Flexure, Part 2: Applying the flexure formula + Drawing Stress Diagrams + Finding Resisting Moment

[@jiwoochie]

Hi! This video was really helpful. I have a question regarding the Tension Force calculation. I don't know if I'm just flat out doing the calculation wrong, but when I do (3.893/2)*(132702.1353), I end up getting 258.586 kN, not 137.077. Am I doing something wrong?

[@StructuralEng]

Hi! You are perfectly right! That is a mistake there. I will pin your comment for others to note the issue. Thank you for watching the videos and your comment!

[@jiwoochie]

@@StructuralEng Thank you for providing clarification! Also, would it be possible for you to do more CVL 313 videos and even possibly CVL 500? These videos have helped me out a lot, so I just wanted to ask. Thank you so much again!

[@karimabouelela3665]

thanks for the video. If we were given in question 6 at location point left to b the bending stress just below the circle. Can we using this stress find the max Moment ? if I use the equation and Find Moment M=(stress below circle* I)/ (distance from centroid to below circle). I will get a Moment. Is this moment the Max moment at location just to the left of B. Also am i able to find max bending using that moment by just changing the 'y' ??

[@StructuralEng]

Thank you for your comment! At a specific crosssection the moment value is the same. In this case the moment at any layer in crosssection B is the same. Remember that we are cutting a specific section (B in this case) and your shear and moment values are certain values for that crosssection. Other than that, the formula you mentioned for finding the moment is correct. Just remember to use consistent units. And yes, you will be able to find max stress by changing y to bottom or top fibres. Let me know if you have any further question! All the best!

[@karimabouelela3665]

@@StructuralEng Man you are the best!! There is one more question i hope you can answer it for example I have W"load" as 2 how can I answer this question: Using the calculated distributed load (W), determine the dimensions of a hollow circular beam (use thickness = 0.5 times of the outer diameter) for part AB, if the maximum bending/flexural stress capacity of the beam material is 12 MPa using a factor of safety of 2.0

[@StructuralEng]

​@@karimabouelela3665 First, you will have to find the applied stress based on the factor of safety; in this case, the applied stress will be 6 MPa. Then based on your W, you will cut your section just to the left of the support and calculate the moment there. Remember to always take the moment about where you cut to make things simple (you don't have to deal with shear force). Now that you have your moment, the only thing remaining is y and I (sigma is equal to My/I). y is half the diameter for a circular hole (top or bottom fibre). Also, remember that it is impossible to have 0.5 of outer diameter as thickness; that basically means a solid section, not a hollow one! However, let's say it is 0.25, not 0.5. In that case, your inner diameter is 0.5 outer diameter. SO based on that, you can write your moment of inertia equation based on only outer diameter. pi/64 (do^4-(do/2)^4), finally you will say 6 MPa is equal to My/I, you have M as a value, and y and I as a function of outer diameter, simplify and that's it! All the best!

[@karimabouelela3665]

@@StructuralEng Thank you boss