system with respect to the other one depends on the intensity of ground motions. Also, in contrary to the short structures, in mid-rise structures utilizing shape memory alloy braces has no benefit, and thus using buckling restrained steel braces is preferred.

Yearly Impact: مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    479-486
Measures: 
  • Citations: 

    0
  • Views: 

    1019
  • Downloads: 

    0
Abstract: 

Civil engineering structures as well as office or apartment building are affected by earthquakes. In some buildings, few or no walls are provided at the first story (pilot). In the structures with difference in story level, major problems is due to discontinuity of floor diaphragm that causes significant changes in period, stiffness and distribution of earthquake force. In this paper, using IDARC software which is nonlinear dynamic analysis program, time history and location of first crack and plastic hinge, time history and location of plastic hinge in short columns, local and global damage index in 4, 8 and 10 story structures with story level difference under the two earthquake records of Elcentro and Tabas with different peak ground accelerations of 0.3g, 0.5g and 0.7g are evaluated. The results show that in both earthquakes, top stories of all structures have the most damage in 0.3g. Global damage index of 8 story structure is more than 4 and 10 story structures in 0.7g of Tabas earthquake, but in Elcentro earthquake some result comes true about 0.5g. In both earthquakes, crack pattern and plastic hinge of beams happen in common part of two structure that have height difference and the damage of beams and columns happen in the frame shorter part of 4 and 8 story structures and in the frame tall part of 10 story structure.

Yearly Impact: مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    487-493
Measures: 
  • Citations: 

    0
  • Views: 

    755
  • Downloads: 

    0
Abstract: 

Flow pattern around bridge pier and its effects is one of the interest of hydraulic engineers. Since numerical models are progressing as a tool to analyses flow fields, in this paper numerical simulation of flow pattern around bridge pier is studied and its consequent effects on backwater is investigated. Fluent model (version 6) is used and water surface is simulated using volume of fraction (VOF) method. Comparison of numerical and experimental results show good agreement.

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Issue Info: 
  • Year: 

    2011
  • Volume: 

    45
  • Issue: 

    4
  • Pages: 

    495-504
Measures: 
  • Citations: 

    0
  • Views: 

    1159
  • Downloads: 

    0
Abstract: 

Assessment of seismic bearing capacity of strip foundations has been the concern of only few researchers in the field of geotechnical earthquake engineering during the last decades. The previous works have mostly assumed that in the presence of a horizontal earthquake acceleration (kh.g) besides the body force due to gravity, the ratio of the shear stresses to the normal stresses along the ground surface is equal to kh and the load inclination beneath the footing with respect to vertical equals to tan-1(kh). But this assumption does not seem to be always correct. For example in the case of multi span frames where only some spans may be braced and the support conditions at the end of the columns may not be uniform, the load inclination beneath some footings may not be equal to tan-1(kh). This paper presents the seismic bearing capacity factors Ng, Nq and Nc of a rigid strip foundation resting on a horizontal ground surface, when the load inclination beneath the footing is not equal to tan-1(kh). All calculations are executed by the well known stress characteristic method, commonly referred to as the slip-line method. It is assumed that the soil behaves rigid perfectly plastic and obeys the well known Mohr-Coulomb failure criteria under plane strain conditions. It is assumed that the state of the stress everywhere in the neighborhood of the foundation is at failure. It is also assumed that everywhere along the surface of the foundation, the ratio of the shear to the normal stress is equal to the horizontal earthquake acceleration coefficient (kh). The Ng parameter was calculated based on the both-sides failure mechanism, whereas the Nq and Nc parameters were calculates based on the single-side failure mechanism. The Nc parameter for cohesive media was calculated using the rule of equivalent states. Some graphs and tables are presented that could be used in order to assess the seismic bearing capacity factors of rigid strip foundations obtained by the stress characteristic method for various load inclinations. It is shown that the seismic bearing capacity factors, just like the static bearing capacity factors, increase considerably with reduction in the load inclination and vice versa. Further, this important outcome of some previous research works has been confirmed once again that the earthquake's effect on each of the body force as well as the overburden is as important as the earthquake's effect on the load inclination which should not be neglected. It is also shown that because of the non-symmetric nature of the seismic loading, the disposal of the characteristic lines as well as the pressure distribution below the foundation is non-symmetric. In other words, the foundation would be subjected to a moment in addition to the vertical and horizontal reactions, as a result of the non-symmetric soil pressure distribution during earthquakes.

Yearly Impact: مرکز اطلاعات علمی Scientific Information Database (SID) - Trusted Source for Research and Academic Resources

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