The work reported here is directed towards the
problem of measuring and modeling non-linear damping
in steel space frame civil engineering structures.
In order to gain a better understanding of the damping
mechanism in such structures, tests were performed on
a full scale bolted lattice structure and the results
of section A show that the joint' damping can be
represented approximately in the form:
FD =C (1 +e IXIn)
where n=1.
Other situations. where this form of non-linear
damping occurs is in the case of fluid flow past a solid
body. In offshore structures the hydro-dynamic force
due to drag effects are found to be proportional to
velocity squared. For non linear material damping, n,
takes a value of 6.
In section B. various methods of solution to
the non-linear dynamical system under random excitation
were studied and it was found that the 'Equivalent Non-
Linear Differential Equationl, (ENL) method yields a better
measure of the response of the non-linear system to white
noise excitation than other approximate methods. Analytical
expressions are derived for the mean-square response,
probability density function and level crossing rates.
With the modified IENLI method (MENL) it is shown how one
can extract the non-linear damping and excitation power
spectral density. A good correlation is obtained between
experimental and theoretical results
