Little bit confusion I come across everytime I try to solve a mechanics or structure problem..

Dude, sorry to say but you're pretty wrong in this conversation.

Let's say you take a W-section (W8x24, for example), and you split it into its web and flange components. Assuming it's full plastic capacity:

D=8", tw=0.25", Bf=6.5", tf=0.4" -fyi, numbers below are for web area = D*tw

Web plastic modulus = 4 Flange plastic modulus = 19

Web contribution to MCapacity = 4 / (4+19) = 17.4% Flange contribution to Mcapacity = 1 - 0.174 = 82.6%

Even making the web the same thickness (0.4"), it will still only account for 25.7% of your full plastic moment capacity (for this beam). If you consider LTB, flanges become even more important. You'll see this in any kind of beam; in bending, the flanges do way more work in resisting deflections and moment.

The web helps with some of the moment capacity but is really there for shear and to space and support the flanges so that they can better resist bending.

/r/civilengineering Thread Parent