Offshore Structure Loads and Strength - Offshore Structures: Design, Construction and Maintenance - page 30

Damage to architectural finishes.

●

Operational requirements for drainage (free surface or piped fluids). ●

Unless stricter limits are established by the platform owner ' s company or

regulator, the limits of deflection (presented in “ Deflections ” below) should

apply.

Vibrations
All sources of vibration should be considered in the design of the structure.
At a minimum, the following should be reviewed for their effect on the
structure:

● Operating mechanical equipment, including that used in drilling operations.
● Vibrations from variations of fluid flow in piping systems, in particular
slugging.
● Oscillations from vortex shedding on slender tubular structures.
● Global motions from the effect of environmental actions on the total
platform structure.
● Vibrations due to earthquake and accidental events.
Design limits for vibration should be established from operational limits set
by equipment suppliers and from the requirements for personnel comfort, health
and safety.
It is important to note that large cantilevers, whether they are simple beams
or trusses forming an integral part of the topside platforms, but excluding masts
or booms, normally should be proportioned to have a natural period of less than
1 second in the operating condition.

Deflections
The final deflected shape,

Δ max , of any element or structure has three components:
Δ max = Δ 1 +Δ 2 −Δ 0 (2.2)

where Δ 0 is any precamber of a beam or element in the unloaded state if it exists,

Δ 1 is the deflection from the permanent loads (actions) immediately after loading
and

Δ 2 is the deflection from the variable loading and any time-dependent defor-
mations from permanent loads.
The maximum values for vertical deflections, based on ISO 9001, are given
in Table 2.8 .
The limiting values for vertical deflection based on a load and resistance factor
design (LRFD) are given in Table 2.9 .
Lower limits may be necessary to limit ponding of surface fluids and to
ensure that drainage systems function correctly.
Horizontal deflections generally should be limited to 0.3% of the height
between floors. For multifloor structures, the total horizontal deflection should