• Composites Research
• /
• v.26 no.2
• /
• pp.91-98
• /
• 2013

A three-dimensional finite analysis method was proposed to predict the failure of composite double-lap bolted joints, which is based on the stiffness degradation method using damage variables and Hashin's three-dimensional failure criteria. Ladeveze's theory using damage variables to consider the matrix/shear damage was combined with stiffness degradation in fiber direction. Four different failure modes were considered including matrix compression/shear, matrix tension/shear, fiber compression, and tension failures. The friction between bolt and composite and the clamping force were considered using a commercial finite element software ABAQUS. The damage model was incorporated using the user-defined subroutine of the software. The predicted result was verified with the existing test result for bearing tension double shear and showed the deviation ranging 7~16% from test results.

• Journal of the Korea Concrete Institute
• /
• v.24 no.5
• /
• pp.509-516
• /
• 2012

The aims of this research is to develop a fire resistant admixture to enhance high-pressured pumping of high-strength concrete (HSC) with a compressive strength of 60~80 MPa. Generally, the efficiency of HSC high-pressured pumping is dramatically reduced due to entanglement of short fibers added to prevent fire spalling. Therefore, the fire resistant admixture that can facilitate pumping of fire resistant HSC is urgently needed presently. The fire resistant HSC mix is comprised of Polypropylene fiber, Nylon fiber and Polymer powder. The test results showed that the slump-flow was improved by approximately 70% of the HSC without fire resistant admixture. However, the air void content was increased slightly due to the addition. The standard design compressive strength at 28-days was satisfied, while its flexural strength was similar to the concrete without the admixture. Since the flexural strength was 12~15% of its compressive strength, the general trend of flexural to compressive strength ratio in normal concrete was maintained. Even though its elastic modulus was decreased by adding the admixture, the study results showed that the concrete can be used for construction since all of the test results exceeded the code requirements.

• Journal of the Korea Concrete Institute
• /
• v.22 no.1
• /
• pp.19-27
• /
• 2010

Aging and severe environments are major causes of damage in reinforced concrete (RC) structures such as buildings and bridges. Deterioration such as concrete cracks, corrosion of steel, and deformation of structural members can significantly degrade the structural performance and safety. Therefore, effective and easy-to-use methods are desired for repairing and strengthening such concrete structures. Various methods for strengthening and rehabilitation of RC structures have been developed in the past several decades. Recently, FRP composite materials have emerged as a cost-effective alternative to the conventional materials for repairing, strengthening, and retrofitting deteriorating/deficient concrete structures, by externally bonding FRP laminates to concrete structural members. The main purpose of this study is to investigate the effectiveness of adaptive neuro-fuzzy inference system (ANFIS) in predicting behavior of circular type concrete column retrofitted with FRP. To construct training and testing dataset, experiment results for the specimens which have different retrofit profile are used. Retrofit ratio, strength of existing concrete, thickness, number of layer, stiffness, ultimate strength of fiber and size of specimens are selected as input parameters to predict strength, strain, and stiffness of post-yielding modulus. These proposed ANFIS models show reliable increased accuracy in predicting constitutive properties of concrete retrofitted by FRP, compared to the constitutive models suggested by other researchers.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.701-704
• /
• 2008

Actuality, amount of electric power is rising together with business expansion. But the most power plant is consisted a thermal power. People have been burning fuel like a coal, and it bring the cinder concrete. Fly-ash is use to the high-degree in construction material, but in case of bottom-ash had been disused the whole quantity. Intermittently, the academic world laid his studies for bottom-ash. Thus, this study contents are a characteristic of be not harden concrete incorporating fine aggregate, a strength of harden concrete, elastic modulus and a unit mass. And there do for the sake to examine utility value of bottom-ash and improve of light weight concrete.

• Journal of the Korea Institute of Building Construction
• /
• v.14 no.2
• /
• pp.170-176
• /
• 2014

This study examined the effect of chemical attack on the stress-strain relationship of alkali-activated Hwangtoh concrete. Water-to-binder ratio and air content were selected as mixture parameters. The stress-strain relationship of concrete was measured at chemical immersion times of 0, 7, 28, 56, and 91 days from an age of 28 days. Based on the test results, the reduction in compressive strength of alkali-activated hwangtoh concrete owing to chemical attack was formulated. In sddition the present study demonstrated that the stress-strain behavior of concrete under chemical attack is significantly dependent on the air content and chemical immersion time, indicating the rate of decrease of modulus of elasticity was greater than that of compressive strength at the same immersion time. As a result, the stress-strain behavior of concrete under chemical attack was significantly inconsistent with the conventional models specified in the CEB-FIP provision.

