Tick:
As I said above, because HSLA steels are stronger, a material property, we are inclined to design lighter structures, IF we can tolerate the deflections and vibrations. Or, we over design to fix the deflection problem, thus under utilizing the premium material, stresswise. So, as you know, your boss has it bass acwards. As for increasing the thickness, that should increase the member stiffness and lower the stresses, these are section property related. But when you use stock or std. shapes, you do tend to get a bunch of material in places you don’t really need it. As is possible, I try to use stock shapes and sections, but am never afraid to fab. a section to put the material where I need it to achieve what I really want. Just pay attention to the fab. cost vs. saving weight and achieving what you want. Many times using std. shaped leads to such awful details elsewhere that they screw up the whole design and aren’t worth it. Show your boss the bending stress equations and the deflection equations for a simple beam, for example, so he can see what, and how drastically, some of these different properties change the results. The same principles generally apply to more complex structures, although the equations get more complex, or finally the analysis must be done by computer.
Drawoh:
If common sense were really so common, why is its application so uncommon? But, in this case, that particular common sense is wrong, even though it might be an uneducated extension of what one might first assume or guess, bosses included. But, then we all know where bad assumptions lead us...
We are really dealing with two different things here: material properties such as E (modulus of elasticity), Fy & Fu yield strength and ultimate strength, G (shear modulus), etc.; and section properties such as I (moment of inertia), S (section modulus), r (radius of gyration), etc., which when combined with member length and structural configuration, etc. lead to structural stiffness.
As Ivymike suggests you really have to study the formulas which govern what we are doing here to see exactly how each of the properties effects the results, or what we are trying to achieve. And, in his example maybe a hollow rod would offer the same stiffness and column capacity, while reducing the weight and mass. Maybe a higher strength material with the same compressive capacity would lead to a lower mass. Maybe a lighter weight material with slightly lower strength would do the trick. You have to manipulate those various properties and quantities, through those equations, to your advantage.
