• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.638-644
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• 2002

The stress-strain relationship of polymer concrete flexural member was evaluated using C-shaped polyester concrete specimen, the compressive strength of which is 1400 kgf/$\textrm{cm}^2$. Eccentric compression test was performed to estimate the parameters, ${\alpha}$, ${\beta}$1, ${\gamma}$ for equivalent rectangular stress block. The ultimate moment strength ware obtained from the bending test on reinforced polymer concrete beams which were prepared with S different tensile steel ratios with a shear span ratio of 4.0. These values were compared with theoretical ultimate moment strengths, which were obtained using the parameters ${\alpha}$=0.61 and ${\beta}$1=0.73 from stress-stain curves of C-shaped specimens. The results showed that, when tensile steel ratio was over 0.50 $\rho$b, the experimentally obtained moment strengths were well matched with theoretically calculated values. In order to develop accurate criteria for polymer concrete flexural members, however, many other expermental studies for parameter determination are necessary using C-shaped specimens which have various compressive strengths and different sizes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.171-176
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• 2016

This paper proposes road safety facilities applying Hot-dip zinc-aluminum-magnesium alloy-coated steel sheets and coils to reduce the loss of function caused by the corrosion of steel in the service state. Vehicle crash simulations and full-scale crash tests were carried out to provide reliable information on evaluating the crash performance with the products of road safety facilities built with hot-dip zinc-aluminum-magnesium alloy-coated steel. From the results of the simulations and full-scale crash tests, the impact behaviors evaluated by the three-dimensional crash simulations considering the strain-rate dependency in a constitutive model were similar to those obtained from the full-scale crash test results. The full-scale crash test results met the crashworthiness evaluation criteria; hence, the proposed bridge barrier in this paper is ready for field applications.

• Journal of Korean Society of Steel Construction
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• v.11 no.1 s.38
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• pp.33-42
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• 1999

In the present study, crack initiation criteria, static failure and tensile mode fatigue behavior for a rail steel are evaluated to assure the railway vehicle's safety. The transverse fissure, which is the most critical damage in the rail, is initiated by the maximum shear stress and its location is subsurface. In addition, the possibility of transition from the shear mode to the mixed mode increases with increasing the length of subsurface crack. Because of the brittleness by the welding, the fracture toughness of the welded part is lower than of the base metal. For low ${\Delta}K$, the stage II fatigue crack growth rates of the welded part is slower than of the base metal but, for high ${\Delta}K$, this different behavior for fatigue crack growth rate is nearly diminished. These trends are more remarkable for low stress ratio, R=0.1. It is believed that this behavior is caused by the change of the microstructure which that of the welded part is coarser than of base metal.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.4
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• pp.333-342
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• 2002

World widely, the occurrences of earthquakes have been increased recently. Speculating from cases of earthquakes in the world, it is reported that damages have been made underground structures like cut-and-cover tunnels, especially on the upper of tunnel with a shallow depth and the backfilled area adjacently by earthquakes. Earthquakes have a tendency to increase recently in Korea but it is deficient in seismic design criteria. In this study, Shaking table test on both soil and EPS blocks was performed to analyze the efficiency of the seismic performance of the cut-and-cover tunnels according to characteristic of backfill materials and embanking material. It turned out to be effective in improving the seismic performance according to analysis of strain and bending stress of tunnel by earthquakes.

• Structural Engineering and Mechanics
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• v.74 no.4
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• pp.567-576
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• 2020

Considerable controversy surrounds the choice of the best abutment type for implant prosthetics. The two most common structures are hex and non-hex abutments. The non-hex abutment typically furnishes a larger contact area between itself and the implant than that provided by a hex structure. However, when a hex abutment is loaded, the position of its contact area may be deeper than that of a non-hex abutment. Hence, the purpose of this study is to determine the different biomechanical behaviors of an internal bone-level implant based on the abutment type-hex or non-hex-and clinical crown length under static and cyclic loadings using finite element analysis (FEA). The hex structure was found to increase the implant and abutment stability more than the nonhex structure among several criteria. The use of the hex structure resulted in a smaller volume of bone tissues being at risk of hypertrophy and fatigue failure. It also reduced micromovement (separation) between the implant components, which is significantly related to the pumping effect and possible inflammation. Both static and fatigue analyses, used to examine short- and long-term stability, demonstrated the advantages of the hex abutment over the non-hex type for the stability of the implant components. Moreover, although its impact was not as significant as that of the abutment type, a large crown-implant ratio (CIR) increased bone strain and stress in the implant components, particularly under oblique loading.

