Ah, of course! Thank you!
The stiff direction is when the cross-section looks like a lying H if we consider vertical load. You realize this when you think about the expression for the moment of inertia: bh^3/12. Material with height contributes more to the moment than that with large width due to the cubic term. It can be easier to understand if you think of the moment of inertia as the sum of a lot of small increments where each increment has the contribution bh^3/12.hordak said:
Yes, that goes without saying, now that you pointed it out! =)
Since you are so ambitious, you can also read a bit about serviceability limit state and ultimate limit state. What you design against during deflection is the serviceability limit state, for example. You might be completely familiar with this, but if you're not, you can quickly skim through the following Powerpoint from LTH: http://www.kstr.lth.se/fileadmin/kstr/pdf_files/vbk013/foerelaes/kapitel__10_2015.pdf
Go for it! =)
Go for it! =)
Definitely need to read up on that, thanks! After a night's work, I will have to postpone it until tomorrow to have a slightly clearer mind =)
I happened to encounter a structural engineer who calculated the beam and concluded that an IPE 160 would be sufficient, taking into account the prevailing snow zone (3.5), the roof's own weight (0.4), and wind load of 0.6. Utilization rate of 57% and maximum deflection of just over 12 mm. It's a bit weaker than what has been discussed here earlier, I think 12 mm feels like a lot, not sure how sensitive it is for a overhead garage door?
Best answer
It is not always easy to recap a discussion that took place several months ago.
12 mm is indeed less than 1/300 of 4.2 meters (which is 14 mm) but still a bit much considering the position and role of the steel beam. IPE is a beam type that is narrower than HEA, but it requires greater height in return for equivalent bending stiffness. The difference between an IPE 160 and an HEA 160 is quite large. The moment of inertia is 869*10^4 mm4 for IPE 160 and 1673*10^4 mm4 for HEA 160. With the same parameters your structural engineer used, an HEA 160 would result in a deflection of half, i.e., 6mm. I find that more reasonable.
12 mm is indeed less than 1/300 of 4.2 meters (which is 14 mm) but still a bit much considering the position and role of the steel beam. IPE is a beam type that is narrower than HEA, but it requires greater height in return for equivalent bending stiffness. The difference between an IPE 160 and an HEA 160 is quite large. The moment of inertia is 869*10^4 mm4 for IPE 160 and 1673*10^4 mm4 for HEA 160. With the same parameters your structural engineer used, an HEA 160 would result in a deflection of half, i.e., 6mm. I find that more reasonable.
Understand that, though it felt a bit odd to start a new thread in the forum - my hope was that someone (you) would see and respond without feeling obliged 
There has been quite a bit of snow here and it was only last week that the garage roof became free of snow and the theory could start to turn into practice.
Thanks for your answer Justus, I'll go with that line!
There has been quite a bit of snow here and it was only last week that the garage roof became free of snow and the theory could start to turn into practice.
Thanks for your answer Justus, I'll go with that line!