Seismic Performance Evaluation of RC Beam-Column Connections in Special and Intermediate Moment Frames

This article presents the results of a research project aimed at investigating the seismic performance criteria of beam-column connections in reinforced concrete (RC) moment frames. A total of 112 RC beam-column connection tests were examined in detail. All the test specimens were qualified as either special moment frame (SMF) or intermediate moment frame (IMF) connections, based on the design and detailing requirements of ACI 318-08 [2008, Ch. 21]. The performance acceptance criteria, originally defined for steel moment frame connections in the 1997 edition of the AISC Seismic Provisions, were employed to evaluate the seismic performance of the RC connection specimens. Most of the specimens that satisfied the ACI 318 design requirements applying for SMFs were found to be ductile up to a plastic drift of 3% without any major degradation in strength, which satisfied the AISC performance acceptance criteria. This is most likely attributed to the stringent ACI 318-08 requirements for joints in SMFs. On the other hand, more than 40% of the IMF connections were not satisfactory based on the AISC criteria applying for steel IMF connections. Joint shear stress level showed more significant effect on their seismic performance than the column-to-beam flexural strength ratio. It is believed that inadequate joint detailing prevented these connections from developing their full beam flexural capacity, which resulted in premature strength deterioration and subsequent failure. Based on the findings, it is recommended that design requirements for beam-column connections in RC IMFs should be revisited and enhanced; otherwise, the R-factor assigned for RC IMFs should be somewhat reduced to accommodate their smaller ductility than intended by the ACI 318 requirements.