Shear force and bending moment diagram practice problem #4

[@m.umarhasan7882]

This is how you teach the science of engineering statistics. I wonder how come those indian videos have so many views!l. They are just solving numericals without explaining why we are doing it! Watched only 3 videos on your channel and now I can recall the 6 months worth of learning I had back in the univ.

[@caterina6609]

this is so helpful thank you sir ,if there people who are glad watching your video series for sure i am.GOD BLESS YOU

[@Engineer4Free]

Thanks Caterina =)

[@greatpharoh0303]

That's perfect man, love your videos by the way! They are so organized and easy to understand! I have been struggling with this stuff for years, but your videos really clear things up!

[@ZXC-ey3zu]

My mechanics prof is good(I understand what she's teaching), but you're better (now I can easily pass the examination next week, I'm feeling it)

[@koshinnn]

wow thanks dude i finally understood all these after looking at all your examples thumbs up

[@Engineer4Free]

Awesome, thanks the best kind of feedback I can ask for!!!! =) =)

[@adrianpazgarcia1181]

I love this Chanel

[@PoliteMudau]

You are the best ❤

[@mallyclips9213]

These have been really helpful, thank you!

[@Engineer4Free]

Thanks Mally =)

[@devvyas6751]

thanks to you i got hundred percent in my quiz :))

[@Engineer4Free]

That is awesome!!!! Great job!! =)

[@OneWingedBadass]

Can you do one with a triangular distributed load please?

[@akesubannarat]

the forces are going in the clockwise direction, would they be negative in the equation?

[@LadyLalien]

Hi! I wonder why, in the calculations of MA, you write "10 KNm*4m*6m"? Is it becuase you first calculate the length of the force acting down, then time it with the place of the middle of that force? Is this instead of calculating with the whole length of the beam? Thank you for your great content, it really helps. Your videos are recommended to us by our teacher :)

[@yelyel2620]

Very well explained! Thank you, Ive been having problems with this for semesters now. Question though, does it mean that the parabolic/curved lines are only drawn in the moment diagram where there's a uniform load?

[@MikFrost00]

Hey! Could you please explain me why the parabolas shape is like the "a" coefficient (ax^2+bx+c) is negative?

[@Engineer4Free]

The easiest way to think of why it is concave down, is to imagine numerically integrating the corresponding area on the SFD. Slice the section up into thin vertical slices, and you will see that they are taller on the left side. Taller = more area. More area = greater slope on BMD. Greater slope on the left side of BMD means the left side of the parabola needs to be steeper than the right side. Because we know the change in magnitude across the section is positive (because the corresponding area of the SFD is positive) , and the slope is steeper on the left side, there is only one way to draw the parabola, and that is concave down. Thats the non mathy way that I like to remember it by.

[@alexm9141]

@@Engineer4Free Awesome explanation

[@ericchen559]

I amd confused that why the shear moment is negative at the beginning, I remember that for statics the shear mmoment in the assumption is upward, so it is positive, but the SFD told me that the BMD is correct, it is so complex.....

[@rahvxz03]

Hi sir, may I ask if Ay can be a negative number?

[@Engineer4Free]

Yes, it is possible. If the net applied force is pointing down (as it is in this video) then Ay will respond by pointing up. Because we define positive y direction to be up, then Ay is positive. If we had the net applied forces on the beam pointing up, then it would be opposite, and Ay would be negative. A situation where this could happen would be uplift cause by wind loading on the bottom of the beam.

[@rahvxz03]

@@Engineer4Free Thank you for the information! really appreciate it

[@michellegaughan1003]

Why have you drawn your moment in an anti clockwise direction?

[@Engineer4Free]

Are you referring to the reaction moment at A? It’s common to define counter clockwise as positive for moments, then draw unknowns in that same sense. If you find the moment has a positive magnitude, then the sense stays counterclockwise, and if you find it to have a negative value then you know it should really be flipped.

[@nicolaskanisius1622]

This is perfect, I really love your videos! What kind of whiteboard software do you use?

[@ezedintofik9085]

This is very helpful bro. But one thing I wanna ask is that why did you just used MA in a CCW direction since our conventional dixn is the opposite. Thank You tho.

[@Engineer4Free]

In general for solving sum of moments about a point in a 2D problem it is common to use CCW as the positive sense for a moment. The is not the same convention that is referred to in the top right of the screen for an internal moment on the left of a virtual cut, which happens to be opposite.

[@YumenAggr]

Thank you so much for this

[@Engineer4Free]

You're welcome!! Thanks for watching 😊😊

[@Andy-pl9we]

could you please explain why the moment is anti-clockwise?

