Observations on structural system reliability and the role of modal correlations

Modern advances in structural reliability have covered a variety of areas, but implementation into building standards and design manuals has only recently begun, especially in the United States. Because of the necessity of reducing the very complex problem to one that can be handled practically in a code format, applications heretofore in both North America and Europe have been primarily based on single member reliability. However, in order to ascertain even an approximate appreciation of true safety, a systems analysis is most important. A previously developed very simple system evaluation technique is used and modified in this study because of its potential for practical implementation. Most of the investigation here is concerned with the sensitivity of the method to resistance correlations. Specifically, a simple portal frame is illustrated with beam-column correlation, column-column correlation, and within-member correlation. Actual data on reinforced concrete are combined with a Taylor series approximation for moment capacity in a limit analysis. The importance of correlations is demonstrated.