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Structural Engineering and Geotechnics - Volume:7 Issue: 1, Winter 2017

Journal of the Structural Engineering and Geotechnics
Volume:7 Issue: 1, Winter 2017

  • تاریخ انتشار: 1396/01/06
  • تعداد عناوین: 8
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  • Hooman Mazlooma, Maryam Firoozi Nezamabadi * Pages 1-13
    The aim objective of this study is to investigate the effects of near-field earthquakes on the response of mid-rise buildings with tubular structure. For this purpose, a 20-story building with a square plan of six by six bays, all with 6 m span, and story height of 3.70 m is considered. Axial force of columns, shear lag, and inter-story drift values are used as the main response parameters. Nonlinear time history analyses (NLTHA) of the considered building were conducted by using once the two-component, and once more three-component accelerograms of both far- and near-field selected earthquakes for comparison. Numerical results of NLTHA show that inclusion of a vertical component of ground motion leads to around 17% and 32% increase, in average, in axial forces of side and corner columns respectively in case of far-field earthquakes. These increases were respectively 22% and 37% in case of near-field earthquakes. The vertical ground motion also leads to around 11% and 15% increase, in average, in shear lag of side and corner columns respectively in case of far-field earthquakes, and 13% and 19% increase in case of near-field earthquakes. The amount of increase in inter-story drift values due to the vertical ground motion was observed in range of 24% and 27% for far- and near-field earthquakes respectively.
    Keywords: Nonlinear Time History Analysis (NLTHA), Two-, Three-Component Earthquake Accelerograms, Axial Forces of Side, Corner Columns, Shear lag, Inter-Story Drifts
  • Mahmoudreza Shiravand *, Ahmadreza Torabipour Pages 15-22
    Due to lack of the proper and well behavior of steel moment-resisting connections subjected to the great and major earthquakes, excessive researches have been conducted to mitigate the damages on the primary elements and connections. Therefore, elimination of residual drift and increasing the plastic rotation capacity for the connectors in the panel zone are required. The main purpose of this study is to numerically investigate the behavior of the recent kind of the steel moment connections which are called as steel self-centering post-tensioned connections. The steel post-tensioned connections consisted of some high strength strands for self-centering feature plus energy dissipater angles for adjustment of plastic deformation. This paper studies on the steel self-centering post-tensioned connections using the finite element method. The obtained results are verified based on the experimental study. Accordingly, the energy dissipation, rigidity percentage, and ductility factor of the connections are determined. Results revealed the perfect self-centering with the proper ductility factor. Furthermore, it was observed that the post-tensioned steel connections have a high plastic rotation capacity without any damages to the column and beam.
    Keywords: Steel Post-Tensioned Connections, Self-Centering Feature, Finite element method, Ductility Factor, Dissipation Energy
  • Mohammad Reza Farhadi, Hassan Aghabarati, Hadi Niromand Jazi Pages 23-29
    The system of steel shear wall is an initiative resistance system against the lateral load such as an earthquake and the wind that has been researched in the last three decades. Currently, this system is noticed more than other systems because of adequate stiffness, ductility, and more energy absorption. The system of steel shear wall with corrugated sheets has been offered as an innovative system, since the construction of panels for hard-set steel shear wall is expensive and also it causes the increscent of weight construction. This type of system has been developed using of hard outer plate from geometry of corrugation shape that has better buckling strength than hard-set and flat case in this study. This study is conducted to compare the strength and energy dissipation capacity of three different steel shear walls: unstiffened, trapezoidally vertical corrugated and trapezoidally horizontal corrugated under vibration load of AISC 341-10 instruction with 100mm movement. The results reveal that although the ultimate strength of the unstiffened model is nearly 17% larger compared to that of the corrugated models, energy dissipation capacity of the corrugated models are approximately 52% larger compared to the unstiffened model.
    Keywords: Finite element method, Cyclic Loading, Corrugated, energy, Shear Wall
  • Alireza Hajiani Boushehrian, Azadeh Rezaee *, Arash Vafamand Pages 31-45
    One of the main concerns to design earth dam is the stability of the upstream slope of the earth dam in phase of rapid drawdown. Confined pore water pressure reduces the effective stress in this mode, so possibility of the instability and slippage will be increased. The main goal of this research is to investigate changes in the pore water pressure by using horizontal drains in upstream slope of the earth dams and the improvement in case of the factor of safety. In this study, firstly, the homogeneous and heterogeneous modes of the earth dam are considered and then rapid drawdown mode are modeled in two upstream slope modes without the horizontal drain and with the upstream slope including up to seven horizontal drains. These two modes are modeled by using GEOSTUDIO software. According to the obtained results, improvement by horizontal drains leads to increase in dissipation of pore water pressure and also increase the stability of the safety factor of the upstream slope up to 24% for homogeneous dams and 17% for heterogeneous dams. Practical equations were also presented to show the relation between the numbers of horizontal drains, the factor of safety and the pore water pressure. In order to study the influence of the horizontal drains on the upstream slope of the earth dams during the rapid drawdown condition, Molasadra earth dam geometry is used both in the modes of homogenous and heterogeneous dam. Molasadra dam and power station is located in about 13 kilometers of southwest of Sadeh county, around of Eghlid town in the north of Fars province in Iran.
