جستجوی مقالات مرتبط با کلیدواژه « عملکرد لرزه ای » در نشریات گروه « عمران »

Helical nails are a new type of reinforcement element that has been widely used during the last decade. This has caused that despite their widespread use, the seismic behavior of geotechnical structures reinforced by them is still unknown. Therefore, the present attempted study to evaluate the effects of some structural parameters on the dynamic performance of helical soil-nailed walls (HSNWs) using shaking table tests. For this purpose, eight reduced-scale wall models were constructed with different inclinations, lengths, and arrangements of helical nails and then subjected to input excitations with different durations. The response of each model to base excitation was determined in the form of fundamental frequency, acceleration amplification, facing displacement, and failure mechanism. The results showed that although a uniform increase in the nail length along the wall height significantly improved the seismic performance of the HSNWs, this improvement could also be achieved to some extent by increasing the length of the nails locally in the lower and upper halves of the walls reinforced by horizontal and inclined nails, respectively. The use of inclined nails instead of horizontal ones was an efficient solution to reduce the lateral displacement, acceleration amplification, and changes in the frequency content. The effectiveness of this solution was reduced with the use of shorter nails in the upper half of the wall and eventually minimized by reducing the length of the nails across the wall height. The nails located in the lower half of the wall were identified as having the greatest effect on the seismic performance of HSNWs when horizontal nails were used. The opposite occurred when inclined nails were used. A parabolic failure surface with a specific inflection point was observed to be the potential failure surface of the HSNW. The dimensions of the potential failure surface increased with an increase in the length and inclination of the nails. Also, a combination of overturning and base sliding was identified as the predominant deformation mode in HSNWs, although the base sliding mode faded with an increase in nail inclination.

Observations from past earthquakes and studies conducted by various re-searchers show the effect of facade on the seismic performance of the structure. Structure, veneer wall and faced need to be stable and inde-pendent in their deformation. The most important goal in the upcoming study is to investigate the effect of materials on the in-plane behavior of external walls and building facades based on the existing common imple-mentation methods. Based on this, 3 samples of Cyclic lateral loads were tested in a controlled manner under displacement and the results of their behavior in terms of form, failure patterns, cyclic curves, cover, bilinear, ductility, reduction of equivalent hardness were investigated. The results of the analyzes showed that adding a facade to the structure, depending on the type and characteristics of the facade materials, has a significant effect on increasing the initial stiffness in range of 4 to 6 time and resistance in range of 2 time. Facade isolation reduces interframe damage and also re-duces facade damage and adverse interframe-frame interaction it seems that the seismic performance of the brick facade is better compared to the stone facade and has less effect on changing the seismic performance of the structure. Key words: facade isolation, seismic performance, brick fa-cade, stone facade

In recent decades, different structural systems have been proposed to make tall buildings with suitable seismic performance. According to the art of architecture roll, especially in tall structures, and its effect on the taking attention of tourists and international investors, engineers turned towards systems that compose suitable structural performance with beauty. One of these systems is called diagrid structural system. In this paper after reviewing a number of researches conducted in this field, beside the study of seismic performance, coefficient of behavior of these types of structures are calculated by static nonlinear analysis method using SAP2000 structural analysis software. In this research, 9 structure models with the number of floors 18, 36 and 54 were modeled with three angles of 50.2, 67.4 and 74.5. By examining the results, it was observed that the mean coefficient of behavior for 18, 36 and 54 story models is about 2.70, 3.00 and 3.85 respectively. also, the results shows that using the diagrids by angles of 67.4 and 74.5 degrees, the value of stiffness is increases, and the displacement of the roof floor and the it's period decrees, also the structure is more economical in terms of material consumption, so the optimal angles should be this range, which more flexibility is created in the plan and elevation of the structure.

