Distribution of strong earthquake input energy in tall buildings equipped with damped outriggers

Abstract

The seismic design of optimal damped outrigger structures relies on the assumption that most of the input energy will be absorbed by the dampers, whilst the rest of the structure remains elastic. When subjected to strong earthquakes, nevertheless, the building structure may exhibit plastic hinges before the dampers begin to work. In order to determine to which extent the use of viscously damped outriggers would avoid damage, both the host structure's hysteretic behaviour and the dampers' performance need to be evaluated in parallel. This article provides a parametric study on the factors that influence the distribution of seismic energy in tall buildings equipped with damped outriggers: First, the influence of outrigger's location, damping coefficients, and rigidity ratios core-to-outrigger and core-to-column in the seismic performance of a 60-story building with conventional and with damped outriggers is studied. In parallel, nonlinear behaviour of the outrigger with and without viscous dampers is examined under small, moderate, strong, and severe long-period earthquakes to assess the hysteretic energy distribution through the core and outriggers. The results show that, as the ground motion becomes stronger, viscous dampers effectively reduce the potential of damage in the structure if compared to conventional outriggers. However, the use of dampers cannot entirely prevent damage under critical excitations. KEYWORDSdamped outrigger, energy distribution, hysteretic energy, strong earthquakes, tall buildings, viscous damper 1 | INTRODUCTION Outrigger systems consist of a series of cantilever truss beams or shear walls connecting the building core with the perimeter columns. As a result, the axial forces acting at the end of the outriggers help the reduction of the total deflection of tall buildings by increasing the restoring moment.Dampers have been introduced between the perimeter columns and the outriggers, resulting in an increase in the overall damping of the building, instead of an increase of static stiffness and strength. [1] A well-known first implementation of this system in twins' 60-story buildings is reported in Willford and Smith. [2] Park et al. [3] reported the installation of damped outriggers in a 68-story tower in South Korea. In a recent review, [4] Smith reported two more applications of damped outriggers in tall buildings. All the authors point out that the addition of supplementary damping systems not only reduced the overall vibration response, but also construction costs.Numerical and experimental studies have been conducted to extend these damper-based control capabilities towards an improved reduction of the dynamic response, [3,[5][6][7] including seismic scenarios. [8][9][10][11][12][13][14][15][16][17] However, few studies explore the performance of damped outriggers under strong earthquake motion. Generally, studies are based on the use of peak ground acceleration (PGA) values up to 0.4 g, whereas strong earthquakes may exhibit PGAs of about 1.0 g. At the same time, most of the resea...

Energy dissipation and performance assessment of double damped outriggers in tall buildings under strong earthquakes

“…For instance, no change and a decrease from 0.23 to 0.14 under strong and severe motion, respectively, are the results of comparing the cases of the conventional and double damped configurations. This relatively small decrease in E H / E I may be explained by two observations: (a) As indicated by a previous study of the authors, the dampers' damping coefficient ( C d ) and the outrigger's location (λ) are the parameters that most influence the tall building's response. Because these two parameters have been already optimized in each of the studied configurations, further improvements, beyond each optimal, are unlikely to take place; (b) as suggested by columns E D / E I and E dampers / E I , most of the energy dissipated by the dampers seems to be partially subtracted from that dissipated from the inherent structural damping.…”

“…From previous studies, it is clear that under optimal design conditions, the addition of viscous dampers reduces both the OTM and overall stresses in the core, outriggers, and perimeter columns.…”

“…Properties of the steel are derived from Eurocode 3 . More details on the non‐linear settings of these FE models in Diana‐FEA can be found elsewhere …”

“…This article provides an analytical framework to comparatively assess the distribution of seismic energy in tall buildings equipped with viscous damped outriggers, that is, with outriggers that have one or more viscous damper installed between their ends and the perimeter columns. Because previous research developed by the authors showed that the energy dissipation capacity of a single set of outrigger will not prevent damage under strong earthquakes, a subsequent question was whether adding another set of outriggers would enhance such performance. In other words, if a single damped outrigger structure is designed to reach an optimal damping ratio, could this damping ratio still be increased by the addition of another set of outriggers?…”

Analysis of outrigger‐braced reinforced concrete supertall buildings: Core‐supported and tube‐in‐tube lateral systems

“…An opposing concentrated moment is generated in the core upon applying lateral loads as shown in Figures and . Recent research has been carried out on the seismic response of outrigger‐braced buildings (e.g., other studies).…”