• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.3
• /
• pp.31-37
• /
• 2018

This study evaluates the dynamic tensile behavior of HPFRCC according to compressive strength levels of 100, 140 and 180 MPa. Firstly, the compressive stress-strain relationship of 100, 140 and 180 MPa class HPFRCC was analyzed. As a result, the compressive strengths were 112, 150 and 202 MPa, respectively, and the elastic modulus increased with increasing compressive strength. The static tensile strengths of HPFRCC of 100, 140 and 180 MPa were 10.7, 11.5 and 16.5 MPa, and tensile strength also increased with increasing compressive strength. On the other hand, static tensile strength and energy absorption capacity at 100 and 140 MPa class HPFRCC showed no significant difference according to the compressive strength level. It was influenced by the specification of specimen and the arrangement of steel fiber. As a result of evaluating the dynamic impact tensile strength of HPFRCC, tensile strength and dynamic impact factor of all HPFRCCs tended to increase with increasing strain rate from 10-1/s to 150/s. In the same strain rate range, the DIF of the tensile strength was measured higher as the compressive strength of HPFRCC was lower. It is considered that HPFRCC of 100 MPa is the best in terms of efficiency. Therefore, it is advantageous to use HPFRCC with high compressive strength when a high level of tensile performance is required, and it is preferable to use HPFRCC close to the target compressive strength for more efficient approach at a high strain rate such as explosion.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.38 no.2
• /
• pp.193-202
• /
• 2018

This paper proposed a crack spacing calculation formulation which is an important parameter for calculating the crack width, that is the main factor for verification of serviceability limit states and durability performance evaluation of reinforced concrete members. The basic equation of average crack spacing is derived by considering the bond characteristics which is the governing equation for the analysis of cracking behavior in reinforced concrete members. In order to consider the effect of the cover thickness and concrete compressive strength, the crack spacing measured in 124 direct tensile tests performed by several researchers was analyzed and each coefficient was proposed. And, correlation analysis was performed from 80 specimen data where the maximum and average crack spacing were simultaneously measured, and a correlation coefficient that can easily predict the maximum crack spacing from the average crack spacing was proposed. The results of the proposed average crack spacing equation and maximum crack spacing correlation were compared with those current design code specification. The comparisons of proposed equations and the Korean design codes show that the proposed formulation for the average crack spacing and the maximum crack spacing improves the accuracy and reliability of prediction compared to the corresponding provisions of the Korean Concrete Structural Design Code and Korean Highway Bridge Design Code (Limit States Design).

• The Journal of the Korea Contents Association
• /
• v.8 no.5
• /
• pp.246-259
• /
• 2008

This study was to minimize the trial and error in the primary step of the C4I system(ATCIS) of the each army corps on the front line, and test the economy and efficiency was tested by reviewing related papers and the system characteristics of other countries. The relationship was researched by analyzing the collected survey data and survey data related to the user's requirement level such as the army standards, that is, commonality, timeliness, simplification, automaticity, field availability and viability, multi-stage security and interoperability, unification. The result showed that the C4I system was efficiently operated through the system reliability for the specification of the system and operation manual, maneuverability and security, adaptability of the war field and system support and management, and good education and training about system operation, and less system maintenance and supplementary element. As a result, the development plan confirmed that the continuous operator education and the construction of the maintenance, and the upgrade digitalization(C4ISR+D) with the korean characteristics based on IT of network systems, and system development of the measurement model of the operator performance must be continuously supplemented in the near future.

• Journal of KIISE:Software and Applications
• /
• v.32 no.12
• /
• pp.1283-1291
• /
• 2005

One of the problems in boosting Java performance using a Just-in-Time (JIT) compiler is removing redundant array bound checks. In conventional static compilers, many powerful algorithms have been developed, yet they are not directly applicable to JIT compilation where the compilation time is part of the whole running time. In the current JIT compilers, we tan use either a naive algorithm that is not powerful enough or an aggressive algorithm which requires the transformation into a static single assignment (SSA) form of programs (and back to the original form after optimization), thus causing too much overhead not appropriate for JIT compilation This paper proposes a new algorithm based on an inequality graph which can eliminate array bounds check codes aggressively without resorting to the SSA form. When we actually perform this type of optimization, there are many constraints in code motion caused by the precise exception rule in Java specification, which would cause the algorithm to miss many opportunities for eliminating away bound checks. We also propose a new method to overcome these constraints.

• Clean Technology
• /
• v.19 no.4
• /
• pp.423-429
• /
• 2013

This study aimed to develop flowable backfill material using oyster shell, coal ash, and surplus soil. The high temperature (> $800^{\circ}C$) reaction was required to convert $CaCO_3$ to CaO. The solid specimens formed by pozzlanic reaction between CaO and coal ash showed low unconfined compressive strength. The effect of kaolin and blast furnace slag was also examined. It was found that CaO and coal ash could not be utilized due to high cost and low performance. The use of oyster shell without calcination ($CaCO_3$) was evaluated. The specimens composing of oyster shell and cement showed the higher unconfined compressive strength than that composing of coal ash and cement. However, use of oyster shell is limited in mortar due to the presence of salt. Addition of soil into oyster shell-coal ash-cement mixture satisfied the specification of flowable backfill material by optimizing their ratio.

