• Earthquakes and Structures
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• v.18 no.1
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• pp.27-44
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• 2020

This work presents a comparison of three performance-based seismic design methods (PBSD) as applied to plane steel frames having eccentric braces (EBFs) and buckling restrained braces (BRBFs). The first method uses equivalent modal damping ratios (ξ_k), referring to an equivalent multi-degree-of-freedom (MDOF) linear system, which retains the mass, the elastic stiffness and responds in the same way as the original non-linear MDOF system. The second method employs modal strength reduction factors (${\bar{q}}_k$) resulting from the corresponding modal damping ratios. Contrary to the behavior factors of code based design methods, both ξ_k and ${\bar{q}}_k$ account for the first few modes of significance and incorporate target deformation metrics like inter-storey drift ratio (IDR) and local ductility as well as structural characteristics like structural natural period, and soil types. Explicit empirical expressions of ξ_k and ${\bar{q}}_k$, recently presented by the present authors elsewhere, are also provided here for reasons of completeness and easy reference. The third method, developed here by the authors, is based on a hybrid force/displacement (HFD) seismic design scheme, since it combines the force-base design (FBD) method with the displacement-based design (DBD) method. According to this method, seismic design is accomplished by using a behavior factor (q_h), empirically expressed in terms of the global ductility of the frame, which takes into account both non-structural and structural deformation metrics. These expressions for q_h are obtained through extensive parametric studies involving non-linear dynamic analysis (NLDA) of 98 frames, subjected to 100 far-fault ground motions that correspond to four soil types of Eurocode 8. Furthermore, these factors can be used in conjunction with an elastic acceleration design spectrum for seismic design purposes. Finally, a comparison among the above three seismic design methods and the Eurocode 8 method is conducted with the aid of non-linear dynamic analyses via representative numerical examples, involving plane steel EBFs and BRBFs.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.2
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• pp.121-131
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• 1986

The stiffness matrix of circularly curved frame elements including the warping effects is formulated by the solutions of vlasov's differential equations, and the procedure for the elastic static analysis of curved girder systems by the displacement method is presented. The validity of this method has been demonstrated by comparing the analysis results with other solutions. And if the tangential lines of the two frame element axes connected at any nodal point coincide, the transformation to the global coordinate system can be omitted when we analyze the structures consisting of circularly curved elements. The theory introduced in this thesis can be applied with sufficient accuracy to the structures built up with horizontally circular curved frame elements which have closed or open cross sections and are symmetric to the axis perpendicular to the plane of the curvature, such as prestressed concrete box girder bridges.

• Journal of computational fluids engineering
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• v.10 no.2
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• pp.38-47
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• 2005

Substructuring methods are often used in finite element structural analyses. In this study a multi-level substructuring(MLSS) algorithm is developed and proposed as a possible candidate for finite element fluid solvers. The present algorithm consists of four stages such as a gathering, a condensing, a solving and a scattering stage. At each level, a predetermined number of elements are gathered and condensed to form an element of higher level. At the highest level, each sub-domain consists of only one super-element. Thus, the inversion process of a stiffness matrix associated with internal degrees of freedom of each sub-domain has been replaced by a sequential static condensation of gathered element matrices. The global algebraic system arising from the assembly of each sub-domain matrices is solved using a well-known iterative solver such as the conjugare gradient(CG) or the conjugate gradient squared(CGS) method. A time comparison with CG has been performed on a 2-D Poisson problem. With one domain the computing time by MLSS is comparable with that by CG up to about 260,000 d.o.f. For 263,169 d.o.f using 8 x 8 sub-domains, the time by MLSS is reduced to a value less than $30\%$ of that by CG. The lid-driven cavity problem has been solved for Re = 3200 using the element interpolation degree(Deg.) up to cubic. in this case, preconditioning techniques usually accompanied by iterative solvers are not needed. Finite element formulation for the incompressible flow has been stabilized by a modified residual procedure proposed by Ilinca et al.[9].

• The Journal of Pediatrics of Korean Medicine
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• v.17 no.2
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• pp.173-198
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• 2003

Back ground : Cerebral palsy(CP) is a static encephalopathy caused by an insult to the brain during the prenatal, perinatal, or postnatal period (ie, up to 2 years). CP can lead to global dysfunction but always includes motor problems Objective : The purpose of this study is to investigate the current tendency of oriental approach to the CP and promote oriental treatment of CP in Korea Method : Investigation of current literature and clinical paper in Korea and Chinese Result and Conclusion : 1) CP fall under the category of wu-chi(five kinds of retardations : 五遲), wu-ruan(five kinds of flaccidity : 五軟), wu-ying(five kinds of Stiffness : 五硬) in oriental medicine and correspond to naoxing-tanhuan in current chinese medicine. 2) CP is mainly caused by weakness of the liver and kidney(肝腎不足), weakness of the spleen and stomach(脾胃虛弱), and the method of treatment is tonify the liver and kidney(補益肝腎), tonify the spleen and replenish qi(補脾益氣), but yu-chi(the faculty of speech : 語遲) is caused by deficiency of the heart(心虛) so that treated with method of invigorating the heart and nourishing blood(補心養血). Recently blood stagnancy the stagnation of qi(氣滯血瘀) is considered as the cause of CP, promoting qi circulation to invigorate blood(行氣活血) is mentioned the treatment of method. 3) In addtion to a herbal medication and acupuncture, the various treatments of scalp acupuncture(頭鍼), acupoint injection(穴位注射), catgut embedding therapy(埋鍼) etc. had been applicated to CP and for the objective evaluation of remedial value, TCD, EEG, BMD have been used.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.35-40
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• 2005