In this study, the seismic performance of the reduced beam section (RBS) steel moment-resisting frame (SMRF) equipped with composite steel plate shear wall (CSPSW) and high-performance fiber-reinforced cementitious composites (HPFRCC) is investigated using Abaqus software. The finite element model of HPFRCC-CSPSW was validated using experimental results. Then, the seismic performance of the six-story SMRF with common SPSW, as well as HPFRCC composite CSPSW systems under near-field (NF) and far-field (FF) earthquakes, was investigated and the results (bearing capacity, stress, deformation, and energy absorption) were compared. For this purpose, 5 NF and 5 FF seismic records were used. The results showed that the energy absorption and shear capacity of HPFRCC-CSPSW increased significantly but the maximum stress value decreased compared to common SPSW. The seismic performance of the investigated systems largely depends on the type of earthquake. However, in both SPSW and HPFRCC-CSPSW systems, the maximum displacement and the base shear under the NF earthquakes were higher than those of FF earthquakes. Besides, for all NF and FF earthquakes, maximum displacement in the SPSW system occurred in lower stories, but in the frame with CSPSW, the major displacement occurred in the upper stories. The highest increase in shear capacity and energy absorption of the system in FF earthquakes was for the Tabas accelerometer (75 and 128%, respectively) and the Imperial Vali earthquake (94 and 101%, respectively). Also, the maximum displacement in SPSW and HPFRCC-CSPSW systems occurred in Northridge (14.6 cm) and Tabas (16.2 cm) NF earthquakes, respectively; the Chichi earthquake also had the greatest damage to the structure under FF earthquakes.

Studies have been shown that conventional concentrically braced frames have undesirablity seismic performance since satisfy the displacement-controlled conditions in moment resistant frames are difficult. Then in the decades of 1970, researchers developed a system that had a good performance in strength and stiffness and in lateral displacement-controlled conditions either, the reason for this can be expressed that eccentrically braced frame (EBF) link acts as a fuse. Considering the limited research conducted in the field of investigating the seismic performance of eccentrically braced systems under strong ground motions by powerful dynamic nonlinear analyses, as well as knowing as much as possible the seismic behavior of these types of frames and choosing a suitable system to deal with seismic forces, the necessity of this research was felt. Therefore, in this paper, the seismic performance of 5, 10, and 15-story eccentrically braced frames with link beams with different types of performance in the ranges of shear, shear-flexural, and flexural performances has been investigated using incremental dynamic analyses (IDAs) under near-field ground motions. The results showed that, the performance of EBFs with Shear link in collapse prevention (CP) performance level are more desirable than EBFs with shear-flexural link and also performance of EBFs with shear-flexural link are more desirable than EBFs with Flexural link.

The main objective of the present numerical study is to investigate the seismic vulnerability of the caisson-type gravity quay walls with improved backfill soil located on a non-liquefiable dense seabed soil layer. In this regard, the effects of different improvement patterns applied to the liquefiable backfill on the seismic response of the wall are evaluated and compared. For this purpose, the Lagrangian explicit finite difference method and the UBCSAND constitutive model are utilized. First, a basic two-dimensional numerical model of the caisson quay wall is created and its response is validated against the corresponding experimental observations. Afterward, by performing non-linear time history dynamic analysis under the effect of various seismic events with different risk levels, 11 series of probabilistic seismic fragility curves are developed within the performance-based design framework for the caisson quay walls with 10 different backfill improvement patterns and also for the caisson quay wall without improvement. According to the damage probability of the wall with various improvement patterns at different seismic levels as well as the area of the improved zone behind the wall, the effectiveness and efficiency of the proposed improvement patterns on enhancing the seismic performance of the system are evaluated and discussed. The results show that the backfill replacement and modification improve the seismic performance of the wall and reduce its vulnerability in all seismic levels. By applying different backfill improvement patterns, the permanent horizontal displacement at the top of the wall after earthquake decreases on average between 40% and 73% compared to the wall without improvement. The triangle and trapezoidal geometrical patterns with the base at the bottom have the most positive effect on reducing both the horizontal displacement of the wall and the possibility of its seismic damage.

In the present paper, the effects of viscoelastic dampers and lead-rubber bearing (LRB) isolators on the seismic behavior of irregular steel buildings at height have been investigated. To this aim, a number of steel frames with flexural frame bearing system were modeled as 5, 9 and 13 stories and their seismic performance was evaluated in three modes: (1) without damper and isolator, (2) equipped with viscoelastic damper and (3) equipped with rubber core lead separator. After modeling the buildings in PERFORM-3D finite element software, by performing nonlinear static (pushover) and nonlinear dynamic (nonlinear time history) analyzes, the effect of damper and separator on the behavior of irregular steel buildings has been investigated. The results showed that the viscoelastic dampers and LRB isolators improve the seismic performance of steel buildings; The use of viscoelastic dampers in steel buildings with flexural frame system has increased the rigidity of the building and consequently the base shear force compared to single flexural frame and buildings equipped with LRB isolators. The results also showed that in all buildings, the base shear created in the isolated structure is much less than other control methods, which is due to the nature of seismic separation, ie reducing the force applied to the building.

