4 - Memorial University of Newfoundland DAI

In 1983, Nalaraja 1341 carried out a program 01 strtlettml illlcgrity mont.
iloring through vibration measaremnnts 01 three nxcd stccl plntlornls inn tl~c
North Sea His objectives were to develop monitorins systms to ol>erntc
continuously over a period 01 two years and to prove tls lensibiiity oi audl
systems to detect structural dama~. The resulta showed that only lile lowcsl
natural frequencies could be idenlilied without ambiguity,nnd tlrom lwqao~,.
cin were stable throughout lhe monitoring period. Temporary red~~ctiaa 01
these frequencies, caused by an increase in deck mass associated will, drilling
activity, was detected. it wns suggested tinat deck mas sho!tlcl be an~otlitarrcl
to distinguish the lmuency vnrialian assoeinled wilh primary stnnctuml
damage and foundstion stillnear reduction. I1 wa ~cknnwi~rlgcd lhnl lllc:
vibration monitoring systems conaisting ol sccolcro~nclcn at the wnlcr aar-
1- and deck of line structure can only delecl global eLal>gea. Navrrlld~~uu,
ambient monitoring systems wore rocommended for cot>li~rttnur nnlnt~ilcrri~ng
of the global condition of an offshore platlorm (;&id.).
Jones el el. (351 described the latest rsloty and porlormn!lcc nmnitoring
techniques that are employed on struclum and vesrcls c.~gaged ik Cannndi.~tn
offshore oil and gas erploralion projects. The results ofseverai monitoring
programs were discussed. In rolerence 1361, a system idc~~lifientior~ tccl,niq~w,
which uses a state spncc equation was ud. It wir~ p mpd lhnt orm tlr!
eigenvalues and eigenveetorsaf the system are dclermined, tl>e mnsn, alifimrxs
and damping can be ohlained. Hcnco changes 01 lhc mntrix elcrnenl~ will
provide tho identification oilhe location and ~cvcrmccafll~e xtrurtural dxm-
age. Moan el 01. 1371 pmented a hriofdeacriplion 01 thc likaly conditions lor
offshore steel piatlorms. The thmrctieal hnsis lor lwo Bnite clement motibocla
lor non-linear collapse analrjia was pmnlcd, lollowed by a bricl ol~tlinc of