Influence of Tie Configuration on Seismic Behaviour of Ultra High Performance Concrete Columns

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Ultra-High-Performance Concrete (UHPC) is one of the latest advances in concrete technology as it overcomes the shortcomings of conventional concrete such as low strength to weight ratio, high permeability, low tensile strength, low ductility, and volume instability. Confinement is capable of increasing capacity of the concrete structure to sustain large deformation without a substantial strength loss. The present study discusses the influence of tie configuration, percentage of longitudinal reinforcement and tie spacing in improving the confinement and behaviour of UHPC columns. In order to determine the behaviour of UHPC column, half scaled specimens of original short column with four different tie configurations were used. The configurations considered for the study included a double legged ties (A), welded ties with bars running centrally across the length and width (B), ties with inclined bars connecting two adjacent mid-points (C) and ties with bars connecting two adjacent sides at one-third distances (D). For the same tie configuration, the transverse reinforcement ratios are varied by changing the diameter of the ties. The specimens were tested under quasi static reverse cyclic loading under a constant axial load. The test results were represented and compared in terms of load-deflection envelope, ductility and cracking patterns. Tie configuration C exhibited better performance in stiffness and ductility, when compared with other configurations. For same parameters, “B” and “D” configuration displayed better behaviour than “A” configuration. This variation in performance was due to increase in transverse reinforcement percentage and the consequent effectiveness of core confinement. Transverse reinforcement percentage of “B” and “C” configurations is less than “D” configuration. The enhancements of properties of “B” and “C” configurations are better than “D” configuration. It was due to the effective core confinement of “B” and “C” configuration. For the same tie configuration, ultimate load, initial stiffness and relative ductility increases with increase in transverse reinforcement percentage. UHPC columns with “C” type tie configuration can effectively use in moderate and high seismic areas and its performance can be improved by increasing the transverse reinforcement ratio.