Experimental and analytical investigations on bond of reinforcement and nonlinear response of reinforced concrete columns
Creators: name: Fawaz, Ghassan
name: 0000-0002-8658-4187
Publisher: name: The University of Texas at Austin
Year: 2020
Subjects: Iron-based shape memory alloys (Fe-SMA)
Reinforcing bar
Bond strength
Bond-slip behavior
Activation temperature
Transfer length
RC columns
Cyclic loading
Finite element models
Low-cycle fatigue
Bond-slip
Debonding
Large-scale testing
Seismic
End rotation
Bar slip

description: Bond of reinforcement has a major influence on the behavior of reinforced concrete (RC) structures. Even though bond has been extensively studied over the past decades, there are still a number of knowledge gaps requiring investigation. This dissertation presents three studies related to the basic bond behavior of reinforcement and the influence of bond-slip on the seismic response of RC columns. The first investigation characterizes the bond behavior of iron-based shape-memory alloy (Fe-SMA) bars. Fe-SMA reinforcement provides new opportunities for design and strengthening of concrete structures thanks to their shape memory effect. However, there is currently little data on its bond performance. Experiments were conducted to study the bond-slip behavior of ribbed Fe-SMA bars embedded in concrete specimens with different levels of passive confinement. Fe-SMA bars presented a similar bond performance as conventional reinforcement, but their bond strength was reduced with heat activation in low-confined specimens. An analytical model is also proposed to calculate the transfer length of Fe-SMA bars in prestressing applications. The second investigation proposes nonlinear finite element models to accurately simulate the cyclic response of RC columns, including the effect of bond-slip. Concrete is modeled using a triaxial constitutive model recently proposed in the literature. A commonly used uniaxial steel model is modified to account for low-cycle fatigue rupture using a phenomenological criterion. The bond-slip behavior of bars is modeled using a zero-thickness interface element and a bond stress-slip law that predicts bond deterioration caused by generalized slip demands, tensile yielding of steel, and concrete damage. The proposed models accurately predict the cyclic response and failure of previously tested column components. The third investigation focuses on the effects of strain penetration and bond modification on the lateral response of RC columns. Two large-scale column specimens were tested under cyclic loading. One specimen had conventional reinforcement details, while the other had headed bars that were partially debonded along the footing to alleviate strain concentrations. Both specimens formed plastic hinges and failed due to rupture of longitudinal bars. The specimen with partial debonding presented less damage and a larger deformation capacity. Experimental data indicated that the debonding strategy reduced peak tensile strains, and increased bar slip and fixed-end rotations. However, it also reduced the lateral load resistance of the column. Companion finite element analyses have indicated that the reduction in peak lateral strength is caused by lower steel stress demands when concrete cover fails.