Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 485

η f = 0.46

Reduction factor

×

N f.d = 0.46 991.8 = 456 kN

Design Resistance at 20

° C, using fire safety factors :

N b.fi.t.Rd =( γ M.fi )

Effective length factor, k = 0.7 (pinned base)
Slenderness

χ fi /1.2) Ak y.q.max ( f y /

λ , kl/I = 0.7 (3.5)/0.0457 = 53.6
λ 1 = 86.8 as calculated a b ove
Normalized slenderness

λ = λ / λ 1 = 0.62

λ 20 = 0.62 (k y.20.max /k E.20.max )
For C, there is no reduction on yield strength or the elastic modulus,

as per Table 7.11 .
k y.20.max = k E.20.max = 1.0
Reduction factor in fire,

θ =20 °

χ f = 0.77

N b.f.t.Rd = (0.77/1.2) 0.275/1 = 1159.6 kN

Critical Temperature of Column :
Degree of utilization

× 6530 × 1 ×

μ 0 = 456/1159.6 = 0.39

Critical temperature θ cr = 622.4 ° C

7.7.6 Case Study: Deck Fire
The platform in this case is a complex platform (consisting of many platforms),
located in the Gulf of Suez in the Red Sea. The platform is used for drilling. The
fire occurred in 2003 due to the sudden rupture of a gas riser ( Figure 7.9 ). As a
result of the rupture, the riser, which contained gas under pressure, caused a hydro-
carbon fire jet that directly affected the bottom of the main deck ( Figure 7.10 ). The
assessment process was:

FIGURE 7.9 Fire on the main deck.