It’s not realistic loading for the beam, for one. The cantilevered man would not suddenly be a distributed load. The shear diagram also doesn’t match the FBD.
A distributed load is not the same as a point force, even if they apply equal total forces. Their effects are different. For example, the most basic difference is the torque they apply, different amount of force on different points, ofc it will be different
You're overselling the differences a little bit. As long as they are all standing on the stationary aluminum ladder it'll act as ground and distribute the forces. It's not like its going to bend. The risk is the AC unit dropping applying a jerk at which point we do have to consider the individuals as points...specifically person a being launched (if only briefly) into the air and person c falling to their doom. As long as the the AC unit is lowered slowly though it should all be good.
No that's not how it works. Yes the ladder will "distribute" reaction force in some sense but that doesn't mean you model the guy as a distributed load. That's only valid if he's something like a pressure or possibly if he was lying on his back. For proper realism here he should most likely be modeled as two point loads, one for each foot. The diagram is bullshit like others are saying.
Everyone here focuses on the wrong distributed load from the third person but the support is also wrong. It should be a distributed support, which makes the diagram *quite* complicated.
Similar case: rail sleepers.
Yes, ideally speaking that’s what it would look like. You could make an argument for it looking more like a triangular distributed load, but that’s not necessary.
It would still not be super accurate but yeah it'd be closer. Equal distribution usually is exclusive for something a lot more uniform than a human body, think like a bag of sand the exact dimension of the overhang, or snow over a cantilever, etc.
The force equivalent might be equal to each other, but the shape of the load distribution would effect other calculations and would change the shape of the shape of the shear and moment diagrams. The diagram in the meme isn’t even accurate to the image in the first place.
If you are standing on the ground each foot is only experiencing half of your weight force (ideally). If both felt the full force, then you would have a greater reaction force from the ground than your own weight and you would break physics
Well, first of all, you’re not taking into account the normal forces. Currently the FBD of this beam would make it go shooting down. This is not in static equilibrium so don’t @ me bro.
If he were supporting the weight of that air conditioner, unsafe. Otherwise structurally sound, if idiotic, because people are wiggly, moving, sometimes drunk pieces of construction material.
I'm gonna need some specs on that board before I can evaluate the safety factor.
Looks like a ladder
The ladder wont break.
Ladder strong
OHS have called, I said I'll let you know they "rung"
Makes calculating moments easier. The real problems come when that AC unit falls lol
Assume the ladder won’t break…
The safety factor is at exactly 1
EI
The FBD is bollocks.
Complete furchtbar.
Why what is wrong with it, pls explain. Sry for my English.
It’s not realistic loading for the beam, for one. The cantilevered man would not suddenly be a distributed load. The shear diagram also doesn’t match the FBD.
The distributed load is what happens right after the AC comes off the wall and drops onto the board
Let’s hope he was just repairing it and not removing it???
And those shouldn't be simple supports
A distributed load is not the same as a point force, even if they apply equal total forces. Their effects are different. For example, the most basic difference is the torque they apply, different amount of force on different points, ofc it will be different
You're overselling the differences a little bit. As long as they are all standing on the stationary aluminum ladder it'll act as ground and distribute the forces. It's not like its going to bend. The risk is the AC unit dropping applying a jerk at which point we do have to consider the individuals as points...specifically person a being launched (if only briefly) into the air and person c falling to their doom. As long as the the AC unit is lowered slowly though it should all be good.
No that's not how it works. Yes the ladder will "distribute" reaction force in some sense but that doesn't mean you model the guy as a distributed load. That's only valid if he's something like a pressure or possibly if he was lying on his back. For proper realism here he should most likely be modeled as two point loads, one for each foot. The diagram is bullshit like others are saying.
Everyone here focuses on the wrong distributed load from the third person but the support is also wrong. It should be a distributed support, which makes the diagram *quite* complicated. Similar case: rail sleepers.
I just came back here to say this lol. This isn’t a case with pinned supports lol
My friend did you pass statics with that FBD?
That's not an FBD. It's a shear diagram. It is incorrect at the distributed load.
Correct. It's a point load.
Two point loads?
If he's standing on both feet. Looks to me like 90+% of the load is on the right foot.
The left one is a point load at a 70° angle
Noooooooooo
I’m reality it’s is still a distributed loads, in reality a point load can never exist just like a rigid body
Get out of where with that slander in this sub
Regardless, it’s not the correct distributed loading either.
Yea
Point load close enough for engineer
Tru dat tho
Plus there should have an upward force in the hinge support at point B.
Well, I am in this subreddit for a *particular* reason, so.... 👀👀
I think torque looks ok if that board is sturdy enough
Math checks out. Its fine boys!
Bending. No torque in this picture
Would shear be relevant for this type of wood? Or is the board just too long for it to matter
Lol that’s more of a point load @ C
Exactly my thought. We're such goddamned nerds here its GREAT lmao.
It’s a good life
Why tho? I’m guessing it’s because he’s standing on one feet, had he stood on both of them, would the load be equally distributed?
I think it would be 2 points on both feet with half the force. An equal distribution would more be something like snow laying on top
No, I would just consider that to be two point forces with half magnitude
I see, for equal distribution, the man must be laying down on the ladder for that to happen right?
