• Journal of The Korean Astronomical Society
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• v.33 no.1
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• pp.47-55
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• 2000

Nonpotential characteristics of magnetic fields in AR 5747 are examined using Mees Solar Observatory magnetograms taken on Oct. 20, 1989 to Oct. 22, 1989. The active region showed such violent flaring activities during the observational span that strong X-ray flares took place including a 2B/X3 flare. The magnetogram data were obtained by the Haleakala Stokes Polarimeter which provides simultaneous Stokes profiles of the Fe I doublet 6301.5 and 6302.5. A nonlinear least square method was adopted to derive the magnetic field vectors from the observed Stokes profiles and a multi-step ambiguity solution method was employed to resolve the $180^{\circ}$ ambiguity. From the ambiguity-resolved vector magnetograms, we have derived a set of physical quantities characterizing the field configuration, which are magnetic flux, vertical current density, magnetic shear angle, angular shear, magnetic free energy density, a measure of magnetic field discontinuity MAD and linear force-free coefficient. Our results show that (1) magnetic nonpotentiality is concentrated near the inversion line in the flaring sites, (2) all the physical parameters decreased with time, which may imply that the active region was in a relaxation stage of its evolution, (3) 2-D MAD has similar patterns with other nonpotential parameters, demonstrating that it can be utilized as an useful parameter of flare producing active region, and (4) the linear force-free coefficient could be a evolutionary indicator with a merit as a global nonpotential parameter.

• International Journal of Highway Engineering
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• v.10 no.4
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• pp.91-101
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• 2008

A multi layered elastic analysis program, IDYSPAP, was developed. The objective of this study was to develop the IDYSPAP program on Graphic User Interface environment for field engineers using Visual Basic, which was considered span of multi-wheels and maximum 4 axles using superposition of linear elastic theorem. It is suggested that this study considers algorithm with dynamic properties of asphalt layer on various temperature and non-linear properties of subbase and subgrade on stress non-linearity for asphalt pavement structure. This Program was modified to divide asphalt layer automatically according to layer division concept. The developed program was verified with initial measuring data in test road sections of KEC (Korea Expressway Co.) using laboratory test results.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.13 no.4
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• pp.461-473
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• 2000

This paper deals with a numerical model for the time-dependent analysis of steel and concrete composite beams with partial shear connection. A linear partial interaction theory is adopted in formulation of structural slip behavior, and the effect of concrete creep and shrinkage are considered. The proposed model is effective in simulating the slip behavior, combined with concrete creep and shrinkage, of multi-span continuous composite beams. Finally, correlation studies and several parameter studies are conducted with the objective to establish the validity of the proposed model.

• Earthquakes and Structures
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• v.8 no.3
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• pp.573-589
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• 2015

In order to investigate the seismic behavior of highway bridges under near-fault earthquakes, a parametric study was conducted for different regular and irregular bridges. To this end, an existing regular viaduct Highway Bridge was used as a reference model and five irregular samples were generated by varying span length and pier height. The seismic response of the six highway bridges was evaluated by three dimensional non-linear response history analysis using an ensemble of far-fault and scenario-based near-fault records. In this regard, drift ratio, input and dissipated energy as well as damage index of bridges were compared under far- and near-fault motions. The results indicate that the drift ratio under near-fault motions, on the average, is 100% and 30% more than far-fault motions at DBE and MCE levels, respectively. The energy and damage index results demonstrate a dissipation of lower energy in piers and a significant increase of collapse risk, especially for irregular highway bridges, under near-fault ground motions.

• Structural Engineering and Mechanics
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• v.13 no.2
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• pp.211-230
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• 2002

The objective of this study is to investigate the dynamic behavior of elastic beams subjected to moving loads. Although analytical methods are available, they have limitations with respect to complicated structures. The use of computer technology in recent years is an effective way to solve the problem; thus using the latest technology this study establishes a finite-element solution procedure to investigate dynamic behaviors of a typical elastic beam having a set of constant geometric properties and various span lengths. Both the dead load of the beam and traffic load are applied in which the traffic load is considered a concentrated moving force with various traveling passage speeds on the beam. Dynamic behaviors including deflection, shear, and bending moment due to moving loads are obtained by both analytical and finite element methods; for simple structures, they have an excellent agreement. The numerical results show that based on analytical methods the fundamental mode is good enough to estimate the dynamic deflection along the beam, but is not sufficient to simulate the total response of the shear force or the bending moment. The linear dynamic behavior of the elastic beams subjected to multiple exciting loads can easily be found by linear superposition, and the geometric nonlinear results caused by large deformation and axial force of the beam are always underestimated with only a few exceptions which are indicated. In order to make the results useful, they have been nondimensionalized and presented in graphical form.

