Abstract
This work presents force and shape control strategies for adaptive structures subjected to quasi-static loading. The adaptive structures are designed using an integrated structure-control optimization method developed in previous work, which produces minimum ‘whole-life energy’ configurations through element sizing and actuator placement optimization. The whole-life energy consists of an embodied part in the material and an operational part for structural adaptation during service. Depending on the layout, actuators are placed in series with the structural elements (internal) and/or at the supports (external). The effect of actuation is to modify the element forces and node positions through length changes of the internal actuators and/or displacements of the active supports. Through active control, the stress is homogenized and the displacements are kept within required limits so that the design is not governed by peak demands. Actuation has been modelled as a controlled non-elastic strain distribution, here referred to as eigenstrain. Any eigenstrain can be decomposed into two parts: an impotent eigenstrain only causes a change of geometry without altering element forces while a nilpotent eigenstrain modify element forces without causing displacements. Four control strategies are formulated: (C1) force and shape control to obtain prescribed changes of forces and node positions; (C2) shape control through impotent eigenstrain when only displacement compensation is required without affecting the forces; (C3) force control through nilpotent eigenstrain when displacement compensation is not required and (C4) force and shape control through operational energy minimization. Closed-form solutions to decouple force and shape control through nilpotent and impotent eigenstrain are given. Simulations on a slender high-rise structure and an arch bridge are carried out to benchmark accuracy and energy requirements for each control strategy and for different actuator configurations that include active elements, active supports and a combination of both.
Highlights
The construction sector is an important field of action in the on-going global effort to reduce anthropogenic greenhouse gas emissions (GHG) that aims to mitigate the potential consequence of climate crisis
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This work has presented the formulation of four control strategies for adaptive structures equipped with linear actuators: (C1) force and shape control to obtain prescribed changes of forces and node positions; (C2) shape control through impotent eigenstrain when displacement compensation is required without affecting the forces; (C3) force control through nilpotent eigenstrain when displacement compensation is not required and (C4) force and shape control through operational energy minimization
Summary
The construction sector is an important field of action in the on-going global effort to reduce anthropogenic greenhouse gas emissions (GHG) that aims to mitigate the potential consequence of climate crisis A significant share of buildings and structures GHG life cycle emissions is embodied because it arises from the manufacturing of components, construction, transport and demolition (Bekker, 1982). Load-bearing systems have an important share of the environmental impact embodied in the built environment due to the large amount of material required for their construction and energy-intensive fabrication processes (Cole and Kernan, 1996; Kaethner and Burridge, 2012). According to the International Energy Agency (IEA), the embodied carbon (EC) of building structures, substructures and enclosures is responsible for 28% of global building sector emissions E. Agency, 2017), call for new and radical solutions to reduce structures material usage and environmental impact. Since load-bearing structures are typically subjected to loads that are significantly lower than the design loads, it means that most structures are overdesigned for the majority of their service life
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