• Tunnel and Underground Space
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• v.28 no.6
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• pp.584-595
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• 2018

This study conducted direct shear test on about 290 sorts of materials such as sandy soil, clayey soil and gravely soil to present proper standard on shear strength of soil. Shear strength of soil in large scale tends to show that angle of internal friction increases as sand contents grow and it ranges $23.5^{\circ}{\sim}34.9^{\circ}C$ with cohesion of 2.0 kPa~15.7 kPa. Elastic modulus was visibly distinct by load, and which increased approximately 80% as vertical load grows. Angle of internal friction arranging $15.0^{\circ}{\sim}28.6^{\circ}$ on clayey soil decreased as clay contents rises and cohesion increase in regular scale. Elastic modulus tends to increase initial elastic modulus with almost same growing rate. While angle of internal friction on gravely soil indicates $29.9^{\circ}{\sim}36.7^{\circ}$ which hardly shows distinctive features. According to test in detail, cohesion of SW (well-graded sand), SP (poorly-graded sand), SC (clayey sand) and SM (silty sand) indicates value by 94%, 78% and 59% comparing to SC, SW and SP respectively. Angle of internal friction of ML (low-liquid limit silt) and CL (low-liquid limit clay) appears almost same features, and MH (high-liquid limit silt) despite of 88% value of ML. Cohesion among them varies with similar growing rate.

• Journal of Welding and Joining
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• v.32 no.4
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• pp.55-62
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• 2014

The use of light-weight Al alloys in the automotive industry is increasing to meet requirements for fuel efficiency and emission reduction. Joining Al alloy to the conventional steel sheet is also very important issue with the increased use of Al alloy, and several joining processes have been introduced to enhance joining strength between dissimilar metals. This paper deals with a galvanic corrosion in the dissimilar metal joining. Salt spray tests up to 2000 hours were conducted on a self-piercing rivet, spot welded, adhesive bonded and weld-bonded joints, and cross-sections and tensile shear strength according the salt spray duration were analyzed at every 500-hour. Self-piercing rivet joint had relative low initial strength but the joint strength did not change regardless of the salt spray duration. The strength of other joints (spot welded, adhesive bonded and weld-bonded joints) decreased with the increase of salt spray duration and the corrosion behaviour of each joint was discussed.

• Steel and Composite Structures
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• v.42 no.2
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• pp.221-241
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• 2022

Perfobond rib connectors are widely used in composite structures to achieve the composite action between the steel and the concrete, and empirical expressions for their strength and secant stiffness have been obtained by numerical simulations or push-out tests. Since perfobond connections are generally in an elastic state in the service process and the structural analysis are always based on the elastic properties of the members, the secant stiffness is not applicable for the normal structural analysis. However, the tangent stiffness of perfobond connections has not been introduced in previous studies. Moreover, the perfobond connections are bearing tension and shear force simultaneously when the composite beams subjected to torque or local loads, but the current studies fail to arrive at the elastic stiffness considering the combined effects. To resolve these discrepancies, this paper investigates the initial elastic stiffness of perfobond connections under combined forces. The calculation method for the elastic stiffness of perfobond connections is analyzed, and the contributions of the perfobond rib, the perforating rebar and the concrete dowel are investigated. A finite element method was verified with a high value of correlation for the test results. Afterwards, parametric studies are carried out using the reliable finite element analysis to explore the trends of several factors. Empirical equations for predicting the initial elastic stiffness of perfobond connections are proposed by the numerical regression of the data extracted by parametric studies. The equations agree well with finite element analysis and test results, which indicates that the proposed empirical equations reflect a high accuracy for predicting the initial elastic stiffness of perfobond connections.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.1
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• pp.8-15
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• 2012

The initial clamping forces of high strength bolts depending on different faying surface conditions drop within 1,000 hours regardless of loading, any other external force or loosening of the nut. This study is focused on an expectation model for relaxation of high strength bolt, which is confined to creep on coated faying surfaces after initial clamping. The range of this experiment is limited to estimate the relaxation of bolted joints coated by inorganic zinc primer. The candidate bolts were dacro-coated tension control bolts. The parameters of coated thickness for the faying surface were 96, 168,and $226{\mu}m$ respectively. From experiments, it exhibited that the logarithmic function for creep strain was derived due to the parameter of coating thickness. By using the creep strain, subsequently the quantitative model for estimating long term relaxation of high strength bolt can be taken with the elapsed time. The experimental results showed that the relaxation after the initial clamping of high strength bolt rose to a much higher range from 10% to 18% due to creep of the coating as the coating thickness was increased. This study showed that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force of high strength bolt.

