• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.171-176
• /
• 2000

As huge energy transfer systems like a nuclear power plant, steam power plant and petrochemical plant are operated for a long time, mechanical properties are changed by degradation. The life time of the systems can be affected by the mechanical properties. BI(Ball Indentation) test has a potential to replace conventional fracture tests like a uniaxial tensile test, fracture toughness test, hardness test and so on. In this paper, we would like to present the aging evaluation technique by the BI method. The four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. Tensile tests, fracture toughness tests, hardness tests and BI tests were performed. The results of the BI tests were in good agreement with fracture characteristics by a standard fracture test method. The IDE(Indentation Deformation Energy) of a BI technique as a new parameter for evaluating a degradation was suggested and the new IDE parameter clearly depicts the degradation degree.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2009.05b
• /
• pp.45-48
• /
• 2009

The performance of concrete mainly depend upon its water-cement ratio. If water percentage is excess in concrete, it may cause the degradation of performance. Because of these reasons, the change of water content is managed by using various evaluation method of unit water content. And criterion for the change of water content is regulated and used. However the criterion is set only considering production error and measurement error but criterion does not consider performance degradation of concrete. Therefore this study tries to investigate degradation of performance while adding extra water by artificial manipulation or management error in concrete, The contents of extra water for tests are set as 0, 20, 40, 60kg/m3, to examine the performance degradation of concrete, strength, shrinkage, cracks, carbonation are tested This study conclude that, when extra water content is excess than 20kg/m3 in concrete, then performance level of concrete declined rapidly. 80 it is very important to maintain quality of concrete for its better performance.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.9
• /
• pp.2271-2279
• /
• 1993

In the case of life prediction on the structures and machines after long service, it is natural to consider a degradation problems. Most of degradation data form practical structures are isolated data obtained at the time of periodical inspection or repair. From such data, it may be difficult to obtain the degradation curve available and necessary for life prediction. In this paper, for the purpose of obtaining a degradation curves, developed the simulate degradation method and fatigue test and Charpy impact test were conducted on the degraded, simulate degraded and recovered materials. Fatigue life prediction were conducted by using the relationship between fracture transition temperature (DBTT : vTrs) obtained from the Charpy impact test through the degradation process and fatigue crack growth constants of m and C obtained from the fatigue test.

• Structural Engineering and Mechanics
• /
• v.28 no.1
• /
• pp.39-52
• /
• 2008

Column shear failures observed during recent earthquakes and experimental data indicate that shear deformations are typically associated with the amount of transverse reinforcement, column aspect ratio, axial load, and a few other parameters. It was shown that in some columns shear displacements can be significantly large, especially after flexural yielding. In this paper, a piecewise linear model is developed to predict an envelope of the cyclic shear response including the shear displacement and corresponding strength predictions at the first shear cracking, peak strength, onset of lateral strength degradation, and loss of axial-load-carrying capacity. Part of the proposed model is developed using the analysis results from the Modified Compression Field Theory (MCFT). The results from the proposed model, which uses simplified equations, are compared with the column test data.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05b
• /
• pp.333-336
• /
• 2006

In general, polymer materials undergo degradation when exposed to ultraviolet radiation, which can cause dissociation of chemical bonds. FRP composites which are used in strengthening existing structure are usually adhered on the concrete surface, its mechanical properties as well as appearance such as color, surface conditions are affected by sunlight and expecially ultraviolet light. In this study, variations of tensile strength after exposure for certain period of time through accelerated exposure by Xe arc methods specified in KS F 2274 are measured in order to examine strength degradation characteristics of FRP composite. As a result of ultraviolet light test for FRP composite after accelerated exposure for 0, 500, 1000, 1500 hour, discoloration of FRP composite occurs according to the passage of time. But, few strength degradations of FRP composite are observed due to exposure of ultraviolet ray with an small variation of tensile strength.

• Proceedings of the KSR Conference
• /
• 2004.10a
• /
• pp.1156-1161
• /
• 2004

The factors affecting the long-term design strength of geogrid for railroad reinforcement can be classified into factors on creep deformation, installation damage, temperature, chemical degradation, biological degradation. Especially, creep deformation and installation damage are considered as main factors to determine the long-term design strength of geogrid. This paper describes the results of a series of experimental study, which are carried out to assess the combined effect of installation damage and creep deformation for the long-term design strength of geogrid reinforcement. In this study, a series of field tests are carried out to assess installation damage of a various geogrids according to different fill materials, and then creep tests are conducted to assess the creep properties of both undamaged and damaged geogrids.

