Mechanical Engineering: Trusses, Bridges & Other Structures (16 of 34) Pratt Bridge: Example 1

Рет қаралды 90,841

8 жыл бұрын

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In this video I will find the compression/tension and magnitude of each member, and the forces at each support of a pratt bridge problem.
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• Mechanical Engineering...

Пікірлер: 58

@ANJA-mj1to 9 ай бұрын

GREAT PRESENTATION PROFESSOR! Like scientific structural and civil engineer thank you for effective presentation. Including vertical members that swpe down toword the centar opposit of the HOWE TRUSS. Long - span railyroad bridge characterized by additinal diagonals extending on two. The ability was to spand great distance using simple methods BUT VERY WELL known ( like span anchor points up to 76,4 m.) So we have extremly effective high strenght bridge for long distance. With luck on your other workout worldwide in 2023.!

@MichelvanBiezen 9 ай бұрын

Thank you!

@kevito111 8 жыл бұрын

from the bottom of my heart, thanks teacher.

@fredyguevara3304 3 жыл бұрын

Professor. Thank you very kindly! I need all the help I can in this area and in all areas, so thank you very much for teaching the world!

@MichelvanBiezen 3 жыл бұрын

Glad it was helpful!

@engissol 3 жыл бұрын

ENGISSOL 2D Truss Analysis software features a powerful finite element solver to analyze trusses consisting of elements with rotational releases at their both ends. The deformed configuration under external loads is calculated and the axial force diagram of the structure provided by the user is represented. The creation of the model is an easy and quick task as the user can take advantage of the intelligent user interface of the software. Its versatile graphical user interface, the predifend libraries and many other available features can save you time and effort. Moreover, the program also supportes non-linear static analysis (second order analysis) for the consideration of P-Delta effects.

@andrewsteinfeldt422 3 жыл бұрын

All of this analysis is valid IF the load is all applied at point G, unless my analysis is not correct. So, separate analysis must accomplished when the load moves.... This truss looks suspiciously like a bridge. So it would make more sense to assume the loads are applied along the lower member. And then, it is all different! Nevertheless, no matter how we approach the analysis, the engineer must make sure that all of the joints and members can support ANY possible load that may be experienced or it could fail. Good thing we have computers as was mentioned in another post. 🤯

@gladnoah9426 8 жыл бұрын

thank you very much sir I really do enjoy your videos......I have quite a few questions tho 1. I was wondering why the x-component of a force wasn't considered in most of the videos. 2. could we have been able to just find their angles and use sin rule?

@jzzz1139 5 жыл бұрын

thank you, it's really helpful

@tacodragon9266 2 жыл бұрын

Sorry professor, assuming that you had another 2 nodal points in the bottom going from A-G and the top now going from H-L of your Pratt bridge how would you solve the remaining member forces LK,KJ,LC,CD?

@sbcristi6088 4 жыл бұрын

sir, what method are u using?

@123yingying123 5 жыл бұрын

thanks sir you saved my life

@abeltesfai9242 6 жыл бұрын

Thank you so much

@dilawarbugti1430 5 жыл бұрын

love you sir G the great 😍😍 thank you

@douwedeboer7984 6 жыл бұрын

Dear Michel, i,ve hit a snag calculating a warren truss bridge, wich is suspended at the top. Exactly the opposit of the example in your video and with a difficult load distribution.. may i send you a sketch FBD of my problem, perhaps you may be able to help me out. kind regards, Douwe de Boer graduate student engineering from Holland

@jonelpolot1681 6 жыл бұрын

king of statics.

@lindaleung6691 4 жыл бұрын

Isn't HE a zero force member - no downward force along HE along joint H? At joint H, the upward component force of compression HB is balanced by the downward component force of tension HD. So there should be 0 downward force along member HE. (I hope I recall it right that tension pulls on a joint and compression pushes on a joint.)

@nickcheese9600 Жыл бұрын

no, its not, there is a downward force of 6Kn so HE must have a vertical force.

@allinall9257 6 жыл бұрын

Sir What is the name of formulae that was used over the triangle. Force applied/respective length

@princem5155 5 жыл бұрын

It's just a Pythagorean triple

@JGambrosia 7 ай бұрын

5:55 I’m a bit confused on why GD has 0 force on it. There’s a 6kN force acting down at point D, wouldn’t there be a tension force? Does HD and FD provide tensions compensate for the 6kN force at D? (Edit: they do) Why doesn’t GD also contribute along with FD and HD?

@MichelvanBiezen 7 ай бұрын

The force is handled by the FD and HD members. That is the purpose of these types of bridge structures.

@JGambrosia 7 ай бұрын

@@MichelvanBiezen yes i am aware of that. But i’m just a bit startled that if i tackled the problem on my own, i would have assumed that much like HE and FC, GD would also have a tension force. I don’t think i would have been able to come to the conclusion that there would be no tension force on GD. I can’t think of any systematic way of actually determining that there would be no force on GD. To me it looks like along with HD and FD, GD would also contribute, so the force in the y direction would be evenly distributed among the 3. But thats not the case. Was my assumption reasonable at first glance?

@MichelvanBiezen 7 ай бұрын

There is a systematic approach. We have some examples of that, where you make imaginary "cuts" at different places to determine the tension and compression of each beam. You can also draw force triangles starting on one side of the bridge and then work from one side to the other side. We have examples of that as well.

@kudamichaelchenjerai4751 3 жыл бұрын

Wow thank you

@MichelvanBiezen 3 жыл бұрын

You’re welcome 😊

@a.kovachev1196 3 жыл бұрын

Thank you. And how did i know if the structure is stable or not?

