27 © Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin · Steel Construction 6 (2013), No. 1 Articles DOI: 10.1002/stco.201300005 Florea Dinu* Dan Dubina Calin Neagu Experimental and numerical evaluation of an RBS coupling beam for moment-resisting steel frames in seismic areas Beams with a span-to-depth ratio < 4 are not very common in the design of moment- resisting frames. For such beams, the shear stresses may become a controlling factor in the design, as the moment capacity is influenced by the presence of the shear. This is an important matter when such a beam is part of a seismic resisting system that is designed according to the dissipative concept. In this case the contribution from the shear force affects the dissipation capacity and plastic mechanism. This paper presents the test- based evaluation of moment frames with short beams and reduced beam section (RBS) connections, for the purpose of exploring the application of the plastic hinge model. Full- scale specimens, taken from an 18-storey building, have been tested. The test results and their interpretation are summarized here. 1 Introduction Owing to their inherent ductility, mo- ment-resisting frames are often used in systems resisting seismic forces. Inelas- tic behaviour is intended to be accom- modated through plastic hinges in beams near the beam-to-column con- nections, and also at column bases. Al- though considered as deemed-to-com- ply connections, welded beam-to-col- umn connections have experienced serious damage and even failures dur- ing strong seismic events. These failures have included fractures of the beam fange-to-column fange groove welds, cracks in column fanges and cracks through the column section [1]. To re- duce the risk of the brittle failure of such connections, either connection strengthening or beam weakening can be applied. The frst approach con- sists of providing sufcient connec- tion overstrength, e. g. by means of haunches or cover plates. The second approach can beneft from the “re- duced beam section” (RBS) or “dog- bone” concept, initially proposed by Plumier [9] and then developed and patented by ARBED, Luxembourg. (In 1995 ARBED waived all patent and claim rights associated with RBS for the beneft of the structural design community.) Proper detailing of the RBS, in- cluding fange cut-outs and beam-to- column welds, is needed to ensure the formation of plastic hinges in the re- duced zones. It is economical to keep the width of bays within certain limits because long bays make the structure fexible and therefore increase the drift, which may control the design. On the other hand, short bays can reduce the dissi- pation capacity due to the presence of large shear forces. As a result, the con- nection qualifcation specifes mini- mum span-to-depth ratios to be used for moment frame connections. When prequalifed connections are utilized outside the parametric limitations, project-specifc qualifcation must be performed to permit the prediction of behaviour and acceptance criteria [1]. This paper presents part of a re- search project that was carried out to check the validity of the moment frame connections of an 18-storey structure. The paper describes the calibration of Selected and reviewed by the Scientifc Committee of the 7 th International Workshop of Connections in Steel Structures, 30 May–2 June 2012, Timişoara, Romania * Corresponding author: forea.dinu@ct.upt.ro Cristian Vulcu Ioan Both Sorin Herban Fig. 1. Plan and elevation of building