• Steel and Composite Structures
• /
• 제21권5호
• /
• pp.1017-1029
• /
• 2016

When a welded circular hollow section (CHS) tubular joint is subjected to brace axial loading, failure position is located usually at the weld toe on the chord surface due to the weak flexural stiffness of the thin-walled chord. The failure mode is local yielding or buckling in most cases for a tubular joint subjected to axial load at the brace end. Especially when a cyclic axial load is applied, fracture failure at the weld toe may occur because both high stress concentration and welding residual stress along the brace/chord intersection cause the material in this region to become brittle. To improve the ductility as well as to increase the static strength, a tubular joint can be reinforced by increasing the chord thickness locally near the brace/chord intersection. Both experimental investigation and finite element analysis have been carried out to study the hysteretic behaviour of the reinforced tubular joint. In the experimental study, the hysteretic performance of two full-scale circular tubular T-joints subjected to cyclic load in the axial direction of the brace was investigated. The two specimens include a reinforced specimen by increasing the wall thickness of the chord locally at the brace/chord intersection and a corresponding un-reinforced specimen. The hysteretic loops are obtained from the measured load-displacement curves. Based on the hysteretic curves, it is found that the reinforced specimen is more ductile than the un-reinforced one because no fracture failure is observed after experiencing similar loading cycles. The area enclosed by the hysteretic curves of the reinforced specimen is much bigger, which shows that more energy can be dissipated by the reinforced specimen to indicate the advantage of the reinforcing method in resisting seismic action. Additionally, finite element analysis is carried out to study the effect of the thickness and the length of the reinforced chord segment on the hysteretic behaviour of CHS tubular T-joints. The optimized reinforcing method is recommended for design purposes.

• 대한기계학회논문집A
• /
• 제37권6호
• /
• pp.775-782
• /
• 2013

본 연구에서는 마찰교반용접재의 피로균열전파 거동의 공간적 불규칙성을 고찰하기 위한 연구의 일환으로써, 최적의 조건에서 마찰교반용접된 7075-T651 알루미늄 합금 용접부의 LT-방향의 각각 5개의 피로균열전파 시험편에 대하여 일정 응력확대계수범위 제어하의 피로균열전파 실험을 수행하여 마찰교반용접부의 교반용접부재(WM)와 열영향부재(HAZ) 그리고 모재(BM)에 대한 피로균열전파 거동을 실험적으로 고찰하였다. WM재의 피로균열전파율이 가장 빠르게 나타났으며, 그 다음 HAZ재와 WM재 순으로 나타났다. 게다가 시험편간 피로균열전파율의 변동성은 WM시험편에서 가장 높았고, 반면 BM재에서 가장 낮게 나타났다.

• Earthquakes and Structures
• /
• 제4권4호
• /
• pp.429-449
• /
• 2013

Current Design Codes for Reinforced Concrete (RC) interior beam-column joints are based on limited experimental studies on the seismic behavior of eccentric joints. To supplement existing information, an experimental study was conducted that focused on the effect of eccentricity of the deeper beams with respect to the shallow beams. A total of eight one-third scale interior joints with beams of different depths were subjected to reverse cyclic loading. The primary variables in the test specimens were the amount of joint transverse reinforcement and the cross section of the shallow beams. The overall performance of each test assembly was found to be unsatisfactory in terms of joint shear strength, stiffness, energy dissipation and shear deformation. The results indicated that the vertical eccentricity of spandrel beams in this type of joint led to lower capacity in joint shear strength and severe damage of concrete in the joint core. Increasing the joint shear reinforcement was not effective to alter the failure mode from joint shear failure to beam yielding which is favorable for earthquake resistance design, whereas it was effective to reduce the crack width at the small loading stages. Based on the observed behavior, the shear stress of the joint core was suggested to be kept as low as possible for a safe and practical design of this type of joint.

