It was not thought that there would be some major flaws in the design of widely used steel moment frames until the Northridge Earthquake hit the California on January 17, 1994. Until then, steel moment frames were practiced as the most ductile system and were used in buildings from few stories to skyscrapers. The heavy devastation from Northridge Earthquake was an alarm for all the people related to the design and construction of such structures and pushed everybody to act fast to find some possible solutions to such never-expected-problems. Following the earthquake, FEMA entered into a cooperative agreement with the SAC joint venture in order to get a transparent picture of the problems in the seismic performance of steel moment frames and to come up with suitable recommendations. The research was specifically done to address the following things: to inspect the earthquake-affected buildings in order to determine the damage incurred in the buildings, to find out ways to repair the damaged buildings and upgrade the performance of existing buildings, and to modify the design of new buildings in order to make them more reliable for seismic performance. Among the various new design suggestions, the Reduced Beam Section (RBS) connection has been one of the most efficient and reliable option for high ductility demands. The purpose of this research was to study the behavior of concrete slabs in the performance of steel moment frames with reduced beam sections based on ductility, strength and stiffness. The slab is an integral part of a building. It is always wiser to consider the slab in order to assess accurately the seismic behavior of a building under the earthquake loading. In this research, two sets of finite element models were analyzed. Each set had one bare steel moment frame and one concrete slab frame which acted as a composite section. The connections were designed using the AISC Seismic Design manual (AISC 2012). The finite element modeling was done using NISA DISPLAY-IV (NISA 2010). All the models, with and without the slab were analyzed under the same boundary conditions and loads. Both non-linear and linear analyses were performed. The results from non-linear analysis were used to compare the ductility and strength whereas linear analysis results were used to compare the stiffness between bare steel and composite frame models.
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