Critique of critical shear crack theory for fib Model Code articles on shear strength and size effect of reinforced concrete beams

Abdullah Dönmez, Zdeněk P. Bažant*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

The size effect of Muttoni et al.'s critical shear crack theory (CSCT) is shown to be quite close (with differences up to 15%) and asymptotically identical to the energetic size effect law (SEL), which has been extensively verified experimentally and theoretically (and is adopted for the 2019 ACI Code, Standard 318, for both beam shear and punching). However, the CSCT derivation and calculation procedure obfuscates the mechanics of failure. It is shown to rest on six scientifically untenable hypotheses, which would have to be taught to students as an article of faith. They make CSCT untrustworthy outside the testing range; ditto for beams with T, I and box cross section, or for continuous beams. The present conclusions are supported by experimentally calibrated finite element simulations of crack path and width, of stress distributions and localizations during failure, and of strain energy release. The simulations also show the CSCT to be incompatible with the “strut-and-tie” model, which is (for 2019 ACI Code) modernized to include the size effect in the compression strut. Finally, further deficiencies are pointed out for the Modified Compression Field Theory (MCFT), currently embedded in the Model Code.

Original languageEnglish (US)
Pages (from-to)1451-1463
Number of pages13
JournalStructural Concrete
Volume20
Issue number4
DOIs
StatePublished - Aug 1 2019

Keywords

  • brittleness
  • concrete fracture
  • design codes
  • energy criteria
  • finite elements simulations
  • fracture mechanics
  • mechanics of concrete
  • scaling
  • shear failure
  • structural strength

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • Materials Science(all)
  • Mechanics of Materials

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