Seismic Behavior, Evaluation, and Retrofit of Older Reinforced Concrete Structural Walls

This dissertation describes an analytical study on the seismic behavior, evaluation, and retrofit of older reinforced concrete structural walls. The designs of many reinforced concrete structural walls built in the past were dominated by gravity loads, resulting in construction details that are now recognized to be critical. In this dissertation, a set of prototype and parametric walls is designed to represent concrete walls from the 1960s and early 1970s in regions of the U.S. with high seismicity. The parametric walls are determined by changing the wall cross-section geometry, amount of flexural reinforcement, amount of concrete confinement, and wall height. High-rise (10-story) walls where the nonlinear lateral load behavior is governed primarily by flexural effects and medium-rise (5-story) walls where the behavior is governed by both nonlinear flexural and nonlinear shear effects are included. Low-rise shear-critical walls where the shear strength is not sufficient to allow for the wall flexural strength to be reached at the base, resulting in brittle shear-dominated failure modes with little flexural deformations are not considered. Analytical models of the walls are constructed to capture their nonlinear behavior under reversed-cyclic lateral loads. A concrete fiber that can model nonlinear shear effects and a steel fiber that can model the buckling of reinforcing bars are implemented in the DRAIN-2DX Program. Comparisons between the analytical and test results of older reinforced concrete walls indicate that the models are able to reasonably estimate the wall behavior including nonlinear shear effects. Using these models, nonlinear static reversed-cyclic lateral load analyses are conducted to evaluate the behavior of the prototype and parametric walls before and after retrofit. The following retrofit methods are investigated: (1) reducing flexural reinforcement; (2) increasing concrete confinement; and (3) increasing reinforced concrete wall web thickness. It is found that nonlinear shear deformations can play a significant role on the behavior and retrofit of the walls under lateral loading. The results also show that older concrete structural walls may exhibit limited lateral displacement capacity without retrofit or with the application of a single retrofit approach. A combination of different retrofit methods may be needed to achieve an effective retrofit strategy.