tensegrity tree plan, sherwood visitor complex

8/9/2019 Tensegrity Tree Plan, Sherwood Visitor Complex

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Viewing level vertical systems are the same as the glazed curtain walling system atground level.

Views out are vital and all areas of the curtain walling, except those around theWCs are fully glazed. Top hung opening lights are incorporated to provide naturalventilation.

The roof is finished in timber shingles to maintain the overall timber appearance ofthe building.


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The foliage

The foliage is the cr owning feature of the Tree.

Numerous options were investigated which conclude that the most appropriatesolution was a tensegrity structure. A balance of tension and compression forcesresulting in a cable and post structure that would float around the viewing level atthe top of the timber hyperboloid. Compression members are held, not touchingone another, by a series of tension cables.


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The canopy of foliage that surmounts the Tree is created by a system of tensegritystructures. Each of these structures consists of a web of elements that are joinedin such a way as to be self-supporting. Constructed at ground level, they are liftedinto place using a crane or an MEWP, and are anchored to the hyperboloid trunk

of the Tree using a simple pin joint. Once in place, they will combine to evoke thecomplex radial patterning of branches, twigs and leaves.

Each separate structure is based upon a different base geometry, derived from thegeometrical models explored by Richard Buckminster Fuller. The following basegeometrical elements are used to form the individual structures:

Twelve stage X-module tensegrity torus Four-fold tensegrity obelisk Four-stage X-module column

Having established the basis for each separate tensegrity structure, the individual

elements within them will be tailored using a complex computer algorithm. This willadjust the length of compression/tension members and the corresponding pointsof connection between them in order to create a more irregular and natural-lookingseries of geometries. The resulting structures will retain their inherent strengthand structural integrity while acquiring an organic quality in keeping with thedesign concept of building as tree.

Once installed at the top of the tower, these elements will sit together as adiaphanous structural canopy, creating the effect of a system of branches radiatingoutwards from the trunk of a tree.

Tensegrity as foliage


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example tripod

Tensegrity geometrical studies

Tensegrity Primitives

Tensegrity primitives are basic, stable tensegrity units. In 3-dimensional space, thesimplest unit is made of 3 compression element. There is no limit to the complexity

of these units, tensegrity torii, spheres or domes can be made of several hundredmembers

example torus


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Torus primitive Torus primitive : extended pieces

Tensegrity torus

One example, that could build the lower part of the tree foliage is a tensegritytorus. This torus is one stable unit that consists of 24 compression and 120 tension

members.

The random appearance can be emphasised by e.g. extending co mpressionmembers.


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Adding tripod units:

- Adjacent pieces share 1compression member

- 2 additional cables stabilizestructure

Different tripod units:

- Varying the internal anglesin a specific way results indifferent stable units

Compression members can haveany shape and they can cantilever

beyond the tension cable cage

Tensegrity Tripod

Another approach to get complex tensegrity assemblies is to add simple primitivesto clusters. An advantage is that each primitive unit is stable, and a piece by piece

erection can be done.The example tripod unit consists of 3 compression and 9 tension members.Adding tripod units can result in a big variety of shapes. While adding these units,a certain degree of freedom can be achieved by using different tripods and byshifting or rotating them along the shared compression member.


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Twelve stage X-module tensegrity torus

Primary element of repetition

Element shown in radial repetition Torus_Plan View

Torus Element_Plan View


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Full Torus with element shown in radial repetition

Torus element close up view

First distorted torus in position

Second distorted torus in position


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Adjacent pieces can be fixed atdifferent angles

Adjacent pieces can be shiftedalong the shared axis

Torus made of tripod units

Branch made of tripod units


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Digital model showing triangulated shard compression elements around hyperboloid structure


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Four-stage X-module column

Four-stage X-module column in position Four-stage X-module column compression members

Four-stage X-module column compression and tension members


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Four-fold tensegrity obelisk

Four-fold tensegrity obelisk compression members

Four-fold tensegrity obelisk compression and tension members

Four-fold tensegrity obelisk timbermodel.

Four-fold tensegrity obelisk as branch

Four-fold tensegrity obelisk as root


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How does Tensegrity work ?

