Graduate Thesis Or Dissertation
 

Seismic Performance of Square Reinforced Concrete Columns Retrofitted with Titanium Alloy Bars

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  • Large numbers of reinforced concrete (RC) bridges were built in the past that are now considered seismically deficient. The structural members most likely to be considered deficient are the supporting columns. Typical deficient columns contain inadequate transverse reinforcement and poorly detailed lap splice lengths above the foundation. Insufficient lap splice lengths can lead to bond failure and an inability to develop the strength of the longitudinal reinforcement. Deterioration of the mechanical bond between the longitudinal reinforcement bars and the surrounding concrete reduces the stiffness and strength of the column-footing joint and provides limited or no ductility. In addition, widely spaced transverse reinforcement may not adequately confine the base of the column. This permits premature buckling of the longitudinal reinforcement that may occur between transverse bar locations and poor confinement of the concrete core. Complete replacement of these bridges is not practical due to limited resources thus, rehabilitation of existing deficient infrastructure is a practical approach. In this research, titanium alloy bars (TiABs) were explored as an alternative material to retrofit RC columns with poorly detailed reinforcing steel above the footing. The well-defined material properties of TiABs have the potential to provide effective and economical seismic strengthening of deficient RC columns. Compared to conventional reinforcing steel, they have relatively low stiffness, high strength, high ductility, and are fully resistant to corrosion in the operating environment. The proposed installation allows for inspection of the members and the environmental durability of the TiABs make them a viable long-term solution for column strengthening. To evaluate the potential for using TiABs to remediate seismically deficient RC columns with poor lap splice details and inadequate transverse reinforcement that were common in the U.S. prior to 1970, four full-scale columns were tested. One was a control specimen without strengthening and the other three (3) had externally mounted TiABs. The specimens were subjected to fully reversed cyclic lateral loading in the laboratory. The experimental results showed improved ductility and stable cyclic response with minor flexural strength degradation in the specimens retrofitted with TiABs and the failure modes of the columns were altered from non-ductile lap splice failure in the conventionally reinforced column to ductile flexural failure in the retrofitted columns. They demonstrated that TiABs offer a new option for effectively strengthening seismically deficient square bridge columns.
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