Assessment of eurocode provisions for eccentrically loaded concrete-encased columns with out-of-code parameters.

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Kasumba, Caron
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The University of Zambia
This study aims to comprehensively evaluate the viability of applying the current eccentric compressive design provisions outlined in Eurocode 4 (EC4) for concrete-encased steel composite columns with out-of-code parameters. Specifically, the research undertakes an in-depth analysis of the impact of material and geometric properties on the compressive design provisions prescribed by EC4, particularly under eccentric loading conditions, and checking the viability of applying these provisions specifically for high strength concretes and steels. In addition, this study aims to identify any potential shortcomings in the current design guidelines and to suggest modifications that can enhance their accuracy when applying these provisions beyond code specifications. Despite no reported failures or complaints associated with the current provisions, it is important to note that there has been limited work to assess these provisions in relation to experimental or detailed non-linear finite element analyses and the current provisions are limited to C60/75 concrete and S460 steel despite recent advancements in high strength concrete and steel. This lack of assessment means that the extent to which the current provisions provide the required levels of safety when extended beyond code specifications remains uncertain. To address these objectives, the research delves into a comprehensive literature review encompassing both experimental and numerical investigations that delve into the compression behavior of eccentrically loaded concrete encased columns, including both in-code and out-of-code parameters. By critically examining the methodologies employed in these experiments, the research aims to ensure that the collected data is both reliable and consistent. The evaluation process involves the compilation of experimental and numerical data gathered from the literature. This data is then rigorously assessed against the actual behavior exhibited by concrete-encased steel composite columns. The findings reveal that while the current compressive design provisions within EC4 effectively predict the behavior of concrete-encased steel composite columns with in-code parameters, they exhibit notable inaccuracies when it comes to eccentric loading and out-of-code parameter. In fact, a substantial 46% of the columns examined in the database are found to be under-designed based on these provisions. Consequently, the study proposes refined compressive design provisions that take into account the concept of modification factors.The suggested modifications incorporate adjustments to model factors to account forcolumns outside the scope of the code. It is important to recognize that this adjustment may lead to designs that are more conservative even for the columns with out-of-code parameters. However, the resultant design approach offers a 95% probability of producing designs that are suitably conservative. This not only enhances the ductility and energy absorption capacity of the columns but also improves their overall structural performance. Ultimately, the findings from this study offer valuable insights into the intricate behavior of concrete-encased steel composite columns with out-of-code parameters. Moreover, the study provides constructive recommendations aimed at refining the accuracy of the existing design guidelines for extension to use of high strength concretes and steel in these composite columns.
Thesis of Master of Engineering in Structural Engineering.