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SUMMARY:Tensegrity Structures.Part 1: Form-finding of Repetitive Tensegrit
 y Structures\, Part 2: Zero Stiffness Tensegrity Structures - R. Pandia Ra
 j and Mark Schenk (CUED)
DTSTART:20071123T150000Z
DTEND:20071123T160000Z
UID:TALK8859@talks.cam.ac.uk
CONTACT:Nami Norman
DESCRIPTION:Part 1:R. Pandia Raj \n\nTensegrity structures can be consider
 ed as structures consisting of a continuous network of cables\, together w
 ith discontinuous struts\, that rely on prestress to be stiff and stable -
  they can be made rigid in a particular configuration by a state of self-s
 tress. Tensegrity towers are a form of tensegrity structure which are comp
 act in two dimensions\, but extend in a third direction. The first tensegr
 ity tower was built by Kenneth Snelson in 1948\, and he was also responsib
 le for the famous 1969 Needle Tower in Washington. The self equilibrated c
 onfigurations of these structures were not found by formal analysis\, but 
 rather were based on the insight and experience of the designer. However\,
  it is interesting that many of the found forms are highly symmetric\, con
 sisting of a repeat of a module that itself has high symmetry. We will sho
 w that incorporating this symmetry into a structural analysis of the tower
  gives great insight to find the equilibrium configurations of these struc
 tures. Further\, the form-finding process for tensegrity structures with h
 igher symmetry will also be discussed in the talk.\n\nPart 2:Mark Schenk (
 CUED) \n\nThis talk describes a special class of 'tensegrity structures' t
 hat  \nstraddle the border between mechanisms and structures: Zero Stiffne
 ss  \nTensegrity Structures. Zero stiffness describes the ability of a str
 ucture  \nto change its shape without requiring any external force. In oth
 er words\,  \nthe structure will have a constant potential energy througou
 t is working  \nrange and is therefore neutrally stable. We have introduce
 d this concept  \nto tensegrity structures by using special tension member
 s with an apparent  \nzero rest length. These can for instance be manufact
 ured by coiling  \nprestressed springs.\n\nThe zero-stiffness modes introd
 uced to tensegrities in this way are not  \ninternal mechanisms\, as they 
 involve first-order changes in the special  \nmember lengths. Rather\, the
 se modes correspond to an infinitesimal affine  \ntransformation of the st
 ructure that preserves the length of conventional  \nmembers. Furthermore\
 , the modes are preserved over finite displacements.  \nThe zero-stiffness
  modes are present if and only if the directional  \nvectors of those memb
 ers lie on a projective conic: this geometric  \ninterpretation provides s
 everal interesting observations regarding zero  \nstiffness tensegrity str
 uctures.\n
LOCATION:Engineering Department - LR6
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