• Structural Engineering and Mechanics
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• v.54 no.2
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• pp.291-304
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• 2015

Compared with the identification of linear structures, it is more challenging to conduct identification of nonlinear structure systems, especially when the locations of structural nonlinearities are not clear in structural systems. Moreover, it is highly desirable to develop methods of parametric identification using partial measurements of structural responses for practical application. To cope with these issues, an identification method is proposed in this paper for the detection and parametric identification of structural nonlinear restoring forces using only partial measurements of structural responses. First, an equivalent linear structural system is proposed for a nonlinear structure and the locations of structural nonlinearities are detected. Then, the parameters of structural nonlinear restoring forces at the locations of identified structural nonlinearities together with the linear part structural parameters are identified by the extended Kalman filter. The proposed method simplifies the identification of nonlinear structures. Numerical examples of the identification of two nonlinear multi-story shear frames and a planar nonlinear truss with different nonlinear models and locations are used to validate the proposed method.

• Earthquakes and Structures
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• v.18 no.3
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• pp.275-284
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• 2020

The scope of this study is the comparison between experimental results of tests performed on a base isolated building using helical wire rope isolators (WRs), and results of Nonlinear Response History Analyses (NRHAs) performed using SAP 2000, a commercial software for structural analysis. In the first stage of this research, WRs have been tested under shear deformation beyond their linear range of deformation, and analytical models have been derived to describe the nonlinear response of the bearings under different directions of loading. On the following stage, shaking table tests have been carried out on a 1/3 scale steel model isolated at the base by means of curved surface sliders (CSS) and WRs. The response of the structure under ground motion excitation has been compared to that obtained using numerical analyses in SAP 2000. The feasibility of modelling the nonlinear behavior of the tested isolation layer using multilinear link elements embedded in SAP 2000 is discussed in this paper, together with the advantages of using WRs as supplemental devices for CSSs base isolated structures.

• Steel and Composite Structures
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• v.33 no.6
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• pp.877-889
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• 2019

The developments of double skin composite (DSC) walls with novel enhanced C-channel connectors (DSCW-EC) were reported. Followed axial compression tests on prototype walls were carried to evaluate structural performances of this novel DSC composite structures. The testing program consists of five specimens and focused on the layout of the novel enhanced C-channel (EC) connectors, which include the web direction of C-channels, steel-faceplate thickness, vertical and horizontal spacing of C-channels. Crushing in concrete core and buckling of steel faceplate were two main observed failed modes from the compression tests. However, elastic or plastic buckling of the steel faceplate varies with designed parameters in different specimens. The influences of those investigated parameters on axial compressive behaviors of DSCW-ECs were analyzed and discussed. Recommendations on the layout of novel EC connectors were then given based on these test results and discussions. This paper also developed analytical models for predictions on ultimate compressive resistance of DSCW-ECs. Validation against the reported test results show that the developed theoretical models predict well the ultimate compressive resistance of DSCW-ECs.

• Smart Structures and Systems
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• v.26 no.1
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• pp.23-33
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• 2020

Majority of the damage in engineering structures is nonlinear. Damage sensitive features (DSFs) extracted by traditional methods from linear time series models cannot effectively handle nonlinearity induced by structural damage. A new DSF is proposed based on vector space cosine similarity (VSCS), which combines K-means cluster analysis and Bayesian discrimination to detect nonlinear structural damage. A reference autoregressive moving average (ARMA) model is built based on measured acceleration data. This study first considers an existing DSF, residual standard deviation (RSD). The DSF is further advanced using the VSCS, and then the advanced VSCS is classified using K-means cluster analysis and Bayes discriminant analysis, respectively. The performance of the proposed approach is then verified using experimental data from a three-story shear building structure, and compared with the results of existing RSD. It is demonstrated that combining the linear ARMA model and the advanced VSCS, with cluster analysis and Bayes discriminant analysis, respectively, is an effective approach for detection of nonlinear damage. This approach improves the reliability and accuracy of the nonlinear damage detection using the linear model and significantly reduces the computational cost. The results indicate that the proposed approach is potential to be a promising damage detection technique.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.2
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• pp.19-27
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• 2002

The early damage detection of large structures is very important to prevent the disaster due to its global failure. In this paper, a crack detection method of the beam-analogy structure based on the wavelet transformation of mode shape is presented. The method can effectively detect the singularity of mode shape caused to the inconsistency of bending moment and shear force at the damaged part using the discrete wavelet of mode shape and its inverse transforms of detail components. To investigate the validity and the applicability of the presented damage detection method, numerical simulation and experiment are carried out for the idealized beam and the real ship structures.

