CRACK WIDTH CONTROL IN WELDED FABRIC REINFORCED CENTRALLY LOADED TWO-WAY CONCRETE SLABS

MOST EXISTING RESEARCH DEALS WITH CRACK WIDTH STUDIES IN BEAMS AND ONE-WAY MEMBERS. THIS INVESTIGATION COVERS THE EFFECT OF TWO-WAY ACTION ON CRACK WIDTH DEVELOPMENT, CRACK PATTERN EVALUATION AND CRACK WIDTH CONTROL. A CRACKING HYPOTHESIS IS PRESENTED EXPLAINING THE FUNDAMENTAL CRACKING BEHAVIOR AND PROPAGATION IN TWO-DIMENSIONAL REINFORCED CONCRETE MEMBERS SUCH AS THE TWO-WAY SLABS IN THIS INVESTIGATION. A MODEL IS FORMULATED TO RELATE THE MOST IMPORTANT PARAMETERS WHICH CONTROL CRACK DEVELOPMENT IN THE SLABS, AND IS TESTED AND PROVED VALID BY STATISTICAL INFERENCE. TESTS TO FAILURE WERE PERFORMED ON 22 SLABS 5 FT 8 IN. SQUARE, TEN OF WHICH WERE FULLY CLAMPED AT THE BOUNDARIES. THE LOAD WAS CENTRALLY APPLIED ON A FINITE AREA 6 IN. SQUARE. CRACK WIDTH DEVELOPMENT WAS OBSERVED WITH ILLUMINATED POWERFUL MICROSCOPES AT CLOSE INTERVALS ON THE MAJOR CRACKS. STRAIN IN THE WIRE REINFORCEMENT WAS ELECTRONICALLY RECORDED IN THE VICINITY OF THE LOCATIONS WHERE THE CRACK WIDTHS WERE OBSERVED. COMPRESSIVE STRAINS IN THE CONCRETE AND DEFLECTIONS AT CRITICAL LOCATIONS WERE ALSO RECORDED. ALL SLABS FAILED IN FLEXURE. SHEAR REINFORCEMENT AND SHEAR HEADS WERE USED TO PREVENT PREMATURE FAILURE BY PUNCHING SHEAR. THE SIZE AND SPACING OF THE WIRE FABRIC WERE THE VARIABLE INDEPENDENT PARAMETERS SERVING WITH THE CONCRETE STRETCHED AREAS AS A MESH INDEX. THEY WERE VARIED TO EXTREMES IN THE DIFFERENT SPECIMENS TO OBSERVE THEIR INFLUENCE ON THE CRACKING BEHAVIOR AND CRACK WIDTHS. TWENTY-SEVEN CONTROL BEAMS WERE ALSO TESTED TO FAILURE, EACH HAVING A CLEAR SPAN OF 5 FT TO 8 IN. TO CORRELATE THE WIDTH OF THE MEASURED CRACK AT THE TENSILE FACE OF THE TWO-WAY SLAB WITH THE WIDTH AT THE REINFORCEMENT LEVEL. CRACKING EQUATIONS WERE DEVELOPED FOR CRACK CONTROL IN TWO-WAY CENTRALLY LOADED SLABS WITH VARYING DEGREES OF RESTRAINT AT THE BOUNDARIES. ANALYSIS OF THE DATA SHOWED THAT CRACK WIDTHS IN THE SIMPLY SUPPORTED CASE ARE GENERALLY 1.6 TIMES THOSE IN THE FULLY CLAMPED CASE. THIS INVESTIGATION PROVED THAT CRACK WIDTH IN SLABS CAN BE EFFECTIVELY CONTROLLED. FAILURE PATTERNS IN FLEXURE, WHETHER BY DOMINANT PRIMARY YIELD LINES OR BY PRIMARY ORTHOGONAL CRACK GRID MECHANISM WAS GOVERNED BY THE PROPOSED MESH INDEX. WHERE INITIAL CONTROLLING CRACKS WERE YIELD LINES, CRACK WIDTHS WERE MUCH LARGER THAN WHEN THE INITIAL CONTROLLING CRACKS WERE IN THE FORM OF AN ORTHOGONAL GRID. /ACIJP/

  • Corporate Authors:

    American Concrete Institute

    38800 Country Club Drive
    Farmington Hills, MI  USA  48331
  • Authors:
    • Nawy, E G
  • Publication Date: 1968

Subject/Index Terms

Filing Info

  • Accession Number: 00213810
  • Record Type: Publication
  • Source Agency: Am Concrete Inst Journal & Proceedings
  • Report/Paper Numbers: Title No Sp 20-12
  • Files: TRIS
  • Created Date: Sep 28 1970 12:00AM