Seismic performance of the slotted beam detail in reinforced concrete moment resisting frames.

Abstract

During recent seismic events, traditional reinforced concrete structures that have been shown to have performed as designed have had to be demolished due to prohibitive rehabilitation costs. The main contributors to rehabilitation costs were residual building inclination and damage to the structural system. In traditional reinforced concrete moment frames, this damage has been shown to be attributable either directly, or indirectly, to the formation of plastic hinge zones and the undesirable behaviour that can result. This research investigated and developed the reinforced concrete slotted beam as a means to increase the performance and safety of reinforced concrete moment frames during an earthquake. The slotted beam can significantly decrease damage sustained to the frame and floor of a building, while maintaining current build costs. The objective of this research was to develop the reinforced concrete slotted beam detail to a state in which it was ready for use by the New Zealand construction industry. To achieve this objective, many aspects of reinforced concrete slotted beam design, construction and performance were investigated. Existing design recommendations developed by previous researchers were examined through the design of a realistic large scale superassembly. Based on the results and observations of the experiment, design recommendations were modified and developed. The superassembly was subjected to full biaxial seismic displacements to investigate complex three-dimensional interactions between structural elements within a building typology representative of New Zealand construction. The practicality of the design, manufacture and erection of the reinforced concrete slotted beam detail was examined through the involvement of industry to construct the superassembly. The lessons learnt throughout the design and construction process were used to develop recommendations, which aimed to expedite the specification of the reinforced concrete slotted beam detail. Well-detailed traditional reinforced concrete structures have had to be demolished following earthquakes due to concerns regarding the residual capacity of the connections. The slotted beam detail increases the plastic strain in the bottom longitudinal reinforcement. Hence, the residual capacity of the slotted beam following a seismic event was examined. Portions of superassembly SA1 were extracted and tested to determine the effect that previous loading had on both performance and reliability. An economically viable method for retrofitting the slotted beam was developed to decrease the life-cycle costs of a slotted beam building by preventing the necessity for demolition after a major earthquake if it were deemed that the residual capacity was not great enough, or not known with sufficient certainty. Recommendations for the design and implementation of a retrofit scheme for the slotted beam were developed. Preventing the need to retrofit slotted beam connections following an earthquake is preferable. Hence, external dampers that were either easily replaceable or could withstand multiple earthquakes were tested for both retrofit and new-build applications. A structure that exhibits reduced damage during an earthquake, returns to plumb and requires little repair prior to reoccupation is the goal of seismic building design. This can be achieved using the slotted beam detail in conjunction with external energy dissipation devices. Given the rise in the popularity of numerical models for both research and design, it was important to develop a numerical model that was not only capable of reproducing realistic slotted beam behaviour in three dimensions, but could be quickly set up using only gross section and material properties. The new numerical model was verified against experimental data before being used to compare both connection and structural responses of slotted beam and traditional systems.