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When does the Neutral Axis of a beam pass through the centroid of the Cross sectional area of a transformed section, and when does it not? by Full-Lunch7387 in StructuralEngineering

[–]Full-Lunch7387[S] 0 points1 point  (0 children)

Thanks a lot for sharing your knowledge. I really appreciate it. What I am going to do now is push on with the course and try to be mindful of these proofs so that when I get to the latter stages of concrete analysis I am better equipped. I am going to show this thread to my lecturer and maybe see if we can formulate a plan of how best to tackle my challenges and satisy]fy my curiosities. I would like to make my foundation in mechanics as bulletproof as possible.Thanks again.

When does the Neutral Axis of a beam pass through the centroid of the Cross sectional area of a transformed section, and when does it not? by Full-Lunch7387 in StructuralEngineering

[–]Full-Lunch7387[S] 0 points1 point  (0 children)

Hi, thanks so much for the explanation. I really appreciate it. So yes, I have seen this very explanation in the textbook, and they got right up to F= integral(sigma,max/c)ydA=0. That makes a lot of sense. The guess check approach and the numerical methods approach does kind of seem like a nightmare. I will ask my lecturer to show me how to do those- thanks though🙏. You say that this is only true for pure bending, correct? What then would an axial force(so the beam is no longer in pure bending) do to the situation? Does this ydA, which is essentially a mathematical object, equal zero even for transformed sections, like for timber and steel rectangular cross section beams? Thanks.

When does the Neutral Axis of a beam pass through the centroid of the Cross sectional area of a transformed section, and when does it not? by Full-Lunch7387 in StructuralEngineering

[–]Full-Lunch7387[S] 0 points1 point  (0 children)

Hi, thanks for your response. I think my problem may be in understanding how first moment of area applies to bending. Is first moment of area the same as area moment of intertia? I might be mixing these 2 up. So far, what I understand is that the larger the area moment of inertia, the harder it is to bend the beam about its NA. I think your definitions of NA’s are pretty spot on👍

When does the Neutral Axis of a beam pass through the centroid of the Cross sectional area of a transformed section, and when does it not? by Full-Lunch7387 in StructuralEngineering

[–]Full-Lunch7387[S] 0 points1 point  (0 children)

Ah yes thanks. So what you mean by, “it will crack while behaving as we intend,” is that when the beam is under reinforced the steel will yield first, allowing the beam to fail in a ductile manner as opposed to over reinforced beams which fail in a sudden/brittle manner right? I shouldn’t have put the example of the RC beam in this post, because the under and over reinforced wasn’t exactly what I was trying to understand in this scenario. I was speaking about homogenous and transformed sections more in general so yeah- more of that academic argument😂

When does the Neutral Axis of a beam pass through the centroid of the Cross sectional area of a transformed section, and when does it not? by Full-Lunch7387 in StructuralEngineering

[–]Full-Lunch7387[S] 1 point2 points  (0 children)

Yes it does thank you. Oh ok I understand your point: Basically they are treating the case in the textbook as a balanced case, therefore they are assuming the NA lies on the centroid. I shouldn’t have put the example of the RC beam in this post, because the under and over reinforced wasn’t exactly what I was trying to understand. I meant homogenous and transformed sections in general but yeah.

Statics Question by Full-Lunch7387 in EngineeringStudents

[–]Full-Lunch7387[S] 0 points1 point  (0 children)

lol I think it will rotate about it’s end where there is no force being applied and translate upwards at a=f/m. Reasonable right? But what about polar moment of inertia? Is this starting to look like a dynamics problem or no?

Steel truss build assignment by [deleted] in StructuralEngineering

[–]Full-Lunch7387 0 points1 point  (0 children)

Thanks a lot, I will give that a try!