• Wind and Structures
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• v.23 no.3
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• pp.253-273
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• 2016

Ice accretions on stay cables may result in the instable vibration of galloping, which would affect the safety of cable-stayed bridges. A large number of studies have investigated the galloping vibrations of transmission lines. However, the obtained aerodynamics in transmission lines cannot be directly applied to the stay cables on cable-stayed bridges. In this study, linear and nonlinear single degree-of-freedom models were introduced to obtain the critical galloping wind velocity of iced stay cables where the aerodynamic lift and drag coefficients were identified in the wind tunnel tests. Specifically, six ice shapes were discussed using section models with geometric scale 1:1. The results presented obvious sudden decrease regions of the aerodynamic lift coefficient for all six test models. Numerical analyses of iced stay cables associated to a medium-span cable-stayed bridge were carried out to evaluate the potential galloping instability. The obtained nonlinear critical wind velocity for a 243-meter-long stay cable is much lower than the design wind velocity. The calculated linear critical wind velocity is even lower. In addition, numerical analyses demonstrated that increasing structural damping could effectively mitigate the galloping vibrations of iced stay cables.

• Wind and Structures
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• v.16 no.2
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• pp.157-178
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• 2013

Output-only modal parameter identification is based on the assumption that external forces on a linear structure are white noise. However, harmonic excitations are also often present in real structural vibrations. In particular, it has been realized that the use of forced acceleration responses without knowledge of external forces can pose a problem in the modal parameter identification, because an external force is imparted to its impulse acceleration response function. This paper provides a three-stage identification procedure as a solution to the problem of harmonic and white noise excitations in the acceleration responses of a linear dynamic system. This procedure combines the uses of the mode indicator function, the complex mode indication function, the enhanced frequency response function, an iterative rational fraction polynomial method and mode shape inspection for the correlation-related functions of the force-embedded acceleration responses. The procedure is verified via numerical simulation of a five-floor shear building and a two-dimensional frame and also applied to ambient vibration data of a large-span roof structure. Results show that the modal parameters of these dynamic systems can be satisfactorily identified under the requirement of wide separation between vibration modes and harmonic excitations.

• Structural Engineering and Mechanics
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• v.77 no.2
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• pp.261-272
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• 2021

The energy-saving block and invisible multi-ribbed frame composite wall (EBIMFCW) is a new type of load-bearing wall. The study of this paper focus on it is hysteresis rule under horizontal cyclic loading. Firstly, based on the experimental data of the twelve specimens under horizontal cyclic loading, the influence of two important parameters of axial compression ratio and shear-span ratio on the restoring force model was analyzed. Secondly, a tetra-linear restoring force model considering four feature points and the degradation law of unloading stiffness was established by combining theoretical analysis and regression analysis of experimental data, and the theoretical formula of the peak load of the EBIMFCW was derived. Finally, the hysteretic path of the restoring force model was determined by analyzing the hysteresis characteristics of the typical hysteresis loop. The results show that the curves calculated by the tetra-linear restoring force model in this paper agree well with the experimental curves, especially the calculated values of the peak load of the wall are very close to the experimental values, which can provide a reference for the elastic-plastic analysis of the EBIMFCW.

• Earthquakes and Structures
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• v.3 no.2
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• pp.181-201
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• 2012

The benchmark on the ASCE cable-stayed bridge has gathered since its proposal the interest of many specialists in the field of the structural control and the dynamic response of long span bridges. Starting from the original benchmark statement in the MATLAB framework, a refined version of the bridge model is developed in the ANSYS commercial finite element environment. A passive structural control system is studied through non linear numerical analyses carried out in time domain for several seismic realizations in a multiple support framework. An innovative electro-inductive device is considered. Its positive performance is compared with an alternative version considering traditional metallic dampers.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.151-158
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• 2002

In the present design concept, the nonlinear behaviour of bridges is at lowed under large earthquake. The nonlinearity is, however, localized like pier, bearing, etc. Especially, pier columns are most important members for seismic performance. It is, however, difficult to solve the problem how the nonlinearity of columns should be modelled. In this study, the fiber element is used for modelling pier column. The element is a kind of structural elements like frame element, and it can model the distributed plasticity of plastic hinge. A 3 span continous bridge is taken for seismic analysis. First, the nonlinear static analysis the column at fixed support are performed so that the characteristics of column is analyzed. Second, Linear and nonlinear dynamic analysises using simplified model for longitudinal direction are carried out and the results are analyzed.