An overview is presented of life-cycle optimisation in the establishment of reliability-and performance-based seismic design requirements for multi-storey systems. Alternative approaches are presented for the development of seismic vulnerability functions that do not require the determination of lateral deformation capacities. The influence of damage accumulation on the evolution of the seismic reliability functions is discussed, and some results are presented about the sensitivity of the seismic reliability and performance functions to the contribution of energydissipating devices to the lateral strength and stiffness of multi-storey frames. The process of structural damage accumulation resulting from the action of sequences of seismic excitations is taken into account in the assessment of life-cycle system reliability and performance, and in the formulation of reliability and optimisation criteria and methods for the establishment of structural design requirements and for the adoption of repair and maintenance strategies. Problems related to the transformation of research results into practically applicable seismic design criteria are briefly discussed. Several illustrative examples are presented.

Structural reliability analyses of fixed marine platforms subjected to storm wave loading are performed to assess deck elevations. Platforms are modeled as a series system consisting of the deck and jacket bays. The structural reliability analyses are carried out assuming dominant failure modes for the system components. Upper and lower bounds of the probability of failure are computed. The variation of the reliability index per bay component as a function of wave height, with a focus on those wave heights that generate forces on the deck, is analyzed. A comparison is given for the deck probability of failure and the lower bound probability of failure of the jacket in order to assess how the deck or the jacket controls the probability of failure of the system. Results are also given for reliability analyses considering different deck elevations. Finally, an analysis of the total probabilities of failure, unconditioned on wave heights, is given.

This paper presents the definition of lower deck elevation (LDE) of fixed offshore platforms in Mexican part of the Gulf of Mexico (GoM), which were applied in the Mexican code for design and assessment of fixed offshore structures NRF-003-PEMEX-2007. This was obtained as a result of a decision methodology developed here, an optimization algorithm composed of an objective minimization function subject to a safety restriction and by the application of a set of real structural maintenance and equipment replacement costs. Platform projected service life dependent total costs of LDE contemplate expected costs of structural and equipment maintenance after the occurrence of tropical cyclones and northers, and the expected cost of equipment mobilization. This work regards a group of offshore platforms in the Bay of Campeche whose elevation lies between 15.85 and 19.10 m above mean sea level, as well as recent metocean hazard information. Similar expected values of total costs due to maintenance and repair were obtained, while safety constrains demand the LDE not to be less than +19.10 m.

A group of tower type offshore structures in 125 m. water depth is studied. The objective is to determine design and assessment parameters for this kind of structures. The increment in the initial cost of a structure in order to reduce the probability of failure 10 times (ΔCi) yields in the optimal probability of failure. A life quality index (LQI) approach allows making a comparison. Safety factors were obtained as function of ΔCi and hydrocarbons production of the platform.

This paper studies the fatigue problem of risers in marine platforms located in the Bay of Campeche, Mexico. Considering the future wave loads on these systems, the lifetime of these structures is obtained. Possibly, these systems have problems of fatigue in the zones where large stress concentrations appear. The risers fatigue analysis with a regular pipeline section is carried out taking into account operational and environmental load conditions. Due to operation, among others, the risers are subject to internal pressure, thermal expansion, and the type of fluid that transports. In order to take into account the environmental conditions one it is considered that the riser is subject to waves, current and ground movement, which were suitably modeled in the analysis. The supports on the platform, in the riser zone, were considered. They take into account the movements and their corresponding lateral stiffness. To evaluate the load cycles to which the risers are subject, for the study zone, the annual rates of occurrence and all the sea states have been considered. In addition, all the possible heights and directions of the wave that might be present in the Bay of Campeche have been considered the accumulated damage caused by the diverse cycles of stresses by means of the Palmgren Miner rule are assessed. This study includes the analysis of representative number of risers with different diameters and recent inspections. This allows us to know, in an approximated way, the present condition of the risers; it an give us suitable information for the calculation of the fatigue reliability and therefore define the present levels of structural safety of these facilities.