The evaluation of the fragility functions is an analytical approach that allows different ground motions to be used at varying intensity levels and represent various characteristics of low-intensity and high-intensity shakings. The fragility curves demonstrate the structure’s probability of collapse, or other limit states, as a function of some ground motion intensity measures (IM). The intensity measure is often quantified by spectral acceleration (Sa) or peak ground acceleration (PGA). Based on the statistical procedures, the parameters of the fragility functions are computed by assessing the results of nonlinear dynamic time history analyses. Therefore, the probability of failure associated with a prescribed criterion (e.g. the maximum inter-story drift) is estimated based on the probabilistic distribution relations.This paper evaluates the effects of internal flexural frames on the seismic performance of diagrid structures based on fragility curves. This evaluation is achieved by designing a group of 24-story studied diagrid models with various diagonal angles of 49, 67, and 74 according to the Iranian Standard No. 2800 (4th edition) and the Iranian National Building Code (Steel Structures-Issue 10). Then, some specific interior gravity frames of the studied diagrid models are replaced with bending frames. The seismic vulnerability of the studied diagrid structures with and without internal bending frames is assessed using nonlinear time history and incremental dynamic analyses (IDA) under near-field earthquake records containing different directivity effects. Finally, the fragility curves for the studied structures were obtained based on the lognormal probabilistic distribution function for the seismic performance limit states including IO, LS, CP, and global instability (GI). Moreover, the seismic performance levels of the studied structures were determined based on the FEMA 356.The results of performed nonlinear time history analyses indicate that the application of internal bending frames in diagrid structures would reduce the value of inter-story drift in upper floor levels, especially when the angles of exterior diagonal members are large. The results also show that the global instability of diagrid structures without internal bending frames can occur at a faster rate than the skeletal models with internal bents. Also, the contribution of the internal bending frames in improving the nonlinear behavior of diagrid structures depends on the perimeter triangular patterns. Due to this dependency, the increase in the angle of the inclined members in skeletal geometric configuration can increase the effectiveness of the internal bending frames in preventing the occurrence of global dynamic instability. The fragility curves of the studied diagrid structures illustrate that the internal bending frames reduce potentially excessive seismic performance levels. Furthermore, the internal bending frames amplify the seismic energy dissipation capability of the diagrid structures.

Schools and buildings with educational uses are considered as important buildings in most of the design regulations due to their large population. According to the Iranian Earthquake Regulations, these buildings with any type of structural system, must be designed in such a way that they have at least a level of safety performance against severe earthquakes. Concrete schools in Kermanshah province have a significant frequency due to economic considerations, availability of materials and proper execution speed. Meanwhile, a special type of these schools has been executed with great frequency in most cities of Kermanshah province. On the other hand, in the study of educational spaces after the November 2017 Sarpol-e-Zahab earthquake in Kermanshah province, several cases of structural and non-structural damages have been observed in schools. For this reason, in this study, the seismic performance of this type of schools, under the influence of possible earthquakes, as well as their vulnerability are evaluated by nonlinear static analysis methods and increasing dynamic analysis (IDA). Then, by performing nonlinear static analysis, the envelope curve of the structure is extracted and important parameters such as ductility and the coefficient of behavior are calculated. Moreover, by performing the IDA for this type of schools, the failure curves subjected to various records in comparison with the increasing acceleration are presented and studied. The results show that the behavior and vulnerability of this structure are different according to the type of site and different records of near and far zones of the earthquake. Also, the structure of this school has an acceptable performance despite the irregularity in the plan.