    Keywords: Homogeneous Earth Dam, Heterogeneous Earth Dam, Horizontal Drains, Rapid Drawdown, Slope Stability Analysis
  • Saeideh Alsadat Mousavi *, Mehran Seyed Razzaghi Pages 47-54
    One of the serious damages of tremendous earthquakes is the damage to bridges as the major components in an arterial road network, as relief operation is interrupted following cutting roads. Regardless of the magnitude and severity of an earthquake, other factors are also important in the strength and seismic performance of concrete bridges. Freezing-thawing cycles are among the factors, which erode the piers of concrete bridges over time. Therefore, it is necessary to evaluate the seismic vulnerability of bridges for future designs.
    This research aims at discussing the effect of freeze-thaw cycles on the seismic performance of concrete bridges using fragility curves. Fragility curves express the conditional probability to reach or exceed a level of damage as a function of ground motion parameters. The curves have been developed analytically using a probabilistic method. Ground motion parameter, peak ground acceleration, structural criterion, and relative displacement of piles were considered. The non-linear time history analysis in OpenSees was used for demand determination. The curves were drawn for the slight, moderate, and extensive damage levels in two modes of before and after damage caused by thawing and freezing, i.e. the mode in which the compressive strength of column section expose reduced. With respect to the fragility curves, the strength reduction increases bridge vulnerability, especially on slight damage levels. Comparing with the cyclic curves of the most vulnerable column in two modes of before and after the damage showed that energy absorption capacity lowered with the expose compressive strength reducing.
    Keywords: Concrete bridges, Concrete Compressive Strength, Freezing-Thawing Cycles, Seismic Vulnerability, Fragility Curve, nonlinear time history analysis, Damage Levels, peak ground acceleration
  • Saeed Kia Darbandsari *, Maryam Firoozi Nezamabadi Pages 55-65
    Hexagrid structural system is an innovated system with structural behavior which is similar to a tubular system. In this paper, a numerical study is conducted to estimate the seismic performance of horizontal hexagrid concerning the combined horizontal and vertical hexagrid, tubular and diagrid structural systems. First 30 and 50 story buildings are modeled using ETABS, then pushover and nonlinear dynamic analyses are performed on buildings using PERFORM 3D. Results indicate that the horizontal hexagrid system under nonlinear dynamic analysis has the least roof displacement; buildings capacity curves also demonstrate that the horizontal hexagrid is the most efficient system, as it brings lowest roof displacement along with high energy dissipation.
    Keywords: High-rise Building, Lateral Resisting System, Hexagrid System, Nonlinear Static, Dynamic Analysis, Seismic Performance
  • Pouria Hajikarimi, Reza Attarnejad * Pages 67-73
    Rotating beams have been considerably appealing to engineers and designers of complex structures i.e. aircraft’s propeller and windmill turbines. In this paper, a new flexibility-based method is proposed for the dynamic analysis of rotating non-prismatic Euler-Bernoulli beams. The flexibility basis of the method ensures the true satisfaction of equilibrium equations at any interior point of the elements. Following structural/mechanical principles, exact shape functions and consequently exact structural matrices i.e. consistent mass, geometric stiffness and flexural stiffness matrices are derived in terms of special so-called “Basic Displacement Functions”. The method is considered as the logical extension of conventional finite element method. Being straightforward formulated, the method can be incorporated into any standard finite element programs. The method poses no restrictions on either type of cross-section or variation of cross-sectional dimensions. The effects of rotational speed parameter and taper ratio on the variation of natural frequencies are studied and the results compare well with the other existing methods in the technical literature.
    Keywords: Free Vibration, Non-prismatic, Euler-Bernoulli beam, Basic Displacement Functions, Energy methods
  • Masoumeh Farshbaf *, Abdolreza S. Moghadam Pages 75-83
    Residual drifts after severe earthquakes interrupt serviceability of buildings. Retrofitting of such buildings is in many cases very difficult and consumes lots of time and money. Recently, there are some attempts to develop the seismic design procedures to not only satisfy life safety criteria but also lead to more economical buildings. One of these modern methods of improving seismic performance of the steel structures is using systems with ability of rocking. The main features of these new systems are to concentrate the damages in specific easily repairable locations of structures, to dissipate more energy and to reduce and limit the residual deformations. In this paper the effects of the column-foundation connection stiffness on the seismic performance of rocking steel braced frame are studied. Nonlinear dynamic time history analyses are applied, using seven far-field ground motion records in two intensity levels. The response parameters are mean of the maximum vertical accelerations of rocking columns, drifts, performance levels, in addition of the positive and negative vertical displacements. The results of this study indicate the positive effect of increase in the tensile stiffness and decrease of compressive stiffness in the column base connection on vertical accelerations, uplift and performance levels in the models with viscous dampers.
    Keywords: rocking steel braced frame, Viscous Dampers, column-foundation connection, compressive stiffness, tensile stiffness