| Summary: | The need to ascertain the drift capacity of reinforced concrete columns frequently arises
in the displacement-based seismic design and assessment method. Drift capacity at
column lateral strength degradation, as well as the column capacity to sustain axial load
after the loss of lateral strength, is sought for each column. Such predictions can only be
made in a probabilistic sense, due to lack of experimental data, model imperfections and
variability in the intervening parameters. The probabilistic models developed in this study
incorporate these sources of uncertainty and are capable of estimating the probability of
column failure for a given drift demand. The probabilistic models not only provide
engineers the prediction of column drift capacities but also help engineers to determine
the critical columns and the priority of column retrofit.
The prediction of column response is also one of the objectives in this study. Two
approaches are proposed to classify columns. First, a probabilistic failure mode index
model is developed to identify column failure modes: flexure failure, flexure-shear failure
and shear failure. Second, a two-zone column classification method is proposed to
approximately distinguish the shear response dominated columns (Zone S) and the
flexural response dominated columns (Zone F) based on three column parameters.
Two probabilistic drift capacity models at 20% reduction in lateral strength are
developed; one for columns classified in Zone S, and another for columns in Zone F. The
key parameters affecting the drift capacity at 80% lateral strength for reinforced concrete
columns are identified through the assessment of probabilistic drift capacity models.
Based on the shear-friction mechanism, a probabilistic drift capacity model at axial
failure is developed for shear-damaged columns.
Several examples are presented to demonstrate the applications of the probabilistic
models. The probabilistic failure mode index model can be employed to assess the
probability of each failure mode for a given column. The probabilistic drift capacity
models can be used to construct the fragility estimate of reinforced concrete columns
with respect to the drift demand. The variability in the fragility estimate due to epistemic
uncertainties is captured by confidence bounds at specified probability levels. The
assessment of failure mode probability, as well as the fragility estimate, for a column
damaged during the Northridge Earthquake is presented. Other results derived from the
probabilistic capacity models include the assessment of numerical acceptance criteria for
column drift in FEMA 356, the fragility estimates for a range of column properties, and
the application of normalized fragility curves. An additional advantage of the
probabilistic drift capacity models is the potential incorporation in structural reliability
analysis to assess the probability of global structural system collapse. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate
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