• 제어로봇시스템학회논문지
• /
• 제11권1호
• /
• pp.77-83
• /
• 2005

This paper deals with determination of motions of a humanoid robot using genetic algorithm. A humanoid robot has some problems of the structural instability basically. So, we have to consider the stable walking gait in gait planning. Besides, it is important to make the smoothly optimal gait for saving the electric power. A mobile robot has a battery to move autonomously. But a humanoid robot needs more electric power in order to drive many joints. So, if movements of walking joints don't maintain optimally, it is difficult for a robot to have working time for a long time. Also, if a gait trajectory doesn't have optimal state, the expected life span of joints tends to be decreased. To solve these problems, the genetic algorithm is employed to guarantee the optimal gait trajectory. The fitness functions in a genetic algorithm are introduced to find out optimal trajectory, which enables the robot to have the less reduced jerk of joints and get smooth movement. With these all process accomplished by a PC-based program, the optimal solution could be obtained from the simulation. In addition, we discuss the design consideration for the joint motion and distributed computation of the humanoid, ISHURO, and suggest its result such as the structure of the network and a disturbance observer.

• Steel and Composite Structures
• /
• 제23권1호
• /
• pp.17-29
• /
• 2017

The seismic performance of steel beam to concrete-encased composite column with unsymmetrical steel section joints is investigated and reported within this paper. Experimental and analytical evaluation were conducted on a total of 8 specimens with T-shaped and L-shaped steel section under lateral cyclic loading and axial compression. The test parameters included concrete strength, stirrup ratio and axial compression ratio. The response of the specimens was presented in terms of their hysterisis loop behavior, stress distribution, joint shear strength, and performance degradation. The experiment indicated good structural behavior and good seismic performance. In addition, a three-dimensional nonlinear finite-element analysis simulating was conducted to simulate their seismic behaviors. The finite-element analysis incorporated both bond-slip relationship and crack interface interaction between steel and concrete. The results were also compared with the test data, and the analytical prediction of joint shear strength was satisfactory for both joints with T-shaped and L-shaped steel section columns. The steel beam to concrete-encased composite column with unsymmetrical steel section joints can develop stable hysteretic response and large energy absorption capacity by providing enough stirrups and decreased spacing of transverse ties in column.

• Earthquakes and Structures
• /
• 제11권4호
• /
• pp.665-680
• /
• 2016

This paper focuses on the study of seismic behavior of steel reinforced concrete special-shaped column-beam joints. Six specimens, which are designed according to the principle of strong-member and weak-joint core, are tested under low cyclic reversed load. Key parameters include the steel form in column section and the ratio of column limb height to thickness. The failure mode, load-displacement curves, ductility, stiffness degradations, energy dissipation capacity and shear deformation of joint core of the test subassemblies are analyzed. The results indicate that SRC special-shaped column-beam joints have good seismic behavior. All specimens failed due to the shear failure of the joint core, and the failure degree between the two sides of joint core is similar for the exterior joint but different for the corner joint. Compared to the joints with channel steel truss, the joints with solid web steel skeleton illustrate better ductility and energy dissipation capacity, but the loading capacity and stiffness are roughly close. With the increasing of the ratio of column limb height to thickness, the joints illustrate higher loading capacity and stiffness, better energy dissipation capacity, but worse ductility.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1998년도 가을 학술발표회 논문집
• /
• pp.43-50
• /
• 1998

The current design equations for ultimate strength of tubular joints are based on a limited number of experimental results performed on simple joints with simple loading conditions and depend on value of the branch to the chord diameter- ratio $\beta$ too much. Therefore, the purpose of this study is to estimate the ultimate strength of CHS tilbular joints considering the effects of branch inclination angles $\theta$, chord length to diametel ratio $\alpha$ and chord end conditions by finite element analysis. The analyses are performed using finite element software ADINA that is capable of modeling elasto-plastic material behavior as well as geometric nonlinearities. The results show that the current use of sin $\theta$ in normalized design equations for inclined branches is reasonable, but somewhat conservative. When compared with the previous experimental database, the close numerical results are obtained from the parametric studies on the static strength of T-, Y-, DT- and X-joints. Also, a new design equation for ultimate stregth of CHS tubular joints is derived using a modified version of the ring model which can include the effects of $\alpha$ and chord end condtion.

