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1

Determining Frequency-Energy Dependencyof Nonlinear Normal Modes and Internal ResonancesUsing a Numerical Independent Approach

Ghariblou Arash, Mahmoudi Mussa

Computer Assisted Methods in Engineering and Science

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2022

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Vol. 29, no. 3

261--292

EN

Application of linear normal modes to the nonlinear area provides an in-depth investigation of structures. In this paper, a straightforward approach is proposed to investigatenonlinear normal modes (NNMs) thoroughly and focus on all possible solutions and bifurcations, independent of all initial assumptions and prior solutions. In this context, afterdiscretization of the response domain over an appropriate resolution, a periodicity algorithm is suggested to capture the solutions that meet the NNMs criteria. Afterward, thefrequency and energy of the system during accepted responses and degrees of freedom(DOFs)’ relations are derived. Finally, after verifying the proposed approach and acquir-ing new internal resonances, the frequency-energy plots and NNMs of a nonlinear elasticsystem with more substantial nonlinearities and a two-story steel structure with nonlinearmaterial are studied. It is worth noting that the periodicity algorithm and capturing allpossible solutions and bifurcations are among the apparent novelties of the current paper.

2

Investigation of the Occurrence of Progressive Collapse in High-Rise Steel Buildings with Different Braced Configurations

Saberi Hamid, Saberi Vahid, Sadeghi Abbasali, Pooyasefat Abbas, Noroozinejad Farsangi Ehsan

Civil and Environmental Engineering Reports

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2021

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Vol. 31, no. 4

33--54

EN

The progressive collapse phenomenon refers to a chain of damages in a structure where all or a large part of the structure is destroyed by an initial local collapse in it, which can lead to very disastrous results. Therefore, the prevention of progressive collapse has become a necessary action in the design and analysis of buildings and it is vital to investigate this topic more accurately. This study aims to present a proposed pattern in the configuration of braces at the height of a high-rise steel building for reducing the probability of progressive collapse. In this regard, the vertical displacement of 18-story structure with four scenarios of column removal and five concentric bracing patterns including V, Inverted V, X, discontinuous X-bracing at height, and a combination of Xbracing in the side spans and discontinuous X-bracing at height in the middle spans are investigated and compared. In this study, the Alternative Path Method (APM) is used based on the GSA guideline for the analysis of progressive collapse. The results of this research showed that the use of X-bracing in the side spans and discontinuous X-bracing in the middle spans in nonlinear static and dynamic analyses performed better in reducing the probability of progressive collapse than other bracing configurations. Finally, it is recommended to use discontinuous X-bracing at the height that would place the bracings in one direction and providing alternative paths for force transferring in the structure.

3

Seismic response characteristics of a base isolated cable-stayed bridge under moderate and strong ground motions

Javanmardi A., Ibrahim Z., Ghaedi K., Jameel M., Khatibi H., Suhatril M.

Archives of Civil and Mechanical Engineering

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2017

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Vol. 17, no. 2

419--432

EN

In this study, the seismic behavior of an existing steel cable-stayed bridge equipped with lead-rubber bearing subjected to moderate and strong earthquakes is investigated. The bridge is located at high seismic zone and experienced an earthquake in 1988 which caused the failure of one of its anchorage plate of the support. Herein, the bridge was modeled in three dimensions and the base isolators implemented at the abutments and deck-tower connection. The bridge seismic responses were evaluated through nonlinear dynamic time-history analysis. The comparative analysis confirmed that the base isolation system was an effective tool in reducing seismic force transmit from substructure to superstructure. Furthermore, the overall seismic performance of cable-stayed bridge significantly enhanced in longitudinal and transverse directions. However, it is observed that the axial force of the tower in substructure increased due to the isolation system induced torsional deformation to the superstructure under transverse seismic loads.

4

Introduction and evaluation of a damping determination method based on the Short-Term Fourier transform and Resampling (STFR)

Hentschel O. P., Panning-von Scheidt L., Wallaschek J., Denk M.

Journal of Theoretical and Applied Mechanics

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2015

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Vol. 53 nr 2

395--407

EN

In the present paper, a frequency domain method for damping determination is presented. The described method is especially developed for low damped systems with well separated eigenfrequencies. Using the Short-Term Fourier transform and Resampling (STFR) of the signal, decay curves of several mode shapes can be identified and amplitude-dependent damping values can be calculated. Additionally, two common methods for damping determination are explained briefly. Finally, the quality of the introduced method is evaluated comparing the variances of the identified damping values by means of different methods. In this context, the damping for beams clamped in a suspended way is analyzed. Stainless steel is used as the specimen material.

5

Experimental and numerical investigation of rotational friction dampers with multi units in steel frames subjected to lateral excitation

Mirzabagheri S., Sanati M., Aghakouchak A. A., Khadem S. E.

Archives of Civil and Mechanical Engineering

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2015

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Vol. 15, no. 2

479--491

EN

Performance of rotational friction dampers with two and three units was evaluated experimentally because of a lack of research data on performance of these dampers with multi units. Results of multi-unit dampers were compared with the results of one-unit damper. Increasing trend in dissipating energy was observed. Then, the behavior of these dampers in frames of 3, 7 and 12 stories was studied by modeling the damper directly. Nonlinear time history dynamic analysis was used. It was observed that by increasing the number of stories in the buildings, dampers with multi units should be used to perform properly against earthquake. The equivalent damping method was also investigated to consider the effects of this damper without direct modeling of the damper. Effective damping of the frames equipped with this type of damper was estimated and used in nonlinear time history dynamic analysis and it was observed that the responses of these structures with dampers can be approximated by the responses of moment resisting frames without damper but with damping equal to the effective damping due to rotational friction damper.

6

Earthquake analysis of arch dams including the effects of foundation discontinuities and proper boundary conditions

Ferdousi A., Mostafa Gharabaghi A. R., Ahmadi M. T., Chenaghlou M. R., Emami Tabrizi M.

Journal of Theoretical and Applied Mechanics

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2014

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Vol. 52 nr 3

579--594

EN

The interaction between dam foundation and rocks plays a significant role in the design and analysis of concrete arch dams. In the current study, comprehensive dynamic analysis of the dam-reservoir-foundation system is performed by developing a non-linear finite element program. The objective of this paper is to study the seismic behavior of a concrete arch dam taking into account the effects of foundation discontinuities and foundation inhomogeneity on the stability. Proper modeling truncated boundary conditions at the far-end of the foundation and reservoir fluid domain as well as to correctly apply the in-situ stresses for the foundation rock represents field conditions in the model more realistically. In this paper, the nonlinear seismic response of the dam-reservoir-foundation system includes dam-canyon interaction, dam body contraction joint opening, discontinuities (possible sliding planes) of the foundation rock and the failure of the joined rock and concrete materials. The results for the Karun 4 dam as a case study revealed the substantial effect of modeling discontinuities and boundary conditions of the rock foundation under seismic excitation that needs to be considered in the design of new dams and can be applied to seismic safety evaluation of the existing dams.