Wake-up call for creep, myth about size effect and black holes in safety: What to improve in fib model code draft

Zdeněk P. Bažant*, Qiang Yu, Mija H. Hubler, Vladimír Křistek, Zdeněk Bittnar

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

15 Scopus citations

Abstract

Although the 2010 Draft of jib 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 106, is directly unobservable, just like a black hole. But indirect evidence from the size effect indicates that the distribution translts from Gaussian to Weibulian as the structure size increases. This transltion 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.

Original languageEnglish (US)
Title of host publicationfib Symposium PRAGUE 2011
Subtitle of host publicationConcrete Engineering for Excellence and Efficiency, Proceedings
EditorsVlastimil Sruma
PublisherCzech Concrete Society
Pages731-746
Number of pages16
ISBN (Electronic)9788087158296
StatePublished - Jan 1 2011
Eventfib Symposium PRAGUE 2011: Concrete Engineering for Excellence and Efficiency - Praha, Czech Republic
Duration: Jun 8 2011Jun 10 2011

Publication series

Namefib Symposium PRAGUE 2011: Concrete Engineering for Excellence and Efficiency, Proceedings
Volume2

Other

Otherfib Symposium PRAGUE 2011: Concrete Engineering for Excellence and Efficiency
Country/TerritoryCzech Republic
CityPraha
Period6/8/116/10/11

Keywords

  • Bridge deflections
  • Concrete creep model
  • Jib Model Code
  • Shear failure
  • Size effect
  • Structural safety

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • Architecture

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