Abstract
The restriction of the width-thickness ratio (b/t) of flange plates has been tried by many authors, in respect of the plastic. or limit Design. In their reports, plates are stressed by uniform normal stresses along their length. In the case of flange plates of beams, such plates exist only when beams suffer pure bending moment. Between beams under pure bending moment and those under moment gradient their behaviers and characters are different. Therefor, the buckling load of flange plates of beams under moment gradient must be thought differently from that of plates stressed uniformly along their length. In this report, it is shown that the flange buckling load of beams under moment gradient has possibility to be over the full-plastic-moment load of the beam and the restriction of b/t can be relaxed. But, concrete values of the restriction of b/t will be shown in Part-III after the analysis of ultimate loads and rotation capsities.
