Effects of detailing on panel zone seismic behaviour in special moment resisting frames with unequal beam depths

Special moment resisting frames (SMRF) are commonly used as lateral-load resisting systems in seismic design. The results of recent studies have shown that the seismic performance of such frames can be improved by paying particular attention to the detailing of their panel zones (PZ) and beams. Panel zones with unequal beam depths appear to be a special case of connection detailing, which has not received sufficient attention so far and could lead to complications in everyday engineering practice. Some full-scale experiments of connections with unequal beam depths were performed, using different continuity plate arrangements (inclined and straight plates), and different corner clip lengths. A companion analytical study was also conducted, for which results have shown that the correct selection of inclined or straight continuity plates, with special detailing of the PZ, could keep the behaviour of the latter within safe margins. Such considerations could prevent the occurrence of failure in the PZ, and significantly improve the seismic resistance of SMRF with unequal beam depths.

Experimental Investigation of Reduced Beam Section Moment Connections without Continuity Plates

The AISC 2002 Seismic Provisions for Structural Steel Buildings recommend that usage and sizing of beam flange continuity plates across the column web shall be based on tests. The Recommended Seismic Design Criteria for New Steel Moment-Frame Buildings ( FEMA-350) state that unless project-specific testing is performed to demonstrate that continuity plates are not required, moment-resisting connections should be provided with continuity plates when the thickness of the column flange is below a minimum value. One of the preferred moment connections for seismic-resistant steel frames is the reduced beam section (RBS) moment connection, which has performed well under cyclic loads in laboratory testing. To demonstrate the effectiveness of the RBS moment connection without continuity plates in the panel zone, a series of four full-scale tests of exterior beam-column connections was carried out. All materials were A572 Grade 50 steel; the beams were W30×132, two of the assemblies used W14×283 columns, and the other two used W18×211 columns. The beams were welded to the columns using complete joint-penetration welds. All four tests demonstrated that the RBS connections without continuity plates developed a total interstory drift angle greater than 0.04 radians and met the requirements for special moment frames.