PRESTRESSING THE NEGATIVE MOMENT REGION OF COMPOSITE BEAMS

TWO SIMPLY SUPPORTED STEEL-CONCRETE BEAMS WITH PRESTRESSED SLABS DESIGNATED PSC-1S AND PSC-2S WERE TESTED UNDER NEGATIVE MOMENT (SLAB IN TENSION). THESE BEAMS WERE DESIGNED TO SIMULATE THE PRESTRESSED NEGATIVE MOMENT REGION OF A 2-SPAN CONTINUOUS COMPOSITE BEAM. EACH OF THE SIMPLE SPAN BEAMS HAD A SPAN LENGTH OF 15 FT. THE CROSS SECTION OF EACH BEAM CONSISTED OF A 6-IN X 60-IN REINFORCED CONCRETE SLAB CONNECTED TO A W21X62 ROLLED STEEL BEAM BY 4-IN HIGH BY 3/4-IN DIAMETER HEAD STEEL STUDS. THE STUD CONNECTORS WERE ATTACHED TO THE STEEL BEAMS IN TWO PATTERNS; CONCENTRATED GROUPS AND EQUALLY SPACED. A PRESTRESS FORCE WAS APPLIED TO THE SLAB OF EACH BEAM BY MEANS OF FOUR 7/8-IN DIAMETER STRESSTEEL BARS PLACED IN FOUR THIN STEEL TUBES WHICH WERE CAST INTO THE SLAB. IN ONE BEAM THE PRESTRESS FORCE WAS APPLIED PRIOR TO MAKING THE SHEAR CONNECTION, WHILE IN THE OTHER, THE PRESTRESS FORCE WAS APPLIED AFTER THE SHEAR CONNECTION WAS MADE. THE PURPOSES WERE: (1) TO STUDY THE EFFECT OF PRESTRESSING ON THE BEHAVIOR OF COMPOSITE BEAMS UNDER NEGATIVE MOMENT. (2) TO COMPARE THE EFFECTIVENESS OF CONCENTRATED GROUPS OF STUD CONNECTORS WITH EQUALLY SPACED CONNECTORS. THE RESULTS OF THESE TESTS ARE REPORTED AND THE FOLLOWING CONCLUSIONS WERE MADE: (1) COMPOSITE ACTION OF THE FULL TRANSFORMED SECTION CAN BE OBTAINED IN THE NEGATIVE MOMENT REGION BY PLACING SHEAR CONNECTORS THROUGHOUT THIS REGION AND APPLYING A SUITABLE PRESTRESS FORCE TO THE SLAB. (2) PRESTRESSING CAN BE USED TO EFFECTIVELY CONTROL SLAB CRACKING IN THE NEGATIVE MOMENT REGION. CRACKS CAN BE ELIMINATED UP TO CERTAIN LOAD LEVELS DEPENDING UPON THE AMOUNT OF PRESTRESS FORCE WHICH IS APPLIED. (3) WHEN THE SAME MAGNITUDE OF PRESTRESSING FORCE IS USED, SLAB CRACKING IS MORE EFFECTIVELY CONTROLLED WHEN THE SLAB IS PRESTRESSED BEFORE THE SHEAR CONNECTION IS MADE. (4) CONCENTRATED GROUPS OF SHEAR CONNECTORS PROVIDE AN ADEQUATE SHEAR CONNECTION WHEN THE NUMBER OF CONNECTORS USED IS THE SAME AS THE NUMBER THAT WOULD BE USED IF THE DESIGN CALLED FOR THE CONNECTORS TO BE EQUALLY SPACED. (5) SATISFACTORY COMPOSITE BEHAVIOR CAN BE OBTAINED WHEN A LOW SHRINKAGE GROUT IS USED TO MAKE THE CONCRETE SLAB COMPOSITE WITH THE STEEL BEAM. /AUTHOR/

• Corporate Authors:

  Lehigh University

  Bethlehem, PA  United States  18015

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590

  Pennsylvania Department of Transportation

  1215 Transportation and Safety Building
  Harrisburg, PA  United States  17120
• Authors:
  • Sarnes, F W
  • Daniels, J H
• Publication Date: 1971-8

Subject/Index Terms

• TRT Terms: Beams; Composite materials; Engineering moments; Fasteners; Fracture mechanics; Prestressing; Reinforced concrete; Shear reinforcement; Slabs; Steel
• Uncontrolled Terms: Composite beams; Shear connectors
• Old TRIS Terms: Moments
• Subject Areas: Bridges and other structures; Highways; Materials;

Filing Info

• Accession Number: 00208022
• Record Type: Publication
• Source Agency: Federal Highway Administration
• Report/Paper Numbers: Study No 68-28
• Files: TRIS, USDOT, STATEDOT
• Created Date: Feb 15 1972 12:00AM