• Safety and Health at Work
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• v.6 no.3
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• pp.218-226
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• 2015

Background: The present study aimed to analyze the index value trends of injured employed persons (IEPs) covered in Pakistan Labour Force Surveys from 2001-02 to 2012-13. Methods: The index value method based on reference years and reference groups was used to analyze the IEP trends in terms of different criteria such as gender, area, employment status, industry types, occupational groups, types of injury, injured body parts, and treatment received. The Pearson correlation coefficient analysis was also performed to investigate the inter-relationship of different occupational variables. Results: The values of IEP increased at the end of the studied year in industry divisions such as agriculture, forestry, hunting, and fishing, followed by in manufacturing and construction industry divisions. People associated with major occupations (such as skilled agricultural and fishery workers) and elementary (unskilled) occupations were found to be at an increasing risk of occupational injuries/diseases with an increasing IEP trend. Types of occupational injuries such as sprain or strain, superficial injury, and dislocation increased during the studied years. Major injured parts of body such as upper limb and lower limb found with increasing trend. Types of treatment received, including hospitalization and no treatment, were found to decrease. Increased IEP can be justified due to inadequate health care facilities, especially in rural areas by increased IEP in terms of gender, areas, received treatment, occupational groups and employment status as results found after Pearson correlation coefficient analysis. Conclusion: The increasing trend in the IEP% of the total employed persons due to agrarian activities shows that there is a need to improve health care setups in rural areas of Pakistan.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.6
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• pp.35-43
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• 2010

This study was carried out to find reliable relations between various concrete strength properties which are used as input data in concrete pavement design program. Concretes were made from different sources of coarse grained(granite, limestone and sandstone) and fine grained aggregates such as natural sand, washed sand and crushed sand. From strength test results, model equations were obtained based on the relation between strengths. For each coarse grained aggregate, models for compression-flexural strengths, compression-split tensile strengths, compressive strength-modulus and flexural-split tensile strengths with age were obtained. For concrete mixed with gneiss granite aggregates, concrete strengths were obtained from numerical mean values of concrete strengths mixed with fine grained aggregates. In addition models for concrete split tensile strengths and modulus values were provide by averaging numerically the estimated values obtained from the derived relationship and the experimental values. This is due to more scattered values of split tensile strengths and modulus values than other strength properties. Finally criteria for drying shrinkage strain as well as Poisson's ratio for concrete used in pavement were presented for all mixes with differed coarse grained aggregates.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.239-248
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• 2002

A constitutive model unifying plasticity and crack damage mode)s was developed to address the cyclic behavior of reinforced concrete planar members. The stress of concrete in tension-compression was conceptually defined by the sum of the compressive stress developed by the strut-action of concrete and the tensile stresses developed by tensile cracking. The plasticity model with multiple failure criteria was used to describe the isotropic damage of compressive crushing affected by the anisotropic damage of tensile cracking. The concepts of the multiple fixed crack damage model and the plastic flow model of tensile cracking were used to describe the tensile stress-strain relationship of multi-directional cracks. This unified model can describe the behavioral characteristics of reinforced concrete in cyclic tension-compression conditions, i.e. multiple tensile crack orientations, progressively rotating crack damage, and compressive crushing of concrete. The proposed constitutive model was implemented to finite element analysis, and it was verified by comparison with existing experimental results from reinforced concrete shear panels and walls under cyclic load conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.25-33
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• 1986

In this paper, the frontal method based elastic-plastic F.E.M. program for mini-computer was developed. Since, the executable source program size was restricted by the system core memory size on the mini-computer, the active variables were memorized by the element base and the nonactive varables were memorized to the external disc file. The active variables of the finally developed program were reduced enough to execute about 1,000 freedom finite element on the mini-computer on which available variables were restricted as 32,767 integers. A modified CT fracture test specimen was examined to test the developed program. The calculated results were compared with experimental results concerning on the crack tip plastic deformation zone. Recrystallization technique was adopted to visualize the intensive plastic deformation regions. The Von-Mises criterion based calculation results were well agreed with the experimental results in the intensive plastic region which was over than 2% offset strain. The F.E.M. results using the developed program were well agreed with the theoritical plastic boundary which was calculated by the stress intensity factor as r$_{p}$=(K$_{1}$$^{2}$/2.pi..sigma.$_{y}$$^{2}$).f(.theta.).).).

• International Journal of High-Rise Buildings
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• v.1 no.3
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• pp.181-194
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• 2012

Chile is characterized by the largest seismicity in the world which produces strong earthquakes every $83{\pm}9years$ in the Central part of Chile, where it is located Santiago, the capital of Chile. The short interval between large earthquakes magnitude 8.5 has conditioned the Chilean seismic design practice to achieve almost operational performance level, despite the fact that the Chilean Code declares a scope of life safe performance level. Several Indexes have been widely used throughout the years in Chile to evaluate the structural characteristics of concrete buildings, with the intent to find a correlation between general structural conception and successful seismic performance. The Indexes presented are related only to global response of buildings under earthquake loads and not to the behavior or design of individual elements. A correlation between displacement demand and seismic structural damage is presented, using the index $H_o/T$ and the concrete compressive strain ${\varepsilon}_c$. Also the Chilean seismic design codes pre and post 2010 Maule earthquake are reviewed and the practice in seismic design vs Performance Based Design is presented. Performance Based Design procedures are not included in the Chilean seismic design code for buildings, nevertheless the earthquake experience has shown that the response of the Chilean buildings has been close to operational. This can be attributed to the fact that the drift of most engineered buildings designed in accordance with the Chilean practice falls below 0.5%. It is also known by experience that for frequent and even occasional earthquakes, buildings responded elastically and thus with "fully operational" performance. Taking the above into account, it can be said that, although the "basic objective" of the Chilean code is similar to the SEAOC VISION2000 criteria, the actual performance for normal buildings is closer to the "Essential/Hazardous objective".