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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.

Since the force generated by a magneto-rheological (MR) damper has large nonlinearity, the performance of an MR damper is dependent on response characteristics such as frequency and amplitude. Soil–structure interaction (SSI) is generally known to have a large effect on the seismic response of a building structure. In this study, the performance of an MR damper in mitigating the seismic response of a building structure is evaluated considering the SSI effects. First, the performance variance of an MR damper due to the change of the structural natural period is investigated by constructing its normalized response spectrum through the numerical analysis of many earthquake wave records and the natural period of a structure. The variable friction force of an MR damper is normalized by the structural base shear force, and its amplitude and decrement of response are quantitatively evaluated. Then, the response characteristics of the SSI system due to the lengthening of the structural natural period and various soil conditions are numerically evaluated based on the response spectrum analysis. Finally, the numerical results with and without considering the SSI effects are comparatively evaluated for the building structure with an MR damper. The comparison results show that the SSI effect should be considered in order that the undesirable effect of an MR damper on the structural control would not be neglected. Copyright © 2007 John Wiley & Sons, Ltd.

In this paper, a half-scaled substructure test was performed to evaluate the failure mode of an existing transmission tower subjected to wind load. A loading scheme was devised to reproduce the dead and wind loads acting on the prototype transmission tower. The load was enforced on the model structure using two actuators and a triangular jig mounted on the reduced model. Preliminary numerical analysis was carried out to evaluate the stability and member force of the specimen for the design load. When the substructured transmission tower was loaded by 270% of its maximum allowable buckling load, local buckling occurred in joints of leg members with weak constraints. From the experimental results, such as load–displacement curves, displacements, and strains of members, it was concluded that the local buckling was due to the additional eccentric force caused by unbalanced deformation of the specimen.

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.

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.

Two types of friction-type reinforcing members (FRM) are proposed for the purpose of upgrading wind resistant performance of a transmission tower and verified through cyclic loading tests. First, a suitable installation scheme of the FRM is investigated through numerical analysis. Tower-leg-reinforcing type and brace type installation schemes are examined, and numerical analysis shows that the latter is more effective due to the vertical cantilever type behavior of the transmission tower. Based on this result, two types of the FRMs, dissipating energy in slotted bolted connections, are proposed. The one utilizes the relative displacement between the FRM and the tower leg, and the other utilizes that between the separated angles consisting of the FRM as a slip deformation of the slotted bolted connection. Proposed FRMs are installed on each tower leg of the 1/2 scale substructure models of an actual transmission tower body. From cyclic loading tests, the latter type of the proposed FRMs dissipates energy more effectively and is less sensitive to the work tolerance and initial deformation.

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.

A new equivalent linearization technique is proposed for a friction damper–brace system (FDBS) idealized as an elastoplastic system. The proposed equivalent linearization technique utilizes secant stiffness and dissipated energy based on the probability distribution of the extremal displacement of the FDBS. In addition, a conversion scheme to convert an elastically designed equivalent linear systems to a FDBS is given. For comparative study, an existing model update technique based on system identification is modified to constraint elements to be updated. For the purpose of verification, shaking table tests for a small scale three-story shear building model, in which a rotational FDBS is installed, are conducted and equivalent linear systems are obtained using the proposed technique and the model update technique. Natural frequencies, modal damping ratios and response quantities predicted by those equivalent linear systems are compared with experimentally obtained ones. Finally, effects of the maximum friction force on the proposed equivalent linearization technique are investigated through numerical analysis of SDOF systems with a FDBS.

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.