Posted by David Sherman on Sunday, December 03, 2006 at 8:48PM :
In Reply to: Re: Flange vs web, depends on stress direction? posted by Michael Fanoni on Sunday, December 03, 2006 at 7:51PM :
To resist bending, the vertical forces in a beam turn into tension in the lower flange and compression in the upper. The web, if it's the same thickness as the flanges, is usually overly-thick except in very short, very heavily loaded beams, where it can buckle like a loaded column. A truck frame is a long beam for structural design purposes so buckling of the flange isn't an issue unless it's been very severely weakened. Of course a truck frame has holes and brackets and bends in different places and loads applied in various spots, so it's not very simple to analyze. A "strengthening" plate could even weaken a design by moving a load to a place that was already severely stressed. Given that I've seen more than a few old PWs with bent frames, it's definitely possible to overload them.