• Textile Coloration and Finishing
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• v.17 no.5 s.84
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• pp.26-36
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• 2005

This study was carried to evaluate mechanical characteristics of Poly(ethylene terephthalate) fabrics (by Kawabata evaluation system(KES)) which was systematically treated with $O_2$ low temperature plasma and chitosan acetate solution. Furthermore, surface structure was investigated by SEM, AFM, air permeability and wettability. Tensile energy(WT), shear rigidity(G) and surface roughness(MIU) properties calculated by KES-FB have increased with increasing plasma treatment time, while bending rigidity(G) and energy of compression(WC) value were decreased compared with those of the untreated. SEM photographs showed the identification of chitosan coating but did not confirm the plasma etching structure. Air permeability was decreased according to plasma treatment time with increasing concentrations of chitosan. The water absorption rate made rapid progress by chitosan treatment.

• Advances in Computational Design
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• v.2 no.3
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• pp.211-223
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• 2017

This research presented a numerical and experimental study on the seismic performance of first-generation base-isolated and fixed-base nuclear power plants (NPP). Three types of the base isolation system were applied to rehabilitate the first-generation nuclear power plants: frictional pendulum (FP), high-damping rubber (HDR) and lead-rubber (LR) base isolation. Also, an Excel program was proposed for the design of the abovementioned base isolators in accordance with UBC 97 and the Japan Society of Base Isolation Regulation. The seismic assessment was performed using the pushover and nonlinear time history analysis methods in accordance with the FEMA 356 regulation. To validate the adequacy of the proposed design procedure, two small-scale NPPs were constructed at Universiti Teknologi Malaysia's structural laboratory and subjected to a pushover test for two different base conditions, fixed and HDR-isolated base. The results showed that base-isolated structures achieved adequate seismic performance compared with the fixed-base one, and all three isolators led to a significant reduction in the containment's tension, overturning moment and base shear.

• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1139-1148
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• 2006

This paper addresses the analytical modeling and dynamic response of the advanced composite rotating blade modeled as thin-walled beams and incorporating viscoelastic material. The blade model incorporates non-classical features such as anisotropy, transverse shear, rotary inertia and includes the centrifugal and coriolis force fields. The dual technology including structural tailoring and passive damping technology is implemented in order to enhance the vibrational characteristics of the blade. Whereas structural tailoring methodology uses the directionality properties of advanced composite materials, the passive material technology exploits the damping capabilities of viscoelastic material (VEM) embedded into the host structure. The VEM layer damping treatment is modeled by using the Golla-Hughes-McTavish (GHM) method, which is employed to account for the frequency-dependent characteristics of the VEM. The case of VEM spread over the entire span of the structure is considered. The displayed numerical results provide a comprehensive picture of the synergistic implications of both techniques, namely, the tailoring and damping technology on the dynamic response of a rotating thin-walled b ε am exposed to external time-dependent excitations.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.8
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• pp.821-827
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• 2015

This study concentrates on a wave energy converter with floaters that extracts the ocean's energy by moving up and down with the wave motion. The floater is connected to an arm structure, including a hydraulic cylinder that drives a hydraulic generator. This study focuses on a structural analysis of the floater unit, including arm and cylinder components, platform and jack-up system, along with spud columns. Previous studies have been conducted for miniature models for experimentation, but this study focuses on the full-scale model structural analysis. Static structural analysis is conducted using fine numerical grids. Due to the complexity of the whole model, it is analyzed in separate pieces. The floater unit, with arm and cylinder, are combined into one system. The platform is analyzed separately as a single system. There are four jack-up systems for each spud column; only one jack-up system is analyzed, as uniform loads are assumed on each system. There are several load cases for each system, all of which are analyzed thoroughly for stress (von Mises, shear, and normal) and deformation. Acceptable results were obtained for most of the components; unsafe components were redesigned.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.5
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• pp.555-563
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• 1985

Two-dimensional turbulent wake flow behind a circular cylinder is investigated experimentally by suing linearized constant temperature hot wire anemometer. Turbulent fluctuations and mean velocity defects are measured in the rage of 5 dia.- 500 dia. downstream from the cylinder and for the Reynolds numbers of 2000-4000. Results with statistical treatment and digital data processing techniques are as follows: (1) The transition region from near wake to far wake is 30 dia. - 50 dia. downstream from the cylinder. (2) In the near wake, it is found that strong periodic ( f=845Hz) coherent structure exists. (3) It shows that the inertial subrange is 180Hz-2000Hz in self preservation region.