• Fire Science and Engineering
• /
• v.33 no.5
• /
• pp.149-154
• /
• 2019

The stability of firefighting pipes is crucial in the event of an earthquake. In Korea, specification-based designs are used in accordance with NFSC. However, engineering performance-based designs are used for buildings that have special requirements. For firefighting pipes, tree type pipe networks are usually utilized in buildings; however, they are characterized by several limitations. Hence, grid type and loop type networks are being utilized lately. Earthquake-resistant designs for firefighting pipes in Korea utilize NFPA 13 as the cookbook. Nevertheless, an engineering analysis is required to verify its reliability. The NFPA 13 standard used in Korea is a design method for engineers who lack earthquake engineering analysis knowledge of pipes and adapt ASCE and ASME guidelines. Earthquake resistant designs in Korea review braces only. Hence, various analyses under load conditions, such as the internal pressure of a pipe, force exerted by a continuous load, and an earthquake, are required to ensure reliability. An engineering earthquake-resistance analysis showed that tree type pipe networks are less stable than grid and loop type pipe networks. A comparison of earthquake-resistance analysis based on stress and strain revealed that strain analysis exhibited a conservative result value in the range of over-stress. Therefore, for the earthquake-resistance analysis of pipes, it is rational that engineers perform analysis to achieve the required standards through engineering analysis rather than uniform calculations, which should also be analyzed considering various analysis conditions.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.2
• /
• pp.110-116
• /
• 2013

A concrete structure has become bigger and higher because of development of construction technology and a change in construction environment. Also it tends to focus on repairing, reinforcement and exterior in harmony with environment for structure maintenance and performance improvement. The research is about eco friendly durable painting applicable to concrete structure using civil and architecture. it purpose to improve external beauties and durable problems due to flexibility by variation of temperature, adhesion of exterior wall, crack and delamination in existing organic and mineral painting. For those problems, we made a eco friendly pre-paint that is made with preliminary treatment mixture as a highly enriched waterproof agent and adhesive increasing agent in preprocessing mixture. Then we performed an experiment on durability of prevention neutralization of concrete, durability abrasion, hiding power, adhesion, temperature resistance and resistance to chemical attack. The result of an experiment shows that hiding power is over 0.96 in standard test, durability abrasion test got higher value 1mg than water paint 75mg and tensile strength is 6 times higher than standard waterproof specification.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.10 no.1 s.47
• /
• pp.41-49
• /
• 2006

Through the 1982 Urahawa-ohi and the 1995 Kobe earthquakes, a number of bridge columns were observed to develop a flexural-shear failure due to the bond slip as a consequence of premature termination of the column longitudinal reinforcement. Because the seismic behavior of RC bridge piers is largely dependent on the performance of the plastic hinge legion of RC bridge piers, it is desirable that the seismic capacity of RC bridge pier is to evaluate as a curvature ductility. The provision for the lap splice of longitudinal steel was not specified in KHBDS(Korea Highway Bridge Design Specification) before the implementation of 1992 seismic design code, but the lap splice of not more than 50%, longitudinal reinforcement was newly allowed in the 2005 version of the KHBDS. The objective of this research is to investigate the distribution and ductility of the curvature of RC bridge column with the lap splice of longitudinal reinforcement in the plastic hinge legion. Six (6) specimens were made in 600 mm diameter with an aspect ratio of 2.5 or 3.5. These piers were cyclically subjected to the quasi-static loads with the uniform axial load of $P=0.1f_{ck}A_g$. According to the slip failure of longitudinal steels of the lap spliced specimen by cyclic loads, the curvatures of the lower and upper parts of the lap spliced region were bigger and smaller than the corresponding paris of the specimen without a lap splice, respectively. Therefore, the damage of the lap spliced test column was concentrated almost on the lower part of the lap spliced region, that appeared io be failed in flexure.

• Journal of the Korean GEO-environmental Society
• /
• v.16 no.8
• /
• pp.13-20
• /
• 2015

Due to the population growth and exhaustion of resource, the development on the harsh environment such as cold weather is emerging as an alternative for new resource development. The permafrost area covers about 14 percent of the world's land area and the global construction market for such area is rapidly expanded. Whereas the developed countries have already recognition of the need for research of coldest place and invested heavily in technology development, the domestic technology for the coldest place development is less developed and related research has rarely been performed. There is not a detailed national specification standard for the strength and deformation properties of the earthworks at sub-zero temperature but simple field directions. Therefore, the D compaction tests were conducted on the sand with fine contents of 0%, 5%, 10% and 15% at room temperature ($18^{\circ}C$), $-3^{\circ}C$ and $-8^{\circ}C$ to investigate the effect of the compaction energy on the compacted soils at sub-zero temperatures. Based on the test results, the larger compaction energy, the larger maximum dry unit weight under sub-zero temperature and D type compaction at $-3^{\circ}C$ show similar max. dry unit weights as those obtained from the compaction at the room temperature. However, compaction at $-8^{\circ}C$ showed significant performance degradation regardless of the compaction energy.

• Journal of the Korea Concrete Institute
• /
• v.25 no.2
• /
• pp.187-194
• /
• 2013

Fiber reinforced polymer (FRP) has been gathering interest from designers and engineers for its possible usage as a replacement reinforcement of a steel reinforcing bar due to its advantageous characteristics such as high tensile strength, non-corrosive material, etc. Since it is manufactured with various contents ratios, fiber types, and shapes without any general specification, test results for concrete members reinforced with these FRP reinforcing bars could not be systematically used. Moreover, since investigations for FRP reinforced members have mainly focused on short-term behavior, the purpose of this study is to evaluate long-term behaviors of glass FRP (GFRP) reinforcing bar and concrete beams reinforced with GFRP. In this paper, test results of tensile and bond performance of GFRP reinforcing bar and creep behavior are presented. In the creep tests, results showed that 100 years of service time can be secured when sustained load level is below 55% of tensile strength of GFRP reinforcing bar. A modification factor of 0.73 used to calculate long-term deflection of GFRP reinforced beams was acquired from the creep tests for GFRP reinforced concrete beams. It is expected that these test results would give more useful information for design of FRP reinforced members.