Tensegrity Structures And Their Application To Architecture
Published on Nov 24, 2016
Tensegrity is a relatively new principle (50 years old) based on the use of isolated components in compression inside a net of continuous tension members, in such a way that the compressed members (usually bars or struts) do not touch each other and the pre-stressed tensioned members (usually cables or tendons) delineate the system spatially and in a self-equilibrated state.
Tensegrity structures are 3-D trusses where some members are always in tension while others are in compression. The Tensegrity concept offers a high level of geometrical and structural efficiency and results in modular and lightweight structures. However, the concept of Tensegrity is still not a part of the main stream structural design wing due to various reasons.
The main aim of this work is to prove if it is possible to find some applications for such an atypical kind of structure, in spite of its particular flexibility and relatively high deflections. For that it is essential to understand the structural principles of floating compression or tensegrity, and to define the fundamental forces acting on it
Concept Of Tensegrity Structures
Tensegrity structures are structures based on the combination of a few simple but subtle and deep design patterns: 1. Loading members only in pure compression or pure tension, meaning the structure will only fail if the cables yield or the rods buckle.
• Preload or tensional pre-stress , which allows cables to be rigid in tension.
• Mechanical stability, which allows the members to remain in tension/compression as stress on the structure increases.
Because of these patterns, no structural member experiences a bending moment . This can produce exceptionally rigid structures for their mass and for the cross section of the components.
A conceptual building block of tensegrity is seen in the 1951 Skylon tower which follows the typical tensegrity structure concept. But there are variations such as the Needle Tower which involve more than three cables meeting at the end of a rod. These cables define the position of the end of the rod which is considered as a well-defined point in space and the other additional cables are simply attached to this well-defined point.
Eleanor Hartley points out visual transparency as an important aesthetic quality of these structures. Korkmaz put forward that the concept of tensegrity is suitable for adaptive architecture due to its lightweight characteristics.
BENEFITS OF TENSEGRITY
Tensegrity as a structural system offers many advantages over conventional structural systems. The benefits offered are elaborated as follows:
4.1 Tension Stabilizes the Structure
A compressive member loses stiffness as it is loaded, whereas a tensile member gains stiffness as it is loaded. Stiffness is lost in two ways in a compressive member: In the absence of any bending moments in the axially loaded members, the forces act exactly through the mass centre. The material spreads which increases the diameter of the central cross section; whereas tensile members reduce its cross-section under load. In the presence of bending moments since the line of application of force is away from the centre of mass, the bar becomes softer due to the bending motion. For most materials, the tensile strength of a longitudinal member is larger than its buckling strength (sand, masonry, and unreinforced concrete are exceptions to this rule). Hence, a large stiffness-to-mass ratio can be achieved by increasing the use of tensile members.
4.2 Tensegrity Structures are Efficient
Efficiency of a structure increases with the minimal mass design for a given set of stiffness properties. Tensegrity structures use longitudinal members arranged in a very unusual pattern to achieve maximum strength with small mass.
4.3 Tensegrity Structures are Deployable
Since the compressive members of Tensegrity structures are either disjoint or connected with ball joints, large displacement, deployability and stowage in a compact volume is possible in Tensegrity structures. This feature offers operational and portability advantages. A portable bridge, or a power transmission tower made as a Tensegrity structure could be manufactured in the factory, stowed on a truck or helicopter in a small volume, transported to the construction site, and deployed using only winches for erection through cable tension. Deployable structures can save transport costs by reducing the mass required, or by eliminating the requirement of humans for assembly.
4.4 Tensegrity Structures are Easily Tunable
The same deployment technique can also make small adjustments for fine tuning of the loaded structures, or adjustment of a damaged structure. Structures that are designed to allow tuning will be an important feature of next generation mechanical structures, including Civil Engineering structures.
4.5 Tensegrity Structures Can Be More Reliably Modelled
All members of a Tensegrity structure are axially loaded. Perhaps the most promising scientific feature of Tensegrity structures is that while the structure as a whole bends with external static loads, none of theindividual members of the Tensegrity structure experience bending moments. Generally, members that experience deformation in two or three dimensions are much harder to model than members that experience deformation in only one dimension. Hence, increased use of tensile members is expected to yield more efficient structures.
4.6 Tensegrity Structures can Perform Multiple Fuctions
A given tensile or compressive member of a Tensegrity structure can serve multiple functions. It can simultaneously be a load-carrying member of the structure, a sensor (measuring tension or length), an actuator (such as nickel-titanium wire), a thermal insulator, or an electrical conductor. Therefore by proper choice of materials and geometry the electrical, thermal, and mechanical energy in a material or structure can be controlled.
4.7 Tensegrity Structures are Motivated from Biology
The representation of a spider fibre show that the hard β- pleated sheets are discontinuous and the tension members (amino acid matrix) form a continuous network. Hence, the nano-structure of the spider fibre is a Tensegrity structure.
Nature’s endorsement of Tensegrity structures in the form of spider fibre is the strongest natural fibre. Similarly if Tensegrity is nature’s preferred building architecture, then the same incredible efficiency possessed by natural systems can be transferred to manmade systems too.
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