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  • Articles  (219)
  • 2010-2014  (219)
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  • Articles  (219)
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  • 1
    Publication Date: 2014-12-19
    Description: Based on the Bingham parallel-plate model, a simplified design method of shear-valve magnetorheological (MR) dampers is proposed considering the magnetic circuit optimization. Correspondingly, a new MR damper with a full-length effective damping path is proposed. The prototype dampers are also fabricated and studied numerically and experimentally. According to the test results, the Bingham parallel-plate model is further modified to obtain a damping force prediction model of the proposed MR dampers. This prediction model considers the magnetic saturation phenomenon. The study indicates that the proposed simplified design method is simple, effective and reliable. The maximum damping force of the proposed MR dampers with a full-length effective damping path is at least twice as large as those of conventional MR dampers. The dynamic range of damping force increases by at least 70%. The proposed damping force prediction model considers the magnetic saturation phenomenon and it can realize the actual characteristic of MR fluids. The model is able to predict the actual damping force of MR dampers precisely.
    Print ISSN: 1671-3664
    Electronic ISSN: 1993-503X
    Topics: Geosciences
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  • 2
    Publication Date: 2014-12-19
    Description: The response of pile foundations near a quay wall under liquefaction-induced lateral spreading remains a complex problem. This study presents the results of a shake-table test on a 2×2 pile group behind a sheet-pile quay wall that was subjected to lateral spreading. The quay wall was employed to trigger liquefaction-induced large lateral ground deformation. The discussions focus on the behavior of the pile and the soil and on the bending moment distributions within the group pile and the restoring force characteristics at the superstructure. Overall, the piles exhibited apparent pinning effects that reduced soil deformation. In addition, the rear-row piles near the quay wall experienced larger bending moments than did the front-row piles, indicating significant pile group effects. The tests showed that lateral spreading could be a primary cause of larger monotonic deformations and bending moments. It can also be concluded that the monotonic bending moments were significantly decreased due to the presence of slow soil flow. The stiffness at the superstructure was reduced because of accumulated excess pore pressure before liquefaction, and it was recovered during lateral spreading. The present study further enhances current understanding of the behavior of low-cap pile foundations under lateral spreading.
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    Electronic ISSN: 1993-503X
    Topics: Geosciences
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  • 3
    Publication Date: 2014-12-19
    Description: Appropriate estimates of earthquake response spectrum are essential for design of new structures, or seismic safety evaluation of existing structures. This paper presents an alternative procedure to construct design spectrum from a combined normalized response spectrum (NRS C ) which is obtained from pseudo-velocity spectrum with the ordinate scaled by different peak ground amplitudes (PGA, PGV, PGD) in different period regions. And a consecutive function f ( T ) used to normalize the ordinates is defined. Based on a comprehensive study of 220 strong ground motions recorded during recent eleven large worldwide earthquakes, the features of the NRS C are discussed and compared with the traditional normalized acceleration, velocity and displacement response spectra (NRS A , NRS V , NRS D ). And the relationships between ground amplitudes are evaluated by using a weighted mean method instead of the arithmetic mean. Then the NRS C is used to define the design spectrum with given peak ground amplitudes. At last, the smooth spectrum is compared with those derived by the former approaches, and the accuracy of the proposed spectrum is tested through an analysis of the dispersion of ground motion response spectra.
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    Electronic ISSN: 1993-503X
    Topics: Geosciences
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  • 4
    Publication Date: 2014-12-19
    Description: An optimization method for the consistent evaluation of two Rayleigh damping coefficients is proposed. By minimizing an objective function such as an error term of the peak displacement of a structure, the two coefficients can be determined with response spectral analysis. The optimization method degenerates into the conventional method used in current practices when only two modes of vibration are included in the objective function. Therefore, the proposed method with all significant modes included for simplicity in practical applications results in suboptimal damping coefficients. The effects of both spatial distribution and frequency content of excitations as well as structural dynamic characteristics on the evaluation of Rayleigh damping coefficients were investigated with a five-story building structure. Two application examples with a 62-story high-rise building and a 840 m long cable-stayed bridge under ten earthquake excitations demonstrated the accuracy and effectiveness of the proposed method to account for all of the above effects.
    Print ISSN: 1671-3664
    Electronic ISSN: 1993-503X
    Topics: Geosciences
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  • 5
    Publication Date: 2014-12-19
    Description: Antiplane response of two scalene triangular hills and a semi-cylindrical canyon by SH-waves is studied using wave function expansion and complex function method. Firstly, the analytical model is divided into three parts, and the displacement solutions of wave fields are constructed based on boundary conditions in the three regions. Three domains are then conjoined to satisfy the “conjunction” condition at shared boundary. In addition, combined with the zero-stress condition of semi-cylindrical canyon, a series of infinite algebraic equations for the problem are derived. Finally, numerical examples are provided and the influence of different parameters on ground motion is discussed.
