• Journal of Korean Society of Steel Construction
• /
• v.20 no.5
• /
• pp.617-624
• /
• 2008

Well-designed steel moment connections will undergo local buckling before they exhaust their available rotation capacity, and inelastic post-buckling deformation plays a major role in defining the connection rotation capacity. An approximate analytical method to model strength degradation and failure of beam plastic hinges due to local buckling and estimation of the seismic rotation capacity of fully restrained beam-column connections in special steel moment-resisting frames under both monotonic and cyclic loading conditions is proposed in this study. This method is based on the plastic mechanism and a yield line plastic hinge (YLPH) model whose geometry is determined using the shapes of the buckled plastic hinges observed in experiments. The proposed YLPH model was developed for the improved WUF-W and RBS connections and validated in comparison with experimental data. The effects of the beam section geometric parameters on the rotation capacity were discussed in the companion paper (parametric studies).

• Magazine of the Korea Concrete Institute
• /
• v.7 no.1
• /
• pp.145-155
• /
• 1995

The purpose of this paper is to present an analysis method which can exactly analyze load-deflection relationships. crack propagations and stresses and strains of steel reinforccnlent and concrete in hehaviors of elastic, mclastic and ultlmate ranges of reinforced concretc beams under monotonically increasing loads. For these purposes, the material nonlinearities are taken into account by comprising the tension. compression and shear models of cracked concrete and a model for reinforcement in the concrete. Smeared crack model is used as a modeling of concrete. The steel reinforcement is assumed to be in an uniaxial stress state and modeled srncaretl layers of eqivalent thickness and line elernents for correct positiori arid behavior. For the verification of application and validity of the method proposed in this paper, several numerical examples are analyzed and compared with those from other researchers. As a results, this method shown in 3.5-15(%) error is correct.

• Magazine of the Korea Concrete Institute
• /
• v.8 no.6
• /
• pp.223-234
• /
• 1996

The purpose of this paper is to present an analysis method by using the finite element method which can exactly analyze load-deflection relationships, crack propagations. and stresses and strains of reinforcements, tendons, and concrete in behaviors of elastic. inelastic and ultimate ranges of reinforced and prestressed concrete slabs under monotonically increasing loads. For t h i s purpose, the m a t e r i a l and geometric nonlinearities are taken into account in this study. The total Lagrangian formulation based upon the simplified Von Karman strain expressions is used to take into account the geometric nonlinearities of the structure. The material nonlinearities are taken into account by comprising the tension, compression. and shear models of cracked concrete and models for reinforcements and tendons in the concrete : and also a so-called smeared crack model is incorporated. The reinforcements and t,endons are assumed to be in a uniaxial stress state and are modelled as smeared layers of equivalent thickness. For the verification of application and validity of the method proposed in this paper, several numerical examples are analyzcd and compared with experimental results. As a result, this method can successfully predict the nonlinear and inelastic behaviors throughout the fracture of reinforced and prestressed concrete slabs.

• Journal of the Korea Concrete Institute
• /
• v.15 no.1
• /
• pp.17-24
• /
• 2003

One of the reasons for brittle failure in reinforced concrete structures subjected to severe earthquake is due to large local bond-slippage of bars resulting in fast bond degradation between reinforcing bars and concrete. This study aims to evaluate effects of bar deformation height on bond performance, specially, bond degradation under cyclic loading. Bond test specimens were constructed with machined bars with high relative rib areas. The degree of confinement by transverse bars is also another key parameters in this bond test. From test results, amounts of energy dissipation are calculated and compared for each parameter. Test results show that bond strength and stiffness drops significantly as cycles increases. The confinement and high relative rib area are effective to delay bond degradation, as the reduction of bond strength of cyclic loading compared to monotonic loading decreased for bars with large confinement and high relative rib areas. The energy dissipation also increases as the degree of confinement and relative rib area increases. However, tested bars with very high rib areas show that the bond may be damaged at relatively small slip because of high stiffness. The study will help to understand the bond degradation mechanism due to bar deformation height under cyclic loading and be useful to develop new deformed bars with high relative rib areas.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.13-13
• /
• 2009

