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Showing 5 results for Asymmetric Structures

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.
H. Shakib, A. Ghasemi,
Volume 5, Issue 4 (12-2007)

An attempt has been made to explore the general trends in the seismic response of planasymmetric structures when subjected to near-fault and far-fault ground motions. Systems with structural wall elements in both orthogonal directions considering actual and common nonlinear behavior under bi-directional excitation were studied. Idealized single-storey models with uni-axial eccentricity were employed. The main findings are: The rotational response trend considering actual behavior method would be different from common behavior method assumption, when the system subjected to near-fault motions. In the former case, the minimum rotational response could be achieved, when stiffness and strength centers are located on opposite side of the mass center. In the latter case, stiffness eccentricity determines the minimum and maximum rotational response. General trends in the rotational demand for far-fault motions, considering two type behavior assumptions, are similar to the last case. Moreover, in near-fault motions, when stiffness and strength centers are located on opposite side of the mass center, stiff side displacement demand would be greater than that soft side which is contrary to the conventional guidelines. While, in farfault motions similar to near-fault motions which stiffness and strength centers are located on one side of the mass center, displacement demand would be according to conventional guidelines.
H. Shakib, Gh. R. Atefatdoost,
Volume 12, Issue 1 (3-2014)

An approach was formulated for the nonlinear analysis of three-dimensional dynamic soil-structure interaction (SSI) of asymmetric buildings in time domain in order to evaluate the seismic response behavior of torsionally coupled wall-type buildings. The asymmetric building was idealized as a single-storey three-dimensional system resting on different soil conditions. The soil beneath the superstructure was modeled as nonlinear solid element. As the stiffness of the reinforced concrete flexural wall is a strength dependent parameter, a method for strength distribution among the lateral force resisting elements was considered. The response of soil-structure interaction of the system under the lateral component of El Centro 1940 earthquake record was evaluated and the effect of base flexibility on the response behavior of the system was verified. The results indicated that the base flexibility decreased the torsional response of asymmetric building so that this effect for soft soil was maximum. On the other hand, the torsional effects can be minimized by using a strength distribution, when the centre of both strength CV and rigidity CR is located on the opposite side of the centre of mass CM, and SSI has no effect on this criterion.
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.
Hamed Tajammolian, Faramarz Khoshnoudian, Nasim Partovi Mehr,
Volume 14, Issue 8 (12-2016)

This study is devoted to investigate the effects of mass eccentricity in seismic responses of base-isolated structures subjected to near field ground motions. Superstructures with 3, 6 and 9 stories and aspect ratios equal to 1, 2 and 3 have been idealized as steel special moment frames resting on a reasonable variety of Triple Concave Friction Pendulum (TCFP) bearings considering different period and damping ratios for the isolators. Three-dimensional linear superstructure mounted on nonlinear isolators are subjected to 3 components of near-field ground motions. Under 25 near-field ground motions, effects of mass eccentricity on the main system parameters are studied. These parameters are selected as the main engineering demands including maximum isolator displacement and base shear as well as peak superstructure acceleration. The results indicate that the mass eccentricities has not a remarkable effect on isolator displacement. In contrary to displacement, torsional effect of mass eccentricity raise the base shear up to 1.75 times in a three-story superstructure. Additionally, mass eccentricity can amplify the roof acceleration of a nine-story model approximately 3 times in comparison with a symmetric superstructure. It is also concluded that eccentricity in the direction of the subjected earthquake has the most impact on base shear while the isolator displacement and roof acceleration has mostly influenced by the eccentricity perpendicular to the earthquake path.

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