Assessment of Existing Structures and Repairs - Offshore Structures: Design, Construction and Maintenance - page 486

FIGURE 7.10 Fire-related effects on the main truss.

An on-site inspection survey, in which different levels of damage were
observed in various structural and piping components on the platform.

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Categorization of the damage level of different structural elements of the
platform in accordance with API 579, Section 11 .

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Measurement of the actual dimensions of the structural elements of the
platform.

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Assessment of the material properties of different structural elements of the
platform.

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Provision of the necessary information for structural modeling of the platform.

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Figure 7.11 shows the fire-related deformation of the main and secondary
beams. The part of the platform deck that was directly affected by the fire is
illustrated in Figure 7.12 . The main element of the platform deck that transfers
the load to the piles is the truss system (see Figure 7.13 ). Unfortunately, in this
case the truss system was also affected by the fire; the hatch part was exposed to
temperatures greater than 732 ° C and other parts were exposed to temperatures

from 427 to 732 C.

Figures 7.14 and 7.15 present the locations of the damage and zones highly
affected by the fire on the platform deck for the main and secondary beams and
the main truss system, respectively.
The isometric view in Figure 7.14 shows the deck beams that were directly
affected by the fire. Site measurements were performed by taking a sample of
structural elements of the platform not affected and affected by fire; the test
included structural dimensions and hardness readings.
Estimation of the material properties is based on the hardness readings. All
materials weaken with increasing temperature and steel is no exception.
Strength loss for steel is generally accepted to begin at about 300

°