Civil Engineering Reference
In-Depth Information
Chapter 7
Assessment of Existing Structures
and Repairs
7.1 INTRODUCTION
Worldwide, oil and gas offshore projects have the same problem: platforms are
aging. The peak of oil exploration and development extended from the mid
1970s to the mid 1980s, especially in the Middle East, so platforms now
have been aging for over 40 years. As stated in other chapters of this text, off-
shore structure platforms offer unique considerations in design, construction
and applied loads.
When compared to traditional onshore structures, offshore structure plat-
forms are very different. In this chapter, we focus on those differences. Because
there are many steel structures, many researchers and many codes (i.e., ACI,
BS, EC and Egyptian code, Indian code) worldwide, the methodology of assess-
ment for traditional onshore structures can be very different from that for off-
shore structures. In addition, many steel structures have failed for different
reasons, which provides us insight into evaluation and assessment of the
structures.
Most of the offshore structure platform designs are performed according to
API RP2A; however, API focuses its design on platforms for construction in the
Gulf of Mexico (GoM), the area where construction of fixed offshore platforms
was pioneered. (Around 1960, platform design was based on engineering
offices
'
experience, and engineering firms proposed the API RP2A standard
based on their experience. Since its initial development, API RP2A has under-
gone many revisions.) Because globally there are only a few thousand offshore
platforms and the number of failed platforms is not great, there are only a few
failed platforms (most of them due to fire) available for case studies, and there
are a minimum number of engineering companies that have experience in rea-
listic assessment of offshore platforms.
Before beginning the assessment process, it is important to highlight that
structural analyses of old platforms were performed and the offshore structure
has a special nature because the main forces affecting it are waves and wind,
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