Extreme Bridge Loads
Full Session with Abstracts
340050-3 - Experimental and Numerical Investigation of High Strength Concrete Bridge Columns with Hybrid Confinement
Friday, April 20
1:30 PM - 5:00 PM
Reinforced Concrete (RC) columns built using high strength concrete (HSC) have been shown to provide better performance and economy over normal strength concrete by reducing section sizes, allowing the usage of larger spans and reducing the total number of columns required. However, HSC exhibits brittle behavior and the amount of internal steel transverse reinforcement required to achieve ductile behavior is prohibitively large. This limits its application in high seismic regions. Concrete-Filled Fiber Tube (CFFT) presents an alternative to conventional steel reinforcement. It involves the usage of a Fiber Reinforced Polymer (FRP) tube which performs the dual functions of acting as a formwork for the concrete and providing confinement to the encased concrete. The confinement provided by CFFT is passive since it gets applied post the dilation of concrete. Due to the passive nature of confinement, the amount of FRP required to achieve sufficient ductility is quite large. Active confinement applied by thermal prestressing of Shape Memory Alloy (SMA) spirals has been shown to provide significantly greater ductility than passive confinement for the same amount of lateral pressure. Hence, this research investigates experimentally and numerically the usage of limited amount of SMA spirals in the plastic hinge region of CFFT bridge columns filled with HSC to improve their flexural ductility using a hybrid confinement scheme that combines active and passive confinement. First, experimental testing of concrete cylinders wrapped with Glass-FRP (GFRP) sheets and SMA spirals under cyclic axial compression is undertaken. The behavior of these cylinders is then compared with HSC cylinders wrapped only with GFRP jackets with varying thickness. Results indicate that the introduction of active confinement using SMA spirals has a prestressing effect on the GFRP jackets and the axial strain corresponding to GFRP rupture increases by more than 35%. The SMA spiral also prevents the sudden failure of concrete post the rupture of GFRP jacket and increases the ultimate strain by more than 3 times as compared to cylinders wrapped only with GFRP. To understand the implication of the material stress-strain characteristic on the global behavior, RC bridge columns made using CFFT with different thickness are subjected to pushover analysis and their drift capacities are compared with CFFT RC columns which have been confined with SMA spirals in their plastic hinge region. The drift capacity of CFFT column is seen to increase significantly on addition of a limited amount of SMA.