Case Study on the Seismic Performance of Reinforced Concrete Intermediate Moment Frames Using ACI Design Provisions

In reinforced concrete design, seismic provisions outline three types of moment resisting frames for use in high, moderate, and low seismic regions. However, there has been no methodology for assessing the performance of these structures other than through observations from actual seismic events or physical testing. The Applied Technology Counsel (ATC) has developed the ATC-63 Methodology (now FEMA P695) for assessing the seismic performance of structures through mathematical simulation, which may be used to assess the performance of reinforced concrete frames. This study investigates the performance of reinforced-concrete intermediate moment frames (IMF) used in moderate seismic zones. In this study, a four-story and six-story IMF were designed; once using current American Concrete Institute (ACI) seismic provisions and again with the addition of a strong-column weak-beam ratio. The earthquake simulation and dynamic analysis software OpenSees was then used to model the frames and analyze their structural performance. The ATC-63 Methodology as outlined in FEMA P695: Quantification of Building Seismic Performance Factors was used to assess the performance, focusing namely on the IMF's median collapse capacity, in terms of spectral acceleration. Three major findings applicable to IMFs of the type and height modeled were produced from the study. First, the results indicate that the current IMF provisions of ACI-318 2008 do provide acceptable seismic performance. Second, the addition of a strong-column weak-beam ratio did not offer significant improvement over current provisions. Third, the study indicates a potential concern for shear failure occurring that the models would not detect. Further investigation is needed to address this concern. These results add insight into the design provisions for intermediate moment frames and contribute to the technical base for future criteria and study.