The accumulated damage in aging Steel Structures, especially due to fatigue, is considered as a critical phenomenon that affects safety and serviceability of civil engineering structures. Although, fatigue damage is influenced by various parameters such as the frequency of loading, sequence of load application, material properties, geometry, etc, in practice simplified S-N curve is typically used for condition assessment. In order to mitigate risks of catastrophic failure resulting from fatigue brittle nature, even in normally ductile materials, researchers have generated several non-linear damage models to predict the remaining service life of the structure considered. These models are mainly based on the S-N curve, material dependent parameters and loading conditions. However, due to the complexity of the fatigue phenomenon and expensive-long term full scale experimental testing, the models presented in literature have shown high degree of uncertainty due to simplifications of mathematical models, parametric uncertainties and varying loading conditions. Furthermore, the usage of S-N curve generated from experimental work is limited to identical loading mechanism and constant boundary conditions. Therefore, this study presents a structural health monitoring approach to overcome the limitation and inaccurate estimation of damage quantification models. The suggested framework relies on fatigue damage prediction models incorporated with real time damage records. All sources of uncertainty are incorporated in the health monitoring scheme to guarantee an optimal statistical identification of the state damage. The accuracy and robustness of the presented scheme will be assessed through a set of controlled experiments and numerical simulation of real case scenario.

Due to the increasing number of fire accidents that are able to leave behind great losses and complete collapse of structures, structural fire safety has become a major consideration in the design of high rise buildings. The aim of this research is to evaluate how certain factors can influence the critical time (fire resistance) of concrete encased dual Ishaped steel columns under fire loads using ABAQUS. The parameters that were considered are: the applied load level, stiffness of surrounding structure to column, section dimensions, concrete cover, and axial distance from concrete surface to longitudinal bars. In order to achieve the posted objective, numerical investigation using ABAQUS software was used. The analysis method considered is an alternative of Heat Transfer Method. This approximate method is based on dividing the section into layers at the location of experimentally recorded temperature-time histories and then linking load amplitude to its corresponding layer. In the study, twelve models were generated which belong to three types of sections subjected to high and low load levels, as well as, high and low surrounding stiffness. It was found that decreasing the load level and increasing the concrete cover have a big influence in increasing the critical time of the column. The effect of increasing the stiffness of the surrounding on reducing the critical time is insignificant and can be eliminated by designers. However, the effect of slenderness (section dimensions) on the restraining axial force requires further investigation.

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