Structural durability is an important criterion that must be evaluated for every type of structure. Concerning reinforced concrete members, chloride diffusion process is widely used to evaluate durability, especially when these structures are constructed in aggressive atmospheres. The chloride ingress triggers the corrosion of reinforcements; therefore, by modelling this phenomenon, the corrosion process can be better evaluated as well as the structural durability. The corrosion begins when a threshold level of chloride concentration is reached at the steel bars of reinforcements. Despite the robustness of several models proposed in literature, deterministic approaches fail to predict accurately the corrosion time initiation due the inherent randomness observed in this process. In this regard, structural durability can be more realistically represented using probabilistic approaches. This paper addresses the analyses of probabilistic corrosion time initiation in reinforced concrete structures exposed to chloride penetration. The chloride penetration is modelled using the Fick's diffusion law. This law simulates the chloride diffusion process considering time-dependent effects. The probability of failure is calculated using Monte Carlo simulation and the first order reliability method, with a direct coupling approach. Some examples are considered in order to study these phenomena. Moreover, a simplified method is proposed to determine optimal values for concrete cover.

Fixed marine structures is widely utilized as production or oil recovering platform in the shallow sea, and are also subject to random loading. Jacket structures subject to random loading pose difficulties in both analysis and design, with solutions commonly only viably acquired employing a numerical technique. Performance of offshore jacket platforms is highly related to configuration of the braces. In this regard, probabilistic scheme is a good option for evaluating jacket structures. In this paper, the performance of Resalat jacket structure located in the Persian Gulf with different kinds of bracing configuration is investigated. We present a new measuring index for optimum arrangement of bracing configuration which is defined as probabilistic design criterion. The Latin Hypercube Sampling (LHS) method, which is a more advanced and appropriate form of the Monte Carlo simulation technique, is used to investigate different configurations. Hereof, probabilistic analysis is performed on different configurations of platform structure using the LHS method. The elastic modulus is employed as the random input variable for probabilistic analysis, and the maximum values of stress and horizontal displacement are selected as the random output variables. Also, at the end of the calculations, the optimum configuration can be found. It is demonstrated that the proposed probabilistic optimization algorithm is capable of effectively determining the optimum configuration of jacket platform structures. Therefore, an optimum bracing configuration can be useful in evaluating and designing the fixed marine structures.

This paper develops a reliability-based computational methodology for modeling nonstationary random critical earthquake loads on structures using the site response spectra.The power spectral density function and the envelope parameters of the ground acceleration are taken to be unknown and are computed such that the structural reliability index is minimized subjected to constraints reflecting known knowledge on the site seismicity.Specifically، bounds on the total energy، zero-crossing rate and entropy rate of the earthquake signal and positivity requirements are considered. These constraints are derived from the site response spectra. The formulation combines methods of structural reliability analysis، response surface fitting، FORM and nonlinear programming. Numerical illustrations on reliability-based critical earthquake inputs for elastic and inelastic frame structures are presented.

This paper develops a reliability-based computational methodology for modeling nonstationary random critical earthquake loads on structures using the site response spectra. The power spectral density function and the envelope parameters of the ground acceleration are taken to be unknown and are computed such that the structural reliability index is minimized subjected to constraints reflecting known knowledge on the site seism city. Specifically, bounds on the total energy, zero-crossing rate and entropy rate of the earthquake signal and positivity requirements are considered. These constraints are derived from the site response spectra. The formulation combines methods of structural reliability analysis, response surface fitting, FORM and nonlinear programming. Numerical illustrations on reliability-based critical earthquake inputs for elastic and inelastic frame structures are presented.