Reliability-Based Design of Oil and Gas Platform Deck Structural Steel Beam Girder

Abstract

This study investigates the reliability-based design of steel beam
girders supporting oil and gas separator deck platforms, with the
objective of optimising safety and material efficiency.
Conventional deterministic design, which applies conservative
safety factors, was complemented with probabilistic methods using
the Hasofer–Lind Reliability Index and the First-Order Reliability
Method (FORM). The deck system was configured with reduced
stanchions for spatial efficiency and subjected to combined
operational and environmental loads. Deterministic analysis
showed that increasing supports improved performance: maximum
shear reduced from 138.2 kN at two supports to 33.4 kN at five,
bending moment from 823.6 kNm to 95.9 kNm, and deflection from
124.8 mm to 16.6 mm. Probabilistic results revealed greater
sensitivity, with the reliability index (β) improving as live-to-dead
load ratios increased but falling below the JCSS target (β = 4) at
higher live loads, with values as low as −1.04. Dead load increases
consistently reduced β, while deflection reliability improved
markedly with additional supports, rising from 0.40 at two supports
to 4.65 at five. Overall, deflection governed structural reliability,
indicating that deterministic design alone may mask serviceability
risks. Reliability-based approaches therefore enable more accurate
safety evaluation and rational optimisation of support
configurations in offshore deck systems.