• Journal of Korean Society of Steel Construction
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• v.28 no.1
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• pp.1-12
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• 2016

An experimental study was conducted to evaluate the static shear strength of stirrup-reinforced cast-in anchors. The test parameters considered herein are an existence of front bearing bar and concrete crack. M36 anchor was used with an edge distance of 180mm. HD-10 bars were used for all reinforcing bars and the stirrups were placed with 100mm spacing. The shear resistance increased by 16% when the front bearing bar was installed. Meanwhile, the resistance reduced only 5% in the cracked concrete compared with the uncracked concrete. The test results showed that ACI 318 and ETAG 001 specifications could estimate the shear strength of stirrup-reinforced anchors conservatively and a rational method was proposed. A consideration on the fracture strength of stirrup-reinforced anchor is also given.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.628-631
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• 2010

환경문제에 대한 관심으로 자동차에 대한 경량화가 요구되는 동시에 안전규제가 강화 되고 있어, 높은 인장강도를 가지는 고강도 강의 차체 적용 비율이 점차 증가하고 있다. 또한, 자동차 1대를 조립하기 위한 저항 점용접 횟수를 줄이고, 용접부에 충격안정성을 확보하기 위한 관심이 고조되고 있다. 따라서, 국내 자동차 산업에서 용접부의 신뢰성을 보장하기 다양한 비파괴 검사를 적용하고 있으며, 생산 공정에 적용하고 있다. 그중에서 용접 전극 사이에서 동저항(Dynamic resistance, 용접 공정중모재의 저항값의 변화)을 계측하여 용접성을 평가하는 방법이 제시되고, 차체 조립공정 중에 적용하려는 시도가 이루어지고 있다. 본 연구에서는 자동차 차체용 냉간 압연강판(590MPa dual-phase steel)을 인버터 DC 저항 점 용접하여, 용접전극 사이에서 동저항을 측정 하였다. 용접성은 인장전단 강도로 평가하였고, 용접 공정 변수는 용접 전류, 용접 시간, 가압력을 선정하였다. 동저항 그래프의 ${\alpha}$-peak와 ${\beta}$-peak값을 인장전단 강도에 따라 회귀 분석하여, 동저항에 따른 인장전단 강도를 예측하였다. 추가적으로, 용접부의 외관 형상 중에 압흔 깊이와 압흔자국 지름에 대한 회귀분석을 실시하였으며, 용접부 형상에 대한 신뢰성을 부여하였다.

• Journal of Korean Society of Steel Construction
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• v.22 no.4
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• pp.389-398
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• 2010

The flexural strength of composite HSB I-girders under a positive moment was investigated using the moment-curvature analysis method to evaluate the applicability of the current AASHTO LRFD design specifications to such girders. A total of 2,391 composite I-girder sections that satisfied the section proportion limits of the AASHTO LRFD specifications was generated by the random sampling technique to consider a wide range of section properties. The flexural capacities of the sections were calculated inthe nonlinear moment-curvature analysis in which the HSB600 and HSB800 steels were modeled as an elasto-plastic strain-hardening material, and the concrete, as a CEB-FIP model. The effects of the ductility ratio and the compressive strength of the concrete slab on the flexural strength of the composite girders made of HSB and SM520-TMC steels were analyzed. The numerical results indicated that the current AASHTO LRFD equation can be used to calculate the flexural strength of composite girders made of HSB600 steel. In contrast, the current AASHTO LRFD equation was found to be non-conservative in its prediction of the flexural strength of composite HSB800 girders. Based on the numerical results of this study for 2,391 girders, a new design equation for the flexural strength of composite HSB800 girders in a positive moment was proposed.

• Journal of Korean Society of Steel Construction
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• v.23 no.3
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• pp.385-395
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• 2011

The flexural strength of composite HSB hybrid I-girders under positive moment is investigated by the moment-curvature analysis method to evaluate the applicability of the current AASHTO LRFD design specification to such girders. The hybrid girders are assumed to have the top flange and the web fabricated from HSB600 steel and the bottom flange made of HSB800 steel. More than 6,200-composite I-girder sections that satisfy the section proportion limits of AASHTOL RFD specifications are generatedby the random sampling technique to consider a statistically meaningful wide range of section properties. The flexural capacities of the sections are calculated by the nonlinear moment-curvature analysis in which the HSB600 and HSB800 steels are modeled as an elastoplastic, strain-hardening material and the concrete as CEB-FIP model. The effects of ductility ratio and compressive strength of concrete slab on the flexural strength of composite hybrid girders make of HSB steels are analyzed. Numerical results indicated that the current AASHTO-LRFD equation can be used to calculate the flexural strength of composite hybrid girders fabricated from HSB steel.

