جستجوی مقالات مرتبط با کلیدواژه « near field earthquake » در نشریات گروه « عمران »

In the event of progressive seismic collapse, the entire columns are not removed and can weaken in a time-dependent manner. For example, the possibility of reducing the carrying capacity of a column is higher in the maximum acceleration of the ground. Therefore, since earthquakes have different parameters such as frequency content, maximum acceleration, effective vibration duration, and other things, they can subject a structure to different effects. This is the special distinction of this phenomenon in contrast to progressive failure under gravity loads, which multiplies its importance. In this article, the ductility of simple and bending frames with special divergent bracing against progressive collapse is evaluated from a seismic point of view. The analysis used is non-linear time history analysis, according to 14 acceleration maps of the near-pulse area of FEMA P695, and non-linear static analysis, which was performed in SAP2000 software. The results showed that the maximum demand for the floor drift angle and rotation of the floor connecting beam in the two scenarios of removing the first and fourth floors for the special bending frame with special eccentrically bracing is 50% of the values of the simple frame with special eccentrically bracing. Except for the bending beam, in the scenario of removing the fourth floor, the maximum values of the floor drift angle for both frames were 0.024 radians, and for the maximum rotation of the floor beam, 0.056 and 0.061 radians, respectively.

Studies on behavior of structures under the effect of earthquakes in the near-field earthquakes, compared to far-field earthquakes, have shown more effects of this type of earthquake on the structure. Most of these effects depend on the characteristics of forward-directivity and flip-step with permanent displacement effect. The characteristics of near-filed earthquakes should be considered in the design and analysis of structures. The present research, aimed to investigate the effect of directivity characteristics of near-field earthquakes on the response of concrete structures. To this aim, first the different records of ChiChi earthquake in different stations have been determined as the basis for selecting accelerograms. Then, using analytical methods, the response spectrum of these records, considering the effect of forward-directivity and without it (removing dominant pulses) in the east-west and north-south directions was determined. Next, using time history analysis on two concrete structures of 10 and 15 stories, the drift (relative displacement) and the inter-story base shear in the structures was investigated for seven records of ChiChi earthquake. The results showed that due to the unpredictable nature of the earthquake, the drift and base shear responses of stories in both structures have been increased or decreased in different directions in some cases. Therefore, it can be seen that directivity does not always have a uniform effect on the behavior of the structure and does not follow a fixed pattern. Also, the results showed that by increase in the height of the structure and as a result of increasing its period, the effect of forward-directivity on the response of the structure increases. This is despite the fact that in many cases of shorter structures, the directivity does not have much effect on the response of the structure and even in some cases; it has caused a decrease in the response.

During the past years, researchers have developed ideas to thoroughly investigated into the behavior of structural bracing systems. Accordingly, one of these emerging systems is the Strong Back Bracing System (SBBS) by which the inter-storey drifts are maintained constant to prevent occurrence of failure. This system is comprised of the components of conventional concentrically braced frames together with a strong truss whose presence is aimed at uniform distribution of drifts along height of the building. This truss precludes concentration of damages in one or several stories in the concentrically braced frames. On the other hand, the near-filed earthquakes differ from the far-field ones in terms of both amplitude and frequency content. Thus, it is required to study the effects of such earthquakes on behavior of the SBBS. In addition to earthquake, the soil underlying the structure can affect the structural responses especially in cases when structure rests on soft soils. This system is comprised of the components of conventional concentrically braced frames together with a strong truss whose presence is aimed at uniform distribution of drifts along height of the building. This truss precludes concentration of damages in one or several stories in the concentrically braced frames. On the other hand, the near-filed earthquakes differ from the far-field ones in terms of both amplitude and frequency content. Thus, it is required to study the effects of such earthquakes on behavior of the SBBS. In addition to earthquake, the soil underlying the structure can affect the structural responses especially in cases when structure rests on soft soils. Typically, the codes provide methods for structural analysis assuming that the structure is located on a rigid base whereas in reality, this assumption does not always hold true highlighting the need for inclusion of soil-structure interaction into the analyses. Accordingly, this paper deals with seismic behavior of the structures equipped with the SBBS considering the soil-structure interaction under near and far-field earthquakes. In this respect, 3, 6 and 12-storey structures resting on stiff and loose soil (soil type II and IV according to classification of Standard 2800) have been analyzed. To this end, nonlinear time-history analyses using seven far and near-field earthquakes for both cases of rigid and flexible base, have been carried out. The results indicate that maximum roof displacement of 3, 6 and 12-storey structures founded on stiff soils (soil type II) vary insignificantly under the far and near-field earthquakes. Conversely, in the case of soft soils (soil type IV), displacements have increased by 2.93 to 18.22%. Moreover, it was found that drift ratios for the structures on stiff soil, in the case of 3 and 6-storey structures, increases slightly and reduced by 6.75% for the 12-storey structure. In the case of soft soil, all structures under the near-field motion, incurred increase in drift ratios by 11.67% and in the case of far-field, 3 and 6-storey structures experienced 4.86% decrease and conversely, the 12-storey structure encountered 7.7% increase. In addition, ratio of residual drift of the 3, 6 and 12-storey structures under average of near-field earthquakes, has decreased and increased by 8.52 and 36.02 in the case of stiff and soft soils, respectively.