현재 열간단조 금형을 제작함에 있어 육성용접을 실시하는 방법이 금형강 STD61, STD11 등으로 제작하는 방법에 비해 보수나 비용적인 측면에서 이점을 가지고 있기 때문에 점차적으로 증가하고 있는 추세이다. 열간단조 공정에서 금형은 $1000^{\circ}C$이상의 고온재료와 반복접촉하게 된다. 이때 이형제의 사용은 급속냉각 및 급속가열의 열피로를 가속시킨다. 또한, 금형은 반복충격에 의한 기계적 피로를 받게 된다. 이러한 금형의 사용환경을 고려한 FCW는 종래 고가의 $2.8{\sim}3.2{\Phi}$인 외국산 FCW를 사용하였으나 이를 대체한 $3.2{\Phi}$ 태경 FCW가 국내에서 개발되었다. 하지만 개발된 FCW를 사용하여 제작된 금형의 수명이 부족한 현상이 발생하였다. 이에 금형의 수명을 연장시킬 수 있는 내균열성 및 내열충격성을 확보한 태경 FCW의 개발과 개발된 FCW의 성능평가가 요구되었다. 특히 열간단조 금형에 있어서 중요한 내열충격성의 경우 가열과 냉각의 반복 Cycle에 의한 Thermal shock의 평가가 대부분이며 높은 Cycle로 인해 많은 시간이 걸리며, 또한 가열과 냉각을 오갈 수 있는 고가의 시험장치가 요구된다. 그러므로 개발된 FCW 육성용접부의 내균열성 및 내열충격성을 평가할 수 있는 방법에 대한 연구와 특히 내열충격성을 시간이 적게 걸리면서도 경제적으로 평가할 수 있는 방법에 대한 연구가 필요하다. 본 연구의 목적은 열간단조 금형 육성용접부의 내균열성 및 열충격특성을 평가할 수 있는 방법에 대한 검토와 특히 내열충격성에 대해 J.W.Kim등의 시험방법을 참고하여 시간이 적게 걸리면서 저 비용으로 열 충격특성을 평가할 수 있는 시험법을 고안하는 것이다. 이를 위한 방법으로 육성용접부의 내균열성을 평가하기 위한 상온 Bending을 실시하였고, 내열충격성을 평가하기 위한 염욕로를 이용하는 고온 Bending을 고안하여 실시하였다. 상온 Bending, 고온 Bending 모두 3점 굽힘시험을 적용하였다. 고온 Bending의 가열방법으로는 염욕로를 사용하여 시편이 대기중에서 약 $850^{\circ}C$의 온도가 될 수 있도록 하였다. 시편은 각각 열처리를 하여 요구 경도를 확보하였고, 이를 염욕로에서 5분간 가열 및 유지하여 취출 후 굽힘하중을 가하여 변위의 정도로 열충격을 평가하는 방법을 사용하였다. 상온 Bending은 극한변형량과 파단부 극한응력으로, 고온 Bending은 고온 극한변형량으로 평가를 하였고, 외국산 FCW를 사용한 육성용접부를 비교대상으로 하였다. 평가 결과 개발된 국산 $3.2{\Phi}$ 태경 FCW의 성능은 외국산 FCW와 유사하거나 우수한 것으로 평가되었고, 실제 금형을 제작하여 현장에 적용한 결과 금형의 수명이 연장된 것이 나타났다.

• Proceeding of KASS Symposium
• /
• 2005.05a
• /
• pp.183-190
• /
• 2005

The purpose of this study is to investigate experimentally the shear resisting behavior of the reinforced concrete beams strengthened with reinforcement materials(CFRP). Five specimens were manufactured and tested under, static monotonic loading. The main variables In the test were a space and volume of reinforcement. The test result indicated that the method of CFRP increase significantly the shear strength of a reinforced concrete beam

• Magazine of the Korea Concrete Institute
• /
• v.4 no.1
• /
• pp.119-126
• /
• 1992

AC] 318-H9 Recommended that when the specified compressive strength of concrete in a column is greater than 1. 4 times that specified for a floor system, top surface of the colurrm concrete shall extend 2ftU;OOrrun) into the slab from the face of colUlml to avoid unexpected brittle failure. The purpose of this investigation is to suggest the basic information for the structural safety, The major variables are com preSSlve strength of concrete, shear confinement ratio, and loading types. The test results showed that the load capaCIty of speCImen subjected to monotOI1lC loading had more than that of specimen subjected to one way cyclic loading. The failure modes of specimens under cyclic loading were concentrated at 5-20cm apart region from beam-column joint face and ductility index are increased with increasing of shear confinement ratio. Keywords: ACI 318-89, High and Low Strength Concrete, Beam-Column Joint, Shear Confinement Ratio, Loading Type, Ductility Index, Extension Distance.

• Journal of Korean Society of Steel Construction
• /
• v.20 no.5
• /
• pp.625-632
• /
• 2008

In the companion paper (Model Development), an analytical model estimating the available rotation capacity of fully restrained beam-column connections in special steel moment-resisting frames was proposed. In this paper, two limit states were considered as the connection rotation capacity criteria: (i) strength degradation failure when the strength falls below the nominal plastic strength due to the local buckling of the beam's cross-section and (ii) low-cycle fatigue fracture caused by plastic strain accumulation at the buckled flange after only a few cycles of high-amplitude deformation. A series of analyses are conducted using the proposed model with two limit states under monotonic and cyclic loadings. Beam section geometric parameters, such as flange and web slenderness ratios, varied over the practical ranges of H-shapedbeams to observe their effect on the rotation capacity and low-cycle fatigue life of pre-qualified WUF-W connections.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.11 no.1
• /
• pp.79-87
• /
• 1991

An efficient numerical procedure for material and geometric nonlinear analysis of reinforced concrete shells under monotonically increasing loads through their elastic, inelastic and ultimate load ranges is developed by using the finite element method. The 8-node Serendipity isoparametric element developed by the degeneration approach including the transverse shear deformation is used. A layered approach is used to represent the steel reinforcement and to discretize the concrete behavior through the thickness. The total Lagrangian formulation based upon the simplified Von Karman strain expressions is used to take into account the geometric nonlinearity of the structure. The material nonlinearities are taken into account by comprising the tension, compression, and shear models of cracked concrete and a model for reinforcement in the concrete; and also a so-called smeared crack model is incorporated. The steel reinforcement is assumed to be in a uniaxial stress state and is modelled as a smeared layer of equivalent thickness. This method will be verified a useful tool to account for geometric and material nonlinearities in detailed analysis of reinforced concrete concrete shells of general form through numerical examples of the sequential paper( ).

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.9 no.4
• /
• pp.187-194
• /
• 2005

The purpose of this study is to investigate experimentally the shear resisting behavior of the reinforced concrete beams strengthened with reinforcement materials. Seven specimens were manufactured and tested under static monotonic loading. The main variables in the test were the method and direction of reinforcement. This research is about the experiment of shear capacity of reinforced concrete beams strengthened with CFRP-rod, in the filling-up method. The test result indicated that the method of CFRP increase significantly the ultimate shear strength of a reinforced concrete beam.