Mechanics of Materials - 3D Combined loading example 1 part 2

[@morolayomi]

I've got a question that would really piece everything together, at 5:15 where you entered a positive moment of 300000, what happens if the moment was -300000 instead? Would this mean it is 47.7 but in compression?

[@sabarafiei9334]

thank you very much

[@juancantera9638]

Am I wrong or are you getting the bending wrong? Shouldn’t Mx bend the pipe on the opposite direction? Same with My. If I point my thumb in the y-direction, my fingers curl into point A, thus wouldn’t it be in compression?

[@engineeringdeciphered]

I’m “keeping” the top half of the beam, so my “cut” is at the bottom. So, for example, a positive y moment, my right hand is underneath the cut and underneath the top piece that I’m keeping. So my right thumb is pointing to +y and my fingers are not curling to A, my fingers are curling on the other side. Does that make sense?

[@juancantera9638]

@@engineeringdeciphered Yes, that clears it up, thank you.

[@mrtylmz2209]

@@engineeringdeciphered So if I want to do the calculations about the bottom part of the pipe, the forces and moments will be Fx=-1500 N, Fy=1000 N, Fz=0 N, Mx=-200 kN, My=-300 kN, and Mz=600 kN because of action-reaction. Sir, is that right?

[@engineeringdeciphered]

@@mrtylmz2209 yes

[@mrtylmz2209]

@@engineeringdeciphered Thank you very much.

[@Justlight2893]

Doesn't the beam twist in the direction of torque? So, shouldn't the shear stress be towards positive-y at point A?

[@engineeringdeciphered]

Also: we are finding the stress at the “cut.” This is what the “cut” feels from the other half of the beam that we have thrown away.

[@ahmadsleiman37]

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