Due to the relatively high use of steel buildings in Iran and the importance of rigid steel beam-to-column connections, which are among the vital components in this type of buildings, the need to better understand the behavior of these connections against earthquakes has been noted. Also due to the special characteristics of the near-field earthquakes, which is different than far-field earthquakes and it has its own characteristics; and the fact that some catastrophic earthquakes occurred in Iran, such as the Bam earthquake (2003) and the Tabas earthquake (1978) had the characteristics of the near-field earthquakes, which can show the importance of the near-field ground motions; the purpose of this study was to propose a loading protocol for special steel moment- resisting frames under near-field earthquakes for Iran. Therefore, first, by examining the earthquakes that have occurred in Iran during several years, near-field earthquakes have been selected. Steel buildings of 3, 5, 7, 9, 12 and 20 floors were designed and analyzed according to the rules and regulations of Iran, then for each of the designed steel buildings a critical frame was determined; the values of the scale factors are also specified. After performing nonlinear time‐history analysis and applying the proposed near-field ground motions to all of the critical frames, inter-story drift angles for all frames was obtained and compared. The third floor of the 3-story critical frame was selected as the critical floor; which is a story whose results will be used to construct a loading protocol; The basic rainflow counting and simplified rainflow counting were performed for the critical inter-story drift angles results; The proposed loading protocol are derived based on the MCE-level seismic hazard and 84th percentile values of key seismic demand parameters. These parameters are number of damaging cycles, maximum inter-story drift, sum of inter-story drift range, inter-story drift range and residual inter-story. The rationality of the proposed loading protocol was justified by showing the cumulative distribution function. The proposed loading protocol has 23 damage half-cycles, including 3 pulse half-cycles with inter-story drift ranges of 0.060, 0.100 and 0.078 radians; which are calculated by the basic rainflow counting method. The maximum inter-story drift was obtained 0.065 radians. In the final half cycle, the mean value is the same as the residual inter-story drift of 0.03 radians. Also, the sum of the inter-story drift ranges is equal to 0.684 radians. The proposed loading protocol was compared with the SAC near-field earthquake protocol, the maximum inter-story drifts in the proposed protocol is 0.065 radians and in the SAC protocol is 0.06 radians. Furthermore the pulse cycles in the proposed protocol have inter-story drift ranges equal to 0.060, 0.100 and 0.078 radians; while the three pulse half-cycles at the beginning of the SAC loading protocol have inter-story drifts of 0.08, 0.05 and 0.04; respectively. Therefore, the proposed loading protocol has a higher inter-story drift and stronger pulse cycles than the SAC near-field earthquake protocol; but the total number of cycles defined in the SAC protocol is greater than the proposed protocol.

