• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.6
• /
• pp.731-738
• /
• 2013

This paper describes a fault-tolerant driving control strategy for an independent steer-by-wire system in sixwheel-drive/six-wheel-steering vehicles. An algorithm has been designed to realize vehicle maneuverability that is as close as possible to that of non-faulty vehicles by inducing high slip ratio of the wheel through a faulty steer-by-wire system in order to reduce the lateral tire force, which is resistant to the yaw motion. Considering the transition of the longitudinal tire force of a wheel with a faulty steer-by-wire component, the longitudinal tire forces are optimally distributed to the other wheels. Fault-tolerant driving performance has been investigated via computer simulations. Simulation studies show that the proposed algorithm can significantly improve the maneuverability of a vehicle with a faulty steer-by-wire system as compared to the optimal traction distribution method.

• The Journal of Korea Robotics Society
• /
• v.10 no.4
• /
• pp.186-192
• /
• 2015

This paper proposes a robust balance and driving control for omni-directional ball robot(generally called ball-bot) with two axis mecanum wheel. Slip between ball and mecanum wheel actuator inevitably occurs along diagonal axis due to its instantaneous strong torque. In order to reduce and saturate slip, exact distance calculation scheme especially for rotational movement is essential. So this research solved Euler-Lagrange dynamics for proposed two axis ball robot based on practical mechanical modeling. Robust balance control was carried out by PID controller according to the pitch and roll angles of ball robot by using sensor fusion between AHRS and wheel encoder. Proposed PID controller enhances stability by reducing steady state error and settling time. Proposed slip control algorithm for omni-directional ball robot has been demonstrated by experiments for balance control and arbitrary driving control.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.12 no.2
• /
• pp.131-138
• /
• 2008

Fiber-reinforced polymer (FRP) sheets have been successfully used to retrofit a number of existing concrete buildings and structures because of their excellent properties (high strength, light weight and high durability). Bond characteristics between FRP sheets and concrete should be investigated to ensure an effective retrofitting system. RC structures strengthened with FRP sheets are often subjected to cyclic load (traffic, seismic, temperature, etc.). This research addresses a local bond stress-slip relationship under cyclic loading conditions for the FRP-concrete interface. 18 specimens were prepared with three types of FRP sheets (aramid, carbon, and polyacetal) and two types of sheet layer(one or two). The characteristics of bond stress-slip were verified through experimental results on load-displacement relationship.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.13 no.2
• /
• pp.245-256
• /
• 2000

A moment-curvature relationship to simulate the behavior of reinforced concrete beam under cyclic loading is introduced. Unlike previous moment-curvature models and the layered section approach, the proposed model takes into consideration the bond-slip effect by using monotonic moment-curvature relationship constructed on the basis of the bond-slip relation and corresponding equilibrium equation at each nodal point. In addition, the use of curved unloading and reloading branches inferred from the stress-strain relation of steel gives more exact numerical result. The advantages of the proposed model, comparing to layered section approach, may be on the reduction in calculation time and memory space in case of its application to large structures. The modification of the moment-curvature relation to reflect the fixed-end rotation and pinching effect is also introduced. Finally, correlation studies between analytical results and experimental studies are conducted to establish the validity of the proposed model.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.4A
• /
• pp.267-279
• /
• 2009

A numerical model that can simulate the nonlinear behavior of ultra high strength fiber reinforced concrete (UHSFRC) structures subjected to monotonic loading is introduced. The material properties of UHSFRC, such as compressive and tensile strength or elastic modulus, are different from normal strength reinforced concrete. The uniaxial compressive stress-strain relationship of UHSFRC is designed on the basis of experimental result, and the equivalent uniaxial stress-strain relationship is introduced for proper estimation of UHSFRC structures. The steel is uniformly distributed over the concrete matrix with particular orientation angle. In advance, this paper introduces a numerical model that can simulate the tension-stiffening behavior of tension part of the axial member on the basis of the bond-slip relationship. The reaction of steel fiber is considered for the numerical model after cracks of the concrete matrix with steel fibers are formed. Finally, the introduced numerical model is validated by comparison with test results for idealized UHSFRC beams.

