The web and flange thicknesses of H - beams are important factors determining their performance. The web thickness mainly affects the shear - resistance of the beam. A thicker web can withstand greater shear forces, which are crucial when the beam is subjected to loads that cause it to deform by sliding along a plane. In structures like multi - story buildings, where the beams need to transfer vertical loads from upper floors to lower ones, a sufficient web thickness ensures that the beam can handle these shear forces without failure. The flange thickness, on the other hand, impacts the bending - resistance of the beam. A thicker flange can resist larger bending moments, as it provides more material to resist the tensile and compressive stresses generated during bending. For example, in a long - span roof structure, thicker flanges in the H - beams can help maintain the shape of the roof and prevent excessive sagging under the weight of snow or the self - weight of the roofing materials.