In high-rise reinforced concrete buildings, using base-isolating systems can increase the response of the structure. To overcome this problem, it is suggested to increase the stiffness of the building by utilizing lateral load-bearing systems such as shear walls. In the present study, the seismic response of fixed-base and lead-rubber bearing isolated dual-system reinforced concrete buildings has been compared using nonlinear time history analysis procedure according to the 2800 V4 standard and ASCE/SEI7-16 code provisions. For this purpose, 10, 15, and 20-story reinforced concrete buildings, in a similar and regular plan, with special moment frame and shear wall dual systems have been selected as a case study. A 20-story building has been considered as a tall building in this study. Results show that the response of the base-isolated structures including the mean, median, and 16% and 84% percentiles of drift ratio, floor acceleration, and base shear has a significant decrease compared to the fixed-base buildings according to the above-mentioned code provisions. Results indicate that base-isolated buildings with respect to fixe-based buildings, based on the ASCE / SEI 7-16 code compared with the 2800 V4 standard, maximum drift in the structures has a 23% more decrease and mean acceleration and base shear have an 11% more decrease. The results obtained in this study can be the basis for the development of the 2800 standard provisions to investigate the seismic response of base-isolated reinforced concrete structures at a near-fault site.

In this study, structures equipped with friction dampers under the influence of far-field and near-field earthquakes are investigated. How they slide and vibrate, which includes displacement, velocity and acceleration, is calculated by numerical analysis. And the response of the structure under the effect of far-field and near-field earthquakes on the one hand and also considering the simple friction model of Columbus and the more complete model of velocity-dependent friction (Stribeck friction) is compared. Although the possibility of a far-field earthquake is very likely, but the occurrence of large earthquakes near cities that are near faults is undeniable, and these earthquakes have certain specifications that distinguish them from far-field earthquakes. Some of these specifications are such that if neglected, they will lead to underestimation of the seismic force in the design of structures. Examples of these specifications are fling step effect and the presence of velocity pulse in the component perpendicular to the fault that is caused as a result of the phenomenon of forward directivity.Due to the nonlinear behavior of the damping force (FD), programming has been used to perform nonlinear analytical dynamics. Also, behavioral models in Open Sees software are used to investigate the behavior of Stribeck friction for friction damper and to compare its results with the results obtained from accurate analysis. The results show that simplifications of the sliding friction model, on the one hand, and lack of focus on near-field earthquakes, on the other hand, result in underestimation of displacements, especially in member forces. Considering Stribeck friction, error rate is reduced and results are improved.

Liquid storage tanks are very important structures for storing various types of fluids in urban and industrial areas. Therefore, designing, manufacturing, and evaluating their performance for different conditions is very important. In this study, the behavior of steel tanks with changes in the ratio of height to diameter of the structure under the effects of far and near field earthquakes has been analyzed and studied. For this purpose and for better analysis of these structures, 4 models of steel tanks with different height to diameter ratios and in empty and 90% full states have been subjected to seismic analysis using modeled ANSYS finite element software. To better investigate the trend of seismic effects on steel tanks, selected far and near-field earthquakes have been scaled to the same amount of 0.5g. The results showed that in empty tank conditions, by increasing the ratio of height to diameter to more than 1, the maximum values of displacement in the far and near-field earthquake are close to each other. The results also show the extraordinary importance of adding water to the response of steel tanks due to far-field earthquakes for a height to diameter ratio of more than 1. In most cases, by increasing the ratio of height to diameter of the structure and adding the fluid to the analysis, the values of the first main stress and the maximum reaction of the horizontal abutment in the two modes of analysis under the effects of the far and near-field earthquakes get closer to each other. The results show that in order to analyze and investigate steel tanks affected by earthquakes, in addition to near field earthquakes, far-field earthquakes should be studied and analyzed.

Earthquake as a natural hazard jeopardizes civil structures and infrastructures. Iran is a seismically susceptible country compelling experts to adopt appropriate counter measures in design practices. In this regard the structural control conceptis well known from which semi active control methodologies have been addressed vastly by scholars during last two decades. These methods impose controlling actions by changing stiffness and damping traits of the structure. In addition to provisions to be considered in the structure side, earthquake properties originated from distance to source fault should be dealt with as near and far field categories. In this paper, we are aimed to evaluate efficacy of a liquid damper with adjustable blades in a semi active scenario. Generally, liquid dampers have low installation and maintenance costs that make them as a suitable choice in many applications. The structural model is single degree of freedom subjected to 6 far field and 6 near field earthquakes. A fuzzy algorithm has been developed to handle the blades rotation in the semi active control.The algorithm adjusts the blade angle based on corresponding damping ratios adopted from a previous research. Results of analyses demonstrate that the damper can reduce structural responses significantly. This reduction about responses from near field ground motions are greater than those of far field ground motions.

