• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4_1
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• pp.23-32
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• 1992

The objective of this study is to identify the quantitative relationships among the important physical factors associated with failure of steel members under strong seismic excitations through very low-cycle fatigue tests. Very low-cycle fatigue is meant to be structural fatigue causing cracks and rupture in about 5~30 cycle ranges. The angle specimen was subjected to repeated axial Ioad after undergoing inelastic buckling. The test results reveal that the energy absorption capacities vary heavily with the history of loading and the failure mode. The maximum values of residual local strain at the initiation of a visible crack due to the very low-cycle fatigue were of the order of 25~40%, regardless of loading patterns, deflection modes, and width-to-thickness ratios.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.3
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• pp.309-316
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• 2015

A state-based peridynamic model is able to describe a general constitutive model from the standard continuum theory. The response of a material at a point is dependent on the deformation of all bonds connected to the point within the nonlocal horizon region. Therefore, the state-based peridynamic model permits both the volume and shear changes of the material which is promising to reproduce the complicated dynamic brittle fracture phenomena, such as crack branching, secondary cracks, cascade cracks, crack coalescence, etc. In this paper, the two-dimensional state-based peridynamic model for a linear elastic plane stress solid is employed. The damage model incorporates the energy release rate and the peridynamic energy potential. For brittle glass materials, the impact of the crack-parallel compressive stress waves on the crack branching pattern is investigated. The peridynamic solution for this problem captures the main features, observed experimentally, of dynamic crack propagation and branching. Cascade cracks under strong tensile loading and secondary cracks are also well reproduced with the state-based peridynamic simulations.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.203-212
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• 2008

The cyclic behavior and energy dissipation mechanism of short coupling beams with various reinforcement layouts were studied. For numerical analysis of coupling beams, nonlinear truss model was used. The results of numerical analysis showed that the coupling beams with conventional reinforcement layout showed pinched cyclic behavior without significant energy dissipation, whereas the coupling beams with diagonal reinforcement exhibited stable cyclic behavior without pinching. The energy dissipation of the coupling beams was developed mainly by diagonal reinforcing bars developing large plastic strains rather than concrete which is a brittle material Based on this result, simplified equations for evaluating the energy dissipation of coupling beams were developed. For verification, the predicted energy dissipation was compared with the test results. The results showed that the simplified equations can predict the energy dissipation of short coupling beams with shear span-to-depth ratio less than 1.25 with reasonable precision, addressing various design parameters such as reinforcement layout, shear span-to-depth ratio, and the magnitude of inelastic displacement. The proposed energy equations can be easily applied to performance-based seismic evaluation and design of reinforced concrete structures and members.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.97-106
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• 1993

This is the study on fracture life under the interaction of creep and fatigue. It is difficult to explain the interaction of the creep and fatigue with indication of frequency but the dependency of the time should be considered. The formulation of material varieties causing by interaction of creep and fatigue is required in the accumulative damage method. The strain range partition method requires some of modification corresponding to the changes in temperature and load. All of other method also comprehended with above mentioned problems. Generally, in this field, the variety of stress-strain and suitable parameter is required and connective study between the macro and micro results seems to be insufficient. The linear damage rule is acquiring the support generally but it requires modification in the hgigh temperature instruments. The variety of stress effecting on crack and variety of stress on the metallurgical side are considered to be problems in the future days.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.3
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• pp.31-38
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• 1989

This paper concentrates on the analysis of reinforced concrete(R/C) structures subjected to monotonic loading, from zero to ultimate loads. Tensile cracking, the nonlinear stress-strain relationship for concrete and reinforcement are taken into account the concrete is assumed to be elastic in tension region and elasto-hardening plastic in compression region. The Kupfer's failure criteria and associated flow rule are adopted to govern the plastic behavior of the concrete. The reinforcing bar is considered as a elasto-hardening platic material. The tension stiffening effect of the concrete between cracks is also considered. The numerical error depends on the used finite element mesh size is reduced by correcting the slope of strain softening region of the concrete according to the developed energy criteria.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.451-458
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• 2004