The superelastic viscous damper (SVD) relies on shape memory alloy (SMA) cables for re-centering capability and employs a viscoelastic (VE) damper that consists of two layers of a high damped (HD) blended butyl elastomer compound to augment its energy dissipation capacity. An analytical model of a five-story and nine-story steel special moment frames building with the installed SVDs and BRBs are developed to determine the dynamic response of the structure. Nonlinear response history analyses are conducted to evaluate the behavior of controlled and uncontrolled buildings under 44 ground motion records. All the buildings are subjected to incremental dynamic analysis (IDA), so the effects of SMA on seismic performance of the buildings would be investigated through seismic concepts. Based on the results, utilizing SMA connections in smart buildings not only could keep interstory drift control performance almost similar to conventional buildings but also could substantially reduce economic loss with significant control of unwanted residual deformations in structural fuses due to their unique ability of induced recentering behavior in structural performance. The results probabilistically determine the seismic performance acceptability of studied smart buildings based on the impact of key structural response parameters (i.e., maximum interstory drift, residual interstory drift, and energy dissipation) on the seismic performance of the structure.

It is essential to properly understand the seismic behavior of reinforced concrete (RC) columns confined by stirrups that experience different corrosion rates. The current study investigated the effect of seismic performance indicators such as strength loss, energy dissipation rate, ductility and hysteresis damping on specimens and models for different stirrup corrosion rates. Analysis revealed the adverse effects of corrosion on the bond performance between the concrete and steel bars which affected the seismic performance of the columns. It was observed that severe corrosion of the stirrups undermined confinement of the concrete core and caused the seismic response to degrade. This changed the failure mode from a ductile to a brittle state. As the corrosion rate of the stirrups increased, their ductility and energy dissipation capacity decreased such that the amount of decrease depended on the corrosion rate. An attenuation relationship is proposed for the corrosion rate of the stirrups for different stirrup yield strengths, concrete compressive strengths, concrete covers and stirrup spacing. The values estimated by the proposed relationship were shown to be in acceptable agreement with the analytical results.

Intake towers form the entrance to the reservoir spillway or diversion system and thus play a key role in the seismic resistance of the whole system. safety and proper functioning of the intake towers in the event of a major earthquake is very important, since the release controlled by the reservoir can help to prevent the failure of the dam after an earthquake by reducing the water pressure. In addition, the current seismic assessment based on linear elastic constitutive model cannot adequately describe the seismic capacity of intake towers. Thus, to investigate the proper functioning of intake towers in the event a earthquake, it is necessary to introduce IDA that takes into fully assess the seismic performance of intake towers based on nonlinear dynamic analysis. In this paper by modeling the intake tower of the Briones dam, intake tower in three conditions of the intake tower, the intake tower-reservoir (outside water) and the tower-reservoir-inside water, under the influence of 12 earthquake records, each of which has a magnitude of seven in the earthquake intensity scale, has been investigated. The displacement at the top of the intake tower, damage of the intake tower body and the maximum tensile stress of the rebar in the intake tower were studied in all the three condition are considered as damage measure (DM), and the results were reported in the form of IDA curves. Then based on the results, the function and different limit-states (key points) of the intake tower structure are determined.

Bridges play a key role in transportation networks, and damage to them during an earthquake may delay emergency rescues and first-aid efforts. Thus, the development of structures with low damage and reduced downtime after extreme earthquake events is necessary. Post-tensioned self-centering (SC) systems improve the serviceability of bridges by eliminating residual displacements after severe earthquakes. In these systems, post-tensioned tendons have a critical role in self-centering piers so that they return the structure to its initial position and remain their functionality. In this study, the seismic performance of post-tensioned rocking bridge piers was investigated and compared with monolithic reinforced piers through time history analysis. Demand and capacity of bridges in models with different heights were investigated using incremental dynamic analysis (IDA). The probability of failure of each bridge has been investigated by studying the fragility analyses based on the maximum drift ratio and the stress of the tendons. According to the results, the collapse probability of bridges with conventional piers is higher than their corresponding bridge models with SC piers. Adding dampers to the SC piers increases the lateral load capacity of the model and decreases the probability of failure under an earthquake record with specific peak ground acceleration (PGA). On the other hand, using dampers in SC piers improves the energy dissipation capacity of the system and reduces the possibility of tendon yield by reducing the maximum displacement.