    Print ISSN: 1671-3664
    Electronic ISSN: 1993-503X
    Topics: Geosciences
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  • 6
    Publication Date: 2014-12-19
    Description: Seismic demand estimation for a structure is a critical issue for seismic performance assessment so that the potential damage can be estimated realistically. Many researchers proposed simplified methods to estimate the demand of a structure under strong ground motions. However, most of them did not consider degradation and collapse potential of the structures. Even some of theme considered the degradation effect, stiffness and strength degradation effects were considered separately without collapse potential caused by dynamic instability. In this study, collapse potential of SDOF systems caused by dynamic instability with stiffness and strength degradation has been investigated. Nonlinear time history analyses were performed, using an energy-based, strength and stiffness degraded hysteretic model that considers the collapse potential, with 160 earthquake acceleration time histories. An equation was proposed for the estimation of collapse period of SDOF systems as a function of certain strength reduction factor, ductility level and post-capping stiffness ratio. Finally, effects of parameters of the considered hysteretic model and local site conditions on the collapse period were investigated.
    Print ISSN: 1671-3664
    Electronic ISSN: 1993-503X
    Topics: Geosciences
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  • 7
    Publication Date: 2014-12-19
    Description: To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel (HSS), six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.
    Print ISSN: 1671-3664
    Electronic ISSN: 1993-503X
    Topics: Geosciences
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  • 8
    Publication Date: 2014-12-19
    Description: This paper presents a method for seismic vulnerability analysis of bridge structures based on vector-valued intensity measure (vIM), which predicts the limit-state capacities efficiently with multi-intensity measures of seismic event. Accounting for the uncertainties of the bridge model, ten single-bent overpass bridge structures are taken as samples statistically using Latin hypercube sampling approach. 200 earthquake records are chosen randomly for the uncertainties of ground motions according to the site condition of the bridges. The uncertainties of structural capacity and seismic demand are evaluated with the ratios of demand to capacity in different damage state. By comparing the relative importance of different intensity measures, S a ( T 1 ) and S a ( T 2 ) are chosen as vIM. Then, the vector-valued fragility functions of different bridge components are developed. Finally, the system-level vulnerability of the bridge based on vIM is studied with Dunnett-Sobel class correlation matrix which can consider the correlation effects of different bridge components. The study indicates that an increment IMs from a scalar IM to vIM results in a significant reduction in the dispersion of fragility functions and in the uncertainties in evaluating earthquake risk. The feasibility and validity of the proposed vulnerability analysis method is validated and the bridge is more vulnerable than any components.
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    Electronic ISSN: 1993-503X
    Topics: Geosciences
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  • 9
    Publication Date: 2014-12-19
    Description: This article extends a signal-based approach formerly proposed by the authors, which utilizes the fractal dimension of time frequency feature (FDTFF) of displacements, for earthquake damage detection of moment resist frame (MRF), and validates the approach with shaking table tests. The time frequency feature (TFF) of the relative displacement at measured story is defined as the real part of the coefficients of the analytical wavelet transform. The fractal dimension (FD) is to quantify the TFF within the fundamental frequency band using box counting method. It is verified that the FDTFFs at all stories of the linear MRF are identical with the help of static condensation method and modal superposition principle, while the FDTFFs at the stories with localized nonlinearities due to damage will be different from those at the stories without nonlinearities using the reverse-path methodology. By comparing the FDTFFs of displacements at measured stories in a structure, the damage-induced nonlinearity of the structure under strong ground motion can be detected and localized. Finally shaking table experiments on a 1:8 scale sixteen-story three-bay steel MRF with added frictional dampers, which generate local nonlinearities, are conducted to validate the approach.
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    Topics: Geosciences
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  • 10
    Publication Date: 2014-12-19
    Description: A pushover procedure with a load pattern based on the height-wise distribution of the combined modal story shear and torsional moment is proposed to estimate the seismic response of 3D asymmetric-plan building frames. Contribution of the higher modes and torsional response of asymmetric-plan buildings are incorporated into the proposed load pattern. The proposed pushover method is a single-run procedure, which enables tracing the nonlinear response of the structure during the analysis and averts the elusiveness of conducting multiple pushover analyses. The proposed method has been used to estimate the response of two moment-resisting building frames with 9 and 20 stories. The obtained results indicate the appropriate accuracy and efficiency of the proposed procedure in estimating the trend of the drift profiles of the structures resulted from nonlinear time history analyses.
    Print ISSN: 1671-3664
    Electronic ISSN: 1993-503X
    Topics: Geosciences
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