A method for nonstationary seismic response analysis of an offshore gu
yed tower is presented. The equation of motion is formulated for the h
orizontal motion of the guyed tower using a multidegrees-of-freedom mo
del. The nonlinear hydrodamping and the nonlinear restoring force of t
he guyline system are included in analysis with the aid of the equival
ent linearizations. The nonstationarity of the earthquake excitation i
s modelled by imposing a time varying envelope function onto a station
ary random component, The nonstationary responses are obtained in term
s of time dependent variance functions. By taking the autocorrelation
function of the nonstationary ground acceleration in terms of sinusoid
al and exponential functions of time, an analytical procedure is devel
oped for computing time varying variances of the tower responses. Expe
cted maximum responses are evaluated thereafter. Example analysis indi
cates that the nonstationary method gives consistent estimates for the
maximum responses, if the earthquake duration is taken to be longer t
han the duration of strong excitation, Comparison is made with the res
ults obtained by the conventional spectral method based on the station
ary assumption. Copyright (C) 1996 Elsevier Science Ltd.