Response Control Systems By Tuned Dynamic Mass System for a 200-Meter-Tall Tower-Supported Steel Stack Structure

Abstract eng:
In the wake of major earthquakes such as the 1995 Hyogo-ken Nanbu Earthquake, the design of towering structures like tower-supported steel stacks of thermal power plants has become dominated more by earthquake loads than wind loads. There is a growing need, therefore, for seismic reinforcement. This paper introduces a case of seismic renovation of a 200-meter-tall tower-supported steel stack structure. The requirements of this work were as follows: (1) Construct without putting the stack out of service. (2) Attach seismic response control systems to the lower part of the steel tower if possible. (3) Achieve seismic performance within the elastic limit against assumed ground motion (peak ground acceleration: about 300 cm/s2, peak ground velocity: about 70 cm/s). As a result, the target performances has been achieved by attaching a pantograph-type response control system with a toggle mechanism and a dynamic mass (DM) damper system to the lower part of the steel stack designed to control the bending mode of vibration. The main improvements are as follows: (1) Complex natural value analysis has shown that the damping ratio of first mode h 1 of the original structure was 1% and that of the response-controlled structure was 14%. Although it is difficult to provide high damping to a slender, easily bendable structure, the response control system ensures high damping. (2) Earthquake response achieved by attaching the response control system was 40 percent smaller than the response of the original structure. (3) The stress ratio of main column members of the original structure was 1.36 and that of the responsecontrolled structure was 0.99. The stress ratio of the other members of the original structure was 1.20 and that of the response-controlled structure was 0.93. All members were within the elastic limit.

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