Highly deformable confined rubberised concrete elements for seismic applications

Short columns in reinforced concrete (RC) structures are particularly vulnerable to seismic actions. Even though steel reinforcement can be designed to impart adequate ductility, the deformability of these structural members is limited by the relatively low strain capacity of conventional concrete (CC). Recent research on rubberized concrete (RuC) and confined RuC has shown that this novel material can develop significant axial and lateral strain and it holds great potential for the development of innovative structural solutions for applications where large deformations are required. This study aims to investigate the use of confined rubberised concrete (CRuC) in elements with high shear deformation demand, as well as provide a proof-of-concept for a cost-effective base-isolation system made of confined rubberised concrete columns. The first part of this study examines the behaviour of short columns in a one-bay one-storey building made of conventional RC. The building collapsed with the brittle failure of the short column at a small drift ratio of 0.37% for the unrestrained column. The experimental results are used to validate a numerical model in Abaqus, which in turn is used to develop a strut and tie model (STM) to predict the behavior of RC short columns. The validated numerical and analytical models are utilized to investigate the use of highly deformable CRuC short columns. The results show that CRuC enables the development of high ductility/deformability in the columns and promotes stress redistribution within the frame, thus offering a viable solution for enhanced global capacity and deformability. The seismic behaviour of two buildings with short columns is examined in the second phase of this study through a series of shake-table tests. While the conventional RC building exhibited short column failure, the building with CRuC short columns (CRuC-EQ) was able to withstand 25% more peak ground acceleration (PGA) than the CC building (2.0g), without showing any sign of severe damage. The CRuC short columns were able to achieve up to 7.7% drift ratio, compared to 2% for the CC short columns. The analytical STM developed was modified to fit each building and the models were subjected to the same seismic load protocol as per the experiment. The experimental and numerical results show a good agreement, which validates the model for seismic modelling. The last part of this study investigates both experimentally and analytically the concept of a CRuC baseisolation system. The low stiffness bilinear behaviour of CRuC can be exploited to provide high damping through hysteresis, as well as lengthen the natural period of the structure to lessen the acceleration response. The CRuC-EQ building was mounted on four CRuC isolators and then tested on a shake-table with the same seismic load protocol. The isolators exhibited large drift ratios (up to 17%), and they successfully reduced the response of the superstructure at high PGA values. The concept of a CRuC base-isolation system was further examined through a series of numerical analyses and it was found that the implementation of such an innovative solution can successfully reduce inter storey drift (up to 67%), base-shear (up to 32%), and base-moment (up to 62%).