STRENGTH OF BEAMS AS DETERMINED BY LATERAL BUCKLING

USUAL SPECIFICATIONS FOR THE DESIGN OF BEAMS PROVIDE FOR REDUCING THE ALLOWABLE UNIT STRESS OF THE COMPRESSION FLANGE AS THE UNSUPPORTED SPAN LENGTH INCREASES, TO GUARD AGAINST LATERAL BUCKLING. SUCH PROVISIONS RELATE THIS REDUCTION ONLY TO THE RATIO OF UNSUPPORTED BEAM LENGTH TO FLANGE WIDTH, THUS NEGLECTING THE INFLUENCE OF (1) THE HORIZONTAL MOMENT OF INERTIA OF THE COMPRESSION FLANGE, AND (2) THE RESTRAINT AFFORDED BY THE TENSION FLANGE, WHICH DECREASES AS THE DEPTH OF THE BEAM INCREASES. MATHEMATICAL FORMULAS ARE DEVELOPED BY AN EXTENSION AND EVALUATION OF THE TREATMENT OF THIS PROBLEM GIVEN BY S. TIMOSHENKO. TYPICAL FORMULAS ARE PROPOSED FOR INCLUSION IN SPECIFICATIONS, AND ADDITIONAL FORMULAS FOR SPECIAL INVESTIGATIONS ARE DERIVED AND THEIR APPLICATION DESCRIBED. BY INVESTIGATING THE STRENGTH OF STEEL BEAMS IN LATERAL BUCKLING, IT HAS BEEN SHOWN THAT THE CRITICAL STRESSES OF ROLLED BEAMS CAN BE GROUPED TO FOLLOW A GOOD PATTERN AND THAT WORKING FORMULAS CAN BE DERIVED FROM THEM. FOR ALL COMPUTATIONS IT IS ASSUMED THAT THE BEAMS AT THEIR SUPPORTS ARE HELD IN VERTICAL POSITIONS. BEAMS WITH ECCENTRICALLY APPLIED LOADS ARE TORSIONAL PROBLEMS AND HAVE NOT BEEN INCLUDED. COMMONLY USED BEAM SECTIONS AND PLATE GIRDERS ARE DISCUSSED. CHANNELS, ZEES, ANGLES, AND OTHER UNSYMMETRICAL SECTIONS ARE SELDOM USED AS LONG BEAMS, AND IT IS PROPOSED TO ALLOW THE SAME UNIT STRESS FOR THEM AS FOR SYMMETRICAL SECTIONS. THE DEVIATION OF STRESSES OF THE PROPOSED FORMULAS FROM THOSE OF OTHER BEAM FORMULAS IS NEGLIGIBLE FOR SHORT BEAMS, AND THESE UNSYMMETRICAL SECTIONS DO NOT SEEM TO DESERVE SPECIAL CONSIDERATION.

  • Supplemental Notes:
    • Vol 112, PaPER NO 2326, PP 1245-1320, 15 FIG, 10 TAB,
  • Authors:
    • De, VRIES K
  • Publication Date: 1947

Media Info

Subject/Index Terms

Filing Info

  • Accession Number: 00208514
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Oct 14 1994 12:00AM