The main goal of the 2030 sustainable development plan is to develop access to renewable, sustainable, reliable and cost-effective energy. One of the renewable energy sources is wind energy, which is produced using wind turbines. These turbines are mainly used in coastal or offshore areas that are seismic and liquefied. The development of these turbines in areas with high seismic potential and liquefied soils has necessitated the use of piles and other deep foundations. In this paper, the effect of liquefied soil layer characteristics on the soil-mono pile interaction under the effects of far and near field earthquake records has been investigated. Dynamic nonlinear time history analyses were performed by considering four types of liquefied sand with a thickness of 5 m, under 2 kW turbine load and the effect of 14 earthquake records. Nonlinear analyses are performed in OpenSees software by considering the appropriate behavioral model for soil layers and the interaction between the pile and the soil. The results showed that in earthquakes with a PGA less than 0.4 g and in sandy soils with a density of more than 70% liquefaction does not occur. The highest displacement is related to the pile located in T1 soil, which has the lowest internal friction angle (ɸ = 30) and the lowest soil compaction percentage. With the occurrence of liquefaction in the middle layer, the support level of the monopile is transferred from ground to the end of the liquefiable layer. Based on the results the values of maximum pore pressure, flexural moment and shear force of the soil under near and far-field records decrease with increasing soil density that is more evident for far-field earthquakes.

Considering the statistical and probabilistic characteristics of construction conditions, the investigation of dynamic overloads' effects on the urban excavation wall is of great importance. In the present study, the performance of nailed and braced excavations under two vibrational dynamic excitations, traffic and near-field earthquake loads, have been investigated in four regions of Ahvaz. Critical boreholes with the lowest static bearing capacity have been selected by analyzing the layers' strength parameters in each region. Numerical models have been designed to limit the seismic waves' reflection at the excavation boundaries with 20 x 100 meters and with absorbing walls. Also, the damping ratio was assumed to be 2%. A harmonic wave at different speeds has simulated the excitation caused by the traffic passage. Resonant frequencies due to traffic induced vibration have been recorded in the speed range of 56 to 72 km/hr. Due to the traffic load, the bracing and the nailing systems showed less vertical and lateral displacements, respectively. Moreover, the excavations have been analyzed under ten acceleration with compatible near field characteristics of the Ahwaz plan acceleration (0.25g). The Kiyanpars region showed the highest vertical displacement difference between the two systems in the range of 0.032 m to 0.006 m. Due to earthquake loads, the bracing system showed less vertical displacement. The error of the analytical models' results in vertical displacement was 10% and 26% and in lateral displacement was 5% and 20% less than a nailed excavation located in the Kiyanpars region under traffic passage.

With the increase in the population of cities and the lack of spaces for construction, the creation of diverse uses, architecture and beauty of structures, ،he performance of a magnetic damper with a fuzzy controller to reduce the vibrations of an irregular hard structure under near and near earthquakes has been investigated. In the present study, the performance of a magnetic damper with a fuzzy controller reduce the vibrations of an irregular stiffness structure under near and far field earthquakes has been investigated. The capacity of the introduced magnetic damper is equal to 1000 kN, which is installed in the first floor between the floor level and the ceiling level of the first floor. Three different types of irregularities in height, including hardness irregularities with a coefficient of 60%, are used in a 10-story structure and are modeled in the OpenSees software. These irregularities have been investigated in three different elevation locations including the lower half of the structure height (floors 1 to 5), the lowest floor (1st floor) and the middle floor of the structure (5th floor). Based on the numerical analyzes performed for these structures under the excitation of near and far field earthquakes, the residual displacement is reduced by an average of 23.15% and 45.64%, respectively. In addition to improving criteria such as maximum displacement, shear, and base anchorage in both types of earthquakes, the most improvement occurred for the irregular structure on the first floor and the least for the irregular structure in the middle floor.

