Ductile plastic hinge zones in beams of reinforced concrete frames are known to incur extensive damage and elongate. This ‘beam elongation’ can inflict serious damage to adjacent floor diaphragms, raising concerns of life safety. In light of this, the slotted reinforced concrete beam was investigated as a promising non-tearing floor substitute for conventional design. It consists of a conventional reinforced concrete beam, modified with a narrow vertical slot adjacent to the column face, running approximately three-quarters of the beam depth. Seismic rotations occur about the remaining concrete “top-hinge”, such that deformations are concentrated in the bottom bars of the beam, away from the floor slab, and beam elongation is minimised. The inclusion of the slot raised several design issues which needed to be addressed. These were the shear transfer across the top-hinge, buckling of bottom longitudinal reinforcement, low cycle fatigue, bond anchorage of reinforcement in interior joints, interior joint design, detailing with floor units and beam torsion resulting from eccentric floor gravity loads. These issues were conceptually investigated in this project. It was found that most issues could be resolved by providing additional reinforcement and/or specifying alternative detailing. As part of the experimental investigation, quasi-static cyclic tests were performed on in-plane beam-column joint subassemblies. Specimens tested included exterior and interior joint subassemblies with slotted-beams and a conventional exterior joint as a benchmark. This was followed by a test on a slotted-beam interior joint subassembly with precast floor units and imposed gravity load. Experimental tests revealed significant reductions in damage to both the beam and floor when compared to conventional beams. Issues of bar buckling, bond-slip and altered joint behaviour were also highlighted, but were resolved in the final test. A simple analytical procedure to predict the moment-rotation response of slotted-beams was developed and verified with experimental results. This was used to perform sensitivity studies to determine appropriate limits for the concrete top-hinge depth, top-to-bottom reinforcement ratio and depth of diagonal shear reinforcement. For the numerical investigation, a multi-spring model was developed to represent the flexural response of slotted-beams. This was verified with experimental tests and implemented into a five-storey, three-bay frame for earthquake time history analyses. To provide a benchmark, a conventional frame was also setup using the plastic hinge element developed by Peng (2009). Time history analyses showed that the slotted-beam frame response was very similar to the response of a conventional frame. Due to greater hysteretic damping, there was a slight reduction in the average interstorey drift and lateral displacement envelopes. The slotted-beam frame also exhibited 40% smaller residual drifts than the conventional frame. The research carried out in this thesis showed slotted reinforced concrete beams to be an effective non-tearing floor solution, which could provide a simple and practical substitute for conventional reinforced concrete design.

The recent earthquakes in Christchurch have made it clear that issues exist with current RC frame design in New Zealand. In particular, beam elongation in RC frame buildings was widespread and resulted in numerous buildings being rendered irreparable. Design solutions to overcome this problem are clearly needed, and the slotted beam is one such solution. This system has a distinct advantage over other damage avoidance design systems in that it can be constructed using current industry techniques and conventional reinforcing steel. As the name suggests, the slotted beam incorporates a vertical slot along part of the beam depth at the beam-column interface. Geometric beam elongation is accommodated via opening and closing of these slots during seismically induced rotations, while the top concrete hinge is heavily reinforced to prevent material inelastic elongation. Past research on slotted beams has shown that the bond demand on the bottom longitudinal reinforcement is increased compared with equivalent monolithic systems. Satisfying this increased bond demand through conventional means may yield impractical and economically less viable column dimensions. The same research also indicated that the joint shear mechanism was different to that observed within monolithic joints and that additional horizontal reinforcement was required as a result. Through a combination of theoretical investigation, forensic analysis, and database study, this research addresses the above issues and develops design guidelines. The use of supplementary vertical joint stirrups was investigated as a means of improving bond performance without the need for non-standard reinforcing steel or other hardware. These design guidelines were then validated experimentally with the testing of two 80% scale beam-column sub-assemblies. The revised provisions for bond within the bottom longitudinal reinforcement were found to be adequate while the top longitudinal reinforcement remained nominally elastic throughout both tests. An alternate mechanism was found to govern joint shear behaviour, removing the need for additional horizontal joint reinforcement. Current NZS3101:2006 joint shear reinforcement provisions were found to be more than adequate given the typically larger column depths required rendering the strut mechanism more effective. The test results were then used to further refine design recommendations for practicing engineers. Finally, conclusions and future research requirements were outlined.