• Structural Engineering and Mechanics
• /
• 제89권1호
• /
• pp.61-75
• /
• 2024

Strengthening of hollow structural sections using through-bolts is a cost-effective and straightforward approach. It's a versatile method that can be applied during both design and service phases, serving as a non-disruptive and budget-friendly retrofitting solution. Existing research on axially loaded hollow sections T-joints has demonstrated that this technique can amplify the joint strength by 50%, where single bolt could enhance the strength of the joint by 35%. However, there's a gap in understanding their use for K-joints. As the behavior of K-joints is more complex, and they are widely existent in structures, this study aims to bridge that gap by conducting comprehensive parametric study using finite element analysis. Numerical investigation was conducted to evaluate the effect of through bolts on K-joints focusing on using single through bolt to achieve most of the strengthening effect. A full-scale parametric model was developed to investigate the effect of various geometric parameters of the joint. This study concluded the existence of optimal bolt location to achieve the highest strength gain for the joint. Moreover, a rigorous statistical analysis was conducted on the data to propose design equations to predict optimal bolt location and the corresponding strength gain implementing the verified by finite element models.

• 한국강구조학회 논문집
• /
• 제21권5호
• /
• pp.451-459
• /
• 2009

본 논문은 냉간성형 각형강관 T형 접합부의 면내 휨모멘트를 평가하는데 목적이 있다. 이전 연구로부터, 주관 폭에 대한 지관 폭의 비가 0.71이하인 T형 접합부는 뚜렷한 최대 휨강도를 나타내지 못하는 접합부의 파괴모드는 주관 플랜지의 휨파괴이다. Zhao에 의해 수행된 실험을 포함한 결과로부터 주관 폭두께비는 ${16.7{\leq}2{\gamma}(=B/T){\leq}33}$이고, 주관 폭에 대한 지관 폭의 비인 폭비는 ${0.34{\leq}{\beta}(=b_{1}/B){\leq}0.71}$의 범위인 냉간성형 각형강관 T형 접합부에 대한 최대 휨강도 정의를 위한 변형제한치는 주관폭(B)의 1% 변형이며, 최대 휨강도는 1.5M1%B로 정의할 수 있다. 기본형에 대한 항복선 모델과 기존 연구자들에 의해 수정 제안된 항복선 모델식을 검토하여 실험결과와 비교한 결과, Zhao의 제안식이 가장 좋은 대응도와 분포도를 보였다. 따라서, 각형강관 T형 접합부에 대한 면내 설계 휨강도식으로 Zhao가 수정 제안한 항복선 모델식을 적용하는 것이 가장 합리적인 것으로 생각된다.

• 대한기계학회논문집A
• /
• 제37권9호
• /
• pp.1109-1116
• /
• 2013

본 연구의 목적은 마찰교반용접된 7075-T651 알루미늄 합금 용접부에 대한 피로균열전파율의 공간적 불규칙성을 고찰하기 위한 것이다. 본 연구에서는 이전의 피로균열전파 실험 데이터를 활용하였다. 피로균열전파율의 공간적 불규칙성을 명확히 이해하기 위하여, 피로균열전파 실험은 일정 응력확대 계수범위 제어하에서 수행되었다. 재질, 즉 마찰교반용접된 7075-T651 알루미늄 합금 용접부의 용접재와 모재에 대하여 피로균열전파율의 공간적 불규칙성을 조사하기 위하여 실험 데이터가 해석되었다. 결론적으로 용접재의 변동성이 모재의 변동성보다 높게 나타났으며, Weibull 통계 해석에 의하여 변동성을 평가할 수 있음을 알았다.