[@Engineer4Free]

Yeah, please see videos 66 and 67 here: engineer4free.com/statics for the explanation. It’s because of the positive sign convention for beam bending.

[@bro123ism]

How do you know that an internal moment exists and how do you assume which direction i.e counter clockwise or clockwise

[@Engineer4Free]

Lateral loads and or applied moments on a beam will cause internal bending moments. I prefer to imaging how the applied lateral load or moment would tend to rotate the structure around the point of interest if it was able to. That will give you a clockwise or counterclockwise sense to designate the moment's positive or negative sign.

[@khazaniah9417]

what about Ax? is it unnecessary in this problem

[@Engineer4Free]

There are no externally applied forces with a horizontal component, so if you draw the FBD of the whole structure and take sum of forces in x direction, the whole expression is just Ax = 0. Depending on your professor, you may be able to just ignore it it like I do. Won't hurt to explicitly write Ax=0 though if you have the time.

[@rachidabkari2342]

thank you so much sir you really helped me alot

[@Engineer4Free]

You’re welcome, glad I could!! 💕

[@MphoRaboho-cw9xz]

tell me why I'm only finding this page the day before my exam

[@engtarawneh90]

What is the application or program you're using?

[@Engineer4Free]

I've got a list of all the hardware and software that I use at engineer4free.com/tools =)

[@Thundercraft190]

Thanks great help!

[@Engineer4Free]

You’re welcome!! 🙂

[@renegadevestige1639]

Just wondering, what is the maximum bending moment?

[@Engineer4Free]

In this case it is - 400kNm. Just look on the BMD for the maximum magnitude. Sometimes you will be looking specifically for max positive or maxx negative value seperatly, but if not, then it's just the max absolute value

[@rolandoquispebasualdo6546]

Buen ejemplo, bastante didáctico. Gracias

[@Engineer4Free]

De nada. ¡Gracias por ver! Más aquí: engineer4free.com/structural-analysis👌

[@abdelrahmanmostafa8104]

When should i draw the curve in convex or concave shape?

[@Engineer4Free]

Are you referring to parabolic section of the BMD or the shape of the deflected structure?

[@abdelrahmanmostafa8104]

@@Engineer4Free parabolic section

[@Engineer4Free]

The slope of the parabola (BMD) is greater where the magnitude of the triangle (SFD) is greater. From left to right, the parabola will increase towards positive if the area of SFD is positive. Parabola will decrease in value if the area of SFD is negative. Knowing if the Vale if the parabolic section of BMD is increasing or decreasing is important if we are skipping all the magnitude of plotting it as a function of x, which is the case in this video. Combining the knowledge of BMD increasing or decreasing, and knowing which side will have a greater slope, leaves only one way to draw the parabola's up/down concavity. You can reason your way to the slope thing by imagining that we slice the SFD triangle shape into skinny vertical parts. The parts that are taller have more area than the ones that are shorter. The area represents the change in value on the BMD across that width. So bigger changes in value equal greater slopes in that area compared to areas with shorter slices. I wrote this on my phone so I hope it makes sense.

[@abdelrahmanmostafa8104]

@@Engineer4Free thanks alot

[@NCarolina4455]

Please, please respond. I see how our moment is 400 kn-m, but how did you tell it was counter clockwise? And wouldnt that make the moment positive, if it is in the counter-clockwise direction?

[@Engineer4Free]

Hey. Imagine for a second that there is a pin at A rather than a rigid connection. If that was the case, then all three applied forces would cause the member to rotate clockwise about A. When considered together, and still imagining that there is a pin at A, the net applied force would cause a clockwise rotation of the member about A. What that indicates is that the net external forces are causing a clockwise moment about A. Now this member is in static equilibrium, so in addition to resisting the vertical forces, the moment reaction at A must be equal and opposite to the applied moment that it is feeling. The support at A is feeling a clockwise moment, so the reaction to counter it must be counterclockwise.

[@majaz417]

@@Engineer4Free So for BMD, we actually considering the actual moment of the beam only yes? Thank you sir ! Helps a lot for my project.

[@explosivebest3703]

I wonder why the US does their Bending Moment Diagrams backwards compared to a lot of the rest of the western world. Here in NZ, positive is below the zero line.

[@Engineer4Free]

Yeah depending on where you live they will be mirror images of each other. Drawing positive below the line or "on the tension side" makes your life easier when it comes to frames, but for beams, the integration is a bit more clear when you draw it above. It's confusing though to have two conventions. When I was in uni, I had profs from different parts of the world and learned both ways =/

[@hakimsikder1387]

you saved me thank you so much May Allah bless you

[@Engineer4Free]

Thanks Hakim, glad I can help =)

[@nawack1]

Thanks a lot sir

[@Engineer4Free]

You're welcome =)

[@571173]

What is maximum bending moment

[@Engineer4Free]

-400 kNm

[@atlifreysi]

hi man, good video. i was just wondering if you have any videos on how to find the stuff on 0:54, i don't really understand that. love your channel and website, you are doing great work!

