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

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.

Next video in this series can be seen at:

[ANJA-mjto]

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.!

[fredyguevara]

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!

[kevito]

from the bottom of my heart, thanks teacher.

[andrewsteinfeldt]

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. 🤯

[tacodragon]

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?

[engissol]

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.

[JGambrosia]

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? <—***

[gladnoah]

thank you very much sir I really do enjoy your 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?

[lindaleung]

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.)

[athirahridzuan]

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

[douwedeboer]

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

[simonjeras]

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

[allinall]

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

[kaderfarah]

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

[a.kovachev]

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

[mercellcapital]

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

[ismailhakkakbaba]

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

[petermaroney]

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

[rckygrhm]

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

[sashamuller]

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