SA63: Cable Subjected to Concentrated Load

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[@engrabdihalimmhussein5787]

My favourite channel as a sophomore engineer

[@MohammedAL-Mamory]

Can you show us how to deal with the stability of compsite structures in the next lacture

[@ThePanik63]

why cannot you calculate inner tension forces just by vector sum of point load plus tension in the cable next to point load if that one is known?

[@DrStructure]

If the positions of the joints are known, so that we can calculate the angles that the segments make with the horizontal axis, we can do as you are suggesting. But if the angles are not known, we end up having both unknown angles and unknown internal tension forces at the joint. That results in 4 unknowns. The vector sum idea works if there are at most two unknowns at the joint.

[@deecee6780]

At the second example(with road signs) I am really confused when you can cut the cable into sections. Do you cut it into sections to terminate the other support?

[@DrStructure]

In that problem, there are 6 unknowns (four unknown reaction forces at the supports and two unknown heights), which means we need to write 6 equation in order to determine the unknowns. The equations are: Sum of the forces in the x direction = 0 Sum of the forces in the y direction = 0 Sum of the moments about A = 0 Sum of the moments about B = 0 Sum of the moments about C = 0 Sum of the moments about D = 0 Furthermore, in writing each moment equation we need to cut the cable just to the right of the joint so as to not include the support reactions at the right end of the system in the equation. This is very similar to how we deal with beams and trusses, we cut them, then write the equilibrium equations for one of the substructures only. If we did not cut the cable when writing the four moment equations, we would end up with a set of dependent equations which we could not be solved for the unknowns.

[@deecee6780]

@@DrStructure Ah okay.. It makes sense to me now. Thank you very much sir! Keep safe!

[@ronnylov]

This is epic

[@ShanStatefootball]

Dear Dr.Structure , Can u tell me Which software is used for the presentation like this video series? Thanks.

[@DrStructure]

Adobe Illustrator, Camtasia Studio, and Reallusion software.

[@arjun3533]

Thanks a lot to Dr structure .for your great efforts.which is really helpful a lot. Can u please made lectures on plastic analysis .?

[@seungjunyoo8739]

Why don't we consider moment by tension at joint? Why do we consider moment by only left side element? there should be moment by force on right side.

[@DrStructure]

1. A cable is not a rigid member, it cannot handle any bending moment, or even a compressive force. Imagine one end of a cable/rope being attached to a heavy object (say, a car) and you are holding to the other side of the rope. The only force you can exert on that rope is a pulling force. The rope collapsed if you pushed on it, or if you try to bend it. 2. Yes, we can apply the equilibrium equation to the right subsystem as well. We can choose either the left or the right subsystem when writing such equilibrium equations. We chose the left subsystem in the lecture.

[@biagiogugliotta]

Hello Professor, DR Structures. Thank you for a wonderful channel. I have a question regarding heights h1 h2 h3 H 4. @2:57 min How did you interpret problem to get a value for h2? Is this an educated assumption. It would seem that differing values of h2 would translate to different reaction force H. Thank you! Biagio upstate New York.

[@DrStructure]

Correct, different values for h2 result in different tension forces in each cable segment. That height (initial sag) is a design consideration, similar to the length of a beam, for example. If the cable is a part of a traffic light system, that h can be based on the clearance requirements at the intersection. As you correctly stated, depending on the application, we can come up with an educated assumption for one of the h values.

[@gopalpangeni6826]

love from nepal

[@abdiqadirabdiali4798]

Easy and nice explanation. Would you please help me. I know You use Vedioscribe for drawing, formulas how do you make it. Thnks again

[@DrStructure]

We use MathType to typeset the equations.

[@nelumkariyawasam5727]

Sir how you got h2 and h4 without calculations.pls can you explain it again

[@DrStructure]

They are not calculated; they are assumed to be given. Otherwise, we will end up with too many unknowns.

[@mayeezy254]

Solving the eqns at 7:48 was a bit challenging as unlike the previous example there is no 0 value

[@ma.zysakeithf.acosta8682]

how did solve problem 2?

[@deecee6780]

At what equation di you start to solve it?

[@DrStructure]

@@deecee6780 We have six equations in six unknowns, they need to be solved simultaneously.

[@DrStructure]

@@ma.zysakeithf.acosta8682 We have six equations in six unknowns, they need to be solved simultaneously.

[@deecee6780]

@@DrStructure oh okay. Thank you very much.. I need to polish first my algebra haha

[@civilengineeringstudy]

Link to SA64.

[@DrStructure]

kzbin.info/www/bejne/aYLNmGB3mtB5odk

[@cesarbenavides1369]

example at 2:41, you forget Sum of M@E = 0, and then, we need only know h4 to solve all unknowns.

[@DrStructure]

The moment equation you mentioned is a redundant one. That is, for the entire cable system, we can only write one moment equilibrium equation (we can write the moment equation either about point A or point E, but not both). Any additional moment equation written for the entire cable (without cutting it) becomes useless/redundant.

[@arcadebeast2219]

So in a real question you can just assume the heights h2 and h4 if you dont have enough equilibrium equations to solve this problem without any real reasoning?

[@DrStructure]

No, we cannot pick values randomly, without any reasoning. Textbook problems always provide sufficient information for solving the problem. In real life problems, the geometry of the system is generally known. For example, if the system is for a traffic light support at a street intersection, the height are generally selected by the designer to ensure proper clearance. If for some reason, some of the heights remain unknown, the system becomes statically indeterminate, in which case we can use advanced techniques, such as the finite element method to analyze the cable system.

[@xyzabc6898]

@@DrStructure Sir,please tell me which software u use to make this Animated tutorial..its great....i also want to make tutorials on Mathematics, please tell me......

[@DrStructure]

@@xyzabc6898 We use Adobe Illustrator for creating the writings/drawings and for animating them, Iclone for character animation, and Camtasia Studio for video production.

[@xyzabc6898]

@@DrStructure Thanks Sir for telling me the name of Softwares.....Sir,if i also use these 3 softwares,then can i make Tutorial for Maths ????????ur guidance is my need....u r doing very good work.....without guidance,its very very difficult for me to make videos...i m super-beginner in this,so understand Sir about condition of my techncal skill.

[@DrStructure]

@@xyzabc6898 If you don't have prior experience in using such software tools, it would be quite a challenge to create lecture videos similar to what you see on this channel. It will take you a while to learn and ins and outs of whatever platform you decide to use for creating lectures. You need to do a bit of research to find out what options are available to you and which ones constitute a good starting point. In that vein, you may want to take a look at whiteboard animation software such as VideoScribe. PowerPoint may also be a viable option for creating slides that embody animations and turning them into videos. Mathematical expression can be easily inserted in Powerpoint using plugins like MathType.