[@Engineer4Free]

Hey Atli, thanks for the comment! Yeah at 0:54 I am applying the equations of 2D static equilibrium for the member, which are ΣFx=0, ΣFy=0, ΣMa=0. There are no horizontal forces in the problem so I just don't bother writing it out. If you need more practice with finding these, just review 2D statics problems. Try videos 25-34 here: engineer4free.com/statics and maybe check out some of the practice problems in that section too. Cheers!

[@greatpharoh0303]

Why is it -400 kN m to start off. Isn't the area start in the positive direction and shear is +80? Please clear up anyone if possible.

[@Engineer4Free]

Hey, draw a FBD of the structure wihh a virtual cut infinitely close to A (just to the right of A). On the left of it, you'll have 80kN point load up acting on it from Ay, and 400kNm moment acting counter clockwise from Ma. On the right side, where the cut is, you'll have your internal shear "v" and internal bending moment" M". For static equilibrium, the forces and moments need to net out to zero. Because the virtual cut is infinitely close, the distance between Ay and v is infinitely small, so the moment that they would cause as a force couple tends to zero. So the only moment actoing on tis fbd is Ma, and M then must be equal and opposite. So it must be clockwise with a magnitude of 400kNm. Clockwise to the right of a virtual cut is opposite the positive sign convention (I think it's video 66 and 67 that you need to watch here: engineer4free.com/statics about sign convention). So opposite positive means it's negative, M will be - 400kNm infinitesimally close to A, so that's why the BMD starts with that value. As for shear, the sum of vertical forces must also net to zero, so v must oppose the uoward 80kN from Ay. So v is 80kN down. Down is the positive direction for shear on the right of a vertical cut, so that's why the SFD is +80kN at A. Watch those other vids in the statics page on sign convention, and if you have time, even the few examples in there that solve these the long way, it will help build understanding when you do in the fast way as in this video. I wrote this on my phone so sorry if there's typos. 👌

[@siegeclimbing9818]

can you please upload videos regarding how to draw BMD and FORCE diagm when shear force diag is given alone

[@Engineer4Free]

Hey yeah I currently don't have any that do that specifically, but in all my SFD/BMD example videos (videos 1-9 here engineer4free.com/structural-analysis) the BMD is drawn purely off the SFD. You can inspect the SFD and BMD to learn about the applied loads and reactions. When the SFD jumps values, there is a point load there. If the jump is "down" then so is the point load with that magnitude. If the jump is "up" then so is the point load with that magnitude. If the SFD is sloped down linearly, then there is a downward oriented uniform distributed load in that region, who's magnitude is equal to the slope. If the BMD jumps, then there is an applied moment at that point with a magnitude equal to the jump. If the jump is up, then the applied moment is clockwise, if the jump is down, then the moment is applied counterclockwise.When I say up and down, I'm referring to reading the jump going left to right. I'm also assuming you draw BMDs the way I do, not inverted. Hope that helps, If you need practise, just take the 9 examples from my videos and draw only the structure and SFD, and then practise finding the BMD and applied loads, you can check after if you have done it right. Cheers.

[@angelisfpv]

Shearforce diagram should be negative

[@kidusbahiru4369]

the video is good and you explain well but you need improvement on teaching others. Pretend that i don't know anything about moment and shear diagram

[@Engineer4Free]

Hi Kidus, thanks for the feedback. This video is part of a senior level series I did on structural analysis, and in particular, this video is a review of SFDs and BMDs, which does assume prior knowledge. The structural analysis series that I'm talking about is here: engineer4free.com/structural-analysis and this is the fourth video in the playlist. I did make several videos on SFDs/BMDs for the complete beginner where I assume no prior knowledge, those are videos 66-72 here: engineer4free.com/statics In those videos I take a much slower and more detailed approach to explaining the concept and drawing the diagrams. Please do check those out, I hope they help!

[@nicholascollins2823]

Parabibilc

[@dimejiadaramewa4443]

pls be more detailed with what you're trying to teach...this isn't good

[@Engineer4Free]

This lesson is part of a senior level course in structural analysis ( engineer4free.com/structural-analysis ) and this method is a "fast way" that assumes you're comfortable with the topic. For more detailed ad slow introduction to SFDs and BMDs, see videos 66 - 72 here: engineer4free.com/statics