• Journal of the Korea Concrete Institute
• /
• v.28 no.5
• /
• pp.611-620
• /
• 2016

In the construction of nuclear power plants, only 420 MPa reinforcing bars are allowed and, therefore, so many large-diameter bars are placed, which results in steel congestion. Consequently, re-bar works are difficult and the quality of RC structures may be deteriorated. To solve the steel congestion, 550 MPa bars are necessary. Among many items for verifying structural performance of reinforced concrete with 550 MPa bars, the 43 mm hooked bars are examined in this study. All specimens failed by side-face blowout and the side cover explosively spalled at maximum loads. The bar force was initially transferred to the concrete primarily by bond along a straight portion. At the one third of maximum load, the bond reached a peak capacity and began to decline, while the hook bearing component rose rapidly. At failure, most load was resisted by the hook bearing. For confined specimens with hoops, the average value of test-to-prediction ratios by KCI code is 1.45. The modification factor of confining reinforcement which was not allowed for larger than 35 mm bars can be applied to 43 mm hooked bars. For specimens with 70 MPa concrete, the average value of test-to-prediction ratios by KCI code is 1.0 which is less than the values of the other specimens. The effects of concrete compressive strength should be reduced. An equation to predict anchorage capacity of hooked bars was developed from regression analysis including the effects of compressive strength of concrete, embedment length, side cover thickness, and transverse reinforcement index.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.11
• /
• pp.157-166
• /
• 2008

To investigate the relationship between compressive strength ($q_u$) of Lightweight Air-mixed soil (LAS) and its physical deformation coefficient ($E_{50}$), a series of unconfined compressive tests have been performed on specimens of LAS according to various dredged soil types by percentage of sand, silt and clay. From the results it was found that the cement content ($C_i$) and unit weight (${\gamma}_m$) are most influence factors on strength, and percentage of sand, silt, clay by grain size analysis (KS F2302) have more effect on compressive strength than other physical properties of soil. It was also found that the rate of strength (a) increases with curing time, but it reduces with the increase of percentage of clay ($C_%$).

• Composites Research
• /
• v.22 no.3
• /
• pp.82-88
• /
• 2009

The effect of open and filled holes on the strength behavior of carbon fiber reinforced polymeric (CFRP) composites was investigated. The strength was measured at room temperature dry, cold temperature dry, $-55^{\circ}C$, and elevated temperature wet, $108.3^{\circ}C$ on several different laminate configurations. Based on the experimental data presented, it is shown that the filled hole tensile strength is larger than that of open hole by reducing damage around the hole due to the constraint imposed by the fastener. The tensile strength at cold temperature dry, $-55^{\circ}C$ is increased with the brittleness by the thermal expansion coefficient of fiber and matrix. The compressive strength at elevated temperature wet, $108.3^{\circ}C$ is decreased by the cause of interfacial deterioration between fiber and matrix with moisture absorption.

• Journal of the Korea Concrete Institute
• /
• v.29 no.3
• /
• pp.307-314
• /
• 2017

Concrete is a durable and cost-benefit construction material, however performance degradation occurs due to steel corrosion exposed to chloride attack. Penetration of chloride ion usually decreases due to hydrates formation and reduction of pores, and the reduced chloride behavior is considered through decreasing diffusion coefficient with time. In the work, HPC (High Performance Concrete) samples are prepared with 3 levels of W/B (water to binder) ratios of 0.37, 0.42, and 0.27 and 3 levels of replacement ratios of 0%, 30% and 50%. Several tests containing chloride diffusion coefficient, passed charge, and compressive strength are performed considering age effect of 28 days and 180 days. Chloride diffusion is more reduced in OPC concrete with lower W/B ratio and GGBFS concrete with 50% replacement ratio shows significant reduction of chloride diffusion in higher W/B ratio. At the age of 28 days, GGBFS concrete with 50% replacement ratio shows more rapid reduction of chloride diffusion than strength development, which reveals that abundant GGBFS replacement has effective resistance to chloride penetration even in the early-aged condition.

• Tunnel and Underground Space
• /
• v.28 no.5
• /
• pp.476-492
• /
• 2018

In this study, various laboratory experiments were conducted on tuff, basalt and diorite specimens, which were obtained in the southern part of Korean Peninsula. Experiments were performed under dry and water saturated conditions. Results showed that strength degradation and change of deformation characteristics were remarkable although the specimens had small porosity. Based on the results, regression models that are capable of predicting important mechanical rock properties, such as uniaxial compressive strength, Young's modulus, Brazilian tensile strength were proposed. P-wave velocity and Shore hardness were selected as independent variables and the results showed satisfactory prediction performance for the experimental data collected in this study.