Dear All,

The task of adjusting the length of supporting rods is easily carried out
using the shortening effect of imposed negative thermal variations.
Indeed almost all FE programs allow for the imposition of a thermal
variation on a rod or truss element. So, You can model all your structure
with the proper weights, obtaining a deformed configuration.
After, you can compute the thermal variation (alfa L delta T = shortening
needed by each rod to restore straightness of the component), and apply it
to all the bars.
The interacting stiffness effect will lead to a solution not fully
satisfying the requirements, but anyway you will be able to iterate the
computation adding some more shortening effect to the bars in order to
arrive to an acceptable solution.

Moreover, your computation will give you the real shortening that you must
apply in the construction phase (i.e. by screws or jacks), simply computing
the final "alfa L delta T".

This trick is always used when you want to study some cable system with
initial prestress.

Good Luck.

prof. ing. Andrea Benedetti
DISTART Dep., University of Bologna
2, Viale Risorgimento,
40136 Bologna, ITALY
phone : 0039-051-209.32.47
fax   : 0039-051-209.32.36
E-mail: [log in to unmask]