FLANGE PROPORTIONS FOR CURVED PLATE GIRDERS

THE RESULTS OF ANALYTICAL STUDIES DEALING WITH LOCAL FLANGE BUCKLING OF HORIZONTALLY CURVED PLATE GIRDERS ARE DISCUSSED. THE RELATIONSHIP BETWEEN THE FACTOR OF SAFETY AGAINST LOCAL BUCKLING AND THE RATIO OF WARPING TORSIONAL NORMAL STRESS TO BENDING STRESS IS PLOTTED FOR SEVERAL VALUES OF THE FLANGE WIDTH-THICKNESS RATIO. TWO POSSIBLE ALLOWABLE STRESS DESIGN CRITERIA ARE USED TO DETERMINE THE FACTOR OF SAFETY. IN THE FIRST, THE TOTAL STRESS AT THE FLANGE TIP, WARPING PLUS BENDING, IS LIMITED TO 0.55 F SUB Y. IN THE SECOND, THE TOTAL STRESS AT THE QUARTERPOINT OF THE FLANGE WIDTH IS LIMITED TO 0.55 F SUB Y. THE INFLUENCE OF RESIDUAL STRESSES IS INCLUDED IN THE RESULTS FOR GIRDERS FABRICATED BY HEAT-CURVING OR FLAME-CUTTING CURVED PLATES AND THEN WELDED. BOTH A-36 AND A-441 STEEL GIRDERS ARE CONSIDERED. THE RESULTS INDICATE THAT THE FACTOR OF SAFETY AGAINST LOCAL BUCKLING USING THE FIRST CRITERION FOR CURVED GIRDERS FABRICATED BY WELDING OR HEAT-CURVING AND HAVING WIDTH-THICKNESS RATIOS EQUAL TO OR LESS THAN THOSE CURRENTLY GIVEN BY THE AASHO SPECIFICATION REMAINS SUBSTANTIALLY THE SAME AS FOR STRAIGHT GIRDERS. FOR THE SECOND CRITERION, THE FACTOR OF SAFETY DECREASES AS THE RATIO OF WARPING TO BENDING NORMAL STRESS INCREASES. CRITICAL WIDTH-THICKNESS REQUIREMENTS FOR GIRDERS FABRICATED BY COLD-BENDING ARE SHOWN TO BE SMALLER THAN THE PRESENT AASHO LIMIT IF LOCAL BUCKLING IS TO BE PREVENTED DURING THE FABRICATION PROCESS. /AUTHOR/