@nickcheese9600 Жыл бұрын

did you find anything out?

@hend7600 3 жыл бұрын

thank you

@MichelvanBiezen 3 жыл бұрын

You're welcome

@petermaroney3625 4 жыл бұрын

Great video. When calculating for HB how did you conclude the y- component was 9 KN? Thank you!

@petermaroney3625 4 жыл бұрын

I got it! Haha but your explanation would be appreciated just to make sure I have the right thought process.

@MichelvanBiezen 4 жыл бұрын

First we find the force at B using the moment of torque of the structure. Then the key is to realize that the sum of all the forces at any junction always equal zero. So we can draw the force diagrams at every junction.

@athirahridzuan5743 4 жыл бұрын

Sir may I ask why is it that the magnitude of forces must proportional to the length of members?

@MichelvanBiezen 4 жыл бұрын

Length is one of the factors, but also the angles and the loads. Better not count on that but systematically work through the structure from one end to the other.

@simonjeras9269 6 жыл бұрын

Isnt it better to assign every beam on tansion at start and for result we get minus sign

@MichelvanBiezen 6 жыл бұрын

Did you try it and then get the correct answers?

@simonjeras9269 6 жыл бұрын

Michel van Biezen. I will next weekend

@kaderfarah7430 7 жыл бұрын

Identification of compression and tension isnt clear teacher for me all other consept and caculations are well. Thanks for posting

@MichelvanBiezen 7 жыл бұрын

Take a look at videos 27 through 29 in this playlist: MECHANICAL ENGINEERING 8 TRUSSES AND BRIDGES

@mercellcapital 3 жыл бұрын

what if you don't have a 3,4,5 triangle

@MichelvanBiezen 3 жыл бұрын

It can be any triangle. The 3,4,5 triangle just keeps the numbers simpler so we can concentrate on the principles.

@ismailhakkakbaba5748 3 жыл бұрын

hi guys, I'm trying to find the answer. pls help. (I hope I am going to be able to explain my question) I have 30 feet long fink truss system in my roof. i want to raise entire roof all together (one piece) . house is concrete block 30' x 22'. ceiling height is 8 feet. I wanna raise it up to 10 feet (2 more feet).can anyone help me about where is the lifting point? how can i raise my entire roof with heavy duty steel lifting shore. Which point of the trust is the best point to push the entire roof up? thank you

@MichelvanBiezen 3 жыл бұрын

It would not be a single point, but multiple points. Typically they place supports close to where the load bearing walls are, which are the walls designed to carry the weight of the roof, and then slowly raise those point bit by bit at each support, like 1 cm at a time, going around to each support. My advise is to talk to someone locally who constructs houses who would know the answer to your question in your particular case.

@ismailhakkakbaba5748 3 жыл бұрын

@@MichelvanBiezen thank you for the reply. my plan is something like that kzfaq.info/get/bejne/nLp7ZreVrbeup3k.html. Instead of using hydraulic jack, I'm going to use Heavy Duty Steel Lifting Shore. But I don't know where to put the 6"x6" to hold the entire roof?

@ismailhakkakbaba5748 3 жыл бұрын

@@MichelvanBiezen PLS look at 11:10 min kzfaq.info/get/bejne/nLp7ZreVrbeup3k.html

@rckygrhm1 8 жыл бұрын

you just got the cosine of 53.13 out of your head, I think you've done this stuff before.....

@MichelvanBiezen 8 жыл бұрын

+Richard Graham Yes, that is a common angle with rounded solutions when you take the sine or cosine of that angle.

@sashamuller9743 4 жыл бұрын

Do engineers do this for every beam in an entire bridge XD?

@MichelvanBiezen 4 жыл бұрын

Now there are computer programs where the entire bridge structure (with all its members) are calculated for stress and tension loads.

@MrAminmohamed 2 жыл бұрын

Can i propose a technic ?

@MichelvanBiezen 2 жыл бұрын

Certainly.

@MrAminmohamed 2 жыл бұрын

@@MichelvanBiezen can we extend each bar to the vertical symetric axis and just say that top connected bars are in compression and bottom connected are in tension.Can we add vectors on those lines folowing gravity direction from top to bottom and say that Howe move stress away from the center and Pratt contain it to the center? I want to teach that in middle school, Stem teacher but not master of the subject.Thanks

@MichelvanBiezen 2 жыл бұрын

Well, I would first work out this example problem the way it was shown in the video. That is an old established technique to solve these types of problems. Then I would solve it the way you suggest and see if you get the same results and if you do, determine which way is the easiest to solve the problem.. That would be the best way to compare

@MrAminmohamed 2 жыл бұрын

@@MichelvanBiezen The goal is to teach middle school student to understand the behaviour of the structure without calculation. If it is working using symetry any student could analyse quickly those structure without expensive software.Try it you should be able to perform a kind of finite element analysis by head. I can predict wich bar of the truss will fail the first and I have zero calculation knowledge of trusses. I asked my students do it on real pictures they do the same thing as FEM analysis. BTW to find the stress on the vertical bar we think that in a given triangle stress should be compensated then you cant have the three bars of the same colors. Also we already know that top horizontal bars are in compression and bottom in tension. If it is confirm true then we should start to teach that in all middle school class.

@MichelvanBiezen 2 жыл бұрын

I think that is a good approach. Yes, teaching students at a young age to think about it like that will help in their understanding.