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Conceptual design methodology for modular lightweight structures in cement matrix composites

Friday, 23 February, 2007 - 17:00
Campus: Brussels Humanities, Sciences & Engineering campus
Ellen De Bolster
phd defence

In this work, a conceptual design methodology is developed for modular lightweight structures, consisting of hypar-shaped construction elements. The construction elements all have a sandwich cross-section and faces in cement matrix composites. Due to the lightweight characteristic of the structures under study, the environmental loadings and specifically their fluctuations become important structural issues, as is their effect in serviceability limit state. They are accounted for in a quasi-static design approach in which an initial static design (that is obtained as is the case for common heavy-weight structures) is adapted through subsequent static calculation-iterations, accounting for the changed live load and related material response. The most important live load to consider is the wind, since wind exhibits high fluctuations on a daily basis. In this work, the wind is defined deterministically through the use of long term data yielding different combinations of {frequency of occurrence, wind direction, wind force}. The non-elastic cement matrix composites, in which the structures are materialized, respond to the repeated wind loading by a reduction in stiffness and an increase in residual strain. Both material properties are modelled in this work at four distinct tensile stress levels through the use of phenomenological material models. Finally, the conceptual design methodology that combines the determination and application of the wind and the related material response is then validated according to several case-studies.