The present article involves evaluating the efficiency of an active viscous damper in controlling vibrations caused by near and far field earthquakes. Being installed on chevron bracing systems, the damper is able to provide necessary controlling forces to diminish vibration amplitude up to its' saturation limit. Many researchers have worked on the concept of seismic active control under far field waves. But the efficiency of this system is not guaranteed in near field ones due to time delay phenomenon. Pulse and shock entity of near field seismic waves leads to decreasing active control effects and the present research also proves the fact. A computer based algorithm is developed using Newmark instantaneous optimal control method in MATLAB software.The performance of this code is validated and evaluated based on three different reference problems. Then the analysis results of a 7-storey structure are calculated based on the code. The analyses are developed using both controlled and uncontrolled states. Also near field and far field earthquake records are used in this process and the results are compared in different tables and graphs. Based on the results, it seems that active control systems in spite of their effectiveness in near field earthquakes, needs necessary scheming and changes in the process.

Recent growth in the construction of wind farms with concrete piles in seismic areas with liquefaction potential has necessitated the evaluation of the seismic performance of these structures. In this paper, the effect of liquefaction on the seismic response of wind turbines supported by reinforced concrete mono-pile is investigated. Nonlinear dynamic analysis has been performed by finite element method in OpenSees software. Beams on a nonlinear Winkler foundation method was applied. The responses of reinforced concrete mono-pile foundation was studied for two sets of far and near field earthquake record and four different groups were considered for liquefied sandy soils with different coefficients of internal friction, shear wave velocity, relative compaction percentage and porosity. The results showed that with increasing the coefficient of internal friction and soil compaction rate, the amount of excess pore pressure of the soil adjacent to the RC mono-pile decreases. Also, as the thickness of the liquefied layer increases, the pressure of the extra pore water around the mono-pile will decrease but the displacement of the mono-pile will increase

In this study, the effects of the concrete rings as well as the far and near field earthquake on the frequency and seismic behavior of the intake tower have been investigated. For modeling and analysis with considering the interaction of water and structure, ANSYS software which is based on the finite element method is used. For a better analysis of these models, two far and near field earthquakes have been selected and scaled to the same maximum value acceleration. To evaluate the effects of concrete rings on the behavior of the intake tower, 33 intake tower models have been modeled by considering concrete rings in different numbers and height levels. In the following, 66 analyzes have been performed for three modes of the tower, including only the structure of the intake tower without a reservoir, the intake tower with the surrounding reservoir and without inside water, and the intake tower with the surrounding reservoir and inside of the tower is full. The results of displacement, stress, and base reactions of the intake tower under the relevant analyzes have been compared with each other. Based on the results, it was found that the effects of a near-field earthquake at maximum displacements and stresses are far greater than a far-field earthquake. However, the values of the responses depend on the frequency of the earthquake in addition to its proximity to the field. The results also showed that surrounding water and internal water have different effects on the seismic response of intake towers affected by near and far-field earthquakes. The presence of water increases the effective duration of the earthquake on the response of the intake tower, especially in the near field earthquake. The results showed that by adding circular rings, the frequencies of the intake towers undergo significant changes, which require seismic analysis to evaluate its effects. In the case of an intake tower without a surrounding reservoir and an intake tower with a surrounding reservoir and without inside water, the maximum values of displacement decrease with increasing the height of the concrete rings and decreasing the distance between them. For an intake tower with a surrounding reservoir and full inside, in the case of far-field earthquake analysis, the greatest reduction in displacement occurs for an intake tower with a ring at 25 meters, while for a near field earthquake, in this case, the amount of displacement is further reduced with an increasing height level of concrete rings. The pattern of changes in the first principal stresses for all the studied models is also in accordance with the changes in the values of the maximum displacement. The maximum values of the base reaction for the intake tower without surrounding reservoir and the intake tower with the surrounding reservoir and without inside water for near field earthquake are greater than for the far-field earthquake while for the intake tower with surrounding reservoir and full inside for far-field earthquake it is more than a near field earthquake which is due to the frequency content of the desired earthquakes. Eventually, the results showed that adding concrete platforms at high and close to each other has very good and positive effects also reduces the maximum values of stress, base reaction, displacement, and relative displacement.

