TRANSVERSE FORCE TRANSFER IN THE BEARING AREA OF NOTCHED PRESTRESSED CONCRETE GIRDERS (PART 1)

QUERKRAFTUEBERTRAGUNG IM AUFLAGERBEREICH AUSGEKLINKTER SPANNBETONTRAEGER (TEIL I)

AN INITIAL SURVEY OF THE LITERATURE SHOWED THAT THEORETICAL STUDIES OF THE STATE OF STRESS IN THE ENDS OF NOTCHED PRESTRESSED CONCRETE BEAMS WERE CONCERNED PRIMARILY WITH THE MAGNITUDE AND DISTRIBUTION OF THE TRANSVERSE TENSILE STRESSES RESULTING FROM CONCENTRATED ATTACK BY FORCES IN THE PRESTRESSED MEMBER, AND WITH DETERMINATION OF THE CRACKING LOAD. THE INCLINATION OF THE PRESTRESSED MEMBER AND GEOMETRIC RELATIONS WERE VARIED. THE ACTION OF STEEPLY INCLINED ADDITIONAL STRESS MEMBERS, OFTEN USED IN PRACTICE, AND OF STRESS MEMBERS ANCHORED IN THE LOWER PART OF THE NOTCH, HAD NOT SO FAR BEEN EXAMINED. IN THE FINITE ELEMENT CALCULATION OF THE STRESS FIELD CARRIED OUT IN THIS PROJECT, THESE PARAMETERS WERE INCLUDED. THE BASIS OF THE CALCULATIONS WAS THE PRACTICAL GEOMETRY OF THE NOTCHING, IN WHICH THE HEIGHT OF THE NOTCH IS EQUAL TO HALF THE DEPTH OF THE BEAM, AND THE LENGTH OF THE NOTCH CORRESPONDS TO 0.3. TIMES THE DEPTH OF THE BEAM. THE STRESS CALCULATION INDICATES THE STRESS-DECREASING INFLUENCE OF A HAUNCH IN THE REGION OF THE RE-ENTERING CORNER FOR MOST COMBINATIONS OF LOADING. THIS MAY BE SIGNIFICANT FOR THE ONSET OF CRACKING. FROM THE CALCULATION OF THE STATE OF STRESS FOR VARIOUS INCLINATIONS OF PRESTRESSED MEMBER AND VARIABLE HEIGHT OF THE PRESTRESSING FORCE, IT MAY BE CONCLUDED THAT FOR CASES OF STEEPLY INCLINED PRESTRESSED MEMBERS WHERE THE PROPORTION OF NORMAL FORCE IS RELATIVELY LOW, EVEN IF THE TOTAL BEARING FORCE IS COVERED BY THE TRANSVERSE FORCE COMPONENTS OF THE PRESTRESSING, TENSILE STRESSES STILL OCCUR IN THE REGION OF THE RE-ENTERING CORNER. FROM THIS IT MAY BE CONCLUDED THAT THE TRANSVERSE FORCE COMPONENTS OF THE PRESTRESSING FORCE ARE NOT COMPLETELY ACTIVATED UNTIL THERE IS MARKED CRACKING. IF PRESTRESSING FORCES ARE INTRODUCED BELOW THE BEARING POINT, THESE CAUSE A NOT INSIGNIFICANT INCREASES IN THE STRESSES AT THE RE-ENTERING CORNER. IF THE PRESTRESSING FORCES INTRODUCED ARE CONCENTRATED, THE TENSILE STRESSES AT THE RE-ENTERING CORNER ARE SUPERIMPOSED BY THE TRANSVERSE TENSILE STRESSES RESULTING FROM THE INTRODUCTION OF THE FORCE. THUS PREFERENCE SHOULD BE GIVEN TO THE INTRODUCTION OF FORCE OVER AN AREA, SINCE THIS DECREASES THE DANGER OF CRACKING AND ALSO ENSURES THAT THE TRANSVERSE FORCE COMPONENTS OF THE PRESTRESSING DRAWN ON TO ABSORB PARTS OF THE BEARING FORCE ARE ALSO FULLY AVAILABLE IN THE REGION OF THE BEARING.