CRACKING OF REINFORCED CONCRETE UNDER EXTERNAL LOAD

RECENT STUDIES OF CRACKING BY BROMS HAVE INDICATED THE PRESENCE OF INTERNAL CRACKS THAT ARE NOT VISIBLE ON THE SURFACE. THE COMPATIBILITY OF THIS PHENOMENA WITH THREE POSSIBLE CRACK MECHANISMS IS DISCUSSED. THE "CLASSICAL" MECHANISM WAS DEVELOPED FROM OBSERVATIONS OF SURFACE CRACKS. THE MECHANISM IS BASED ON THE ASSUMPTIONS THAT BOND STRESSES AT THE CONCRETE-REINFORCEMENT INTERFACE DEVELOP TENSILE STRESSES IN THE CONCRETE; TENSILE STRESSES ARE UNIFORMLY DISTRIBUTED OVER THE CONCRETE SECTIONS, AND A CRITICAL CONCRETE SECTION FAILS WHEN THE AVERAGE TENSILE STRESS EXCEEDS THE TENSILE STRENGTH. THESE ASSUMPTIONS ARE NOT COMPATIBLE WITH INTERNAL CRACKING, WHICH INDICATES A VARYING CONCRETE TENSILE STRESS. BROMS PROPOSED A CRACK MECHANISM BASED ON AN ELASTICITY STRESS ANALYSIS THAT INDICATED THAT BOND FORCES INDUCED LARGE TENSILE STRESSES NEAR THE REINFORCEMENT BUT LOWER TENSILE STRESSES NEAR THE SURFACE. CRACKS INITIATE NEAR THE REINFORCEMENT WHEN THE LOCAL STRESS EXCEEDS THE TENSILE STRENGTH. THE CRACK GROWS TOWARD THE SURFACE AND MAY BE ARRESTED WHEN THE REGION OF LOWER INITIAL TENSILE STRESSERS IS REACHED. ACTUALLY THE CRACK ALTERS THE INITIAL STRESS FIELD, AND THE CRACK TIP NEVER REACHES A REGION OF LOW TENSILE STRESS IF THE CONCRETE CARRIES A GIVEN BOND FORCE. A THIRD MECHANISM IS PROPOSED THAT IS BASED ON COMPATIBILITY OF CONCRETE AND REINFORCEMENT DISPLACEMENTS. CRACKS INITIATE IN THE REGION OF HIGH TENSILE STRESS NEAR THE REINFORCEMENT AND GROW TOWARD THE SURFACE. THE CONCRETE SECTION BECOMES MORE FLEXIBLE AS THE CRACK PROPAGATES. BOND AND TENSILE STRESSES REDUCE UNTIL THE CRACK BECOMES STABLE AND IS ARRESTED. THIS MECHANISM IS DISCUSSED IN TERMS OF FRACTURE MECHANICS. /ACIJP/

  • Corporate Authors:

    American Concrete Institute

    38800 Country Club Drive
    Farmington Hills, MI  USA  48331
  • Authors:
    • Bianchini, A C
    • Kesler, C E
    • Lott, J L
  • Publication Date: 1968

Subject/Index Terms

Filing Info

  • Accession Number: 00209298
  • Record Type: Publication
  • Source Agency: Am Concrete Inst Journal & Proceedings
  • Report/Paper Numbers: Title No Sp 20-5
  • Files: TRIS
  • Created Date: Sep 28 1970 12:00AM