• Journal of the Korea Concrete Institute
• /
• v.21 no.6
• /
• pp.773-780
• /
• 2009

Experiments on steel-concrete interface are performed to investigate and determine the mechanical roles and properties of interface parameters. The intrinsic different nature of bonded and unbonded interfaces are addressed based on the experimental observations that were obtained from two types of tests considering bonded and unbonded interfaces. The unbonded tests are performed for the specimens that are in unbonded when the initially bonded specimens are tested first. Four cases of lateral confinements including pure slip, and low and medium levels of lateral pressure are taken into account to investigate the effects of lateral confinements on interface behavior. It is shown that the maximum shear strengths, the levels of residual strengths and the Mode II fracture energy release rates are linearly related to the confinement levels. Based on the experimental evidences obtained from this study, the values of interface parameters required in a steel-concrete interface constitutive model will be presented in the companion paper.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1994.04a
• /
• pp.181-188
• /
• 1994

Generally, the structural material shows rate dependent behaviors, which require to constitute different strain-stress relations according to strain rates. Conventional rate- independent constitutive equations used in general purpose finite analysis programs are inadequate for dynamic finite strain problems. In this paper, a rate dependent constitutive equation for elastic-plastic material was developed. The plastic stretch rate was modeled based on slip model with dislocation velocity and density so that there is no yielding condition, and no loading conditions. Non-linear hardening rule was also introduced for finite strain. Material constants of present constitutive equation were determined by experimental data of mild steel. The constitutive equation was applied to uniaxile tension. It was appeared that the present constitutive equation well simulates rate dependent behaviors of mild steel.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.1390-1393
• /
• 2005

The hardening model based on the dislocation mechanics is employed to study the experimentally observed high tensile elongations of NiAl along the [110] orientation at intermediate temperatures. In the hardening model proposed, a mobility of dislocation is assumed to be restricted to glide through the slip plane by forest dislocation and thermally activated cross-slip event. Overall deformation behavior of NiAl was greatly influenced by temperature-dependent dislocation mobility that both experimental and simulated yield stresses decreased as temperature increased. The results of simulation showed anomalous hardening behaviors analogous to those of experiment at certain circumstances. This behavior occurred due to the hardening contributions generated by cross-slip events that disable the dislocation motion in the primary slip systems. By comparing simulation results with experiments, it is confirmed that the proposed hardening model can represent anomalous tensile elongations due to the hardening by forest dislocations and cross-slip events.

• Journal of the Korean Geotechnical Society
• /
• v.17 no.2
• /
• pp.123-134
• /
• 2001

본 연구에서는 화강풍화토 지반상 unpropped diaphragm wall의 거동을 연구하기 위하여 벽체의 근입깊이와 지하수위 조건을 변화시키면서 원심모형실험을 수행하였다. 원심모형실험시 diaphragm wall은 두께 8mm인 알루미늄합금을 사용하였으며, 지반굴착을 재현하기 위하여 zinc chloride 기법을 이용하였다. 수치해석은 대부분의 지반공학문제에 적용할 수 있는 SAGE CRISP 프로그램을 이용하였다. 수치해석에서 모형지반은 수정 Cam-Clay 모델, diaphragm wall은 탄성모델, 지반과 diaphragm wall 사이의 경계면요소는 슬립모델을 사용하여 2차원 평면변형률 조건으로 해석을 수행하였다. 모형실험 결과 파괴면의 직선적인 형태로 파괴면내의 배면측 지반은 벽체를 향하여 하향의 변위를 일으키면서 벽체의 회전에 의해 파괴되었다. 실험 및 유한요소해석 결과 지반의 최대침하량과 최대침하량이 발생하는 위치는 잘 일치하였으며, 깊이에 따른 벽체변위는 선형적인 관계를 나타내었다. 또한, 최대 휨모멘트와 근입깊이로 정규화한 최대 휨모멘트 발생위치($h_{Mmax}$/d=0.4)는 잘 일치하였다.

• Journal of the Korea Concrete Institute
• /
• v.26 no.2
• /
• pp.109-116
• /
• 2014

The flexural behavior test of UHPC segmental box girder which has 160 MPa compressive strength and 15.4 m length was carried out. The effect of steel fibers in combination with reinforcing bars on improving the ductile performance of UHPC box girder was evaluated by comparing the flexural behavior of the UHPC segmental box girders made by the two kinds of mixing portion. The test variables are volume fraction of steel fibers and the arrangement of reinforcing bars. The behavior of UHPC box girder BF2 composed of 1% volume fraction of steel fibers and longitudinal reinforcing bars in web and upper flange with stirrup showed the similar ductile behavior with the girder BF1 composed of 2% volume fraction without stirrup in elastic stress region. But BF1 had the better stiffness and showed the more ductile behavior in inelastic stress region. Segmental interfaces of UHPC box girder have not any crack and slide until the final flexural collapse load.