This study describes the basic concept and the applicability of Hybrid Reinforcement System using conventional steel reinforcing bars and Fiber Reinforced Polymer bars. The concrete bridge decks are assumed to be supported by beams and reinforced with two layers of reinforcing bars. In concrete bridge deck using HRS, the top tensile force for negative moment zone on beam supports is assumed to be resisted by FRP reinforcing bars, and the bottom tensile force for positive moment zone in the middle of hem supports is assumed to be resisted by conventional steel reinforcing bars, respectively. The FRP reinforcing bars are non-corrosive. Thus, the steel reinforcement is as far away as possible from the top surface of the deck and protected from intrusion of corrosive agent. HRS concrete bridge deck has sufficient ductility at ultimate state as the following reasons; 1) FRP bars have lower elastic modulus and higher ultimate strain than steel re-bars have, 2) FRP bars have lower ultimate strain if provided higher reinforcement ratio, 3) ultimate strain of FRP bars can be reduced if FRP bars are unbonded. Test results showed that FRP and HRS concrete slabs are not failed by FRP bar rupture, but failed by concrete compression in the range of ordinary reinforcement ratio. Therefore, in continuous concrete bridge deck using HRS, steel reinforcing bars for positive moment yield and form plastic hinge first and compressive concrete fail in the bottom of supports or in the top of the middle of supports last. Thus, bridge deck consumes significant inelastic strain energy before its failure.

• Journal of KSNVE
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• v.10 no.6
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• pp.1075-1082
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• 2000

The paper describes the vibration and stability of tapered beams on two-parameter elastic foundations. The two-parameter elastic foundations are constructed by distributed Winkler springs and a shearing layer as of ten used in soil models. The shear deformation and the rotatory inertia of a beam are taken into account. Governing equations are derived from energy expressions using Hamilton\`s principle. The associated eigenvalue problems are solved to obtain the free vibration frequencies or the buckling loads. Numerical results for the vibration of a beam with an axial force are presented and compared when other solutions are available. Vibration frequencies, mode shapes, and critical forces of a tapered Timoshenko beam on elastic foundations under an axial force are investigated for various thickness ratios, shear foundation parameters, Winkler foundation parameters and boundary conditions.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.803-810
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• 2007

An analytical method capable of predicting various stress-strain responses in axially loaded concrete confined with FRP (fiber reinforced polymers) composites in a rational manner is presented. Its underlying idea is that the volumetric expansion due to progressive microcracking in mechanically loaded concrete is an important measure of the extent of damage in the material microstructure, and can be utilized to estimate the load-carrying capacity of concrete by considering the corresponding accumulated damage. Following from this, an elastic modulus expressed as a function of area strain and concrete porosity, the energy-balance equation relating the dilating concrete to the confining device interactively, the varying confining pressure, and an incremental calculation algorithm are included in the solution procedure. The proposed method enables the evaluation of lateral strains consecutively according to the related mechanical model and the energy-balance equation, rather than using an empirically derived equation for Poisson's ratio or dilation rate as in other analytical methods. Several existing analytical methods that can predict the overall response were also examined and discussed, particularly focusing on the way of considering the volumetric expansion. The results predicted by the proposed and Samaan's bilinear equation models correlated with observed results with a reasonable degree, however it can be judged that the latter is not capable of predicting the response of lateral strains correctly due to incorporating the initial Poisson's ratio and the final converged dilation rate only. Further, the proposed method seems to have greater benefits in other applications by the use of the fundamental principles of mechanics.

• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.559-570
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• 2014

In this study, compression and shear characteristics of laminated rubber bearings and lead rubber bearings with various parameters are investigated by using material and geometric nonlinear three-dimensional finite element analysis. Rubber coupon tests are performed to make a model of the laminated rubber bearings. In addition, the material constants of the rubber are calculated by the curve fitting process of stress-strain relationship. The finite element analysis and experimental tests of the laminate rubber bearings are used to verify the validity of the rubber material constants. It is seen that the compression behavior of the laminated rubber bearings and lead rubber bearings mainly varies depending on the first shape factors and their shear behavior significantly varies depending on the second shape factors. In addition, the horizontal stiffness and energy dissipation capacity of lead rubber bearing are increased when the diameter of a lead bar is increased.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.1
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• pp.1-10
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• 1997

Current seismic design philosophy for reinforced concrete (RC) structures on energy dissipation through large inelastic defomations. A nonlinear dynamic analysis which is used to represent this behavior is time consuming and expensive, particularly if the computations have to be repeated many times. Therefore, the selection of an efficient yet accurate alogorithm becomes important. The main objective of the present study is to propose a new technique herein called the prediction approach with siffness measure (PASM) method in the convetional direct integration methods, the triangular decomposition of matrix is required for solving equations of motion in every time step or every iteration. The PASM method uses a limited number of predetermined decomposed effective matrices obtained from stiffness states of the structure when it is deformed into the nonlinear range by statically applied cyclic loading. The method to be developed herein will reduce the overall numerical effort when compared to approaches which recompute the stiffness in each time step or iteration.