Etude et modelisation du comportement sismique lineaire et non lineaire des structures metalliques multi-etagees contreventees par differentes configurations.

Abstract

Current provisions of the Algerian seismic code RPA99 version 2003, are inspired from American seismic design philosophy (UBC and AISC), and are based upon the knowledge of the eighties and nineties of last century in several aspects of technological and analysis of steel frames as they do not take into account the recent advances made in the field of earthquake engineering and do not follow the improved provisions in modern codes. Some of the deficiencies in existing provisions can be summarised: no recommended inelastic analyses (Pushover and Time-history), they not address any provisions on EBFs bracing systems, world-wide used as lateral resisting systems even in developing countries, i.e. Turkey and Iran, the absence of provisions concerning the semi-rigid connections and ambiguity concerning the recognition of soft weak-storey frames mechanism. The philosophy of the weak beam vs. strong column principle, is not explicitly stated in RPA99. The themes addressed in this PhD research work are part of possible improvements of existing recommendations relating to steel structures in RPA99 in future version. In fact, considering the above remarks and other considerations, the works embodied in this thesis have been aimed to contribute, through the results of compressive parametric studies, to future revision of the code RPA99 regarding the nonlinear analyses, EBFs and the soft-storey conditions. Actually, the study undertaken in this thesis stems from two different studies. Firstly, this thesis presents the results of comprehensive parametric study through geometrical 2D multi-storeys frames of three kinds of structural systems with different topologies: MRFs, MRFs-CBF and MRFs-EBFs. These models implanted in SAP2000 NL software in order to assess the global elastic and inelastic behaviours, taking into account material and geometric non linearities with relevant parameters thought to influence the seismic response, such as: structure slenderness, aspect ratio, type of bracing systems, number of storeys etc. Another analogous parametric analyses, highlighting the effect soft weak-storey have been performed on frames having irregular vertical stiffness in elastic and inelastic ranges taking into account geometric and material nonlinearities. The second part of the undertaken research work is this thesis concerns the elastic and inelastic behaviour seismic links which characterise EBFs structures. Primarily, a comparative parametric study on shear links was carried out with some available data in literature. Then, a study was conducted to assess the elastic and inelastic behaviours of a large range of long and short links subjected to the AISC (2005) loading protocol throughout 3D FEA models implanted in ABAQUS. Models take into account both geometric and material nonlinearities with large deflection and large strain capability. Also, the influence of web stiffeners on links was numerically investigated with different configuration of links. Encouraging results have been found as compared to recent research works (Čaušević 2008) for shear links and (Imani 2015; Suswanto 2017) for links subjected to monotonic cyclic loadings concerning key parameters. Finally, the author seriously believes that the time has come for RPA99, in its future version should to include nonlinear pushover analysis at least in its basic form with the fundamental mode of vibration, to adopt EBF structures as a lateral bracing system, with the provisions taken from international seismic codes i.e. EC8, AISC, because their provisions are very close to each other as they are all based on the works of Professor Popov and his colleagues, and to use any type of bracing system to reinforce structures with irregular vertical rigidity in the ground floor to avoid the formation of weak soft-storey mechanism.