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Showing 6 results for Target Displacement

Ghodrati Amiri G., Sedighi S.,
Volume 2, Issue 4 (12-2004)

In the past decade design procedure changed to �performance-based design� from�force-based design�, by this mean many researchers focused on nonlinear static analysis (NSA)and the procedure named �PUSHOVER�. Advantages of this method are defining the inelasticbehavior of structure without nonlinear dynamic analysis (NDA) effort and also defining plastichinges formation in critical elements, and the order of formed plastic hinges. In spite of these goodadvantages NSA is limited to short and planar structures and application of that in tall andtorsionaly asymmetric structures may yield unreliable results.In this study reliability of NSA is investigated by performing both nonlinear static and dynamicanalysis on six 2D moment resisting concrete frames. Non linear dynamic analysis has been doneby the suggested method in FEMA356 guideline called �Target Displacement Method�. A groupof 4 different lateral increasing loads were used in pushover analysis and 3 different groundmotions were applied in NDA. Results indicate that same responses can be obtained by performingNSA, but errors will be increased by frames height increment.
F. R. Rofooei, N. K. Attari, A. Rasekh, A.h. Shodja,
Volume 4, Issue 3 (9-2006)

Pushover analysis is a simplified nonlinear analysis technique that can be used to estimate the dynamic demands imposed on a structure under earthquake excitations. One of the first steps taken in this approximate solution is to assess the maximum roof displacement, known as target displacement, using the base shear versus roof displacement diagram. That could be done by the so-called dynamic pushover analysis, i.e. a dynamic time history analysis of an equivalent single degree of freedom model of the original system, as well as other available approximate static methods. In this paper, a number of load patterns, including a new approach, are considered to construct the related pushover curves. In a so-called dynamic pushover analysis, the bi-linear and tri-linear approximations of these pushover curves were used to assess the target displacements by performing dynamic nonlinear time history analyses. The results obtained for five different special moment resisting steel frames, using five earthquake records were compared with those resulted from the time history analysis of the original system. It is shown that the dynamic pushover analysis approach, specially, with the tri-linear approximation of the pushover curves, proves to have a better accuracy in assessing the target displacements. On the other hand, when nonlinear static procedure seems adequate, no specific preference is observed in using more complicated static procedures (proposed by codes) compared to the simple first mode target displacement assessment.
M. Poursha,
Volume 11, Issue 2 (6-2013)

Double- unsymmetric-plan medium-rise buildings subjected to bi-directional seismic excitation are complex structures where higher-mode effects in plan and elevation are important in estimating the seismic responses using nonlinear static or pushover analysis. Considering two horizontal components of the ground motions makes the problem more intricate. This paper presents a method for nonlinear static analysis of double unsymmetric-plan low- and medium-rise buildings subjected to the two horizontal components of ground motions. To consider bi-directional seismic excitation in pushover analyses, the proposed method utilizes an iterative process until displacements at a control node (centre of mass at the roof level) progressively reach the predefined target displacements in both horizontal directions. In the case of medium-rise buildings, continuous implementation of modal pushover analyses is used to take higher-mode effects into account. To illustrate the applicability and to appraise the accuracy of the proposed method, it is applied to the 4- and 10-storey torsionally-stiff and torsionally-flexible buildings as representative of low- and medium-rise buildings, respectively. For the purpose of comparison, modal pushover analysis (MPA) is also implemented considering the two horizontal components of the ground motions. The results indicate that the proposed method and the MPA procedure can compute the seismic demands of double unsymmetric-plan low- and medium-rise buildings with reasonable accuracy however, seismic responses resulting from the proposed method deteriorate at the flexible edge of the torsionally-flexible buildings
A. R. Habibi, Keyvan Asadi,
Volume 12, Issue 1 (3-2014)

Setback in elevation of a structure is a special irregularity with considerable effect on its seismic performance. This paper addresses multistory Reinforced Concrete (RC) frame buildings, regular and irregular in elevation. Several multistory Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks, as well as the regular frames in elevation, are designed according to the provisions of the Iranian national building code and Iranian seismic code for the high ductility class. Inelastic dynamic time-history analysis is performed on all frames subjected to ten input motions. The assessment of the seismic performance is done based on both global and local criteria. Results show that when setback occurs in elevation, the requirements of the life safety level are not satisfied. It is also shown that the elements near the setback experience the maximum damage. Therefore it is necessary to strengthen these elements by appropriate method to satisfy the life safety level of the frames.
M. Mahmoudi, T. Teimoori, H. Kozani,
Volume 13, Issue 4 (12-2015)

The current building codes provide limited prescriptive guidance on design for protection of buildings due to progressive collapse. Progressive collapse is a situation in which a localized failure in a structure, caused by an abnormal load, such as explosions or other happenings. Three procedures, often employed for determination of the structural response during progressive collapse i.e. linear static procedure (LSP), nonlinear static (NSP) and nonlinear dynamic (NDP) analyses. In nonlinear static analysis, a force-based method is applied and the structure is pushed down to the target force. In this research, a new displacement-based method will be proposed for nonlinear static analysis. In displacement-based method, the structure is pushed down to target displacement instead of target force (similar to the one in seismic pushover analysis). To make a nonlinear static analysis, instead of increasing the load around the area of the removed column, a maximum displacement is calculated and the upper node of the removed column is pushed up to target displacement. Here, to determine the target displacement, results from nonlinear dynamic and linear static analyses are compared. This paper tries to present a formula to calculate the target displacement using the linear static rather than the nonlinear dynamic analysis. For this reason, 3 buildings with 3, 5 and 10 stories have been seismically designed and studied. The results show that, this method is much more accurate in comparison to the recommended approach in current codes. Also, this method does not have the limitations of force-based nonlinear static analysis.

Alireza Habibi, Ehsan Jami,
Volume 15, Issue 2 (3-2017)

The seismic performance levels are discrete damage states selected from among the infinite spectrum of possible damage states that buildings could experience as a result of earthquake response. The observation of building damage during strong motion earthquakes showed that correlation of structural damage with a single parameter such as peak ground acceleration or the total seismic duration is low while peak ground acceleration is often used as a main seismic parameter to evaluate seismic performance of structures. Main objective of this study is to determine the relationship between several seismic acceleration parameters and the Target Displacement (TD) of steel frame structures, which is an important parameter to identify performance levels. For this purpose, first, nonlinear analysis is performed on the SAC 3- and 9-story frames subjected to several far-field earthquakes and then target displacements and seismic parameters are calculated for each structure.The relationship between the target displacement and seismic parameters is evaluated in the form of correlation coefficient. It is shown that PGA has poor correlation with the target displacement. On the other hand, HOUSNER intensity, spectral pseudo-acceleration, spectral pseudo-velocity and peak ground velocity exhibit strong correlation with TD.

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