Most of the bridges in the world are generally designed and built according to the old criteria and regulations, These bridges should be subjected to seismic improvement studies and strengthen with appropriate method if needed. One of the practical methods for assessing the performance of a structure under different levels of seismic hazard is the fragility models, which are presented as fragility curves. The fragility curve expresses the conditional probability of reaching or exceeding a limit state as a function of ground motion parameters and the probabilistic method is also used to consider the different states and uncertainties that affect structures and earthquakes.Boxed cross-section arch bridges have good mechanism for bearing vertical loads due to stability and proper distribution of gravity loads. LRB seismic isolation systems are used to improve the seismic performance of the bridge. This study investigates the seismic behavior of the Nanin Bridge Arc Case in Switzerland, which has a cross-section overpass deck with a LRB Then, by evaluating the structural response states and the capacity of the members. Examination of the results of the seismic response of this structure as well as the probability functions of the frailty curve in different situations showed that the use of this system resulted in a significant reduction in the amount of earthquake damage at all levels of failure in foundation. With the use of Rubber lead seismic isolator, displacement of the structural base, the likelihood of base failure and base shear has been greatly reduced and due to the use of maximum member capacity and reduced member dimensions as well as a significant reduction in the amount of financial damage the system has also benefited.

Fiber Reinforced Polymers (FRP) are often used for structural repairs to improve the strength and ductility of the structures. Previous studies have shown that utilizing active confinement in concrete structures can improve the seismic behavior of concrete columns under pressure. In this study, the behavior of concrete columns actively confined by AFRP fibers was investigated under the combined effects of axial compressive and cyclic lateral loads. Two concrete columns were actively confined by AFRP strips. In addition, a non-confined column (SCR) was utilized as a control specimen. Then all specimens were tested under axial and lateral cyclic loading. Experimental results showed that the ultimate compressive strength and axial strain of specimens with active confinement are improved compared to the SCR specimen. Also, due to the increased number of small cracks in the specimen, a higher extent of energy was absorbed under the applied loading. The loading protocol caused no rupture in the AFRP strips, and no shear crack and brittle failure in the specimens were observed.

Damage sustained of electrical transformers in past strong earthquakes led to irrecoverable and severe economic losses of them. The seismic performance evaluation is associated with the loss of proper functioning of the transformer. This study deals with modeling existing isolated electrical transformer structures to evaluate the effects of variables that may affect the seismic performance and dynamic characteristics. The results probabilistically determine the seismic performance acceptability of study isolated electrical transformer structures based on the impact of key structural response parameters on the seismic performance of the transformer. Analyses of systems for a wide range of parameters are performed. The effects of horizontal and vertical near-fault pulse-like ground motions, the displacement capacity of the seismic isolation system, limit states of electrical bushings, and details of the isolation system design are considered. Also, the probability of failure of the transformer under the near-fault excitations with pulse-like characteristics is investigated. The results of this study demonstrate that three-dimensional seismic isolation systems can improve the seismic performance for a wide range of parameters and can be further effective compared with only horizontal seismic isolation and offer the lowest probabilities of failure for all cases of transformer and isolation system parameters.

Frames with masonry infill are the most common type of structures used in developing countries. Masonry infill affected the initial stiffness and strength of reinforced concrete buildings. The presence of opening in masonry infill is often used for placing doors and windows and it may reduce the seismic performance of the RC frame structure. Nowadays, the impact of the frame and infill on structure is one of the challenges in engineering researches. Engineers generally ignore infill in designing the building and consider it as non-structural part. When the masonry infill is placed in the concrete frame, significantly changes its mechanical properties, the stiffness and strength of the structure increase and ductility of the concrete frame reduce. There is interaction between masonry infill and itchr('39')s frame, so, the frames with infill behave differently than those frames without infill. Disregarding the effect of masonry infill, they can be safe and reliable in terms of resistance in design, since the increasing strength around frame has a positive effect on earthquake strength and overall structural stability, however, it should also be considered that masonry infill will increase the stiffness of the infill-frame and larger portion of the lateral load would attracted by frames. This can be a negative factor when ignore the infill masonry in the design. In the present study, by numerical modeling by nonlinear finite element method, the effect of the presence of masonry infill with different door and window openings on the behavior of concrete frames with seismic and non-seismic details at different axial load levels and different masonry infill thicknesses in seismic performance of frames concrete has been examined. For this purpose, the proposed models are first validated using laboratory results in ABAQUS finite element software. The results of the analysis show that increasing the axial load increases the final strength, effective stiffness and reduces ductility in specimens with masonry infill with different opening of doors and windows and reinforced concrete frame with seismic characteristics. The ultimate strength in specimens with reinforced concrete frame with seismic characteristics shows a slight increase compared to similar samples with reinforced concrete frame with non-seismic characteristics, which can be ignored. Increasing the thickness of the specimens increased the ultimate strength and effective stiffness of the specimens with seismic and non-seismic details. The results of these studies show that the different positions of the openings have significant effects on the behavior of the frames. If the opening is large or moves away from the center of the masonry infill, the final strength drop and stiffness effective reduction will be more.

