Title: Deflection at Incipient Failure as Warning-of-Failure Metric
Author(s): Marcie van Weerdhuizen and F. Michael Bartlett
Publication: Structural Journal
Appears on pages(s): 233-241
Keywords: existing structure assessment; flexural ductility; plastic hinge length; reinforced concrete; reinforcement ratio; reliability index; structural safety; Warning Factor
The target reliability index for the assessment of an existing flexural element depends on the warning of failure provided and therefore on the total deflection at incipient failure. Sensitivity analyses accounting for both the linear-elastic-cracked and plastic responses indicate that the warning of failure depends on the ductility of critical cross sections (and therefore on the flexural reinforcement ratio) and the length of the plastic hinge regions (and therefore on the applied load configuration). Structural redundancy typically reduces the total deflection at incipient member failure and therefore is an inconsistent indicator of warning of failure. The deflections at incipient failure can be normalized as fractions of the span length to quantify the Warning Factor, W, as a function of the reinforcement ratio, span length, and effective beam depth. This continuous variable can replace existing discretized values of the Warning Factor based on somewhat subjective classifications of ductility and redundancy.