WAKE-UP CALL FOR CREEP, MYTH ABOUT SIZE EFFECT AND BLACK HOLES IN SAFETY: WHAT TO IMPROVE IN fib MODEL CODE DRAFT

Although the 2010 Draft of fib Model Code is overall an excellent document, it has some weaknesses which could, and should, be corrected. One is the material model for creep and shrinkage prediction, which not only is theoretically obsolete but also is indefensible in view of the wake-up call provided by recently collected long-term deflections of 56 bridges. The second is a size effect formulation for shear strength whose justification is tantamount to a myth rather than reason. The third consists of the probability distribution of structural strength for failures occurring at macro-crack initiation. The distribution tail that matters, in the probability range of 10-6, is directly unobservable, just like a black hole. But indirect evidence from the size effect indicates that the distribution transits from Gaussian to Weibulian as the structure size increases. This transition may have a major effect on the safety factor. Moreover, dubious uses of the lognormal distribution and another black hole in the covert safety factors implied in the design formulas render a meaningful calculation of failure probability impossible. Some remedies are offered. Proceedings ISBN 978-80-87158-29-6 fib Symposium PRAGUE 2011 Keynote Topic Lecture