• Journal of the korean Society of Automotive Engineers
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• v.5 no.3
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• pp.24-32
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• 1983

전기 동저항 제어실험을 통해 다음과 같은 결론을 얻었다. (1) 점용접 과정에서 동 저항이 용접질(용접강도)을 잘 나타내 준다. 1) 동저항 곡선의 peak가 발생하는 시간이 이르면 일반적으로 늦게 나타난 것보다 용접질이 좋다. (단, expulsion이 발생하지 않을 때까지). 2) peak에서의 저항값과 용접시간 끝에서의 저항값 차이가 클수록 일반적으로 용접질이 좋다. (2) 한 동 저항곡선에 다른 동 저항곡선을 맞추려는 제어를 할 때는 다음과 같은 관계가 있다. 1) P-control로는 동저항을 추적하는 효과를 충분히 얻을 수 없고 적분제어기를 추가한 PI-control을 하면 잘 추적한다. 2) 용접질의 관점으로 볼 때 원하는 용접강도를 얻으려고 PI제어를 하면 그 용접 평균강도에 아주 근사한 강도를 얻을 수 있다.

• Journal of Korean Society of Steel Construction
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• v.19 no.2
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• pp.139-146
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• 2007

The objective of the present study is to provide statistical resistance statistics for steel-concrete composite plate girder sections under positive and negative moments. Statistical properties on yield strength, tensile strength, elongation, and fracture toughness of domestic structural steel products, gathered from an analysis of over 16,000 samples, were evaluated. Using the steel samples for the plate girder, the bias factor and the coefficient of variation of the ultimate flexural resistance for representative composite plate girder sections under positive and negative flexures were presented. In calculating the ultimate flexural resistance of the composite section, the moment curvature relationships were developed using the incremental load approach considering material nonlinearity for the steel girder. The predicted statistics can be used in the future for the efficient calibration of LRFD code.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.333-345
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• 2015

This study evaluated the static and dynamic shear strength of cast-in-place anchors reinforced with hairpin bars in uncracked and cracked concrete. The anchors 30mm in diameter reinforced with D10 hairpin bar were designed with an edge distance of 150mm and an embedment depth of 240mm. The cracked specimens consisted of the orthogonal and parallel cracks to the direction of shear loads, respectively. The dynamic strength was evaluated using seismic qualification tests based on the ACI 355.2 standard. The shear strength of the hairpin reinforced anchor was hardly correlated to the concrete cracks and the dynamic strength was similar to its static shear strength. Finally, a consideration on the design strength of hairpin reinforced anchors was presented.

• Journal of Korean Society of Steel Construction
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• v.26 no.1
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• pp.21-30
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• 2014

In this study, an experimental study was performed to evaluate the shear resistance of cast-in-place(CIP) anchors reinforced with hairpin and stirrup bars under static and dynamic loads. The reinforcement was developed using D6 bars, and the anchors were installed with 20mm diameter and 120mm edge distance. Three tests were conducted for each type of reinforced anchor under static and dynamic shear load with a pulsating frequency of 1 Hz, respectively. It was found that the strength of hairpin-reinforced anchor was affected by the concrete cover and the dynamic tests showed no capacity reduction of anchors compared with static tests. The stirrup-reinforced anchor showed little increase of resistance compared with unreinforced anchor and the resistance under dynamic loading showed nearly same strength by static loading.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.235-244
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• 2021

This study analyzes the applicability of limit state design method on bridge evaluation by considering the experiment of the existing bridge. The test strength of the member is obtained from the PSC beam bridge experiment. The test strength is compared with the calculated strength obtained from the statistical characteristics of material test strength and the two values are almost the same. The response modification factor and dynamic impact factor are obtained from the vehicle loading test. The rating factor is calculated by applying limit state design method as well as current evaluation method and the results are compared. The reliability index of the test bridge is calculated by using the statistical properties of the member strength obtained from material test and simulation. When the statistical properties of the PSC beam tested in this study are applied, the reliability index with a larger value was obtained than the reliability index obtained with the statistical properties of the design code.

• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.53-63
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• 2008

In this study, the cone tip resistances of cemented sand are measured by performing a series of miniature cone penetration tests in large calibration chamber, and the relations with constrained modulus, unconfined compressive strength, and shear strength of cemented sand are suggested. Experimental results show that both the cone tip resistance and constrained modulus of sand increase with increasing cementation effect as well as relative density and confining stress. However, it is observed that the relative density and confining stress have more significant influence on cone tip resistance than constrained modulus of cemented sand. Since the cone penetration into the ground induces the damage of cementation, the cone tip resistance can't properly reflect the cementation effect of sand. An analysis based on the constrained modulus shows that the measured cone tip resistance underestimates the deformation modulus of cemented sand by about $70{\sim}85%$. In addition, this study establishes various relationships among the above soil properties from the regression analysis.