Applicability of composite structures to sway frames

The present research project aims at improving and implementing the knowledge in the field of the applicability composite structures to sway frames. The field of application concerns static as well as seismic loading. The major objective of this research was to find out in how far the design rules for steel frames as given by the Eurocodes are applicable to composite structures and which particularities should be considered more carefully. The project has addressed this aspect by experimental, numerical and analytical activities that are comprehensively highlighted in this present final report, to enable further studies in this field. Reference frames for static and seismic loading have been designed as basis and starting point for the research performed. It was concluded from the beginning that sway frames used in residential or administrative buildings can only comprise a total of three full storeys. More levels usually require core elements to be used for elevators or massive staircases that brace the structure and eliminate the sway effects to the greatest possible extent. Modem design methods such as the semi-continuous joint concept and their effects on the overall structural behaviour were applied to realise an economic and practicable design but not at least to meet the sway-criteria given by the Eurocodes (EC4 and EC8). These criteria could hardly be met due to the fact that the size of the column profiles is also dominated by the practicability of realising the beam-to-column-joints. For high lateral loads such as for earthquakes of high intensity it is almost impossible to be in compliance with the restrictions given by the codes in particular when regarding the serviceability limit state criterion. A Pseudo-dynamic test was performed at ELSA Lab at JRC in Ispra to simulate a composite structure in an high intensity earthquake and a static test representing increasing wind loads was performed at Bochum University. Their critical zones located in the beam-to-column joints were also tested in isolation. Material (Steel profiles, sheetings and reinforcement bars) of the same rolling have been used to get an as good comparison as possible to the overall structural analysis and to allow for non-linear structural analyses by using computer programmes. Tests on modifications to the applied joints were also performed to meet other design requirements and to improve the experimental response. Following the aforementioned research strategy, conclusions for designing and analysing composite frames and joints were drawn. These conclusions are presented in section 10 of this draft final report and concern the general and specific design of moment resisting frames in seismic static loading. It can generally be stated that the overstrength of the material constitutes a problem in designing dissipative zones for both the global behaviour of frames as well as the local one of joints. This aspect is reflected in the assessment of the members/ components that should contribute to the desired level of ductility which essentially determines the seismic response (reflected by the q-factor in EC8) as well as the exploitation of the full plastic chain in static loading. The problem is widely discussed on the basis of numerical results from non-linear dynamic and static analyses.