There are many methods to reinforce the cylindrical structure for light weight design like skin-stringer and semi-monocoque. Isogrid is one of the reinforced structures to improve buckling load. Isogrid has many advantages for complex load case, internal pressure and concentrated load.In this paper, compressive buckling test and non-linear FE analysis of the isogrid panel are described. Diameter of panel is 2.4m and thickness of plate is 11.43mm. The angle which the panel accomplish is about 70 degrees and, its height is about 660mm. Local buckling, global buckling and variation of stiffness after local buckling were observed during buckling test of the panel. MSC/MARC is used for non-linear FE analysis. When analysis, initial imperfection of panel which occurred during plastic forming is considered. The results of analysis for buckling mode and buckling load have good agreements with test.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.6
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• pp.559-566
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• 2017

This paper proposes a new composite deckplate system reinforced with inverted triangular truss girders(called 'D Deck'), which does not require the use of temporary supports at construction stage. The proposed system retains increased stiffness and strength while keeping the absolute floor height change to a minimum level and can be utilized as floor systems of various types beam members such as the conventional wide-flange and U-shaped composite beams. In order to evaluate the performance of the proposed system, five specimens with a span of 5.5 m were fabricated and tested under field loading conditions consisting of several intermediate steps. The load-deflection curves of each specimen were plotted and compared with the nonlinear three-dimensional finite element analysis results. The comparison showed that the effective load sharing between the truss girders and floor deck occurs and the maximum deflection under construction stage loading is well below the limit estimated by the provisions in Korea Building Code.

• Computers and Concrete
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• v.2 no.6
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• pp.423-437
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• 2005

In this study two single-bay, three-storey space frames, one with brick masonry infill in the second and third floors representing a soft-storey frame and the other without infill were designed and their 1:3 scale models were constructed according to non-seismic detailing and the similitude law. The models were excited with an intensity of earthquake motion as specified in the form of response spectrum in Indian seismic code IS 1893-2002 using a shake table. The seismic responses of the soft-storey frame such as fundamental frequency, mode shape, base shear and stiffness were compared with that of the bare frame. It was observed that the presence of open ground floor in the soft-storey infilled frame reduced the natural frequency by 30%. The shear demand in the soft-storey frame was found to be more than two and a half times greater than that in the bare frame. From the mode shape it was found that, the bare frame vibrated in the flexure mode whereas the soft-storey frame vibrated in the shear mode. The frames were tested to failure and the damaged soft-storey frame was retrofitted with concrete jacketing and, subjected to same earthquake motions as the original frames. Pushover analysis was carried out using the software package SAP 2000 to validate the test results. The performance point was obtained for all the frames under study, therefore the frames were found to be adequate for gravity loads and moderate earthquakes. It was concluded that the global nonlinear seismic response of reinforced concrete frames with masonry infill can be adequately simulated using static nonlinear pushover analysis.

• Steel and Composite Structures
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• v.18 no.5
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• pp.1305-1330
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• 2015

The successful application of the component-based approach - widely used to model structural joints - requires knowledge of the mechanical properties of the constitutive joint components, including an appropriate assembly procedure to derive the joint properties. This paper presents a component-method model for a structural joint component that is located in the tension zone of blind-bolted connections to concrete-filled tubular steel profiles. The model relates to the response of blind-bolts with headed anchors under monotonic loading, and the blind-bolt is termed the "Extended Hollo-bolt". Experimental data is used to develop the model, with the data being collected in a manner such that constitutive models were characterised for the principal elements which contribute to the global deformability of the connector. The model, based on a system of spring elements, incorporates pre-load and deformation from various parts of the blind-bolt: (i) the internal bolt elongation; (ii) the connector's expanding sleeves element; and (iii) the connector's mechanical anchorage element. The characteristics of these elements are determined on the basis of piecewise functions, accounting for basic geometrical and mechanical properties such as the strength of the concrete applied to the tube, the connection clamping length, and the size and class of the blind-bolt's internal bolt. An assembly process is then detailed to establish the model for the elastic and inelastic behaviour of the component. Comparisons of model predictions with experimental data show that the proposed model can predict with sufficient accuracy the response of the component. The model furthers the development of a full and detailed design method for an original connection technology.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.519-525
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• 2009

In this study a cohesive zone model was used to simulate the delamination phenomena which occurs by a successive crack initiation and propagation in composite laminates. The cohesive zone model was incorporated to the classical finite element method via cohesive element formulation and then implemented into the user-subroutine UEL of a commercial finite element program Abaqus. To validate the formulation and implementation of the cohesive element the finite element results were compared with the experimental data of double cantilever beam and end notched flexure tests. The numerical results well agree with the experimental load-displacement curves. Also the effect of the elastic stiffness and the size of the cohesive element on the global load-displacement curves were studied numerically. To minimize the mesh-dependency of the crack propagation path and eliminate the zig-zag patterns in the load-displacement curve, cohesive elements should be refined at the crack-tip.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.4
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• pp.231-238
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• 2014

In the buildings, the systems of structures are influenced by the gravity load changes due to room alteration or construction stage. This paper proposes a system identification method establishing mass as well as stiffness to parameters in model updating process considering mass change in the buildings. In this proposed method, modified genetic algorithm, which is optimization technique, is applied to search those parameters while minimizing the difference of dynamic characteristics between measurement and FE model. To search more global solution, the proposed modified genetic algorithm searches in the wider search space. It is verified that the proposed method identifies the system of structure appropriately through the analytical study on a steel beam structure in the building. The comparison for performance of modified genetic algorithm and existing simple genetic algorithm is carried out. Furthermore, the existing model updating method neglecting mass change is performed to compare with the proposed method.