• Restorative Dentistry and Endodontics
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• v.32 no.5
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• pp.445-458
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• 2007

The purpose of this study was to evaluate the bond strength of a new Single step system with different curing mode composites, and to evaluate the effect of the intermediate resins which have different hydrophilicity on bonding ability by means of the micro shear bond testing and TEM examination for the adhesive interface. The adhesive used in this study was an experimental single step system (Bisco Inc., Schaumburg IL). Experimental groups were produced by using six kinds of intermediate resin having different hydrophilicity that was hydrophilic, hydrophobic and most hydrophobic resin and as filled or not after applying adhesive. Each experimental group was further divided into two subgroups whether the adhesive was light cured or not. Dual cured composite (Bis Core, Bisco Ltd., Schaumburg, IL) was placed on the adhesive layer as light cure or self cure mode. The results or bond strength were statistically analyzed using one way ANOVA and multiple comparisons are made using Tukey's test at ${\alpha}\;<\;0.05$ level. The results of this study were as follows ; 1. The application of intermediate resin did not increase the bond strength for light cured composite. 2. The bond strength of an experimental adhesive with self cured composite was significantly increased by the application of intermediate resin layer. 3. The bond strength of adhesive was irrespective of the cure or not of itself before intermediate resin layer applied. 4. As applied hydrophilic resin layer was, the initial bond strength was higher than both hydrophobic and most hydrophobic one used but there was no significance. Using a single step adhesive with dual/self cured composite, the incompatibility between both of them should be solved by the application of intermediate hydrophobic resin to reduce the adhesive permeability. However, Single step adhesive can be used in the light cured composite restoration without any decrease of the initial bond strength.

• Journal of Korean Society of Steel Construction
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• v.24 no.4
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• pp.371-382
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• 2012

Existing shear wall system may cause ductility fallen to the structure which it is on because relatively weak concrete core would easy to be damaged. In this study, steel hysteresis dampers whose stiffness is higher than existing coupling beam and whose strength is easy to change depending on design load was used in coupling beam. The steel hysteresis damper was proposed for the shape connected in double in series, from this, several static test were conducted to verify structural performance of the damper. FEM analysis was also performed, then design equation were suggested.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.29-36
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• 1987

In most of the structural members with initial cracks, the strength tends to decrease as the member size increases. This phenomenon is known as size effect. Among the structural materials of glass, metal or concrete, etc., concrete represents the size effect even without initial crack. According to the previous size effect law, the concrete member of very large size can resist little stress. Actually, however, even the large size member can resist some stress if there is no initial notch. This means that the fracture mechanism of very small or very large size member follows strength criterion, but the medium size member follows non-linear fracture mechanics (NLFM). In this study, the empirical models which are derived based on nonlinear fracture mechanics are proposed according to the regression analysis with the existing test data of large size specimens for uni-axial compression test, splitting tensile test and shear test of reinforced concrete beams.

• Journal of Korean Society of Steel Construction
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• v.17 no.5 s.78
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• pp.569-580
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• 2005

The postbeam joint connection of the existing steel structure moment flexible frame system did not produce sufficient seismic resistance during the earthquakes in Northridge and Kobe, and it sustained brittle fracturing on the joint connection. This study was performed to execute the high-tensile bolt share connection of H-beams web and the full-scale experiment as a parameter of the existing reinforcement of H-flange rib, by making the shape of the existing joint connection. This experiment was performed to determine the extent of the decrease of the number of high-tensile bolts and how to improve workability of the two-phase shear connection of web beam. In addition, this study was performed to enhance the seismic resistant capacity through the enforcement of rib plates. As a result of the experiment of two-phase shear connection of H-beam web and of joint connection to be reinforced by rib plates, the results of this study showed that the initial stiffness, energy-dissipation capacity, and rotational capacity of plasticity was higher than the existing joint connection. As to the rate of increasing the strength and deformation capacity, there were differences between the tension side and compression side because of the position of shear tap. However, as a whole, they have shown excellent seismic resistant capacity. Also, all the test subjects exceeded 4% (rate of delamination), about 0.029 rad (total plastic capacity), and about 130% (maximum strength of joint connection) of fully plastic moment for the original section. Accordingly, this study was considered as it would be available in the design more than the intermediate-level of moment flexible frame.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.79-89
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• 2008

In this study, a series of undrained cyclic triaxial tests were performed with three different consolidation stress ratios ($K_c$=1.0, 1.5, 2.0) to investigate the undrained shear strength characteristics of sands with respect to the amount of contained silt located around the basin of Nak-dong River. The test results show that the more the sand has silt, the lower is cyclic shear stress ratio (CSR) in all $K_c$ and that the higher $K_c$ goes, the larger CSR decreases due to the increase of contained silt. The excessive pore pressure caused during shearing has an influence on the decrease of CSR by the high initial pore pressure in proportion to the amount of contained silt regardless of the $K_c$ value. After consolidation, the analysis of the skeleton void ratio of the sample reveals that the main cause of the decrease of CSR as well as the increase of the initial excessive pore pressure is the increase of the skeleton void ratio in proportion to the amount of contained silt.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.285-298
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• 2003

Shear properies of geosynthetic/geosynthetic and geosynthetic/soil interfaces which are widely met in landfill sites were evaluated from the inclined board tests. The inclined board testing apparatus is known to reproduce the shear behavior on the low normal stress most accurately. In this study, the friction angle of each interface was estimated and the tensile force mobilized at the geosynthetic was measured as well. The test results showed that the friction angle of each interface and the tensile force of the geosynthetics depended on the amount of normal stress, the type of the geosynthetics used, and the combinations of geosynthetics and soils. In addition, the sand/geotextile/geomembrane interface system was simulated in this study, and it was observed that the tensile force developed at the geomembrane decreased due to the protection effect of the geotextile located above the geomembrane. The test results of this research was compared with those of direct shear tests published, too. Finally, by comparing the measured tensile force of the geosynthetics when the initial displacement of the box occurs, when the slope is called as the critical slope, with suggested analytic solution, the accuracy of analytic solution and the applicability to design were identified.