• Journal of the Korea Concrete Institute
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• v.26 no.4
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• pp.555-562
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• 2014

To perform performance-based seismic design of buildings, it is necessary clear goal for usage and stability after an earthquake. To clear this goal, it requires a review of the constituent material of the building and, in particular, a member used as an indicator of the residual strain is useful. There are more usage of prestressed concrete because of prestressing steel witch has characteristics of the origin-oriented. In this study, the goal is estimating of residual strain on the prestressed concrete beam member. The expression for angle of deformed prestressed concrete beam member was obtained from using of curvature on the critical section and the equivalent plastic hinge length based on 'equivalent plastic hinge length method'. Considering the balance of strength and deformation conditions, suitable analysis values were derived from 'split Element Method'. Through various parametric studies, various factors affecting the residual strain were decided. Based on the results of this study, it is expected many researches will be proceed in the future.

• Geotechnical Engineering
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• v.12 no.6
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• pp.127-138
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• 1996

The in-situ consolidation behavior of drainage system-installed deposits has three dimensional characteristics. Therefore, for an approximate 2-D plane strain consolidation analysis, it is necessary to convert the 3-D spatial flow of actual cases into the laminar flow simulated by the 2-D plane strain model. . In this paper, in order to properly model the effect of three dimensional characteristics, an equivalent and efficient model has been applied in a finite element technique for the analysis of the drainage system-installed soil deposits. The equivalent two dimensional model involves equivalent permeabilities and drainage widths. To validate the equivalent two dimensional model, three dimensional analyses were per formed by using the ABAQUS program and the results of 3-D analyses were compared with those of the 2-D analyses. By using the proposed equivalent model, one may be able to appropriately predict the consolidation behavior of drainage system-installed soft deposits.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.400-403
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• 2002

This paper presents a shearographic technique for measuring in-plane strains. During the measurement, the test object is illuminated alternately with two laser beams, symmetrically with respect to the viewing direction. Employing a phase shift technique, the phase distributions due to object deformation for each beam are obtained separately. The difference of the two phase distributions depicts the derivative of in-plane surface displacements. The technique is equivalent to a system of many strain gages.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.12-21
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• 1995

The study was performed to study the effects of strain rate on acoustics emission( AE) during bulging test in corrosive environmentsynthetic sea water. The strain rates used were in the range $4 \times 10^{-6}S^{-1}$ to $1 \times 10^{-4} \times S^{-1}$ and the parameters used to evaluate AE signal characteristics were AE hit and amplitude. It can be observed that the cumulative AE hit and average amplitude during fracture process increase highly at decreasing strain rates while the equivalent fracture strain and the crack length of circumferencial direction become decrease. The peak point of AE signal characteristic parameters approach to the first half of test. When the average amplitude per unit equivalent fracture strain was above 20dB, it was definitly observed stress corrosion cracking phenomena. Additional, we knew that the AE test had the possibility to evaluate SCC susceptibility with various strain rates.

• Computers and Concrete
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• v.15 no.4
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• pp.607-642
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• 2015

The stress-strain relationship of concrete in flexure is one of the essential parameters in assessing the flexural strength and ductility of reinforced concrete (RC) columns. An overview of previous research studies revealed that the presence of strain gradient would affect the maximum concrete stress developed in flexure. However, no quantitative model was available to evaluate the strain gradient effect on concrete under flexure. Previously, the authors have conducted experimental studies to investigate the strain gradient effect on maximum concrete stress and respective strain and developed two strain-gradient-dependent factors k3 and ko for modifying the flexural concrete stress-strain curve. As a continued study, the authors herein will extend the investigation of strain gradient effects on flexural strength and ductility of RC columns to concrete strength up to 100 MPa by employing the strain-gradient-dependent concrete stress-strain curve using nonlinear moment-curvature analysis. It was evident from the results that both the flexural strength and ductility of RC columns are improved under strain gradient effect. Lastly, for practical engineering design purpose, a new equivalent rectangular concrete stress block incorporating the combined effects of strain gradient and concrete strength was proposed and validated. Design formulas and charts have also been presented for flexural strength and ductility of RC columns.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.5 s.39
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• pp.35-43
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• 2004

