Early Prototypes 2 | Responsive Structure & Architecture (ORAMBRA)

THE OFFICE FOR ROBOTIC ARCHITECTURAL MEDIA & BUREAU FOR RESPONSIVE ARCHITECTURE
Copyright © 1998-2008 Tristan d'Estree Sterk

Actuated Tensegrity (page 2 of 3)

Apart from offering variable rigidity, lightweight, and asymmetry in shape, actuated tensegrity structures are extremely useful within architecture because they can be configured in two fundamentally different ways to produce tube or surface structures. These two configurations are important because they provide the necessary diversity required for applications within large, as well as, small-scale buildings.

Types, Prototypes & Methodologies:

Within the field of responsive architecture the way in which buildings change is critical. So while understanding the types of building forms that can be made efficiently with particular classes of structure is important, it is even more important to know the behavioral characteristics of each system and how behavior is tied to actuation and control. The conceptual model that we can use to describe behaviors within actuated tensegrity structures is built around actuation scope and the impact that changes in scope have upon structural rigidity. Scope is the term used to describe the extent or range of actuation from any particular point within the structure. As such, one can say that larger scopes actuate a larger region of a structure whereas smaller scopes actuate smaller regions. Larger scopes also require that larger numbers of actuators work together, while smaller scopes require fewer. Scope responses should relate to the internal and external forces that a structural system is exposed to, where internal forces are those that come from within the system itself (ie. the dead load of building materials) and external forces are those that come from beyond the system (ie. the live loads of wind or bodies moving within a structure). Scope is most easily understood as an actuation limit.

The scope of an actuated response caused by dead loads relates directly to the minimum rigidity required for holding a structure up without it buckling under a load. To give a simple example of how this concept works in practice let's use our own body to envision how our legs transmit load when rigid. By letting our muscles relax within one leg we cause that leg to be less rigid and also transmit less load. Our legs, because they carry more weight when we stand upright than our torso or arms do, need to be more rigid - a point that certainly becomes apparent when we consider what happens to the rigidity of our arms, torso, and legs when we do a hand stand.

Within this new scenario our arms become very rigid while they support the weight of our body. At the same time our legs can soften because they transmit much less load. The optimal rigidity or for any structural system that carries a dead load to the ground is directly related to the load it carries. Thus, the larger the load, the larger the rigidity required becomes.

The maximum rigidity of the system is limited to being less than the maximum compressive and tensile strengths of any member within the assembly. To summarize one can say that within this framework, actuation scope results in decreasing levels of rigidity, as loads become less. Alternatively one may say that actuated structures can get looser toward their top. This methodology of scope control produces structures that have a minimal degree of rigidity and maximum flexibility.

Scope in relation to shape control can also be discussed. Within class three prototypes shape changes that include leaning, extension, collapse, and flattening are all correlated to scope. Scope becomes a tool for enabling different regions of a structural system to become more or less rigid and affect the shape of the structure. For example, by limiting the scope of actuation to one half of a structure, leaning can be induced, while by enabling a global scope, expansion or contraction result. Limiting factors of rigidity, still apply to this system. Rigidity limits impact by restricting the degree of freedom that a structure has to move.

Early Class 3 Prototype (c) Tristan d'Estree Sterk
First developed in 2003 & first published in 2006.

Prototype No. 3
Class 3 actuated tensegrity structure as an early test for a full-scale building envelope that can change shape in response to the environment and building occupants.

Early Class 3 Prototype (c) Tristan d'Estree Sterk
First developed in 2003 & first published in 2006.

Prototype No. 4
These prototypes use thermal memory alloy actuators (NiTi). Simple electric circuits are used to spit and pulse the power provided to drive the actuators as a means of reducing and spreading power requirements over time.

Early Prototypes:

Actuation scope and shape control relate directly to each other but they also are associated to the ways in which structures compensate or respond to live loads. Scope becomes useful in these scenarios because dissimilar building shapes respond differently under the same loading condition. Within this paradigm of control, variable scopes are used to control building shapes that help produce minimally loaded structures when loads are composed of live as well as dead loads. It is most beneficial to think of these types of scope actuation as being complementary to those induced by internal forces. For example, one can consider how a building covered in snow might be able to use shape changes to shake the snow from its roof. Alternatively one might envisage a tower that has a wind load exerted upon it might respond by reducing its aerodynamic profile to minimize shear. Buildings might also use shape changes to subtly shift their centre of gravity and better position themselves to further reduce shear. Each of these scenarios connects shape control to actuator scope. Within class two systems this can be demonstrated by increasing the rigidity of one string of actuators that run in series up a tube structure. When scope is limited to serial actuation these structures respond by shifting their center mass through twisting actions. Figure 3a provides a trace of just such a change.

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PROJECT: Lotus Environmental Sensor Network (2004)
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PROJECT: Filamentosa Ultra-lightweight Skyscaper (2004)
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PROJECT: ideaCloud Grange Beach (1998)
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PROJECT: frais Chicago (2003)
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PROTOTYPE: Films 1 & 2 (actuated class 3)
Prototype

PROTOTYPE: Films 3 & 4 (actuated class 3)
Prototype

PROTOTYPE: Films 5 & 6 (actuated class 2)
Prototype

PAPER: Using Actutated Tensegrity (2003)
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PAPER: Structural Shape Control (2006)
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PAPER: CAAD for Responsive Architecture (2007)
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PAPER: Hybridized Control (2003)
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PAPER: User Centered Interactions (2006)
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PAPER: Cybernetic Form (2000)
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