Uncertainly Analysis of Flexural Overstrength for Capacity Design of RC Beams

Abstract

To ensure an overall ductile structural behavior, the reinforcing steel used in the seismic design of reinforced concrete (RC) structures is governed by certain specific requirements given in many international codes, such as the Eurocodes and the recently released Italian Building Code (IBC). This study’s primary focus is the statistical analysis of reinforcing steel properties, based on data from over 600 material tests. The data sets considered include a wide range of reinforcing steel bars (from 12 to 26 mm) provided by different Italian industries and used for a large structure built in Naples (Southern Italy). The test results are analyzed to determine the appropriate cumulative distribution function for yield and ultimate strengths, as well as the ultimate deformation, and other statistical parameters of interest as defined in the codes. The comparison with previous tests confirms an improvement in the quality of materials, as reflected in reduced variability and increased bias factors, consistent with other investigators’ recent findings. Finally, this study investigates the flexural overstrength of RC beams designed according to the current IBC—consistent with Eurocodes—and the accuracy of code requirements in light of realistic material models both for concrete and reinforcing steel and of uncertainties associated with mechanical models, structural members geometry, and material properties (as obtained in this study for reinforcing steel). The obtained results show that code provisions do not seem conservative and provide a basis for an improved calibration of future editions of seismic design codes for buildings.