• Proceedings of the Korea Concrete Institute Conference
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• 1992.04a
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• pp.143-147
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• 1992

Description of the behavior of the R.C structural members fixed on massive concrete is not normally generalization of recognized configuration for regular R.C. design guidanes. This can be due to the complexity of evaluation of internal resistancy and deflection changes of the members subjected to the various external forces. On the base of axially loaded member fixed on footing, however, the estimation of deflection changes due to flexural force shear force and rotational force is to be carried out in ways of specifying the bond characteristics of axial bars embedded in massive concrete. This work is to quantify adhesion of steel-concrete, initial concrete cracking stress near bar rib, maximum bond stress and residual stress in concrete respectively. In addition to quantification of them for particulate behavior, the suggestions of multi-linear bond stress-slip diagram made in carrying out finite element analyses for adhesion failure, examining concrete cracking status and reviewing existing experimental data lead to alternatively constructed relationship between bond stress and slip for a axial bars embedded massive concrete.

• Structural Engineering and Mechanics
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• v.17 no.6
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• pp.863-878
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• 2004

Steel corrosion in reinforced concrete structures leads to concrete cover cracking, reduction of bond strength, and reduction of steel cross section. Among theses consequences mentioned, reduction of bond strength between reinforcement and concrete is of great importance to study the behaviour of RC members with corroded reinforcement. In this paper, firstly, an analytical model based on smeared cracking and average stress-strain relationship of concrete in tension is proposed to evaluate the maximum bursting pressure development in the cover concrete for noncorroded bar. Secondly, the internal pressure caused by the expansion of the corrosion products is evaluated by treating the cracked concrete as an orthotropic material. Finally, bond strength for corroded reinforcing bar is calculated and compared with test results.

• The Journal of Advanced Prosthodontics
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• v.10 no.1
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• pp.25-31
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• 2018

PURPOSE. The aim of the present study was to record the metal-ceramic bond strength of a feldspathic dental porcelain and a Co-Cr alloy, using the Direct Metal Laser Sintering technique (DMLS) for the fabrication of metal substrates. MATERIALS AND METHODS. Ten metal substrates were fabricated with powder of a dental Co-Cr alloy using DMLS technique (test group) in dimensions according to ISO 9693. Another ten substrates were fabricated with a casing dental Co-Cr alloy using classic casting technique (control group) for comparison. Another three substrates were fabricated using each technique to record the Modulus of Elasticity (E) of the used alloys. All substrates were examined to record external and internal porosity. Feldspathic porcelain was applied on the substrates. Specimens were tested using the three-point bending test. The failure mode was determined using optical and scanning electron microscopy. The statistical analysis was performed using t-test. RESULTS. Substrates prepared using DMLS technique did not show internal porosity as compared to those produced using the casting technique. The E of control and test group was $222{\pm}5.13GPa$ and $227{\pm}3GPa$, respectively. The bond strength was $51.87{\pm}7.50MPa$ for test group and $54.60{\pm}6.20MPa$ for control group. No statistically significant differences between the two groups were recorded. The mode of failure was mainly cohesive for all specimens. CONCLUSION. Specimens produced by the DMLS technique cover the lowest acceptable metal-ceramic bond strength of 25 MPa specified in ISO 9693 and present satisfactory bond strength for clinical use.

• Restorative Dentistry and Endodontics
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• v.18 no.1
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• pp.103-113
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• 1993

The purpose of this study was to evaluate the tensile bond strength of composite resin inlays according to the their internal surface treatment and types of luting cement and compared them with the conventional direct resin filling thchnique. Class II cavities were prepared in 50 extracted human molar teeth, and then equally divided into five groups. Group 1 : Cavities of control group were directly filled with P-50. Group 2 : Cavities of resin inlay group were luted with resin cement. Group 3 : Cavities of resin inlay group were luted with luting G-I cement. Group 4 : Cavities of resin inlay group were luted with resin cement after sandblasting. Group 5 : Cavities of resin inlay group were luted with luting G-I cement after sandblasting. All specimens were polished with same method and stored in normal saline for 24 hours before testing. An Universal Testing machine(Model No. AGS-100A, Shimadzu, Japan) was used to apply tensile loads in the vertical direction, and the force required for separation was recorded with a cross-head speed of 5mm/min and 100kg in full scale. The results were as follows : 1. The mean tensile bond strength was lowest in group luted with luting G-I cement, with measurements of $14.45{\pm}0.78(kg/cm^2)$ and highest in group luted with resin cement after sandblasting, with measurements of $49.6{\pm}2.74(kg/cm^2)$. 2. The tensile bond strength was greater in resin inlay groups luted with resin cement than in control group and resin inlay groups luted with luting G-I cement(P<0.05). 3. The tensile bond strength was lower in resin inlay groups luted with luting G-I cement than in control group(P<0.05). 4. The tensile bond strength was greater in resin inlay groups luted with resin cement or luting G-I cement after sandblasting than without that(P<0.05).