Several factors can affect the responses of structures under seismic loads. The properties of the materials can be different from the parameters required in the design of the structures. This difference can affect the response of the structures. In this research, it is tried to investigate the effect of changing the characteristics of materials on the seismic response of a suspended cable bridge equipped with a RNC separator whit sensitivity analysis. A cable bridge with and without an RNC isolator has been analyzed dynamically nonlinear after initial modeling under a San Fernando record. Then, the effect of random variables on the response of these structures was investigated using Monte Carlo sensitivity tests and the second-order second moment (FOSM). Finally, the accuracy of the FOSM analysis method is evaluated in a Monte Carlo method. Two basic parameter, maximum deck displacement and maximum base shear was considered as structural responses. The results show that, among the specification of concrete strength materials, the yield stress of the reinforcement and the modulus of elasticity of the cables, the most effect on the seismic response of these structures. Also, the sensitivity of these parameters to the isolated bridge is less than the bridge without isolation.

Due to structural safety and residential comfort, the vibration control of tall buildings under earthquake and wind excitations has always been one of the important issues in the structural engineering context. One of the well-established approaches for controlling the structural vibration is the use of Tuned Mass Dampers (TMD) employed with different methods in structures. In this paper, a 10-story shear building with linear behavior is studied under twenty eight far-field and near-field earthquakes in MATLAB. Active Tuned Mass Damper (ATMD) is used to control the structural vibration. According to the earthquake excitation random nature, Fuzzy Logic and Mamdani Inference System are applied to determine the control force. In addition, the Particle Swarm Optimization (PSO) algorithm is used to determine the optimum TMD actuator power, and in this optimization, the effect of the actuator saturation is also considered. Furthermore, a method is introduced for robust optimum design of the suggested controller. Using the proposed control system and the optimum actuator power, structural responses decline about 44 pct. Additionally, due to the existence of uncertainty in earthquake records, applying a controller with average actuator power generally results in 33 pct. structural response reduction, and the performance of the active controlled system always outperforms the passive controlled system with 16 pct. structural response reduction.

This paper deals with numerical study of a newly developed seismic load resisting system called “linked column frame (LCF) system” which can be used to dissipate the earthquake energy and aids the structure to quickly revert to the serviceability level Dominant behavior of this system resembles that of the ductile link beam and as the shear fuse, it mitigate structural damages in various seismic events. In order to investigate the structural behavior of this in the event of near and far-filed earthquakes, after validationg the models by means of laboratory models, 3, 6 and 9-storey buildings were deigned making use of performance based design approach and then, the earthquake-induced responses were investigated by applying near and far-field earthquake records. Based on the results derived from the nonlinear dynamic analysis, the maximum inter - storey drift developed by the near and far-field earthquakes are equal to 3.91, 1.08, 1.65% and 1.74, 3.91 and 4.06, respectively. These values are related to the lower half of the building’s height and in compliance with the comparison between maximum displacement and inter-storey drifts obtained by the method proposed by Shoeibi and Malakoutian et al; the structure takes advantage of the controlled maximum and inter-storey drifts.

Near-field earthquakes have two important effects, Forward Directivity and Fling-step, in which Forward Directivity depends on the direction of occurrence of an earthquake, and Fling-step happens due to permanent displacement of the earth due to tectonic deformations and its integration with the tearing mechanism with a velocity pulse with high amplitude and a uniform step in the displacement time history. Considering that few studies have been done on the effects of fling-step on structures other than Forward Directivity, and also in most earthquake data centers, all earthquakes are filtered using filtering methods and the fling-step effect is eliminated, therefore, four types of 4, 8, 12 and 16-story structures are selected and are designed based on the American Seismic Code (ASCE-10), in accordance with the American Steel Regulation (AISC341-10), in accordance with all the criteria for steel special moment frames. 16 records having fling-step effect are selected and applied to the structures. Also, to show effect of neglecting the fling-step on the response of the structures, the same records having no fling-step are applied to the structures and compared to the unfiltered state. The results showed that fling-step has little effect on the structure response, and filtered records can be used on seismic analysis.