ENHANCEMENT OF DUCTILITY IN SHALLOW FLOOR COMPOSITE BEAMS Panagiotis KIRIAKOPOULOS 1 , Simo PELTONEN 2 , Ioannis VAYAS 3 , Constantine SPYRAKOS 4 , Maria-Eleni DASIOU 5 ABSTRACT Ductility is one of the most important properties for the design of flexural members. A number of rules are based on the assumption that adequate amount of ductility is available. However, securing that the desired ductility requirement can be realized is not a simple task. EN 1994 allows the use of linear elastic methods for global analysis, while the cross-section resistances can be based on rigid-plastic stress blocks providing that class 1 or 2 cross-section are selected. Currently, classification rules are only available for ordinary composite beams, however, for SF-beams, no specific rules are given. The SF-beams integrated in the floor slab form a composite section where the interaction is either intentional, requiring a shear connection, or “unintentional” when no special shear connection is designed. In both cases, the effective cross-section for each design situation has to be recognized. When ductility requirements are included, the shear connection design plays an important role. Design according to plastic theory or abiding by EN 1998 and EN 1991-1-7 requirements presupposes that adequate ductility is available, however rules for verifying adequate ductility appear only in EN 1998. In this paper, results of a test program are presented together with associated FE analysis in various configurations of SF- beams. The importance of appropriate detailing is critically revealed by the results and some preliminary methods for enhancing the ductility of SF-beams are discussed. Keywords: Deltabeams; Shallow floor composite beams; Ductility 1. INTRODUCTION Deltabeam is a slim-floor composite beam that is integrated into the floor. It is designed to be used as structural element combined with all general concrete slab types: hollow-core slabs, filigree slabs, composite steel decking, trapezoidal steel decking slabs and cast-in-situ concrete slabs. Deltabeams act as steel beams before the infill concrete has reached the required strength. After placement of the slabs, the beams are completely filled with concrete on-site through regularly spaced web openings, thus forming a composite structure after the concrete has hardened. Shear resistance of the composite cross- section is considerably higher than that of the steel part because of the contribution of the core concrete. Findings from the investigation of the shear strength of Deltabeams are reported by Leskela et al. (2014). Multiple fire tests (Peltonen 2010) have proven Deltabeam to have an excellent fire resistance (rate higher than R180). These resistance values depend on the thickness of the bottom plate and the number of fire rebars placed inside the boxed core of the beam. The fire rebars compensate the strength loss of the bottom plate, meaning that additional external fire protection is not normally needed. 1 PhD candidate, NTUA, Athens, Greece, Panagiotis.Kiriakopoulos@peikko.com 2 R&D Manager, Peikko Group Ltd, Lahti, Finland, Simo.Peltonen@peikko.com 3 Professor, NTUA, Athens, Greece, vastahl@central.ntua.gr 4 Professor, NTUA, Athens, Greece, cspyrakos@gmail.com 5 PhD candidate, NTUA, Athens, Greece, medasiou@mail.ntua.gr