In this study, the implementation of evolutionary algorithms to the form-finding problem of masonry shell models is presented using Autoclaved Aerated Concrete material. Regarding the significance of design decisions, the study is focused on the conceptual stage of the design process. In this context, the applied method is addressed as multi-objective real-parameter constrained optimization. For the sake of dealing with the shell design problem, two objective functions are considered: minimization of global displacement and minimization of mass. Two multi-objective evolutionary algorithms, namely, Non-Dominated Sorting Genetic Algorithm II and Real-coded Genetic Algorithm with mutation strategy of Differential Evolution Algorithms are compared in terms of computational and architectural performance. As a result, the solutions generated by these algorithms are found much competitive.@en

The use of a single set of outriggers equipped with oil viscous dampers increases the damping ratio of tall buildings in about 6–10%, depending on the loading conditions. However, could this ratio be further increased by the addition of another set of outriggers? Should this additional set include dampers too? To answer these questions, several double damped outrigger configurations for tall buildings are investigated and compared with an optimally designed single damped outrigger, located at elevation 0.7 of the total building's height (h). Using free vibration, double outrigger configurations increasing damping up to a ratio equal to the single-based optimal are identified. Next, selected configurations are subjected to several levels of eight ground motions to compare their capability for avoiding damage under critical excitations. Last, a simplified economic analysis highlights the advantages of each optimal configuration in terms of cost savings. The results show that, within the boundaries of this study, combining a damped outrigger at 0.5h with a conventional outrigger at 0.7h is more effective in reducing hysteretic energy ratios and economically viable if compared with a single damped outrigger solution. Moreover, double damped outrigger configurations for tall buildings exhibit broader display of optimal combinations, which offer flexibility of design to the high-rise architecture.

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The use of outriggers in tall buildings is a common practice to reduce response under dynamic loading. Viscous dampers have been implemented between the outrigger and the perimeter columns, to reduce vibrations produced by strong winds. However, its behaviour under strong earthquakes has been not yet properly investigated. Strong earthquakes introduces larger amount of energy into the building’s structure, compared to moderate earthquakes or strong winds. In tall buildings, such seismic energy is dissipated by several mechanisms including bending deformation of the core, friction between structural and non-structural components, and eventually, damage. This research focuses on the capability of tall buildings equipped with damped outriggers to undergo large deformations without damage. In other words, when ground motion increases due to strong earthquakes, the dampers can be assumed to be the main source of energy dissipation whilst the host structure displays an elastic behaviour. These investigations are based on the assessment of both the energy demands due to large-earthquake induced motion and the energy capacity of the system, i.e. the energy capacity of the main components, namely core, outriggers, perimeter columns and dampers. The objective of this research is to determine if the energy dissipated by hysteresis can be fully replaced by energy dissipated through the action of passive dampers. The results show that the use of a set of outriggers equipped with oil viscous dampers increases the damping ratio of tall buildings in about 6-10%, depending on the loading conditions. 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. Combining a damped outrigger at 0.5 of the total building’s height (h), with a conventional outrigger at 0.7 h is more effective in reducing hysteretic energy ratios and economically viable if compared to a single damped outrigger solution.@en

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.

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This article provides an analytical framework to assess the distribution of seismic energy in outrigger structures equipped with viscous dampers. The principle of damped outriggers for seismic control applications lies on the assumption that the total earthquake energy will be absorbed by the dampers, as the rest of the structure remains elastic during the seismic event. Nevertheless, under large or severe earthquake-induced motion, some plastic hinges or failures may be produced in the structure before the dampers are able to dissipate the total input energy. Therefore, hysteretic behaviour of the host structure need to be evaluated along the dampers’ performance in order to determine how the earthquake input energy is distributed by all the components. In order to effectively assess the inter-dependency between structural properties of tall buildings equipped with damped outriggers and ground motion characteristics of large earthquakes in the control performance, a parametric study -considering building predominant period, position of the outrigger, damping coefficient, and stiffness ratio core/perimeter columns- on the nonlinear behaviour of two building models –fixed and with viscous damper - is examined under two large-earthquake records. The results show that the use of passive control –viscous dampers- gradually reduce the potential of damage in the building structure as they reduce both the input and the hysteretic energy demands, and thus eventually extending the capabilities of the damped outrigger to large-earthquake induced motion control.@en