• Steel and Composite Structures
• /
• v.33 no.2
• /
• pp.245-259
• /
• 2019

The present study aims to investigate the ultimate strength and geometric nonlinear behavior of composite plates containing initial imperfection subjected to combined end-shortening strain and lateral pressure loading by using a semi-analytical method. In this study, the first order shear deformation plate theory is considered with the assumption of large deflections. Regarding in-plane boundary conditions, two adjacent edges of the laminates are completely held while the two others can move straightly. The formulations are based on the concept of the principle of minimum potential energy and Newton-Raphson technique is employed to solve the nonlinear set of algebraic equations. In addition, Hashin failure criteria are selected to predict the failures. Further, two distinct models are assumed to reduce the mechanical properties of the failure location, complete ply degradation model, and ply region degradation model. Degrading the material properties is assumed to be instantaneous. Finally, laminates having a wide range of thicknesses and initial geometric imperfections with different intensities of pressure load are analyzed and discuss how the ultimate strength of the plates changes.

• Steel and Composite Structures
• /
• v.45 no.1
• /
• pp.147-157
• /
• 2022

This study assessed the compressive and tensile strengths and modulus of elasticity of waste polyethylene terephthalate (PET) using the ASTM standard tests. In addition, short carbon and glass fibers were mixed with waste PET to examine the improvements in ductility and strength during compression. The bonding was examined via field-emission scanning electron microscopy. The strength degradation of the waste PET tested under UV was 40-50%. However, it had a compressive strength of 32.37 MPa (equivalent to that of concrete), tensile strength of 31.83 MPa (approximately ten times that of concrete), and a unit weight of 12-13 kN/m3 (approximately half that of concrete). A finite element analysis showed that, compared with concrete, a waste PET pile foundation can support approximately 1.3 times greater loads. Mixing reinforcing fibers with waste PET further mitigated this, thereby extending ductility. Waste PET holds excellent potential for use in foundation piles, especially while mitigating brittleness using short reinforcing fibers and avoiding UV degradation.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.1580-1587
• /
• 2005

To calculate the long-term allowable strength of geosynthetic reinforcement, replacement method was recommended. The isochronous creep curve by S. Turner was used to define the relation between creep strain and allowable strength. In isochronous curve at given time, one can read the allowable strength at allowable creep strain. The allowable strain gets from specification by directors or manufacturers according to the allowable displacement of reinforced structures. The allowable strength can be determined in relation to the allowable horizontal displacement each structures case by case. The effect of install damage on isochronous behaviors of geosynthetic reinforcement was little. In previous study, install damage increase the creep strain slightly. And the degradation was not identified. But it is supposed that degradation increase the creep strain. In conclusion, The recommended model to determine long-term allowable strength of geosynthetic reinforcements considering tensile deformation of reinforcement and soil is fit for proper, correct and economic design for reinforced earth walls.

• Journal of the Korea Concrete Institute
• /
• v.16 no.1 s.79
• /
• pp.111-124
• /
• 2004

This research is a part of a research program to verify the seismic performance of circular reinforced concrete bridge columns with respect to longitudinal steel connection details under cyclic lateral load. A total of 21 column specimens were constructed and tested. Main variables in this test program were longitudinal steel connection details(continuous, lap-spliced, and mechanically connected), confinement steel ratio, and axial force ratio, etc. The test results of the columns with different longitudinal steel connection details showed different failure mode, strength degradation, and seismic performance. From the quasi-static test, it was found that the columns with all longitudinal reinforcement lap-spliced showed significantly reduced ductility. However, seismic performance of the columns with half of longitudinal reinforcement lap-spliced showed limited ductility but much more ductile behaviour than the columns with all longitudinal reinforcement lap-spliced. It was also found that the seismic performance, failure mode and strength degradation of columns with mechanical connected longitudinal reinforcement were similar to those of columns with continuous longitudinal reinforcement.