First mode damping ratio oriented optimal design procedure for damped outrigger systems with additional linear viscous dampers

Tomoki Asai,Yuki Terazawa,Takashi Miyazaki,Pao-Chun Lin,Toru Takeuchi

doi:10.1016/j.engstruct.2021.113229

Tomoki Asai, Yuki Terazawa + Show 3 more

Open Access

https://doi.org/10.1016/j.engstruct.2021.113229

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Abstract

The damped outrigger system is in widespread use as a damping modification system for tall buildings that provides high additional damping in addition to the bending back effect against the core. However, while the enhanced seismic performance of damped outrigger systems was confirmed in previous studies all over the world, a general-purpose optimal design method focusing on modal damping ratios has not been established yet. This paper proposes an optimal damper design kit composed of a first mode damping ratio oriented design policy, simple equations of optimal damper-connection stiffness ratio to maximize first mode damping ratio, a machine learning model to estimate first mode natural period and damping ratio. The tenability of the first mode damping ratio-oriented design policy was confirmed by performing complex modal analyses on single to quad damped outrigger systems incorporating linear viscous dampers and assigning realistic stiffness values to the outrigger trusses. The simple design equations of optimal damper-connection stiffness ratio and the machine learning model for first mode characteristics were developed based on a large number of analytical results. The proposed optimal design kit has been made available as a web application-based design tool.

Highlights

The outrigger system is a structural system for tall buildings wherein a rigid core at the center is connected to the perimeter columns via outriggers
0.3–0.4, which are close to the optimal α values corresponding to the maximum second mode damping ratio. These results indicate that optimal outrigger height ratios obtained based on minimizing the seismic response are highly dependent on dominant mode characteristics
The following conclusions were drawn from this study: Based on the results of the present study, ranging from the numerical investigation to the development of the web application-based design tool and the actual design practice, a generalized optimal design procedure for damped outrigger systems with additional linear viscous dampers is proposed as follows: 1) For a single damped outrigger system, the optimal outrigger height ratio minimizing the period, maximizing the damping ratios, and maximizing the seismic response reduction was found to range from

Summary

Introduction

The outrigger system is a structural system for tall buildings wherein a rigid core at the center is connected to the perimeter columns via outriggers. Smith and Willford [3] proposed a damped outrigger system (Fig. 1(b)), in which seismic energy dissipation devices (i.e., dampers) are inserted between the outrigger and the perimeter column. The dampers provide additional damping by operating on the relative vertical motion between the perimeter column and the outrigger during flexure. These types of damped outrigger systems are being widely used to design tall buildings in windy and seismic regions such as the United. Smith and Willford suggested the importance of focusing on modal damping ratios at the design stage to mitigate both the seismic and wind response [3,5]. A generalpurpose optimal design method focusing on modal damping ratios has not been established yet while the enhanced seismic performance of damped outrigger systems is confirmed in previous studies all over the world

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