Due to the seismicity of Iran and the occurrence of irreparable human and financial losses during the past years and in order to reduce these losses due to lateral loads, control methods can be used. Vibration control is a low-cost method among various methods of improving the seismic behavior of structures, which leads to a reduction in the response of the structure under dynamic loads. Control systems are divided into four categories: inactive, active, semi-active and combined. In this research, for the accuracy of modeling, an analytical article conducted by other researchers is used and the results are compared. Then 6 frames without damper and 6 frames with viscous damper with the same number of floors, under the title of short level 3, 5, medium level 7, 10 and high level 12, 15 floors in Itbus software according to 360-AISC- regulations, sixth and tenth topic National building regulations are loaded, designed and controlled. The results show an increase and improvement in the performance of the structure with a viscous damper compared to a normal structure. Reducing the displacement of floors can help reduce issues such as the seam allowance of two buildings as well as the comfort of residents in the event of an earthquake. Reducing floor drift can help improve the behavior of non-structural components and joinery. The presence of viscous dampers has reduced the displacement and drift of floors by even 90%. The presence of a viscous damper makes the drift of the floors more uniform. The presence of a viscous damper reduces the forces applied to the members and increases the capacity of the structure. As a general conclusion, the use of viscous dampers has acceptable results in structural responses and has increased the behavior and capacity of the structure.

This study aims to investigate the effectiveness of engineered cementitious composite (ECC) as a ‎means to enhance the seismic performance of short columns. Eleven ECC short columns and one reinforced concrete (RC) short column were ‎designed and tested under lateral cyclic loading with different fiber volume fractions(0 -1.5%) and shear ‎aspect ratios(3-7). The influence of fiber volume ‎fraction, and shear aspect ratio on crack pattern, hysteresis behavior, energy dissipation, failure ‎modes, and length of yielding region is presented and discussed. The test results show replacing ‎conventional concrete with ECC can effectively improve the seismic behavior of short columns. ‎Further more , ECC short columns show excellent ductility and damage tolerance. Results shows ‎larger plastic hinge lengths were obtained with an increase of aspect ratio and fiber fraction‎.The influence of fiber volume ‎fraction, and shear aspect ratio on crack pattern, hysteresis behavior, energy dissipation, failure ‎modes, and length of yielding region is presented and discussed. The test results show replacing ‎conventional concrete with ECC can effectively improve the seismic behavior of short columns. ‎Further more , ECC short columns show excellent ductility and damage tolerance. Results shows ‎larger plastic hinge lengths were obtained with an increase of aspect ratio and fiber fraction‎

In this study, a series of 1-g shaking table tests using variable-amplitude harmonic excitations were performed on 0.8 m high MSE/Soil nail hybrid wall models to investigate the seismic behavior of this innovative retaining system. Ten finite element models were also prepared with different wall height and nail length to carry out a parametric study. It was found that in models with constant length of steel strip, the deformation mode of MSE/Soil nail hybrid walls highly depends on the length of nails, so that the combination of a base sliding and overturning deformation mode was observed as the predominant mode of deformation. Irrespective of different nail lengths, the pattern of the observed failure mechanisms included a moving block and a combination of a reverse curve and flat failure surface with certain intersection point. Also, a range of ∆x/H = 0.62 - 1.10 % as a transitional level from quasi-elastic to plastic state and based on starting the development of active wedge failure, a range of ∆x/H = 5.0% - 5.6 % as a transitional level from plastic to failure state were determined. On the other hand, according to the significant increase in wall displacements by decreasing the L/H ratio of 0.7, L/H= 0.7 was presented as the critical ratio in seismic conditions.