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Showing 7 results for Nonlinear Static Analysis

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

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, M. R. Mirjalili, N. K. A. Attari,
Volume 10, Issue 4 (12-2012)
Abstract

The nonlinear static procedures (NSPs) proposed by design codes do not lead to reliable results especially for tall buildings.

They generally provide inconsistent estimates of inelastic seismic demands, especially for the top floors due to their inabilities in

considering the higher modes effects. In this paper, a new enhanced pushover procedure is proposed which is based on the

envelope of the structural responses resulting from two separate pushover analyses as a combination rule. Also, the suggested

pushover analyses are performed using a newly proposed modal load pattern, i.e., the Modal Spectra Combination (MSC), and

the ASCE41-06 required first mode load pattern. The MSC load pattern is consisted of a number of mode shapes combined with

appropriate weighting factors that depend on their modal participation factors, modal frequencies and design spectral values. A

number of 2-D steel moment resisting frame models with different number of stories are used to investigate the efficiency of the

proposed method. The inter-story drifts and the maximum plastic beam moment and curvature responses are used as a measure

to compare the results obtained from the nonlinear time-history analyses (NL-THA) and some other NSPs. The results obtained

through rigorous nonlinear dynamic analyses show that the application of the proposed method leads to acceptable results for

steel MRF systems in comparison to other available enhanced NSPs. The OpenSees program is used for numerical analysis.


M. Poursha,
Volume 11, Issue 2 (6-2013)
Abstract

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)
Abstract

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)
Abstract

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.


Niloufar Mashhadiali, Majid Gholhaki, Ali Kheyroddin, Rouzbeh Zahiri-Hashemi,
Volume 14, Issue 8 (12-2016)
Abstract

Steel plate shear walls have long been used as a lateral load resisting system. It is composed of beam and column frame elements, to which infill plates are connected. This paper investigates the progressive collapse-resisting capacity of 50-story building 3D model of the strip model of steel plate shear wall comparing with X-braced and moment frame system based on the removing structural elements from a middle and corner of the exterior frame, in the story above the ground. The collapse behavior is evaluated by different nonlinear static and dynamic analyses using conventional analysis software. In this study, vulnerability of structures is also assessed by sensitivity index (SI) regarding the sensitivity of structures to dynamic effect induced by progressive collapse. To identify vulnerable members, resulting actions of nonlinear static analysis, considering load factor to account for dynamic effect, at the failure mode of structure at the specific performance level are compared by the factor of redundancy related to overall strength of structure, with the linear static analysis of damaged model without considering dynamic effect,. Comparing analysis results indicated that in the steel plate shear wall system, the progressive collapse resisting potential is more than X-braced and moment frame. Sensitive index of highly sensitive elements to dynamic effect stated that in the structural models, beams are more vulnerable in moment frame than X-braced frame and SPSW structure, significantly, and vulnerability of columns in X-braced frame and SPSW system is more than moment frame.


Dr. Abazar Asghari, Mr. Behnam Azimi Zarnagh,
Volume 15, Issue 5 (7-2017)
Abstract

For years, coupling shear walls have been used in  the mid to high-rise buildings as a part of lateral load- resisting system mostly, because of their ability to control the displacement of structures, Recently by changing the design codes from strength based design to performance based  design, nonlinear behavior of coupled walls became important for practical engineers, so that many researchers  are looking for ways to improve and also predict the behavior of coupled walls under severe earthquakes. This paper  presents  the results of   linear,  nonlinear static ( pushover)  and  nonlinear inelastic time-history analysis  of a 10-story  two- dimensional coupling shear wall (CSW) which is perforated with 3 different patterns which are taken from considering  the S22 stress of shell elements used for modeling shear walls,  nonlinear static analysis results confirm that perforation can increase the response modification  factor of coupled walls up to 33 percent and also the results of  linear analysis and design indicate that perforation can reduce the amount of reinforcement of coupling beams and other frame's  structural components. Also results of nonlinear inelastic time history  analysis confirm that by using perforation patterns the base shear- roof displacement hysteretic response get better and the  systems with perforation patterns can absorb more energy under severe earthquakes.



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