The controlling mechanism and the controlling effectiveness of passive mega-sub-controlled frame subjected to random wind loads

Abstract

The passive mega-sub-controlled structure proposed recently is a new form of structures associated with the design and construction of super tall buildings. However, as the dynamic characteristics of a practical passive mega-sub-controlled structure are very complicated, it is difficult to further all-sidedly examine the performance and the controlling effectiveness of this structure by a simple analytical model. In this paper, a new practical steel passive mega-sub-controlled frame is designed with reference to the conventional mega-sub-frame used in Tokyo City Hall. A more realistic analytical model of this structure subjected to random wind loads in which a non-white stochastic process in time and space is used is presented, and the coherence of the wind loads is further considered. The dynamic equations and the response spectrum expressions as well as the mean square response expressions are derived based on complex modal analysis theory. Moreover, the relative mass ratio RM and the relative stiffness ratio RD between the megaframe and the substructures are defined. The controlling effectiveness with different RM and RD is investigated. The results show that there exist some different controlling mechanisms, which are for the first time detected in this paper. As RD is less than certain value, RD<0.477 for this building, the first vibration mode or the first–second vibration modes can be suppressed, and a remarkable controlling effectiveness can be obtained. However, as RD is greater than this value, the first vibration mode cannot be suppressed; the controlling effectiveness is unacceptable and is not like the expectations reported in earlier references.