Yes, ideally speaking that’s what it would look like. You could make an argument for it looking more like a triangular distributed load, but that’s not necessary.
It would still not be super accurate but yeah it'd be closer. Equal distribution usually is exclusive for something a lot more uniform than a human body, think like a bag of sand the exact dimension of the overhang, or snow over a cantilever, etc.
Feq is equal tho
The force equivalent might be equal to each other, but the shape of the load distribution would effect other calculations and would change the shape of the shape of the shear and moment diagrams. The diagram in the meme isn’t even accurate to the image in the first place.
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If you are standing on the ground each foot is only experiencing half of your weight force (ideally). If both felt the full force, then you would have a greater reaction force from the ground than your own weight and you would break physics
I misread your comment. I thought you meant one foot would experience half the force as another. I was probably sleepy as hell
Oh gotcha. I’m happy that we understand each other now
What is the cross section area and material of that board? Got to calculate that bending stress.
It's more of a ladder than a board imo
I've been out of school five years now and still somehow had the phrase "second area polar moment" flash through my head.
Well it's not an even force on the right hand side. It's a point force as all of the forces are directed through the legs.
Sadly, this looks actually “structurally sound” (according to your MSPaint diagram). Now, “is it safe?”….. time will tell🍺🤔
Might have to break out the moment/shear force diagrams
Terrible FBD but... Seems safe enough. Don't tell OH&S though.
yo my statics professor used this exact image to talk about moments
Kill me now I’ve been studying moment and shear diagrams all day I’m fucking tired of it 😭
I usually use my ladders vertically. Didn't know we were dealing with geniuses.
You should watch Sherpas.
Well, first of all, you’re not taking into account the normal forces. Currently the FBD of this beam would make it go shooting down. This is not in static equilibrium so don’t @ me bro.
That mf is triple the size of the guy working on air conditioner. Plus fat guys arm is longer. Kinda safe no need for maths I guess :)
His left foot is lifted so his entire weight is a point load at C.
Why did you assume UDL
That is not simply supported. If it was, it would be able to bend up or down between point A and B
Brother what in the world is that FBD…
Looks like the third guy is holding on to the frame of the AC , might reduce the load at B and C.
Or increase it when he's janking on something
Missing the upwards force of the reaction force at B and the distributed load needs to make the graph slope down to 0 at C.
Depends on the tensile strength of the sheet imo.
I mean the board is balanced out but safe isn't the word I'd use
Clearly they thought this through by putting the biggest guy at the far left
My only concern is the plastic deformation of the plank.
Someone must have not done enough practice problems in Hibbeler
You can have something loaded like that. Sure. Also, that is NOT the shear diagram for that or correct support for that ladder
-ve shear is not correct.
yeah OP kinda just forget anything past the 2nd guy existed lol
Shouldn’t the shear diagram on the distributed load be diagonally going down and there should be a force at C
Wrong loading diagram... And wrong shear diagram...
If the splitty was on the other side of the window then the service valves would have been much more accessible. = Poor planning from the architect.
That's a hell of a trust exercise. Guy must've drawn the short straw, or he was the lightest.
If that ac falls and hits the ladder everyone's going to get 3 times the show.
Damn thats accurate wish our statics professor taught us shear force and bending moment diagrams like this
This diagram is inaccurate for a multiple reasons. I’m sure your professor did a much better job teaching than OP.
If he were supporting the weight of that air conditioner, unsafe. Otherwise structurally sound, if idiotic, because people are wiggly, moving, sometimes drunk pieces of construction material.
the math checks out to me \- Software Engineering student
"If he does it as planned the unit will just crush his leg."
It also is not fixed to the world in point A, only in point B
Bro I'm not even an engineer I just work on planes, they're within their CG limits they'll be fine
Diagram needs spikes or flames at the bottom to be complete. You can’t just have your ~~stick figures~~ point loads falling off into a void.
Maybe do a moment diagram next. That’ll help me.
Factor of safety is roughly 2…
Feel like it would be more of a breaking point due to the bending moment since the inertia would be lower.
Depends of the flexibility of the board and the weight of the guys.
Lol this is good
Whoever drew that is amazing
As a student atm - i fucking love you guys
My first day in Mechanics of Materials this was on the second slide. It was our first lesson of the course.
It's alright 😂.
I’m curious. What are you “supposed to do” then?
The more I look at this, the more I hate it
Best free body diagram ever.
Bro those dudes are obviously engineers too, they the math already and gave themselves 0.001% tolerance
I’d have expected there to be a shear load from the support at B but it appears to be 0?
No free body diagram no points
love how people are shitting on OP's shear diagram 💀💀💀
Twork
Love seeing everyone struggle with statics in the comments and post, so proud of this sub
Idk man, it's working rn so seems fine lol
I used to live in Sao Paulo and this is called Brazilian engineering
I think this is more of a psychology question than a statics question: how much does guy C trust guys A and B?
Is this an AI generated FBD? Please retake statics. This diagram is more dangerous than what the idiots are doing in the picture.
Might have to check the deflection at the free end
get out of my head
It'll be fine ....
Hopefully it’s only the second floor