Small-scale models have been frequently used for seismic performance tests because of limited testing facilities and economic reasons. However, there are not enough studies on similitude law for analogizing prototype structures accurately with small-scale models, although conventional similitude law based on geometry is not well consistent in the inelastic seismic behavior. When fabricating prototype and small-scale model of reinforced concrete structures by using the same material, added mass is demanded from a volumetric change and scale factor could be limited due to aggregate size. Therefore, it is desirable that different material is used for small-scale models. Thus, a modified similitude law could be derived depending on geometric scale factor, equivalent modulus ratio and ultimate strain ratio. In this study, compressive strength tests are conducted to analyze the equivalent modulus ratio of micro-concrete to normal-concrete. Then, equivalent modulus ratios are divided into multi-phase damage levels, which are basically dependent on ultimate strain level. Therefore, an algorithm adaptable to the pseudodynamic test, considering equivalent multi-phase similitude law based on seismic damage levels, is developed. Test specimens, consisted of prototype structures and 1/5 scaled models as a reinforced concrete column, were designed and fabricated based on the equivalent modulus ratios already defined. Finally quasistatic and pseudodynamic tests on the specimens are carried out using constant and variable modulus ratios, and correlation between prototype and small-scale model is investigated based on their test results. It is confirmed that the equivalent multi-phase similitude law proposed in this study could be suitable for seismic performance tests on small-scale models.

• Korean Journal of Materials Research
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• v.17 no.10
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• pp.521-525
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• 2007

The microstructure and mechanical properties of an oxygen free copper processed by accumulative roll bonding(ARB) at low strain rate were studied. The copper sheets were highly strained up to an equivalent strain of ${\sim}6.4$ by ARB process at ambient temperature. The strain rate of the copper during the ARB was $2.6sec^{-1}$. The microstructure and mechanical properties of the ARB-processed copper were compared to those of the specimens processed by ARB at relatively high strain rate ($37sec^{-1}$). The microstructure and mechanical properties of the copper with ARB process was very similar to each other despite of some differences in recovery.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.3
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• pp.109-121
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• 2004

This paper presents an optimal design method for structure-borne durability of a vehicle body structure. Structure-borne durability design requires a new design that can increase fatigue lives of critical areas in a structure and must prohibit transition phenomenon of critical areas that results from modification of the structure at the same time. Therefore, the optimization problem fur structure-borne durability design are consists of an objective function and design constraints of 2 types; type 1-constraint that increases fatigue lives of the critical areas to the required design limits and type 2-constraint that prohibits transition phenomenon of critical areas. The durability design problem is generally dynamic because a designer must consider the dynamic behavior such as fatigue analyses according to the structure modification during the optimal design process. This design scheme, however, requires such high computational cost that the design method cannot be applicable. For the purpose of efficiency of the durability design, we presents a method which carry out the equivalent static design problem instead of the dynamic one. In the proposed method, dynamic design constraints for fatigue life, are replaced to the equivalent static design constraints for stress/strain coefficients. The equivalent static design constraints are computed from static or eigen-value analyses. We carry out an optimal design for structure-borne durability of the newly developed bus and verify the effectiveness of the proposed method by examination of the result.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.515-520
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• 2005

The behavior of jointed rock mass is much different from that of intact rock due to the presence of joints. Similarly, the characteristics of elastic wave propagation in jointed rock are considerably different from those of intact rock. The propagation of elastic waves in jointed rock is greatly dependent on the state of stress. The roughness, filling materials, and spacing of joints also affect wave propagation in jointed rock. If the wavelength of elastic waves is much larger than the spacing between joints, wave propagation in jointed rock mass can be considered as wave propagation in equivalent continuum. A rock resonant column testing apparatus is made to measure elastic waves propagating through jointed rock in the state of equivalent continuum. Three types of wave, i.e, torsional, longitudinal and flexural waves are monitored during rock resonant column tests. Various roughness and filling materials are applied to joints, and rock columns with various spacings are used to understand how these factors affect wave propagation under a small strain condition. The experimental results suggest that the characteristics of wave propagation in jointed rock mass are governed by the state of stress and influenced by roughness, filling materials and joint spacings.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.501-506
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• 1998

This paper is an experimental study on the flexural strength and ductility capacity of reinforced high performance concrete beams with the concrete which has compressive strength of 600~700kg/$\textrm{cm}^2$, slump value of 20~25cm and slump-flow value of 60~70cm. Total 8 beams with different tensile reinforcement ratio and pattern of loading were tested. Form the results of reinforced high performance concrete beams, the equivalent stress block parameters proposed by MacGregor et al. or New Zealand code are recommended to use. Also, an extreme fiber concrete compressive strain of reinforced high performance concrete beams are distributed 0.0033~0.0048. In reinforced high performance concrete beams, reinforcement ratio in order to insure curvature ductility index 2 and 4 propose by ACI code should be less than those of reinforced normal strength concrete beams.