In plate girders, diagonal bucking of web occurs when:
1
the ratio of thickness of flange to clear depth (tf/d) exceeds 65
2
the ratio of clear depth to thickness of flange (d/tf) exceeds 65
3
the ratio of thickness of web to clear depth (tw/d) exceeds 85
4
the ratio of clear depth to thickness of web (d/tw) exceeds 85