Stability and Ductility of Steel Structures 2019 – Wald & Jandera (Eds) © 2019 Czech Technical University in Prague, Czech Republic, ISBN 978-0-367-33503-8 Performances of moment resisting frames with slender steel and composite sections in low and moderate seismic areas H. Degée Hasselt University, Belgium Y. Duchêne Design office Greisch, Belgium B. Hoffmeister RWTH Aachen, Belgium ABSTRACT: Specific investigations have been carried out regarding typical beam profiles commonly used for steel and composite frames. In a first stage, experimental tests on class-3 and class-4 built up steel profiles and composite beam-to-column nodes were performed. The meas- urement results were evaluated with regard to the development of the hysteretic behavior with particular emphasis on the cyclic degradation. These test results have been used as reference for the calibration and validation of numerical models aiming at extending the scope of the experi- mental outcomes through appropriate parametric variations regarding the behavior of nodal con- nections as well as towards the global analysis and behavior of structures made of class 3 and 4 profiles. Based on the outcomes of these investigations, practical design recommendations are finally derived for moment resisting frames located in low and moderate seismicity regions. 1 INTRODUCTION According to current version of Eurocode 8 only cross-sectional classes 1 or 2 are permitted for steel or composite structures when a considerable behaviour factor (≥1.5 or 2.0) is intended to be taken into account. Within moment resisting frames almost all members are affected by this limitation: – Single-bay – single-storey frames: Such structures are part of a highly competitive market requiring a strong optimisation in terms of material requirement and ease of construction. Light weight steel frames are an optimum solution so far, with the exception of seismic regions where the above mentioned restrictions strongly limit their applicability despite their low masses. On the other hand such structures may develop plastic hinges alternatively in the columns or beams and thus offering the possibility to adjust the static stiffness and resistance e.g. by means of haunches. In order to remain competitive however both columns and beams need to be kept slender yielding cross-sectional classes 3 or 4. Such cross- sections however can develop significant cyclic bending capacity which, although at a lower level than the elastic one, can be sufficient in order to resist seismic actions. – Multi-bay – multi-storey composite buildings: Due to the high position of neutral axis of composite cross-sections in negative bending the web of steel profiles is very often to be classified as class 3 or 4 section, although almost all rolled steel profiles may be classified as class 1 or 2 cross-sections. On the other hand in such kind of buildings under seismic actions there are always both positive and negative moments developing at the corners of the frame and thus providing a significant resistance and dissipation capability when the entire system is considered. 321