Fabrication and Installation - Offshore Structures: Design, Construction and Maintenance - page 344

taking environmental loadings into consideration should not be allowed; similarly,
for a load resistance factor design code (LRFD)/partial factor code, the load factor
would be greater than that used for ultimate conditions.
Limit state analysis or a load resistance factor design approach may be
applied according to a recognized code, provided that the total load factor is
not less than the product of all the required factors, multiplied by a further factor
of 1.30.
The material reduction factor should be: for elastic design of steel structures,
not less than 1.15; and for plastic design of steel structures, not less than 1.30.
5.8.3 Lift Point Design
In addition to the structural requirements as described in the previous section,
the following should be taken into account in the lift point design.
Adequate clearance is required between cheek plates, or inside trunnion
keeper plates, to allow for ovalization under load. In general, the width avail-
able for the sling should be not less than (1.25 D + 25 mm), where D is nominal
sling diameter. However, the practical aspects of the rigging and de-rigging
operations may demand a greater clearance than this.
In general, for fabricated lift points, the direction of loading should be in line
with the plate rolling direction. Lift point drawings should show the rolling
direction.
Through-thickness loading of lift points and their attachments to the struc-
ture should be avoided if possible. If such loading cannot be avoided, the mate-
rial used should be documented to be free of laminations, with a recognized
through-thickness designation.
Pinholes should be bored or reamed and should be designed to suit the
shackle proposed. Adequate spacer plates should be provided to centralize
shackles.
Cast padears should be designed taking into account the geometrical considera-
tions, the stress analysis process and the manufacturing process and quality control.
The extent of NDT should be submitted for review. Where repeated use is to
be made of a lift point, a procedure should be presented for re-inspection after
each lift.
5.8.4 Clearances
The clearance around the lifting object and crane vessel should be studied in the
lifting procedure. The required clearances will depend on the nature of the lift,
the proposed limiting weather conditions, the arrangement of bumpers and
guides and the size and motion characteristics of the crane vessel and the trans-
port barge.
Subject to the above, for offshore lifts, the following clearances should nor-
mally be maintained at each stage of the operation.