Behaviour of retrofited precast UHPC and Ni-Ti SMA column-to-foundation connection with CFRP wrapping layers

Abstract

Four precast column-to-foundation connection specimens, previously tested under lateral reversed cyclic loading and constant axial load (first-stage tests), were repaired with Carbon Fibre Reinforced Polymer (CFRP) layers in the areas where plastic hinges had formed and were retested under the same loads (second-stage tests). The columns were originally manufactured with ultrahigh-performance concrete (UHPC) with high stee-fibre content (volumetric steel/fibre ratio 1.9%). The steel bars in the connection were replaced with superelastic Ni-Ti SMA bars that crossed the column/foundation interface. Two types of connection between the precast column and the foundation were analysed: protruding bars and smooth pocket bars (SP). The specimens were subjected to the same constant level of relative axial load in both the first and second-stage tests. The objective was to determine whether the initial performance of precast UHPC and SMA reinforced column-to-foundation connections against lateral cyclic loads can be restored after a seismic event by means of simple and economic retrofitting. The effectiveness of the number of strengthening CFRP layers was also studied (two or three CFRP wrapping layers) for each column-to-foundation connection type. The main results for PB and SP connection specimens with respect to the original specimens were respectively: an average strength capacity loss of 8% and 19%, displacement ductility increase of 8% and 42%, dissipated energy 48% and 53% higher and initial stiffness 9.5% and 21% lower. No significant differences were observed in the repairs done with two or three CFRP wrapping layers.