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.49-50
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• 2010

This study focuses on the bond performance of ribbed type of GFRP rebar to concrete at high temperature and discusses the results of pullout test. Pullout tests of ribbed type of GFRP rebars embedded in concrete were conducted to obtain an accurate bond stress-slip curves and also to closely observe the state of the surface of pulled-out rebars at failure. The effect of temperature on the bond strength is mainly discussed in this paper. Relatively high bond strength was seen in the control specimen which is exposed to room temperature. But, as the internal temperature increases, the bond strength decreases.

• Computers and Concrete
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• v.1 no.4
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• pp.401-416
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• 2004

This paper presents investigation of a three-dimensional (3-D) nonlinear finite element model analysis to examine the behavior of reinforced concrete beams strengthened with Carbon Fiber Reinforced Polymer (CFRP) composites to enhance the flexural capacity and ductility of the beams. Three-dimensional nonlinear finite element models were developed between the internal reinforcement and concrete using a smeared relationship. In addition, bond models between the concrete surface and CFRP composite were developed using a smeared bond for general analyses and a contact bond for sensitivity analyses. The results of the FEA were compared with the experimental data on full-scale members. The results of two finite-element bonding models showed good agreement with those of the experimental tests.

• Journal of the Korea Concrete Institute
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• v.11 no.4
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• pp.107-116
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• 1999

The damage in concrete structures generally starts with microcracking and thus it is important to find and explore these microcracks in concrete in order to ensure appropriate safety and serviceability. The purpose of the present study is to identify the damage characteristics of concrete structures due to cracking by employing the acoustic emission techniques. A comprehensive experimental study has been done. The cracking damage under tensile and flexural loadings have been identified and the bond damage between steel and concrete have been also characterized. It is seen that the amplitudes and energy level of Acoustic Emission(AE) events are found to be relatively small for bond cracking damages and large for tensile cracking damages. The characteristic equations of the AE events for various cracking damages have been proposed based on the present test data. The internal microcracks are progressively developed ahead of a visible actual crack and the present study clearly exhibits these damage mechanism for various types of cracking in concrete. The present study provides useful data which can be used to identify the various types of cracking damages in concrete structures. This will allow efficient maintenance of concrete structures through monitoring of internal cracking based on acoustic emission.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.543-546
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• 1999

The purpose of the present study is to identify the damage characteristics of concrete structures due to cracking by employing the acoustic emission techniques. A comprehensive experimental study has been done. The cracking damages under tensile and flexural loadings have been identified and the bond damage between steel and concrete have been also characterized. It is seen that the amplitudes and energy level of AE events is found to be smaller for bond cracking damages and larger for tensile cracking damages. The characteristic equations of the AE events for various cracking damages have been proposed based on the present test data. The internal microcracks are progressively developed ahead of a visible actual crack and the present study clearly exhibits thses damage mechanism for various types of cracking in concrete. The present study provides very useful data which can be used to identify the various types of cracking damages in concrete structures. This will allow very efficient maintenance of concrete structures through monitoring of internal cracking based on acoustic emission.

• Journal of the Korean Wood Science and Technology
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• v.26 no.4
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• pp.92-97
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• 1998

Four urea-formaldehyde (UF) resins were synthesized as a particleboard (PB) binder with the four different initial formaldehyde/urea mole ratio and the final mole ratio of 1.15. The UF resins were characterized according to the standard method of resin adhesive analysis. PBs were manufactured using liquid UF resins at 5 minutes press time and 6% resin solids levels on an ovendry particle weight basis. A total of 20 PBs was fabricated for 5 panel replication per UF resin types. The panels were tested for physical strength properties per the procedure ASTM D 1037. The formaldehyde emission levels from the PBs bonded with the UF resins were tested according to 2-hour desiccator test method ASTM D 5582. There were no significant differences among UF resin types for internal bond strength of PBs. But there were significant differences among UF resin types for formaldehyde emission level of PBs. The results showed that the formaldehyde emission level was influenced by the UF resin types without reducing the adhesive performance.

• Journal of the Korean Wood Science and Technology
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• v.25 no.3
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• pp.96-104
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• 1997

The objective of this research project was to develop the wooden footpath block to reuse of wood waste. Some physical and mechanical properties of the wooden block such as water absorption, thickness swelling, modulus of rupture, internal bond, density profile and impact resistance were studied. Water absorption and thickness swelling of the wooden block were greatly reduced when the wooden block was pressed inside the forming device than by conventional hot pressing. Also, Modulus of rupture and internal bond of the wooden block were increased greatly when the pressing was completed inside the forming device. The density profile of the wooden block was improved up to 93.5%, minimum to average density ratio. The wooden block manufactured in this study have excellent physical and mechanical prperties in comparison with existing wood based materials. So, these wooden blocks are applicable to footpth block or other exterior members.