In any structural system there must be some kind of continuity to allow forcesto be transmitted from one part of the structure to another. In most man-made

structures, this continuity is achieved through the compression members, withthe occasional tension member being incorporated where it cannot be avoided. Ina Tensegrity system the continuity is achieved through a continuous network oftensile elements, the compression elements being discontinuous. This was whyBuckminster Fuller coined the word Tensegrity, a contraction of tensional integrity.

Anthony Pugh1 gives the following definition of tensegrity:A Tensegrity system is established when a set of discontinuous compressivecomponents interacts with a set of continuous tensile components to define astable volume in space.

Tensegrity is an anticlassical approach to structure and construction, and impliesa reverse in perception: what appears to be compactly standing and solid provesto be suspended and ephemeral. Where instead of compact mass, increasingly thintensile members bordering on the spiritual lend the structure stability.These Internally pre-stressed cable networks can be found abundantly in Nature,predominantly in cell structures.

The first paper, introducing proof o f the concept of Tensegrity in Nature waspublished in January 1998 in the journal Scientific American. Here, we can readDonald Ingbers studies on Lifes Architecture cell growth with cytoskeletonTensegrities.


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Cubic thinking

If nature builds with triangles, why do humans build with cubes? Nothing seems sonatural as our concept of squares and cubes as the proper means to enclose and

define space. The structural modelling experience most of us have had of stackingsquare blocks has set within us deeply ingrained bias for cubic thinking!

Natures framework for building

All natural structures attain stability from the use of triangles. When a structureis built with triangles it does not need extra material for bracing. In keeping withthe law of conservation of resources, natures use of triangular patterning forstabilisation assures the most efficient use of materials.

A brief survey of natural structures reveals the triangular framework for theirformation. The honeycomb uses the least mount of wax to contain the largest

amount of honey. Insect wings, cells, pine cones, leaf structures, the skin patternsof reptiles, the retinal structure of insects, cork cells, pollen, the internal structureof seeds, muscle filaments, marine algae. The protein shell of viruses - the list oftriangulated biological structures is endless. Equally, numerous are the examplesof triangulation in crystalline structures. Crystals are known to form in manyfamiliar shapes such as cubes, but upon inspection of their atomic structure atriangular pattern is revealed. Field ion microscope photos show that the atomicstructure of metals are triangulated as well.


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Triangulation Equals StabilityWhen forces form a shape that is self-stabilised (it holds its shape without anyhelp) they create a structure. Structures attain stability by the use of triangles in

the arrangement of their forces. A triangle is the only shape that will remain rigidwhen constructed with flexible connectors because each angle is braced by itsopposite side.

In any structural system there must be some kind of continuity to allow forcesto be transmitted from one part of the structure to another. In most man-madestructures, this continuity is achieved through the compression members, withthe occasional tension member being incorporated where it cannot be avoided. Ina Tensegrity system the continuity is achieved through a continuous network oftensile elements, the compression elements being discontinuous. This was whyBuckminster Fuller coined the word Tensegrity, a contraction of tensional integrity.Thus, a Tensegrity system can be defined as follows:

A Tensegrity system is established when a set of discontinuous compressivecomponents interacts with a set of continuous tensile components to define astable volume in space.

Synergy in Tensegrity Structures

When tensional and compressional materials are used together in a trulycomplementary way, they form structures, which can bear loads that far exceedestimates based on traditional structural analysis. This is true for all shapesachievable with Tensegrity, which may appear delicate but are suprisingly strongand resilient. Shapes built with the same struts but rigidly connected at the

vertices would not be able to withstand such loads/impact. Structures builtonly with wire would have no shape at all. By using the two materials together,Tensegrity creates shapes that are stronger than those created from each materialseparately. This kind of working together is called Synergy, which means that thebehaviour of the whole is unpredictable, by the behaviour of its parts consideredseparately.


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Leaves

Timber varies in size according to its environmental conditions. To ensure that thisdimensional instability does not effect the tensegrity structure the leaves withinthe foliage will be framed in galvanised steel with timber infill panels.

Visually the steel will provide a contrast to the timber and highlight the leaf edges.Intermediate framing creates a series of veins.

There are 3 different sizes of leaf. The maximum is 11m long and the minimum is 3mlong. All are constructed in a similar way.

tensegrity tree plan, sherwood visitor complex

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