Fabrication and Installation - Offshore Structures: Design, Construction and Maintenance - page 355

5.9 LOAD-OUT PROCESS
After the erection of the jacket and the topside, the load-out process is started;
this process generates load-out forces on the structure as it moves from the
fabrication yard to the barge.
If the load-out is carried out by direct lift, then, unless the lifting arrange-
ment is different from that to be used for installation, lifting forces need not
be computed, because lifting in the open sea creates a more severe loading
condition that requires higher dynamic load factors. If load-out is done by skid-
ding the structure onto the barge, a number of static loading conditions must be
considered, with the jacket structure supported on its side. In load-out of the
jacket, the loading conditions affect the structure in the different positions of
the jacket during the load-out phases, as shown in Figure 5.33 , from movement
of the barge due to tidal fluctuations, marine traffic or change of draft, and from
possible support settlements. Since movement of the jacket is slow, all loading
conditions can be taken as static. Typical values of friction coefficients for cal-
culation of skidding forces are:

steel-on-steel without lubrication, 0.25 ●

steel-on-steel with lubrication, 0.15

●

steel-on-Teflon, 0.10

●

Teflon-on-Teflon, 0.08

●

All structures should be checked for the loads applied during load-out. The
contractor should define explicitly the proposed method of load-out (i.e.,
skidded, trolleyed or lifted). The following should be considered:

1. Dry loads only should be used, together with weights for lifting gear, sea
fastenings and others. The loads should be based on the weight-control
report.
2. For skidded or trolleyed load-out:
● A horizontal load of 15% of the vertical reaction on one skid rail should
be applied.
● Total loss of one vertical support should not affect the structure jacket if
it is being supported by the remaining supports only.
● Supports should be assumed to be hinged.
● Wind loads for a return period of 1 year should be included with this load
condition in the structure analysis check.

In most cases, the total support points are about 6 - 15 supports for the

●

load-out.

The direction of the pull-out force is shown by the arrows in Figure 5.34 .