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Tensegrity Obelisk Construction Data


Copyright © 1998, 2005 by Bob Burkhardt
        Member Descriptions
        [name, end point names, weight (if in objective function),
        second power of length (if a constraint), member category,
        Obj/Con/Exc (put in objective function, use as a constraint or
        exclude from computations), flags]
        For assembly purposes, only the name and end point names are
        of interest.  The other information may be of interest after
        A Practical Guide to Tensegrity Design has been consulted.

<Member> strut13 pt1A pt3c 0.0 sqr(2.5) 1 Con CalcClear Inelastic *
<Member> strut24 pt2A pt4a 0.0 sqr(2.5) 1 Con CalcClear Inelastic *
<Member> strut35 pt3A pt5c 0.0 sqr(2.5) 1 Con CalcClear Inelastic *
<Member> strut46 pt4A pt6a 0.0 sqr(2.5) 1 Con CalcClear Inelastic *

<Member> baset  pt1A pt1B 0.0 sqr(1.5) 2 Exc *
<Member> apext  pt6a pt6b 0.0 sqr(1.0) 2 Con *

<Member> guy1   pt1A pt3b 0.2 0.0      3 Obj *
<Member> guy2   pt2A pt4b 0.2 0.0      3 Obj *
<Member> guy3   pt3A pt5b 0.2 0.0      3 Obj *
<Member> guy4   pt4A pt6b 0.2 0.0      3 Obj *

<Member> TL12   pt1A pt2B 0.9 0.0      4 Obj *
<Member> TS23   pt2A pt3b 2/3 0.0      4 Obj *
<Member> TL23   pt2A pt3A 0.9 0.0      4 Exc *
<Member> tS23   pt2A pt3a 2/3 0.0      4 Obj *
<Member> TS34   pt3A pt4a 2/3 0.0      4 Obj *
<Member> TL34   pt3A pt4B 0.9 0.0      4 Exc *
<Member> tS34   pt3A pt4b 2/3 0.0      4 Obj *
<Member> tL34   pt3a pt4a 0.9 0.0      4 Exc *
<Member> TS45   pt4A pt5b 2/3 0.0      4 Obj *
<Member> tS45   pt4A pt5a 2/3 0.0      4 Obj *
<Member> tL45   pt4c pt5a 0.9 0.0      4 Exc *
<Member> tL56   pt5a pt6a 0.9 0.0      4 Obj *
<Member> tT33   pt3a pt3A 2/3 0.0      4 Obj *
<Member> tT44   pt4a pt4A 2/3 0.0      4 Obj *


        In-Situ Member Lengths
        These are the lengths of the members when they are in place
        and prestress is applied.  The strut lengths are from
        hub center to hub center, as are the tendon lengths.
        These values are in model units.

  strut13:          2.5   strut24:          2.5   strut35:          2.5
  strut46:          2.5     baset:            2     apext:            1
     guy1:      1.61188      guy2:      2.14435      guy3:      2.33364
     guy4:      2.22517      TL12:      1.00969      TS23:      1.56806
     TL23:       1.6292      tS23:     0.929175      TS34:     0.999215
     TL34:      1.46278      tS34:     0.822359      tL34:      1.80241
     TS45:        1.168      tS45:      1.32031      tL45:      1.79639
     tL56:      1.23052      tT33:     0.818674      tT44:     0.666956


        Relative Member Prestress Force Magnitudes
        These values are useful for developing an assembly
        strategy for the structure.  The tighter tendons are much
        easier to tie in place early on, while the looser tendons
        can be left to the last.  This information is also used
        to adjust tendon lengths since the measured length of a tendon
        will be shorter for a highly-stressed tendon with the same
        in-situ length as a tendon which is not so stressed.

  strut13:     -1.56288   strut24:      -1.0168   strut35:    -0.938242
  strut46:     -1.65821     apext:      0.25984      guy1:     0.322376
     guy2:      0.42887      guy3:     0.466727      guy4:     0.445034
     TL12:     0.908718      TS23:      1.04537      tS23:      0.61945
     TS34:     0.666144      tS34:      0.54824      TS45:     0.778668
     tS45:     0.880209      tL56:      1.10747      tT33:     0.545782
     tT44:     0.444637

        Average tendon force magnitude: 0.631169


        Construction Lengths (in inches, 16ths and 32nds)
        The construction length of a tendon is less than the in-situ
        length since when the tendon is measured off it isn't under
        any prestress force.  The construction length for a member
        represents the distance between the locations where it
        departs from the hub.  The struts were cut from
        1-inch by 1-inch hardwood garden stakes.  The tendon material
        was single strands of twisted #18 nylon twine.  Its behavior
        under stress is highly non-linear, so a look-up table
        was used to compute strains.  Prestress forces were assumed
        to affect tendon lengths and not strut lengths.

        Average Tendon Force Magnitude (chart units)> 20
        Length Scale Factor> 48/2.5
        Strut and Tendon Hub Adjustments> 0 0.5
        (adjust the tendon lengths by subtracting a half inch from
         both ends)

  strut13:  48  0 0  strut24:  48  0 0  strut35:  48  0 0  strut46:  48  0 0 
    apext:  17  6 0     guy1:  28  5 0     guy2:  37  7 1     guy3:  40 11 1 
     guy4:  38 14 0     TL12:  16  7 1     TS23:  25 12 1     tS23:  15  7 0 
     TS34:  16  9 1     tS34:  13 10 1     TS45:  19  6 0     tS45:  21 13 1 
     tL56:  19 15 1     tT33:  13  9 1     tT44:  11  0 0 

        Base chord length = (2/2.5)*48" = 38.4" = 38 6 1


        Material Quantities
        This provides an estimate of how much material will
        be needed to assemble the structure, in this case
        inches of garden stake and inches of nylon twine.
        The lengths must be adjusted to take into account the
        fact that the strut extends past the hub and some length
        of tendon is required to tie it to the strut.
        The Quantity value given for each Type does not take
        into account the Cross Section value.  The total
        Quantity given across from Tndns does.

        Length Scale Factor> 48/2.5 
        Strut and Tendon Adjustments> 0 (-6)

                   Cross
            Type Section    Quantity   Count

               0       1           0       0
               1       1         576      12
               2       1     89.3237       3
               3       1     582.046      12
               4       1     874.588      30
          Struts                 576      12
         Tendons             1545.96      45
side view of the zig-zag tensegrity obelisk another side view of the zig-zag tensegrity obelisk
Two Views of the Tensegrity Obelisk
(VRML Model)

Schematic for the Tensegrity Obelisk
Schematic for the Tensegrity Obelisk

          structure file:  obelisk/stage2.rc
           variable file:  obelisk/stage2.dat
stress-strain chart file:  v04oct_d/wellingtn.ssc
         digit list file:  src/standard.dls

CONTACT:

Bob Burkhardt
Tensegrity Solutions
Box 426164
Cambridge, MA 02142-0021
USA

e-mail: bobwb@juno.com

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