MOMENT ROTATION, CRACKING AND DEFLECTION OF SPIRALLY BOUND, PRETENSIONED PRESTRESSED CONCRETE BEAMS

THE ANALYSIS OF REINFORCED AND PRESTRESSED CONCRETE STRUCTURES IN THE ELASTO-PLASTIC AND FULLY PLASTIC RANGES REQUIRES A CONTINUOUS STRESS-STRAIN FUNCTION OF THE CONCRETE. A SEMI-EMPIRICAL EXPRESSION IS PROPOSED AS THE MOST SUITABLE ONE IN THE FULL RANGE OF THE ELASTIC AND PLASTIC BEHAVIOR OF CONCRETE. A TRILINEAR LOAD-DEFLECTION RELATIONSHIP, FROM WHICH THE TOTAL DEFLECTION OF A PRESTRESSED CONCRETE BEAM CAN BE DETERMINED, IS PROPOSED. THE FOLLOWING CONCLUSIONS ARE DRAWN FROM TEST BEAMS AND DISCUSSION OF EXPERIMENTAL RESULTS. ON THE BEHAVIOR OF BOUND CONCRETE IN COMPRESSION: (1) STRENGTH AND DEFORMATION CHARACTERISTICS OF BOUND CONCRETE ARE INFLUENCED BY MANY FACTORS, THE MOST IMPORTANT OF WHICH ARE SPACING AND THE SIZE OF CONFINING REINFORCEMENTS. (2) THERE IS A SIMILARITY BETWEEN THE EFFECT OF TRIAXIAL LOADING AND THE EFFECT OF CONFINING REINFORCEMENT OF CONCRETE. (3) BOTH THE ULTIMATE STRENGTH AND THE DUCTILITY OF CONCRETE INCREASE WITH AN INCREASE IN LATERAL CONFINEMENT IN PRESTRESSED ELEMENTS. (4) THE INFLUENCE OF CONFINEMENT IS GREATER FOR LOW QUALITY THAN FOR HIGH QUALITY CONCRETE. (5) THE INCREASE IN CONCRETE COVER OUTSIDE THE SPIRAL DECREASES THE EFFECT OF CONFINEMENT. (6) WITH THE PROPER TYPE OF CONFINING REINFORCEMENT AND THE MAXIMUM STRAIN IN CONCRETE CAN BE INCREASED TO APPROXIMATELY TEN TIMES THE STRAIN OF UNCONFINED CONCRETE. TEST BEAMS ON THE BEHAVIOR OF SINGLE-SPAN BEAMS SHOWED THAT: (1) THE INFLUENCE OF SPIRAL REINFORCEMENT ON STRESS OR ON STRAIN MAGNITUDES IN THE ELASTIC RANGES WAS INSIGNIFICANT. (2) THE EFFECTIVENESS OF CONFINING REINFORCEMENT ON STRENGTH IS LOWER IN FLEXURAL COMPRESSION THAN IN DIRECT AXIAL COMPRESSION, (3) THE INFLUENCE OF CONFINING REINFORCEMENT ON THE ULTIMATE STRENGTH VALUE OF PRESTRESSED CONCRETE BEAMS WAS NOT VERY SIGNIFICANT. (4) THE DUCTILITY OF PRESTRESSED CONCRETE BEAMS CAN BE INCREASED BY MEANS OF CONFINING REINFORCEMENT, (5) FAILURE OF THE CONFINED COMPRESSION ZONE CAN BE BROUGHT ABOUT BY YIELDING OF SPIRAL REINFORCEMENT, OR BY THE CRUSHING OF CONCRETE BETWEEN THE SPIRALS. (6) THE MOMENT ROTATION CAPACITY OF THE BEAMS WAS INCREASED GREATLY BY THE BIAXIAL STRESS IMPOSED BY THE SPIRAL REINFORCEMENT ON THE COMPRESSION ZONE. (7) COMPRESSION REINFORCEMENT USED IN COMBINATION WITH SPIRAL REINFORCEMENT INCREASES THE RADIUS OF CURVATURE AND DISTRIBUTES THE CRACKS MORE UNIFORMLY. (8) AFTER REACHING THE ULTIMATE MOMENT, THE AVERAGE CRACK WIDTH DOES NOT CHANGE NOTICEABLY, WITH THE EXCEPTION OF THE CRITICAL CRACK OR CRACKS AT THE PLASTIC HINGE ZONE.

  • Supplemental Notes:
    • Bull No 51, 97 PP, 74 FIG, 10 TAB, 31 REF, 2 APP
  • Authors:
    • Nawy, E G
    • Potyondy, J G
  • Publication Date: 1970

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Filing Info

  • Accession Number: 00209324
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 26 1970 12:00AM