Residual Capacity and Reparability of Moderately-Damaged Reinforced Concrete Ductile Frame Structures

Abstract

The experience of recent damaging earthquakes in New Zealand has highlighted the need for robust technical guidance on the reparability and residual seismic capacity of damaged reinforced concrete (RC) structures. The use of capacity design philosophies and the construction of ductile buildings has proven to be an effective method for achieving life-safety and collapse prevention objectives in earthquakes; however, following damaging events, a relatively high rate of demolition is observed in modern structures with low to moderate damage states. To address this issue, the development of engineering guidelines for the residual capacity and reparability of earthquake damaged structures is currently underway. Contributing to these efforts, this thesis addresses some key issues with respect to RC ductile frame structures. This is a common form of construction in New Zealand and saw particularly high rates of demolition following recent damaging earthquakes. Recent studies have investigated the residual capacity and reparability of slender flexure-dominated RC beams, subjected to moderate earthquake damage. Addressing gaps in knowledge, experimental programmes were conducted to investigate the impact of moderate earthquake damage and epoxy-repairs on ductile RC beams with varying aspect ratios. Moderate damage states were shown not to reduce the specimen strength or deformation capacity; however, the recovery of stiffness was found to be related to the aspect ratio of specimens. Supplementing results from the experimental programme, a database of experimental research on the impact of varying loading histories was used to propose a safe deformation limit below which prior earthquake demands will not reduce the deformation capacity of moderately-damaged ductile frame elements, regardless of the number of cycles applied. A database on the reparability of RC frame elements was also formed. This data was used to present recommendations and modification factors for the stiffness, strength, and deformation capacity of heavy and moderately-damaged ductile frame elements. A study on the cyclic stiffness degradation of RC beams was conducted to investigate the impact of moderate damage and epoxy-repairs on the deformation demands of frame elements in future earthquakes. The results showed that under larger design level shaking, no significant changes in deformation demands are expected, while under lower-level serviceability earthquakes, epoxy-repairs can make a substantial contribution in reducing the peak deformation demands, in comparison to damaged frame elements.