STRESSES IN TIMBER STRINGERS

TIMBER AS A BRIDGE MATERIAL IS EQUALLY AS IMPORTANT AS STEEL AND CONCRETE AND HAS ITS PLACE IN THE CONSTRUCTION PICTURE. IT IS NECESSARY, THEREFORE, THAT RESEARCH ON TIMBER KEEP PACE WITH OTHER MATERIALS IN ORDER THAT TIMBER CAN BE UTILIZED TO ITS GREATEST ADVANTAGE. IN 1961 A LARGE SCALE RESEARCH PROGRAM ON FULL SIZE TIMBER TRESTLE STRINGERS WAS STARTED AT THE RESEARCH CENTER. THIS RESEARCH INVOLVED THE STATIC AND FATIGUE STRENGTH OF SOLID-SAWN AND GLUED- LAMINATED MEMBERS OF FIR AND PINE SPECIE. VERY LITTLE LABORATORY WORK HAD BEEN PERFORMED IN THE PAST ON FULL SIZE SPECIMENS AND ALSO VERY LITTLE WORK HAD BEEN CONDUCTED ON THE REPEATED LOAD STRENGTH OF SUCH SPECIMENS. ONE OF THE INTERESTING ASPECTS OF THIS RESEARCH HAS BEEN THAT UNDER STATIC LOADING THE PREDOMINANT TYPE FAILURE HAS BEEN FLEXURE WHEREAS UNDER REPEATED LOADING THE PREDOMINANT FAILURE HAS BEEN IN HORIZONTAL SHEAR. IT HAS ALSO BEEN DEMONSTRATED THAT FOR MOVING LOADS THE CRITICAL POSITION FOR SHEAR IS NOT WHEN THE LOAD IS CLOSE TO THE SUPPORT, BUT RATHER WHEN IT IS AWAY FROM THE SUPPORT A DISTANCE OF ABOUT THREE STRINGER DEPTHS. THE RESULTS OF THESE INVESTIGATIONS HAVE INDICATED THE FATIGUE STRENGTH OF THE VARIOUS TYPE SPECIMENS AT 2,000,000 CYCLES OF LOADING. THE SHEAR VALUES OBTAINED HAVE BEEN IN EXCESS OF THE RECOMMENDED ALLOWABLE WORKING STRESSES AND, THEREFORE, REPRESENT THE MARGIN NECESSARY TO PROVIDE FOR THE EFFECTS OF IMPACT, TREATMENT AND FACTOR OF SAFETY. /ARTICLE/

  • Publication Date: 1967

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  • Accession Number: 00208952
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Apr 21 1994 12:00AM