Abstract:
Recent developments on high-mast arm
structures have increased awareness of the fatigue behavior
associated with these structures. Mast arm structures that are
subjected to cyclic loading conditions tend to fail due to fatigue
failure. Size and thickness of base plate, geometry and thickness
of mast arm, welding thickness and numbers of anchor bolts are
highly influencing on the fatigue performance of a high-mast
lighting tower system. It was found that, dynamic
characteristics and damping ratio of the mast arm also has the
most significant effect on the hotspot stress of the mass arm wall
system. Palmgren Miner theory of cumulative damage method,
Weibull wind distribution and S-N Curves are widely used to
estimate the fatigue life of the structures. Since, there are no
redundancy built into this high-mast arm structures, failure of
these structures would be very hazardous. Generally, failures
are observed around the man access hole, base connection and
anchor bolt location due to high stress concentration at these
locations. Furthermore, lock-in conditions in the second mode
must be investigated as this mode is more critical for bending
response. So, fatigue study of high-mast arm structures should
be performed against excessive stress developed due to resonant
vibration of periodic or random oscillation depending upon the
flow regime.
