Byoung-Wook Moon

Real-Time Hybrid Testing of a Steel-Structure Equipped With Large-Scale Magneto-Rheological Dampers Applying Semi-Active Control Algorithms

This study introduces the quantitative evaluation of the seismic performance of a building structure equipped with MR dampers by using real-time hybrid testing method (RT-HYTEM). A real-scaled 5-story building is used as the numerical substructure, and MR dampers corresponding to an experimental substructure is physically tested by using UTM. First, the force required to drive the displacement of the story, at which the MR damper is located, is measured from the load cell attached to UTM. Then, the measured force is returned to a control computer to calculate the response of the numerical substructure. Finally, the experimental substructure is excited by UTM with the calculated response of the numerical substructure. The RT-HYTEM implemented in this study is validated for that the real-time hybrid testing results obtained by application of sinusoidal and earthquake excitations and the corresponding analytical results obtained by using the Bouc-Wen model as the control force of the MR damper respect to input currents were in good agreement. Furthermore, semi-active control algorithms were applied to the MR damper. The comparison results of experimental and numerical responses demonstrated that using RT-HYTEM was more reasonable in semi-active devices such as MR dampers having strong nonlinearity.Copyright

Experimental Study on the Energy Dissipation Capacity of a Plane Transmission Tower Substructure With Friction-Type Reinforcing Members

Friction-type reinforcing members (FRMs) developed for the purpose of enhancing the wind-resistant performance of transmission towers are tested experimentally. The FRMs, in the middle of which slotted bolted connections (SBCs) are installed, are placed on the outside of tower legs, and provide additional damping and stiffness to the tower structure under bending deformations. First, the SBCs used in the FRMs are tested for various frictional sliding interface conditions. Second, the FRMs are installed on a 1/2 scale plane tower substructure and cyclic loading tests are conducted. Energy dissipation capacity and effects from local deformations of the FRMs and joint slips are investigated. From the test results, remarkable energy dissipation capacity, reaching to the 2.4 times of that before the installation of the FRMs, is observed. However, the local deformation of the SBC and joint slip should be prevented for more reliable design of the FRMs.

Equivalent Damping Ratio Based on Earthquake Characteristics of a SDOF Structure with an MR Damper

Seismic control performance of MR dampers, which have severe nonlinearity, varies with respect to the dynamic characteristics of an earthquake such as magnitude, frequency and duration. In this study, the effects of excitation characteristics on the equivalent linear system of a building structure with the MR damper are investigated through numerical analysis for artificial ground motions generated from different response spectrums. The equivalent damping ratio of the structure with the MR damper is calculated using Newmark and Hall`s equations for ground motion amplification factors. It is found that the equivalent damping ratio of the structure with the MR damper is dependent on the ratio of the maximum friction force of the MR damper over excitation magnitude. Frequency contents of the earthquake ground motion affects the equivalent damping ratio of long-period structures considerably. Also, additional damping effect caused by interaction between the viscousity and friction of the MR damper is observed. Finally. response reduction factors for equivalent linear systems are proposed in order to improve accuracy in the prediction of the actual nonlinear response.

Control Performance of Friction Dampers Using Flexural Behavior of RC Shear Wall System

High-rise apartments of shear wall system are governed by flexural behavior like a cantilever beam. Installation of the damper-brace system in a structure governed by flexural behavior is not suitable. Because of relatively high lateral stiffness of the shear wall, a load is not concentrate on the brace and the brace cannot perform a role as a damping device. In this paper, a friction damper applying flexibility of shear wall is proposed in order to reduce the deformation of a structure. To evaluate performance of the proposed friction damper, nonlinear time history analysis is executed by SeismoStruct analysis program and MVLEM(multi vertical linear element model) be used for simulating flexural behavior of the shear wall. It is found that control performance of the proposed friction damper is superior to one of a coupled wall with rigid beam. In conclusion, this study verified that the optimal control performance of the proposed friction damper is equal to 45 % of the maximum shear force inducing in middle-floor beam with rigid beam.

Energy Dissipation Capacity of Friction-Type Reinforcing Members Installed at a Transmission Tower

Friction-type reinforcing members (FRMs) developed for the purpose of enhancing the wind-resistant performance of transmission towers are tested experimentally. The FRMs, in the middle of which slotted bolted connections (SBCs) are installed, are placed on the outside of tower legs, and provide additional damping and stiffness to the tower structure under bending deformations. Firstly, the SBCs used in the FRMs are tested for various frictional sliding interface conditions. Secondly, the FRMs are installed on a 1/2 scale plane tower substructure and cyclic loading tests are conducted. Energy dissipation capacity and effects from local deformations of the FRMs and joint slips are investigated. From the test results, remarkable energy dissipation capacity, reaching to the 2.4 times of that before the installation of the FRMs, is observed. However, the local deformation of the SBC and joint slip should be prevented for more reliable design of the FRMs.Copyright

Experimental Investigation on the Energy Dissipation of Friction-type Reinforcing Members Installed in a Transmission Tower for Wind Response Reduction

Friction-type reinforcing members(FRM) to enhance the resistance to wind loads of a transmission tower through both stiffness strengthening and damping increase are energy dissipation devices that utilize bending deflection of a tower leg. In this paper, the hysteretic behavior of the transmission tower structure with FRMs was experimentally investigated through cyclic loading tests on a half scale substructure model. Firstly, the variation of friction forces and durability of the FRM depending on the type of friction-inducing materials used in the FRM were examined by performing the cyclic loading tests on the FRM. Secondly, cyclic loading tests of a half-scale two-dimensional substructure model of a transmission tower with FRMs were conducted. Test results show that the FRM, of which desired maximum friction force is easily regulated by adjusting the amplitude of the torque applied to the bolts, have stable hysteretic behaviors and it is found that there exists the optimum torque depending on a design load by investigating the amount of energy dissipation of the FRMs according to the increase of torque.

Rotational Viscoelastic Dampers for the Mitigation of Wind Loads on Transmission Tower Transferred from Transmission Lines

In this study, wind loads transmitted to a transmission tower from transmission lines are mitigated using rotational viscoelastic dampers. First, the wind load characteristics in a transmission tower is investigated considering the effect of the transmission lines through stochastic analysis. The assemblage of the transmission line and insulator are modeled as a double pendulum system connected to the SDOF model of the tower. From the result of the stochastic analysis, the background component of the overturing moment caused by the wind loads acting on the transmission lines are found to have considerable portion in the total overturning moment. Based on this observation result, a strategy Installing rotational viscoelastic damper (VED) between tower arm and transmission line is proposed for the mitigation of the transmission line reactions, which play a role as dynamic loads on a transmission tower. For the purpose of verification, time history analysis is conducted for different wind velocities and VED parameters. The analysis result shows that the rotational VED is effective for the mitigation of the background component rather than the resonance component of the transmission line reactions and achieves the reduction ratio of 50% even for higher wind speed.