جستجوی مقالات مرتبط با کلیدواژه « زلزله ی حوزه دور » در نشریات گروه « عمران »

This paper evaluates the "Response Modification", "Reduction due to ductility" and "Over-strength" factors for steel frames with "Linked Columns Frame" as dual systems. Since, LCF is a relatively modern lateral load resisting system, the necessity of a more comprehensive study is felt for performance evaluation of these frames under strong ground motions. In this regard, steel frames equipped with the linked column frame with 3, 5, 7, 9, and 11 stories are designed based on the Iranian earthquake design code (Standard No. 2800, 4th version) and implemented in Opensees software. Response modification factor (R factor) is calculated based on the result of incremental dynamic analysis (IDA), linear and nonlinear dynamic analysis under far-field earthquakes which have been presented in FEMA-P695. For a more accurate assessment, the shear and flexure performance of link beams is investigated in this study. The results show that R factors change in the height of steel frames with LCF. However, the mean values of the R factor do not necessarily increase or decrease as the number of stories increases. In most cases, R factors for LCFs with shear links are larger than the related result of steel frames containing flexural links. Also, the R factor does not need to consider more than 6.0 for regular LCFs with studied shear link beam.

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.

The purpose of this paper is to assessment the seismic fragility and residual capacity of reinforced concrete frame (RC) with masonry infills subject to mainshock/aftershock sequence in the far and near field ground motions. In standard incremental dynamic analysis (IDA), only the effect of the main shock in the analysis is considered, so the double incremental dynamic analysis (D-IDA) method is used to consider the after shock effects. double incremental dynamic analysis approach is used, based on the combination of the mainshock (MS) at different intensities with a set of spectrum-compatible aftershocks (AS) scaled in amplitude with respect to peak ground. In this study, 20 near field records and 20 far field records were selected. In each analysis, a same record has been used for the main shock and after shock. Also using the results obtained from incremental dynamic analysis, the frame residual capacity diagrams is defined and the infilled frame response is compared with bare frame at different intensities of the main shock. According to the results obtained for infilled, the seismic fragility of the reinforced concrete frame is greatly reduced due to the mainshock and aftershock. It can be said that when only 100% collapse occurs in the bare frame, the probability of the frame collapsing with the infill wall at the same intensity as PGA (maximum ground acceleration) for near and far field earthquake records is significantly reduced.

Due to the advantages of semi-active control methods over passive and active methods, the development and performance of these methods to control the structural response under dynamic lateral loads has been widely considered. One of the most developed devices for semi-active control is Magneto-Rheological (MR) Dampers, for which various models have been proposed to simulate its dynamic behavior. In this paper, a 10-story linear shear building is studied under twenty-eight far and near-field earthquakes in MATLAB. In order to control the vibration of the structure, a Magneto-Rheological Damper with Clipped Optimal Control Algorithm is used. In this simulation, in addition to considering the effect of actuator saturation, the actuator’s dynamics is also considered using the Modified Bouc-Wen model. In addition, the effect of the damper’s position is investigated in the current study for three different configurations (lower, middle and upper stories). Furthermore, using the obtained results from this algorithm, a statistical study was carried out under different types of near and far-field records. The results indicate that placing a Magneto-Rheological damper on the first floor shows the best performance. Results show that the current control system has the best performance under near-field records without pulse, with an average reduction of 21 percent in the structural response.

Throughout the years, tuned mass dampers have been implemented effectively to reduce wind-induced vibrations and earthquake excitations in high-rise buildings. In this paper, the performance of braced frames with rooftop tuned mass damper frame is studied. For this purpose, linear and nonlinear time history dynamic analysis of six steel concentrically braced frames with 3, 5 and 15 stories subjected to near and far field earthquakes are conducted. Based on numerical results obtained in this research, applying a rooftop damper frame is more effective in reducing the seismic response of the braced frames with short periods of vibration than those with moderate and long lateral periods. It is found that rooftop tuned mass damper reduces the floor displacement of the 3-story building by as much as 18 to 66 percent under different earthquake excitations. Results also show that this type of damper frame with appropriate design can result in decreased seismic responses both under near and far field earthquake excitations.